METRNL exerts cytoprotective effects on EPCs via regulation of the E2F1-TXNIP axis in obese limb ischemia.

Background: Obesity increases cardiovascular disease risk by impairing angiogenesis, primarily through dysfunction of endothelial progenitor cells (EPCs). METRNL, a recently identified secreted protein, exhibits diverse biological activities. However, its impact on EPC function and its role in obesity-related microvascular dysfunction remain unclear. This study aims to investigate the effects of METRNL on EPC function and its potential therapeutic mechanisms for promoting angiogenesis.

Method: In vitro, human EPCs derived from peripheral and umbilical cord blood were treated with recombinant METRNL protein (rMETRNL) and exposed to palmitic acid (PA). EPC proliferation, migration, and tube formation were assessed. Apoptosis and pyroptosis levels were evaluated using Western blotting, flow cytometry, scanning electron microscopy (SEM), immunofluorescence (IF), and enzyme-linked immunosorbent assay (ELISA). RNA sequencing, ChIP, and dual-luciferase assays were performed to investigate the regulatory mechanisms. In vivo, an obese mouse model with hind limb ischemia received local injections of METRNL-overexpressing EPCs in the ischemic muscle. Blood flow recovery was monitored using laser Doppler flowmetry and CD31 immunofluorescence.

Results: Replenishment of METNRL alleviated PA-induced apoptosis and pyroptosis of EPCs, while simultaneously enhancing their proliferation, migration, and tube formation. Mechanistically, RNA sequencing revealed that rMETRNL restoration downregulated E2F1 expression, and the protective effects of METRNL were partially reversed by E2F1 overexpression. Further, E2F1 was found to bind the TXNIP promoter region, promoting TXNIP transcription. Elevated TXNIP levels counteracted the beneficial effects of rMETRNL on EPC function in the presence of PA. In vivo, the transplantation of METRNL-overexpressing EPCs into the ischemic hind limbs of obese mice promoted angiogenesis, as evidenced by improved blood flow recovery and increased CD31 immunofluorescence in the ischemic tissues.

Conclusion: Our research emphasizes the potential of METRNL in reducing EPC cellular pyroptosis and promoting angiogenesis by inhibiting the E2F1-TXNIP signaling pathway. METRNL shows promise in treating obesity-related cardiovascular diseases through angiogenic therapy.