EGF IMPROVES RECOVERY FOLLOWING RELIEF OF UNILATERAL URETERAL OBSTRUCTION IN THE NEONATAL RAT

PURPOSE: Renal epidermal growth factor (EGF) is suppressed by unilateral ureteral obstruction (UUO), and we reported previously that exogenous EGF attenuates renal injury due to UUO in the neonatal rat. In this study, we wished to determine whether administration of epidermal growth factor (EGF) improves long-term renal cellular recovery after relief of obstruction. MATERIALS AND METHODS: One ureter of 1 day-old rats was occluded or sham-operated, and rats received daily injections of EGF, 0.1 mg./kg., or saline for the following 7 days. Five days following UUO, the obstruction was removed. Kidneys were removed 28 days following release of UUO or sham operation, and processed for histomorphometry and immunohistochemistry. RESULTS: Kidney weight and the number of glomeruli were reduced in the postobstructed kidney regardless of administration of EGF. However, EGF reduced tubular vimentin by 36% and clusterin expression by 70% (markers of tubular injury), and decreased tubular atrophy by 50% in the postobstructed kidney compared with saline-treated rats. EGF also reduced interstitial alpha-smooth muscle actin and interstitial collagen deposition by 50% in the postobstructed kidney. CONCLUSIONS: Short-term administration of EGF markedly attenuates both tubular and interstitial injury one month following the release of UUO in the neonatal rat. This suggests therapeutic potential for targeted delivery of growth factors to optimize recovery after release of urinary tract obstruction.     

Unilateral ureteral obstruction in neonatal rats leads to renal insufficiency in adulthood

BACKGROUND: Although unilateral ureteropelvic junction obstruction is the most common cause of congenital obstructive nephropathy in infants and children, management remains controversial, and follow-up after pyeloplasty is generally limited to the pediatric ages. We have developed a model of temporary unilateral ureteral obstruction (UUO) in the neonatal rat: One month following the relief of five-day UUO, the glomerular filtration rate (GFR) of the postobstructed kidney was normal despite a 40% reduction in the number of glomeruli and residual vascular, glomerular, tubular, and interstitial injury. METHODS: To determine whether hyperfiltration and residual injury of remaining nephrons leads to progression of renal insufficiency in later life, 31 rats were sham operated or subjected to left UUO at one day of age, with relief of UUO five days later, and were studied at one year of age. GFR was measured by inulin clearance, and the number of glomeruli, tubular atrophy, glomerular sclerosis, and interstitial fibrosis were measured by histomorphometry in sham, obstructed (UUO), and intact opposite kidneys. Intrarenal macrophages and alpha-smooth muscle actin were identified by immunohistochemistry. RESULTS: Despite relief of UUO, ultimate growth of the postobstructed kidney was impaired. The number of glomeruli was reduced by 40%, and GFR was decreased by 80%. However, despite significant compensatory growth of the opposite kidney, there was no compensatory increase in GFR, and proteinuria was increased. Moreover, glomerular sclerosis, tubular atrophy, macrophage infiltration, and interstitial fibrosis were significantly increased not only in the postobstructed kidney, but also in the opposite kidney. CONCLUSIONS: Although GFR is initially maintained following relief of five-day UUO in the neonatal rat, there is eventual profound loss of function of the postobstructed and opposite kidneys because of progressive tubulointerstitial and glomerular damage. These findings suggest that despite normal postoperative GFR in infancy, children undergoing pyeloplasty for ureteropelvic junction obstruction should be followed into adulthood. Elucidation of the cellular response to temporary UUO may lead to improved methods to assess renal growth, injury, and functional reserve in patients with congenital obstructive nephropathy.     

