Neuronal cholesterol metabolism increases dendritic outgrowth and synaptic markers via a concerted action of GGTase-I and Trk.

Miguel Moutinho,Cecília M P Rodrigues,Maria João Gama,Maria João Nunes,Jorge C Correia,Ingemar Björkhem,Ingemar Björkhem,Margarida Castro-Caldas,Margarida Castro-Caldas,Elsa Rodrigues,Angel Cedazo-Minguez,Jorge L Ruas

doi:10.1038/srep30928

Abstract

Cholesterol 24-hydroxylase (CYP46A1) is responsible for brain cholesterol elimination and therefore plays a crucial role in the control of brain cholesterol homeostasis. Altered CYP46A1 expression has been associated with several neurodegenerative diseases and changes in cognition. Since CYP46A1 activates small guanosine triphosphate-binding proteins (sGTPases), we hypothesized that CYP46A1 might be affecting neuronal development and function by activating tropomyosin-related kinase (Trk) receptors and promoting geranylgeranyl transferase-I (GGTase-I) prenylation activity. Our results show that CYP46A1 triggers an increase in neuronal dendritic outgrowth and dendritic protrusion density, and elicits an increase of synaptic proteins in the crude synaptosomal fraction. Strikingly, all of these effects are abolished by pharmacological inhibition of GGTase-I activity. Furthermore, CYP46A1 increases Trk phosphorylation, its interaction with GGTase-I, and the activity of GGTase-I, which is crucial for the enhanced dendritic outgrowth. Cholesterol supplementation studies indicate that cholesterol reduction by CYP46A1 is the necessary trigger for these effects. These results were confirmed in vivo, with a significant increase of p-Trk, pre- and postsynaptic proteins, Rac1, and decreased cholesterol levels, in crude synaptosomal fractions prepared from CYP46A1 transgenic mouse cortex. This work describes the molecular mechanisms by which neuronal cholesterol metabolism effectively modulates neuronal outgrowth and synaptic markers.

Highlights

CYP46A1 transgenic (C46-HA) mouse brain, maintaining cholesterol at physiological levels[13]
It has been recently described that geranylgeranyl transferase I (GGTase-I), the enzyme responsible for geranylgeranylation of sGTPases, is activated by brain-derived neurothrophic factor (BDNF), through direct protein-protein interaction with the tropomyosin-related kinase B (TrkB) receptors, which seems to be crucial for BDNF-induced dendritic development[16]
We have recently shown that increased expression and activity of CYP46A1 induces the activation of the mevalonate pathway, which leads to increased prenylation and activation of sGTPases, including Rho family proteins[15]

Summary

Introduction

CYP46A1 transgenic (C46-HA) mouse brain, maintaining cholesterol at physiological levels[13]. It has been recently described that geranylgeranyl transferase I (GGTase-I), the enzyme responsible for geranylgeranylation of sGTPases, is activated by brain-derived neurothrophic factor (BDNF), through direct protein-protein interaction with the tropomyosin-related kinase B (TrkB) receptors, which seems to be crucial for BDNF-induced dendritic development[16]. It has been reported that cholesterol loss leads to TrkB auto-activation[17] Taking these data into consideration, we hypothesized that there is a crosstalk between CYP46A1-induced sGTPase prenylation and Trk activation, which could mediate the beneficial effects of cholesterol 24-hydroxylase activity on neuronal development and function. This study describes the molecular mechanisms by which CYP46A1 modulates neuronal outgrowth and function, highlighting the cholesterol 24-hydroxylase as an attractive drug target in the physiological and pathological context of cognitive decline and brain disorders

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Conclusion