Interplay of Cholesterol and Actin in Neurotransmitter GPCR Signaling: Insights from Chronic Cholesterol Depletion Using Statin

Abstract

Serotonin 1A receptors are important neurotransmitter receptors in the G protein-coupled receptor (GPCR) family and modulate a variety of neurological, behavioral, and cognitive functions. We recently showed that chronic cholesterol depletion by statins, potent inhibitors of HMG-CoA reductase (the ratelimiting enzyme in cholesterol biosynthesis), leads to polymerization of the actin cytoskeleton that alters lateral diffusion of serotonin 1A receptors. However, cellular signaling by the serotonin 1A receptor under chronic cholesterol depletion remains unexplored. In this work, we explored signaling by the serotonin 1A receptor under statin-treated condition. We show that cAMP signaling by the receptor is reduced upon lovastatin treatment due to reduction in cholesterol as well as polymerization of the actin cytoskeleton. To the best of our knowledge, these results constitute the first report describing the effect of chronic cholesterol depletion on the signaling of a G protein-coupled neuronal receptor. An important message arising from these results is that it is prudent to include the contribution of actin polymerization while analyzing changes in membrane protein function due to chronic cholesterol depletion by statins. Notably, our results show that whereas actin polymerization acts as a negative regulator of cAMP signaling, cholesterol could act as a positive modulator. These results assume significance in view of reports highlighting symptoms of anxiety and depression in humans upon statin administration and the role of serotonin 1A receptors in anxiety and depression. Overall, these results reveal a novel role of actin polymerization induced by chronic cholesterol depletion in modulating GPCR signaling, which could act as a potential therapeutic target.

A Cell-Permeable Fluorescent Probe Reveals Temporally Diverse PI(4,5)P2 Dynamics Evoked by Distinct GPCR Agonists in Neurons

“…4a). We noted that the N-terminus inserted itself deeper into the membrane for PI(4,5)P2 simulations when compared to that of PI(4)P and PI (3,4,5)P3 (Fig. 1e, Extended Table 2).…”

“…Both probes afforded a ~ 1.7-1.8 times higher affinity toward PI(4,5)P2 over PI (3,4,5)P3. Since PI (3,4,5)P3 is present in low nM levels in resting cells while PI(4,5)P2 is present in µM levels we concluded, that the MFR-labelled peptides could act as selective and sensitive PI(4,5)P2 probes in cellulo. The limit-of-detection (LOD) of MFR-12aa toward PI(4,5)P2 was obtained from the in vitro 'turn-on' response as 220 nM while that for MFR-20aa was obtained as 350 nM.…”

“…5b). Both probes afforded a ~ 1.7-1.8 times higher affinity toward PI(4,5)P2 over PI (3,4,5)P3. Since PI (3,4,5)P3 is present in low nM levels in resting cells while PI(4,5)P2 is present in µM levels we concluded, that the MFR-labelled peptides could act as selective and sensitive PI(4,5)P2 probes in cellulo.…”

“…1f). Specifically, in the case of interaction of the peptide with PI (3,4,5)P3 where K17 did not make any contact with the headgroup throughout the course of the 200 ns simulation, the percentage helicity was higher than the other phosphoinositides (Video-1, Fig. 1f).…”

“…1 Bystander lipid molecules are also critical components of a signaling response when a chemical stimulus is received at a cell-surface receptor. 2,3 At the crux of the spatiotemporal dynamics of lipid signaling response are phosphoinositides. 4,5 Indeed, phosphoinositides like phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P2), present in the inner-leaflet of eukaryotic cell membranes, form the link between signal reception at a G-protein coupled receptor (GPCR) and downstream signal transmission.…”