GPR87 promotes renal tubulointerstitial fibrosis by accelerating glycolysis and mitochondrial injury

Search progress of pyruvate kinase M2 (PKM2) in organ fibrosis

Fibrosis is characterized by abnormal deposition of the extracellular matrix (ECM), leading to organ structural remodeling and loss of function. The principal cellular effector in fibrosis is activated myofibroblasts, which serve as the main source of matrix proteins. Metabolic reprogramming, transitioning from mitochondrial oxidative phosphorylation to aerobic glycolysis, is widely observed in rapidly dividing cells such as tumor cells and activated myofibroblasts and is increasingly recognized as a fundamental pathogenic basis in organ fibrosis. Targeting metabolism represents a promising strategy to mitigate fibrosis. PKM2, a key enzyme in glycolysis, plays a pivotal role in metabolic reprogramming through allosteric regulation, impacting both metabolic and non-metabolic pathways. Therefore, metabolic reprogramming induced by PKM2 activation is involved in the occurrence and development of fibrosis in various organs. A comprehensive understanding of the role of PKM2 in fibrotic diseases is crucial for seeking new anti-fibrotic therapeutic targets. In this context, we summarize PKM2's role in glycolysis, mediating the intricate mechanisms underlying fibrosis in multiple organs, and discuss the potential value of PKM2 inhibitors and allosteric activators in future clinical treatments, aiming to identify novel therapeutic targets for proliferative fibrotic diseases.

Focus on Mitochondrial Respiratory Chain: Potential Therapeutic Target for Chronic Renal Failure

The function of the respiratory chain is closely associated with kidney function, and the dysfunction of the respiratory chain is a primary pathophysiological change in chronic kidney failure. The incidence of chronic kidney failure caused by defects in respiratory-chain-related genes has frequently been overlooked. Correcting abnormal metabolic reprogramming, rescuing the "toxic respiratory chain", and targeting the clearance of mitochondrial reactive oxygen species are potential therapies for treating chronic kidney failure. These treatments have shown promising results in slowing fibrosis and inflammation progression and improving kidney function in various animal models of chronic kidney failure and patients with chronic kidney disease (CKD). The mitochondrial respiratory chain is a key target worthy of attention in the treatment of chronic kidney failure. This review integrated research related to the mitochondrial respiratory chain and chronic kidney failure, primarily elucidating the pathological status of the mitochondrial respiratory chain in chronic kidney failure and potential therapeutic drugs. It provided new ideas for the treatment of kidney failure and promoted the development of drugs targeting the mitochondrial respiratory chain.

Hippo/YAP signaling pathway: a new therapeutic target for diabetes mellitus and vascular complications

Diabetic angiopathy, which includes diabetic kidney disease (DKD), cardio-cerebrovascular disease, and diabetic retinopathy (DR) among other diseases, is one of the most common complications affecting diabetic patients. Among these, DKD, which is a major cause of morbidity and mortality, affects about 40% of diabetic patients. Similarly, DR involves retinal neovascularization and neurodegeneration as a result of chronic hyperglycemia and is the main cause of visual impairment and blindness. In addition, inflammation also promotes atherosclerosis and diabetes, with atherosclerosis-related cardiovascular diseases being often a main cause of disability or death in diabetic patients. Given that vascular diseases caused by diabetes negatively impact human health, it is therefore important to identify appropriate treatments. In this context, some studies have found that the Hippo/Yes-associated protein (YAP) pathway is a highly evolutionarily conserved protein kinase signal pathway that regulates organ growth and size through its effector signaling pathway Transcriptional co-Activator with PDZ-binding motif (TAZ) and its YAP. YAP is a key factor in the Hippo pathway. The activation of YAP regulates gluconeogenesis, thereby regulating glucose tolerance levels; silencing the YAP gene thereby prevents the formation of glomerular fibrosis. YAP can combine with TEA domain family members to regulate the proliferation and migration of retinal vascular endothelial cells (ECs), so YAP plays a prominent role in the formation and pathology of retinal vessels. In addition, YAP/TAZ activation and translocation to the nucleus promote endothelial inflammation and monocyte-EC attachment, which can increase diabetes-induced cardiovascular atherosclerosis. Hippo/YAP signaling pathway provides a potential therapeutic target for diabetic angiopathy, which can prevent the progression of diabetes to DR and improve renal fibrosis and cardio-vascular atherosclerosis.

