PHDs/CPT1B/VDAC1 axis regulates long-chain fatty acid oxidation in cardiomyocytes

KN-93 promotes HDAC4 nucleus translocation to promote fatty acid oxidation in myocardial infarction

Myocardial infarction (MI) is a potentially fatal disease that causes a significant number of deaths worldwide. The strategy of increasing fatty acid oxidation in myocytes is considered a therapeutic avenue to accelerate metabolism to meet energy demands. We conducted the study aiming to investigate the effect of KN-93, which induces histone deacetylase (HDAC)4 shuttling to the nucleus, on fatty acid oxidation and the expression of related genes. A mouse model of myocardial infarction was induced by isoprenaline administration. Heart damage was assessed by the detection of cardiac injury markers. The level of fatty acid oxidation level was evaluated by testing the expression of related genes. Both immunofluorescence and immunoblotting in the cytosol or nucleus were utilized to observe the distribution of HDAC4. The interaction between HDAC4 and specificity protein (SP)1 was confirmed by co-immunoprecipitation. The acetylation level of SP1 was tested after KN-93 treatment and HDAC4 inhibitor. Oxygen consumption rate and immunoblotting experiments were used to determine whether the effect of KN-93 on increasing fatty acid oxidation is through HDAC4 and SP1. Administration of KN-93 significantly reduced cardiac injury in myocardial infarction and promoted fatty acid oxidation both in vitro and in vivo. KN-93 was shown to mediate nuclear translocation of HDAC4. HDAC4 was found to interact with SP1 and reduce SP1 acetylation. HDAC4 or SP1 inhibitors attenuated the effect of KN-93 on fatty acid oxidation. In conclusion, KN-93 promotes HDAC4 translocation to the nucleus, thereby potentially enhancing fatty acid oxidation by SP1.

Regulation of Na+-K+-ATPase leads to disturbances of isoproterenol-induced cardiac dysfunction via interference of Ca2+-dependent cardiac metabolism

Reductions in Na+-K+-ATPase (NKA) activity and expression are often observed in the progress of various reason-induced heart failure (HF). However, NKA α1 mutation or knockdown cannot cause spontaneous heart disease. Whether the abnormal NKA α1 directly contributes to HF pathogenesis remains unknown. Here, we challenge NKA α1+/- mice with isoproterenol to evaluate the role of NKA α1 haploinsufficiency in isoproterenol (ISO)-induced cardiac dysfunction. Genetic knockdown of NKA α1 accelerated ISO-induced cardiac cell hypertrophy, heart fibrosis, and dysfunction. Further studies revealed decreased Krebs cycle, fatty acid oxidation, and mitochondrial OXPHOS in the hearts of NKA α1+/- mice challenged with ISO. In ISO-treated conditions, inhibition of NKA elevated cytosolic Na+, further reduced mitochondrial Ca2+ via mNCE, and then finally down-regulated cardiac cell energy metabolism. In addition, a supplement of DRm217 alleviated ISO-induced heart dysfunction, mitigated cardiac remodeling, and improved cytosolic Na+ and Ca2+ elevation and mitochondrial Ca2+ depression in the NKA α1+/- mouse model. The findings suggest that targeting NKA and mitochondria Ca2+ could be a promising strategy in the treatment of heart disease.

Postcontraction [acetylcarnitine] reflects interindividual variation in skeletal muscle ATP production patterns in vivo

