Abstract
Mitochondria are involved in many key cellular processes and therefore need to rely on good protein quality control (PQC). Three types of mechanisms are in place to insure mitochondrial protein integrity: reactive oxygen species scavenging by anti-oxidant enzymes, protein folding/degradation by molecular chaperones and proteases and clearance of defective mitochondria by mitophagy. Drosophila melanogaster Hsp22 is part of the molecular chaperone axis of the PQC and is characterized by its intra-mitochondrial localization and preferential expression during aging. As a stress biomarker, the level of its expression during aging has been shown to partially predict the remaining lifespan of flies. Since over-expression of this small heat shock protein increases lifespan and resistance to stress, Hsp22 most likely has a positive effect on mitochondrial integrity. Accordingly, Hsp22 has recently been implicated in the mitochondrial unfolding protein response of flies. This review will summarize the key findings on D. melanogaster Hsp22 and emphasis on its links with the aging process.
Highlights
Aging is associated with a decline in protein homeostasis that leads to the accumulation of deleterious protein damages
The fact that a reduced mitochondrial metabolism has been associated with Hsp22 expression suggests that this small heat shock protein (sHSP) may influence mitochondria-to-nucleus signaling through a decreased reactive oxygen species (ROS) production (Tower, 2014; Tower et al, 2014)
Drosophila melanogaster Hsp22 is one of the few sHSPs found inside mitochondria independently of the cellular environment together with plants mitochondrial sHSPs (Waters, 2013) and C. elegans Hsp17 (Ezemaduka et al, 2014)
Summary
Aging is associated with a decline in protein homeostasis (proteostasis) that leads to the accumulation of deleterious protein damages. Almost all of them are stress-inducible, but only seven have been shown to be up-regulated during aging (CG14207, l(2)efl, Hsp67Bc, Hsp22, Hsp23, Hsp26, and Hsp27; King and Tower, 1999; Zou et al, 2000; Landis et al, 2004, 2012; Wang et al, 2005; Girardot et al, 2006; Tanguay and Morrow, 2008; Yang and Tower, 2009).
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