Renal Dendritic Cells Ameliorate Nephrotoxic Acute Kidney Injury

Inflammation contributes to the pathogenesis of acute kidney injury. Dendritic cells (DCs) are immune sentinels with the ability to induce immunity or tolerance, but whether they mediate acute kidney injury is unknown. Here, we studied the distribution of DCs within the kidney and the role of DCs in cisplatin-induced acute kidney injury using a mouse model in which DCs express both green fluorescence protein and the diphtheria toxin receptor. DCs were present throughout the tubulointerstitium but not in glomeruli. We used diphtheria toxin to deplete DCs to study their functional significance in cisplatin nephrotoxicity. Mice depleted of DCs before or coincident with cisplatin treatment but not at later stages experienced more severe renal dysfunction, tubular injury, neutrophil infiltration and greater mortality than nondepleted mice. We used bone marrow chimeric mice to confirm that the depletion of CD11c-expressing hematopoietic cells was responsible for the enhanced renal injury. Finally, mixed bone marrow chimeras demonstrated that the worsening of cisplatin nephrotoxicity in DC-depleted mice was not a result of the dying or dead DCs themselves. After cisplatin treatment, expression of MHC class II decreased and expression of inducible co-stimulator ligand increased on renal DCs. These data demonstrate that resident DCs reduce cisplatin nephrotoxicity and its associated inflammation.Innate immune responses are pathogenic in both ischemic and toxic acute renal failure. In response to renal injury, inflammatory chemokines and cytokines are produced both by renal parenchymal cells, such as proximal tubule epithelial cells, and resident or infiltrating leukocytes.^1–4 The elaborated chemokines and cytokines, including TNF-α, IL-18, keratinocyte-derived chemokine, and monocyte chemoattractant protein 1, subsequently recruit additional immune cells to the kidney, such as neutrophils, T cells, monocytes, and inflammatory dendritic cells (DCs), which may cause further injury through pathways that are not fully defined.^2,5–12 DCs are sentinels of the immune system and under steady-state conditions induce tolerance by various mechanisms, including production of TGF-β, IL-10, or indoleamine 2,3-dioxygenase^13–16; expression of PDL-1, PDL-2, or FcγR2B^17,18; clonal deletion of autoreactive T cells¹⁹; and induction of T regulatory cells via the inducible co-stimulator (ICOS) pathway.^20–23 In response to pathogens or products of tissue injury, DCs mature and initiate immunity or inflammatory diseases.^24,25 Monocytes recruited to inflamed tissue can also differentiate into inflammatory DCs and mediate defense against pathogens or contribute to inflammatory tissue responses.^12,26–28Although DCs represent a major population of immune cells in the kidney,²⁹ their role in renal disease is poorly defined. Liposomal clodronate has been used to study the pathophysiologic role of phagocytic cells, which include DCs and macrophages.^3,30–32 An alternative DC-specific approach uses expression of the simian diphtheria toxin receptor (DTR) driven by the CD11c promoter to target DCs for DT-mediated cell death.²⁴ This model has been used extensively to study the role of DCs in various physiologic and pathophysiologic contexts^32,33; however, its application in kidney disease has been limited to recent studies of immune complex–mediated glomerulonephritis.^12,23We have reported that inflammation plays an important role in the pathogenesis of cisplatin-induced acute kidney injury (AKI).^1,4,5,34 Given the dearth of information regarding the role of renal DCs in AKI, this study examined the renal DC population and the impact of its depletion on cisplatin nephrotoxicity. We show that DCs are the most abundant population of renal resident leukocytes and form a dense network throughout the tubulointerstitium. Renal DCs displayed surface markers that distinguished them from splenic DCs. Using a conditional DC depletion model, we determined that DC ablation markedly exacerbates cisplatin-induced renal dysfunction, structural injury, and infiltration of neutrophils.     

Acute Kidney Injury Associates with Increased Long-Term Mortality

Acute kidney injury (AKI) associates with higher in-hospital mortality, but whether it also associates with increased long-term mortality is unknown, particularly after accounting for residual kidney function after hospital discharge. We retrospectively analyzed data from US veteran patients who survived at least 90 d after discharge from a hospitalization. We identified AKI events not requiring dialysis from laboratory data and classified them according to the ratio of the highest creatinine during the hospitalization to the lowest creatinine measured between 90 d before hospitalization and the date of discharge. We estimated mortality risks using multivariable Cox regression models adjusting for demographics, comorbidities, medication use, primary diagnosis of admission, length of stay, mechanical ventilation, and postdischarge estimated GFR (residual kidney function). Among the 864,933 hospitalized patients in the study cohort, we identified 82,711 hospitalizations of patients with AKI. In the study population of patients who survived at least 90 d after discharge, 17.4% died during follow-up (AKI 29.8%, without AKI 16.1%). The adjusted mortality risk associated with AKI was 1.41 (95% confidence interval [CI] 1.39 to 1.43) and increased with increasing AKI stage: 1.36 (95% CI 1.34 to 1.38), 1.46 (95% CI 1.42 to 1.50), and 1.59 (95% CI 1.54 to 1.65; P < 0.001 for trend). In conclusion, AKI that does not require dialysis associates with increased long-term mortality risk, independent of residual kidney function, for patients who survive 90 d after discharge. Long-term mortality risk is highest among the most severe cases of AKI.Acute kidney injury (AKI) affects up to 15.3% of all hospitalized patients.^1,2 Regardless of the underlying cause, AKI is associated with significantly increased in-hospital morbidity, mortality, and costs.^2–16 The majority of previous studies linking AKI to mortality examined in-hospital mortality only and did not address postdischarge morbidity and mortality.^{2,4,7,8,10,11,13–16} Studies examining postdischarge mortality have focused primarily on critically ill patients with AKI that requires dialysis.⁹ Consequently, it remains unclear whether AKI that does not require dialysis is associated with a higher long-term risk for all-cause mortality.One of the challenges of long-term mortality studies is to estimate the mortality risk independently associated with AKI from risk associated with chronic kidney disease (CKD). Some patients have incomplete recovery of their kidney function after AKI, and CKD is associated with a higher risk for mortality.^17,18 To evaluate the independent long-term mortality risk of AKI, it is essential to adjust for postdischarge kidney function. The objective of this study was to estimate the postdischarge, long-term mortality risk associated with AKI while adjusting for residual kidney function in a large cohort of US veterans.     

