N-terminal domain of CTRP9 promotes cardiac fibroblast activation in myocardial infarction via Rap1/Mek/Erk pathway.

Background: In developed nations, myocardial infarction (MI) is one of the main causes of morbidity and mortality, resulting in a significant economic burden and becoming a global public health problem. C1q/tumor necrosis factor-related protein 9 (CTRP9) is a secreted protein comprising a variable domain, a collagenous region, and a C-terminal trimerizing globular C1q (gC1q) domain. In vivo, the full-length CTRP9 (fCTRP9) can be cleaved into the globular domain of CTRP9 (gCTRP9). Here, we tested the cardio-protective impacts of fCTRP9, gCTRP9, and N-terminal domain, including the variable and collagenous domain, of CTRP9 (nCTRP9) in the context of MI.

Methods: Studies comparing the protective properties of fCTRP9 and gCTRP9 against MI in mice hearts were performed both in vitro and in vivo. The role of matrix metalloproteinase-9 (MMP9) in CTRP9 cleavage was examined, and the effects of different CTRP9 domains on cardiac fibrosis and cardiac fibroblast (CF) activation were investigated.

Results: gCTRP9 exerted better protective effects than fCTRP9 against MI, demonstrating superior anti-apoptotic and anti-fibrotic properties. fCTRP9 was cleaved by MMP9, resulting in gCTRP9 and nCTRP9. MMP9 overexpression enhanced the cardioprotective effects of fCTRP9, while nCTRP9 supplementation aggravated cardiac fibrosis in MI mice. Mechanistically, nCTRP9 activated CFs via an increase in Rap1 expression and MEK 1/2 and ERK1/2 phosphorylation.

Conclusions: Different domains of CTRP9 have distinct cardioprotective effects. gCTRP9 shows beneficial effects, while nCTRP9 promotes cardiac fibrosis. These findings highlight the importance of CTRP9 in cardiac function regulation and suggest prospective therapeutic options for MI treatment.