Neurosteroid Hydroxylase CYP7B

Abstract

The major adrenal steroid dehydroepiandrosterone (DHEA) enhances memory and immune function but has no known dedicated receptor; local metabolism may govern its activity. We described a cytochrome P450 expressed in brain and other tissues, CYP7B, that catalyzes the 7␣-hydroxylation of oxysterols and 3␤-hydroxysteroids including DHEA. We report here that CYP7B mRNA and 7␣-hydroxylation activity are widespread in rat tissues. However, steroids related to DHEA are reported to be modified at positions other than 7␣, exemplified by prominent 6␣-hydroxylation of 5␣-androstane-3␤,17␤-diol (A/anediol) in some rodent tissues including brain. To determine whether CYP7B is responsible for these and other activities we disrupted the mouse Cyp7b gene by targeted insertion of an IRES-lacZ reporter cassette, placing reporter enzyme activity (␤-galactosidase) under Cyp7b promoter control. In heterozygous mouse brain, chromogenic detection of reporter activity was strikingly restricted to the dentate gyrus. Staining did not exactly reproduce the in situ hybridization expression pattern; post-transcriptional control is inferred. Lower level staining was detected in cerebellum, liver, and kidney, and which largely paralleled mRNA distribution. Liver and kidney expression was sexually dimorphic. Mice homozygous for the insertion are viable and superficially normal, but ex vivo metabolism of DHEA to 7␣-hydroxy-DHEA was abolished in brain, spleen, thymus, heart, lung, prostate, uterus, and mammary gland; lower abundance metabolites were also eliminated. 7␣-Hydroxylation of 25-hydroxycholesterol and related substrates was also abolished, as was presumed 6␣-hydroxylation of A/anediol. These different enzyme activities therefore derive from the Cyp7b gene. CYP7B is thus a major extrahepatic steroid and oxysterol hydroxylase and provides the predominant route for local metabolism of DHEA and related molecules in brain and other tissues.Brain function is subject to hormonal control, notably by steroids synthesized from the adrenal glands and gonads. Accumulating evidence also points to local steroid synthesis and metabolism in brain; a growing field of investigation focuses on the biological role of brain-active steroids, or "neurosteroids" (1-5). Attention has focused on the major adrenal steroid in primates, dehydroepiandrosterone (DHEA), 1 in view of a possible link with cognitive aging and immunosenescence. DHEA and related steroids, including pregnenolone, have memoryenhancing properties in rodents (6 -8) as well as immunostimulatory effects (9 -11). In primates, levels of DHEA and its sulfate (DHEAS) decline asymptotically with age (12-14). A causal relationship with age-related physiological impairments has been debated (15, 16). Because DHEA replacement therapy has brought mixed results (15,(17)(18)(19), and no dedicated receptor has been described for DHEA, its bioactivity may require local metabolism.B-ring hydroxylation is a major metabolic route for 3␤-hydroxysteroids, including DHEA and pregnenolone, in diverse tissues includ...

Early onset of puberty and early ovarian failure in CYP7B1 knockout mice

“…We have shown previously that the prostates, brains and pituitaries of the CYP7B1 Ϫ/Ϫ mice have lost the capacity to metabolize 3␤Adiol to triols (12). We found that the uteri and mammary glands of CYP7B1 Ϫ/Ϫ female mice have characteristics of tissues chronically exposed to estrogen.…”

“…CYP7B1 Ϫ/Ϫ mice, on a C57BL͞6J background, were provided by Richard Lathe (Pieta Research) (12). C57BL͞6J WT mice were from our colony, maintained in Huddinge University Hospital Animal Facility.…”

“…Its functions in the brain (7,8) and prostate (9)(10)(11) were studied for many years before it was identified as CYP7B1 (12). Analysis of mRNA from various tissues has revealed that, in addition to the brain, prostate, and pituitary, CYP7B1 was also expressed in urogenital organs, such as testis and ovary (12).…”

Estrogen receptor α and imprinting of the neonatal mouse ventral prostate by estrogen

“…ER␤ Ϫ/Ϫ mice from our colony were used (13). ER␣ Ϫ/Ϫ mice were purchased from Taconic, and CYP7B1 Ϫ/Ϫ mice were provided by Richard Lathe (Centre for Genome Research and Centre for Neuroscience, University of Edinburgh, Edinburgh, U.K.) (14) and were bred in our laboratory. These animals were housed in Huddinge University Hospital Animal Facility in a controlled environment on a 12-h light͞12-h dark illumination schedule and fed a standard pellet diet with water provided ad libitum.…”

CYP7B1: One Cytochrome P450, Two Human Genetic Diseases, and Multiple Physiological Functions

“…The human mRNA is present in many organs, with the highest levels detected in kidney and brain (6). The mRNA is also widely distributed among different rat tissues (7). Expression is restricted to the liver, lung, kidney, brain, and reproductive tract in the mouse, with the amount of mRNA being highest in liver and lung.…”