Recurrence of Lupus Nephritis after Kidney Transplantation

The frequency and outcome of recurrent lupus nephritis (RLN) among recipients of a kidney allograft vary among single-center reports. From the United Network for Organ Sharing files, we estimated the period prevalence and predictors of RLN in recipients who received a transplant between 1987 and 2006 and assessed the effects of RLN on allograft failure and recipients'' survival. Among 6850 recipients of a kidney allograft with systemic lupus erythematosus, 167 recipients had RLN, 1770 experienced rejection, and 4913 control subjects did not experience rejection. The period prevalence of RLN was 2.44%. Non-Hispanic black race, female gender, and age <33 years each independently increased the odds of RLN. Graft failure occurred in 156 (93%) of those with RLN, 1517 (86%) of those with rejection, and 923 (19%) of control subjects without rejection. Although recipients with RLN had a fourfold greater risk for graft failure compared with control subjects without rejection, only 7% of graft failure episodes were attributable to RLN compared and 43% to rejection. During follow-up, 867 (13%) recipients died: 27 (16%) in the RLN group, 313 (18%) in the rejection group, and 527 (11%) in the control group. In summary, severe RLN is uncommon in recipients of a kidney allograft, but black recipients, female recipient, and younger recipients are at increased risk. Although RLN significantly increases the risk for graft failure, it contributes far less than rejection to its overall incidence; therefore, these findings should not keep patients with lupus from seeking a kidney transplant.The frequency and clinical impact of recurrent lupus nephritis (RLN) in the kidney allograft of recipients with systemic lupus erythematosus (SLE) varies considerably in both prospective and retrospective studies.^1–25 In 1996, Mojcik and Klippel²⁶ pooled data from a total of 366 allografts transplanted in 338 recipients. In that review, histologic RLN was present in 3.8% of the grafts. Contrasting, in the studies by Goral et al.²⁷ and Nyberg et al.,¹⁰ RLN was reported in a much higher proportion: 30 and 44% of recipients, respectively.The clinical consequences of RLN on patient and allograft survival have ranged from no effect to a significant increase in the risk for graft loss and patient mortality.^24,27–31 In this case-control study, we estimated the period prevalence of RLN in kidney transplant recipients who had ESRD secondary to lupus nephritis and received a transplant between October 1987 and October 2006. We assessed the effects of RLN on graft failure and recipient survival and the risk factors leading to the development of RLN.     

Pregnancy and Maternal Outcomes Among Kidney Transplant Recipients

Fertility rates, pregnancy, and maternal outcomes are not well described among women with a functioning kidney transplant. Using data from the Australian and New Zealand Dialysis and Transplant Registry, we analyzed 40 yr of pregnancy-related outcomes for transplant recipients. This analysis included 444 live births reported from 577 pregnancies; the absolute but not relative fertility rate fell during these four decades. Of pregnancies achieved, 97% were beyond the first year after transplantation. The mean age at the time of pregnancy was 29 ± 5 yr. Compared with previous decades, the mean age during the last decade increased significantly to 32 yr (P < 0.001). The proportion of live births doubled during the last decade, whereas surgical terminations declined (P < 0.001). The fertility rate (or live-birth rate) for this cohort of women was 0.19 (95% confidence interval 0.17 to 0.21) relative to the Australian background population. We also matched 120 parous with 120 nulliparous women by year of transplantation, duration of transplant, age at transplantation ±5 yr, and predelivery creatinine for parous women or serum creatinine for nulliparous women; a first live birth was not associated with a poorer 20-yr graft or patient survival. Maternal complications included preeclampsia in 27% and gestational diabetes in 1%. Taken together, these data confirm that a live birth in women with a functioning graft does not have an adverse impact on graft and patient survival.One of the many perceived benefits of kidney transplantation has been restoration of pituitary-ovarian function and fertility in women of reproductive age. Prenatal advice for women with a functioning kidney transplant has been primarily based on data derived from observational research,^1–13 and the reported live-birth rates achieved in such women range from 43.2¹⁴ to 82%.¹⁵Although an increased pregnancy event number has been reported for women with a functioning kidney transplant,¹⁶ little is actually known about “pregnancy rate changes” during the past 40 yr. More importantly, long-term graft and maternal survival analyses, referred to when advising women who have undergone transplantation and are considering a pregnancy, have been mostly performed without adequate matching,¹² or, alternatively, matching has been used but outcomes followed up for only brief intervals^14,17,18 and in small cohorts.^19–22 Published graft matching studies to date suggest no adverse impact 10 yr after a live birth.¹⁴In most instances, pregnancies in women with a kidney graft have been encouraged. Historically, renal function,^8,15,17,18 baseline proteinuria,²³ intercurrent hypertension,^1,24 and time from transplantation^{1,3,5,8,14,15,18,24,25} have been used to predict adverse event risks to the mother, kidney, and offspring. To this are added the often unquantifiable inherent risks for genetically transmitted diseases or the problems associated with prematurity.^26,27 More recently, epidemiologic evidence suggests low birth weight may be associated with the development of hypertension,²⁸ cardiovascular disease,²⁹ insulin resistance,³⁰ and end-stage renal failure.³¹ Moreover, low birth weight is associated with an increased risk for hypertension, independent of genetic and shared environmental factors.³²Series published to date have not captured all pregnancy events or their outcomes. Limitations of some of the published studies include short duration of follow-up and studies with no adequate or long-term matching for decade and renal function.We examined fertility rates, pregnancy rates, and pregnancy outcomes over 40 yr in an at-risk population, defined as women who were aged between 15 and 49 and had a functioning kidney transplant, using ANZDATA registry data. In addition, maternal and graft outcomes were analyzed, and, uniquely, a matched cohort analysis of 120 nulliparous and 120 parous women who had undergone transplantation enabled analysis of outcomes at 20 yr.     

