The invertebrate blueprint of the connection between aging and immune neuroendocrine responses ISJ 6: 102-105, 2009 ISSN 1824-307X VISIONS AND PERSPECTIVES The invertebrate blueprint of the connection between aging and immune neuroendocrine responses E Ottaviani1, D Malagoli1, C Franceschi2 1Department of Animal Biology, University of Modena and Reggio Emilia, 41100 Modena, Italy 2Department of Experimental Pathology, University of Bologna, 40126 Bologna, Italy Accepted July 13, 2009 Abstract The present paper summarizes the main findings related to aging and immune neuroendocrine responses in invertebrates. In particular, the functional aspects and the genes involved are examined. A possible mechanism of correlation between aging and functioning of immune-neuroendocrine- related genes is also discussed. Key Words: aging; longevity; immune neuroendocrine responses; gerontogenes Introduction Aging, or senescence, is a progressive somatic degeneration that provokes homeostatic modifications with damage to cellular functions and drastic inefficiency in survival. Notwithstanding the presence of various stressors, such as bacteria, virus, radiations, heat, oxygen, and free radicals, the aging process is controlled by a variety of defense functions or anti-stress responses (Franceschi et al., 2000). Indeed, aging is a remodeling phenomenon that involves mainly the immune and neuroendocrine systems, while the aging phenotype can be interpreted as a global, adaptive response of the body to the age-related accumulation of non- repaired damages, so allowing an optimal redistribution/utilization of the resources in order to survive (Garinis et al., 2008; Schumaker et al., 2009). In terms of mammalian immunosenescence, changes in adaptive and innate immunity have been observed. On the one hand, there is the involution of the thymus (Nasi et al., 2006), a profound shrinkage in the T-cell repertoire (Wack et al., 1998), and a massive increase of megaclones of memory cells directed against typical infections of old age (Larbi et al., 2008). On the other, we see the activation of the macrophage that produces a large amount of cytokines and is responsible for the chronic inflammatory process in the aged organisms. This profound correlation between aging and inflammatory status has been described with the neologism “inflamm-aging” (Franceschi et al., 2000). ___________________________________________________________________________ Corresponding author: Enzo Ottaviani Department of Animal Biology University of Modena and Reggio Emilia via Campi 213/D, 41100 Modena, Italy E-mail: enzo.ottaviani@unimore.it Overall, during aging the immune system appears to concentrate on the recognition of external and internal environmental antigens met during life, while neglecting new encounters. Furthermore, immunosenescence seems to be the result of a chronic hyper-stimulation of both adaptive and innate immunity (Fagiolo et al., 1993). The appearance of adaptive clonotypical immunity from lower vertebrates onwards has given rise to great variability in the molecular structures devoted to the recognition of epitopes. In this context, the macrophage, a cell that plays a central role in the innate immunity, has long been neglected by the immunologists and has only recently assumed its own, correct, immune role. Several data indicate that the macrophage has a profound evolutionary root, and in both vertebrates and invertebrates, the phagocytic capacity of these cells has always played a primary role in the stress response and inflammation. These activities share cells and mediators from vertebrates to invertebrates, suggesting a common origin (Ottaviani et al., 2007). This idea is not completely new, but rather a reappraisal and extension of the phagocytosis theory of immunity proposed by Elie Metchnikoff, who was the first to propose the existence of an evolutionary mechanism devoted to the protection of organisms (Metchnikoff, 1901). The macrophage is able not only to perform phagocytosis, but also to respond to different stimuli, such as bacterial products, neuropeptides, neurohormones, cytokines, and to release pro- inflammatory cytokines, e.g., nitric oxide, biogenic amines and neuropeptides, among others (Ottaviani et al., 1997). In this light, various features and mechanisms of aging are a reshaping