Autophagy and protein translation in neural function & neurodegeneration
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Autophagy is a pathway of extreme importance in neurodegenerative disease and aging, as autophagy maintains normal cellular function by degrading aggregate-prone proteins and by supporting protein quality control. Reduced TOR signaling, imposed by rapamycin or dietary restriction, can delay neurological disease onset and ameliorate disease progression, suggesting shared pathways between aging and neurodegeneration. In organisms from yeast to mammals, reduced TOR signaling leads to increased autophagy and reduced protein translation. We, and others, have proposed that increased autophagy may be protective in aggregation-based neuronal diseases, but reduced translation may also be neuroprotective, as it has been shown to extend lifespan in worms and flies. However, other data suggests that maintenance of translation function at the level of S6 kinase is required for fully effective autophagy activation. Indeed, how these pathways are normally regulated, and dysregulated in situations of proteotoxic stress, remain to be established. In particular, the molecular basis of mTOR inhibition of autophagy is unknown, and the issue of cross-talk between the autophagy pathway and S6 kinase regulated protein translation is yet to be resolved. To study autophagy regulation in the nervous system, we developed a method for autophagy induction and monitoring in primary neurons. We have shown that expression of polyglutamine-expanded proteins produces caspase-mediated cell death in primary neurons, and that autophagy induction can protect against this misfolded protein stress. To begin to understand the basis of autophagy regulation in primary neurons, we performed microarray analysis of primary neurons induced to undergo autophagy, and have preliminarily validated gene expression alterations produced by nutrient deprivation. To understand the role of translational control in autophagy regulation and in neuroprotection, we have initiated studies of protein translation status in HD striatal-like cell lines as a prelude to translation state array analysis (TSAA) in these cell lines. Using a combination of in vitro and in vivo studies, we propose to examine the regulation of autophagy, the role of protein translation regulation in autophagy function, and the interaction of these two processes in neurodegenerative polyglutamine disease proteinopathies. In our first aim, we will complete gene expression, microRNA, and translational state array analysis (TSAA) of primary neurons induced to undergo autophagy, as we hypothesize that there must be transcriptional and/or translational regulation of autophagy in mammals, and we expect that such regulation is important for operation of the autophagy pathway in the CNS. In our second aim, we will determine the effect of reduced protein translation upon autophagy induction and neuroprotection in primary neurons, and will use TSAA to test if protein translation alterations occur in Huntington's (HD) disease. In our third aim, we will determine if reduced protein translation is beneficial, deleterious, or inconsequential in a polyglutamine proteinopathy, by crossing HD mice onto a reduced protein translation background, using two different models (S6K1 null and 4E-BP1 transgenic mice). Understanding the intersection of TOR signaling, autophagy pathway function, and protein synthesis regulation should provide crucial insights into normal neural function and neurological diseases caused by misfolded protein stress.