Fetal and Infant Growth Patterns and Kidney Function at School Age

Low birth weight is associated with ESRD. To identify specific growth patterns in early life that may be related to kidney function in later life, we examined the associations of longitudinally measured fetal and infant growth with kidney function in school-aged children. This study was embedded in a population-based prospective cohort study among 6482 children followed from fetal life onward. Fetal and childhood growth was measured during second and third trimesters of pregnancy, at birth, and at 6, 12, 24, 36, and 48 months postnatally. At the age of 6 years, we measured kidney volume by ultrasound. GFR was estimated using blood creatinine levels. Higher gestational age-adjusted birth weight was associated with higher combined kidney volume and higher eGFR (per 1 SD score increase in birth weight; 1.27 cm³ [95% confidence interval, 0.61 to 1.93] and 0.78 ml/min per 1.73 m² [95% CI, 0.16 to 1.39], respectively). Fetal weight, birth weight, and weight at 6 months were positively associated with childhood kidney volume, whereas higher second trimester fetal weight was positively associated with higher GFR (all P values<0.05). Fetal and childhood lengths were not consistently associated with kidney function. In this cohort, lower fetal and early infant weight growth is associated with smaller kidney volume in childhood, whereas only lower fetal weight growth is associated with lower kidney function in childhood, independent of childhood growth. Whether these associations lead to an increased risk of kidney disease needs to be studied further.Low birth weight is associated with higher risks of ESRD and hypertension in later life.^1–3 Clearly, low birth weight is not the causal factor per se leading to kidney diseases in later life. Birth weight is the result of various exposures and growth patterns in fetal life and the starting point of childhood growth. It has been hypothesized that especially third trimester fetal growth restriction leads to persistently smaller kidneys with a reduced number of nephrons, which may predispose the individual to kidney disease in adulthood.^4–6 This hypothesis is supported by both animal and human studies, showing that kidney volume and nephron number are reduced in fetal growth-restricted subjects and hypertensive subjects.^7–9 Although nephrogenesis is known to continue until 36 weeks of gestation and cease thereafter, not much is known about the specific critical periods and early growth patterns related to kidney function in later life.¹⁰ Also, whether and to what extent the associations of low birth weight with CKD are explained by preterm birth are not known.¹ Longitudinal studies suggested that the associations of low birth weight with hypertension were stronger in subjects with rapid weight gain in childhood, but results are inconclusive.^11,12 A similar growth pattern has not been identified as a risk factor for kidney diseases yet.Prospective studies linking fetal and early childhood growth patterns to kidney outcomes in later life might help to identify early critical periods for developing impaired kidney function in later life.Therefore, we examined, in a population-based prospective cohort study among 6482 children followed from early fetal life onward (Figure 1), the associations of birth weight, gestational age, birth weight for gestational age, and longitudinally measured fetal and early childhood growth patterns with kidney size and function at school age. We used subclinical variations of kidney function in childhood as outcomes, because they relate to kidney disease in later life.¹³Open in a separate windowFigure 1.Flow chart: exclusion criteria and numbers of participants are given. Total numbers of available outcome measurements are given.     

Albuminuria and Estimated Glomerular Filtration Rate Independently Associate with Acute Kidney Injury

Acute kidney injury (AKI) is increasingly common and a significant contributor to excess death in hospitalized patients. CKD is an established risk factor for AKI; however, the independent graded association of urine albumin excretion with AKI is unknown. We analyzed a prospective cohort of 11,200 participants in the Atherosclerosis Risk in Communities (ARIC) study for the association between baseline urine albumin-to-creatinine ratio and estimated GFR (eGFR) with hospitalizations or death with AKI. The incidence of AKI events was 4.0 per 1000 person-years of follow-up. Using participants with urine albumin-to-creatinine ratios <10 mg/g as a reference, the relative hazards of AKI, adjusted for age, gender, race, cardiovascular risk factors, and categories of eGFR were 1.9 (95% CI, 1.4 to 2.6), 2.2 (95% CI, 1.6 to 3.0), and 4.8 (95% CI, 3.2 to 7.2) for urine albumin-to-creatinine ratio groups of 11 to 29 mg/g, 30 to 299 mg/g, and ≥300 mg/g, respectively. Similarly, the overall adjusted relative hazard of AKI increased with decreasing eGFR. Patterns persisted within subgroups of age, race, and gender. In summary, albuminuria and eGFR have strong, independent associations with incident AKI.It has long been recognized that an episode of acute kidney injury (AKI) can have serious health consequences.^1–4 Even a relatively small degree of renal injury increases a patient''s risk of a prolonged hospital stay, chronic kidney disease (CKD), ESRD, and death.^2,5–10 Over the last 2 decades, the incidence of hospitalized AKI has increased dramatically.^11–14 Precise estimations vary depending on population and method of case identification, but a recent community-based study of AKI estimated the incidence of nondialysis requiring AKI at 522 per 100,000 population per year and dialysis-requiring AKI at 30 per 100,000,¹³ which is well over that of ESRD.¹⁴ This increase in the burden of disease, taken with the associated poor long-term outcomes, has established AKI as a major public health issue.¹⁴Beyond routine supportive care, there exists little established medical therapy for AKI.¹⁵ Many current lines of research are focused on the prevention of AKI. However, few prospective, population-based studies have evaluated the development of AKI.^3,13,16 Hsu et al.,^13,17 along with multiple observational series in various clinical settings, have clearly established older age and CKD as risk factors for AKI.^18–24 Other observed associations with AKI include black race and male gender.^11,18,25 Proteinuria, an established risk factor in the development of cardiovascular disease,^26,27 ESRD,²⁸ and death,²⁹ is less studied in its role in the development of AKI. Hsu and colleagues demonstrated the prospective association of proteinuria with dialysis-requiring AKI; however, the proteinuria classification was binary and based on dipstick measurement.¹⁷ To our knowledge, no study has quantified the independent dose response of albuminuria with AKI hospitalization, including less severe AKI. Our study''s objective was thus to characterize prospectively the association between baseline urine albumin-to-creatinine ratio (UACR) and hospitalizations for AKI, controlling for established and potential risk factors such as CKD, age, and cardiovascular comorbidities.     

