Collapse of proteostasis represents an early molecular event in Caenorhabditis elegans aging

Abstract

Protein damage contributes prominently to cellular aging. To address whether this occurs at a specific period during aging or accumulates gradually, we monitored the biochemical, cellular, and physiological properties of folding sensors expressed in different tissues of C. elegans. We observed the age-dependent misfolding and loss of function of diverse proteins harboring temperature-sensitive missense mutations in all somatic tissues at the permissive condition. This widespread failure in proteostasis occurs rapidly at an early stage of adulthood, and coincides with a severely reduced activation of the cytoprotective heat shock response and the unfolded protein response. Enhancing stress responsive factors HSF-1 or DAF-16 suppresses misfolding of these metastable folding sensors and restores the ability of the cell to maintain a functional proteome. This suggests that a compromise in the regulation of proteostatic stress responses occurs early in adulthood and tips the balance between the load of damaged proteins and the proteostasis machinery. We propose that the collapse of proteostasis represents an early molecular event of aging that amplifies protein damage in age-associated diseases of protein conformation.daf-16 ͉ folding sensors ͉ hsf-1 ͉ protein misfolding ͉ stress response T he stability of the proteome is challenged by conditions that cause proteotoxic stress including errors during protein synthesis, oxidant-induced covalent modifications, inherited polymorphisms, and misfolding (1-3). Consequently, all cells have highly conserved stress-inducible pathways that detect, prevent, and resolve such damage (4, 5). Accumulation of misfolded proteins titrate the negative regulation of chaperones from HSF-1 (4, 6, 7). Likewise, an E3 ubiquitin ligase was shown to regulate the levels of DAF-16, also indicating a link between stress response activation to the balance between proteostasis capacity and the load of damaged proteins (8). The activation of cellular stress responses limits the accumulation of damaged proteins by suppression of misfolding and enhancing chaperonemediated folding, promoting the enzymatic removal of covalent modifications, and stimulating clearance by ubiquitin-mediated, proteosomal, and autophagic processes (1, 4, 5, 9, 10). The dynamics of these processes during aging, however, are poorly understood.Aging can be characterized by the loss of cellular function and increased vulnerability to environmental and physiological stress that results in enhanced susceptibility to disease. Many agedependent changes have been detected at mid-to-late lifespan of C. elegans, including the accumulation of damaged macromolecules, cell and organellar degeneration, and physiological decline (11-17). Likewise, aggregation and toxicity of diseaseassociated aggregation-prone proteins, such as huntingtin and A␤ peptide, is enhanced during aging in C. elegans and other model systems (18-21).The regulation of aging and the maintenance of proteostasis has been recently established in C. elegans. Downregulatio...

CCAR‐1 is a negative regulator of the heat‐shock response in Caenorhabditis elegans

“…The likelihood of developing diseases of protein dysfunction, such as neurodegenerative disorders, is increased upon aging, due in part to the decline of the HSR during the aging process (Ben‐Zvi, Miller, & Morimoto, 2009; Labbadia & Morimoto, 2015). Activators of the HSR have been suggested as possible therapeutic strategies for diseases of aging (Balch, Morimoto, Dillin, & Kelly, 2008; Calamini & Morimoto, 2012; Neef, Turski, & Thiele, 2010; Westerheide & Morimoto, 2005), but many of the small molecules known to modulate HSF1 activity have cytotoxicity and poor bioavailability.…”

Firefly luciferase mutants as sensors of proteome stress

“…Several sensors have been used to report on PN alterations. In C. elegans, temperature sensitive mutants of the muscle proteins, α-paramyosin and α-myosin, which are tissue-specific and can lead to loss-offunction effects, have been used to measure the folding capacity of cells during heat stress and upon expression of mutant Htt protein (Ben-Zvi et al, 2009;Gidalevitz et al, 2006). Also, proteins such as GFP-CL1, which are limited to reporting changes in specific components of the PN have been employed to measure the degradation capacity of cells (Bence et al, 2001;Nonaka and Hasegawa, 2009).…”

“…Likewise, several studies have shown that the inability of cells to mount an adequate stress response against misfolded proteins results in low Hsp70 proteins levels and augments the aging process (Bonelli et al, 1999;Fargnoli et al, 1990;Gutsmann-Conrad et al, 1998). This affect is presumably due to an increase load of misfolded proteins on the proteostasis machinery that directly or indirectly affects the folding of the metastable proteome of a cell, resulting in widespread failure of diverse pathways (Ben-Zvi et al, 2009). …”

Molecular characterization of the transition to mid-life in Caenorhabditis elegans

“…A model consisting of two subpopulations was consistent with the observations, where a long-lived sub-population showed a robust heat-shock response and a shorter-lived sub-population had a weaker heat-shock response. Ubiquitin-mediated proteolysis to maintain proteostasis was later shown to play an important role in the long-lived population (Ben-Zvi et al 2009). We have demonstrated heterogeneity much earlier in the lifespan.…”