In addition to its role in substrate selection (carbohydrate vs. fat) for oxidative metabolism in muscle, acetylcarnitine production may be an important modulator of the energetic pathway by which ATP is produced. A combination of noninvasive magnetic resonance spectroscopy measures of cytosolic acetylcarnitine and ATP production pathways was used to investigate the link between [acetylcarnitine] and energy production in vivo. Intracellular metabolites were measured in the vastus lateralis muscle of eight males (mean: 28.4 yr, range: 25-35) during 8 min of incremental, dynamic contractions (0.5 Hz, 2-min stages at 6%, 9%, 12%, and 15% maximal torque) that increased [acetylcarnitine] approximately fivefold from resting levels. ATP production via oxidative phosphorylation, glycolysis, and the creatine kinase reaction was calculated based on phosphorus metabolites and pH. Spearman rank correlations indicated that postcontraction [acetylcarnitine] was positively associated with both absolute (mM) and relative (% total ATP) glycolytic ATP production (rs = 0.95, P = 0.001; rs = 0.93, P = 0.002), and negatively associated with relative (rs = -0.81, P = 0.02) but not absolute (rs = -0.14, P = 0.75) oxidative ATP production. Thus, acetylcarnitine accumulated more when there was a greater reliance on "nonoxidative" glycolysis and a relatively lower contribution from oxidative phosphorylation, reflecting the fate of pyruvate in working skeletal muscle. Furthermore, these data indicate striking interindividual variation in responses to the energy demand of submaximal contractions. Overall, the results of this preliminary study provide novel evidence of the coupling in vivo between ATP production pathways and the carnitine system.NEW & NOTEWORTHY Production of acetylcarnitine from acetyl-CoA and free carnitine may be important for energy pathway regulation in contracting skeletal muscle. Noninvasive magnetic resonance spectroscopy was used to investigate the link between acetylcarnitine and energy production in the vastus lateralis muscle during dynamic contractions (n = 8 individuals). A positive correlation between acetylcarnitine accumulation and "nonoxidative" glycolysis and an inverse relationship with oxidative phosphorylation, provides novel evidence of the coupling between ATP production and the carnitine system in vivo.

Voltage-dependent anion channel 1 (VDAC1) overexpression alleviates cardiac fibroblast activation in cardiac fibrosis via regulating fatty acid metabolism

Cardiac fibrosis is characterized by the excessive deposition of extracellular matrix in the myocardium with cardiac fibroblast activation, leading to chronic cardiac remodeling and dysfunction. However, little is known about metabolic alterations in fibroblasts during cardiac fibrosis, and there is a lack of pharmaceutical treatments that target metabolic dysregulation. Here, we provided evidence that fatty acid β-oxidation (FAO) dysregulation contributes to fibroblast activation and cardiac fibrosis. With transcriptome, metabolome, and functional assays, we demonstrated that FAO was downregulated during fibroblast activation and cardiac fibrosis, and that perturbation of FAO reversely affected the fibroblast-to-myofibroblast transition. The decrease in FAO may be attributed to reduced long-chain fatty acid (LCFA) uptake. Voltage-dependent anion channel 1 (VDAC1), the main gatekeeper of the outer mitochondrial membrane (OMM), serves as the transporter of LCFA into the mitochondria for further utilization and has been shown to be decreased in myofibroblasts. In vitro, the addition of exogenous VDAC1 was shown to ameliorate cardiac fibroblast activation initiated by transforming growth factor beta 1 (TGF-β1) stimuli, and silencing of VDAC1 displayed the opposite effect. A mechanistic study revealed that VDAC1 exerts a protective effect by regulating LCFA uptake into the mitochondria, which is impaired by an inhibitor of carnitine palmitoyltransferase 1A. In vivo, AAV9-mediated overexpression of VDAC1 in myofibroblasts significantly alleviated transverse aortic constriction (TAC)-induced cardiac fibrosis and rescued cardiac function in mice. Finally, we treated mice with the VDAC1-derived R-Tf-D-LP4 peptide, and the results showed that R-Tf-D-LP4 prevented TAC-induced cardiac fibrosis and dysfunction in mice. In conclusion, this study provides evidence that VDAC1 maintains FAO metabolism in cardiac fibroblasts to repress fibroblast activation and cardiac fibrosis and suggests that the VDAC1 peptide is a promising drug for rescuing fibroblast metabolism and repressing cardiac fibrosis.