B Cells Limit Repair after Ischemic Acute Kidney Injury

There is no established modality to repair kidney damage resulting from ischemia-reperfusion injury (IRI). Early responses to IRI involve lymphocytes, but the role of B cells in tissue repair after IRI is unknown. Here, we examined B cell trafficking into postischemic mouse kidneys and compared the repair response between control (wild-type) and μMT (B cell-deficient) mice with and without adoptive transfer of B cells. B cells infiltrated postischemic kidneys and subsequently activated and differentiated to plasma cells during the repair phase. Plasma cells expressing CD126 increased and B-1 B cells trafficked into postischemic kidneys with distinct kinetics. An increase in B lymphocyte chemoattractant in the kidney preceded B cell trafficking. Postischemic kidneys of μMT mice expressed higher IL-10 and vascular endothelial growth factor and exhibited more tubular proliferation and less tubular atrophy. Adoptive transfer of B cells into μMT mice reduced tubular proliferation and increased tubular atrophy. Treatment with anti-CD126 antibody increased tubular proliferation and reduced tubular atrophy in the late repair phase. These results demonstrate that B cells may limit the repair process after kidney IRI. Targeting B cells could have therapeutic potential to improve repair after IRI.Ischemia is a leading cause of acute kidney injury (AKI) in both native kidneys and allografts. In allografts, ischemic AKI frequently results in delayed graft function.¹ Many studies have demonstrated that both innate and adaptive immune responses are involved in the pathogenesis of renal injury after renal ischemia-reperfusion injury (IRI).^2,3 On the basis of traditional concepts of adaptive immunity, lymphocytes were not expected to play an important role in the early renal injury after IRI; however, T cells were found to mediate the early phase of IRI in kidney and in other organs, both directly and indirectly.^4–6 B cells also seem to participate in the early injury response of renal IRI,⁷ and B cell products are also important in early IRI response in skeletal muscle.⁸B cells have been identified as important mediators of various autoimmune diseases, such as experimental allergic encephalomyelitis (EAE), collagen-induced arthritis, and inflammatory bowel disease.^9–11 In EAE, B cells seem to function as antigen-presenting cells during the initiation phase.^12,13 In a recent report, B cells were involved in both initiation and progression of EAE.¹⁴ Clinical trials using mAb to CD20 expressed on B cells have suggested beneficial effects in autoimmune diseases such as rheumatoid arthritis, lupus erythematosus, and multiple sclerosis.^15–18 Although ischemic AKI and autoimmune disease are traditionally viewed as different disease categories, they share a crucial feature: A prominent immune/inflammatory response.It was previously shown that B cells traffic into chronically inflamed organs, activate and form ectopic germinal centers, and locally differentiate to plasma cells.^19,20 A number of studies have demonstrated that B cells infiltrate into renal allografts and contribute to rejection^21,22; however, the exact role of B cells that have infiltrated into renal allografts is still unclear. Some studies reported that B cells could cause transplant acute cellular rejection as well as humoral rejection and increase the risk for graft failure independent of C4d peritubular deposition,^23,24 whereas other studies have not shown this clinical correlation.^25,26 One recent article characterized intragraft B cells during renal allograft rejection: Both mature B cells and interstitial plasmablasts correlated with circulating donor-specific antibody concentration and poor response to steroid therapy during rejection.²⁷ The presence of mature B cells was associated with reduced graft survival.On the basis of recent advances in studies of B cells in auto- and alloimmune diseases, the increasingly recognized pathogenic role for lymphocytes in IRI, and lack of treatment to augment repair, we tested the hypothesis that B cells modulate the repair process after kidney IRI. We analyzed the numbers and phenotypes of kidney-infiltrating B cells and the expression of B lymphocyte chemoattractant (BLC) during the repair phase. We found marked trafficking of B cells into the postischemic kidney during repair, with a distinct phenotype at different time points, along with increased BLC expression. We then evaluated the renal repair status of control (wild-type) mice, mature B cell–deficient (μMT) mice, μMT mice with adoptive B cell transfer, and μMT mice with serum transfer. We found that B cells modify tubular repair and proliferation. Finally, we targeted CD126-expressing plasma cells with an anti-CD126 antibody and found a significant improvement in tissue repair after IRI.     

DASH-Style Diet Associates with Reduced Risk for Kidney Stones

The impact of the Dietary Approaches to Stop Hypertension (DASH) diet on kidney stone formation is unknown. We prospectively examined the relation between a DASH-style diet and incident kidney stones in the Health Professionals Follow-up Study (n = 45,821 men; 18 yr of follow-up), Nurses'' Health Study I (n = 94,108 older women; 18 yr of follow-up), and Nurses'' Health Study II (n = 101,837 younger women; 14 yr of follow-up). We constructed a DASH score based on eight components: high intake of fruits, vegetables, nuts and legumes, low-fat dairy products, and whole grains and low intake of sodium, sweetened beverages, and red and processed meats. We used Cox hazards regression to adjust for factors that included age, BMI, and fluid intake. Over a combined 50 yr of follow-up, we documented 5645 incident kidney stones. Participants with higher DASH scores had higher intakes of calcium, potassium, magnesium, oxalate, and vitamin C and had lower intakes of sodium. For participants in the highest compared with the lowest quintile of DASH score, the multivariate relative risks for kidney stones were 0.55 (95% CI, 0.46 to 0.65) for men, 0.58 (95% CI, 0.49 to 0.68) for older women, and 0.60 (95% CI, 0.52 to 0.70) for younger women. Higher DASH scores were associated with reduced risk even in participants with lower calcium intake. Exclusion of participants with hypertension did not change the results. In conclusion, consumption of a DASH-style diet is associated with a marked decrease in kidney stone risk.Diet plays a major role in the development of kidney stones, and dietary changes likely have contributed to the substantial increase in nephrolithiasis over the past several decades.^1,2 A wide variety of dietary factors either promote or inhibit the formation of calcium oxalate kidney stones,^1,2 the most common type of stone.³Despite previously observed associations between individual dietary factors and kidney stone risk,² relatively few studies have examined the impact of overall diet or dietary patterns on risk. The identification of an effective stone prevention diet is difficult partly because most diets are isocaloric: if an individual reduces the intake of certain foods, he or she will increase the intake of other foods to maintain constant energy intake.⁴ As a result, consuming less of one dietary factor (such as animal protein⁵) to decrease stone risk may lead to the consumption of other factors (such as sucrose or fructose⁶) that increase risk.The Dietary Approaches to Stop Hypertension (DASH) diet, which is high in fruits and vegetables, moderate in low-fat dairy products, and low in animal protein represents a novel potential means of kidney stone prevention. The consumption of fruits and vegetables increases urinary citrate,⁷ an important inhibitor of calcium stone formation, and a diet with normal to high calcium content but low in animal protein and sodium decreases the risk of calcium oxalate stone recurrence by 51%.⁸ The DASH diet also lowers BP,⁹ which is particularly appealing given the high rates of prevalent and incident hypertension in stone formers.^10–14 Because the DASH diet would be expected to contain higher amounts of oxalate and vitamin C, both of which may increase calcium kidney stone risk,^15,16 the impact of the DASH diet on stone risk is currently unknown.To examine the relation between a DASH-style diet and the risk of incident kidney stones, we conducted prospective studies in three large cohorts: the Health Professionals Follow-up Study (HPFS), the Nurses'' Health Study I (NHS I), and the Nurses'' Health Study II (NHS II). Previously, we identified associations between individual dietary factors and stone risk in each of these study populations.^5,6,15–18 For the first time, we now report the impact of a specific dietary pattern on risk.     