Recovery from release of ureteral obstruction in the rat: relationship to nephrogenesis

BACKGROUND: Obstructive nephropathy is a major cause of renal insufficiency in infants and children. Despite release of unilateral ureteral obstruction (UUO) in the first five days of life in the rat, renal growth is impaired, while glomerular filtration rate (GFR) is preserved at one month, but decreases markedly by one year. To test the hypothesis that renal recovery from UUO depends on the stage of nephrogenesis at the time of relief of obstruction, renal recovery from relief of five days UUO following completion of nephrogenesis (days 14 to 19) was compared with UUO during nephrogenesis (days 1 to 5). METHODS: Rats underwent UUO or sham operation at one day of age, with relief five days later. In additional groups of neonatal rats, the operation was at 14 days, with relief at 19 days. Three months later, blood pressure, GFR, urine flow, sodium and potassium excretion, and kidney weight were measured. In addition, the number of glomeruli, glomerular maturation, glomerular diameter, tubular atrophy, and interstitial fibrosis were determined in each kidney. The effects of five-day UUO on number of glomeruli was determined also in adult rats one month following relief of obstruction. RESULTS: Three months following relief of UUO during days 14 to 19, renal growth was decreased by 50%, compared to a 30% reduction following relief of UUO during days 1 to 5 (P < 0.05). The number of glomeruli was reduced by approximately 50% regardless of the timing of UUO, but glomerular size was reduced only in rats with UUO from days 14 to 19. Blood pressure and tubular atrophy were increased, and GFR, urine flow, sodium and potassium excretion were decreased in the postobstructed kidney of both neonatal groups. In the adult rat, the five-day UUO did not result in a decrease in the number of glomeruli. CONCLUSIONS: In the period immediately following nephrogenesis, the kidney is particularly susceptible to long-term injury from temporary UUO. This suggests that a delay in relief of significant ureteral obstruction should be avoided if diagnosed in the perinatal or neonatal period.     

Protein restriction ameliorates renal tubulointerstitial nephritis and reduces renal transforming growth factor-beta expression in unilateral ureteral obstruction.

In contrast to the substantial evidence for attenuation of the glomerular lesions by a low-protein (LP) diet, it remains to be determined whether and how such a diet lessens the progression of tubulointerstitial lesions, which show the strongest correlation with renal function. Chronic unilateral ureteral obstruction (UUO) results in interstitial fibrosis of the affected kidney. We investigated the therapeutic effects of an LP diet on the progression of interstitial fibrosis in UUO mice. Sixty ICR mice underwent UUO or sham operation; half of these mice were fed a normal-protein (NP) and the other half a LP diet. They were sacrificed at 3, 7 and 14 days postoperatively. The degree of tubular lesion, the distribution of transforming growth factor-beta (TGF-beta), alpha-smooth muscle actin and fibronectin and the activated TGF-beta 1 level were determined. The LP diet significantly reduced the progression of tubular injury, depositions of fibronectin, tubulointerstitial myofibroblast formation, the interstitial expression of TGF-beta-positive cells (at 14 days; NP = 6.91 +/- 3.35 vs. LP = 1.67 +/- 0.41; p < 0.005), and renal active TGF-beta 1 concentration (at 14 days; NP = 5.72 +/- 2.03 vs. LP = 2.96 +/- 0.72; p < 0.01). We conclude that protein restriction may aid the attenuation of progression of tubulointerstitial fibrosis through the reduction in tubulointerstitial expression of TGF-beta.     

Renal tubulointerstitial injury from ureteral obstruction in the neonatal rat is attenuated by IGF-1

