Pericyte‐like cells undergo transcriptional reprogramming and distinct functional adaptations in acute lung injury

Abstract

We previously reported on the role of pericyte-like cells as functional sentinel immune cells in lung injury. However, much about the biological role of pericytes in lung injury remains unknown. Lung pericyte-like cells are well-positioned to sense disruption to the epithelial barrier and coordinate local inflammatory responses due to their anatomic niche within the alveoli. In this report, we characterized transcriptional responses and functional changes in pericyte-like cells following activation by alveolar components from injured and uninjured lungs in a mouse model of acute lung injury (ALI). Purified pericyte-like cells from lung digests using PDGFRβ as a selection marker were expanded in culture as previously described (1). We induced sterile acute lung injury in mice with recombinant human Fas ligand (rhFasL) instillation followed by mechanical ventilation (1). We then collected bronchoalveolar lavage fluid (BALF) from injured and uninjured mice. Purified pericyte-like cells in culture were exposed to growth media only (control), BALF from uninjured mice, and BALF from injured mice for 6 and 24 hours. RNA collected from these treatment conditions were processed for RNAseq. Targets of interest identified by pathway analysis were validated using in vitro and in vivo assays. We observed robust global transcriptional changes in pericyte-like cells following treatment with uninjured and injured BALF at 6 hours, but this response persisted for 24 hours only after exposure to injured BALF. Functional enrichment analysis of pericytes treated with injured BALF revealed the activation of pro-inflammatory, cell migration, and angiogenesisrelated pathways, whereas processes associated with tissue development and cell differentiation were down-regulated. We validated select upregulated targets in the inflammatory, angiogenic, and cell migratory pathways using functional biological assays in vitro and in vivo. We conclude that lung pericyte-like cells are highly responsive to alveolar compartment content from both uninjured and injured lungs, but injured BALF elicits a more sustained response. The inflammatory, angiogenic, and migratory changes exhibited by activated pericyte-like cells underscore the 2 of 16 | HUNG et al.

Effect of lung pericyte-like cell ablation on the bleomycin model of injury and repair

“…Potential mechanisms include directed trafficking of leukocytes across the interstitium via matrix remodeling and upregulation of leukocyte adhesion molecules, similar to what had been shown in cremaster muscle ( 22 ), and upregulation of chemokines ( 23 ). Indeed, we have previously demonstrated that lung pericyte-like cells upregulate proinflammatory processes similar to what has been shown in other organs, including adhesion molecules (e.g., VCAM and ICAM) and cytokines/chemokines (e.g., MCP-1, CXCL1, and IL-6) ( 10 , 11 ). Although the regulation of lung inflammation is beyond the scope of this report, these findings collectively support further investigation into the novel mechanisms by which pericytes direct leukocyte response in the lung.…”

“…They are critical in the development of vasculature during embryonic development and play a role in maintaining endothelial integrity during homeostasis in a number of organs ( 9 ). Recent work by our group demonstrated a role for pericytes as immune regulators in the lung ( 10 , 11 ). The role of pericytes in lung fibrosis remains a much-debated issue.…”

Lung pericytes as mediators of inflammation

“…We demonstrated that primary mouse lung pericytes express functional TLRs 2/1, 2/6, 4, 7, 9 ( 15 ). In response to TLR agonists, lung pericytes upregulate cytokine expression, including chemokines for neutrophils, monocytes and lymphocytes, and adhesion molecule expression in vitro and in vivo ( 15 , 16 ). Furthermore, cultured mouse lung pericytes exposed to alveolar contents from uninjured and sterilely injured lungs [bronchoalveolar lavage fluid (BALF) collected from uninjured and injured mice] induced inflammatory programs in lung pericytes ( 15 ).…”

“…In this review, we focus on the mechanisms by which pericytes activate local inflammatory responses after lung injury. Work from our group, using transgenic models that label mouse lung pericytes, has demonstrated robust inflammatory responses in pericytes and attenuated lung inflammation when pericytes are selectively depleted ( 14 – 16 , 34 ). Although this review focuses on the role of perivascular cells in lung inflammation, studies in extrapulmonary organs, such as the CNS and the heart, reveal similar biological responses to organ injury ( 35 , 36 ).…”

New Insights into the Alveolar Epithelium as a Driver of Acute Respiratory Distress Syndrome

“…This unique location between the epithelium and endothelium may position pericytes to transmit alveolar epithelial-derived injury signals to the endothelium and thereby play a major role in lung injury development. Indeed, recent studies in mice have identified that pericytes function as immune sensors that respond to alveolar epithelial damage by promoting inflammatory cell recruitment [ 115 , 116 , 117 , 118 ].…”