of old and conserved 102 functions of innate immunity (macrophage-centered) with the new functions of anticipatory immunity (lymphocyte-centered) and the neuroendocrine system (Ottaviani, 1992; Panerai and Ottaviani, 1995). Invertebrates Functional age-related data Aging has been extensively studied in two invertebrate models, Drosophila melanogaster and Caenorhabditis elegans. As far as we know, the freshwater snail Lymnaea stagnalis is one of the first invertebrate models in which the relationship between aging and immune response was examined. In particular, juvenile samples of L. stagnalis presented fewer and less well developed circulating amoebocytes with more limited phagocytic capacity compared to adult specimens, suggesting that the immune system of juvenile snails is less competent (Dikkeboom et al., 1984, 1985). This scenario could also explain the greater susceptibility to Trichobilharzia ocellata infection of juvenile snails compared to adult specimens (Meuleman et al., 1982; Dikkeboom et al., 1985). The response to bacteria and caloric restriction are the main protocols in studying the effects of aging in flies and worms, respectively. It should be underlined that in these investigations, the researchers focused on the longevity aspect. Although these studies are intriguing, some contradictions have been reported. It has been demonstrated that aged flies transcribe more antimicrobial peptide diptericin than young flies when exposed to septic bacterial infection, suggesting that this behaviour is due to immune senescence (Zerofsky et al., 2005). Aging also reduces the capacity to survive bacterial infection (Ramsden et al., 2008). Different findings were reported by Ren et al. (2007), who showed that aged Drosophila can tolerate a significant bacterial load and mount a large immune response without compromising survival. Other experiments have demonstrated that caloric restriction counteracts aging and extends the lifespan of various organisms, including D. melanogaster and C. elegans (Pletcher et al., 2002; Lee et al., 2006). Genetic age-related data In both D. melanogaster and C. elegans several genes have been seen to change their expression with age. In particular, CHICO, a Drosophila homolog of vertebrate IRS1-4, that plays an essential role in the control of cell size and growth is involved in the extension of lifespan in the flies (Böhni et al., 1999; Clancy et al., 2001). Indeed, the use of mutants, such as chico1 homozygotes has resulted in increased median and maximum lifespan in females of up to 48 % and 41 %, respectively. chico1 heterozigotes showed an increase in median lifespan of up to 36 % and 13 % in females and males, respectively (Clancy et al., 2001). In restricted diet conditions, elevated superoxide dismutase (SOD) activity has been associated with an extension of lifespan, while increased SOD activity (CuZn SOD, but not Mn SOD activity) has been detected in chico1 homozygotes (Kabil et al., 2007). When grown on a diet of Escherichia coli, mutant alleles of age-1 and daf-2 increase the lifespan of C. elegans by 65 % and 100 %, respectively (Friedman and Johnson, 1988; Kenyon et al., 1993). A further increase in lifespan is observed (100 % and 200 %, respectively) when the worms are maintained in axenic culture, and this increase is correlated to metabolic rate, suggesting that genes impact on longevity and senescence by regulating metabolic activities (Vanfleteren and De Vreese, 1995). The C. elegans germ-line directly influences its lifespan by modulating the activity of an insulin/IGF-1 pathway that is involved in the regulation of worm aging. Mutants able to reduce the efficiency of DAF-2 (an IGF-1 receptor homologue) extend the worm’s lifespan, and this process requires DAF-16 activity (Hsin and Kenyon, 1999). The gerontogenes are also involved in immune- neuroendocrine responses. The daf-2, age-1 and age-2 genes in C. elegans have been seen to increase resistance to bacterial pathogens (Laws et al., 2004; Evans et al., 2008). Moreover, such mutations, which normally enhance life expectancy, were also able to increase resistance to death caused by bacterial pathogens such as Pseudomonas aeruginosa and Salmonella enterica. These experimental results suggest that longevity is associated with stress resistance and that immunological