Transcription factor EB: A potential integrated network regulator in metabolic-associated cardiac injury

Exercise combined with metformin ameliorates diabetic kidney disease by increasing renal autophagy and reducing oxidative stress in rats with high-fat diet and streptozotocin induced diabetes

Diabetic kidney disease (DKD) is one of the common and serious complications of type 2 diabetes mellitus (T2DM). Metformin is commonly prescribed for the treatment of T2DM, while exercise is frequently recommended as adjunctive therapy. However, the therapeutic efficacy and molecular etiology of combined therapy with exercise and metformin in DKD remain to be elucidated. The present study therefore aimed to investigate the therapeutic effects and mechanisms underlying the combined effects of exercise and metformin on DKD. A rat model of T2DM was constructed by administering a high-fat diet and intraperitoneal injections of streptozotocin (30 mg/kg) for 6 weeks. The rats with T2DM exhibited reduced autophagic flux, increased oxidative stress, and morphological and structural lesions in the kidneys, compared to those of normal rats in the control group. The combination of exercise and metformin alleviated DKD, indicated by the elevation of renal autophagic flux, and a reduction in oxidative stress, renal fibrosis, and histopathological damage to the kidneys. Our findings suggested that exercise combined with metformin has a therapeutic role in DKD, and the study serves as a valuable reference for future research on the treatment of DKD.

CCAAT/Enhancer-Binding Protein Beta Nitration Participates in Hyperhomocysteinemia-Induced Cardiomyocyte Autophagic Flux Blockage by Inhibiting Transcription Factor EB Transcription

Aims: Autophagy is a protective mechanism of cardiomyocytes. Hyperhomocysteinemia (HHcy) elevates oxidative and nitrosative stress levels, leading to an abnormal increase in nitration protein, possibly leading to abnormal autophagy regulation in cardiomyocytes. However, the regulatory effect of HHcy on autophagy at the post-translational modification level is still unclear. Here, we aimed to explore the regulatory mechanism of HHcy on transcription factor EB (TFEB) and nitration of CCAAT/enhancer-binding protein beta (C/EBPβ), a transcriptional repressor of Tfeb, on autophagy in cardiomyocytes. Results: In this study, we established the HHcy rat model by feeding a 2.5% (w/w) methionine diet. The nitration level of C/EBPβ was increased in HHcy, which promoted the entry of C/EBPβ into the nucleus, enhanced the transcriptional suppressive effect of C/EBPβ on Tfeb, and induced insufficient autophagy in cardiomyocytes. Furthermore, we confirmed that the Tyr 274 site of C/EBPβ could undergo nitration induced by HHcy. Once C/EBPβ was nitrated on the Tyr 274 site, the nuclear translocation of C/EBPβ and transcription suppressor function of C/EBPβ on Tfeb were enhanced. Innovation and Conclusion: We find that C/EBPβ is a transcriptional repressor of Tfeb, and HHcy induces the nitration at the Tyr 274 site of C/EBPβ, leading to autophagic flux blockage in cardiomyocytes. These data indicated that nitrated C/EBPβ might be a potential therapeutic target against HHcy-induced autophagy insufficiency of cardiomyocytes. Antioxid. Redox Signal. 42, 165-183.

PINK1 modulates Prdx2 to reduce lipotoxicity-induced apoptosis and attenuate cardiac dysfunction in heart failure mice with a preserved ejection fraction

INTRODUCTION

Heart failure with preserved ejection fraction (HFpEF) is a complex condition characterized by metabolic dysfunction and myocardial lipotoxicity. The roles of PTEN-induced kinase 1 (PINK1) and peroxiredoxin-2 (Prdx2) in HFpEF pathogenesis remain unclear.

OBJECTIVE

This study aimed to investigate the interaction between PINK1 and Prdx2 to mitigate cardiac diastolic dysfunction in HFpEF.

METHODS

In vivo, PINK1-knockout mice and cardiac-specific PINK1-overexpressing transgenic mice were used to establish an HFpEF mouse model via a high-fat diet and L-NAME. Myocardial lipotoxicity was induced by palmitic acid in vitro. Immunoprecipitation, western blotting and immunofluorescence analysis were performed to elucidate the molecular mechanisms involved.

RESULTS

We determined that PINK1 and Prdx2 were downregulated in the HFpEF mouse model. In vivo, PINK1 ablation exacerbated the reduction in Prdx2 expression, worsening cardiac dysfunction in HFpEF mice. Conversely, PINK1 overexpression restored Prdx2 levels and decreased reactive oxygen species and apoptosis, thereby reducing fibrosis and inflammation and ameliorating cardiac diastolic dysfunction in HFpEF mice. In vitro, an interaction between the N-terminal region (amino acids 1-133) of PINK1 and Prdx2 was identified. The overexpression of PINK1 induced Prdx2 expression and effectively attenuated palmitic acid-induced apoptosis through the c-Jun amino-terminal kinase (JNK) and mitogen-activated protein kinase (p38) pathways, whereas siRNA-mediated Prdx2 knockdown abolished the protective effect of PINK1.

CONCLUSION

PINK1 alleviates lipotoxicity-induced myocardial apoptosis and improves diastolic dysfunction in HFpEF through Prdx2, highlighting PINK1 overexpression as a potential therapeutic strategy for HFpEF.

