The skin and sebaceous glands are capable of synthesizing cholesterol de novo from acetate (22-24). Although this cholesterol is utilized in cell membranes, in the formation of the epidermal barrier, and is secreted in sebum, its use as a substrate for steroid hormone synthesis had not been established until recently. In order for steroid synthesis to occur, cholesterol needs to be translocated from the outer to the inner mitochondrial membrane. This process is regulated by the steroidogenic acute regulatory protein (25). Additional enzymes and cofactors needed to convert cholesterol into a steroid include P450 cholesterol side chain cleavage, adrenodoxin reductase, cytochrome P450c17, and steroidogenic factor-1. Expression of each of these proteins was found in human facial skin, sebocytes, and in a recently developed simian virus (SV) 40-immortalized human sebocyte cell line (SEB-1) (26). These data demonstrate that the skin is in fact a steroidogenic tissue. The clinical significance of this finding in mediating androgenic skin disorders such as acne, hirsutism, or androgenetic alopecia remains to be established.
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