Expression and regulation of steroid metabolizing enzymes in cells of the nervous and skeletal systems

Almokhtar, M. 2018. Expression and regulation of steroid metabolizing enzymes in cells of the nervous and skeletal systems. Special focus on vitamin D metabolism. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy 242. 58 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0154-9. Little is known about the mechanisms of vitamin D actions in the brain and bone. In this study, the metabolism of vitamin D and its regulation in various cell cultures of the nervous and skeletal systems were examined. Human osteosarcoma Saos-2 cells, human primary osteoblasts (hOB) and murine motor neuron-like NSC-34 cells were found to express mRNA for all enzymes required in vitamin D3 metabolism as well as the vitamin D receptor (VDR) that mediates vitamin D actions. Also, production of 24,25-dihydroxyvitamin D3 was found in these cells. Studies on vitamin D metabolism in NSC-34 cells and in primary neuron-enriched cells from rat cerebral cortex indicate formation of a previously unknown major metabolite formed from 25-hydroxyvitamin D3. Evaluation of the NSC-34 cells suggests that this cell line could be a novel model for studies of neuronal vitamin D metabolism and its regulation by endogenous and exogenous compounds. Treatment with glucocorticoids down regulated mRNA expression for the CYP24A1 gene in Saos-2 and hOB cells. Additionally, the glucocorticoid prednisolone showed suppression of CYP24A1-mediated metabolism and CYP24A1 promoter activity in Saos-2 cells. In NSC-34 cells, CYP24A1 mRNA levels were up-regulated by prednisolone, 1α,25-dihydroxyvitamin D3 and its synthetic analogues, EB1089 and tacalcitol. Formation of an endogenous glucocorticoid, 11-deoxycortisol, was observed in Saos-2 cells. Effects of glucocorticoids on the vitamin D system in bone cells may contribute to the adverse side effects in long-term treatment with glucocorticoids. Also, there may be a correlation between the administration of corticosteroids and adverse effects in the CNS. Expression and effects of vitamin D on steroidogenic enzymes were studied in primary neuron-enriched rat cortex cells, primary rat astrocytes and human neuroblastoma SH-SY5Y cells. These different cell cultures all expressed CYP17A1, whereas only astrocytes expressed 3β-hydroxysteroid dehydrogenase (3β-HSD). 1α,25-Dihydroxyvitamin D3 suppressed mRNA levels and enzyme activity of CYP17A1 in SH-SY5Y cells and astrocytes. 1α,25Dihydroxyvitamin D3 suppressed enzyme activity and mRNA levels of 3β-HSD in astrocytes. The results suggest that vitamin D-mediated regulation of CYP17A1 and 3β-HSD may play a role in the nervous system. The results presented here contribute to our understanding of vitamin D metabolism and effects of glucocorticoids in the brain and bone. Mokhtar Almokhtar, Department of Pharmaceutical Biosciences, Box 591, Uppsala University, SE-75124 Uppsala, Sweden. © Mokhtar Almokhtar 2018 ISSN 1651-6192 ISBN 978-91-513-0154-9 urn:nbn:se:uu:diva-333920 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-333920) “Selection is the very keel on which our mental ship is built. And in the case of memory its utility is obvious. If we remembered everything, we should on most occasions be as ill off as if we remembered nothing.” –William James (1890, p.680)