Abstract 17211: Targeting Mitogen-Activated Kinase Alleviates Free Heme-Induced Endothelial Barrier Dysfunction and Vascular Leakage in Lungs

Introduction: Several studies confirm that free heme in circulation due to hemolysis causes endothelial barrier dysfunction. We recently demonstrated that hemolysis-induced vascular leakage with barrier dysfunction was a contributory factor to the development of pulmonary hypertension (PH). However, the precise molecular mechanisms involved in the pathology of heme induced barrier disruption still remains to be elucidated. Hypothesis: Previous studies by us showed that free heme activated the p38/MAPK pathway. Therefore, we hypothesized that targeting mitogen-activated protein kinase kinase 3 (MKK3) a key regulator of this pathway would alleviate heme induced vascular leakage. Methods: Barrier dysfunction in human micro-vascular endothelial cells (HLMVEC) was monitored using noninvasive electrical impedance and immunostaining. We used an MKK3 knockout mouse model to assess the efficacy of targeting the p38/MAPK pathway. Results: We found a rapid drop in the HLMVEC barrier integrity with heme, in a dose dependent manner (p<0.05). Investigating the barrier proteins showed that heme significantly affected the tight junction proteins, zona occludens-1, claudin1, and claudin5 (p<0.05). We also found the p38MAPK/HSP27 pathway, involved in regulating the endothelial cytoskeleton remodeling, to be significantly altered with heme treatment, both in the HLMVEC and mice (p<0.05). However, heme treated mice showed no significant change in E-selectin, ICAM1 and VCAM1, indicating that the primary rapid target of heme was the p38/MAPK pathway and not the inflammatory pathways. Finally, injecting mice with heme-FITC-dextran and then following its release into the lungs demonstrated that the MKK3 KO significantly prevented heme induced vascular leakage (p<0.05). Conclusion: We demonstrate that heme induces a rapid barrier dysfunction by disruption of endothelial barrier proteins via the p38/MAPK pathway. Also, knocking out MKK3, a crucial regulator of the p38/MAPK pathway significantly decreased heme induced vascular leakage, a contributory factor to PH. Taken together, our results show that targeting the MKK3/p38MAPK axis represents a decisive treatment strategy in alleviating heme induced barrier dysfunction in cardiovascular diseases.