Protective Effects of Bombyx batryticatus Protein-Rich Extract Against Cisplatin-Induced Nephrotoxicity in HEK293 Cells and a Mouse Model

Cisplatin, a potent and prominent chemotherapeutic drug, has considerable side effects, including nephrotoxicity, which limits its therapeutic application and efficacy. Therefore, the development of agents that protect normal cells while preserving cisplatin's chemotherapeutic properties is of utmost importance. This study aimed to explore the protective effects of Bombyx batryticatus protein-rich extract (BBPE) against cisplatin-induced nephrotoxicity in a cisplatin-treated mouse model and human embryonic kidney (HEK293) cells. Apoptosis was assessed in HEK293 cells to determine the cytoprotective effects of BBPE and its effects on the generation of cisplatin-induced reactive oxygen species (ROS) and mitochondrial transmembrane potential (MTP) collapse. Although cisplatin induced nephrotoxicity in HEK293 cells, pretreatment with BBPE showed significant protective effects against cisplatin-induced nephrotoxicity by regulating the expression levels of pro- and antiapoptotic proteins. The cytoprotective effects of BBPE were mediated by decreased ROS production and MTP loss in cisplatin-treated HEK293 cells. The in vitro results were confirmed in the cisplatin-treated mouse model. Pretreatment with BBPE protected against cisplatin-induced nephrotoxicity by restoring malondialdehyde, superoxide dismutase, and catalase levels in kidney tissue and blood urea nitrogen and creatinine serum levels. Furthermore, histopathological assessment and terminal dUTP nick end-labeling staining showed that BBPE mitigated cisplatin-induced nephrotoxicity in kidney tissues. Overall, BBPE may act as a potent agent for alleviating cisplatin-induced nephrotoxicity, thereby increasing the safety of cisplatin-based chemotherapy.

Tubular TMEM16A promotes tubulointerstitial fibrosis by suppressing PGC-1α-mediated mitochondrial homeostasis in diabetic kidney disease

Tubulointerstitial fibrosis (TIF) plays a crucial role in the progression of diabetic kidney disease (DKD). However, the underlying molecular mechanisms remain obscure. The present study aimed to examine whether transmembrane member 16A (TMEM16A), a Ca2+-activated chloride channel, contributes to the development of TIF in DKD. Interestingly, we found that TMEM16A expression was significantly up-regulated in tubule of murine model of DKD, which was associated with development of TIF. In vivo inhibition of TMEM16A channel activity with specific inhibitors Ani9 effectively protects against TIF. Then, we found that TMEM16A activation induces tubular mitochondrial dysfunction in in vivo and in vitro models, with the evidence of the TMEM16A inhibition with specific inhibitor. Mechanically, TMEM16A mediated tubular mitochondrial dysfunction through inhibiting PGC-1α, whereas overexpression of PGC-1α could rescue the changes. In addition, TMEM16A-induced fibrogenesis was dependent on increased intracellular Cl-, and reducing intracellular Cl- significantly blunted high glucose-induced PGC-1α and profibrotic factors expression. Taken together, our studies demonstrated that tubular TMEM16A promotes TIF by suppressing PGC-1α-mediated mitochondrial homeostasis in DKD. Blockade of TMEM16A may serve as a novel therapeutic approach to ameliorate TIF.

Novel insights into STAT3 in renal diseases

Signal transducer and activator of transcription 3 (STAT3) is a cell-signal transcription factor that has attracted considerable attention in recent years. The stimulation of cytokines and growth factors can result in the transcription of a wide range of genes that are crucial for several cellular biological processes involved in pro- and anti-inflammatory responses. STAT3 has attracted considerable interest as a result of a recent upsurge in study because of their role in directing the innate immune response and sustaining inflammatory pathways, which is a key feature in the pathogenesis of many diseases, including renal disorders. Several pathological conditions which may involve STAT3 include diabetic nephropathy, acute kidney injury, lupus nephritis, polycystic kidney disease, and renal cell carcinoma. STAT3 is expressed in various renal tissues under these pathological conditions. To better understand the role of STAT3 in the kidney and provide a theoretical foundation for STAT3-targeted therapy for renal disorders, this review covers the current work on the activities of STAT3 and its mechanisms in the pathophysiological processes of various types of renal diseases.

PCK1 Protects against Mitoribosomal Defects in Diabetic Nephropathy in Mouse Models

SIGNIFICANCE STATEMENT

Renal gluconeogenesis plays an important role in the pathogenesis of diabetic nephropathy (DN). Proximal tubular phosphoenolpyruvate carboxykinase1 (PEPCK1) is the rate-limiting enzyme in gluconeogenesis. However, the functions of PEPCK1 have not been elucidated. We describe the novel role of PEPCK1 as a mitoribosomal protector using Pck1 transgenic (TG) mice and knockout mice. Pck1 blocks excessive glycolysis by suppressing the upregulation of excess HK2 (the rate-limiting enzyme of glycolysis). Notably, Pck1 overexpression retains mitoribosomal function and suppresses renal fibrosis. The renal and mitoribosomal protective roles of Pck1 may provide important clues for understanding DN pathogenesis and provide novel therapeutic targets.