BACKGROUND: The administration of insulin-like growth factor-1 (IGF-1) has been shown to ameliorate the renal injury resulting from ischemic acute renal failure. As there are a number of similarities between acute renal failure and obstructive nephropathy, we examined the effects of IGF-1 on the renal cellular response to unilateral ureteral obstruction (UUO) in the neonatal rat. METHODS: Forty-five rats were subjected to UUO or sham operation within the first 48 hours of life and received IGF-1 (2 mg/kg/day) or saline for the following three or seven days, after which kidneys were removed for study by morphometry and immunohistochemistry. To determine the effects of UUO on endogenous expression of IGF-1 and its receptor, six additional rats were subjected to UUO or sham operation, and mRNA was measured by solution hybridization. RESULTS: There was no effect of seven days of UUO on the renal expression of endogenous IGF-1 or its receptor. Moreover, seven days of exogenous IGF-1 did not improve the suppression of nephrogenesis, the delay in glomerular maturation, or the reduction in tubular proliferation induced by ipsilateral UUO. However, in the obstructed kidney, IGF-1 reduced tubular expression of vimentin, apoptosis, and tubular atrophy by 38 to 50% (P < 0.05). In addition, IGF-1 also decreased renal interstitial collagen deposition in the obstructed kidney by 44% (P < 0.05). Following three days of UUO, the administration of IGF-1 also reduced tubular apoptosis (P < 0.05), but did not alter tubular proliferation. CONCLUSIONS: IGF-1 has a profound salutary effect on the tubular and interstitial response to UUO in early development, without affecting glomerular injury or development. These results suggest that IGF-1 may have therapeutic potential in the management of congenital obstructive nephropathy.     

Variable chronic partial ureteral obstruction in the neonatal rat: a new model of ureteropelvic junction obstruction

BACKGROUND: Congenital ureteropelvic junction (UPJ) obstruction is a common developmental anomaly. To elucidate the mechanisms underlying the renal consequences of congenital UPJ obstruction, we have developed a new model of variable partial unilateral ureteral obstruction (UUO) in the neonatal rat. METHODS: Rat pups were subjected to sham-operation, complete UUO, or variable partial UUO within the first day of life. After 14 or 28 days, the relative number of glomeruli, cell proliferation, tubular apoptosis, tubular atrophy, and interstitial fibrosis were quantitated in histologic sections. Glomerular filtration rate (GFR) was determined after 28 days of partial or complete UUO. RESULTS: Following 70% to 75% reduction in ureteral diameter, renal growth from 14 to 28 days was reduced by 60%, and the number of glomeruli decreased by 50%. Renal pelvic diameter increased in proportion to the severity of obstruction following 14 days of partial UUO, and by 28 days, was maximally dilated regardless of the luminal diameter. Renal proliferation was increased, while tubular apoptosis, tubular atrophy, and interstitial fibrosis were less severe 14 days following partial UUO than in complete UUO. GFR was reduced by 80%, and proteinuria developed following 28 days of partial UUO. CONCLUSION: Renal function is impaired by chronic ipsilateral partial UUO, which reduces the number of nephrons, and leads to progressive renal pelvic dilatation. Tubular atrophy and interstitial fibrosis develop prior to significant renal pelvic dilatation. Correlation of clinically measurable parameters with renal morphometry or imaging studies in this model may lead to new approaches to the management of congenital UPJ obstruction.     

Long-term effects of 24-hr unilateral ureteral obstruction on renal function in the rat

To characterize the pattern of recovery following release of unilateral ureteral obstruction of 24-hr duration, rats were studied with whole kidney clearance techniques, 3 hrs, 8, 14, and 60 days after release. The single nephron glomerular filtration rate (SNGFR) of superficial and juxtamedullary nephrons was estimated with a modification of Hanssen's technique in rats studied 8 and 60 days after ureteral release. The whole kidney glomerular filtration rates (GFR) were decreased markedly 3 hrs after relief of obstruction, but gradually increased and by 14 days, the GFR of the postobstructed kidney (POK) and the contralateral kidney (CK) were comparable. This recovery of GFR was not a consequence of a homogeneous improvement in SNGFR. At 8 days, more than 15% of superficial and juxtamedullary nephrons were not filtering in the POK. This decrease in the percent of filtering nephrons persisted to 60 days post release, indicating a permanent loss of nephron units. The SNGFR of the residual nephrons of the POK was significantly greater than that of the CK at 8 and 60 days following ureteral release. Thus, acute unilateral ureteral obstruction results in a permanent loss of filtering nephrons, which is offset by hyperfiltration of those remaining. Abnormalities in renal tubule function persisted beyond the time (14 days) when whole kidney GFR had returned to normal. These abnormalities were in distal tubule function. Urine osmolality was consistently lower at all time intervals post release, as was net acid excretion. The results of the present study suggest that these abnormalities are a consequence of the reduction in the number of filtering juxtamedullary nephrons and/or to abnormalities in collecting duct function.     