The Physiological and Pathological Role of Acyl-CoA Oxidation

Fatty acid metabolism, including β-oxidation (βOX), plays an important role in human physiology and pathology. βOX is an essential process in the energy metabolism of most human cells. Moreover, βOX is also the source of acetyl-CoA, the substrate for (a) ketone bodies synthesis, (b) cholesterol synthesis, (c) phase II detoxication, (d) protein acetylation, and (d) the synthesis of many other compounds, including N-acetylglutamate-an important regulator of urea synthesis. This review describes the current knowledge on the importance of the mitochondrial and peroxisomal βOX in various organs, including the liver, heart, kidney, lung, gastrointestinal tract, peripheral white blood cells, and other cells. In addition, the diseases associated with a disturbance of fatty acid oxidation (FAO) in the liver, heart, kidney, lung, alimentary tract, and other organs or cells are presented. Special attention was paid to abnormalities of FAO in cancer cells and the diseases caused by mutations in gene-encoding enzymes involved in FAO. Finally, issues related to α- and ω- fatty acid oxidation are discussed.

CRAT links cholesterol metabolism to innate immune responses in the heart

Chronic inflammation is associated with increased risk and poor prognosis of heart failure; however, the precise mechanism that provokes sustained inflammation in the failing heart remains elusive. Here we report that depletion of carnitine acetyltransferase (CRAT) promotes cholesterol catabolism through bile acid synthesis pathway in cardiomyocytes. Intracellular accumulation of bile acid or intermediate, 7α-hydroxyl-3-oxo-4-cholestenoic acid, induces mitochondrial DNA stress and triggers cGAS-STING-dependent type I interferon responses. Furthermore, type I interferon responses elicited by CRAT deficiency substantially increase AIM2 expression and AIM2-dependent inflammasome activation. Genetic deletion of cardiomyocyte CRAT in mice of both sexes results in myocardial inflammation and dilated cardiomyopathy, which can be reversed by combined depletion of caspase-1, cGAS or AIM2. Collectively, we identify a mechanism by which cardiac energy metabolism, cholesterol homeostasis and cardiomyocyte-intrinsic innate immune responses are interconnected via a CRAT-mediated bile acid synthesis pathway, which contributes to chronic myocardial inflammation and heart failure progression.

Insights into SGLT2 inhibitor treatment of diabetic cardiomyopathy: focus on the mechanisms

Among the complications of diabetes, cardiovascular events and cardiac insufficiency are considered two of the most important causes of death. Experimental and clinical evidence supports the effectiveness of SGLT2i for improving cardiac dysfunction. SGLT2i treatment benefits metabolism, microcirculation, mitochondrial function, fibrosis, oxidative stress, endoplasmic reticulum stress, programmed cell death, autophagy, and the intestinal flora, which are involved in diabetic cardiomyopathy. This review summarizes the current knowledge of the mechanisms of SGLT2i for the treatment of diabetic cardiomyopathy.

Identification of fatty acid metabolism-based molecular subtypes and prognostic signature to predict immune landscape and guide clinical drug treatment in renal clear cell carcinoma

Three subtypes of samples were generated based on genes involved in fatty acid metabolism in The Cancer Genome Atlas (TCGA)-RCC patients using a non-negative matrix factorization (NMF) algorithm. 32 co-expressed modules were identified using WCGNA. We constructed a four-gene signature in our training set using least absolute shrinkage selection operator regression analysis and verified it in our testing and overall sets. A relevant study analysis in clinical trials was conducted, which showed the model had good stability and potential application value for predicting outcomes. We analyzed the immune microenvironment using MCPcounter, CIBERSORT, quanTIseq, TIMER and ESTIMATE algorithms, and the result indicated risk was positively related to T cells, B-lineage, and fibroblasts and negatively correlated with monocytic lineage, myeloid dendritic cells, neutrophils, and endothelial cells, and CPT1B was positively related to T cells, CD8 + T cells, Cytotoxic lymphocytes and NK cells, and negatively correlated with myeloid dendritic cells, fibroblasts, endothelial cells. Tumor mutation burden was positively related to risk score and the expression of CPT1B using the R packages corrplot, circlize. Through the R package pRRophetic, drug sensitivity tests showed that the low-risk score group would benefit more from sunitinib and less from pazopanib, sorafenib, temsirolimus, gemcitabine and doxorubicin than the high-risk score group. We performed the relevant basic assay validation for CPT1B, and the proliferation ability of RCC cells was inhibited after the knockdown of protein expression of CPT1B. In conclusion, we established a four-gene model that can predict outcomes of RCC with potential applications in diagnosis and treatment.

