Caspase-11 promotes NLRP3 inflammasome activation via the cleavage of pannexin1 in acute kidney disease.

Ischemia/reperfusion (I/R) injury is a major cause of acute kidney injury (AKI) in clinic. The activation of NLRP3 inflammasome is associated with inflammation and renal injury in I/R-induced AKI. In the current study we explored the molecular and cellular mechanisms for NLRP3 inflammasome activation following renal I/R. Mice were subjected to I/R renal injury by clamping bilateral renal pedicles. We showed that I/R injury markedly increased caspase-11 expression and the cleavage of pannexin 1 (panx1) in the kidneys accompanied by NLRP3 inflammasome activation evidenced by the activation of caspase-1 and interlukin-1ß (IL-1ß) maturation. In Casp-11-/- mice, I/R-induced panx1 cleavage, NLRP3 inflammasome activation as well as renal functional deterioration and tubular morphological changes were significantly attenuated. In cultured primary tubular cells (PTCs) and NRK-52E cells, hypoxia/reoxygenation (H/R) markedly increased caspase-11 expression, NLRP3 inflammasome activation, IL-1ß maturation and panx1 cleavage. Knockdown of caspase-11 attenuated all those changes; similar effects were observed in PTCs isolated from Casp-11-/- mice. In NRK-52E cells, overexpression of caspase-11 promoted panx1 cleavage; pretreatment with panx1 inhibitor carbenoxolone or knockdown of panx1 significantly attenuated H/R-induced intracellular ATP reduction, extracellular ATP elevation and NLRP3 inflammasome activation without apparent influence on H/R-induced caspase-11 increase; pretreatment with P2X7 receptor inhibitor AZD9056 also attenuated NLRP3 inflammasome activation. The above results demonstrate that the cleavage of panx1 by upregulated caspase-11 is involved in facilitating ATP release and then NLRP3 inflammasome activation in I/R-induced AKI. This study provides new insight into the molecular mechanism of NLRP3 inflammasome activation in AKI.

Caspase-11/4 and gasdermin D-mediated pyroptosis contributes to podocyte injury in mouse diabetic nephropathy.

Diabetic nephropathy (DN) is characterized by sterile inflammation with continuous injury and loss of renal inherent parenchyma cells. Podocyte is an essential early injury target in DN. The injury and loss of podocytes are closely associated with proteinuria, the early symptom of renal injury in DN. However, the exact mechanism for podocyte injury and death in DN remains ambiguous. In this study we investigated whether pyroptosis, a newly discovered cell death pathway was involved in DN. Diabetic mice were generated by high-fat diet/STZ injections. We showed that the expression levels of caspase-11 and cleavage of gasdermin D (GSDMD-N) in podocytes were significantly elevated, accompanied by reduced expression of podocyte makers nephrin and podocin, loss and fusion in podocyte foot processes, increased inflammatory cytokines NF-κB, IL-1ß, and IL-18, macrophage infiltration, glomerular matrix expansion and increased urinary albumin to creatinine ratio (UACR). All these changes in diabetic mice were blunted by knockout of caspase-11 or GSDMD. Cultured human and mouse podocytes were treated with high glucose (30 mM), which significantly increased the expression levels of caspase-11 or caspase-4 (the homolog of caspase-11 in human), GSDMD-N, NF-κB, IL-1ß, and IL-18, and decreased the expression of nephrin and podocin. Either caspase-4 or GSDMD knockdown by siRNA significantly blunted these changes. In summary, our results demonstrate that caspase-11/4 and GSDMD-mediated pyroptosis is activated and involved in podocyte loss under hyperglycemia condition and the development of DN.

KLF4 initiates sustained YAP activation to promote renal fibrosis in mice after ischemia-reperfusion kidney injury.

Acute renal injury (AKI) causes a long-term risk for progressing into chronic kidney disease (CKD) and interstitial fibrosis. Yes-associated protein (YAP), a key transcriptional cofactor in Hippo signaling pathway, shuttles between the cytoplasm and nucleus, which is required for the renal tubular epithelial cells repair in the acute phase of AKI. In this study we investigated the role of YAP during ischemia-reperfusion (IR)-induced AKI to CKD. Mice were subjected to left kidney IR followed by removal of the right kidney on the day before tissue harvests. Mouse shRNA expression adenovirus (Ad-shYAP or Ad-shKLF4) and mouse KLF4 expression adenovirus (Ad-KLF4) were delivered to mice by intrarenal injection on D7 after IR. We showed that the expression and nucleus distribution of YAP were persistently increased until the end of experiment (D21 after IR). The sustained activation of YAP in post-acute phase of AKI was accompanied by renal dysfunction and interstitial fibrosis. Knockdown of YAP significantly attenuated IR-induced renal dysfunction and decreased the expression of fibrogenic factors TGF-ß and CTGF in the kidney. We showed that the expression of the transcription factor KLF4, lined on the upstream of YAP, was also persistently increased. Knockdown on KLF4 attenuated YAP increase and nuclear translocation as well as renal functional deterioration and interstitial fibrosis in IR mice, whereas KLF4 overexpression caused opposite effects. KLF4 increased the expression of ITCH, and ITCH facilitated YAP nuclear translocation via degrading LATS1. Furthermore, we demonstrated in primary cultured renal tubular cells that KLF4 bound to the promoter region of YAP and positively regulates YAP expression. In biopsy sample from CKD patients, we also observed increased expression and nuclear distribution of YAP. In conclusion, the activation of YAP in the post-acute phase of AKI is implicated in renal functional deterioration and fibrosis although it exhibits beneficial effect in acute phase. Reprogramming factor KLF4 is responsible for the persistent activation of YAP. Blocking the activation of KLF4-YAP pathway might be a way to prevent the transition of AKI into CKD.