Molecular and cellular pathophysiology of obstructive nephropathy

Congenital obstructive nephropathy remains one of the most-important causes of renal insufficiency in children. This review focuses on the unique interactions that result from urinary tract obstruction during the period of renal development in the neonatal rodent. Following unilateral ureteral obstruction (UUO), growth of the obstructed kidney is impaired and compensatory growth by the intact opposite kidney is related directly to the duration of obstruction. Development of the renal vasculature is delayed by UUO, and the activity of the intrarenal renin-angiotensin system is enhanced throughout the period of obstruction. Glomerular maturation is also delayed by UUO, and nephrogenesis is permanently impaired. The effects of UUO on the developing tubule are also profound, with a suppression of proliferation, stimulation of apoptosis, and the maintenance of an immature phenotype by tubular epithelial cells. Expression of tubular epidermal growth factor is suppressed and transforming growth factor-β1 and clusterin are increased. Maturation of interstitial fibroblasts is delayed, with progression of tubular atrophy and interstitial fibrosis resulting in part from continued activation of the renin-angiotensin system and oxygen radicals. Future efforts to prevent the consequences of congenital urinary tract obstruction must account for the dual effects of obstruction: interference with normal renal development and progression of irreversible tubulointerstitial injury. Received: 9 September 1998 / Revised: 9 November 1998 / Accepted: 13 November 1998     

Rapamycin attenuates unilateral ureteral obstruction-induced renal fibrosis

Unilateral ureteral obstruction (UUO) is a well-characterized hydronephrosis model exhibiting interstitial inflammatory-cell infiltration and tubular dilatation followed by tubulointerstitial fibrosis of the obstructed kidney. Our recent report indicates that rapamycin is effective for 50% of transplant recipients with chronic allograft nephropathy. In this study, we investigate the effect of rapamycin on UUO-induced renal fibrosis. UUO or sham-operated rats were randomly assigned to rapamycin or vehicle and were killed on days 7 and 14 after UUO or sham operation. Rapamycin decreased cross-sectional and gross-morphology changes in the obstructed kidney significantly. Rapamycin markedly blunted the increase in weight of the obstructed kidney, obstructed kidney length, and the obstructed/non-obstructed kidney weight ratio (by 74.6, 42.8, and 61.6% on day 14, respectively, all P<0.01). The scores for tubular dilatation, interstitial volume, interstitial collagen deposition, and alpha-smooth muscle actin (alpha-SMA) after UUO were significantly reduced by rapamycin. Rapamycin also decreased the number of infiltrative anti-ED1-positive cells and the gene expression of transforming growth factor (TGF)-beta1 (84.8 and 80.2% on day 7) after UUO (both P<0.01). By double immunostaining and Western analysis, rapamycin blocked the TGF-beta1-induced loss of E-cadherin expression and de novo increase of the expression of alpha-SMA in a dose-dependent manner. In conclusion, rapamycin significantly attenuated tubulointerstitial damage in a UUO-induced rat model of renal fibrosis, suggesting that rapamycin may have the potential to delay the progression of tubulointerstitial renal fibrosis.     

IN-1130, a novel transforming growth factor-beta type I receptor kinase (ALK5) inhibitor, suppresses renal fibrosis in obstructive nephropathy

