Saikosaponin-d inhibits proliferation by up-regulating autophagy via the CaMKKß-AMPK-mTOR pathway in ADPKD cells.

Autosomal dominant polycystic kidney disease (ADPKD) is a common heritable human disease. Recently, the role of repressed autophagy in ADPKD has drawn increasing attention. Here, we investigate the mechanism underlying the effect of Saikosaponin-d (SSd), a sarcoplasmic/endoplasmic reticulum Ca2+ ATPase pump (SERCA) inhibitor. We show that SSd suppresses proliferation in ADPKD cells by up-regulating autophagy. We found that treatment with SSd results in the accumulation of intracellular calcium, which in turn activates the CaMKKß-AMPK signalling cascade, inhibits mTOR signalling and induces autophagy. Conversely, we also found that treatment with an autophagy inhibitor (3-methyladenine), AMPK inhibitor (Compound C), CaMKKß inhibitor (STO-609) and intracellular calcium chelator (BAPTA/AM) could reduce autophagy puncta formation mediated by SSd. Our results demonstrated that SSd induces autophagy through the CaMKKß-AMPK-mTOR signalling pathway in ADPKD cells, indicating that SSd might be a potential therapy for ADPKD and that SERCA might be a new target for ADPKD treatment.

Triptolide delays disease progression in an adult rat model of polycystic kidney disease through the JAK2-STAT3 pathway.

The aim of our current study was to investigate the long-term effect and the mechanism of triptolide in an adult nonorthologous rat model of polycystic kidney disease (PKD). Male wild-type (+/+) and Cy/+ cystic Han:SPRD rats were treated with vehicle or triptolide from 4 to 16 wk of age. Rats were killed at 16 wk of age for blood, urine, and organ collection. Human-derived WT9-12 PKD cells were treated with triptolide with or without IL-6 pretreatment. Cell proliferation, apoptosis, and cytotoxicity were determined. Western blotting and immunohistochemistry analysis were performed to evaluate the activation of IL-6-JAK2-STAT3 pathway. Renal function was protected by 12 wk of triptolide treatment in cystic Han:SPRD rats as shown by reduced blood urea nitrogen, serum creatinine, and proteinuria levels. Cyst and kidney growth were also retarded by triptolide treatment in Cy/+ rats. We further found that the proliferation index was reduced by triptolide in cystic rats, which was correlated with the reduced expression of IL-6/IL-6 receptor, decreased phosphorylation of JAK2-STAT3, and increased expression of suppressor of cytokine signaling 3 (SOCS3). The inhibitory effect of triptolide was further studied in WT9-12 cells. Triptolide inhibited cell proliferation and the activation of JAK2-STAT3 pathway in PKD cells, but it increased the expression of SOCS3. Pretreatment with IL-6 attenuated the inhibitory effect of triptolide on STAT3 phosphorylation. Our study revealed a long-term beneficial effect of triptolide in PKD that was probably through inhibition of the JAK2-STAT3 pathway.

Olmesartan Prevents Microalbuminuria in db/db Diabetic Mice Through Inhibition of Angiotensin II/p38/SIRT1-Induced Podocyte Apoptosis.

BACKGROUND/AIMS: Blockage of the renin-angiotensin II system (RAS) prevents or delays albuminuria in diabetic patients. The aim of this study was to investigate the inhibitory mechanism of the angiotensin receptor blocker olmesartan on albuminuria in a murine model of diabetic nephropathy. METHODS: Male db/db diabetic mice were fed with placebo or 20 mg/kg olmesartan by daily gavage for 12 weeks. Conditionally immortalized mouse podocytes were treated with glucose, angiotensin II, olmesartan or p38 inhibitor s8307 in different experimental conditions after differentiation. RESULTS: Olmesartan reduced albuminuria in db/db mice without change in body weight and glycemia. The increase of apoptotic cells and decrease of podocytes in the diabetic glomerulus were prevented by olmesartan. Moreover, olmesartan restored silent mating type information regulation 1 (SIRT1) expression in diabetic glomeruli. Furthermore, olmesartan treatment suppressed p38 phosphorylation but did not restore adenosine 5'-monophosphate-activated protein kinase (AMPK) phosphorylation in the diabetic glomerulus. In vitro study revealed that olmesartan prevented angiotensin II/p38/SIRT1 induced podocyte apoptosis, but it only slightly prevented high glucose/AMPK/SIRT1 induced podocyte apoptosis. In addition, the p38 inhibitor s8307 reversed SIRT1 expression and angiotensin II induced podocyte apoptosis. CONCLUSIONS: Olmesartan reduced albuminuria in diabetic nephropathy through inhibiting angiotensin II/p38/SIRT1 triggered podocyte apoptosis.

