Characterization of human PDGFR-β-positive pericytes from IPF and non-IPF lungs.

Pericytes are key regulators of the microvasculature through their close interactions with the endothelium. However, pericytes play additional roles in tissue homeostasis and repair, in part by transitioning into myofibroblasts. Accumulation of myofibroblasts is a hallmark of fibrotic diseases such as idiopathic pulmonary fibrosis (IPF). To understand the contribution and role of pericytes in human lung fibrosis, we isolated these cells from non-IPF control and IPF lung tissues based on expression of platelet-derived growth factor receptor-β (PDGFR-β), a common marker of pericytes. When cultured in a specialized growth medium, PDGFR-β+ cells retain the morphology and marker profile typical of pericytes. We found that IPF pericytes migrated more rapidly and invaded a basement membrane matrix more readily than control pericytes. Exposure of cells to transforming growth factor-β, a major fibrosis-inducing cytokine, increased expression of α-smooth muscle actin and extracellular matrix genes in both control and IPF pericytes. Given that pericytes are uniquely positioned in vivo to respond to danger signals of both systemic and tissue origin, we stimulated human lung pericytes with agonists having pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). Both control and IPF lung pericytes increased expression of proinflammatory chemokines in response to specific PAMPs and DAMPs released from necrotic cells. Our results suggest that control and IPF lung pericytes are poised to react to tissue damage, as well as microbial and fibrotic stimuli. However, IPF pericytes are primed for migration and matrix invasion, features that may contribute to the function of these cells in lung fibrosis.