The transforming growth factor-beta (TGF-beta) plays a central role in the progression of renal fibrosis. TGF-beta transduces its signal through the activin receptor-like kinase (ALK)5. IN-1130, a novel small molecule ALK5 inhibitor, inhibited the purified kinase domain of ALK5-mediated Smad3 phosphorylation with an IC(50) value of 5.3 nM. IN-1130 proved to be highly selective in a panel of 27 serine/threonine and tyrosine kinases including p38alpha mitogen-activated protein kinase. We evaluated the efficacy of IN-1130 to block renal fibrogenesis induced by unilateral ureteral obstruction (UUO) in rats. Either vehicle (saline) or IN-1130 (10 and 20 mg/kg/day) was intraperitoneally administered to UUO rats for 7 and 14 days. Phosphorylated Smad2 (pSmad2) and markers of fibrosis were analyzed in kidney tissues. In UUO control kidneys, interstitial fibrosis including tubular atrophy, loss and dilation, inflammatory cell infiltration, and fibroblast cell proliferation was prominent. These morphological changes were notably reduced by IN-1130 treatment. IN-1130 decreased levels of TGF-beta1 messenger RNA (mRNA), type I collagen mRNA, and pSmad2, compared to UUO control rats. As determined by measuring the hydroxyproline content, total kidney collagen amount was increased in UUO control kidneys, but significantly reduced by IN-1130 treatment, which was comparable to results of histochemical staining for collagen. IN-1130 also suppressed the expression of alpha-smooth muscle actin (alpha-SMA) and fibronectin in UUO kidneys. Our results show that IN-1130 suppressed the fibrogenic process of UUO, further underscoring the potential clinical benefits of IN-1130 in the treatment of renal fibrosis.     

Selectins mediate macrophage infiltration in obstructive nephropathy in newborn mice

BACKGROUND: Urinary tract obstruction during development leads to tubular atrophy and causes interstitial fibrosis. Macrophage infiltration into the interstitium plays a central role in this process. Selectins, a family of three adhesion molecules, are involved in leukocyte recruitment to sites of inflammation and immune activity. We investigated the role of selectins in obstructive nephropathy in newborn mice. METHODS: Triple selectin-deficient mice (EPL-/-), L-selectin deficient mice (L-/-) and wild type mice (WT) were subjected to complete unilateral ureteral obstruction (UUO) or sham operation within the first 48 hours of life, and were sacrificed 5 and 12 days later. Kidneys were removed, and sections were stained for macrophage infiltration (mAb F4/80), apoptosis (TUNEL), tubular atrophy (periodic acid-Schiff) and interstitial fibrosis (Masson trichrome). RESULTS: Selectin deficient mice showed a marked reduction in macrophage infiltration into the obstructed kidney compared to WT at day 5 and day 12 after UUO. Tubular apoptosis was strongly reduced in EPL-/- at day 5 after UUO, and in EPL-/- and L-/- at day 12 after UUO when compared to WT. The number of apoptotic tubular cells was correlated with macrophage infiltration, suggesting that macrophages stimulate tubular apoptosis in obstructive nephropathy. In addition, tubular atrophy and interstitial fibrosis were significantly diminished in EPL-/- and L-/- compared to WT at day 12 after UUO. CONCLUSION: Following UUO, selectins mediate macrophage infiltration into the obstructed kidney, which in turn may induce tubular apoptosis, tubular atrophy and interstitial fibrosis.     

Induction of p27KIP1 after unilateral ureteral obstruction is independent of angiotensin II.

