Administration of dexamethasone protects mice against ischemia/reperfusion induced renal injury by suppressing PI3K/AKT signaling

Dexamethasone (DEX), a ligand for glucocorticoid receptor (GR), has long been used in the clinical practice due to its anti-inflammatory and immunosuppressive properties. Given that ischemia/reperfusion (IR)-induced renal injury is featured by the excessive immune response; the current study is therefore designed to address the impact of dexamethasone on IR-induced renal injury, a common disorder in the clinical settings. Precondition of mice with 4 mg/kg of dexamethasone significantly attenuated IR-induced injury as manifested by the improved renal function along with ameliorated pathological changes and suppressed inflammatory infiltration. Mechanistic studies revealed that dexamethasone promotes GR activation, and by which it attenuates the signals for PI3K/AKT activation. Attenuated PI3K/AKT signaling thus suppresses inflammatory response which then protects kidneys from IR-induced injury. All together, our data support that dexamethasone could be a good alternative therapy for prevention and treatment of IR-induced renal injury in the clinical practice.     

A novel Danshensu/tetramethylpyrazine protects against Myocardial Ischemia Reperfusion Injury in rats

A new Danshensu/tetramethylpyrazine derivative (ADTM) with cardio-protection effects such as antioxidant, arterial relaxation, pro-angiogenesis and antiplatelet activities. Platelet activating factor receptor (PAFR) plays a key role in myocardial ischemia reperfusion (MIR) injury. This study aims to investigate the protective role of ADTM in MIR injury and clarify the potential role of PAFR. We measured the effects of ADTM on MIR injury in rats in vivo and hypoxia re-oxygenation (HR) injury in neonatal rat ventricular myocytes (NRVMs) in vitro. The results show that ADTM can significantly improve the IR-induced decline in heart function as increasing EF and FS, and restore the decreased cardiac hemodynamic parameters (LVSP, ± dp/dt max) and increased the level of LVEDP, decrease the infarct size of damaged myocardium and lactate dehydrogenase (LDH) activity in serum. Additionally, ADTM inhibits cardiomyocytes apoptosis, caspase-3 activity, and inflammatory response as well as down-regulates the MIR-induced IL-1β and TNFα production. Next, PAFR expression was significantly down-regulated in cardiomyocytes of MIR model in vivo and in vitro after treated with ADTM compare to IR group. At the same time, ADTM and PAFR small interfering RNA (siRNA) could inhibit cardiomyocytes apoptosis and inflammation during HR, while PAF presents the opposite effect. Furthermore, the above effects of PAF in HR induced cardiomyocytes were reversed by co-treatment of ADTM. Our findings demonstrate for the first time that ADTM protects against MIR injury through inhibition of PAFR signaling, which provides a new treatment for MIR.     

A Tissue-Specific Role for Nlrp3 in Tubular Epithelial Repair after Renal Ischemia/Reperfusion

