RCN1 downregulation-driven endoplasmic reticulum stress impairs endothelial function and diabetic foot ulcer healing

Diabetic foot ulcers (DFUs) are a leading cause of disability and mortality, with endothelial dysfunction playing a key role in the development of non-healing ulcers. A primary driver of endothelial cell impairment in this context is endoplasmic reticulum (ER) stress, triggered by glycolipotoxicity, though the underlying mechanisms are not fully understood. In this study, we observed that diabetic mice displayed poor ulcer healing associated with reduced angiogenesis and downregulated Reticulocalbin 1 (RCN1) expression. Proteomic analysis in human umbilical vein endothelial cells (HUVECs) identified a strong link between RCN1 and the damaging effects of glycolipotoxicity on endothelial cell function, leading to impaired tubule formation, reduced migratory capacity, and increased apoptosis in endothelial cells. Mechanistic RNA sequencing analysis highlighted a significant role for RCN1 in regulating ER function. RCN1 overexpression alleviated ER stress by reducing Protein kinase R-like endoplasmic reticulum kinase (PERK) phosphorylation and C/EBP homologous protein (CHOP) expression, both induced by glycolipotoxicity or Thapsigargin (TG), while RCN1 silencing intensified these effects. Additionally, TRIM11-mediated ubiquitination, influenced by glycolipotoxicity, regulated RCN1 stability, specifically promoting angiogenesis through RCN1 modulation. RCN1 overexpression accelerated ulcer healing in diabetic mice by suppressing ER stress proteins and enhancing angiogenesis, whereas RCN1 inhibition further delayed ulcer healing. In human DFU samples, proteomic analysis revealed that low RCN1 levels were linked to disrupted ER functional proteins, with RCN1 serum levels decreasing as diabetes progressed to DFU. Following surgical debridement treatment, RCN1 levels increased in patients with improved DFU healing outcomes. These findings suggest that ER stress, initiated by RCN1 inhibition in response to glycolipotoxicity, leads to endothelial dysfunction and apoptosis, ultimately contributing to the non-healing of DFUs.