TMBIM6 prevents VDAC1 multimerization and improves mitochondrial quality control to reduce sepsis-related myocardial injury

BACKGROUND

The regulatory mechanisms involved in mitochondrial quality control (MQC) dysfunction during septic cardiomyopathy (SCM) remain incompletely characterized. Transmembrane BAX inhibitor motif containing 6 (TMBIM6) is an endoplasmic reticulum protein with Ca²⁺ leak activity that modulates cellular responses to various cellular stressors.

METHODS

In this study, we evaluated the role of TMBIM6 in SCM using cardiomyocyte-specific TMBIM6 knockout (TMBIM6^CKO) and TMBIM6 transgenic (TMBIM6^TG) mice.

RESULTS

Myocardial TMBIM6 transcription and expression were significantly downregulated in wild-type mice upon LPS exposure, along with characteristic alterations in myocardial systolic/diastolic function, cardiac inflammation, and cardiomyocyte death. Notably, these alterations were further exacerbated in LPS-treated TMBIM6^CKO mice, and largely absent in TMBIM6^TG mice. In LPS-treated primary cardiomyocytes, TMBIM6 deficiency further impaired mitochondrial respiration and ATP production, while defective MQC was suggested by enhanced mitochondrial fission, impaired mitophagy, and disrupted mitochondrial biogenesis. Structural protein analysis, Co-IP, mutant TMBIM6 plasmid transfection, and molecular docking assays subsequently indicated that TMBIM6 exerts cardioprotection against LPS-induced sepsis by interacting with and preventing the oligomerization of voltage-dependent anion channel-1 (VDAC1), the major route of mitochondrial Ca²⁺ uptake.

CONCLUSION

We conclude that the TMBIM6-VDAC1 interaction prevents VDAC1 oligomerization and thus sustains mitochondrial Ca²⁺ homeostasis as well as MQC, contributing to improved myocardial function in SCM.

Effect of ketogenic diet on exercise tolerance and transcriptome of gastrocnemius in mice

Ketogenic diet (KD) has been proven to be an optional avenue in weight control. However, the impacts of KD on muscle strength and exercise endurance remain unclear. In this study, mice were randomly allocated to normal diet and KD groups to assess their exercise tolerance and transcriptomic changes of the gastrocnemius. KD suppressed body-weight and glucose levels and augmented blood ketone levels of mice. The total cholesterol, free fatty acids, and β-hydroxybutyric acid levels were higher and triglycerides and aspartate aminotransferase levels were lower in KD group. There was no notable difference in running distance/time and weight-bearing swimming time between the two groups. Furthermore, KD alleviated the protein levels of PGC-1α, p62, TnI FS, p-AMPKα, and p-Smad3, while advancing the LC3 II and TnI SS protein levels in the gastrocnemius tissues. RNA-sequencing found that 387 differentially expressed genes were filtered, and Cpt1b, Acadl, Eci2, Mlycd, Pdk4, Ptprc, C1qa, Emr1, Fcgr3, and Ctss were considered to be the hub genes. Our findings suggest that KD effectively reduced body weight but did not affect skeletal muscle strength and exercise endurance via AMPK/PGC-1α, Smad3, and p62/LC3 signaling pathways and these hub genes could be potential targets for muscle function in KD-treated mice.

