Biology subjects

Covey, D. F.

Publications and source records attributed to Covey, D. F..

21 records · Page 2Linked to original sources

bioRxiv2020

Site-specific effects of neurosteroids on GABAA receptor activation and desensitization

This study examines how site-specific binding to the three identified neurosteroid binding sites in the 1{beta}3 GABAA receptor (GABAAR) contributes to neurosteroid allosteric modulation. We found that the potentiating neurosteroid, allopregnanolone, but not its inhibitory 3{beta}-epimer epi-allopregnanolone, binds to the canonical {beta}3(+)-1(-) intersubunit site that mediates receptor activation by neurosteroids. In contrast, both allopregnanolone and epi-allopregnanolone bind to intrasubunit sites in the {beta}3 subunit, promoting receptor desensitization and the 1 subunit promoting ligand-specific effects. Two neurosteroid analogues with diazirine moieties replacing the 3-hydroxyl (KK148 and KK150) bind to all three sites, but do not potentiate GABAAR currents. KK148 is a desensitizing agent, whereas KK150 is devoid of allosteric activity. These compounds provide potential chemical scaffolds for site-specific and general neurosteroid antagonists. Collectively, these data show that differential occupancy and efficacy at three discrete neurosteroid binding sites determine whether a neurosteroid has potentiating, inhibitory, or competitive antagonist activity on GABAARs.

biophysics↗

bioRxiv2020

25-Hydroxycholesterol amplifies microglial IL-1β production in an apoE isoform-dependent manner

Genome-wide association studies associated with Alzheimers disease (AD) have implicated pathways related to both lipid homeostasis and innate immunity in the pathophysiology of AD. However, the exact cellular and chemical mediators of neuroinflammation in AD remain poorly understood. The oxysterol 25-hydroxycholesterol (25-HC) is an important immunomodulator produced by peripheral macrophages with wide-ranging effects on cell signaling and innate immunity. Genetic variants of the enzyme responsible for 25-HC production, cholesterol 25-hydroxylase (CH25H), have been found to be associated with AD. In the present study, we found that the CH25H expression is upregulated in human AD brain tissue and in transgenic mouse brain tissue bearing amyloid-{beta} (A{beta}) plaques or tau pathology. Treatment with the toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS) markedly upregulates CH25H expression in the mouse brain in vivo. LPS also stimulates CH25H expression and 25-HC secretion in cultured mouse primary microglia. We also found that LPS-induced microglial production of the pro-inflammatory cytokine IL1{beta} is markedly potentiated by 25-HC and attenuated by genetic deletion of CH25H. Microglia expressing apolipoprotein E4 (apoE4), a genetic risk factor for AD, produce greater amounts of 25-HC than apoE3-expressing microglia following treatment with LPS. Remarkably, treatment of microglia with 25-HC results in a much greater level of IL1{beta} secretion in LPS-activated apoE4-expressing microglia than in apoE2- or apoE3-expressing microglia. Blocking potassium efflux or inhibiting caspase-1 prevents 25-HC-potentiated IL1{beta} release in apoE4-expressing microglia, indicating the involvement of caspase-1/NLRP3 inflammasome activity. 25-HC may function as a microglial secreted inflammatory mediator in brain, promoting IL1{beta}-mediated neuroinflammation in an apoE isoform-dependent manner (E4>>E2/E3) and thus may be an important mediator of neuroinflammation in AD.

neuroscience↗

bioRxiv2018

Multiple Functional Neurosteroid Binding Sites on GABAA Receptors

Neurosteroids are endogenous modulators of neuronal excitability and nervous system development and are being developed as anesthetic agents and treatments for psychiatric diseases. While GABAA receptors are the primary molecular targets of neurosteroid action, the structural details of neurosteroid binding to these proteins remain ill-defined. We synthesized neurosteroid analogue photolabeling reagents in which the photolabeling groups were placed at three positions around the neurosteroid ring structure, enabling identification of binding sites and mapping of neurosteroid orientation within these sites. Using middle-down mass spectrometry, we identified three clusters of photolabeled residues representing three distinct neurosteroid binding sites in the human 1{beta}3 GABAA receptor. Novel intrasubunit binding sites were identified within the transmembrane helical bundles of both the 1 and {beta}3 subunits, adjacent to the extracellular domains. An intersubunit site in the interface between the {beta}3(+) and 1(-) subunits of the GABAA receptor pentamer was also identified. Computational docking studies of neurosteroid to the three sites predicted critical residues contributing to neurosteroid interaction with the GABAA receptors. Electrophysiological studies based on these predictions indicate that both the 1 intrasubunit and {beta}3-1 intersubunit sites are critical for neurosteroid action.

neuroscience↗