Mitochondrial Dysfunction in Individuals with Diabetic Kidney Disease: A Systematic Review

Role of mitochondrial dysfunction in kidney disease: Insights from the cGAS-STING signaling pathway

ABSTRACT

Over the past decade, mitochondrial dysfunction has been investigated as a key contributor to acute and chronic kidney disease. However, the precise molecular mechanisms linking mitochondrial damage to kidney disease remain elusive. The recent insights into the cyclic guanosine monophosphate-adenosine monophosphate (GMP-AMP) synthetase (cGAS)-stimulator of interferon gene (STING) signaling pathway have revealed its involvement in many renal diseases. One of these findings is that mitochondrial DNA (mtDNA) induces inflammatory responses via the cGAS-STING pathway. Herein, we provide an overview of the mechanisms underlying mtDNA release following mitochondrial damage, focusing specifically on the association between mtDNA release-activated cGAS-STING signaling and the development of kidney diseases. Furthermore, we summarize the latest findings of cGAS-STING signaling pathway in cell, with a particular emphasis on its downstream signaling related to kidney diseases. This review intends to enhance our understanding of the intricate relationship among the cGAS-STING pathway, kidney diseases, and mitochondrial dysfunction.

Promoting mitochondrial dynamics by inhibiting the PINK1-PRKN pathway to relieve diabetic nephropathy

Diabetes is a metabolic disorder characterized by high blood glucose levels and is a leading cause of kidney disease. Diabetic nephropathy has been attributed to dysfunctional mitochondria. However, many questions remain about the exact mechanism. The structure, function and molecular pathways are highly conserved between mammalian podocytes and Drosophila nephrocytes; therefore, we used flies on a high-sucrose diet to model type 2 diabetic nephropathy. The nephrocytes from flies on a high-sucrose diet showed a significant functional decline and decreased cell size, associated with a shortened lifespan. Structurally, the nephrocyte filtration structure, known as the slit diaphragm, was disorganized. At the cellular level, we found altered mitochondrial dynamics and dysfunctional mitochondria. Regulating mitochondrial dynamics by either genetic modification of the Pink1-Park (mammalian PINK1-PRKN) pathway or treatment with BGP-15, mitigated the mitochondrial defects and nephrocyte functional decline. These findings support a role for Pink1-Park-mediated mitophagy and associated control of mitochondrial dynamics in diabetic nephropathy, and demonstrate that targeting this pathway might provide therapeutic benefits for type 2 diabetic nephropathy.

Increased Diabetes Complications in a Mouse Model of Oxidative Stress Due to 'Mismatched' Mitochondrial DNA

Associations between chronic diabetes complications and mitochondrial dysfunction represent a subject of major importance, given the diabetes pandemic and high personal and socioeconomic costs of diabetes and its complications. Modelling diabetes complications in inbred laboratory animals is challenging due to incomplete recapitulation of human features, but offer mechanistic insights and preclinical testing. As mitochondrial-based oxidative stress is implicated in human diabetic complications, herein we evaluate diabetes in a unique mouse model that harbors a mitochondrial DNA from a divergent mouse species (the 'xenomitochondrial mouse'), which has mild mitochondrial dysfunction and increased oxidative stress. We use the streptozotocin-induced diabetes model with insulin supplementation, with 20-weeks diabetes. We compare C57BL/6 mice and the 'xenomitochondrial' mouse, with measures of heart and kidney function, histology, and skin oxidative stress markers. Compared to C57BL/6 mice, the xenomitochondrial mouse has increased diabetic heart and kidney damage, with cardiac dysfunction, and increased cardiac and renal fibrosis. Our results show that mitochondrial oxidative stress consequent to divergent mtDNA can worsen diabetes complications. This has implications for novel therapeutics to counter diabetes complications, and for genetic studies of risk, as mtDNA genotypes may contribute to clinical outcomes.