Ischemia/reperfusion injury is a major cause of acute kidney injury. Improving renal repair would represent a therapeutic strategy to prevent renal dysfunction. The innate immune receptor Nlrp3 is involved in tissue injury, inflammation, and fibrosis; however, its role in repair after ischemia/reperfusion is unknown. We address the role of Nlrp3 in the repair phase of renal ischemia/reperfusion and investigate the relative contribution of leukocyte- versus renal-associated Nlrp3 by studying bone marrow chimeric mice. We found that Nlrp3 expression was most profound during the repair phase. Although Nlrp3 expression was primarily expressed by leukocytes, both leukocyte- and renal-associated Nlrp3 was detrimental to renal function after ischemia/reperfusion. The Nlrp3-dependent cytokine IL-1β remained unchanged in kidneys of all mice. Leukocyte-associated Nlrp3 negatively affected tubular apoptosis in mice that lacked Nlrp3 expression on leukocytes, which correlated with reduced macrophage influx. Nlrp3-deficient (Nlrp3KO) mice with wild-type bone marrow showed an improved repair response, as seen by a profound increase in proliferating tubular epithelium, which coincided with increased hepatocyte growth factor expression. In addition, Nlrp3KO tubular epithelial cells had an increased repair response in vitro, as seen by an increased ability of an epithelial monolayer to restore its structural integrity. In conclusion, Nlrp3 shows a tissue-specific role in which leukocyte-associated Nlrp3 is associated with tubular apoptosis, whereas renal-associated Nlrp3 impaired wound healing.Ischemia/reperfusion (IR) injury is a major cause of acute kidney injury¹ and increases the risk of developing chronic kidney disease (CKD).² After injury, wounded tissue organizes an efficient response that aims to combat infections, clear cell debris, re-establish cell number, and reorganize tissue architecture. First, necrotic tissue releases danger-associated molecular patterns, such as high-mobility group box-1³ or mitochondrial DNA,⁴ which leads to chemokine secretion⁵ and a subsequent influx of leukocytes. Second, neutrophils and macrophages clear cellular debris but also increase renal damage because depletion of neutrophils⁶ or macrophages within 48 hours of IR will reduce renal damage.⁷ At approximately 72 hours of reperfusion, the inflammatory phase transforms into the repair phase and is characterized by surviving tubular epithelial cells (TECs) that dedifferentiate, migrate, and proliferate to restore renal function.⁸Previously, we have shown that Toll-like receptor (TLR) 2 and TLR4 play a detrimental role after acute renal IR injury.^{9, 10, 11} In addition, TLR2 appeared also pivotal in mediating tubular repair in vitro after cisplatin-induced injury,¹² indicating a dual role for TLR2. The cytosolic innate immune receptor Nlrp3 is able to sense cellular damage¹³ and mediates renal inflammation and pathological characteristics after IR^{14, 15, 16} or nephrocalcinosis.¹⁷ Next to the detrimental role of Nlrp3 in different renal disease models and consistent with the dual role of TLR2, Nlrp3 was shown to protect against loss of colonic epithelial integrity.¹⁸ We, therefore, speculate that Nlrp3, which contributes to sterile renal inflammation during acute renal IR injury, might also drive subsequent tubular repair.To test this hypothesis, we investigated the role of leukocyte- versus renal-associated Nlrp3 with respect to tissue repair after renal IR. We observed that both renal- and leukocyte-associated Nlrp3s are detrimental to renal function after renal IR injury; however, this is through different mechanisms. Leukocyte-associated Nlrp3 is related to increased tubular epithelial apoptosis, whereas renal-associated Nlrp3 impairs the tubular epithelial repair response. Our data suggest Nlrp3 as a negative regulator of resident tubular cell proliferation in addition to its detrimental role in renal fibrosis and inflammation.^{14, 19}     

The opposite roles of nNOS in cardiac ischemia–reperfusion-induced injury and in ischemia preconditioning-induced cardioprotection in mice

The role of neuronal nitric oxide synthase (nNOS) in cardiac ischemia–reperfusion (IR) and ischemia preconditioning (IP) is still controversial. Here, we focused on the possible roles of nNOS in cardiac IR and IP. Wild type C57BL/6 (WT) mice were subjected to coronary artery occlusion for 30 min followed by 24-h reperfusion (IR). Cardiac injury (infarct size and apoptotic cell number) was increased, associated with elevation of oxidative stress (lipid peroxidation) and nitrative stress (nitrotyrosine formation). A potent nNOS inhibitor, L-VNIO, and a superoxide dismutase mimetic and peroxynitrite scavenger, MnTBAP, significantly reduced IR-induced increases of oxidative/nitrative stress and cardiac injury. IR-induced cardiac injury in nNOS^−/− (KO) mice was significantly lower than that in WT mice. MnTBAP markedly reduced IR-induced cardiac injury by suppression of oxidative/nitrative stress in KO mice. Cardiac IP was performed by three cycles of 5-min IR before 30-min ischemia followed by 24-h reperfusion. IP attenuated IR-induced cardiac injury in WT mice associated with reductions of oxidative/nitrative stress. IP-induced reduction of cardiac injury and oxidative/nitrative stress were eliminated by pretreatment with L-VNIO. In contrast with WT mice, IP had no protective effects in nNOS KO mice. In conclusion, nNOS played a dual role during cardiac IR and IP; nNOS exacerbated IR-induced injury by increasing oxidative/nitrative stress and contributed to IP-induced protection by inhibition of oxidative/nitrative stress.     

