Transforming Growth Factor β(1) Oppositely Regulates the Hypertrophic and Contractile Response to β-Adrenergic Stimulation in the Heart

BACKGROUND: Neuroendocrine activation and local mediators such as transforming growth factor-β(1) (TGF-β(1)) contribute to the pathobiology of cardiac hypertrophy and failure, but the underlying mechanisms are incompletely understood. We aimed to characterize the functional network involving TGF-β(1), the renin-angiotensin system, and the β-adrenergic system in the heart. METHODS: Transgenic mice overexpressing TGF-β(1) (TGF-β(1)-Tg) were treated with a β-blocker, an AT(1)-receptor antagonist, or a TGF-β-antagonist (sTGFβR-Fc), were morphologically characterized. Contractile function was assessed by dobutamine stress echocardiography in vivo and isolated myocytes in vitro. Functional alterations were related to regulators of cardiac energy metabolism. RESULTS: Compared to wild-type controls, TGF-β(1)-Tg mice displayed an increased heart-to-body-weight ratio involving both fibrosis and myocyte hypertrophy. TGF-β(1) overexpression increased the hypertrophic responsiveness to β-adrenergic stimulation. In contrast, the inotropic response to β-adrenergic stimulation was diminished in TGF-β(1)-Tg mice, albeit unchanged basal contractility. Treatment with sTGF-βR-Fc completely prevented the cardiac phenotype in transgenic mice. Chronic β-blocker treatment also prevented hypertrophy and ANF induction by isoprenaline, and restored the inotropic response to β-adrenergic stimulation without affecting TGF-β(1) levels, whereas AT(1)-receptor blockade had no effect. The impaired contractile reserve in TGF-β(1)-Tg mice was accompanied by an upregulation of mitochondrial uncoupling proteins (UCPs) which was reversed by β-adrenoceptor blockade. UCP-inhibition restored the contractile response to β-adrenoceptor stimulation in vitro and in vivo. Finally, cardiac TGF-β(1) and UCP expression were elevated in heart failure in humans, and UCP – but not TGF-β(1) – was downregulated by β-blocker treatment. CONCLUSIONS: Our data support the concept that TGF-β(1) acts downstream of angiotensin II in cardiomyocytes, and furthermore, highlight the critical role of the β-adrenergic system in TGF-β(1)-induced cardiac phenotype. Our data indicate for the first time, that TGF-β(1) directly influences mitochondrial energy metabolism by regulating UCP3 expression. β-blockers may act beneficially by normalizing regulatory mechanisms of cellular hypertrophy and energy metabolism.