Modified Hu-lu-ba-wan protects diabetic glomerular podocytes via promoting PKM2-mediated mitochondrial dynamic homeostasis

BACKGROUND

Mitochondrial dysfunction is implicated in the progression of diabetic kidney disease (DKD). Damaged mitochondria produce excessive reactive oxygen species (ROS) that can cause apoptosis. Mitochondrial dynamics control the quality and function of mitochondria. Targeting mitochondrial dynamics may reduce ROS-induced apoptosis and improve renal injury in DKD. Modified Hu-lu-ba-wan (MHLBW) shows distinct clinical effects on DKD patients, which are related to its role in antioxidant stress modulation. However, the relevant mechanisms of MHLBW have not been clearly explored.

PURPOSE

This study was aimed to evaluate the therapeutic effects of MHLBW on spontaneous DKD mice and clarify the potential mechanisms.

METHODS

The main components of MHLBW were identified by HPLC. Using db/db mice as DKD models, we evaluated the therapeutic effects of MHLBW on mice after an 8-week administration. We investigated the molecular mechanism of MHLBW in regulating mitochondrial dynamic homeostasis, podocyte apoptosis, and glomerular damage. After that, computational docking analysis and in vitro experiments were conducted for further mechanism verification.

RESULTS

Intragastric administration of MHLBW for 8 weeks in db/db mice significantly improved glucose metabolism, basement membrane thickening, mesangial expansion, glomerular fibrosis, and podocyte injury. MHLBW can reverse podocyte apoptosis via promoting mitochondrial dynamic homeostasis, which was related to regulating the PKM2/ PGC-1α/Opa1 pathway. Berberine (BBR), one of the components of MHLBW, exhibited preeminent affinity with PKM2 as reflected by computational docking analysis. In cultured podocytes, BBR can also prevent apoptosis by promoting PKM2-mediated mitochondrial dynamic homeostasis.

CONCLUSION

Our study demonstrates that MHLBW can treat DKD by inhibiting glomerular damage and podocyte apoptosis through positive regulation of PKM2-mediated mitochondrial dynamic homeostasis. These results may provide a potential strategy against DKD.

[Linagliptin improves diabetic kidney disease in rats by promoting mitochondrial biogenesis through the AMPK/PGC-1α/TFAM pathway]

OBJECTIVE

To investigate whether linagliptin improves diabetic kidney disease (DKD) by promoting mitochondrial biosynthesis via activating adenosine monophosphate activated protein kinase/peroxisome proliferator-activated receptor gamma coactivator 1α/mitochondrial transcription factor A (AMPK/PGC-1α/TFAM) pathway.

METHODS

With 6 male SD rats feeding normal chow as the control group, 16 SD rat models of DKD induced by intraperitoneal injection of 45 mg/kg STZ and high-fat and high-glucose feeding for 4 weeks were randomized into DKD model group and linagliptin treatment group. The rats in the latter two groups were subjected to daily intragastric administration of vehicle or 5 mg/kg linagliptin (dissolved in 5 g/L sodium carboxymethylcellulose, final concentration of 2 mg/mL) for 12 weeks with further high-fat and high-glucose feeding. After the treatments, the rats were sacrificed and blood samples from the abdominal aorta and kidney tissues were collected for testing blood glucose, liver function and lipid metabolism; HE, PAS, Masson, Sirius red staining and electron microscopy were used to observe renal tissue damage. Renal expressions of transforming growth factor β1 (TGF-β1), fibronectin (FN) and collagen I (Col I) were detected by immunohistochemistry, and the changes in membrane potential (ΔψM) and ATP enzyme content were analyzed to assess mitochondrial damage; The expressions of AMPK/PGC-1α/TFAM pathway proteins were detected using Western blotting.

RESULTS

Compared with DKD model rats, the rats receiving linagliptin treatment showed significantly decreased blood glucose level (P < 0.01) and improved proteinuria (P < 0.05) with obviously alleviated renal ultrastructural damage and fibrosis, increased ATPase content and ΔψM (P < 0.0001), and enhanced renal expressions of P-AMPK/AMPK, PGC-1α and TFAM (P < 0.05).