Plasmacytoid dendritic cells promote acute kidney injury by producing interferon-α

Acute kidney injury (AKI) is a common clinical complication associated with high mortality in patients. Immune cells and cytokines have recently been described to play essential roles in AKI pathogenesis. Plasmacytoid dendritic cells (pDCs) are a unique DC subset that specializes in type I interferon (IFN) production. Here, we showed that pDCs rapidly infiltrated the kidney in response to AKI and contributed to kidney damage by producing IFN-α. Deletion of pDCs using DTR^BDCA2 transgenic (Tg) mice suppressed cisplatin-induced AKI, accompanied by marked reductions in proinflammatory cytokine production, immune cell infiltration and apoptosis in the kidney. In contrast, adoptive transfer of pDCs during AKI exacerbated kidney damage. We further identified IFN-α as the key factor that mediated the functions of pDCs during AKI, as IFN-α neutralization significantly attenuated kidney injury. Furthermore, IFN-α produced by pDCs directly induced the apoptosis of renal tubular epithelial cells (TECs) in vitro. In addition, our data demonstrated that apoptotic TECs induced the activation of pDCs, which was inhibited in the presence of an apoptosis inhibitor. Furthermore, similar deleterious effects of pDCs were observed in an ischemia reperfusion (IR)-induced AKI model. Clinically, increased expression of IFN-α in kidney biopsies was observed in kidney transplants with AKI. Taken together, the results of our study reveal that pDCs play a detrimental role in AKI via IFN-α.     

Apoptosis of leukocytes triggered by acute DNA damage promotes lymphoma formation

Apoptosis triggered by p53 upon DNA damage secures removal of cells with compromised genomes, and is thought to prevent tumorigenesis. In contrast, we provide evidence that p53-induced apoptosis can actively drive tumor formation. Mice defective in p53-induced apoptosis due to loss of its proapoptotic target gene, puma, resist γ-irradiation (IR)-induced lymphomagenesis. In wild-type animals, repeated irradiation injury-induced expansion of hematopoietic stem/progenitor cells (HSCs) leads to lymphoma formation. Puma^−/− HSCs, protected from IR-induced cell death, show reduced compensatory proliferation and replication stress-associated DNA damage, and fail to form thymic lymphomas, demonstrating that the maintenance of stem/progenitor cell homeostasis is critical to prevent IR-induced tumorigenesis.     

低氧诱导因子1α基因修饰脂肪干细胞修复小鼠急性肾损伤

背景：干细胞移植为肾损伤的治疗提供了一个新的途径,治疗基因转染干细胞可增强对疾病的治疗效果。 目的：探讨低氧诱导因子1α基因修饰的脂肪源性干细胞移植对急性肾损伤小鼠肾脏结构和功能的影响。 方法：连续2 d向BALB/C裸鼠腹腔注射10 mg/kg顺铂诱导急性肾损伤小鼠模型。造模24 h后经小鼠尾静脉注射含1×10⁵个脂肪源性干细胞或转染低氧诱导因子1α的脂肪源性干细胞的细胞悬液,3 d后留取小鼠血液及肾组织标本进行实验。以注射200 μL生理盐水的急性肾损伤小鼠作为模型对照,以正常小鼠作为正常对照。 结果与结论：脂肪源性干细胞干预后急性肾损伤小鼠血清肌酐、尿素氮水平降低,肾组织病理改变及肾小管上皮细胞的凋亡病变减轻,肾组织炎症因子RANTES、肿瘤坏死因子α表达降低,白细胞介素10表达升高;其中低氧诱导因子1α基因修饰的脂肪源性干细胞对肾组织细胞凋亡及炎症因子表达作用更明显。免疫荧光染色可见移植的脂肪源性干细胞的存活,但未见其向肾小管上皮细胞转化。结果表明脂肪源性干细胞移植可改善急性肾损伤小鼠的肾脏结构和功能,经低氧诱导因子1α基因修饰后的脂肪源性干细胞作用更显著。     

Expression of Fas and Fas Ligand on Mouse Renal Tubular Epithelial Cells in the Generalized Shwartzman Reaction and Its Relationship to Apoptosis

