Resident PW1⁺ progenitor cells participate in vascular remodeling during pulmonary arterial hypertension

Rationale: Pulmonary arterial hypertension is characterized by vascular remodeling and neomuscularization. PW1⁺ progenitor cells can differentiate into smooth muscle cells (SMCs) in vitro. Objective: To determine the role of pulmonary PW1⁺ progenitor cells in vascular remodeling characteristic of pulmonary arterial hypertension. Methods and Results: We investigated their contribution during chronic hypoxia-induced vascular remodeling in Pw1nLacZ⁺/-mouse expressing β-galactosidase in PW1⁺ cells and in differentiated cells derived from PW1⁺ cells. PW1⁺ progenitor cells are present in the perivascular zone in rodent and human control lungs. Using progenitor markers, 3 distinct myogenic PW1⁺ cell populations were isolated from the mouse lung of which 2 were significantly increased after 4 days of chronic hypoxia. The number of proliferating pulmonary PW1⁺ cells and the proportion of β-gal⁺ vascular SMC were increased, indicating a recruitment of PW1⁺ cells and their differentiation into vascular SMC during early chronic hypoxia-induced neomuscularization. CXCR4 inhibition using AMD3100 prevented PW1⁺ cells differentiation into SMC but did not inhibit their proliferation. Bone marrow transplantation experiments showed that the newly formed β-gal⁺ SMC were not derived from circulating bone marrow-derived PW1⁺ progenitor cells, confirming a resident origin of the recruited PW1⁺ cells. The number of pulmonary PW1⁺ cells was also increased in rats after monocrotaline injection. In lung from pulmonary arterial hypertension patients, PW1-expressing cells were observed in large numbers in remodeled vascular structures. Conclusions: These results demonstrate the existence of a novel population of resident SMC progenitor cells expressing PW1 and participating in pulmonary hypertension-associated vascular remodeling.