Reduced Fatty Acid Use from CD36 Deficiency Deteriorates Streptozotocin-Induced Diabetic Cardiomyopathy in Mice

CD36 knockdown attenuates pressure overload-induced cardiac injury by preventing lipotoxicity and improving myocardial energy metabolism

Introduction: The heart predominantly derives its energy from fatty acid (FA) oxidation. However, the uncoupling of lipid uptake and FA oxidation can result in abnormal cardiac lipid accumulation and lipotoxicity, particularly in the context of heart failure. CD36 is a critical mediator of FA uptake in cardiac tissue. Studies have shown that genetic deletion of CD36 can prevent the onset of cardiac hypertrophy and dysfunction in murine models of obesity and diabetes. Nevertheless, the precise role of CD36 knockdown or knockout in the development and progression of cardiac dysfunction under conditions of pressure overload remains unclear. Objective: This study aims to investigate the feasibility of CD36 partially knockdown in the prevention of cardiac lipotoxicity and functional impairment in pressure overload heart. Methods: Cardiac-specific CD36 totally knockout (CKO) and partially knockdown (CKD) mice were induced by genetics deletion and AAV-9 CD36 shRNA injection, respectively. Both CD36 CKO and CKD mice were subjected to transverse aortic constriction (TAC) operation to induce cardiac pressure overload. Cardiac function was measured by echocardiography. Cardiac lipid accumulation, FA oxidation and metabolic sate were also examined. Results: TAC operation induced significant cardiac dysfunction and pathological cardiac remodeling, accompanied by aberrant intra-myocardial lipid deposition and impaired FAO capacity. CD36 CKO attenuated aberrant lipid accumulation in the failing heart, while aggravated TAC-induced cardiac energy deprivation and oxidative stress. In contrast, CD36 CKD ameliorated TAC-induced lipid accumulation and excessive oxidative stress in the mice heart, accompanied by improved mitochondrial respiration function. Moreover, CD36 CKD induced a robust increase in glycolytic flux into the TCA cycle, which led to preserved ATP generation. As a result, CD36 CKD prevented the development of pressure overload-induced cardiac hypertrophy and dysfunction. Conclusion: In this study, we reported that CD36 CKD, not CD36 CKO, was able to protect against cardiac functional impairment in the pressure-overload heart. Manipulating CD36 was a feasible strategy to achieve an optimal point which maintain cardiac energy supply while avoiding lipotoxicity.

Mitochondrial energy metabolism in diabetic cardiomyopathy: Physiological adaption, pathogenesis, and therapeutic targets

Diabetic cardiomyopathy is defined as abnormal structure and function of the heart in the setting of diabetes, which could eventually develop heart failure and leads to the death of the patients. Although blood glucose control and medications to heart failure show beneficial effects on this disease, there is currently no specific treatment for diabetic cardiomyopathy. Over the past few decades, the pathophysiology of diabetic cardiomyopathy has been extensively studied, and an increasing number of studies pinpoint that impaired mitochondrial energy metabolism is a key mediator as well as a therapeutic target. In this review, we summarize the latest research in the field of diabetic cardiomyopathy, focusing on mitochondrial damage and adaptation, altered energy substrates, and potential therapeutic targets. A better understanding of the mitochondrial energy metabolism in diabetic cardiomyopathy may help to gain more mechanistic insights and generate more precise mitochondria-oriented therapies to treat this disease.

Cardiac Metabolism and Contractile Function in Mice with Reduced Trans-Endothelial Fatty Acid Transport

The heart is a metabolic omnivore that combusts a considerable amount of energy substrates, mainly long-chain fatty acids (FAs) and others such as glucose, lactate, ketone bodies, and amino acids. There is emerging evidence that muscle-type continuous capillaries comprise the rate-limiting barrier that regulates FA uptake into cardiomyocytes. The transport of FAs across the capillary endothelium is composed of three major steps-the lipolysis of triglyceride on the luminal side of the endothelium, FA uptake by the plasma membrane, and intracellular FA transport by cytosolic proteins. In the heart, impaired trans-endothelial FA (TEFA) transport causes reduced FA uptake, with a compensatory increase in glucose use. In most cases, mice with reduced FA uptake exhibit preserved cardiac function under unstressed conditions. When the workload is increased, however, the total energy supply relative to its demand (estimated with pool size in the tricarboxylic acid (TCA) cycle) is significantly diminished, resulting in contractile dysfunction. The supplementation of alternative fuels, such as medium-chain FAs and ketone bodies, at least partially restores contractile dysfunction, indicating that energy insufficiency due to reduced FA supply is the predominant cause of cardiac dysfunction. Based on recent in vivo findings, this review provides the following information related to TEFA transport: (1) the mechanisms of FA uptake by the heart, including TEFA transport; (2) the molecular mechanisms underlying the induction of genes associated with TEFA transport; (3) in vivo cardiac metabolism and contractile function in mice with reduced TEFA transport under unstressed conditions; and (4) in vivo contractile dysfunction in mice with reduced TEFA transport under diseased conditions, including an increased afterload and streptozotocin-induced diabetes.