Previously we reported that the consecutive injection of lipopolysaccharide (LPS) into LPS-sensitized mice for the generalized Shwartzman reaction (GSR) appeared to induce the injury of renal tubular epithelial cells via apoptosis. The aim of this study was to characterize the mechanism of renal tubular epithelial cell injury in GSR. The expression of Fas and Fas ligand was immunohistochemically detected on renal tubular epithelial cells from GSR-induced mice, although neither Fas nor Fas ligand was found in cells from untreated control mice or in cells from mice receiving a single injection of LPS. GSR-induced renal tubular epithelial cell injury was produced in neither Fas-negative MRL-lpr/lpr mice nor Fas ligand-negative MRL-gld/gld mice. The administration of anti-gamma interferon antibody together with a preparative injection of LPS prevented the expression of Fas and Fas ligand and the apoptosis of renal tubular epithelial cells. A provocative injection of tumor necrosis factor alpha into LPS-sensitized mice augmented Fas and Fas ligand expression and the apoptosis of renal tubular epithelial cells. The administration of tumor necrosis factor alpha to interleukin-12-sensitized mice resulted in Fas and Fas ligand expression and the apoptosis. Sensitization with interleukin-12 together with anti-gamma interferon antibody did not cause the apoptosis of renal tubular epithelial cells. It was suggested that the Fas/Fas ligand system probably plays a critical role in the development of renal tubular epithelial cell injury through apoptotic cell death.     

Nephroprotective effect of methanol extract of Moringa oleifera leaves on acute kidney injury induced by ischemia-reperfusion in rats

BackgroundMoringa oleifera is known to exhibit protection against oxidative damage due to its rich content of compounds with antioxidant activity. This study investigated the protective effect of the methanol extract of Moringa oleifera (MO) in a rat model of renal ischemia-reperfusion (IR) injury.MethodsForty two wistar rats were randomly assigned to six groups of seven rats each, as follows: A, control group; B, sham-operated group; C, IR group; D, IR + low dose (200 mg/kg) MO; E, IR + high dose (400 mg/kg) MO and F, IR + Vitamin C (200 mg/kg). Unilateral ischaemia was induced by occluding the left renal artery for 45 minutes followed by reperfusion up to 24 hours.ResultsMoringa oleifera significantly (p<0.05) ameliorated IR-induced increases in malondialdehyde (MDA), protein carbonyls (PC) and advanced oxidation protein products (AOPP), while also decreasing serum BUN and Creatinine levels. Moreover, the low dose of MO caused reductions in renal NO and H₂O₂ levels, while increasing renal GPx and GST activities. Histopathology revealed marked improvement of tissue alterations induced by IR with both doses of MO.ConclusionOverall, the methanol extract of M. oleifera effectively attenuated the deleterious effects of renal IR via alleviation of tissue oxidative stress.     

Macrophages promote heat stress nephropathy in mice via the C3a-C3aR-TNF pathway

Heat-stress nephropathy (HSN) is associated with recurrent dehydration. However, the mechanisms underlying HSN remain largely unknown. In this study, we evaluated the role of dehydration in HSN and kidney injury in mice. Firstly, we found that complement was strongly activated in the mice that were exposed to dehydration; and among complement components, the interaction between C3a and its receptor, C3aR, was more closely associated with kidney injury. Then two-month-old mice were intraperitoneally injected with 2% dimethyl sulfoxide (DMSO) or the C3aR inhibitor SB290157 during dehydration. DMSO-treated mice exhibited excessive macrophage infiltration, renal cell apoptosis, and kidney fibrosis. In contrast, SB290157-treated mice had no apparent kidney injury. By fluorescence-activated cell sorting (FACS), we found that SB290157 treatment in mice remarkably inhibited macrophage infiltration and suppressed CCR2 expression in macrophages. In addition, C3a binding to C3aR promoted macrophage polarization toward the M1 phenotype and increased the production of TNF-α, which induced renal tubular epithelial cell (RTEC) apoptosis in vivo and in vitro. Interestingly, C3a treatment failed to directly induce TNF-α production and apoptosis in RTECs. However, TNF-α production in response to C3a treatment was significantly elevated when RTECs were cocultured with macrophages, suggesting that macrophages rather than RTECs are the target of C3a-C3aR interaction. At last, we proved that infusion of macrophages which highly expressed TNF-α would significantly deteriorate HSN in TNF-KO mice when they were exposed to recurrent dehydration. This study uncovers a novel mechanism underlying the pathogenesis of HSN, and a potential pathway to prevent kidney injury during dehydration.     