Common Variants in Mendelian Kidney Disease Genes and Their Association with Renal Function

Many common genetic variants identified by genome-wide association studies for complex traits map to genes previously linked to rare inherited Mendelian disorders. A systematic analysis of common single-nucleotide polymorphisms (SNPs) in genes responsible for Mendelian diseases with kidney phenotypes has not been performed. We thus developed a comprehensive database of genes for Mendelian kidney conditions and evaluated the association between common genetic variants within these genes and kidney function in the general population. Using the Online Mendelian Inheritance in Man database, we identified 731 unique disease entries related to specific renal search terms and confirmed a kidney phenotype in 218 of these entries, corresponding to mutations in 258 genes. We interrogated common SNPs (minor allele frequency >5%) within these genes for association with the estimated GFR in 74,354 European-ancestry participants from the CKDGen Consortium. However, the top four candidate SNPs (rs6433115 at LRP2, rs1050700 at TSC1, rs249942 at PALB2, and rs9827843 at ROBO2) did not achieve significance in a stage 2 meta-analysis performed in 56,246 additional independent individuals, indicating that these common SNPs are not associated with estimated GFR. The effect of less common or rare variants in these genes on kidney function in the general population and disease-specific cohorts requires further research.CKD affects approximately 10% of the general population in industrialized nations, and is significantly associated with cardiovascular morbidity and mortality.^1–4 Traditional risk factors for CKD, including diabetes and hypertension, fail to fully explain the increased risk of CKD,^5–9 suggesting other factors including a genetic component. Family studies indicate familial aggregation of CKD and ESRD risk.¹⁰ For example, family studies have shown that genetic factors account for 36%–75% of the variability in kidney function, with similar estimates for disease susceptibility and CKD progression.^10–14 Therefore, unraveling the genetic underpinnings of CKD bears the potential of discovering novel disease mechanisms as a basis for research into much needed therapeutic targets and strategies.Genome-wide association studies (GWAS) recently identified several genomic loci associated with kidney traits.^15–21 The strongest of these associations is at the UMOD locus,^{15,17,18,20,22,23} a gene in which rare variants are known to cause autosomal-dominant kidney diseases with high risk for ESRD: MCKD2 (Online Mendelian Inheritance in Man [OMIM] database #603860), HNFJ1 (OMIM #162000), or GCKD (OMIM #609886). In addition, other kidney disease genes in which mutations follow Mendelian inheritance patterns were uncovered in GWAS of kidney function (SLC7A9, SLC34A1)¹⁷ and albuminuria (CUBN)²¹ in the general population. Similar examples exist for traits such as hypertension and dyslipidemia, in which common variants in genes causing inherited Mendelian diseases are identified in population-based GWAS.^24,25These findings lead us to hypothesize that additional common variants in monogenic kidney disease genes^26,27 are associated with kidney function in the general population but have not yet been identified by GWAS efforts due to power limitations related to multiple testing for nearly 2.5 million SNPs. Thus, we aimed to (1) create a comprehensive, curated database of monogenic kidney disease genes, (2) analyze the association of common genetic variants in these candidate genes with serum creatinine-based estimated GFR (eGFR) and secondarily with CKD in the general population, and (3) examine SNPs beneath the genome-wide threshold that would have been overlooked in prior GWAS of eGFR and CKD.^15,17–19     

Kidney and Recipient Weight Incompatibility Reduces Long-Term Graft Survival

Long-term function of kidney allografts depends on multiple variables, one of which may be the compatibility in size between the graft and the recipient. Here, we assessed the long-term consequences of the ratio of the weight of the kidney to the weight of the recipient (KwRw ratio) in a multicenter cohort of 1189 patients who received a transplant between 1995 and 2006. The graft filtration rate increased by a mean of 5.74 ml/min between the third and sixth posttransplantation months among patients with a low KwRw ratio (<2.3 g/kg; P < 0.0001). In this low KwRw ratio group, the graft filtration rate remained stable between 6 months and 7 years but then decreased at a mean rate of 3.17 ml/min per yr (P < 0.0001). In addition, low KwRw ratios conferred greater risk for proteinuria, more antihypertensive drugs, and segmental or global glomerulosclerosis. Moreover, a KwRw ratio <2.3 g/kg associated with a 55% increased risk for transplant failure by 2 years of follow-up. In conclusion, incompatibility between graft and recipient weight is an independent predictor of long-term graft survival, suggesting that avoiding kidney and recipient weight incompatibility may improve late clinical outcome after kidney transplantation.The effect of nephron reduction has long been described in animal models as well as in humans^1,2 and is thought to be a potential “nonimmunologic” risk factor for chronic graft dysfunction after kidney transplantation.^3,4 The paradigm generally considered to account for the deleterious effect of nephron reduction on graft function is that of “adaptive” hyperfiltration of the remaining glomeruli, ultimately leading to glomerulosclerosis.^5–7 In accordance with this hypothesis, individuals who have undergone nephrectomy have been shown to develop high BP and proteinuria decades after the nephrectomy,^8–11 as in the case of older recipients with a higher body mass index¹²; however, renal insufficiency only appears in the case of a 75% reduction in kidney mass and after at least 10 years of follow-up.⁹ Kidney transplantation has been proposed as an accelerated model of nephron reduction resulting from the accumulation of several unfavorable factors. For example, repeated injuries, from initial brain death of the donor¹³ to ischemia-reperfusion injury,¹⁴ negatively affect the transplant. Moreover, superimposed immunologic and nonimmunologic events further decrease the initial nephron mass of a transplant and serve only to exacerbate the consequences of hyperfiltration related to its single kidney status.Given that kidney weight (Kw) and glomerular volume (but not nephron number) correlate with body surface area (BSA),¹⁵ several studies have already analyzed the effect of donor and recipient BSA mismatches.^7,16–19 The effect of kidney graft size and recipient weight (Rw)^20,21 has also been studied; however, the direct impact of matching the Kw itself (which correlates with both glomerular volume and nephron number)¹⁵ to the Rw has been studied only in relatively small cohorts of <300 patients and only in living donors,^22,23 where the graft does not incur the same accumulating injuries as those from deceased donors.We previously reported on the results of a first study²⁴ focusing on the impact of graft weight on clinical outcome; however, within the relatively short survey period of the latter study (mean 32 months; range 8 days to 94 months), no impact on short-term graft survival was observed. Because renal failure has been described a decade after nephron reduction,^3,10,25 we reappraised our historical cohort to which an additional 47 patients were included (whole population n = 1189) at a mean of 6.2 years from transplantation (range 8 days to 13 years). We now report that the magnitude of the Kw and Rw incompatibility is significantly associated not only with sustained “adaptive” hyperfiltration and early proteinuria but also with an increased risk for hypertension requiring more medication, a higher incidence of segmental or global glomerulosclerosis, and a significantly poorer long-term transplant survival.     