BACKGROUND: Unilateral ureteral obstruction (UUO) is characterized by proliferation of tubular and interstitial cells, and infiltration of the renal parenchyma with macrophages/monocytes. These alterations lead ultimately to tubulointerstitial fibrosis and tubular atrophy. Some of these changes are caused by an activated renin-angiotensin system (RAS). We have previously demonstrated that angiotensin II induces the expression of the cell cycle inhibitor p27KIP1 in cultured tubular cells. The current study tested the hypothesis that interference with the RAS may modulate renal expression of p27KIP1 after UUO. METHODS: The ureter of the left kidney of Sprague-Dawley rats was ligated. Sham-operated animals served as controls. Rats were randomized in four groups and received one of the following: no therapy, enalapril, losartan, or triple therapy (hydralazine, reserpine, hydrochlorothiazide). Kidneys were removed and cortical protein lysates were prepared for the detection of p27KIP1 by Western blotting. Immunohistochemistry was performed for p27KIP1, PCNA, ED-1, and alpha-smooth muscle actin. Apoptosis was quantified by TUNEL-staining. RESULTS: p27KIP1 expression as detected by Western blotting reached a maximum 10 days after UUO. Tubular and interstitial cells contributed to this increase in p27KIP1 expression whereas the number of glomerular p27KIP1 positive cell did not change. p27KIP1-positive cells were macrophages/monocytes (positive ED-1 staining) or had the characteristics of myofibroblasts (positive alpha-smooth muscle actin staining). Tubular and interstitial proliferation [proliferating cell nuclear antigen (PCNA)-positive staining] and apoptosis [terminal deoxy transferase uridine triphosphate nick end labeling (TUNEL) staining] also was increased after UUO. However, individual cells stained either positive for p27KIP1 or PCNA, but not both. Although enalapril and losartan reduced the number of macrophages/monocytes and attenuated the degree of tubular and interstitial apoptosis, these drugs did not influence p27KIP1 expression. There was no change in the number of p27KIP1-positive cells in the contralateral kidney undergoing hypertrophy. CONCLUSION: Induction of p27KIP1 in this model represents an endogenous response to likely limit proliferation that is independent of angiotensin II. Since there was no close correlation between apoptosis and p27KIP1 expression, it may be that the overall number of p27KIP1 expressing cells sets a general restriction point for apoptosis rather than defines an individual level of cell fate.     

Macrophage infiltration and renal damage are independent of matrix metalloproteinase 12 in the obstructed kidney

Aim: To determine whether matrix metalloproteinase‐12 (MMP‐12) plays a functional role in renal interstitial macrophage accumulation, interstitial fibrosis or tubular apoptosis in the unilateral ureteric obstruction (UUO) model. Background: MMP‐12 is an enzyme that can cleave a number of extracellular matrix proteins and plays a role in macrophage‐mediated injury in experimental models of emphysema and antibody‐dependent glomerular disease. Macrophages are thought to promote renal fibrosis and tubular damage in the obstructed kidney. Furthermore, upregulation of MMP‐12 expression by infiltrating macrophages in the obstructed kidney has been described, but the potential role of MMP‐12 in renal injury induced by this non‐immune insult is unknown. Methods: Groups of eight MMP‐12 gene deficient (MMP‐12^?/?) and wild type (WT) C57BL/6J mice were killed 3, 7 or 14 days after UUO. Results: Analysis of three different lineage markers found no difference in the degree of interstitial macrophage accumulation between MMP‐12^?/? and WT UUO groups at any time point. Examination of renal fibrosis by total collagen staining, α‐SMA + myofibroblast accumulation, and TGF‐β1, PAI‐1 and collagen IV mRNA levels showed no difference between MMP‐12^?/? and WT UUO groups. Finally, tubular damage (KIM‐1 levels) and tubular apoptosis (cleaved caspase‐3) in the obstructed kidney was not affected by MMP‐12 gene deletion. Conclusion: In contrast to lung injury and antibody‐dependent glomerular injury, MMP‐12 is not required for renal interstitial macrophage accumulation, interstitial fibrosis or tubular damage in the obstructed kidney.     

Acute Ureteral Obstruction and Glomerulotubular Function in Rats

Urinary tract obstruction is a common cause of acute renal failure (ARF). During unilateral ureteral obstruction (UUO) arteriolar vasoconstriction, increase in tubular pressure, and ultrafiltrate retrodiffusion occur. We studied renal function of rats with surgical UUO for 24 hr. After this period of UUO, the contralateral kidney was removed and the right ureter was deobstructed. The control uninephrectomized group consisted of normal rats submitted to left uninephrectomy (UNx). Functional studies were performed 12 and 24 hr, and 7 days after deobstruction and UNx. We measured creatinine clearance, and fractional excretion of sodium and lithium. Using conventional formulas we calculated fractional proximal and distal sodium reabsorption. Initially we observed a reduction in glomerular filtration rate (GFR) after deobstruction (12 and 24 hr). However, after 7 days, the GFR was significantly higher in deobstructed rats than in controls (340.3 ± 18.3 vs. 286.4 ± 9.3 μL/min/100 g, p < 0.01). The dry kidney weight was also increased in these rats. The fractional sodium excretion was increased in deobstructed rats, mainly in early studies (12 and 24 hr). Whereas fractional proximal reabsorption was reduced in both groups, the fractional distal reabsorption was significantly decreased in the deobstructed group compared to UNX controls (93.9 ± 0.9 vs. 98.9 ± 0.1% after 24 hr, p < 0.01). Our data showed that UUO influenced both glomerular and tubular functions. A salient finding was the overcorrection of GFR 7 days after deobstruction. The renal release of hormones and growth factors could mediate these alterations in renal function through their vascular, tubular, and proliferative actions.     

