Synergistic activation of AMPK prevents from polyglutamine-induced toxicity in Caenorhabditis elegans.

Expression of abnormally long polyglutamine (polyQ) tracks is the source of a range of dominant neurodegenerative diseases, such as Huntington disease. Currently, there is no treatment for this devastating disease, although some chemicals, e.g., metformin, have been proposed as therapeutic solutions. In this work, we show that metformin, together with salicylate, can synergistically reduce the number of aggregates produced after polyQ expression in Caenorhabditis elegans. Moreover, we demonstrate that incubation polyQ-stressed worms with low doses of both chemicals restores neuronal functionality. Both substances are pleitotropic and may activate a range of different targets. However, we demonstrate in this report that the beneficial effect induced by the combination of these drugs depends entirely on the catalytic action of AMPK, since loss of function mutants of aak-2/AMPKα2 do not respond to the treatment. To further investigate the mechanism of the synergetic activity of metformin/salicylate, we used CRISPR to generate mutant alleles of the scaffolding subunit of AMPK, aakb-1/AMPKß1. In addition, we used an RNAi strategy to silence the expression of the second AMPKß subunit in worms, namely aakb-2/AMPKß2. In this work, we demonstrated that both regulatory subunits of AMPK are modulators of protein homeostasis. Interestingly, only aakb-2/AMPKß2 is required for the synergistic action of metformin/salicylate to reduce polyQ aggregation. Finally, we showed that autophagy acts downstream of metformin/salicylate-related AMPK activation to promote healthy protein homeostasis in worms.

Metformin to treat Huntington disease: A pleiotropic drug against a multi-system disorder.

Huntington disease (HD) is a neurodegenerative disorder produced by an expansion of CAG repeats in the HTT gene. Patients of HD show involuntary movements, cognitive decline and psychiatric impairment. People carrying abnormally long expansions of CAGs (more than 35 CAG repeats) produce mutant huntingtin (mHtt), which encodes tracks of polyglutamines (polyQs). These polyQs make the protein prone to aggregate and cause it to acquire a toxic gain of function. Principally affecting the frontal cortex and the striatum, mHtt disrupts many cellular functions. In addition, this protein is expressed ubiquitously, and some reports show that many other cell types are affected by the toxicity of mHtt. Several studies reported that metformin, a widely-used anti-diabetic drug, is neuroprotective in models of HD. Here, we provide a review of the benefits of this substance to treat HD. Metformin is a pleiotropic drug, modulating different targets such as AMPK, insulin signalling and many others. These molecules regulate autophagy, chaperone expression, and more, which in turn reduce mHtt toxicity. Moreover, metformin alters gut microbiome and its metabolic processes. The study of potential targets, interactions between the drug, host and microbiome, or genomic and pharmacogenomic approaches may allow us to design personalised medicine to treat HD.