Chronic pressure overload cardiac hypertrophy and failure in guinea pigs: II. Cytoskeletal remodeling.

The cytoskeleton is a major regulator of cell shape. To explore potential mechanisms for maladaptation of cardiac myocyte shape in pressure overload-induced congestive heart failure, the abundance and organization of major intra- and extra-myofibrillar cytoskeleton of cardiac myocytes were examined with western blotting and confocal microscopy in guinea pigs with chronic aortic stenosis. It was found that: (1) the amount and distribution of alpha-actinin and myomesin remained unchanged at both the compensated hypertrophy and the congestive heart failure stages; (2) loss of titin was associated with myocyte lengthening in heart failure; (3) desmin protein and filaments in LV myocytes increased progressively with mechanical overload cardiac hypertrophy and subsequent heart failure; (4) a newly developed and validated quantitative confocal microscopic approach disclosed that the microtubule density in isolated LV myocytes increased by 21% at 4 weeks and by 48% 6 months after aortic constriction; (5) at the heart failure stage, microtubule density in LV myocytes showed a statistically significant inverse correlation to the LV maximum +dP/dt and a direct correlation to LV myocyte lengthening; (6) the increased microtubule density in LV myocytes in this model was not due to an increase in total tubulin; and (7) microtubule density in left atrial and right ventricular myocytes also increased when they underwent hypertrophy secondary to left heart failure. These results suggest that the down-regulation of titin and up-regulation of microtubule and desmin filaments may contribute to myocyte lengthening and malfunction in pressure overload congestive heart failure.