Heme Oxygenase-1 Inhibits Renal Tubular Macroautophagy in Acute Kidney Injury

Autophagy is a tightly regulated, programmed mechanism to eliminate damaged organelles and proteins from a cell to maintain homeostasis. Cisplatin, a chemotherapeutic agent, accumulates in the proximal tubules of the kidney and causes dose-dependent nephrotoxicity, which may involve autophagy. In the kidney, cisplatin induces the protective antioxidant heme oxygenase-1 (HO-1). In this study, we examined the relationship between autophagy and HO-1 during cisplatin-mediated acute kidney injury (AKI). In wild-type primary proximal tubule cells (PTC), we observed a time-dependent increase in autophagy after cisplatin. In HO-1^−/− PTC, however, we observed significantly higher levels of basal autophagy, impaired progression of autophagy, and increased apoptosis after cisplatin. Restoring HO-1 expression in these cells reversed the autophagic response and inhibited apoptosis after treatment with cisplatin. In vivo, although both wild-type and HO-1–deficient mice exhibited autophagosomes in the proximal tubules of the kidney in response to cisplatin, HO-1–deficient mice had significantly more autophagosomes, even in saline-treated animals. In addition, ecdysone-induced overexpression of HO-1 in cells led to a delay in autophagy progression, generated significantly lower levels of reactive oxygen species, and protected against cisplatin cytotoxicity. These findings demonstrsate that HO-1 inhibits autophagy, suggesting that the heme oxygenase system may contain therapeutic targets for AKI.Oxidative stress plays a major role in the pathogenesis of cisplatin-induced nephrotoxicity.^1,2 In response to injury, the kidney is able to elicit adaptive and protective mechanisms to limit further damage. One such mechanism is the rapid and robust induction of heme oxygenase-1 (HO-1).^3–5 Heme oxygenase is the rate-limiting enzyme in the degradation of heme to iron, carbon monoxide, and biliverdin.^3,6,7 Studies have shown that HO-1 mRNA is induced in the kidney as early as 3 to 6 hours in animal models of both ischemia/reperfusion and nephrotoxin-induced acute kidney injury (AKI).^3,8 Such induction occurs predominantly in the proximal tubule segment of the nephron,^3,8 which coincides with the location of maximal cisplatin accumulation and oxidative stress.^9,10 Chemical inhibition of HO enzyme activity in rats³ and genetically deficient HO-1 mice¹¹ treated with cisplatin have significantly worse kidney function and tubular injury, suggesting a protective role for HO-1 expression in cisplatin-induced renal tubular cell death, specifically necrosis and apoptosis.Recent evidence indicates that autophagy, a type II programmed cell death, is induced during cisplatin injury in proximal tubular epithelial cells (PTC) and is a protective response.^12–15 Autophagy, a physiologically regulated and evolutionarily conserved process, refers to an intracellular degradation system in which cytoplasmic components, such as damaged organelles, long-lived proteins, protein aggregates, and other macromolecules, are directed to the lysosome.^16–19 Autophagy (also referred to as macroautophagy) begins with the formation of an initiation membrane (vesicle nucleation) that sequesters cytoplasmic components as it expands (vesicle elongation); finally, the edges fuse to form a double-membraned vesicle called autophagosome. This vesicle fuses with the lysosome to form an autolysosome where the sequestered components are degraded by the acidic lysosomal enzymes.^17,20 At least 31 Atg (Autophagy) genes have been identified in yeast and their mammalian orthologs have also been recently characterized.^21–24 Expression of the mammalian orthologs of Atg5, Atg6 (beclin 1), Atg7, and Atg8 (LC3, microtubule-associated protein 1 light chain 3) are used as markers to detect autophagy in mammalian cells.^13,25,26 Both Atg5 and beclin play an important role in autophagosome initiation and vesicle nucleation. Vesicle elongation requires several autophagy proteins such as Atg7 and Atg4. These proteins conjugate the lipid phosphatidylethanolamine to LC3 to form membrane-associated LC3-II. LC3-II is one of the autophagy proteins that specifically interacts only with the autophagic vesicles and remains associated until vesicle breakdown. All of the other proteins associate with the vesicle at different stages of maturation and have alternate functions in the cell. Therefore, LC3-II is a valuable marker to assess the presence of autophagosomes in cells.Several in vitro and in vivo studies suggest that autophagy can induce cell survival or death depending on the stress or the cellular environment.^{12,13,18,22,27} Under normal physiologic conditions, cells use autophagy to maintain homeostasis. If insufficient autophagy occurs, long-lived proteins and damaged organelles accumulate and cell death occurs. Even under certain pathologic conditions, autophagy is induced and is cytoprotective. However, if autophagy is prolonged or unregulated, it can lead to cell death. This suggests that autophagy may act as a cytoprotective mechanism but converges into apoptotic pathways during severe stress. Therefore, it is important to understand how autophagy is modulated as both insufficient and excessive autophagy have deleterious effects.Because both autophagy and HO-1 are induced during cisplatin injury, the purpose of this study was to evaluate whether HO-1 expression modulated autophagy in PTC and protected them from cisplatin-induced cell death. We studied the effects of HO-1 deficiency using HO-1 knockout (HO-1^−/−) mice on the progression of autophagy during cisplatin injury. Also, PTC cultures generated from HO-1^+/+ (heme oxygenase-1 wild-type) and HO-1^−/− mice were analyzed for cisplatin-mediated autophagy and cell death. Furthermore, HO-1^−/− mice that specifically express only the human HO-1 gene (HBAC mice, human HO-1 overexpressing bacterial artificial chromosome mice) were generated and PTC isolated from these mice were used to study the effects of restoring HO-1 expression on autophagy progression during cisplatin injury. Also, ecdysone inducible HO-1 overexpressing renal epithelial cells were generated and analyzed for cisplatin-mediated autophagy.     

