Long-term testosterone deficiency modifies myofilament and calcium-handling proteins and promotes diastolic dysfunction in the aging mouse heart

The impact of long-term gonadectomy (GDX) on cardiac contractile function was explored in the setting of aging. Male mice were subjected to bilateral GDX or sham operation (4 wk) and investigated at 16- 18 mo of age. Ventricular myocytes were field stimulated (2 Hz, 37 degrees C). Peak Ca2+ transients (fura 2) and contractions were similar in GDX and sham-operated mice, although Ca2+ transients (50% decay time: 45.2 +/- 2.3 vs. 55.6 +/- 3.1 ms, P < 0.05) and contractions (time constant of relaxation: 39.1 +/- 3.2 vs. 69.5 +/- 9.3 ms, P < 0.05) were prolonged in GDX mice. Action potential duration was increased in myocytes from GDX mice, but this did not account for prolonged responses, as Ca2+ transient decay was slow even when cells from GDX mice were voltage clamped with simulated "sham" action potentials. Western blots of proteins involved in Ca2+ sequestration and efflux showed that Na+/Ca2+ exchanger and sarco(endo) plasmic reticulum Ca2+-ATPase type 2 protein levels were unaffected, whereas phospholamban was dramatically higher in ventricles from aging GDX mice (0.24 +/- 0.02 vs. 0.86 +/- 0.13, P < 0.05). Myofilament Ca2+ sensitivity at physiological Ca2+ was similar, but phosphorylation of essential myosin light chain 1 was reduced by approximate to 50% in ventricles from aging GDX mice. M- mode echocardiography showed no change in systolic function (e. g., ejection fraction). Critically, pulse-wave Doppler echocardiography showed that GDX slowed isovolumic relaxation time (12.9 +/- 0.9 vs. 16.9 +/- 1.0 ms, P < 0.05), indicative of diastolic dysfunction. Thus, dysregulation of intracellular Ca2+ and myofilament dysfunction contribute to deficits in contraction in hearts from testosterone- deficient aging mice. This suggests that low testosterone helps promote diastolic dysfunction in the aging heart. NEW & NOTEWORTHY The influence of long-term gonadectomy on contractile function was examined in aging male hearts. Gonadectomy slowed the decay of Ca2+ transients and contractions in ventricular myocytes and slowed isovolumic relaxation time, demonstrating diastolic dysfunction. Underlying mechanisms included Ca2+ dysregulation, elevated phospholamban protein levels, and hypophos-phorylation of a myofilament protein, essential myosin light chain. Testosterone deficiency led to intracellular Ca2+ dysregulation and myofilament dysfunction, which may facilitate diastolic dysfunction in the setting of aging.