Divergent Metabolic Regulation of Autophagy and mTORC1—Early Events in Alzheimer’s Disease?

Myra E Conway,Mai A Shafei,Matthew Harris

doi:10.3389/fnagi.2017.00173

Myra E Conway, Mai A Shafei + Show 1 more

Open Access

https://doi.org/10.3389/fnagi.2017.00173

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Abstract

Alzheimer’s disease (AD) is a progressive disease associated with the production and deposition of amyloid β-peptide (Aβ) aggregates and neurofibrillary tangles, which lead to synaptic and neuronal damage. Reduced autophagic flux has been widely associated with the accumulation of autophagic vacuoles (AV), which has been proposed to contribute to aggregate build-up observed in AD. As such, targeting autophagy regulation has received wide review, where an understanding as to how this mechanism can be controlled will be important to neuronal health. The mammalian target of rapamycin complex 1 (mTORC1), which was found to be hyperactive in AD brain, regulates autophagy and is considered to be mechanistically important to aberrant autophagy in AD. Hormones and nutrients such as insulin and leucine, respectively, positively regulate mTORC1 activation and are largely considered to inhibit autophagy. However, in AD brain there is a dysregulation of nutrient metabolism, linked to insulin resistance, where a role for insulin treatment to improve cognition has been proposed. Recent studies have highlighted that mitochondrial proteins such as glutamate dehydrogenase and the human branched chain aminotransferase protein, through metabolism of leucine and glutamate, differentially regulate mTORC1 and autophagy. As the levels of the hBCAT proteins are significantly increased in AD brain relative to aged-matched controls, we discuss how these metabolic pathways offer new potential therapeutic targets. In this review article, we highlight the core regulation of autophagy through mTORC1, focusing on how insulin and leucine will be important to consider in particular with respect to our understanding of nutrient load and AD pathogenesis.

Highlights

Alzheimer’s disease (AD), similar to other neurodegenerative diseases, is characterized by the accumulation of protein aggregates, namely amyloid β-peptide (Aβ) and Tau tangles, which lead to synaptic and neuronal damage, in the hippocampal and the inferior parietal lobule (IPL) regions of the brain, resulting in memory loss (Braak and Braak, 1991; Borlikova et al, 2013)
We review the role of autophagy in AD and discuss how our current understanding of nutrient load and insulin regulation are involved in its dysregulation through the mammalian target of rapamycin (mTOR) pathway
The mechanistic details are far less understood than the insulin/IGF pathway, their importance is gaining impetuous as the amino acid profiles or their metabolic enzymes are altered in several disease conditions, including Type 2 diabetes mellitus (T2DM) and AD (Vannini et al, 1982; Wang et al, 2011; Hull et al, 2015)

Summary

Introduction

Alzheimer’s disease (AD), similar to other neurodegenerative diseases, is characterized by the accumulation of protein aggregates, namely amyloid β-peptide (Aβ) and Tau tangles, which lead to synaptic and neuronal damage, in the hippocampal and the inferior parietal lobule (IPL) regions of the brain, resulting in memory loss (Braak and Braak, 1991; Borlikova et al, 2013). As such, targeting autophagy regulation has received wide review, where an understanding as to how this mechanism can be controlled will be important to neuronal health. Hormones and nutrients such as insulin and leucine, respectively, positively regulate mTORC1 activation and are largely considered to inhibit autophagy.

Results

Conclusion