Pro-oxidant effect of transforming growth factor-β₁ mediates contractile dysfunction in rat ventricular myocytes

Aims: Transforming growth factor-β₁ (TGF- β₁) is a multifunctional cytokine that contributes to pathogenic cardiac remodelling via mechanisms that involve oxidative stress. However, the direct impact of TGF-β₁ on contractile function of ventricular myocytes is incompletely understood. Methods and results: Reactive oxygen species (ROS) production and intracellular glutathione (GSH) were measured by fluorescence microscopy in isolated rat ventricular myocytes pretreated with TGF-β₁ (0.1-10 ng/mL). In separate studies, video edge detection measurements were made to evaluate myocyte contractile function, and confocal microscopy was used to monitor evoked Ca²⁺ transients. TGF-β₁ (1 ng/mL) for 3-4 h significantly increased ROS production by 90% (P < 0.05) and decreased GSH by 34% (P < 0.05) compared with control. These changes paralleled a significant decrease in the rate of myocyte shortening and relaxation by 33% and 43%, respectively (0.5 Hz; P < 0.05), whereas fractional shortening was not altered. Ca²⁺ transients in TGF-β₁-treated myocytes were characterized by a delayed peak and slowing in the rate of decay but no change in peak Ca²⁺ amplitude. Increased ROS production and GSH depletion by TGF-β₁ were prevented by an NAD(P)H oxidase inhibitor or a free radical scavenger, both of which significantly mitigated TGF-β₁-induced myocyte contractile dysfunction. Moreover, pretreating myocytes with exogenous GSH or the GSH precursor N-acetylcysteine also prevented myocyte contractile impairment and abnormal Ca²⁺ transients elicited by TGF-β₁. Conclusion: Our data suggest that TGF-β₁-induced cardiomyocyte contractile dysfunction is associated with enhanced ROS production and oxidative alterations in Ca²⁺ handling proteins regulated by endogenous GSH.