The Role of nmMLCK in the Regulation of Lung Vascular Barrier Integrity During Pulmonary Inflammation

Increased vascular permeability and accumulation of alveolar fluid are cardinal features of lung inflammation such as acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and asthma. Two key molecules implicated in the pathogenesis of these diseases are vascular endothelial growth factor (VEGF), a growth factor that promotes vascular permeability, and the non-muscle isoform of myosin light chain kinase (nmMLCK), a key regulator of vascular barrier function via actin-myosin mediated cell contraction. VEGF is a known factor upregulated in lung during ALI/ARDS and asthma pathogenesis. Also, we have recently demonstrated that nmMLCK mRNA and protein expression are upregulated in asthmatic patients and our previous work has shown that the variants in the gene encoding nmMLCK (MYLK) are associated with severe asthma in African descent individuals, strongly suggesting their involvement in asthmatic pathophysiology. In this study, I hypothesized that nmMLCK mediates VEGF induced vascular hyperpermeability in asthmatic inflammation and have provided strong evidence for a linkage between these two major asthmatic molecules. Using a combination of in vivo, in vitro, and in silico studies, I have demonstrated increased expression of nmMLCK in OVA experimental model of asthma, and this upregulation and activation of nmMLCK is mediated by VEGF. These data demonstrate that increased levels and activity of nmMLCK is strongly associated with asthmatic inflammation. Interestingly, VEGF stimulation significantly increases nmMLCK mRNA and protein expression, with Sp1 transcription factor binding and de-methylation of the nmMYLK promoter being likely mechanisms modulating nmMLCK expression. These mechanistic interactions between two major asthmatic molecules present potential novel candidates for therapeutic targeting to reduce asthmatic inflammation.