Uncovering novel protein pathways regulating bioavailable testosterone through sex hormone-binding globulin.

Bioavailable testosterone (BAT), a critical factor for reproductive, metabolic, and psychological health, is primarily regulated by sex hormone-binding globulin (SHBG). However, the molecular mechanisms driving SHBG-mediated regulation of BAT remain unclear. Identifying key protein regulators offers promising therapeutic opportunities for testosterone-related disorders. We conducted a comprehensive proteome-wide Mendelian randomization (PWMR) and colocalization analysis using large-scale pQTL and GWAS datasets. Mediation MR assessed SHBG's role in regulating BAT, and functional enrichment, protein interaction networks, phenome-wide association studies (PheWAS), and drug prediction were performed to explore therapeutic relevance and safety. We identified 36 proteins that influence BAT via SHBG mediation. Among them, five proteins (MAX, TXNL4B, GLRX2, F13B, SNUPN) showed strong or moderate colocalization with BAT, suggesting shared genetic regulation. MAX and TXNL4B increased BAT by reducing SHBG, while GLRX2, F13B, and SNUPN decreased BAT via elevated SHBG levels. PheWAS suggested potential risks for GLRX2 (depression) and TXNL4B (lipid disorders). Drug and compound prediction highlighted compounds, including cardiac glycosides, antioxidants, and endocrine-disrupting chemicals, targeting these proteins. Our findings reveal novel protein regulators of testosterone bioavailability through SHBG and provide a framework for developing targeted therapeutics. This integrative approach may support safer, more precise treatment strategies for testosterone-related metabolic and endocrine disorders.