Sex-related external factors influence pulmonary vascular angiogenesis in a sex-dependent manner.

Bronchopulmonary dysplasia (BPD) is a disease with a significant sexual dimorphism where males have a disadvantage compared with their female counterparts. Although mechanisms behind this sexual dimorphism are poorly understood, sex differences in angiogenesis have been identified as one possible source of the male disadvantage in BPD. Pulmonary angiogenesis was assessed in vitro using a bead sprouting assay with pooled male or female human pulmonary microvascular endothelial cells (HPMECs, 18-19 wk gestation, canalicular stage of human lung development) in standard (sex-hormone containing) and hormone-stripped medium. We identified sex-specific phenotypes in angiogenesis where male HPMECs produce fewer but longer sprouts compared with female HPMECs. The presence of sex hormones from standard culture medium modifies the male HPMEC phenotype with shorter and fewer sprouts but does not influence the female phenotype. Using a conditioned medium model, we further characterized the influence of the sex-specific secretome. Male and female HPMECs secrete factors that increase the maximum length of sprouts in female, but not male HPMECs. The presence of sex hormones abolishes this response. The male HPMEC secretome inhibits angiogenic sprouting in male HPMECs in the absence of sex hormones. Taken together, these results demonstrate that the pulmonary endothelial cell phenotypes are influenced by sex hormones and sex-specific secreted factors in a sex-dependent manner. We identified a sex-specific phenotype wherein male HPMECs produce fewer but longer sprouts than females. Surprisingly, the presence of sex hormones only modifies the male phenotype, resulting in shorter and even fewer sprouts. Furthermore, we found the sex-specific secretome has a sex-dependent influence on angiogenesis that is also sex-hormone sensitive. These new and surprising findings point to the unappreciated role of sex and sex-related exogenous factors in early developmental angiogenesis.