Effects of attenuated leptin signaling pathways on cardiac function under high-altitude hypoxia
Background: High-altitude hypoxia significantly impacts cardiovascular function, but the effects of adipose/metabolic factors on cardiovascular regulation remain unclear. Thus, a deeper understanding of adipose/metabolic factors' role in cardiovascular function changes is needed. Methods: We assessed lung ventilation function, cardiovascular function, electrocardiogram, plasma CK-MB, sPecam-1, and 11 plasma adipose/metabolic factors in expeditioners at Antarctic Kunlun Station (4087m). To investigate adipose/metabolic factors' effects and mechanisms on cardiac function, we constructed a rat model exposed to simulated hypobaric hypoxia (5000 m) with the same oxygen concentration as Kunlun Station. Echocardiography, ELISA, histology, and gene and protein expression studies were employed to examine cardiac function changes, pathological alterations, and leptin's role in cardiac pathology under acute and chronic hypoxic exposure.  Results: The Antarctic ice plateau environment significantly altered lung ventilation function, weakened cardiac pumping and contractile function, increased systematic vascular resistance (SVR), induced adaptive changes in cardiac conduction, significantly increased plasma CK-MB and Pecam-1, and significantly reduced plasma leptin, resistin, insulin, and lipocalin-2 levels. Decreased leptin was significantly correlated to cardiopulmonary function. Rats chronically exposed to simulated hypobaric hypoxia at 5000m exhibited pulmonary arterial hypertension (PAH), right ventricular hypertrophy (RVH), impaired left ventricular systolic and diastolic function, and significant deteriorated left ventricular global longitudinal strain (GLS), lateral and radial strains of the myocardium, with increased plasma CK-MB and sPecam-1 in hypoxic rats. Protein levels of leptin/ob-Rb, JAK2/STAT3, PI3K/AKT/GSK3ß, and ERK/JNK were decreased in biventricular myocardial tissues of chronic hypoxia-exposed rats, accompanied by increased myocytes hypertrophy, fibrosis, lipid deposition, cell apoptosis, and mitochondrial dysfunction, and decreased metabolic gene levels. Left ventricular transcriptome analysis revealed that decreased myocardial leptin in hypoxic rats regulated cardiac pathology via down-regulated genes related to circadian rhythm, sodium/potassium ion transport, and cell skeleton. Conclusion: Our findings suggest that leptin is a crucial metabolic factor in regulating cardiac pathological changes and cardiac contractile and diastolic function under high altitudes. These regulatory pathways may involve leptin's classical signaling pathways and genes related to circadian rhythm, sodium/potassium ion transport, and cell skeleton in the heart. Overall design: 8 week-old male SD rats exposed to high-altitude hypobaric hypoxia for 14 days with control group exposed to normoxia