Shiga toxin‐2 results in renal tubular injury but not thrombotic microangiopathy in heterozygous factor H‐deficient mice

Haemolytic uraemic syndrome (HUS) is characterized by microangiopathic haemolytic anaemia, thrombocytopenia and renal failure because of thrombotic microangiopathy (TMA). It may be caused by infection with Shiga toxin-producing enteropathic bacteria (Stx-associated HUS) or with genetic defects in complement alternative pathway (CAP) regulation (atypical HUS). We hypothesized that defective complement regulation could increase host susceptibility to Stx-associated HUS. Hence, we studied the response of mice with heterozygous deficiency of the major CAP regulator, factor H, to purified Stx-2. Stx-2 was administered together with lipopolysaccharide to wild-type and Cfh^+/− C57BL/6 animals. Forty-eight hours after administration of the first Stx-2 injection all animals developed significant uraemia. Renal histology demonstrated significant tubular apoptosis in the cortical and medullary areas which did not differ between wild-type or Cfh^+/− Stx-2-treated mice. Uraemia and renal tubular apoptosis did not develop in wild-type or Cfh^+/− animals treated with lipopolysaccharide alone. No light microscopic evidence of TMA or abnormal glomerular C3 staining was demonstrable in the Stx-2 treated animals. In summary, Stx-2 administration did not result in TMA in either Cfh^+/− or wild-type C57BL/6 mice. Furthermore, haploinsufficiency of factor H did not alter the development of Stx-2-induced renal tubular injury.     

The Toll Interleukin-1 Receptor (IL-1R) 8/Single Ig Domain IL-1R-Related Molecule Modulates the Renal Response to Bacterial Infection

Our immune system has to constantly strike a balance between activation and inhibition of an inflammatory response to combat invading pathogens and avoid inflammation-induced collateral tissue damage. Toll interleukin-1 receptor 8 (IL-1R-8)/single Ig domain IL-1R-related molecule (TIR8/SIGIRR) is an inhibitor of Toll-like receptor (TLR)/IL-1R signaling, which is predominantly expressed in the kidney. The biological role of renal TIR8 during infection is, however, unknown. We therefore evaluated renal TIR8 expression during Escherichia coli pyelonephritis and explored its role in host defense using TIR8^−/− versus TIR8^+/+ mice. We found that TIR8 protein is abundantly present in the majority of cortical tubular epithelial cells. Pyelonephritis resulted in a significant downregulation of TIR8 mRNA in kidneys of TIR8^+/+ mice. TIR8 inhibited an effective host response against E. coli, as indicated by diminished renal bacterial outgrowth and dysfunction in TIR8^−/− mice. This correlated with increased amounts of circulating and intrarenal neutrophils at the early phase of infection. TIR8^−/− tubular epithelial cells had increased cytokine/chemokine production when stimulated with lipopolysaccharide (LPS) or heat-killed E. coli, suggesting that TIR8 played an anti-inflammatory role during pathogen stimulation by inhibiting LPS signaling. These data suggest that TIR8 is an important negative regulator of an LPS-mediated inflammatory response in tubular epithelial cells and dampens an effective antibacterial host response during pyelonephritis caused by uropathogenic E. coli.     

Gene silencing of complement C5a receptor using siRNA for preventing ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injury in organ transplantation significantly contributes to graft failure and is untreatable using current approaches. I/R injury is associated with activation of the complement system, leading to the release of anaphylatoxins, such as C5a, and the formation of the membrane attack complex. Here, we report a novel therapy for kidney I/R injury through silencing of the C5a receptor (C5aR) gene using siRNA. Mice were injected with 50 μg of C5aR siRNA 2 days before induction of ischemia. Renal ischemia was then induced through clamping of the renal vein and artery of the left kidney for 25 minutes. The therapeutic effects of siRNA on I/R were evaluated by assessment of renal function, histopathology, and inflammatory cytokines. siRNA targeting C5aR efficiently inhibited C5aR gene expression both in vitro and in vivo. Administering C5aR siRNA to mice preserved renal function from I/R injury, as evidenced by reduced levels of serum creatinine and blood urea nitrogen in the treated groups. Inhibition of C5aR also diminished in vivo production of the pro-inflammatory cytokine tumor necrosis factor-α and chemokines MIP-2 and KC, resulting in the reduction of neutrophils influx and cell necrosis in renal tissues. This study demonstrates that siRNA administration represents a novel approach to preventing renal I/R injury and may be used in a variety of clinical settings, including transplantation and acute tubular necrosis.     

