P748Afterload-induced TRIF-dependent signaling promotes fibrosis but not cardiomyocyte hypertrophy

Abstract

Abstract Background Pressure overload dependent cardiac remodeling is characterized by a continuous functional loss of cardiomyocytes, cardiomyocyte hypertrophy, cell death and fibrosis. The relevance of the MyD88- and NFκB-independent inflammatory TRIF (TIR-domain-containing adapter protein inducing IFN-β) signaling pathway in myocardial hypertrophy is incompletely understood. Methods and results The murine model of afterload induced myocardial hypertrophy (trans-aortic constriction, TAC) was used to investigate the time dependent chemokine expression in C57Bl/6J Wild type (WT) mice after intervention. Myd88- as well as TRIF-dependent chemokines reached their expression maximum at d7 post intervention. This time point was determined for further investigations on TRIF knockout-mice (TRIF−/−) compared to WT mice. While left ventricular (LV) mRNA-expression of TNFalpha and IL6 was upregulated in TRIF−/− mice, CXCL10, CXCL11, RANTES and pathway molecule IRF3 remained unchanged. In the stage of established hypertrophy (35 days after TAC) cytokine levels returned to baseline in WT as well as in TRIF−/− mice. Cellular hypertrophy (increase in cardiomyocyte size) as well as echocardiographic determined increase of LV mass was similar in TRIF−/− and WT mice at d7 as well as at d35 after TAC. Additionally at d7 and d35 the fractional shortening function didn't show any differences between the groups after TAC. On the other hand LV interstitial fibrosis (determined by collagen content) was significantly less distinct in TRIF−/− mice (1.4±0.2%) than in WT mice (2.3±0.3%, (p<0.01 TRIF−/− vs. WT) at d7 following TAC. According to that TGFbeta protein expression was more pronounced in WT (318±85% of sham-operated controls) than in TRIF−/− mice (111±15% of sham-operated controls; p<0.05 TRIF−/− vs. WT). These differences in fibrosis and TGFbeta remained at d35. Even the hydroxyproline concentration was higher in LV tissue of the WT mice than in the TRIF−/− mice d35 after TAC (WT: 93.4±7.7μM, TRIF−/− 54.8±9.0μM, p<0.5 TRIF−/− vs. WT). The expression of TGFbeta signaling pathway associated SMAD proteins (SMAD 3, pSMAD3, SMAD4) was up to two fold higher in WT mice than in TRIF−/− mice. Additionally expression of antifibrotic miR29b was more pronounced in TRIF−/− mice (2.34±0.71) than in WT mice (0.98±0.08) after TAC d7. Conclusion In afterload induced hypertrophy TRIF-dependent signaling doesn't influence cardiomyocyte hypertrophy. But TRIF plays an important role in the regulation of fibrosis in pressure overload dependent remodeling. Through the modulation of the TGF-beta signaling pathway and antifibrotic microRNAs TRIF signaling is involved in the development of interstitial fibrosis. Especially in the early stage of the cardiac remodeling. Acknowledgement/Funding KFO196