Characterization of brain neurons that express enzymes mediating neurosteroid biosynthesis

Abstract

Allopregnanolone (ALLO) and tetrahydrodeoxycorticosterone (THDOC) are potent positive allosteric modulators of GABA action at GABAA receptors. ALLO and THDOC are synthesized in the brain from progesterone or deoxycorticosterone, respectively, by the sequential action of two enzymes: 5␣-reductase (5␣-R) type I and 3␣-hydroxysteroid dehydrogenase (3␣-HSD). This study evaluates 5␣-R type I and 3␣-HSD mRNA expression level in mouse brain by using in situ hybridization combined with glutamic acid decarboxylase 67͞65, vesicular glutamate transporter 2, glial fibrillary acidic protein, and S100␤ immunohistochemistry. We demonstrate that 5␣-R type I and 3␣-HSD colocalize in cortical, hippocampal, and olfactory bulb glutamatergic principal neurons and in some output neurons of the amygdala and thalamus. Neither 5␣-R type I nor 3␣-HSD mRNAs are expressed in S100␤-or glial fibrillary acidic protein-positive glial cells. Using glutamic acid decarboxylase 67͞65 antibodies to mark GABAergic neurons, we failed to detect 5␣-R type I and 3␣-HSD in cortical and hippocampal GABAergic interneurons. However, 5␣-R type I and 3␣-HSD are significantly expressed in principal GABAergic output neurons, such as striatal medium spiny, reticular thalamic nucleus, and cerebellar Purkinje neurons. A similar distribution and cellular location of neurosteroidogenic enzymes was observed in rat brain. Taken together, these data suggest that ALLO and THDOC, which can be synthesized in principal output neurons, modulate GABA action at GABAA receptors, either with an autocrine or a paracrine mechanism or by reaching GABAA receptor intracellular sites through lateral membrane diffusion.3␣-hydroxysteroid dehydrogenase ͉ 5␣-reductase (type I) ͉ GABAergic neurons ͉ glutamatergic neurons T he neurosteroids 3␣-hydroxy-5␣-pregnan-20-one [allopregnanolone (ALLO)] and 3␣,21-dihydroxy-5␣-pregnan-20-one [tetrahydrodeoxycorticosterone (THDOC)] are potent positive allosteric modulators of GABA action at GABA A receptors (1-6). These neurosteroids can be synthesized in the brain from progesterone (7) or deoxycorticosterone (8, 9), respectively, by the sequential action of two enzymes, 5␣-reductase (5␣-R) type I and 3␣-hydroxysteroid dehydrogenase (3␣-HSD) (10).Two types (I and II) of 5␣-Rs, which convert progesterone into 5␣-dihydroprogesterone (5␣-DHP) or convert deoxycorticosterone into 5␣-dihydrodeoxycorticosterone (5␣-DHDOC), have been identified in tissues of rodents and humans (11). Whereas 5␣-R type I and II are abundantly expressed in several peripheral tissues, 5␣-R type I is the most abundant 5␣-R molecular form detected in the adult brains of rats, mice, and humans (11-17). The human brain expresses four types of 3␣-HSD, which, under different optimal conditions, either catalyze the reduction of 5␣-DHP into ALLO or reverse this reaction (18). So far, only one 3␣-HSD isoform has been identified in the rat or mouse brain (19)(20)(21)(22). The mRNA sequences of 5␣-R type I (Ϸ88%) and 3␣-HSD (Ϸ89%) are highly homologous in mouse (5␣-R type I GeneBank access...

Pomegranate polyphenols down-regulate expression of androgen-synthesizing genes in human prostate cancer cells overexpressing the androgen receptor

“…It has previously been shown that mRNA levels of the enzymes are correlated with protein amounts and activities in other studies [46][47][48][49][50] so we did not repeat these studies.…”

Ethanol Alters Local Cellular Levels of (3α,5α)-3-Hydroxypregnan-20-one (3α,5α-THP) Independent of the Adrenals in Subcortical Brain Regions

“…This pattern of 3a,5a-THP expression corresponds with expression of the biosynthetic enzymes 5a-R and 3a-HSD needed for 3a,5a-THP synthesis and metabolism (Agis-Balboa et al, 2006). Therefore, it has been suggested that a major role of 3a,5a-THP may be to modulate neurocircuitry.…”

Mechanisms of neurosteroid interactions with GABAA receptors

“…Given the preference of steroids to affiliate with intracellular and plasma membranes, another implication of these considerations is that autocrine/paracrine actions of endogenous steroids may be particularly important. Recently, it has been suggested that neurosteroid synthetic enzymes are localized within principal, projection neurons in many CNS regions, but not in interneurons (Agis-Balboa et al, 2006). If autocrine actions are particularly important because of lipophilic retention, then we might expect cell-specificity in the actions of endogenous steroids.…”