ESPE Yearbook of Paediatric Endocrinology

Brief Summary: This study investigated the synthesis pathway of pregnenolone (PREG) in the central nervous system. It identified the P450 enzyme CYP1B1 to be responsible for the production of PREG in human glial cells.

Comment: Steroids have important functions in the central and peripheral nervous systems, including modulation of behavior, pain, stress and inflammation. Steroids in the brain can be produced de novo, as well as transported from peripheral tissues (1). Locally produced steroids have genomic actions, and also induce allosteric modulation of neurotransmittor receptors (non-genomic actions).

Pregnenolone (PREG) is an active neurosteroid, and the precursor of other neurosteroids. It has roles in memory formation, neuroplasticity, neuroprotection and has anti-inflammatory properties (2). In clinical trials, PREG shows therapeutic potential in schizophrenia, bipolar depression and chronic pain disorders. However, the biosynthetic pathway of PREG in the brain is unknown. This study investigated the synthesis of PREG in the central nervous system (CNS).

Previously, these authors found very low mRNA levels in human brain of CYP11A1 and undetectable protein levels of CYP11A1, the enzyme responsible for PREG biosynthesis in the adrenal gland (3), indicating that another enzyme has this role in the brain. They used qRT-PCR in human glial cell lines to screen for other CYP450s that might synthesize PREG and identified CYP27A1, CYP1A1 and CYP1B1 as potential candidates. They excluded CYP27A1, since its inhibition or siRNA knock-down did not affect the levels of PREG.

Of the other two candidate enzymes, CYP1B1 but not CYP1A1 was found to produce PREG in glial cells but not in adrenal cells. They came to this conclusion with a series of experiments utilizing enzyme inhibitors, siRNA knock-down experiments and over-expression of CYP1B1 in glial cells. To understand from which substrate PREG is formed, they transfected the cells with cholesterol (LDL). In the cell line where CYP1B1 protein was localized to the mitochondria, there was a dose-dependent increase in PREG production, showing that PREG synthesis can use cholesterol as a substrate.

In conclusion, this study identifies the synthesis pathway of PREG in the CNS, involving the P450 enzyme CYP1B1 and both hydroxycholesterol and cholesterol as substrates. This pathway differs from classical adrenal steroidogenesis. Consideration should be taken when using drugs that pass the blood-brain barrier and compete with the CYP1B1 substrates since this could affect brain function.

References: 1. Baulieu EE. Neurosteroids: a novel function of the brain. Psychoneuroendocrinology. 1998; 23(8): 963-87.2. Lin YC, Cheung G, Espinoza N, Papadopoulos V. Function, regulation, and pharmacological effects of pregnenolone in the central nervous system. Curr. Opin. Endocr. Metab. Res. 2022; 22: 1003103. Lin YC, Cheung G, Porter E, Papadopoulos V. The neurosteroid pregnenolone is synthesized by a mitochondrial P450 enzyme other than CYP11A1 in human glial cells. J Biol Chem. 2022; 298(7): 102110.