The Cholesterol Side‐Chain Cleavage Complex in Human Brain White Matter

Abstract

Specific antibodies obtained in rabbits after injection of bovine cholesterol side-chain cleavage enzymes cytochrome P -~~O S C C , adrenodoxin and adrenodoxin-reductase were used for immunohistochemical studies in human brain. The three enzymes were co-localized in the white matter of the cerebellum. This observation strongly suggests the existence of steroidogenic activity in human oligodendrocytes, as previously reported in the rat, and suggests that the concept of 'neurosteroids' can be applied to A5-38-hydroxysteroid metabolites of cholesterol that accumulate in human brain.Two A5-3P-hydroxysteroid metabolites of cholesterol, pregnenolone (P) and deliydroepiandrosterone (D), have been detected in the brain of several mammalian species (rat, mouse, monkey and occasionally pig and man) (1-3). Definitive identification of the steroid moiety was made in rat brain extracts by gas/liquid chromatography-mass spectrometry (1, 2). These A5-38-hydroxysteroids persisted in brain after removal of steroidogenic organs, and we therefore proposed that their formation and/or accumulation in the brain depends on in situ mechanisms unrelated to the peripheral endocrine gland system. P is the key steroid synthesized from cholesterol in steroidogenic glands. The oxidative side-chain cleavage of cholesterol is operated by a specific enzyme complex, which includes cytochrome P -~~O S C C , adrenodoxin-reductase (Red) and adrenodoxin (Adx) (4). We have used specific antibodies to the bovine adrenal cytochrome P-45Oscc for the immunohistochemical localization of the enzyme in the adult rat brain, and we have found that the white matter was selectively immunostained throughout the brain ( 5 ) . Since the myelin of the white matter is made by a particular type of glial cell, the oligodendrocyte, we have isolated oligodendrocyte mitochondria, incubated them with The concentrations of P and D have been measured in human brains removed at autopsy 5 to 24 h post-mortem (7, 8). The values for P, D and their sulfate esters are much higher than those of the sex steroids in all areas of the brain and in the same range as those reported in the rat (1,2). The values for unconjugated P and D are much higher than their respective values in plasma. Hence, it was tempting to speculate that human brain is capable of de novo biosynthesis of steroids, as reported for the rat brain. Thus, we have attempted to localize, with the immunoperoxidase technique, cytochrome P-45Oscc, Adx and Red in human brain. We used specific antibodies to the adrenal enzymes of cattle origin. Though there are marked structural homologies between bovine and human side-chain cleavage enzymes, we first checked, using a testis sample, that available antibodies could be used for immunohistochemical staining of human tissues. Resu Its The human testisThe Leydig cells were strongly immunostained with the anticytochrome P-45Oscc IgGs, in contrast to the seminiferous tubules which served as control of tissue specificity (Fig. IA). A similar immunoperoxidase staining was ob...

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