The signaling mechanism of Hcy-induced atrial fibrosis mediated by TRPC3

Background High plasma levels of homocysteine (Hcy) are regarded as a risk factor for atrial fibrillation (AF), which is closely associated with the pathological consequence of atrial fibrosis and can lead to heart failure with a high mortality rate; Currently, there is no effective therapy for preventing atrial fibrosis, owing to a lack in fundamental understanding of the underlying mechanism. Here, we show that atrial fibrosis is mediated by the relationship between canonical transient receptor potential 3 (TRPC3) channels and sirtuin type 1 (SIRT1) under the stimulation of Hcy. Methods The left atrial appendage was obtained from patients with either sinus rhythm (SR) or AF, who underwent cardiothoracic surgery, and used to evaluate the relationship between the concentration of Hcy and a potential mechanism of cardiac fibrosis mediated by TRPC3 and SIRT1. We next performed transverse aortic constriction (TAC) in mouse to investigate the relationship. The mechanisms underlying atrial fibrosis involving TRPC3 and SIRT1 proteins were explored by co-immunoprecipitation (co-IP), bio-layer interferometry (BLI) and lentivirus transfection experiments. Quantitative polymerase chain reaction (qPCR) and western blotting (WB) were performed to analyse gene and protein expression, respectively. Results The majority of AF patients displayed atrial fibrosis, as demonstrated by Masson staining and immunohistochemistry. In the mouse model of TAC, more severe fibrosis was detected in the high-Hcy diet (HH) group, compared to NH mice; and the duration of induced AF was longer in the HH groups than in the normal diet (NH) group. Moreover, the HH group exhibited higher expression levels of TRPC3 and related fibrosis proteins, such as TGF-ß and Col-I, than the NH group, despite also showing a higher level of SIRT1 was observed. The activator of SIRT1 (Resveratrol, Res) attenuated the enhancement of TRPC3 and decrease in SIRT1 observed in the HH group. Further cell culture experiments confirmed that Hcy could promote the proliferation and differentiation of fibroblasts, the up-regulation of TRPC3, and the decrease in the protein level of SIRT1. Ultimately, the results of Co-IP and BLI indicated a direct interaction between TRPC3-C terminal domain (569-863) and SIRT1 proteins, in which the two proteins are antagonistic and in combination regulate the pathogenesis of atrial fibrosis. Conclusions The higher level of atrial fibrosis were observed in the HH mouse group, compared with the NH mice group, Such results suggest that AF patients may be more susceptible to atrial fibrosis and possess a high probability of progressing to hyperhomocysteinemia. Moreover, our findings are consistent with the hypothesis that TRPC3 channel up-regulation leads to abnormal accumulation of collagen, with the down-regulation of SIRT1 as an aetiological factor of high Hcy, which in turn predisposes to atrial fibrosis and strongly enhances the possibility of AF.