PI3K as Mediator of Apoptosis and Contractile Dysfunction in TGFβ1-Stimulated Cardiomyocytes.

Paulin Brosinsky,Klaus-Dieter Schlüter,Emilio Hirsch,Jacqueline Heger,Lisa Schulz,Julia Bornbaum,Rainer Schulz,Björn Warga,Alessandra Ghigo,Gerhild Euler

doi:10.3390/biology10070670

Paulin Brosinsky, Klaus-Dieter Schlüter + Show 8 more

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https://doi.org/10.3390/biology10070670

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Journal: Biology	Publication Date: Jul 16, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: University of Giessen, University of Turin

Abstract

Simple SummaryTGFβ1 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. TGFβ1 mediates its effect via the TGFβ receptor I (ALK5) and the activation of SMAD transcription factors. But, TGFβ1 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 TGFβ1–induced cardiomyocytes apoptosis and contractile dysfunction. Pharmacological inhibition of PI3K with Ly294002 reduced TGFβ-induced apoptosis and reduced cell shortening. Inhibition of the PI3Kγ isoform also abolished the TGFβ effect on apoptosis and cell shortening. These data support a role for a PI3K and ALK5/SMAD pathway in TGFβ1-induced apoptosis and impaired cell shortening, which in part appears to be PI3Kγ-dependent.Background: TGFβ1 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. TGFβ1 mediates its effect via the TGFβ receptor I (ALK5) and the activation of SMAD transcription factors, but TGFβ1 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 TGFβ1–induced cardiomyocytes apoptosis and contractile dysfunction. Methods and Results: Incubation of isolated ventricular cardiomyocytes with TGFβ1 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 TGFβ1–stimulated cells. Additionally, TGFβ-induced apoptosis was significantly reduced by the PI3K inhibitor Ly294002. Administration of a PI3Kγ-specific inhibitor AS605240 abolished the TGFβ effect on apoptosis and cell shortening. This was also confirmed in cardiomyocytes from PI3Kγ KO mice. Induction of SMAD binding activity and the TGFβ target gene collagen 1 could be blocked by the PI3K inhibitor Ly294002, but not by the specific PI3Kγ inhibitor AS605240. Conclusions: TGFβ1-induced SMAD activation, cardiomyocyte apoptosis, and impaired cell shortening are mediated via both, the ALK5 receptor and PI3K, in adult cardiomyocytes. PI3Kγ specifically contributes to apoptosis induction and impairment of contractile function independent of SMAD signaling.

Highlights

The transition of compensated hypertrophy to heart failure is accompanied by an increased expression of transforming growth factor β (TGFβ) [1,2] that contributes to cardiomyocyte apoptosis [3], enhanced β-adrenergic signaling [4] and contractile dysfunction [5,6,7], since overexpression of TGFβ in transgenic mice led to a moderate increase of myocardial β-adrenoceptor density and increased prohypertrophic signaling [1]
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Summary

Introduction

TGFβ mediates its signaling by binding to a heteromeric serine/threonine kinase receptor complex in the membrane [8,9], which is composed of the constitutive active type II TGFβ receptor that, upon binding of TGFβ, phosphorylates type I TGFβ receptor (ALK5) [10]. Administration of a PI3Kγ-specific inhibitor AS605240 abolished the TGFβ effect on apoptosis and cell shortening. This was confirmed in cardiomyocytes from PI3Kγ KO mice. Conclusions: TGFβ1-induced SMAD activation, cardiomyocyte apoptosis, and impaired cell shortening are mediated via both, the ALK5 receptor and PI3K, in adult cardiomyocytes. PI3Kγ contributes to apoptosis induction and impairment of contractile function independent of SMAD signaling

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