The Role of Aging on Pulmonary Microvascular Endothelial Cell Barrier Function

Acute respiratory distress syndrome (ARDS) is a life-threatening condition characterized by widespread injury and inflammation within the lungs. Mortality due to ARDS is high, especially in the elderly population, and there are no effective therapeutics available. Mechanical ventilation, a common supportive treatment for ARDS, is necessary for maintaining gas exchange and survival, but can exacerbate the underlying lung injury. Clinical outcomes tend to be more severe in elderly ARDS patients requiring mechanical ventilation; however, the underlying age-associated mechanisms that contribute to these worsened outcomes are ill-defined. One of the key pathophysiological mechanisms that occurs during ARDS and mechanical ventilation is damage to pulmonary microvascular endothelial cells (PMVEC). Specifically, disruption of PMVEC cell-cell junctions that maintain vascular barrier function occurs, leading to vascular fluid leak into the lung tissue, pulmonary edema, and respiratory dysfunction. We hypothesized that aging was associated with PMVEC barrier dysfunction, due to disrupted cell-cell junction integrity, resulting in increased susceptibility to pulmonary injury. To address this, young and aged mice were mechanically ventilated, and lung injury was evaluated, including microvascular permeability and inflammatory signaling. Single-cell RNA-sequencing was used to delineate cell-specific transcriptional changes. In vitro studies were conducted on PMVEC isolated from young and aged mice. Barrier function and cell-cell junction integrity were assessed, and proteomics analysis was performed. The results demonstrated that microvascular permeability was significantly augmented while inflammation was less pronounced in aged mice following mechanical ventilation. Differential gene expression and pathway analyses revealed that aged PMVEC exhibited alterations in cell-cell junction gene transcription. In vitro functional analysis indicated that aged PMVEC exhibited impaired barrier formation under basal conditions, associated with disrupted adherens and tight junction proteins. Finally, mechanistic studies revealed that PMVEC from aged mice had increased actin stress fiber formation vs. PMVEC from young mice. Collectively, these findings demonstrate an age-related predisposition to endothelial barrier dysfunction, resulting from altered cell-cell junction formation and leading to increased injury following mechanical ventilation. Consequently, age-related vascular changes may underlie the increased susceptibility to injury during ARDS and mechanical ventilation in elderly patients.