The effects of selenium against cerebral ischemia-reperfusion injury in rats

It is known that the brain tissue is extremely sensitive to ischemia-reperfusion (IR) injury and therefore, brain ischemia and consecutive reperfusion result in neural damage and apoptosis. The proinflammatory cytokines such as tumor necrosis factor alfa (TNF-α) and interleukin-1 beta (IL-1β) are produced during neurological disorders including cerebral ischemia. On the other hand, nerve growth factor (NGF), which is essential for the differentiation, survival and functions of neuronal cells in the central nervous system, regulate neuronal development through cell survival and cell death signaling. In the present study, we aimed to investigate the effect of selenium (Se) on prefrontal cortex and hippocampal damage in rats subjected to cerebral IR injury. Selenium was injected intraperitoneally at the doses of 0.625 mg/(kg day) after induction of IR injury. Prefrontal cortex and hippocampal damage was examined by cresyl-violet staining. Apostain and caspase-3 immune staining were used to detect apoptosis. TNF-α, IL-1β and NGF levels were also evaluated. Histopathological evaluation showed that treatment with selenium after ischemia significantly attenuated IR-induced neuronal death in prefrontal cortex and hippocampal CA1 regions of rats. Apoptotic cells stained with apostain and caspase-3 were significantly decreased in treatment group when compared with the IR group. Additionally, treatment with selenium decreased the TNF-α and IL-1β levels and increased the NGF levels in prefrontal cortex and hippocampal tissue of animals subjected to IR. The present results suggest that selenium is potentially a beneficial agent in treating IR-induced brain injury in rats.     

Deficit of p66ShcA restores redox-sensitive stress response program in cisplatin-induced acute kidney injury

Overwhelming oxidative stress and compromised tubular cell antioxidant response have been incriminated for cisplatin (Cis)-induced acute kidney injury (AKI). We hypothesized that Cis-induced AKI was the outcome of the deactivated redox-sensitive stress response program (RSSRP). Wild type (WT) and heterozygous p66ShcA(p66^+/−) mice in groups of six were administered either normal saline (WT) or Cis (12.5 mg/kg, intraperitoneal, Cis/WT). Renal biomarkers were collected and kidneys were harvested for renal histology. Cis/WT showed elevated blood urea nitrogen levels and enhanced tubular cell apoptosis, necrosis, and dilated tubules filled with casts when compared to Cis/p66^+/−. Cis/p66^+/− developed only a clinically occult AKI (normal blood urea levels and only microscopic alterations). Immunoblots from the lysates of renal tissues of Cis/WT displayed enhanced expression of phospho-p66ShcA, and phospho-Foxo3A but attenuated expression of MnSOD and catalase; conversely, p66 deficit prevented these alterations in Cis milieu. In in vitro studies, Cis treated mouse proximal tubular cells (MPTCs) displayed enhanced phosphorylation of p66ShcA and no increase in tubular cell expression of MnSOD. In addition, renal tissues of Cis/WT and Cis-treated MPTCs displayed enhanced phosphorylation of p53 and Bax expression. However, MPTC partially silenced for p66ShcA displayed partial inhibition of Cis-induced tubular cell apoptosis as well as necrosis. These findings indicate that Cis-induced AKI is the outcome of the deactivated RSSRP (attenuated anti-oxidant response) and activation of pro-apoptotic (p53-induced Bax expression) pathway.     

Netrin-1 Attenuates Cardiac Ischemia Reperfusion Injury and Generates Alternatively Activated Macrophages

Ischemia reperfusion (IR) injury is a major issue in cardiac transplantation and inflammatory processes play a major role in myocardial IR injury. Netrin-1 is a laminin-related protein identified as a neuronal guidance cue and netrin-1 expressed outside the nervous system inhibits migration of leukocytes in vitro and in vivo and attenuates inflammation-mediated tissue injury. In our study, hearts of C57BL/6 mice were flushed and stored in cold Bretschneider solution for 8 h and then transplanted into syngeneic recipient. We found that netrin-1 decreased cardiomyocyte apoptosis and recruitment of neutrophils and macrophages. Troponin T (TnT) production on 24 h after myocardial IR injury was reduced by netrin-1 administration. Cardiac output at 60 mmHg of afterload pressure was significantly increased in hearts with netrin-1 administration (IR?+?Netrin-1: 59.9?±?5.78 ml/min; IR: 26.2?±?4.3 ml/min; P?<?0.05). Netrin-1 treatment increased expression of the alternatively activated macrophage (AAM) markers arginase-1 (Arg-1) and mannose receptor (MR) and promoted proliferator-activated receptor γ (PPARγ) expression in cardiac allograft. Furthermore, decreased TnT expression and reduced allograft infiltration of neutrophils and monocytes/macrophages by netrin-1 was abolished with addition of PPARγ antagonist. In conclusion, netrin-1 attenuates cardiac IR injury and generates AAM which contributes to the protective effect of netrin-1.     

