Mechanical loading reveals an intrinsic cardiomyocyte stiffness contribution to diastolic dysfunction in murine cardiometabolic disease
Authors: Janssens Johannes V. , Raaijmakers Antonia J.A. , Koutsifeli Parisa , Weeks Kate L. , Bell James R. , Van Eyk Jennifer E. , Curl Claire L. , Mellor Kimberley M. , Delbridge Lea M.D. 
Published: February 2024

ABSTRACTCardiometabolic syndromes including diabetes and obesity are associated with occurrence of heart failure with diastolic dysfunction. There are no specific treatments for diastolic dysfunction, and therapies to manage symptoms have limited efficacy. Understanding of the cardiomyocyte origins of diastolic dysfunction is an important priority to identify new therapeutics. The investigative goal was to experimentally definein vitrostiffness properties of isolated cardiomyocytes derived from rodent hearts exhibiting diastolic dysfunctionin vivoin response to dietary induction of cardiometabolic disease.Male mice fed a high fat/sugar diet (HFSD vs control) exhibited diastolic dysfunction (echo E/e’ doppler ratio). Intact paced cardiomyocytes were functionally investigated in three conditions: non-loaded, loaded and stretched.Mean stiffness of HFSD cardiomyocytes was 70% higher than control. E/e’ for the origin hearts was elevated by 35%. A significant relationship was identified betweenin vitrocardiomyocyte stiffness andin vivodysfunction severity. With conversion from non-loaded to loaded condition, the decrement in maximal sarcomere lengthening rate was more accentuated in HFSD cardiomyocytes (vs control). With stretch, the Ca2+transient decay time course was prolonged. With increased pacing, cardiomyocyte stiffness was elevated, yet diastolic Ca2+elevation was attenuated. Our findings show unequivocally that cardiomyocyte mechanical dysfunction cannot be detected by analysis of non-loaded shortening.Collectively, these findings demonstrate that a component of cardiac diastolic dysfunction in cardiometabolic disease is derived from cardiomyocyte stiffness. Differential responses to load, stretch and pacing suggest that a previously undescribed alteration in myofilament-Ca2+interaction contributes to intrinsic cardiomyocyte stiffness in cardiometabolic disease.KEY POINTSUnderstanding cardiomyocyte stiffness components is an important priority for identifying new therapeutics for diastolic dysfunction, a key feature of cardiometabolic disease.In this study cardiac function was measuredin vivo(echocardiography) for mice fed a high-fat/sugar diet (HFSD, ≥25weeks). Performance of intact isolated cardiomyocytes derived from the same hearts was measured during pacing under non-loaded, loaded and stretched conditionsin vitro.Calibrated cardiomyocyte stretches demonstrated that stiffness (stress/strain) was elevated in HFSD cardiomyocytesin vitroand correlated with diastolic dysfunction (E/e’)in vivo. HFSD cardiomyocyte Ca2+transient decay was prolonged in response to stretch. Stiffness was accentuated with pacing increase while the elevation in diastolic Ca2+was attenuated.Data show unequivocally that cardiomyocyte mechanical dysfunction cannot be detected by analysis of non-loaded shortening.These findings suggest that stretch-dependent augmentation of the myofilament-Ca2+response during diastole partially underlies elevated cardiomyocyte stiffness and diastolic dysfunction of hearts of animals with cardiometabolic disease.Abstract FigureAbstract Figure LegendUnderstanding cardiomyocyte stiffness components is an important priority for identifying new therapeutics for diastolic dysfunction, a key feature of cardiometabolic disease. In this study cardiac function was measuredin vivo(echocardiography) for mice fed a high-fat/sugar diet (HFSD, ≥25weeks). Performance of intact isolated cardiomyocytes derived from the same hearts was measured during pacing under non-loaded, loaded and stretched conditionsin vitro.Calibrated cardiomyocyte stretches demonstrated that stiffness was elevated in HFSD cardiomyocytesin vitroand correlated with diastolic dysfunction (E/e’)in vivo. These findings show that stiff hearts are characterized by stiff cardiomyocytes in metabolic disease.