Gene expression profiling implicates OXPHOS complexes in lifespan extension of flies over-expressing a small mitochondrial chaperone, Hsp22 Hyun-Ju Kim a,1 , Geneviève Morrow a,1 , J. Timothy Westwood b , Sébastien Michaud a,c , Robert M. Tanguay a, * a Laboratory of Cell and Developmental Genetics, Department of Medicine, PROTEO, Pav. C.E.-Marchand, 1030 Ave de la Médecine, Université Laval, Québec, Canada G1V 0A6 b Canadian Drosophila Microarray Centre, Department of Cell and Systems Biology, University of Toronto, Mississauga, Ontario, Canada L5L 1C6 c Unité de Recherche en Pédiatrie, Centre de recherche du CHUL, CHUQ, 2705 Laurier blvd, Québec, Canada G1V 4G2 article info Article history: Received 29 October 2009 Received in revised form 16 December 2009 Accepted 17 December 2009 Available online 29 December 2009 Keywords: Hsp22 Aging Lifespan extension Microarray Mitochondria Heat shock proteins OXPHOS complexes abstract Aging is a complex process accompanied by a decreased capacity to tolerate and respond to various stres- ses. Heat shock proteins as part of cell defense mechanisms are up-regulated following stress. In Drosoph- ila, the mitochondrial Hsp22 is preferentially up-regulated in aged flies. Its over-expression results in an extension of lifespan and an increased resistance to stress. Hsp22 has chaperone-like activity in vitro, but the mechanism(s) by which it increases lifespan in flies are unknown. Genome-wide analysis was per- formed on long-lived Hsp22+ and control flies to unveil transcriptional changes brought by Hsp22. Tran- scriptomes obtained at 45 days, 90% and 50% survival were then compared between them to focus more on genes up- or down-regulated in presence of higher levels of hsp22 mRNA. Hsp22+ flies display an up- regulation of genes mainly related to mitochondrial energy production and protein biosynthesis, two functions normally down-regulated during aging. Interestingly, among the 26 genes up-regulated in Hsp22+ flies, 7 genes encode for mitochondrial proteins, 5 of which being involved in OXPHOS com- plexes. Other genes that could influence aging such as CG5002, dGCC185 and GstS1 also displayed a reg- ulation linked to Hsp22 expression. The up-regulation of genes of the OXPHOS system in Hsp22+ flies suggest that mitochondrial homeostasis is at the center of Hsp22 beneficial effects on lifespan. Ó 2010 Published by Elsevier Inc. 1. Introduction Aging is a complex process accompanied by a decreased capac- ity of cells to tolerate and/or respond to various forms of stress. Many theories have been postulated to explain aging (reviewed in Viña et al., 2007). In the free radical theory of aging (Harman, 1956), aging is caused by the accumulation of macromolecular damages induced by toxic reactive oxygen species (ROS). Since mitochondria are the main generators of ROS as a by-product of ATP synthesis (Aguilaniu et al., 2005), they are at the center of the free radical theory of aging (Harman, 1972; Miquel et al., 1980; reviewed in Viña et al., 2007). Although accepted by many, Harman’s theory is still highly debated (Sanz et al., 2006; Muller et al., 2007; Partridge 2009). Genome-wide experiments in different model organisms have identified aging transcriptional profiles shared across species (McCarroll et al., 2004; Smith et al., 2007). Mitochondrial genes including many components of the mitochondrial respiratory chain, ATP synthase complex and citric acid cycle as well as genes involved in ATP-dependent transport such as primary active transporters, ions transporters and ABC transporters are repressed during aging (McCarroll et al., 2004). Interestingly, the repression of these genes seems to be implemented early in adulthood (McCarroll et al., 2004). Several mutants displaying increased longevity in Caenorhabditis elegans and Drosophila melanogaster have been described. Interest- ingly in addition to having an extended longevity, many of these mutants also displayed increased thermotolerance and resistance to stress (Lin et al., 1998; Kitagawa et al., 2000; Nakamoto et al., 2000; Rogina et al., 2000; Chavous et al., 2001). Heat shock proteins (Hsps) are molecular chaperones that are coordinately expressed in response to stress and have been shown to be major determinants in the acquisition of thermotolerance and stress resistance (Feder and Hofmann, 1999; Verbeke et al., 2001). Along with the antioxi- dant defense system and the ubiquitin/proteasome machinery, Hsps are part of the cell defense mechanisms to prevent accumula- tion of protein damages (Ehrnsperger et al., 2000; Hartl and Hayer- Hartl, 2002; Haslbeck, 2002; Walter and Buchner, 2002). Hsps are divided in subfamilies on the basis of their molecular weight and sequence homology; small Hsps (sHsps), Hsp60, Hsp70 and Hsp90/100. In D. melanogaster there are four main sHsps displaying distinct intracellular localization and developmental expression pattern (reviewed in Michaud et al., 2002). One of these, Hsp22, is localized in the mitochondrial matrix (Morrow et al., 2000) and has been shown to be preferentially up-regulated in aged 0531-5565/$ - see front matter Ó 2010 Published by Elsevier Inc. doi:10.1016/j.exger.2009.12.012 * Corresponding author. Tel.: +1 418 656 3339; fax: +1 418 656 5036. E-mail address: Robert.tanguay@rsvs.ulaval.ca (R.M. Tanguay). 1 These authors contributed equally to this work. Experimental Gerontology 45 (2010) 611–620 Contents lists available at ScienceDirect Experimental Gerontology journal homepage: www.elsevier.com/locate/expgero