The disruption of the balance between fatty acid (FA) uptake and oxidation (FAO) leads to cardiac lipotoxicity, serving as the driving force behind diabetic cardiomyopathy (DbCM). Sirtuin 5 (Sirt5), a lysine de-succinylase, could impact diverse metabolic pathways, including FA metabolism. Nevertheless, the precise roles of Sirt5 in cardiac lipotoxicity and DbCM remain unknown. This study aims to elucidate the role and underlying mechanism of Sirt5 in the context of cardiac lipotoxicity and DbCM. The expression of myocardial Sirt5 was found to be modestly elevated in diabetic heart failure patients and mice. Cardiac dysfunction, hypertrophy and lipotoxicity were exacerbated by ablation of Sirt5 but improved by forced expression of Sirt5 in diabetic mice. Notably, Sirt5 deficiency impaired FAO without affecting the capacity of FA uptake in the diabetic heart, leading to accumulation of FA intermediate metabolites, which mainly included medium- and long-chain fatty acyl-carnitines. Mechanistically, succinylomics analyses identified carnitine palmitoyltransferase 2 (CPT2), a crucial enzyme involved in the reconversion of fatty acyl-carnitines to fatty acyl-CoA and facilitating FAO, as the functional succinylated substrate mediator of Sirt5. Succinylation of Lys424 in CPT2 was significantly increased by Sirt5 deficiency, leading to the inactivation of its enzymatic activity and the subsequent accumulation of fatty acyl-carnitines. CPT2 K424R mutation, which mitigated succinylation modification, counteracted the reduction of enzymatic activity in CPT2 mediated by Sirt5 deficiency, thereby attenuating Sirt5 knockout-induced FAO impairment and lipid deposition. Sirt5 deficiency impairs FAO, leading to cardiac lipotoxicity in the diabetic heart through the succinylation of Lys424 in CPT2. This underscores the potential roles of Sirt5 and CPT2 as therapeutic targets for addressing DbCM.

Maintaining proper mitochondrial respiratory function is crucial for alleviating cardiac metabolic disorders during obesity, and mitophagy is critically involved in this process. Long non-coding RNA H19 (H19) is crucial for metabolic regulation, but its roles in cardiac disorders, mitochondrial respiratory function, and mitophagy during obesity are largely unknown. In this study, palmitic acid (PA)-treated H9c2 cell and Lep^−/− mice were used to investigate cardiac metabolic disorders in vitro and in vivo, respectively. The effects of H19 on metabolic disorders, mitochondrial respiratory function, and mitophagy were investigated. Moreover, the regulatory mechanisms of PA, H19, mitophagy, and respiratory function were examined. The models tested displayed a reduction in H19 expression, respiratory function and mitochondrial number and volume, while the expression of mitophagy- and Pink1/Parkin signaling-related proteins was upregulated, as indicated using quantitative real-time PCR, Seahorse mitochondrial stress test analyzer, transmission electron microscopy, fluorescence indicators and western blotting. Forced expression of H19 helped to the recoveries of respiratory capacity and mitochondrial number while inhibited the levels of mitophagy- and Pink1/Parkin signaling-related proteins. Pink1 knockdown also attenuated PA-induced mitophagy and increased respiratory capacity. Mechanistically, RNA pull-down, mass spectrometry, and RNA-binding protein immunoprecipitation assays showed that H19 could hinder the binding of eukaryotic translation initiation factor 4A, isoform 2 (eIF4A2) with Pink1 mRNA, thus inhibiting the translation of Pink1 and attenuation of mitophagy. PA significantly increased the methylation levels of the H19 promoter region by upregulation Dnmt3b methylase levels, thereby inhibiting H19 transcription. Collectively, these findings suggest that DNA methylation-mediated the downregulation of H19 expression plays a crucial role in cardiomyocyte or H9c2 cells metabolic disorders and induces cardiac respiratory dysfunction by promoting mitophagy. H19 inhibits excessive mitophagy by limiting Pink1 mRNA translation, thus alleviating this cardiac defect that occurs during obesity.