Human Kidney Cell Reprogramming: Applications for Disease Modeling and Personalized Medicine

The ability to reprogram fully differentiated cells into a pluripotent embryonic state, termed induced pluripotent stem cells (iPSCs), has been met with great excitement. iPSC technology has advanced the fundamental study of disease modeling with the potential for cell-replacement therapy, especially in the neuronal and cardiac fields. However, renal medicine as of yet has not benefited from similar advancements. This review summarizes the unique characteristics of iPSCs and their potential applications for modeling kidney disease. Pioneering such endeavors could yield constructs that recapitulate disease phenotypes, open avenues for more targeted drug development, and potentially serve as replenishable sources for replacement of kidney cells in the setting of human disease.Through experimentation involving nuclear fusion came the realization that differentiated somatic cells have potential to show a plasticity that is not unidirectional.^1–3 Subsequent studies suggested the transfer of a single somatic cell nucleus into an enucleated unfertilized egg possessed the ability to not only form all three germ layers but also produce viable offspring.^4–6 Decades later, the direct reprogramming of fibroblasts into a pluripotent state, so-called induced pluripotent stem cells (iPSCs),^7,8 has renewed interest in what constitutes the reprogramming process. An explosion of subsequent studies confirms that a large variety of somatic cells can be efficiently reprogrammed into iPSCs^9–13 and subsequently redifferentiated into other cell types that recapitulate disease phenotypes.^14–16 Such information offers proof-of-principle for the use of iPSCs as useful in vitro modeling systems that could ultimately lead to novel drug development and testing. Additionally, as iPSCs are produced from individual patients, the derivation of patient-specific stem cell lines could provide a limitless source of clinically useful immune and genetically matched cells.Since the pioneering discovery by Takahashi and Yamanaka,^7,8 iPSCs have now been successfully generated from a wide array of human tissues.^14,16–20 Despite such advances, cell reprogramming with respect to the kidney remains in its infancy. Only recently has it been possible to derive iPSCs from kidney mesangial cells²¹ or epithelial cells sourced from urine.²² Furthermore, the directed differentiation of mesangial cell-derived iPSCs to podocyte-like cells (iPSC-podocyte)²³ and the generation of iPSCs from kidney disease patients has only recently been reported.²⁴Here we review our current knowledge regarding the use of pluripotent stem cells targeted at kidney disorders. Specifically, it will address certain shortcomings of traditional model systems, current knowledge regarding the differentiation of pluripotent stem cells into the kidney mesodermal lineage, and the advantages of reprogramming for in vitro disease modeling and therapeutic interventions. Finally, the efficiency and safety of iPSC technology that governs the prospective applications and clinical promise for kidney regeneration will also be discussed.     

Albuminuria and Kidney Function Independently Predict Cardiovascular and Renal Outcomes in Diabetes

There are limited data regarding whether albuminuria and reduced estimated GFR (eGFR) are separate and independent risk factors for cardiovascular and renal events among individuals with type 2 diabetes. The Action in Diabetes and Vascular disease: preterAx and diamicroN-MR Controlled Evaluation (ADVANCE) study examined the effects of routine BP lowering on adverse outcomes in type 2 diabetes. We investigated the effects of urinary albumin-to-creatinine ratio (UACR) and eGFR on the risk for cardiovascular and renal events in 10,640 patients with available data. During an average 4.3-yr follow-up, 938 (8.8%) patients experienced a cardiovascular event and 107 (1.0%) experienced a renal event. The multivariable-adjusted hazard ratio for cardiovascular events was 2.48 (95% confidence interval 1.74 to 3.52) for every 10-fold increase in baseline UACR and 2.20 (95% confidence interval 1.09 to 4.43) for every halving of baseline eGFR, after adjustment for regression dilution. There was no evidence of interaction between the effects of higher UACR and lower eGFR. Patients with both UACR >300 mg/g and eGFR <60 ml/min per 1.73 m² at baseline had a 3.2-fold higher risk for cardiovascular events and a 22.2-fold higher risk for renal events, compared with patients with neither of these risk factors. In conclusion, high albuminuria and low eGFR are independent risk factors for cardiovascular and renal events among patients with type 2 diabetes.Diabetes is a major global health problem, currently affecting an estimated 246 million people worldwide, with a doubling of this prevalence expected in the next 30 yr.¹ Compared with people without diabetes, affected individuals are at increased risk for both cardiovascular events and kidney disease.^2,3 Increased urinary albumin excretion (albuminuria) and reduced GFR both have been demonstrated to be risk factors for progressive kidney failure and cardiovascular disease.^4–9Guidelines therefore recommend the annual assessment of albuminuria and GFR, and this has become accepted as common practice.^10–13 Although both renal functional parameters are believed to be risk factors for cardiovascular events,^4–9 there are limited data as to whether these two factors are associated with adverse outcomes independent not only of other known cardiovascular risk factors but also of each other in people with type 2 diabetes.^14–19The BP-lowering arm of the Action in Diabetes and Vascular disease: preterAx and diamicroN-MR Controlled Evaluation (ADVANCE) study recently reported that the routine administration of a fixed combination of the angiotensin-converting enzyme inhibitor perindopril and the diuretic indapamide to a broad cross-section of patients with type 2 diabetes reduced the risk for cardiovascular and kidney outcomes, regardless of initial BP level.²⁰ More recently, the glucose-lowering arm of ADVANCE reported that intensive glucose lowering based on gliclazide (modified release) reduced the risk for new or worsening nephropathy.²¹ Herein, we present the findings of observational analyses examining the association between albuminuria and GFR at baseline or during follow-up and the risk for cardiovascular events and renal events in type 2 diabetes.     

