Endogenous neurosteroids regulate GABAA receptors through two discrete transmembrane sites

Abstract

Inhibitory neurotransmission mediated by GABA(A) receptors can be modulated by the endogenous neurosteroids, allopregnanolone and tetrahydro-deoxycorticosterone. Neurosteroids are synthesized de novo in the brain during stress, pregnancyand after ethanol consumption, and disrupted steroid regulation of GABAergic transmission is strongly implicated in several debilitating conditions such as panic disorder, major depression, schizophrenia, alcohol dependence and catamenial epilepsy. Determining how neurosteroids interact with the GABA(A) receptor is a prerequisite for understanding their physiological and pathophysiological roles in the brain. Here we identify two discrete binding sites in the receptor's transmembrane domains that mediate the potentiating and direct activation effects of neurosteroids. They potentiate GABA responses from a cavity formed by the alpha-subunit transmembrane domains, whereas direct receptor activation is initiated by interfacial residues between alpha and beta subunits and is enhanced by steroid binding to the potentiation site. Thus, significant receptor activation by neurosteroids relies on occupancy of both the activation and potentiation sites. These sites are highly conserved throughout the GABA(A )receptor family, and their identification provides a unique opportunity for the development of new therapeutic, neurosteroid-based ligands and transgenic disease models of neurosteroid dysfunction.

The role of GABAA receptors in the development of alcoholism

“…Binding sites for GABA (two copies) lies at the interface between α and β (Olsen et al, 2004). Ethanol-and stress-induced neurosteroids potentiate GABA at a binding site located in a cavity formed by α subunit TM domains (Hosie et al, 2006).…”

Steroid modulation of GABAA receptor-mediated transmission in the hypothalamus: Effects on reproductive function

“…Mutational analysis of recombinant α 1 β 2 γ 2 receptors indicates that four transmembrane residues in the α 1 subunit are critical for both potentiation and direct activation of the receptor by the positive neurosteroids (Hosie et al, 2006). These residues are conserved among the α and β subunit family members (Hosie et al, 2006), suggesting substitution of different α or β family members within the 2α2βγ complex may not result in drastically different functional effects of the positive neurosteroids.…”

“…These residues are conserved among the α and β subunit family members (Hosie et al, 2006), suggesting substitution of different α or β family members within the 2α2βγ complex may not result in drastically different functional effects of the positive neurosteroids. This conclusion is supported by electrophysiological studies indicating that changes in α or β subunit composition have only a modest effect on positive neurosteroid potentiation.…”

Neurosteroid Agonist at GABAA Receptor Induces Persistent Neuroplasticity in VTA Dopamine Neurons

“…The cerebellum and striatum expressing a high density of dsubunits are strongly involved in motor control as reviewed in Uusi-Oukari and . In both of these regions, compensatory GABA A receptor changes are known to take place in the d-KO mice (Korpi et al, 2002;Peng et al, 2002), thus preserving the main molecular targets for the neurosteroids (Hosie et al, 2006) also in the absence of the d-subunit. Second, similar to locomotion, both genotypes displayed identical hypothermic response to GAN.…”

“…Neurosteroids act on the GABA A receptor at distinct sites not overlapping with the binding sites of GABA, benzodiazepines, or barbiturates (Gee et al, 1995). Several conserved amino-acid residues responsible for their effects have been located in recombinant GABA A receptor a-and b-subunits (Hosie et al, 2006). Interestingly, the effects of neurosteroids are often abolished in mice deficient in d-subunit-containing GABA A receptors (Mihalek et al, 1999), which are primarily located peri-and extrasynaptically (Nusser et al, 1998).…”