Autophagy Inhibition Sensitizes Renal Tubular Epithelial Cell to G1 Arrest Induced by Transforming Growth Factor beta (TGF-ß).

BACKGROUND Cell cycle arrest and autophagy have been demonstrated to be involved in various transforming growth factor (TGF)-ß-mediated phenotype alterations of tubular epithelial cells (TECs) and tubulointerstitial fibrosis. But the relationship between cell cycle arrest and the autophagy induced by TGF-ß has not been explored well. MATERIAL AND METHODS The effects of autophagy inhibition on TGF-ß-induced cell cycle arrest in TECs were explored in vitro. Human kidney-2 (HK-2) cells were stimulated by TGF-ß with or without a combined treatment of autophagy inhibitor chloroquine (CQ) or bafilomycin A1 (Baf). RESULTS Autophagy inhibition by CQ or Baf promotes the suppression of growth in TGF-ß-treated HK-2 cells, as detected by the Cell Counting Kit-8 (CCK-8) method. In addition, CQ or Baf stimulation enhances G1 arrest in TGF-ß treated HK-2 cells, as investigated using propidium iodide (PI) staining and flow cytometry, which was further confirmed by a decrease in the expression of phosphorylated retinoblastoma protein (p-RB) and cyclin-dependent kinase 4 (CDK4). The upregulation of p21 induced by CQ or Baf may mediate an enhanced G1 arrest in TGF-ß treated HK-2 cells. Western blot analysis showed that TGF-ß-induced expression of extracellular matrix fibronectin was notably upregulated in the presence of autophagy inhibitors. CONCLUSIONS Inhibition of autophagy sensitizes the TECs to G1 arrest and proliferation suppression induced by TGF-ß that contributes to the induction of tubulointerstitial fibrosis.

Autophagy in peritoneal fibrosis.

Peritoneal dialysis (PD) is a widely accepted renal replacement therapy for patients with end-stage renal disease (ESRD). Morphological and functional changes occur in the peritoneal membranes (PMs) of patients undergoing long-term PD. Peritoneal fibrosis (PF) is a common PD-related complication that ultimately leads to PM injury and peritoneal ultrafiltration failure. Autophagy is a cellular process of "self-eating" wherein damaged organelles, protein aggregates, and pathogenic microbes are degraded to maintain intracellular environment homeostasis and cell survival. Growing evidence shows that autophagy is involved in fibrosis progression, including renal fibrosis and hepatic fibrosis, in various organs. Multiple risk factors, including high-glucose peritoneal dialysis solution (HGPDS), stimulate the activation of autophagy, which participates in PF progression, in human peritoneal mesothelial cells (HPMCs). Nevertheless, the underlying roles and mechanisms of autophagy in PF progression remain unclear. In this review, we discuss the key roles and potential mechanisms of autophagy in PF to offer novel perspectives on future therapy strategies for PF and their limitations.

The Role of Parietal Epithelial Cells in the Pathogenesis of Podocytopathy.

Podocytopathy is the most common feature of glomerular disorder characterized by podocyte injury- or dysfunction-induced excessive proteinuria, which ultimately develops into glomerulosclerosis and results in persistent loss of renal function. Due to the lack of self-renewal ability of podocytes, mild podocyte depletion triggers replacement and repair processes mostly driven by stem cells or resident parietal epithelial cells (PECs). In contrast, when podocyte recovery fails, activated PECs contribute to the establishment of glomerular lesions. Increasing evidence suggests that PECs, more than just bystanders, have a crucial role in various podocytopathies, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, diabetic nephropathy, IgA nephropathy, and lupus podocytopathy. In this review, we attempt to dissect the diverse role of PECs in the pathogenesis of podocytopathy based on currently available information.

AMP-activated protein kinase α2 contributes to acute and chronic hyperuricemic nephropathy via renal urate deposition in a mouse model.

Hyperuricemia can induce acute and chronic kidney damage, but the pathological mechanism remains unclear. The potential role of AMP-activated protein kinase (AMPK) α2 in hyperuricemia-induced renal injury was investigated in this study. Acute and chronic hyperuricemic nephropathy was induced by administering intraperitoneal injections of uric acid and oxonic acid to AMPK α2 knockout and wild-type mice. Changes in renal function, histopathology, inflammatory cell infiltration, renal interstitial fibrosis, and urate deposition were analyzed. In both acute and chronic hyperuricemic nephropathy mouse models, knockout of AMPK α2 significantly reduced serum creatinine levels and renal pathological changes. The tubular expression of kidney injury molecule-1 was also reduced in hyperuricemic nephropathy mice deficient in AMPK α2. In addition, knockout of AMPK α2 significantly suppressed the infiltration of renal macrophages and progression of renal interstitial fibrosis in mice with chronic hyperuricemic nephropathy. Knockout of AMPK α2 reduced renal urate crystal deposition, probably through increasing the expression of the uric acid transporter, multidrug resistance protein 4. In summary, AMPK α2 is involved in acute and chronic hyperuricemia-induced kidney injury and may be associated with increased urate crystal deposition in the kidney.

Metformin improves renal injury of MRL/lpr lupus-prone mice via the AMPK/STAT3 pathway.