H-Y Incompatibility Predicts Short-Term Outcomes for Kidney Transplant Recipients

A recent report suggested that female recipients of male deceased-donor kidneys are at increased risk for graft failure because of H-Y antigen mismatch. In an attempt to confirm and extend these results, we studied all adult recipients of deceased-donor kidney transplants from 1990 through 2004 in the US Renal Data System. Compared with all other gender combinations, female recipients of male donor kidneys had a 12% increased risk for graft failure at 1 yr (hazard ratio 1.12; 95% confidence interval 1.05 to 1.19) but no excess risk at 10 yr (hazard ratio 1.03; 95% confidence interval 0.98 to 1.07). We observed a similar pattern of short- and long-term risk for both death-censored graft failure and mortality. The main results were consistent across several prespecified patient subgroups and were robust to sensitivity analyses. In conclusion, compared with other recipient-donor gender combinations, female recipients of male donor kidney transplants in the United States have an increased short-term risk but not long-term risk for adverse outcomes.Allorecognition of human major histocompatibility antigens (i.e., HLA) and the associated immune response has important short- and long-term implications for successful kidney transplantation. Although much effort has been placed on trying to understand and control the immune response to these major histocompatibility antigens, relatively little is known about the role of minor histocompatibility antigens as determinants of outcome. H-Y antigens, derived from the Y chromosome, are a group of minor histocompatibility antigens that are widely expressed in human tissues¹ and have been found to be prognostically important for the survival of recipient–donor gender-mismatched hematopoietic stem cell transplants.^2–9Several studies of heart, lung, liver, and corneal transplantation have suggested that female recipients of male donor organs/tissues are at increased risk for adverse graft outcomes^10–13; however, other studies have failed to show this effect.^14–18 Recently, a report by Gratwohl et al.,¹⁹ using data from the Collaborative Transplant Study (CTS), suggested that, after adjustment for the independent effects of recipient and donor gender, female recipients of male deceased-donor kidney transplants (versus all other recipient–donor gender combinations) were significantly associated with a 6 to 8% increase in the risk for graft failure and a 10 to 11% increase in the risk for death-censored graft failure during 10-yr of follow-up. They termed this phenomenon the “H-Y effect”; however, only 18.6% of the patients in the study by Gratwohl et al. were from North America, and a previous report failed to show an H-Y effect in zero-mismatched, US living-donor kidney transplants.²⁰ In addition, the impact of adjusting for a more extensive set of covariates (including recipient and donor weight) was not assessed.Given their greater susceptibility to unmeasured or residual confounding (as compared with randomized, controlled trials), it is important to reproduce the results of observational studies in different patient populations from different data sources.²¹ In an attempt to confirm the results of Gratwohl et al. and to determine the relevance of the H-Y effect in deceased-donor kidney transplants performed in the United States, we undertook a retrospective cohort study using data from the US Renal Data System (USRDS). We used a modeling strategy similar to that of Gratwohl et al. and then extended it to include additional covariate data, an evaluation of prespecified subgroups, and various sensitivity analyses.     

Tolerance of the Human Kidney to Isolated Controlled Ischemia

Tolerance of the human kidney to ischemia is controversial. Here, we prospectively studied the renal response to clamp ischemia and reperfusion in humans, including changes in putative biomarkers of AKI. We performed renal biopsies before, during, and after surgically induced renal clamp ischemia in 40 patients undergoing partial nephrectomy. Ischemia duration was >30 minutes in 82.5% of patients. There was a mild, transient increase in serum creatinine, but serum cystatin C remained stable. Renal functional changes did not correlate with ischemia duration. Renal structural changes were much less severe than observed in animal models that used similar durations of ischemia. Other biomarkers were only mildly elevated and did not correlate with renal function or ischemia duration. In summary, these data suggest that human kidneys can safely tolerate 30–60 minutes of controlled clamp ischemia with only mild structural changes and no acute functional loss.Ischemia to the human kidney has been implicated as a common contributor to acute and chronic kidney injury from diverse medical and surgical causes.^1–3 However, to our knowledge the direct effect of controlled ischemia on human renal structure and function has never been evaluated prospectively. Current understanding of renal ischemia is derived from animal studies, the renal transplant setting, and retrospective human studies that report conflicting data regarding the response and tolerance of the human kidney to ischemia.^1–6 These studies suggest harmful effects from renal ischemia, resulting in the present dogma of limiting renal ischemia time during surgical procedures to within 20–30 minutes.⁶ Clinical trials in the field of AKI based on promising animal data have disappointed, suggesting that the human and small-animal kidney responses to ischemia may be qualitatively and quantitatively different.^7,8 They have also generated interest in better understanding of the human kidney ischemia response to allow optimal design of strategies to treat AKI, store kidneys for transplantation, and more safely use renal clamp ischemia during abdominal surgery.New biomarkers of renal injury are receiving increasing attention in an effort to achieve earlier diagnosis than provided by serum creatinine, better assess the extent and severity of parenchymal insults from different causes, and serve as markers during clinical trials.^9–14 However, their relationship to underlying structural changes during AKI in humans is unknown.Small renal masses make up 48%–66% of all renal tumors that are diagnosed and 38% of all renal tumors that are excised.¹⁵ There are approximately 65,000 new cases of renal cancer just in the United States, of which about 45,000 are amenable to nephron-sparing surgery.¹⁶ Despite the potential for a better outcome,¹⁷ only 10% of patients eligible for nephron sparing actually undergo a partial nephrectomy because of renal ischemia concerns; most have radical nephrectomy, which is technically easier.¹⁸ Several technically challenging nonclamping approaches have been recently proposed to avoid renal ischemia, with significantly higher complication rates.^19,20 Using open partial nephrectomy for excision of a renal mass involving direct clamp occlusion of the renal blood vessels, we have conducted a prospective study that evaluates for the first time the structural response of the human kidney to clamp ischemia and initial reperfusion in association with assessment of short-term renal functional outcomes and novel biomarkers. Our results document substantial resistance of the human kidney to clamp ischemia and have implications for both the basic understanding of ischemic injury in human kidneys and the care of patients requiring isolated controlled ischemia for partial nephrectomy and other procedures.