c-Myc promotes tubular cell apoptosis in ischemia-reperfusion-induced renal injury by negatively regulating c-FLIP and enhancing FasL/Fas-mediated apoptosis pathway.

c-Myc plays an important role in cell proliferation, differentiation, and cell apoptosis. FasL/Fas pathway is a key regulator of cell apoptosis. This study was aimed to investigate the effects of c-Myc on the FasL/Fas pathway in ischemia-reperfusion (I/R)-induced renal injury. Rats were objected to bilateral renal ischemia for 60 min and reperfused for 24 or 48 h. NRK-52E cells were treated with hypoxia-reoxygenation (H/R) or FasL. Immunohistochemistry was used to identify the distribution of c-Myc. Cell apoptosis was assessed by TUNEL staining. Ad-c-Myc and recombinant pcDAN 3.0 were used to overexpress c-Myc and c-FLIP, respectively. ChIP assay and luciferase assay were used to detect the binding of c-Myc to c-FLIP promoter. In I/R rats, c-Myc was increased significantly and mainly located in renal tubular epithelial cells; meanwhile, c-FLIP was decreased, cleaved caspase-8, cleaved caspase-3 and TUNEL-positive staining cells were increased. Treatment of I/R rats with c-Myc inhibitor 10058-F4 significantly attenuated the decrease in c-FLIP, the increase in cleaved caspase-8, cleaved caspase-3, TUNEL-positive cells, Scr and BUN in I/R rats. In NRK-52E cells, hypoxia and reoxygen induced the increase in c-Myc and decrease in c-FLIP. ChIP and luciferase assay results indicated that c-Myc binds to the promoter region of c-FLIP gene. Overexpression of c-Myc markedly decreased c-FLIP. Overexpression of c-FLIP inhibited the increase in cleaved caspase-8 and caspase-3 induced by FasL. Data indicated that c-Myc is increased in kidneys of I/R rats and negatively regulates the expression of c-FLIP, then enhanced FasL-induced cell apoptosis in I/R stress.

Caspase-11 promotes renal fibrosis by stimulating IL-1ß maturation via activating caspase-1.

Caspase-11 is a key upstream modulator for activation of inflammatory response under pathological conditions. In this study, we investigated the roles of caspase-11 in the maturation of interleukin-1ß (IL-1ß) and development of renal interstitial fibrosis in vivo and in vitro. Mice were subjected to unilateral ureteral obstruction (UUO). The mice were treated with either caspase-11 inhibitor wedelolactone (Wed, 30 mg/kg/day, ig) for 7 days or caspase-11 siRNA (10 nmol/20 g body weight per day, iv) for 14 days. The mice were euthanized on day 14, their renal tissue and blood sample were collected. We found that the obstructed kidney had significantly higher caspase-11 levels and obvious tubular injury and interstitial fibrosis. Treatment with Wed or caspase-11 siRNA significantly mitigated renal fibrosis in UUO mice, evidenced by the improved histological changes. Furthermore, caspase-11 inhibition significantly blunted caspase-1 activation, IL-1ß maturation, transforming growth factor-ß (TGF-ß), fibronectin, and collagen I expressions in the obstructed kidney. Renal tubular epithelial NRK-52E cells were treated in vitro with angiotensin (Ang, 1 µmol/L), which stimulated caspase-11 activation and IL-1ß maturation. Treatment with IL-1ß (20 ng/ml) significantly increased the expression of TGF-ß, fibronectin, and collagen I in the cells. Ang II-induced expression of TGF-ß, fibronectin, and collagen I were suppressed by caspase-11 siRNA or Wed. Finally, we revealed using co-immunoprecipitation that caspase-11 was able to interact with caspase-1 in NRK-52E cells. These results suggest that caspase-11 is involved in UUO-induced renal fibrosis. Elevation of caspase-11 in the obstructed kidney promotes renal fibrosis by stimulating caspase-1 activation and IL-1ß maturation.