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.

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.

SND p102 promotes extracellular matrix accumulation and cell proliferation in rat glomerular mesangial cells via the AT1R/ERK/Smad3 pathway.

SND p102 was first described as a transcriptional co-activator, and subsequently determined to be a co-regulator of Pim-1, STAT6 and STAT5. We previously reported that SND p102 expression was increased in high glucose-treated mesangial cells (MCs) and plays a role in the extracellular matrix (ECM) accumulation of MCs by regulating the activation of RAS. In this study, we further examined the roles of SND p102 in diabetic nephropathy (DN)-induced glomerulosclerosis. Rats were injected with STZ (50 mg/kg, ip) to induce diabetes. MCs or isolated glomeruli were cultured in normal glucose (NG, 5.5 mmol/L)- or high glucose (HG, 25 mmol/L)-containing DMEM. We found that SND p102 expression was significantly increased in the diabetic kidneys, as well as in HG-treated isolated glomeruli and MCs. In addition, HG treatment induced significant fibrotic changes in MCs evidenced by enhanced protein expression of TGF-ß, fbronectin and collagen IV, and significantly increased the proliferation of MCs. We further revealed that overexpression of SND p102 significantly increased the protein expression of angiotensin II (Ang II) type 1 receptor (AT1R) in MCs by increasing its mRNA levels via directly targeting the AT1R 3'-UTR, which resulted in activation of the ERK/Smad3 signaling and subsequently promoted the up-regulation of fbronectin, collagen IV, and TGF-ß in MCs, as well as the cell proliferation. These results demonstrate that SND p102 is a key regulator of AT1R-mediating ECM synthesis and cell proliferation in MCs. Thus, small molecule inhibitors of SND p102 may be a novel therapeutic strategy for DN.

N-acetylcysteine alleviates angiotensin II-mediated renal fibrosis in mouse obstructed kidneys.

AIM: To investigate the effects of ROS scavenger N-acetylcysteine (NAC) on angiotensin II (Ang II)-mediated renal fibrosis in vivo and in vitro. METHODS: Mice were subjected to unilateral ureteral obstruction (UUO), and then treated with vehicle or NAC (250 mg/kg, ip) for 7 days. Histological changes of the obstructed kidneys were observed with Masson's trichrome staining. ROS levels were detected with DHE staining. The expression of relevant proteins in the obstructed kidneys was assessed using Western blotting assays. Cultured rat renal fibroblast NRK-49F cells were used for in vitro experiments. RESULTS: In the obstructed kidneys, Ang II levels were significantly elevated, and collagen I was accumulated in the interstitial spaces. Furthermore, ROS production and the expression of p47 (a key subunit of NADPH oxidase complexes) were increased in a time-dependent manner; the expression of fibronectin, α-SMA and TGF-ß were upregulated. Administration of NAC significantly alleviated the fibrotic responses in the obstructed kidneys. In cultured NRK-49F cells, treatment with Ang II (0.001-10 µmol/L) increased the expression of fibronectin, collagen I, α-SMA and TGF-ß in dose-dependent and time-dependent manners. Ang II also increased ROS production and the phosphorylation of Smad3. Pretreatment with NAC (5 µmol/L) blocked Ang II-induced oxidative stress and ECM production in the cells. CONCLUSION: In mouse obstructed kidneys, the fibrotic responses result from Ang II upregulation can be alleviated by the ROS scavenger N-acetylcysteine.

Insulin deficiency induces rat renal mesangial cell dysfunction via activation of IGF-1/IGF-1R pathway.

AIM: Diabetic nephropathy is one of the major complications of diabetes and the major cause of end-stage renal disease. In this study we investigated the insulin deficiency (ID) induced changes in renal mesangial cells (MCs) and in the kidney of STZ-induced diabetic rats. METHODS: Cultured rat renal MCs were incubated in ID media. Cell proliferation was analyzed using BrdU incorporation assay. The expression of insulin receptor (IR), insulin-like growth factor-1 receptor (IGF-1R), phosphorylated IGF-1R, fibronectin, and collagen IV was determined with Western blot analysis. STZ-induced diabetic rats were treated with an IGF-1R antagonist picropodophyllin (PPP, 20 mg·kg(-1)·d(-1), po) for 8 weeks. After the rats were euthanized, plasma and kidneys were collected. IGF-1 levels in renal cortex were measured with RT-PCR or ELISA. The morphological changes in the kidneys were also examined. RESULTS: Incubation in ID media significantly increased cell proliferation, the synthesis of fibronectin and collagen IV, and the expression of IGF-1 and IGF-1R and phosphorylated IGF-1R in renal MCs. Pretreatment of the cells with PPP (50 nmol/L) blocked ID-induced increases in cell proliferation and the synthesis of fibronectin and collagen IV; knockdown of IGF-1R showed a similar effect as PPP did. In contrast, treatment of the cells with IGF-1 (50 ng/mL) exacerbated ID-induced increases in cell proliferation. In the kidneys of diabetic rats, the expression of IGF-1, IGF-1R and phosphorylated IGF-1R were significantly elevated. Treatment of diabetic rats with PPP did not lower the blood glucose levels, but significantly suppressed the expression of TGF-ß, fibronectin and collagen IV in the kidneys, the plasma levels of urinary nitrogen and creatinine, and the urinary protein excretion. CONCLUSION: Insulin deficiency increases the expression of IGF-1 and IGF-1R in renal MCs and the kidney of diabetic rats, which contributes to the development of diabetic nephropathy.

Involvement of spliced X-box binding protein 1 in renal fibrosis induced by unilateral ureteral obstruction in mice.