KEY POINTS

Our investigation discloses a pivotal relationship between PINK1 and Prdx2 in the context of HFpEF. Notably, PINK1, in addition to its role in mitochondrial autophagy, can increase Prdx2 expression, effectively remove ROS and attenuate cardiomyocyte apoptosis by modulating the JNK and p38 pathways, thereby alleviating myocardial lipotoxicity and improving HFpEF cardiac function. Our studies offer valuable insights, opening avenues for the development of innovative therapeutic strategies in the prevention and treatment of HFpEF.

Targeted dephosphorylation of TFEB promotes its nuclear translocation

Reversible phosphorylation of the transcription factor EB (TFEB) coordinates cellular responses to metabolic and other stresses. During nutrient replete and stressor-free conditions, phosphorylated TFEB is primarily localized to the cytoplasm. Stressor-mediated reduction of TFEB phosphorylation promotes its nuclear translocation and context-dependent transcriptional activity. In this study, we explored targeted dephosphorylation of TFEB as an approach to activate TFEB in the absence of nutrient deprivation or other cellular stress. Through an induction of proximity between TFEB and several phosphatases using the AdPhosphatase system, we demonstrate targeted dephosphorylation of TFEB in cells. Furthermore, by developing a heterobifunctional molecule BDPIC (bromoTAG-dTAG proximity-inducing chimera), we demonstrate targeted dephosphorylation of TFEB-dTAG through induced proximity to bromoTAG-PPP2CA. Targeted dephosphorylation of TFEB-dTAG by bromoTAG-PPP2CA with BDPIC at the endogenous levels is sufficient to induce nuclear translocation and some transcriptional activity of TFEB.

Autophagic-lysosomal damage induced by swainsonine is protected by trehalose through activation of TFEB-regulated pathway in renal tubular epithelial cells

Swainsonine (SW) is the main toxic component of locoweed. Previous studies have shown that kidney damage is an early pathologic change in locoweed poisoning in animals. Trehalose induces autophagy and alleviates lysosomal damage, while its protective effect and mechanism against the toxic injury induced by SW is not clear. Based on the published literature, we hypothesize that transcription factor EB(TFEB) -regulated is targeted by SW and activating TFEB by trehalose would reverse the toxic effects. In this study, we investigate the mechanism of protective effects of trehalose using renal tubular epithelial cells. The results showed that SW induced an increase in the expression level of microtubule-associated protein light chain 3-II and p62 proteins and a decrease in the expression level of ATPase H+ transporting V1 Subunit A, Cathepsin B, Cathepsin D, lysosome-associated membrane protein 2 and TFEB proteins in renal tubular epithelial cells in a time and dose-dependent manner suggesting TFEB-regulated lysosomal pathway is adversely affected by SW. Conversely, treatment with trehalose, a known activator of TFEB promote TFEB nuclear translocation suggesting that TFEB plays an important role in protection against SW toxicity. We demonstrated in lysosome staining that SW reduced the number of lysosomes and increased the luminal pH, while trehalose could counteract these SW-induced effects. In summary, our results demonstrated for the first time that trehalose could alleviate the autophagy degradation disorder and lysosomal damage induced by SW. Our results provide an interesting method for reversion of SW-induced toxicity in farm animals and furthermore, activation of TFEB by trehalose suggesting novel mechanism of treating lysosomal storage diseases.

From the regulatory mechanism of TFEB to its therapeutic implications

Transcription factor EB (TFEB), known as a major transcriptional regulator of the autophagy-lysosomal pathway, regulates target gene expression by binding to coordinated lysosomal expression and regulation (CLEAR) elements. TFEB are regulated by multiple links, such as transcriptional regulation, post-transcriptional regulation, translational-level regulation, post-translational modification (PTM), and nuclear competitive regulation. Targeted regulation of TFEB has been victoriously used as a treatment strategy in several disease models such as ischemic injury, lysosomal storage disorders (LSDs), cancer, metabolic disorders, neurodegenerative diseases, and inflammation. In this review, we aimed to elucidate the regulatory mechanism of TFEB and its applications in several disease models by targeting the regulation of TFEB as a treatment strategy.

Interaction of Fabry Disease and Diabetes Mellitus: Suboptimal Recruitment of Kidney Protective Factors

Fabry disease is a lysosomal disease characterized by globotriaosylceramide (Gb3) accumulation. It may coexist with diabetes mellitus and both cause potentially lethal kidney end-organ damage. However, there is little information on their interaction with kidney disease. We have addressed the interaction between Fabry disease and diabetes in data mining of human kidney transcriptomics databases and in Fabry (Gla-/-) and wild type mice with or without streptozotocin-induced diabetes. Data mining was consistent with differential expression of genes encoding enzymes from the Gb3 metabolic pathway in human diabetic kidney disease, including upregulation of UGCG, the gene encoding the upstream and rate-limiting enzyme glucosyl ceramide synthase. Diabetic Fabry mice displayed the most severe kidney infiltration by F4/80+ macrophages, and a lower kidney expression of kidney protective genes (Pgc1α and Tfeb) than diabetic wild type mice, without a further increase in kidney fibrosis. Moreover, only diabetic Fabry mice developed kidney insufficiency and these mice with kidney insufficiency had a high expression of Ugcg. In conclusion, we found evidence of interaction between diabetes and Fabry disease that may increase the severity of the kidney phenotype through modulation of the Gb3 synthesis pathway and downregulation of kidney protective genes.