The role of aging on endothelial cell-cell junctions and pulmonary microvascular permeability in male mice

Pulmonary microvascular endothelial cell (PMVEC) intercellular junctions are critical for maintaining barrier function and mitigating pulmonary edema. Previously, we demonstrated that aging exacerbated pulmonary microvascular permeability in a model of lung injury. Based on this, we hypothesized that aging was associated with increased PMVEC barrier dysfunction due to impaired cell-cell junction integrity. PMVEC were isolated from young and aged mice and cultured to confluence in vitro. Barrier function, junctional integrity, alterations in the proteome, markers of inflammation, and actin cytoskeleton organization were all assessed. To model injurious conditions, PMVEC were stimulated with inflammatory cytokines. PMVEC from aged mice exhibited increased permeability, both under basal and inflammatory conditions, which was associated with disrupted cell-surface localization of the adherens junction protein, vascular endothelial (VE)-cadherin. Protein abundance of VE-cadherin was increased with age, while levels of the adapter protein, $\gamma$ -catenin, and the tight junction protein, claudin-5, were decreased. Measures of inflammation, including cytokine expression and cell surface abundance of adhesion molecules, did not differ with age. Augmented presence of actin stress fibers was observed in aged PMVEC. We conclude that aging predisposes PMVEC to elevated injury, due to inherent deficiencies in cell-cell junctions and barrier function, potentially mediated through altered actin cytoskeleton organization.