Adventitial Fibrosis and Fibroblast Mechanosensitivity Are Shaped by Sex and Hormonal Status in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is marked by vascular remodeling, yet the role of adventitial fibrosis-and its modulation by sex and hormonal status-remains unclear. We examined stage-specific adventitial remodeling and pulmonary artery adventitial fibroblast (PAAF) mechanosensitivity in male, ovary-intact female, and ovariectomized (OVX) female Sprague-Dawley rats with SuHx-induced PAH. Hemodynamics, pulmonary artery histology, and adventitia-specific transcriptional profiling were integrated with in vitro assays of PAAFs exposed to defined substrate stiffness and stretch. All groups developed comparable increases in mean pulmonary arterial pressure, but vascular resistance shift and adventitial fibrosis diverged by sex: intact females showed attenuated increase in pulmonary vascular resistance and transient collagen accumulation, whereas OVX females mirrored the sustained, male-like progression. Extracellular matrix (ECM) gene activation occurred without smooth muscle actin induction, suggesting noncanonical fibrotic pathways. In vitro, intact female PAAFs required higher substrate stiffness to induce profibrotic gene expression, indicating a hormone-modulated stiffness threshold. OVX PAAFs showed persistent transcriptional reprogramming, while stretch-induced ECM upregulation occurred predominantly in male-derived PAAFs. These findings demonstrate that adventitial fibrosis in PAH is shaped by both hormonal and chromosomal sex, independent of hemodynamic severity, and highlight fibroblast mechanosensitivity as a potential target for stage- and sex-specific interventions.