Endoplasmic reticulum (ER) stress is involved in the process of kidney fibrosis. Spliced X-box binding protein 1 (XBP1S) is the key mediator of ER stress while its role in fibrosis is still poorly understood. This study was aimed to investigate the role of XBP1S in renal fibrosis and evaluate whether valsartan could alleviate fibrosis through XBP1S. Renal interstitial fibrosis was induced by unilateral ureteral obstruction (UUO) in C57BL/6 mice, and UUO mice were daily administered with valsartan (20 mg/kg) through oral gavage. After 7 days of UUO, at euthanasia, left kidney was collected to examine the histological alteration by using haematoxylin-eosin staining, Masson's trichrome staining, Sirius red staining and immunohistochemistry. Western blot was used to assess XBP1S, targets of XBP1S, fibronectin, α-SMA, BAX and BCL2 protein levels. Real-time polymerase chain reaction was performed to assess NADPH oxidase subunits p47-phox and p67-phox mRNA levels. The results showed that XBP1S expression was decreased by about 70% in the UUO mice compared with that in sham mice (P < 0.01), which was reversed by valsartan administration (P < 0.05). Meanwhile, UUO-induced renal interstitial fibrosis was attenuated by valsartan treatment. In addition, the protein levels of fibronectin and α-SMA were upregulated by UUO induction (P < 0.01), and valsartan administration inhibited the protein levels of fibronectin and α-SMA in UUO mice (P < 0.05). Western blot analysis showed that the ratio of BAX to BCL2 protein level was increased in UUO model compared with that in sham mice, and the increment also was diminished by valsartan treatment (P < 0.05). Finally, UUO-induced mRNA levels of p47-phox and p67-phox were significantly attenuated by valsartan administration (P < 0.05). These results showed that valsartan at least partly restores renal interstitial fibrosis by enhancing XBP1S activation through inhibiting oxidative stress and apoptosis in the UUO mice. These results suggest that XBP1S could be a potential therapeutic target for kidney fibrosis.

Vinblastine resets tumor-associated macrophages toward M1 phenotype and promotes antitumor immune response.

BACKGROUND: Massive tumor-associated macrophage (TAM) infiltration is observed in many tumors, which usually display the immune-suppressive M2-like phenotype but can also be converted to an M1-like antitumor phenotype due to their high degree of plasticity. The macrophage polarization state is associated with changes in cell shape, macrophage morphology is associated with activation status. M1 macrophages appeared large and rounded, while M2 macrophages were stretched and elongated cells. Manipulating cell morphology has been shown to affect the polarization state of macrophages. The shape of the cell is largely dependent on cytoskeletal proteins, especially, microtubules. As a microtubule-targetting drug, vinblastine (VBL) has been used in chemotherapy. However, no study to date has explored the effect of VBL on TAM shape changes and its role in tumor immune response. METHOD: We used fluorescent staining of the cytoskeleton and quantitative analysis to reveal the morphological differences between M0, M1, M2, TAM and VBL-treated TAM. Flow cytometry was used to confirm the polarization states of these macrophages using a cell surface marker-based classification. In vivo antibody depletion experiments in tumor mouse models were performed to test whether macrophages and CD8+ T cell populations were required for the antitumor effect of VBL. VBL and anti-PD-1 combination therapy was then investigated in comparison with monotherapy. RNA-seq of TAM of treated and untreated with VBL was performed to explore the changes in pathway activities. siRNA mediated knockdown experiments were performed to verify the target pathway that was affected by VBL treatment. RESULTS: Here, we showed that VBL, an antineoplastic agent that destabilizes microtubule, drove macrophage polarization into the M1-like phenotype both in vitro and in tumor models. The antitumor effect of VBL was attenuated in the absence of macrophages or CD8+ T cells. Mechanistically, VBL induces the activation of NF-κB and Cyba-dependent reactive oxygen species generation, thus polarizing TAMs to the M1 phenotype. In parallel, VBL promotes the nuclear translocation of transcription factor EB, inducing lysosome biogenesis and a dramatic increase in phagocytic activity in macrophages. CONCLUSIONS: This study explored whether manipulating cellular morphology affects macrophage polarization and consequently induces an antitumor response. Our data reveal a previously unrecognized antitumor mechanism of VBL and suggest a drug repurposing strategy combining VBL with immune checkpoint inhibitors to improve malignant tumor immunotherapy.

PD-L1 negatively regulates antifungal immunity by inhibiting neutrophil release from bone marrow.

Programmed death ligand 1 (PD-L1) has been shown to be inducibly expressed on neutrophils to suppress host immunity during polymicrobial sepsis, virus and parasite infections. However, the role of PD-L1 on neutrophil-mediated antifungal immunity remains wholly unknown. Here, we show that the expression of PD-L1 on murine and human neutrophils was upregulated upon the engagement of C-type lectin receptor Dectin-1 with its ligand ß-glucans, exposed on fungal pathogen Candida albicans yeast. Moreover, ß-glucan stimulation induced PD-L1 translocation into nucleus to regulate the production of chemokines CXCL1 and CXCL2, which control neutrophil mobilization. Importantly, C. albicans infection-induced expression of PD-L1 leads to neutrophil accumulation in bone marrow, through mediating their autocrine secretion of CXCL1/2. Furthermore, neutrophil-specific deficiency of PD-L1 impaired CXCL1/2 secretion, which promoted neutrophil migration from bone marrow into the peripheral circulation, thereby conferring host resistance to C. albicans infection. Finally, either PD-L1 blockade or pharmacological inhibition of PD-L1 expression significantly increased neutrophil release from bone marrow to enhance host antifungal immunity. Our data together indicate that activation of Dectin-1/PD-L1 cascade by ß-glucans inhibits neutrophil release from bone marrow reserve, contributing to the negative regulation of antifungal innate immunity, which functions as a potent immunotherapeutic target against life-threatening fungi infections.