challenges are an integral part of the spectrum of environmental stressors. With regards the neuroendocrine response, it has been demonstrated that in Drosophila serotonin controls stress behaviour by regulating the DAF-2 insulin/IGF-1 receptor signalling to the DAF- 16/FOXO transcription factor. Two classes of serotonergic neurons that present distinct serotonergic receptors are able to influence specific aspects of DAF-16/FOXO functions (Liang et al., 2006). A recent finding suggests that in C. elegans, a distinct DAF-16-dependent signalling pathway is involved in the activation of genes that provide resistance to bacterial pathogens (Miyata et al., 2008). These findings offer a molecular and genetic basis for our hypothesis that the immune response and stress (neuroendocrine response) are both highly interconnected and conserved over the course of evolution (Ottaviani and Franceschi, 1997; Ottaviani et al., 2007). Concluding remarks The data reported above points to a relationship between aging and the efficacy of immune and stress responses. However, it is not easy to understand how these events are correlated. DeVeale et al. (2004) raise two questions: 1) Why does the immune response change with age? 2) Is this change aging-related or does it contribute to aging? With regards invertebrates, we can surmize an explanation. We have postulated that the immune and neuroendocrine systems have a common origin in which the macrophage is an immune- neuroendocrine effector system integrating innate 103 Fig. 1 A schematic representation of the macrophage (Ø) as the witness of the common origin of the immune and neuroendocrine systems. A) The normal homeostatic condition; B) During aging immunity, stress and inflammation (Ottaviani and Franceschi, 1997; Ottaviani et al., 2007). This defense network may be interpreted as an equilateral triangle whose angles represent immunity, stress response and inflammation, while the macrophage sits in the middle (Fig. 1A). In this unitarian perspective, these phenomena can be seen as an integrated network, with a common objective, i.e., the maintenance of body homeostasis. However, in different situations, one phenomenon may prevail over the others. As previously reported, the proinflammatory status of aging (inflamm-aging) is the result of the chronic activation of the macrophage. In this condition, the prevalence of inflammation over the other two parameters (immunity and stress) induces a change in the geometric shape to a scalene triangle (Fig. 1B) representing the state of senescence. As far as invertebrates are concerned, old D. melanogaster present an inflammatory status (Pletcher et al., 2007), suggesting that the causes and consequences may be the same in metazoans. From an ecoimmunology point of view, resources in the immune and neuroendocrine systems must be redistributed during aging in order to minimize the cost in terms of energy expenditure (Ottaviani et al., 2008). Our hypothesis of a reduced immune response as a consequence of a persisting inflammatory status could represent an answer to the questions raised by DeVeale et al. (2004). References Böhni R, Riesgo-Escovar J, Oldham S, Brogiolo W, Stocker H, Andruss BF, et al. Autonomous control of cell and organ size by CHICO, a Drosophila homolog of vertebrate IRS1-4. Cell 97: 865-875, 1999. Clancy DJ, Gems D, Harshman LG, Oldham S, Stocker H, Hafen E, et al. Extension of life- span by loss of CHICO, a Drosophila insulin receptor substrate protein. Science 292: 104- 106, 2001. DeVeale B, Brummel T, Seroude L. Immunity and aging: the enemy within? Aging Cell 3: 195-208, 2004. Dikkeboom R, Van der Knaap WP, Meuleman EA, Sminia T. A comparative study on the internal defence system of juvenile and adult Lymnaea stagnalis. Immunology 55: 547-553, 1985. Dikkeboom R, Van der Knaap WP, Meuleman EA, Sminia T. Differences between blood cells of juvenile and adult Lymnaea stagnalis. Cell Tissue Res. 238: 43-47, 1984. Evans EA, Chen WC, Tan MW. The DAF-2 insulin- like signaling pathway independently regulates aging and immunity in C. elegans. Aging Cell 7: 879-893, 2008. Fagiolo U, Cossarizza A, Scala E, Fanales-Belasio E, Ortolani C, Cozzi E, et al. Increased cytokine production in mononuclear cells of healthy elderly people. Eur. J. Immunol. 23: 2375-2378, 1993. 