Dynamic Microenvironmental Stiffness and Serum Composition Modulate Sex-Specific Pulmonary Artery Adventitial Fibroblast Activation

Pulmonary arterial hypertension (PAH) is a non-reversable condition that causes stiffening and narrowing of the pulmonary arteries. Many factors have been correlated with the initiation of pulmonary vascular remodeling in PAH. Female patients are more susceptible to, but have increased survival for, PAH, which the underlying mechanisms are not fully understood. This study focuses on human pulmonary arterial adventitial fibroblast (hPAAF) activation, which increases production of extracellular matrix proteins and microenvironmental stiffness in the pulmonary arteries. Here, we employed soft hydrogels that were dynamically stiffened to observe how the age and sex of human serum influenced hPAAF activation in response to microenvironmental stiffening. Results showed female and male cells responded differently to increases in microenvironmental stiffness and serum composition. Female hPAAF activation was relatively high on both soft and stiffened hydrogels, with little difference in activation between the two conditions, unless cultured in younger (age < 50) female serum. Male hPAAFs were less activated than female cells on soft hydrogels and less responsive to increases in microenvironmental stiffness regardless of serum composition. Increased circulating sex-hormone concentrations decreased activation on soft hydrogels, while increasing activation on stiffened hydrogels. Male-cell activation was highly influenced by progesterone, which was measured to be high in the commercially available fetal bovine serum tested here. Collectively, these results suggest that it may be possible to model the estrogen paradox observed in PAH in vitro and that it is critical for researchers to report cell sex and serum source when conducting in vitro experimentation.