Investigating the Mechanisms of Cholesterol 25-Hydroxylase in Promoting Pulmonary Fibrosis

Abstract

Pulmonary fibrosis is a chronic and fatal disease characterized by progressive lung scarring. In many cases, its etiology is not fully understood, and treatment options are limited due to the complexity of profibrotic signaling pathways and the interplay between multiple cell types involved in the pathogenesis. Emerging studies have linked disruptions in lipid metabolism to pulmonary fibrosis, though the underlying mechanisms remain poorly defined, and some studies have reported contradictory findings. Our lab recently identified that cholesterol 25-hydroxlase (CH25H), an enzyme that converts cholesterol to 25-hydroxycholesterol (25-HC), promotes lung fibrosis elicited by diverse exposures including the common aeroallergen Alternaria Alternata and the chemotherapeutic agent bleomycin. To further understand the cellular and molecular mechanism(s) by which this occurs, we assessed the function of 25-HC in murine lung in vivo and in human fibroblasts in vitro. We found that 25-HC upregulates type 1 collagen expression in murine lungs and in human lung fibroblasts, suggesting that it promotes the activation of fibroblasts to myofibroblasts, a pathological cell state that readily remodels and stiffens the extracellular matrix. We showed that 25-HC-induced collagen upregulation in human lung fibroblasts is dependent on RORa activation, and also likely involves LXR and av integrin/FAK activation. Furthermore, CH25H is upregulated in lung fibrobalsts by several pro-fibrotic factors including TGF-β1, bleomycin, and the type 2 inflammatory cytokines IL-4 and IL- 13. Collectively, our findings suggest that CH25H drives pulmonary fibrosis through promoting lung fibroblast activation via the 25-HC/RORa axis. This potentially suggests a novel mechanism through which dysregulated cholesterol metabolism exacerbates pulmonary fibrosis and may offer new therapeutic targets for the disease.