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

Modulating HIF-1α/HIF-2α homeostasis with Shen-Qi-Huo-Xue formula alleviates tubular ferroptosis and epithelial-mesenchymal transition in diabetic kidney disease

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic kidney disease (DKD) is one of the main types of chronic kidney disease, which seriously affects the quality of life of patients. Shen-Qi-Huo-Xue formula (SQHXF), based on the Shen-Qi-Di-Huang decoction, is a traditional Chinese medicine formula for DKD. This study explored the mechanism of action of SQHXF on DKD through analysis of drug components, in vivo and in vitro experiments.

AIM OF THE STUDY

To elucidate the regulatory mechanisms of HIF-1α/HIF-2α homeostasis on ferroptosis and epithelial-mesenchymal transition (EMT) in renal tubular epithelial cells and the mechanism of action of SQHXF against DKD.

METHODS

The components of SQHXF were analyzed using UPLC-Q Exactive HF/MS. The effects of SQHXF on renal function, urinary proteins, glucose-lipid metabolism, hepatic function, renal tissue hypoxia, ferroptosis and EMT were analyzed following gavage of DKD model mice with different SQHXF doses. The effects of changes in HIF-1α and HIF-2α expression on ferroptosis and EMT, as well as the modulatory effects of SQHXF-containing serum, were assessed in vitro. The potential feedback mechanism of HIFs/ferroptosis/EMT was elucidated using HIF-1α knockdown and a ferroptosis inhibitor.

RESULTS

One-hundred and fifty compounds in SQHXF were tested for bloodstream entry. In vivo study showed that SQHXF was able to reduce creatinine, uric acid, fasting plasma glucose, 24-h urinary protein, low-density lipoprotein cholesterol, and aspartate aminotransferase levels, up-regulate HIF-1α, down-regulate HIF-2α, reduce ferroptosis, and alleviate renal fibrosis and EMT in tubular epithelial cells. HIF-1α/HIF-2α imbalance promoted ferroptosis and EMT in HK-2 cells, which was attenuated by SQHXF-containing serum. HIF-1α knockdown decreased HIF-2α expression and reduced ferroptosis and EMT. Inhibition of ferroptosis reduced EMT but failed to regulate HIF-1α and HIF-2α.

CONCLUSIONS

SQHXF alleviated ferroptosis and EMT, improved liver and kidney function, reduced proteinuria, and alleviated renal lesions by maintaining equilibrium between HIF-1α and HIF-2α.

Mitochondria-targeting therapeutic strategies for chronic kidney disease

Chronic kidney disease (CKD) is a multifactorial health issue characterised by kidney impairment that has significant morbidity and mortality in the global population. Current treatments for CKD fail to prevent progression to end-stage kidney disease, where management is limited to renal replacement therapy or kidney transplantation. Mitochondrial dysfunction has been implicated in the pathogenesis of CKD and can be broadly categorised into abnormalities related to excessive oxidative stress, reduced mitochondrial biogenesis, excess mitochondrial fission and dysregulated mitophagy. Mitochondria-targeting therapeutic strategies target many of the outlined mechanisms of mitochondrial dysfunction, and an overview of recent evidence for mitochondria-targeting therapeutic strategies is explored in this review, including naturally derived compounds and novel approaches such as fusion proteins. Mitochondria-targeting therapeutic strategies using these approaches show the potential to stabilise or improve renal function, and clinical studies are needed to further confirm their safety and efficacy in human contexts.

The multifaceted effects of mitochondria in kidney diseases

Mitochondria serve as the primary site for aerobic respiration within cells, playing a crucial role in maintaining cellular homeostasis. To maintain homeostasis and meet the diverse demands of the cells, mitochondria have evolved intricate systems of quality control, mainly including mitochondrial dynamics, mitochondrial autophagy (mitophagy) and mitochondrial biogenesis. The kidney, characterized by its high energy requirements, is particularly abundant in mitochondria. Interestingly, the mitochondria display complex behaviors and functions. When the kidney is suffered from obstructive, ischemic, hypoxic, oxidative, or metabolic insults, the dysfunctional mitochondrial derived from the defects in the mitochondrial quality control system contribute to cellular inflammation, cellular senescence, and cell death, posing a threat to the kidney. However, in addition to causing injury to the kidney in several cases, mitochondria also exhibit protective effect on the kidney. In recent years, accumulating evidence indicated that mitochondria play a crucial role in adaptive repair following kidney diseases caused by various etiologies. In this article, we comprehensively reviewed the current understanding about the multifaceted effects of mitochondria on kidney diseases and their therapeutic potential.