CONCLUSIONS

Linagliptin improves proteinuria and renal fibrosis in rat models of DKD possibly by activating the AMPK/PGC-1α/TFAM pathway to promote mitochondrial biosynthesis.

Resveratrol prevents Drp1-mediated mitochondrial fission in the diabetic kidney through the PDE4D/PKA pathway

To explore the role of PDE4D in diabetic nephropathy (DN) and investigate whether resveratrol protects against DN via inhibiting PDE4D. Diabetic db/db mouse and glomerular mesangial cell line (GMCs) were used to investigate the role of PDE4D and the protective effect of resveratrol on renal fibrosis under high glucose (HG) environment. Resveratrol alleviated the progress of DN via inhibiting mitochondrial fragmentation and restoring the expression of PDE4D, PKA, phosphorylated Drp1-Ser637 and Drp1 in kidney of db/db mice. In HG-exposed GMCs, resveratrol treatment decreased the expression of PDE4D, increased PKA level, and inhibited Drp1-mediated mitochondrial fission. In contrast, PDE4D over-expression blunted the inhibitory effects of resveratrol on Drp1 expression and mitochondrial fission. Moreover, PKA inhibitor H89 blunted the effects of resveratrol on phosphorylated Drp1-Ser637 expression and mitochondrial fission in HG-treated GMCs. Inhibition of mitochondrial fission with Drp1 inhibitor Mdivi-1 alleviated mitochondrial dysfunction in GMCs under HG. These findings indicate PDE4D plays an important role in the process of DN. Resveratrol attenuates the development of DN by preventing mitochondrial fission through inhibiting PDE4D, which regulates the expression of phosphorylated Drp1-Ser637 directly.

Regulation of autophagy by natural polyphenols in the treatment of diabetic kidney disease: therapeutic potential and mechanism

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes and a leading cause of end-stage renal disease worldwide. Autophagy plays an important role in maintaining cellular homeostasis in renal physiology. In DKD, the accumulation of advanced glycation end products induces decreased renal autophagy-related protein expression and transcription factor EB (TFEB) nuclear transfer, leading to impaired autophagy and lysosomal function and blockage of autophagic flux. This accelerates renal resident cell injury and apoptosis, mediates macrophage infiltration and phenotypic changes, ultimately leading to aggravated proteinuria and fibrosis in DKD. Natural polyphenols show promise in treating DKD by regulating autophagy and promoting nuclear transfer of TFEB and lysosomal repair. This review summarizes the characteristics of autophagy in DKD, and the potential application and mechanisms of some known natural polyphenols as autophagy regulators in DKD, with the goal of contributing to a deeper understanding of natural polyphenol mechanisms in the treatment of DKD and promoting the development of their applications. Finally, we point out the limitations of polyphenols in current DKD research and provide an outlook for their future research.

SUPPRESION OF MITOCHONDRIAL RESPIRATION IS A FEATURE OF CELLULAR GLUCOSE TOXICITY

Glucose toxicity is central to the myriad complications of diabetes and is now believed to encompass neurodegenerative diseases and cancer as well as microvascular and macrovascular disease. Due to the widespread benefits of SGLT2 inhibitors, which affect glucose uptake in the kidney proximal tubular cell, a focus on cell metabolism in response to glucose has important implications for overall health. We previously found that a -Warburg-type effect underlies diabetic kidney disease and involves metabolic reprogramming. This is now supported by quantitative measurements of superoxide measurement in the diabetic kidney and systems biology analysis of urine metabolites in patients. Further exploration of mechanisms underlying mediators of mitochondrial suppression will be critical in understanding the chronology of glucose-induced toxicity and developing new therapeutics to arrest the systemic glucose toxicity of diabetes.