Abstract Body (Do not enter title and authors here): Introduction: The failing myocardium displays disrupted intracellular signaling, leading to pathological remodeling. Heart failure includes two major subtypes: HFrEF and HFpEF, characterized by distinct molecular mechanisms. Mitogen-activated protein kinase kinase 6 (MAP2K6), a key activating p38 MAPK, regulates cellular stress responses and metabolic adaptation, which are contribute HFpEF pathogenesis. We found MAP2K6 is upregulated in HFpEF and downregulated in HFrEF; therefore, we aimed to investigate the functional consequences of MAP2K6 upregulation in HFpEF, which remain poorly understood.
Hypothesis: MAP2K6 upregulation in HFpEF promotes pathological remodeling by impairing the cardiomyocyte stress response.
Methods/Results: Transcriptomic analysis of human myocardial tissues showed MAP2K6 was upregulated in HFpEF and downregulated in HFrEF. Single-cell RNA sequencing localized this differential expression to cardiomyocytes. Western blot analysis confirmed these patterns in human myocardium. To assess the functional effects of MAP2K6 upregulation, we used adenoviral-mediated overexpression of MAP2K6 (MAP2K6 OE) in cardiomyocytes. Under basal conditions, MAP2K6 overexpression did not induce notable changes in LDH, nor hypertrophic markers (ANP, BNP, and MYH7). Moreover, no increase in p38 phosphorylation was observed. However, following endothelin-1 (ET-1) stimulation, MAP2K6 OE cells exhibited a markedly amplified response, characterized by elevated LDH release (change in LDH with/without ET-1: 113.9 AU in controls (p =0.75) vs. 475.8 AU in MAP2K6 OE (p=0.04)), upregulation of hypertrophic markers, and enhanced p38 activation, indicating an increased sensitivity to pro-hypertrophic stress. Metabolically, MAP2K6 OE increased both mitochondrial respiration (OCR) and glycolysis (ECAR) under basal conditions. However, while ET-1 stimulation enhanced OCR and ECAR in control cells, MAP2K6 OE cardiomyocytes failed to show further significant increases in OCR (change in OCR with/without ET-1: 174.5 ± 18.7 pmol/min in controls (p< 0.001) vs. 59.2 ± 25.0 pmol/min in MAP2K6-OE (p=0.12)) and ECAR, indicating impaired metabolic reserve and flexibility.
Conclusion: MAP2K6 is differentially upregulated in HFpEF, which could sensitize cardiomyocytes to hypertrophic stress while blunting metabolic adaptability, supporting its role in HFpEF pathophysiology and its potential as a therapeutic target.