Pi3k As Mediator Of Apoptosis And Contractile Dysfunction In Tgf Beta(1)-Stimulated Cardiomyocytes

Simple Summary TGF beta(1) is a growth factor that plays a major role in the remodeling process of the heart by inducing cardiomyocytes dysfunction and apoptosis, as well as fibrosis, thereby restricting heart function. TGF beta(1) mediates its effect via the TGF beta receptor I (ALK5) and the activation of SMAD transcription factors. But, TGF beta(1) is also known as activator of phosphoinositide-3-kinase (PI3K) via the non-SMAD signaling pathway. The aim of this study was to investigate whether PI3K is also involved in TGF beta(1)-induced cardiomyocytes apoptosis and contractile dysfunction. Pharmacological inhibition of PI3K with Ly294002 reduced TGF beta-induced apoptosis and reduced cell shortening. Inhibition of the PI3K gamma isoform also abolished the TGF beta effect on apoptosis and cell shortening. These data support a role for a PI3K and ALK5/SMAD pathway in TGF beta(1)-induced apoptosis and impaired cell shortening, which in part appears to be PI3K gamma-dependent. Background: TGF beta(1) is a growth factor that plays a major role in the remodeling process of the heart by inducing cardiomyocyte dysfunction and apoptosis, as well as fibrosis thereby restricting heart function. TGF beta(1) mediates its effect via the TGF beta receptor I (ALK5) and the activation of SMAD transcription factors, but TGF beta(1) is also known as activator of phosphoinositide-3-kinase (PI3K) via the non-SMAD signaling pathway. The aim of this study was to investigate whether PI3K is also involved in TGF beta(1)-induced cardiomyocytes apoptosis and contractile dysfunction. Methods and Results: Incubation of isolated ventricular cardiomyocytes with TGF beta(1) resulted in impaired contractile function. Pre-incubation of cells with the PI3K inhibitor Ly294002 or the ALK5 inhibitor SB431542 attenuated the decreased cell shortening in TGF beta(1)-stimulated cells. Additionally, TGF beta-induced apoptosis was significantly reduced by the PI3K inhibitor Ly294002. Administration of a PI3K gamma-specific inhibitor AS605240 abolished the TGF beta effect on apoptosis and cell shortening. This was also confirmed in cardiomyocytes from PI3K gamma KO mice. Induction of SMAD binding activity and the TGF beta target gene collagen 1 could be blocked by the PI3K inhibitor Ly294002, but not by the specific PI3K gamma inhibitor AS605240. Conclusions: TGF beta(1)-induced SMAD activation, cardiomyocyte apoptosis, and impaired cell shortening are mediated via both, the ALK5 receptor and PI3K, in adult cardiomyocytes. PI3K gamma specifically contributes to apoptosis induction and impairment of contractile function independent of SMAD signaling.