Novel mechanisms for caspase inhibition protecting cardiac function with chronic pressure overload

Abstract

Myocyte apoptosis is considered a major mechanism in the pathogenesis of heart failure. Accordingly, manipulations that inhibit apoptosis are assumed to preserve cardiac function by maintaining myocyte numbers. We tested this assumption by examining the effects of caspase inhibition (CI) on cardiac structure and function in C57BL/6 mouse with pressure overload model induced by transverse aortic constriction (TAC). CI preserved left ventricular (LV) function following TAC compared with the vehicle. TAC increased apoptosis in non-myocytes more than in myocytes and these increases were blunted more in non-myocytes by CI. Total myocyte number, however, did not differ significantly among control and TAC groups and there was no correlation between myocyte number and apoptosis, but there was a strong correlation between myocyte number and an index of myocyte proliferation, Ki67-positive myocytes. Despite comparable pressure gradients, LV hypertrophy was less in the CI group, likely attributable to decreased wall stress. Since changes in myocyte numbers did not account for protection from TAC, several other CI-mediated mechanisms were identified including: (a) lessening of TAC-induced fibrosis, (b) augmentation of isolated myocyte contractility, and (c) increased angiogenesis and Ki67-positive myocytes, which were due almost entirely to the non-myocyte apoptosis, but not myocyte apoptosis, with CI. CI maintained LV function following TAC not by protecting against myocyte loss, but rather by augmenting myocyte contractile function, myocyte proliferation, and angiogenesis resulting in reduced LV wall stress, hypertrophy, and fibrosis.

Mst1 inhibition rescues β1-adrenergic cardiomyopathy by reducing myocyte necrosis and non-myocyte apoptosis rather than myocyte apoptosis

“…Given that 75 % of the cells in the heart are non-myocytes [17], we discriminated the effects of the cardiomyopathy and its rescue with DN-Mst1 on myocyte vs. non-myocyte apoptosis. The finding that apoptosis predominantly occurred in non-myocytes and DN-Mst1 predominantly rescued non-myocyte apoptosis, supports the hypothesis that DN-Mst1 protects against necrosis, since non-myocytes, e.g., fibroblasts, macrophages, neutrophils, endothelial cells [33, 34, 36, 40], are all known to be involved in inflammation [9, 18, 39], which is more closely coupled to necrosis, rather than apoptosis [7, 10, 20, 22, 29, 38]. In further support of the role of necrosis, we also found that myocardial fibrosis, which is generally thought to be an outcome of necrosis rather than apoptosis [3, 10], was also rescued in the bigenic mice.…”

Disruption of type 5 adenylyl cyclase prevents β-adrenergic receptor cardiomyopathy: A novel approach to β-adrenergic receptor blockade

“…However, the current results are consistent with our previous findings that the apoptosis occurs predominantly in nonmyocytes in several models of cardiomyopathy, including ischemic cardiomyopathy (50) and hypertrophic cardiomyopathy (18,51). Based on our previous studies, the cell types of apoptotic nonmyocytes mainly include macrophages, neutrophils, fibroblasts, and endothelial cells (50,51). The role of nonmyocyte apoptosis in the heart in mediating or preventing the cardiomyopathy is not clear, since the nonmyocytes are a double-edged sword.…”

“…Whereas this might be understood, recognizing that over 70% of cells in the heart are nonmyocytes, it seems inconsistent with the currently held concept that apoptosis leads to cardiac dysfunction through reducing myocyte numbers (4,19). However, the current results are consistent with our previous findings that the apoptosis occurs predominantly in nonmyocytes in several models of cardiomyopathy, including ischemic cardiomyopathy (50) and hypertrophic cardiomyopathy (18,51). Based on our previous studies, the cell types of apoptotic nonmyocytes mainly include macrophages, neutrophils, fibroblasts, and endothelial cells (50,51).…”

“…These techniques have all been used extensively (36, 50 -52, 64). To further discriminate apoptosis in myocytes from smaller nonmyocytes, tissue sections (5 m thickness) were costained with ␣-actinin for myocytes as previously described (18,50,51).…”

Blockade of EMAP II protects cardiac function after chronic myocardial infarction by inducing angiogenesis

“…5μm thickness of serial heart tissue sections were used for histological assessment and immunohistochemical staining. In order to discriminate proliferation in non-myocytes and myocytes, tissue sections were counterstained with wheat germ agglutinin (WGA) Alexa Fluor-488 conjugate (Invitrogen) or troponin I, a myocyte marker, as described in our previous study [22]. …”