Hsp22 is a heat shock protein in the fly genome. Like other heat shock proteins it is involved in hormesis, wherein cells repair themselves more aggressively in response to heat, toxins, and other forms of stress. If the stress is mild or short-lived then the result is a net reduction in cellular damage. If this persists for long enough then the individual experiences improved health and longevity: increased cellular repair efforts and altered levels of heat shock proteins are observed in many of the approaches shown to slow aging in laboratory species. There is consequently some interest in the development of therapies based on triggering increased cellular housekeeping without the need for the initial stress, and manipulating levels of heat shock proteins seems like a good starting point:
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 unfolded protein response of flies. This review will summarize the key findings on D. melanogaster Hsp22 and emphasis on its links with the aging process.