Effects of neurosteroids on a model membrane including cholesterol: A micropipette aspiration study

Abstract

Amphiphilic molecules supposed to affect membrane protein activity could strongly interact also with the lipid component of the membrane itself. Neurosteroids are amphiphilic molecules that bind to plasma membrane receptors of cells in the central nervous system but their effect on membrane is still under debate. For this reason it is interesting to investigate their effects on pure lipid bilayers as model systems. Using the micropipette aspiration technique (MAT), here we studied the effects of a neurosteroid, allopregnanolone (3α,5α-tetrahydroprogesterone or Allo) and of one of its isoforms, isoallopregnanolone (3β,5α-tetrahydroprogesterone or isoAllo), on the physical properties of pure lipid bilayers composed by DOPC/bSM/chol. Allo is a well-known positive allosteric modulator of GABAA receptor activity while isoAllo acts as a non-competitive functional antagonist of Allo modulation. We found that Allo, when applied at nanomolar concentrations (50-200 nM) to a lipid bilayer model system including cholesterol, induces an increase of the lipid bilayer area and a decrease of the mechanical parameters. Conversely, isoAllo, decreases the lipid bilayer area and, when applied, at the same nanomolar concentrations, it does not affect significantly its mechanical parameters. We characterized the kinetics of Allo uptake by the lipid bilayer and we also discussed its aspects in relation to the slow kinetics of Allo gating effects on GABAA receptors. The overall results presented here show that a correlation exists between the modulation of Allo and isoAllo of GABAA receptor activity and their effects on a lipid bilayer model system containing cholesterol.

Exploring the Impact of the Microbiome on Neuroactive Steroid Levels in Germ-Free Animals

“…Both steroid hormones and neurosteroids, which are both found in the nervous system, are collectively referred to as neuroactive steroids and are important physiological regulators of nervous system functioning [23]. In particular, DHP controls reproductive functions, as well as glutamatergic and GABAergic neurotransmission [24], whereas isoallopregnanolone influences the lipid bilayer model system containing cholesterol [25,26]. In the brain, androgen molecules have been shown to regulate dendritic spine maturation [27,28], behaviour [29,30], neurite growth [31], neurogenesis and neuronal survival [32], apoptosis [33] and catecholamine production [34].…”

Neurosteroids as novel antidepressants and anxiolytics: GABA-A receptors and beyond

“…Studies of enantiomeric steroids are important because enantiomers (unlike stereoisomers) have identical physico-chemical properties, including logP, and differ only in their rotation of polarized light (Alakoskela et al, 2007). Studies of NAS enantiomers provided the first strong evidence that NAS interact with chiral (likely protein) sites rather than exerting effects by changes in membrane properties, even though 5α-reduced steroids increase the liquid disordered state of membranes resulting in higher lateral membrane mobility (Balleza et al, 2015; Sacchi et al, 2015). Using fluorescent enantiomeric steroids, Chisari et al (2009) found that only NAS with the natural configuration of natural neurosteroids were able to potentiate GABA currents while both enantiomers accumulated identically in cell membranes and intracellular compartments.…”

A study of the initial adhesive force of cells on silk fibroin-based materials using micropipette aspiration

“…Micropipette aspiration technique was utilized to investigate the adhesive force of a single cell quantitatively. However, some of these studies have technical difficulties, such as the need for protein scaffolding of the cells to avoid membrane rupture when they are pulled by a nano- or micro-needle [ 6 , 7 ]. The first step of cell-surface adhesion was considered as the initial contact of cells with materials, in which cells were in round shape but no cytoskeletal change yet.…”