Downregulation of fibromodulin attenuates inflammatory signaling and atrial fibrosis in spontaneously hypertensive rats with atrial fibrillation via inhibiting TLR4/NLRP3 signaling pathway

BACKGROUND: Myocardial fibrosis is an important factor in the induction and maintenance of atrial fibrillation (AF). Fibromodulin (FMOD) promotes fibrotic gene expression. However, its specific role in spontaneously hypertensive rats (SHR)‐AF remains unclear. METHODS: We analyzed FMOD mRNA and protein expression in rat atrial tissues using RT‐qPCR, Western blot analysis, and immunohistochemistry. Histopathological examination of atrial tissues was performed using hematoxylin and eosin (H&E), Masson's trichrome, and Picrosirius red staining. The levels of inflammatory and fibrosis‐related proteins were measured using Western blot analysis. RESULTS: FMOD relative mRNA and protein expression levels were notably upregulated in atrial tissues of both AF groups (normal‐AF and SHR‐AF groups) than that in atrial tissues of the no‐AF group (normal and SHR group). This effect was particularly pronounced in the SHR‐AF group. Pathological changes revealed that the extracellular matrix, collagen, collagen fibers, and left atrial diameter were notably increased in the atrial tissues from the SHR‐AF group compared to those in the atrial tissues from the SHR group, whereas the left ventricular fractional shortening and left ventricular ejection fraction were notably lower. Expression of TLR4, MyD88, NLRP3, TGF‐β1, collagen I, and collagen II mRNA were clearly higher in atrial tissues from the SHR‐AF group than in those from the SHR group. Protein levels of TLR4, MyD88, NLRP3, Cleavage‐Caspase‐1, Cleavage‐IL‐1β, TGF‐β1, p‐Smad2, collagen I, and collagen II were clearly higher in atrial tissues from the SHR‐AF group than in those from the SHR group. FMOD knockdown inhibited atrial fibrosis, collagen accumulation, and the TLR4/MyD88/NLRP3 signaling pathway. CONCLUSION: Downregulation of FMOD attenuated inflammatory signaling and atrial fibrosis in SHR‐AF by inhibiting the TLR4/NLRP3 signaling pathway. Therefore, FMOD may be a promising therapeutic target in AF.