Intercellular transfer of SerpinE2 activates PI3K-AKT and β-catenin signaling to promote cardiac hypertrophy

Abstract Background Effective inhibition of pathological cardiac hypertrophy is critical for managing various cardiovascular diseases, especially in cold environments. The communication between cardiomyocytes and fibroblasts, mediated by secreted proteins, plays a significant role in the development and progression of pathological cardiac hypertrophy. Serpin Family E Member 2 (serpinE2), secreted by fibroblasts into the extracellular space, has been implicated in this process. However, whether serpinE2 can be internalized by cardiomyocytes and whether cold exposure influences this process remains unclear. Materials and methods Mice were subjected to cold exposure (4 °C, 12 h/day for 8 weeks), and cardiac hypertrophy was induced by transverse aortic constriction (TAC). SerpinE2 expression was silenced by short interfering RNA (siRNA). Cardiac fibroblasts were stimulated with angiotensin II (Ang II) to induce serpinE2 secretion. Exogenous recombinant serpinE2, labeled with DyLight 488 or His-tag, was used to evaluate its internalization and functional role in cardiomyocytes. Internalization was inhibited by using antibodies against serpinE2, heparin, or endocytosis inhibitors (β-cyclodextrin, nystatin, dynasore, and chlorpromazine). Chromatin immunoprecipitation followed by quantitative polymerase chain reaction (PCR) was used to assess the binding of the transcription factor CDX1 to the serpinE2 promoter. Results Cold exposure significantly increased serpinE2 mRNA and protein expression in mouse hearts. SerpinE2 levels were also upregulated in plasma and cardiac tissue following TAC. Knockdown of serpinE2 attenuated TAC-induced hypertrophy, restored left ventricular function, and reduced atrial natriuretic peptide, brain natriuretic peptide, and β-myosin heavy chain fragment levels. Exogenous serpinE2 promoted cardiomyocyte hypertrophy, an effect that was reversed by serpinE2 knockdown. Co-culture with conditioned medium from Ang II-stimulated fibroblasts increased serpinE2 expression in cardiomyocytes. Exogenous serpinE2 was internalized via endocytosis, which was inhibited by antibodies, heparin, and endocytosis blockers. Internalized serpinE2 activated the protein kinase B (AKT)/β-catenin pathway in cardiomyocytes. CDX1 bound to the serpinE2 promoter and promoted its transcription in fibroblasts. CDX1 overexpression increased serpinE2 and collagen expression, while its suppression had the opposite effect. Administration of exogenous fibroblast growth factor 4 (FGF4) or overexpression of FGF4 plasmid upregulated CDX1, serpinE2, and collagen expression in fibroblasts. Conclusions SerpinE2 expression is responsive to cold stress and mediates intercellular communication between fibroblasts and cardiomyocytes. Fibroblast-secreted serpinE2 is internalized by cardiomyocytes via endocytosis, promoting hypertrophy through activation of the phosphatidylinositol 3-kinase (PI3K)-AKT/β-catenin pathway. The FGF4-CDX1 axis regulates serpinE2 expression and secretion in cardiac fibroblasts.