Abstract 3440: Affixin/beta Parvin Activates STAT3 In The Heart And Protects From Apoptosis
The sarcomeric z-disc is increasingly recognized as a “hot spot” in cardiac signal transduction and the pathogenesis of cardiomyopathy. Affixin (β-parvin), which is highly expressed in cardiomyocytes, has also been shown to localize to the z-disc. However, its functional relevance in the heart is still unclear. In order to begin to assess its molecular role, we overexpressed affixin in neonatal rat cardiomyocytes (NRCMs) using an adenoviral vector. Overexpression of affixin led to an increase of 28 % in cell size (p<0.001) compared to cells infected with a control vector. To identify signalling pathways involved in affixin-mediated cardiac hypertrophy, we performed a yeast-two-hybrid screen employing affixin as a bait. The Signal transducer and activator of transcription 3 (STAT3) was detected as a direct binding partner of affixin, which was subsequently verified by Co-immunoprecipitation. Moreover, overexpression of affixin resulted in enhanced STAT3 DNA-binding in electro mobility shift essays as well as increased phosphorylation of STAT3. Realtime PCR experiments revealed a marked induction of STAT3-dependent genes, including angiotensinogen (+496%, p<0.05), HSP70 (+231%, p<0.01), Janus Kinase 2 (+230%, p<0.05) and MnSOD (+146%, p<0.05). On a functional level, overexpression of affixin protected cardiomyocytes from doxorubicine-induced apoptosis: While incubation with doxorubicin led to an increase of apoptotic cells by 280% in control NRCMs, cardiomyocytes overexpressing affixin displayed only a small increase of apoptotic cells (+40%, p<0.05). Finally, in an angiogenesis assay we could demonstrate that medium from affixin-overexpressing cardiomyocytes increases tubuli formation of HUVEC cells (+18%, p<0.01), suggesting a proangiogenic effect of affixin-overexpressing NRCMs. Taken together, we describe an unexpected function for affixin in the activation of STAT3-signalling in cardiomyocytes. Consistent with increased STAT3 activity, affixin-treated cells revealed mild hypertrophy, protection against apoptosis and enhanced angiogenesis. This novel molecular mechanism could thus play an important role in cardioprotection, i.e. during ischemia-reperfusion or increased biomechanical stress.