Cigarette smoke decreases mitochondrial porin expression and steroidogenesis

Steroidogenic acute regulatory protein (StAR) facilitates the movement of cholesterol from the outer to inner mitochondrial membrane for steroidogenesis. Here, we investigated the effect of cigarette smoke (CS) on steroidogenesis using adrenal mitochondria isolated from mice chronically exposed to CS. Steroidogenesis was decreased approximately 78% in CS-exposed mitochondria, as measured by synthesis of the steroid hormone precursor pregnenolone. This effect was accompanied by decreased mitochondrial import of 35S-StAR. Further characterization of the imported 35S-StAR by native gradient PAGE revealed the presence of a high molecular weight complex in both control and CS-exposed groups. Following density gradient fractionation of 35S-StAR that had been extracted from control mitochondria, precursor StAR could be found in fractions 2–6 and smaller-sized StAR complexes in fractions 6–13. In the CS-exposed group, the appearance of precursor shifted from fraction 1–6 and the smaller complexes in fractions 6–9 disappeared. Mass spectrometric analysis revealed that the 35S-StAR-associated protein complex was composed of several resident matrix proteins as well as the OMM resident, VDAC. VDAC expression was greatly reduced by CS, and blockage of VDAC with Koenig's polyanion decreased pregnenolone synthesis in isolated mitochondria. Taken together, these results suggest that VDAC may participate in steroidogenesis by promoting StAR interaction with the OMM and that CS may inhibit steroidogenesis by reducing VDAC–StAR interactions.