Noncanonical Metabotropic Glutamate Receptor 5 Signaling in Alzheimer's Disease

Metabotropic glutamate receptor 5 (mGluR5) is ubiquitously expressed in brain regions responsible for memory and learning. It plays a key role in modulating rapid changes in synaptic transmission and plasticity. mGluR5 supports long-term changes in synaptic strength by regulating the transcription and translation of essential synaptic proteins. β-Amyloid 42 (Aβ42) oligomers interact with a mGluR5/cellular prion protein (PrPC) complex to disrupt physiological mGluR5 signal transduction. Aberrant mGluR5 signaling and associated synaptic failure are considered an emerging pathophysiological mechanism of Alzheimer's disease (AD). Therefore, mGluR5 represents an attractive therapeutic target for AD, and recent studies continue to validate the efficacy of various mGluR5 allosteric modulators in improving memory deficits and mitigating disease pathology. However, sex-specific differences in the pharmacology of mGluR5 and activation of noncanonical signaling downstream of the receptor suggest that its utility as a therapeutic target in female AD patients needs to be reconsidered. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Metabotropic Glutamate Receptor 5 Knockout Rescues Obesity Phenotype in a Mice Model of Huntington´s Disease

Obesity represents a serious global public health problem and is characterized by a low-grade chronic inflammatory state, which can increase the risk of comorbidities, such as: atherosclerosis, diabetes and insulin resistance. In this study, we investigated the effects of the genetic deletion of the metabotropic glutamate receptor 5 (mGluR5) on the modulation of obesity features in BACHD mice, a mouse model of Huntington´s disease. For that, we crossed BACHD and mGluR5 knockout mice (mGluR5−/−) in order to obtain the following groups: Wild type (WT), mGluR5−/−, BACHD and BACHD/mGluR5−/− (double mutant mice). Our results showed that the double mutant mice present decreased body weight as compared to BACHD mice at all tested ages and reduced visceral adiposity as compared to BACHD mice at 6 and 12 months of age. Additionally, 12-month-old double mutant mice present increased adipose tissue levels of adiponectin, decreased leptin levels, and increased IL-10/TNF ratio as compared to BACHD mice. Taken together, our data propose that the absence of mGluR5 reduce weight gain and visceral adiposity in BACHD mice, along with a decrease in the inflammatory state in the visceral adipose tissue (VAT), which may indicate that mGluR5 may play a role in adiposity modulation.