L-carnitine attenuated hyperuricemia-associated left ventricular remodeling through ameliorating cardiomyocytic lipid deposition

Hyperuricemia (HUA) is associated with left ventricular remodeling (LVR) and thereby causes the initiation and development of a large number of cardiovascular diseases. LVR is typically accompanied by cardiomyocyte energy metabolic disorder. The energy supply of cardiomyocytes is provided by glucose and fatty acid (FA) metabolism. Currently, the effect of HUA on cardiomyocytic FA metabolism is unclear. In this study, we demonstrate that UA-induced cardiomyocyte injury is associated with cytoplasmic lipid deposition, which can be ameliorated by the FA metabolism-promoting drug L-carnitine (LC). UA suppresses carnitine palmitoyl transferase 1B (CPT1B), thereby inhibiting FA transport into the mitochondrial inner matrix for elimination. LC intervention can ameliorate HUA-associated left ventricular anterior wall thickening in mice. This study showed that FA transport dysfunction plays is a critical mechanism in both cardiomyocytic injury and HUA-associated LVR and promoting cytoplasmic FA transportation through pharmacological treatment by LC is a valid strategy to attenuate HUA-associated LVR.

Cardiomyocyte Cell-Cycle Regulation in Neonatal Large Mammals: Single Nucleus RNA-Sequencing Data Analysis via an Artificial-Intelligence–Based Pipeline

Adult mammalian cardiomyocytes have very limited capacity to proliferate and repair the myocardial infarction. However, when apical resection (AR) was performed in pig hearts on postnatal day (P) 1 (AR_P1) and acute myocardial infarction (MI) was induced on P28 (MI_P28), the animals recovered with no evidence of myocardial scarring or decline in contractile performance. Furthermore, the repair process appeared to be driven by cardiomyocyte proliferation, but the regulatory molecules that govern the AR_P1-induced enhancement of myocardial recovery remain unclear. Single-nucleus RNA sequencing (snRNA-seq) data collected from fetal pig hearts and the hearts of pigs that underwent AR_P1, MI_P28, both AR_P1 and MI, or neither myocardial injury were evaluated via autoencoder, cluster analysis, sparse learning, and semisupervised learning. Ten clusters of cardiomyocytes (CM1–CM10) were identified across all experimental groups and time points. CM1 was only observed in AR_P1 hearts on P28 and was enriched for the expression of T-box transcription factors 5 and 20 (TBX5 and TBX20, respectively), Erb-B2 receptor tyrosine kinase 4 (ERBB4), and G Protein-Coupled Receptor Kinase 5 (GRK5), as well as genes associated with the proliferation and growth of cardiac muscle. CM1 cardiomyocytes also highly expressed genes for glycolysis while lowly expressed genes for adrenergic signaling, which suggested that CM1 were immature cardiomyocytes. Thus, we have identified a cluster of cardiomyocytes, CM1, in neonatal pig hearts that appeared to be generated in response to AR injury on P1 and may have been primed for activation of CM cell-cycle activation and proliferation by the upregulation of TBX5, TBX20, ERBB4, and GRK5.

Evaluation of long-chain fatty acid respiration in neonatal mouse cardiomyocytes using SeaHorse instrument

Metabolic switches play a critical role in the pathophysiology of cardiac diseases, including heart failure. Here, we describe an assay for long-chain fatty acid oxidation in neonatal mouse cardiomyocytes by using a SeaHorse Flux Analyzer (Agilent). This protocol is a simplified but robust adaptation of the standard protocol that enables metabolic measurements in cells isolated from transgenic mouse models, which can be timesaving and informative. Cell isolation and culture represent a critical point that may require bench optimization.

For complete details on the use and execution of this protocol, please refer to Angelini et al. (2021).

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Isolation and culture of neonatal mouse cardiomyocytes

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Measurement of long-chain fatty acid oxidation using SeaHorse Flux Analyzer

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Guidance on quantification of the generated SeaHorse dataset

Publisher's note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.