OBJECTIVE: Lupus nephritis (LN) is a major complication and cause of death among patients with SLE. This research used in vivo and in vitro experiments to explore the therapeutic potential of metformin in kidney injury from LN-induced inflammation. METHODS: In vivo study, 8-week-old MRL/MpJ-Faslpr/J (MRL/lpr) mice were randomly divided into two groups (n=12 each): daily administration of 0.3 mg/mL metformin in drinking water and control (water only). Body weight and urinary samples were measured biweekly. Mice were sacrificed after 8-week treatment to harvest serum, lymph nodes, spleen and kidneys. In vitro study, human kidney-2 (HK-2) cells were pretreated with 1 mM metformin for 1 hour and then stimulated with 20 µg/mL lipopolysaccharides (LPS) or 10 ng/mL tumour necrosis factor-α (TNF-α) for another 48 hours. Protein was collected for subsequent analysis. RESULTS: We found that metformin administration improved renal function in MRL/lpr lupus-prone mice, measured by decreased urea nitrogen and urinary proteins. Metformin reduced immunoglobulin G and complement C3 deposition in glomeruli. The treatment also downregulated systemic and renal inflammation, as seen in decreased renal infiltration of F4/80-positive macrophages and reduced splenic and renal MCP-1 (monocyte chemoattractant protein-1) and TNF-α, and renal IL-1ß (interleukin 1ß) expression. Metformin administration decreased renal expression of necroptosis markers p-RIPK1 (phosphorylated receptor-interacting protein kinase 1) and p-MLKL, along with tubular injury marker KIM-1 (kidney injury molecule-1) in lupus mice. In addition, metformin alleviated the necroptosis of HK-2 cells stimulated by LPS and TNF-α, evidencing by a decrease in the expression of necroptosis markers p-RIPK1, p-RIPK3 and p-MLKL, and the inflammasome-related markers NLRP3 (NLR family pyrin domain containing 3), ASC (apoptosis-associated speck-like protein containing a CARD), caspase-1. Mechanistically, metformin treatment upregulated p-AMPK (phosphorylated AMP-activated protein kinase) and downregulated p-STAT3 (phosphorylated signal transducer and activator of transcription 3) expression in the kidneys. Moreover, AMPKα2 knockdown abolished the protective effects of metformin in vitro. CONCLUSIONS: Metformin alleviated kidney injury in LN though suppressing renal necroptosis and inflammation via the AMPK/STAT3 pathway.

Research Advances in the Mechanisms of Hyperuricemia-Induced Renal Injury.

Uric acid is the end product of purine metabolism in humans, and its excessive accumulation leads to hyperuricemia and urate crystal deposition in tissues including joints and kidneys. Hyperuricemia is considered an independent risk factor for cardiovascular and renal diseases. Although the symptoms of hyperuricemia-induced renal injury have long been known, the pathophysiological molecular mechanisms are not completely understood. In this review, we focus on the research advances in the mechanisms of hyperuricemia-caused renal injury, primarily on oxidative stress, endothelial dysfunction, renal fibrosis, and inflammation. Furthermore, we discuss the progress in hyperuricemia management.

Protection of procyanidin B2 on mitochondrial dynamics in sepsis associated acute kidney injury via promoting Nrf2 nuclear translocation.

In septic acute kidney injury (SAKI), the positive feedback between damaged mitochondria and accumulation of reactive oxygen species results in cell and tissue damage through multiple mechanisms. Removing the damaged mitochondria or neutralizing the reactive oxygen species has been considered beneficial to alleviating cell damage. The antioxidant Procyanidin B2 has been reported to inhibits reactive oxygen species and thereby reduces cell injury. However, it is unclear whether this effect is associated with clearance of damaged mitochondria. Here, we evaluated the efficacy of procyanidin B2 on SAKI, and focused on its effects on mitochondrial dynamics and removing damaged mitochondria via mitophagy. The results showed that the renal function, renal tubular cell vacuolization and oxidative stress were decreased in SAKI mice treated with procyanidin B2, moreover, skewed mitochondrial fusion/fission, mitochondrial mediated apoptosis and impaired mitophagy were improved in SAKI mice treated with procyanidin B2. In mechanism, the improvement of procyanidin B2 on mitochondrial dynamics were associated with increased nuclear translocation of the transcription factor, Nrf2. In summary, our findings highlighted that the protective efficacy of procyanidin B2 in reducing cellular damage in SAKI, and mechanisms improving mitochondrial dynamics and quality control at least in part by promoting Nrf2 translocation into the nucleus.

Disturbance of mitochondrial dynamics and mitophagy in sepsis-induced acute kidney injury.

AIMS: The renal tubule cells require a large number of mitochondria to supply ATP due to their high-energy demand during reabsorption and secretion against chemical gradients and result in mitochondria susceptible to disorder and injury during stress conditions. Injured mitochondria are eventually degraded by mitophagy, and disturbances in mitophagy are associated with the pathogenesis of acute kidney injury (AKI) such as diabetic nephropathy and glomerulosclerosis. However, whether a disturbance in mitophagy has occurred and the role it plays in (SAKI) is still unclear. Therefore, the aim of this study was to investigate the key features of mitophagy and mitochondrial dynamics in sepsis-induced acute kidney injury (SAKI). MAIN METHODS: In this study, a murine septic AKI model induced by cecal ligation and puncture (CLP) was built; mitophagy and mitochondrial dynamics were measured in mice kidney in different time point. KEY FINDINGS: The results showed that mitochondrial dynamics were characterized by fission/fusion aberrant, however more inclined to fission, and mitochondrial associated apoptosis was elevated over-time during SAKI. Furthermore, mitophagy was impaired in the later phase of SAKI, although elevated in early stage of SAKI. The results indicate that the underlying mechanisms of impaired mitophagy may associate with the cleavage of Parkin via caspases activated by NLRP3, at least partly. SIGNIFICANCE: It is conceivable that this selective autophagic process and quality control machinery was impaired, leading to the accumulation of damaged mitochondria, oxidative stress, and cell death. Therefore, a targeted approach, by enhancing mitophagy during SAKI, may be a promising therapeutic strategy.