Glomerulotubular disconnection in neonatal mice after relief of partial ureteral obstruction

Ureteropelvic junction obstruction is a common cause of congenital obstructive nephropathy. To study the pathogenesis of nephropathy, a variable-partial, complete or a sham unilateral ureteral obstruction (UUO) was produced in mice within 2 days of birth. The obstruction was released in some animals at 7 days and kidneys harvested at 7-42 days of age for histologic and morphometric study. Renal parenchymal growth was stunted by partial UUO with the impairment proportional to the duration and severity of obstruction. Proximal tubule apoptosis and glomerulotubular disconnection led to nephron loss. Relief of partial UUO arrested glomerulotubular disconnection, resolved tubule atrophy, and interstitial fibrosis with remodeling of the renal architecture. Relief of severe UUO did not result in recovery. Compensatory growth of the contralateral kidney depended on the severity of obstruction. Our studies indicate that relief of moderate UUO will minimize nephron loss. Application of this technique to mutant mice will help develop future therapies to enhance nephron recovery.     

Unilateral ureteral obstruction in early development alters renal growth: dependence on the duration of obstruction

PURPOSE: Over 90% of nephrogenesis in the rat takes place postnatally in the first 10 days, analogous to the midtrimester human fetus. We wished to determine the relationship between the duration of unilateral ureteral obstruction and growth and morphology of both kidneys following relief of the obstruction in the neonatal rat. MATERIALS AND METHODS: One ureter of 1 day-old rats was sham-operated or occluded and released 1, 2, 3, or 5 days later, or not released. Fourteen or 28 days later, renal mass, tubular atrophy, and interstitial fibrosis were determined in the obstructed and contralateral kidney of each group. RESULTS: At 28 days, there was a linear relationship between kidney/body weight ratio and duration of obstruction, such that the decrement in renal mass resulting from ipsilateral obstruction was precisely compensated by an equal increment in the mass of the contralateral kidney (both, p <0.0001). Tubular atrophy was increased 100-fold in kidneys of rats with 28 days continuous ipsilateral obstruction, while relief of obstruction after 2 to 5 days reduced tubular atrophy by 90% (p <0.01). Interstitial fibrosis was also markedly reduced by relief of obstruction, with the severity of fibrosis being proportional to the duration of obstruction. CONCLUSIONS: We conclude that ureteral obstruction during the critical period of nephrogenesis impairs growth of the obstructed kidney and stimulates growth of the contralateral kidney in direct proportion to the duration of obstruction. Moreover, counterbalance between the two kidneys is finely regulated. Even 2 days of ureteral obstruction (with subsequent relief) induces contralateral renal growth, and induces ipsilateral tubular atrophy. However, the time dependence of renal injury on duration of obstruction suggests that earlier relief of obstruction in the developing kidney may allow greater ultimate preservation of functional renal mass.     