BACKGROUND

Phosphoenolpyruvate carboxykinase (PEPCK) is part of the gluconeogenesis pathway, which maintains fasting glucose levels and affects renal physiology. PEPCK consists of two isoforms-PEPCK1 and PEPCK2-that the Pck1 and Pck2 genes encode. Gluconeogenesis increases in diabetic nephropathy (DN), escalating fasting and postprandial glucose levels. Sodium-glucose cotransporter-2 inhibitors increase hepatic and renal gluconeogenesis. We used genetically modified mice to investigate whether renal gluconeogenesis and Pck1 activity are renoprotective in DN.

METHODS

We investigated the expression of Pck1 in the proximal tubule (PTs) of streptozotocin (STZ)-treated diabetic mice. We studied the phenotypic changes in PT-specific transgenic (TG) mice and PT-specific Pck1 conditional knockout (CKO) mice.

RESULTS

The expression of Pck1 in PTs was downregulated in STZ-treated diabetic mice when they exhibited albuminuria. TG mice overexpressing Pck1 had improved albuminuria, concomitant with the mitigation of PT cell apoptosis and deposition of peritubular type IV collagen. Moreover, CKO mice exhibited PT cell apoptosis and type IV collagen deposition, findings also observed in STZ-treated mice. Renal fibrotic changes in CKO mice were associated with increasing defects in mitochondrial ribosomes (mitoribosomes). The TG mice were protected against STZ-induced mitoribosomal defects.

CONCLUSION

PCK1 preserves mitoribosomal function and may play a novel protective role in DN.

Research progress on the mechanism of renal interstitial fibrosis in obstructive nephropathy

Renal fibrosis is a common result for various chronic kidney diseases developing to the end stage. It is a pathological process characterized by the destruction of normal kidney structure and the subsequent replacement with fibrous tissue, which primarily involves fibroblast proliferation and extracellular matrix deposition. Obstruction is a common cause of renal fibrosis, and obstructive renal fibrosis is a common disease in urology. Obstructive renal fibrosis, characterized by its insidious onset, is the result of a complex interplay of multiple factors. These factors encompass renal tubular epithelial cell injury, the presence of a hypoxic microenvironment in affected kidney tissue, inflammatory cell infiltration, release of inflammatory mediators, and the release of renal fibrosis growth factors, among others. This paper reviews the research progress on the mechanism and treatment of renal interstitial fibrosis.

GPR97 deficiency ameliorates renal interstitial fibrosis in mouse hypertensive nephropathy

Hypertensive nephropathy (HTN) ranks as the second-leading cause of end-stage renal disease (ESRD). Accumulating evidence suggests that persistent hypertension injures tubular cells, leading to tubulointerstitial fibrosis (TIF), which is involved in the pathogenesis of HTN. G protein-coupled receptors (GPCRs) are implicated in many important pathological and physiological processes and act as important drug targets. In this study, we explored the intrarenal mechanisms underlying hypertension-associated TIF, and particularly, the potential role of GPR97, a member of the adhesion GPCR subfamily, in TIF. A deoxycorticosterone acetate (DOCA)/salt-induced hypertensive mouse model was used. We revealed a significantly upregulated expression of GPR97 in the kidneys, especially in renal tubules, of the hypertensive mice and 10 patients with biopsy-proven hypertensive kidney injury. GPR97-/- mice showed markedly elevated blood pressure, which was comparable to that of wild-type mice following DOCA/salt treatment, but dramatically ameliorated renal injury and TIF. In NRK-52E cells, we demonstrated that knockdown of GPR97 suppressed the activation of TGF-β signaling by disturbing small GTPase RhoA-mediated cytoskeletal reorganization, thus inhibiting clathrin-mediated endocytosis of TGF-β receptors and subsequent Smad activation. Collectively, this study demonstrates that GPR97 contributes to hypertension-associated TIF at least in part by facilitating TGF-β signaling, suggesting that GPR97 is a pivotal intrarenal factor for TIF progression under hypertensive conditions, and therapeutic strategies targeting GPR97 may improve the outcomes of patients with HTN.

Hippo signaling in acute kidney injury to chronic kidney disease transition: current understandings and future targets

Acute kidney injury (AKI)-to-chronic kidney disease (CKD) transition is a slow but persistent progression toward end-stage kidney disease. Earlier reports have shown that Hippo components, such as Yes-associated protein (YAP) and its homolog TAZ (Transcriptional coactivator with PDZ-binding motif), regulate inflammation and fibrogenesis during the AKI-to-CKD transition. Notably, the roles and mechanisms of Hippo components vary during AKI, AKI-to-CKD transition, and CKD. Hence, it is important to understand these roles in detail. This review addresses the potential of Hippo regulators or components as future therapeutic targets for halting the AKI-to-CKD transition.