Abstract Body (Do not enter title and authors here): Introduction：We previously reported that cardiac Tregs exhibited a unique phenotype after acute myocardial infarction (AMI) and promoted tissue repair through the secretion of secreted acidic cysteine-rich glycoprotein (Sparc). However, the underlying mechanisms remained unclear. We hypothesize that Treg-derived Sparc following AMI exerts protective effects by promoting collagen synthesis in cardiac fibroblasts and collagen deposition in the heart. Absence of Treg-derived Sparc can lead to impaired scar formation and increased cardiac rupture.
Methods：Mice with Treg-specific Sparc knockout (Foxp3^CreSparc^flox/flox) and DEREG mice transferred with Sparc-deficient Tregs were subjected to AMI. Echocardiography, immunohistochemistry, transmission electron microscopy and RNA sequencing were used to investigate the impact of Treg-derived Sparc deficiency on cardiac repair after AMI. Additionally, co-culture experiment of cardiac fibroblasts and Sparc-overexpressing Tregs were conducted, Western blot was used to explore the activation levels of pathways, both Western blot and Reverse Transcription-Polymerase Chain Reaction were used to explore the expression levels of α-SMA, type I collagen, and type III collagen.
Results：The expression of Sparc in cardiac Tregs peaked at 7 days post MI. The absence of Treg-derived Sparc led to increased mortality and cardiac rupture rates both in Foxp3^CreSparc^flox/flox mice and DEREG mice transferred with Sparc-deficient Tregs. Additionally, impaired scar formation was observed in Foxp3^CreSparc^flox/flox mice, characterized by reduced collagen maturity and disorganized and loose collagen fiber organization in the infarcted area. RNA sequencing revealed that the deficiency of Treg-derived Sparc significantly downregulated the extracellular matrix synthesis-related pathways in the cardiac infarcted zone. In vitro co-culture experiments showed that cardiac fibroblasts co-cultured with Sparc-overexpressing Tregs exhibited significant activation of the SAPK/JNK/c-JUN pathway and increased secretion of type I collagen.
Conclusion：Treg-derived Sparc can promote collagen synthesis in cardiac fibroblasts by inducing the activation of SAPK/JNK/c-JUN pathway, and can promote the maturation of scar tissue in the infarcted area, playing an important role in facilitating tissue repair and preventing heart rupture after AMI.