Renal structural and functional repair in a mouse model of reversal of ureteral obstruction

The end point of immune and nonimmune renal injury typically involves glomerular and tubulointerstitial fibrosis. Although numerous studies have focused on the events that lead to renal fibrosis, less is known about the mechanisms that promote cellular repair and tissue remodeling. Described is a model of renal injury and repair after the reversal of unilateral ureteral obstruction (UUO) in male C57bl/6J mice. Male mice (20 to 25 g) underwent 10 d of UUO with or without 1, 2, 4, or 6 wk of reversal of UUO (R-UUO). UUO resulted in cortical tubular cell atrophy and tubular dilation in conjunction with an almost complete ablation of the outer medulla. This was associated with interstitial macrophage infiltration; increased hydroxyproline content; and upregulated type I, III, IV, and V collagen expression. The volume density of kidney occupied by renal tubules that exhibited a brush border was measured as an assessment of the degree of repair after R-UUO. After 6 wk of R-UUO, there was an increase in the area of kidney occupied by repaired tubules (83.7 +/- 5.9%), compared with 10 d UUO kidneys (32.6 +/- 7.3%). This coincided with reduced macrophage numbers, decreased hydroxyproline content, and reduced collagen accumulation and interstitial matrix expansion, compared with obstructed kidneys from UUO mice. GFR in the 6-wk R-UUO kidneys was restored to 43 to 88% of the GFR in the contralateral unobstructed kidneys. This study describes the regenerative potential of the kidney after the established interstitial matrix expansion and medullary ablation associated with UUO in the adult mouse.     

Osteopontin regulates renal apoptosis and interstitial fibrosis in neonatal chronic unilateral ureteral obstruction

Congenital obstructive nephropathy is a major cause of renal insufficiency in children. Osteopontin (OPN) is a phosphoprotein produced by the kidney that mediates cell adhesion and migration. We investigated the role of OPN in the renal response to unilateral ureteral obstruction (UUO) in neonatal mice. OPN null mutant (-/-) and wild-type (+/+) mice were subjected to sham operation or UUO within the first 2 days of life. At 7 and 21 days of age, fibroblasts (fibroblast-specific protein (FSP)-1), myofibroblasts (alpha-smooth muscle actin (SMA)), and macrophages (F4/80) were identified by immunohistochemical staining. Apoptotic cells were detected by terminal deoxy transferase uridine triphosphate nick end-labeling technique and interstitial collagen by Masson trichrome or picrosirius red stain. Compared to sham-operated or contralateral kidneys, obstructed kidneys showed increases in all parameters by 7 days, with further increases by 21 days. After 21 days UUO, there was an increase in tubular and interstitial apoptosis in OPN -/- mice as compared to +/+ animals (P<0.05). However, FSP-1- and alpha-SMA-positive cells and collagen in the obstructed kidney were decreased in OPN -/- compared to +/+ mice (P<0.05), whereas the interstitial macrophage population did not differ between groups. We conclude that OPN plays a significant role in the recruitment and activation of interstitial fibroblasts to myofibroblasts in the progression of interstitial fibrosis in the developing hydronephrotic kidney. However, OPN also suppresses apoptosis. Future approaches to limit the progression of obstructive nephropathy in the developing kidney will require targeting of specific renal compartments.     

A porcine model of relief of 3 days unilateral ureteral obstruction: study on the damage and self-repairing capability of the kidney

Objective To explore the reversibility of early stage tubular interstitial injury as well as the timing of reparation through the pig relief of unilateral ureteral obstruction (R-UUO) model. Methods Eight three-month-old female Guangxi BA-MA mini pigs were selected for the construction of R-UUO models. Five time points were set which were UUO 0 day, UUO 3 days, R-UUO 7 days, R-UUO 14 days, and R-UUO 21 days. Renal function, histological structure, and protein expressions of α-smooth muscle actin (α-SMA), vimentin and E-cadherin were evaluated at different time points. Results After 3 days of UUO, compared with UUO 0 day, serum creatinine levels were increased obviously and the kidney tissues presented varying degrees of damage. The expressions of α-SMA and vimentin were increased and E-cadherin expression was decreased (P＜0.05). Following R-UUO after 3 days of UUO, compared to UUO, serum creatinine levels were significantly decreased. Renal pathological tissue damage was repaired. The expressions of α-SMA and vimentin were decreased and E-cadherin expression was increased (P＜0.05). Conclusions The pig R-UUO animal model may provide a good platform to study the kidney injury and repair. The tubular injury may be fully reversed and repaired when removing the pathogenic factors if the renal tubular injury was at an earlier stage.