The role of metabolic memory in diabetic kidney disease: identification of key genes and therapeutic targets

Diabetic kidney disease (DKD) is characterized by complex pathogenesis and poor prognosis; therefore, an exploration of novel etiological factors may be beneficial. Despite glycemic control, the persistence of transient hyperglycemia still induces vascular complications due to metabolic memory. However, its contribution to DKD remains unclear. Using single-cell RNA sequencing data from the Gene Expression Omnibus (GEO) database, we clustered 12 cell types and employed enrichment analysis and a cell‒cell communication network. Fibrosis, a characteristic of DKD, was found to be associated with metabolic memory. To further identify genes related to metabolic memory and fibrosis in DKD, we combined the above datasets from humans with a rat renal fibrosis model and mouse models of metabolic memory. After overlapping, NDRG1, NR4A1, KCNC4 and ZFP36 were selected. Pharmacology analysis and molecular docking revealed that pioglitazone and resveratrol were possible agents affecting these hub genes. Based on the ex vivo results, NDRG1 was selected for further study. Knockdown of NDRG1 reduced TGF-β expression in human kidney-2 cells (HK-2 cells). Compared to that in patients who had diabetes for more than 10 years but not DKD, NDRG1 expression in blood samples was upregulated in DKD patients. In summary, NDRG1 is a key gene involved in regulating fibrosis in DKD from a metabolic memory perspective. Bioinformatics analysis combined with experimental validation provided reliable evidence for identifying metabolic memory in DKD patients.

Sacubitril/valsartan ameliorates tubulointerstitial fibrosis by restoring mitochondrial homeostasis in diabetic kidney disease

BACKGROUND

Tubulointerstitial fibrosis plays an important role in the progression of diabetic kidney disease (DKD). Sacubitril/valsartan (Sac/Val) exerts a robust beneficial effect in DKD. However, the potential functional effect of Sac/Val on tubulointerstitial fibrosis in DKD is still largely unclear.

METHODS

Streptozotocin-induced diabetic mice were given Sac/Val or Val by intragastric administration once a day for 12 weeks. The renal function, the pathological changes of tubule injury and tubulointerstitial fibrosis, as well as mitochondrial morphology of renal tubules in mice, were evaluated. Genome-wide gene expression analysis was performed to identify the potential mechanisms. Meanwhile, human tubular epithelial cells (HK-2) were cultured in high glucose condition containing LBQ657/valsartan (LBQ/Val). Further, mitochondrial functions and Sirt1/PGC1α pathway of tubular epithelial cells were assessed by Western blot, Real-time-PCR, JC-1, MitoSOX or MitoTracker. Finally, the Sirt1 specific inhibitor, EX527, was used to explore the potential effects of Sirt1 signaling in vivo and in vitro.

RESULTS

We found that Sac/Val significantly ameliorated the decline of renal function and tubulointerstitial fibrosis in DKD mice. The enrichment analysis of gene expression indicated metabolism as an important modulator in DKD mice with Sac/Val administration, in which mitochondrial homeostasis plays a pivotal role. Then, the decreased expression of Tfam and Cox IV;, as well as changes of mitochondrial function and morphology, demonstrated the disruption of mitochondrial homeostasis under DKD conditions. Interestingly, Sac/Val administration was found to restore mitochondrial homeostasis in DKD mice and in vitro model of HK-2 cells. Further, we demonstrated that Sirt1/PGC1α, a crucial pathway in mitochondrial homeostasis, was activated by Sac/Val both in vivo and in vitro. Finally, the beneficial effects of Sac/Val on mitochondrial homeostasis and tubulointerstitial fibrosis was partially abolished in the presence of Sirt1 specific inhibitor.

CONCLUSIONS

Taken together, we demonstrate that Sac/Val ameliorates tubulointerstitial fibrosis by restoring Sirt1/PGC1α pathway-mediated mitochondrial homeostasis in DKD, providing a theoretical basis for delaying the progression of DKD in clinical practice.