Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Physiology and Pharmacology
Supervisor
Gill, Sean E.
Abstract
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.
Summary for Lay Audience
Lung injury can lead to a deadly condition called acute respiratory distress syndrome (ARDS). There are currently no treatments for ARDS beyond supporting patients’ breathing using a mechanical ventilator. Unfortunately, mechanical ventilation can worsen lung injury, and this seems to occur more readily in older patients. The underlying causes of these adverse outcomes in older patients are unknown, but one possibility is damage to the blood vessels in the lungs. The cells that comprise the blood vessels form a barrier between the fluid within the vessel and the surrounding lung tissue, akin to a water pipe in a house. This barrier is maintained due to attachment of these cells through specialized proteins that seal the gaps, similar to staples and glue. During ARDS and mechanical ventilation, this barrier breaks, allowing fluids and other substances from the vessel to leak into the lungs. We hypothesized that aging leads to increased blood vessel damage because the proteins that hold the cells together stop functioning. To study this, we mechanically ventilated young and old mice and measured blood vessel leakiness in their lungs. Additionally, we employed advanced analysis tools to examine the genes and proteins in the cells, particularly those in the blood vessel cells, of the lungs. We also isolated blood vessel cells from the lungs of young and aged mice and grew them outside the animal on plastic dishes until they formed a single layer, mimicking the barrier formed by the blood vessel wall. We assessed barrier leakiness and how well the proteins attached to each other. Our findings revealed that older mice exhibited greater blood vessel leak after mechanical ventilation, as well as alterations in the genes involved in the attachment of blood vessel cells. The isolated cells from older mice exhibited impaired barrier formation, due to the absence, or reduction at the cell wall, of the proteins that adhere the cells. These observations suggest that as we age, the blood vessels in our lungs are more susceptible to damage due to the absence of certain proteins, potentially contributing to the poorer outcomes observed in older patients with lung injury.
Recommended Citation
Manji, Aminmohamed, "The Role of Aging on Pulmonary Microvascular Endothelial Cell Barrier Function" (2025). Electronic Thesis and Dissertation Repository. 10726.
https://ir.lib.uwo.ca/etd/10726