Apoptosis of tubular epithelial cells in rats with chronic renal failure

Tubular injury leading to tubular atrophy and tubular loss is one of the characteristic features of chronic renal failure. To reveal the mechanism of tubular atrophy in chronic renal failure, the involvement of apoptosis was studied byin situ nick end labeling of biotinylated deoxyuridine by terminal deoxy nucleotidyl transferase (TUNEL) as well as by electron microscopy. TUNEL-positive cells and heterophagosomes containing apoptotic body-like structures having nuclear fragments with condensed chromatin were observed in the renal tubular epithelium 8 weeks after nephrectomy. It has become apparent from our study that atrophy of the tubules in chronic renal failure results, to some extent, from cell deletion by apoptosis.     

Deletion of Mir155 Prevents Fas-Induced Liver Injury through Up-Regulation of Mcl-1

Fas-induced apoptosis is involved in diverse liver diseases. Herein, we investigated the effect of Mir155 deletion on Fas-induced liver injury. Wild-type (WT) mice and Mir155 knockout (KO) mice were i.p. administered with the anti-Fas antibody (Jo2) to determine animal survival and the extent of liver injury. After Jo2 injection, the Mir155 KO mice exhibited prolonged survival versus the WT mice (P < 0.01). The Mir155 KO mice showed lower alanine aminotransferase and aspartate aminotransferase levels, less liver tissue damage, fewer apoptotic hepatocytes, and lower liver tissue caspase 3/7, 8, and 9 activities compared with the WT mice, indicating that Mir155 deletion prevents Fas-induced hepatocyte apoptosis and liver injury. Hepatocytes isolated from Mir155 KO mice also showed resistance to Fas-induced apoptosis, in vitro. Higher protein level of myeloid cell leukemia-1 (Mcl-1) was also observed in Mir155 KO hepatocytes compared to WT hepatocytes. A miR-155 binding site was identified in the 3′-untranslated region of Mcl-1 mRNA; Mcl1 was identified as a direct target of miR-155 in hepatocytes. Consistently, pretreatment with a siRNA specific for Mcl1 reversed Mir155 deletion–mediated protection against Jo2-induced liver tissue damage. Finally, restoration of Mir155 expression in Mir155 KO mice abolished the protection against Fas-induced hepatocyte apoptosis. Taken together, these findings demonstrate that deletion of Mir155 prevents Fas-induced hepatocyte apoptosis and liver injury through the up-regulation of Mcl1.miRNAs are a class of small noncoding RNAs that regulate gene expression through binding to specific sequences of their targeted mRNAs.¹ miR-155 was initially identified as a specific miRNA for hematopoietic and immune cells and is among the first miRNAs linked to immunity and inflammation.^2–4 Indeed, miR-155 has been shown to modulate the production of cytokines in various immune cells; the expression of Mir155 is up-regulated in multiple immune cell lineages on stimulation with Toll-like receptor ligands, inflammatory cytokines, and specific antigens.^5–9 Subsequent studies have shown that miR-155 also mediates functions outside the hematopoietic and immune systems.^10,11 In the liver, miR-155 has been shown to play a role in hepatocarcinogenesis,^12–15 although its mechanism of action remains to be further defined. miR-155 has also been shown to contribute to alcohol-induced liver injury through induction of tumor necrosis factor α production in macrophages.¹⁶ Interestingly, the level of miR-155 is increased in serum and plasma in patients with alcoholic and inflammatory liver injuries.^17,18 These observations suggest a potential role of miR-155 in liver injury and liver diseases. However, at present, the biological functions and mechanisms of miR-155 in liver cells have not been delineated.The current study aimed to determine the effect and mechanism of miR-155 in Fas and lipopolysaccharide (LPS)/d-galactosamine (D-GalN)–mediated liver injury in mice. Our data show that deletion of Mir155 protects against Fas-induced hepatocyte apoptosis and liver injury but not LPS/D-GalN–induced liver injury. The role of miR-155 in hepatocytes was demonstrated by in vitro studies using hepatocytes isolated from Mir155 knockout (KO) mice. Myeloid cell leukemia-1 (Mcl-1) was identified as a direct target of miR-155 in hepatocytes. Our results reveal a novel role of miR-155 in hepatocytes for regulation of Mcl1 and protection against Fas-induced apoptosis.