Claudin 1 dysregulation disrupts coronary microvascular integrity and impairs cardiac function.

BACKGROUND AND AIMS: Claudin 1 (Cldn1) is a tight junction protein primarily known for its role in epithelial and endothelial barrier function. However, the role of Cldn1 in coronary microvascular barrier remain unclear. The aim of this study is to investigate the biological effects of Cldn1 dysregulation on coronary vascular permeability, inflammation, fibrosis, and left ventricular function. METHODS: Cldn1 was silenced in human cardiac microvascular endothelial cells (HMVECs) and C57Bl/6 mice using oligonucleotide-based next generation siRNA duplex. Additionally, global transgenic mice with endothelial cell-specific overexpression of Cldn1 were created under the regulation of the CD144 (VE-cadherin) promoter. Permeability was assessed using FITC-dextran assay in vitro and Evans blue dye leakage (Mile's assay) in vivo. Cardiac morphology and function were measured by cardiac MRI, and myocardial pathology was analyzed by immunohistochemistry and Transmission Electron Microscopy (TEM). PCR and Western blotting confirmed Cldn1 expression changes. RESULTS: Cldn1 knockdown reduced protein levels by 46% (p = 0.004) and significantly increased endothelial permeability in HMVEC (p = 0.0007). In mice, Cldn1 knockdown significantly increased Evans blue dye leakage (p = 0.025), macrophage infiltration (p = 0.018), and interstitial collagen (p = 0.048). TEM confirmed endothelial damage particularly affecting the basement membrane structure. Cardiac MRI showed reduced stroke volume (p = 0.004) and ejection fraction (p = 0.043). Cldn1 overexpression reduced vascular permeability (p = 0.002) without altering cardiac function under basal condition. CONCLUSION: Cldn1 plays an important role in maintaining coronary microvascular barrier integrity. Its loss leads to increased permeability, inflammation, fibrosis, and impaired cardiac function, while overexpression enhances barrier function without affecting cardiac performance under baseline conditions.