Organic solute transporter alpha (OSTα)

Organic solute transporter alpha (OSTα, encoded by SLC51A) is a critical component of the OSTα/OSTβ heterodimeric transporter complex, primarily responsible for sodium-independent facilitated transport of bile acids, conjugated steroids (e.g., estrone sulfate, dehydroepiandrosterone sulfate), and structurally related molecules across the basolateral membrane of epithelial cells, especially in the small intestine, liver, and kidney[1][2][4][6][8]. For functional transporter activity, OSTα must heterodimerize with OSTβ (SLC51B)[2][8]; individually, these proteins do not function as transporters. OSTα/OSTβ plays an essential role in the enterohepatic recirculation of bile acids—critical for lipid absorption—and protecting hepatocytes from bile acid toxicity during cholestatic stress[4][8]. Physiologically, gene expression is highest in tissues involved in bile acid handling (intestine, liver, kidney, adrenal gland), and the transporter is regulated by bile acid signaling through nuclear receptors (notably FXR)[4][8]. Genetic deficiency of SLC51A leads to progressive familial intrahepatic cholestasis type 6 (PFIC6), and upregulation of OSTα/β is observed in certain liver diseases such as NASH and cholestasis[6][8]. Interactions with, or inhibition by, drugs can be clinically significant in drug-induced liver injury and modulation of bile acid metabolism[8].

Other names

SLC51AOST-alphaOSTASLC51A1Solute carrier family 51 subunit alphaOrganic solute transporter subunit alphaPFIC6

Facilitation of bile acid and steroid conjugate efflux/uptake via facilitated diffusion, mediated by the OSTα/OSTβ heterodimer Upregulation by farnesoid X receptor agonists (e.g., obeticholic acid induces OSTα/β expression)