Resveratrol delays polycystic kidney disease progression through attenuation of nuclear factor κB-induced inflammation.

BACKGROUND: Inflammation plays an important role in polycystic kidney disease (PKD). The current study aimed to examine the efficacy of the anti-inflammatory compound resveratrol in PKD and to investigate its underlying mechanism of action. METHODS: Male Han:SPRD (Cy/+) rats with PKD were treated with 200 mg/kg/day resveratrol or vehicle by gavage for 5 weeks. Human autosomal dominant (AD) PKD cells, three-dimensional (3D) Madin-Darby canine kidney cells and zebrafish were treated with various concentrations of resveratrol or the nuclear factor κB (NF-κB) inhibitor QNZ. RESULTS: Resveratrol treatment reduced blood urea nitrogen levels and creatinine levels by 20 and 24%, respectively, and decreased two-kidney/total body weight ratio by 15% and cyst volume density by 24% in Cy/+ rats. The proliferation index and the macrophage infiltration index were reduced by 40 and 43%, respectively, in resveratrol-treated cystic kidneys. Resveratrol reduced the levels of the pro-inflammatory factors monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-α (TNF-α) and complement factor B (CFB) in Cy/+ rat kidneys in parallel with the decreased activity of NF-κB (p50/p65). The activation of NF-κB and its correlation with pro-inflammatory factor expression were confirmed in human ADPKD cells and kidney tissues. Resveratrol and QNZ inhibited the expression of MCP-1, TNF-α and CFB and reduced NF-κB activity in ADPKD cells. Moreover, NF-κB blockage minimized the inhibition of inflammatory factor production by resveratrol treatment. Furthermore, resveratrol or QNZ inhibited cyst formation in the 3D cyst and zebrafish models. CONCLUSIONS: The NF-κB signaling pathway is activated and partly responsible for inflammation in polycystic kidney tissues. Targeting inflammation through resveratrol could be a new strategy for PKD treatment in the future.

The C-terminal tail of polycystin-1 regulates complement factor B expression by signal transducer and activator of transcription 1.

Inhibition of the overactivated alternative complement pathway in autosomal dominant polycystic kidney disease (ADPKD) retards disease progression in animal models; however, it remains unknown how complement factor B (CFB) is upregulated in ADPKD. Here, we showed that the overexpression of CFB in cystic kidneys is associated with increased JAK2/STAT1 activity and enhanced expression of the polycystin-1 C-terminal tail (PC1-CTT). Overexpression or blockage of STAT1 increased or decreased CFB expression and CFB promoter activity. Moreover, overexpression of PC1-CTT induced JAK2/STAT1 activation and CFB upregulation in renal tubular epithelial cells. Furthermore, PC1-CTT overexpression increased human CFB promoter activity, whereas dominant negative STAT1 plasmids or mutation of putative STAT1 responsive elements decreased PC1-CTT-induced CFB promoter activity. The effect of CFB on macrophage differentiation was tested on a mouse macrophage cell line. Bioactive CFB dose dependently promoted macrophage M2 phenotype conversion. In addition, conditioned media from renal epithelial cells promoted macrophage M2 phenotype conversion which was blocked by STAT1 inhibition in a dose-dependent manner. Conditioned media from PC1-CTT-transfected renal epithelial cells further promoted macrophage M2 phenotype conversion, which was suppressed by fludarabine or a CFB antibody. In addition, we show that NF-κB acts downstream of PC1-CTT and may partly mediate PC1-CTT-induced CFB expression. In conclusion, our study reveals possible mechanisms of CFB upregulation in ADPKD and a novel role of PC1-CTT in ADPKD-associated inflammation. Furthermore, our study suggests that targeting STAT1 may be a new strategy to prevent inflammation in the kidney of patients with ADPKD.