Sex-linked Lung Estrobolome May Contribute to Pulmonary Hypertension Penetrance of Bmpr2 R899X Mutation via an ET-1 ^high Endoregulatory Macrophage Phenotype

Mutations in the bone morphogenetic protein receptor 2 (BMPR2) are a major genetic driver of pulmonary arterial hypertension (PAH), yet their penetrance is strikingly sex-biased: females are disproportionately affected, while males experience poorer outcomes. While hormonal and chromosomal factors have been implicated, the biological basis for this disparity remains not fully understood. Here, we investigated the role of the lung microbiome in sex-linked PAH pathogenesis. We hypothesized that increased BMPR2 mutation penetrance in females is partly driven by the accumulation of potent vasoactive molecules, such as endothelin-1 (ET-1), in response to lung microbiome dysbiosis. Using humanized Bmpr2 ^+/R899X mice, we integrate lung metagenomics with basic functional immune profiling to show that females develop a distinct microbiome profile, characterized by increased microbial-derived lipopolysaccharide (LPS), potentially fueling the pathogenic effects of the estrogen metabolite 16α-hydroxyestrone (16α-OHE). These signals converge on macrophages, where co-exposure led to a hyperactivated state characterized by enhanced phagocytosis and ET-1 secretion. Tissue-level analyses confirmed immune cell infiltration and spatial association with elevated ET-1, providing evidence that these factors may contribute to the onset of sex-linked PAH. Taken together, these findings identify a previously unrecognized microbiome-estrogen-immune axis that amplifies BMPR2 dysfunction and provides a mechanistic basis for female-biased disease penetrance.