Objective: To explore the role of glycolysis in cardiac fibroblast (CF) activation and cardiac fibrosis after myocardial infarction (MI).Method:In vivo: 2-Deoxy-D-glucose (2-DG), a glycolysis inhibitor, was injected into the abdominal cavity of the MI or sham mice every day. On the 28th day, cardiac function was measured by ultrasonic cardiography, and the hearts were harvested. Masson staining and immunofluorescence (IF) were used to evaluate the fibrosis area, and western blot was used to identify the glycolytic level. In vitro, we isolated the CF from the sham, MI and MI with 2-DG treatment mice, and we also activated normal CF with transforming growth factor-β1 (TGF-β1) and block glycolysis with 2-DG. We then detected the glycolytic proteins, fibrotic proteins, and the concentrations of lactate and glucose in the culture medium. At last, we further detected the fibrotic and glycolytic markers in human fibrotic and non-fibrotic heart tissues with masson staining, IF and western blot.Result: More collagen and glycolytic protein expressions were observed in the MI mice hearts. The mortality increased when mice were treated with 2-DG (100 mg/kg/d) after the MI surgery (Log-rank test, P < 0.05). When the dosage of 2-DG declined to 50 mg/kg/d, and the treatment was started on the 4th day after MI, no statistical difference of mortality between the two groups was observed (Log-rank test, P = 0.98). The collagen volume fraction was smaller and the fluorescence signal of α-smooth muscle actin (α-SMA) was weaker in mice treated with 2-DG than PBS. In vitro, 2-DG could significantly inhibit the increased expression of both the glycolytic and fibrotic proteins in the activated CF.Conclusion: Cardiac fibrosis is along with the enhancement of CF activation and glycolysis. Glycolysis inhibition can alleviate cardiac fibroblast activation and cardiac fibrosis after myocardial infarction.

Persistent inflammation disrupts functional recovery after spinal cord injury (SCI). Peroxisome proliferator-activated receptor gamma (PPAR-γ) activation promotes functional recovery in SCI rats by inhibiting inflammatory cascades and increasing neuronal survival. We sought to clarify the relationship between PPAR-γ activation and NACHT, LRR and PYD domain-containing protein 3 (NLRP3) inflammasome suppression, and the role of NF-κB in activating the NLRP3 inflammasome in neurons. In SCI rats, we found that rosiglitazone (PPAR-γ agonist) inhibited the expression of caspase-1. In in vitro neurons, G3335 (PPAR-γ antagonist) reversed the rosiglitazone-induced inhibition of caspase-1, interleukin 1 (IL-1β), and interleukin 6 (IL-6). Rosiglitazone inhibited the expression of NLRP3, caspase-1, IL-1β, and IL-6. However, the activator of NLRP3 could counteract this inhibition induced by PPAR-γ activation. NF-κB did not participate in the process of rosiglitazone-induced inhibition of NLRP3. Consistent with our in vitro results, we verified that locomotor recovery of SCI rats in vivo was regulated via PPAR-γ, NLRP3, and NF-κB. These results suggest that PPAR-γ activation exerts an anti-inflammatory effect by suppressing the NLRP3 inflammasome—but not NF-κB—in neurons and that PPAR-γ activation is a promising therapeutic target for SCI.

Ketogenic diet (KD) is popular in diabetic patients but its cardiac safety and efficiency on the heart are unknown. The aim of the present study is to determine the effects and the underlined mechanisms of KD on cardiac function in diabetic cardiomyopathy (DCM). We used db/db mice to model DCM, and different diets (regular or KD) were used. Cardiac function and interstitial fibrosis were determined. T‐regulatory cell (Treg) number and functions were evaluated. The effects of ketone body (KB) on fatty acid (FA) and glucose metabolism, mitochondria‐associated endoplasmic reticulum membranes (MAMs), and mitochondrial respiration were assessed. The mechanisms via which KB regulated MAMs and Tregs were addressed. KD improved metabolic indices in db/db mice. However, KD impaired cardiac diastolic function and exacerbated ventricular fibrosis. Proportions of circulatory CD4⁺CD25⁺Foxp3⁺ cells in whole blood cells and serum levels of IL‐4 and IL‐10 were reduced in mice fed with KD. KB suppressed the differentiation to Tregs from naive CD4⁺ T cells. Cultured medium from KB‐treated Tregs synergically activated cardiac fibroblasts. Meanwhile, KB inhibited Treg proliferation and productions of IL‐4 and IL‐10. Treg MAMs, mitochondrial respiration and respiratory complexes, and FA synthesis and oxidation were all suppressed by KB while glycolytic levels were increased. L‐carnitine reversed Treg proliferation and function inhibited by KB. Proportions of ST2L⁺ cells in Tregs were reduced by KB, as well as the production of ST2L ligand, IL‐33. Reinforcement expressions of ST2L in Tregs counteracted the reductions in MAMs, mitochondrial respiration, and Treg proliferations and productions of Treg cytokines IL‐4 and IL‐10. Therefore, despite the improvement of metabolic indices, KD impaired Treg expansion and function and promoted cardiac fibroblast activation and interstitial fibrosis. This could be mainly mediated by the suppression of MAMs and fatty acid metabolism inhibition via blunting IL‐33/ST2L signaling.