104 Franceschi C, Bonafè M, Valensin S, Olivieri F, De Luca M, Ottaviani E, et al. Inflamm-aging. An evolutionary perspective on immunosenescence. Ann. NY Acad. Sci. 908: 244-254, 2000. Friedman DB, Johnson TE. A mutation in the age-1 gene in Caenorhabditis elegans lengthens life and reduces hermaphrodite fertility. Genetics 118: 75-86, 1988. Garinis GA, van der Horst GTJ, Vijg J, Hoeijmakers JHJ. DNA damage and ageing: new-age ideas for an age-old problem. Nat. Cell Biol. 10: 1241- 1247, 2008. Hsin H, Kenyon C. Signals from the reproductive system regulate the lifespan of C. elegans. Nature 399: 362-366, 1999. Kabil H, Partridge L, Harshman LG. Superoxide dismutase activities in long-lived Drosophila melanogaster females: chico1 genotypes and dietary dilution. Biogerontology 8: 201-208, 2007. Kenyon C, Chang J, Gensch E, Rudner A, Tabtiang R. A C. elegans mutant that lives twice as long as wild type. Nature 366: 461-464, 1993. Larbi A, Franceschi C, Mazzatti D, Solana R, Wikby A, Pawelec G. Aging of the immune system as a prognostic factor for human longevity. Physiology (Bethesda) 23: 64-74, 2008. Laws TR, Harding SV, Smith MP, Atkins TP, Titball RW. Age influences resistance of Caenorhabditis elegans to killing by pathogenic bacteria. FEMS Microbiol. Lett. 234: 281-287, 2004. Lee GD, Wilson MA, Zhu M, Wolkow CA, de Cabo R, Ingram DK, et al. Dietary deprivation extends lifespan in Caenorhabditis elegans. Aging Cell 5: 515-524, 2006. Liang B, Moussaif M, Kuan CJ, Gargus JJ, Sze JY. Serotonin targets the DAF-16/FOXO signaling pathway to modulate stress responses. Cell Metab. 4: 429-440, 2006. Metchnikoff E. Immunity in infective diseases, Cambridge University Press, Cambridge, UK, 1901. Meuleman EA, Huyer AR, Luub TWJ. The effects of the age o the host and the miracidial dose on the development of Trichobilharzia ocellata in Lymnaea stagnalis. Trop. Geogr. Med. 34: 298, 1982. Miyata S, Begun J, Troemel ER, Ausubel FM. DAF- 16-dependent suppression of immunity during reproduction in Caenorhabditis elegans. Genetics 178: 903-918, 2008. Nasi M, Troiano L, Lugli E, Pinti M, Ferraresi R, Monterastelli E, et al. Thymic output and functionality of the IL-7/IL-7 receptor system in centenarians: implications for the neolymphogenesis at the limit of human life. Aging Cell 5: 167-175, 2006. Ottaviani E. Some facts and speculation on the origin of the immunoneuroendocrine system and its correlation with aging. Ann. NY Acad. Sci. 663: 331-334, 1992. Ottaviani E, Franceschi C. The invertebrate phagocytic immunocyte: clues to a common evolution of immune and neuroendocrine systems. Immunol. Today 18: 169-174, 1997. Ottaviani E, Franchini A, Franceschi C. Pro- opiomelanocortin-derived peptides, cytokines, and nitric oxide in immune responses and stress: an evolutionary approach. Int. Rev. Cytol. 170: 79-141, 1997. Ottaviani E. Malagoli D, Capri M, Franceschi C. Ecoimmunology: is there any room for the neuroendocrine system? BioEssays 30: 868- 874, 2008. Ottaviani E, Malagoli D, Franceschi C. Common evolutionary origin of the immune and neuroendocrine systems: from morphological and functional evidences to in silico approaches. Trends Immunol. 28: 497-502, 2007. Panerai AE, Ottaviani E. Immunoendocrine reshaping with age. Int. Rev. Immunol. 12: 75- 84, 1995. Pletcher SD, Kabil H, Partridge L. Chemical complexity and genetics of aging. Annu. Rev. Ecol. Evol. Syst. 38: 299-326, 2007. Pletcher SD, Macdonald SJ, Marguerie R, Certa U, Stearns SC, Goldstein DB, et al. Genome-wide transcript profiles in aging and calorically restricted Drosophila melanogaster. Curr. Biol. 12: 712-723, 2002. Ramsden S, Cheung YY, Seroude L. Functional analysis of the Drosophila immune response during aging. Aging Cell 7: 225-236, 2008. Ren C, Webster P, Finkel SE, Tower J. Increased internal and external bacterial load during Drosophila aging without life-span trade-off. Cell Metab. 6: 144-152, 2007. Schumaker B, Hoeijmakers JH, Garinis GA. Sealing the gap between nuclear DNA damage and longevity. Mol. Cell. Endocrinol. 299: 112-117, 2009. Vanfleteren JR, De Vreese A. The gerontogenes age-1 and daf-2 determine metabolic rate potential in aging Caenorhabditis elegans. FASEB J. 13: 1355-1361, 1995. Wack A, Cossarizza A, Heltai S, Barbieri D, D'Addato S, Franceschi C, et al. Age-related modifications of the human alphabeta T cell repertoire due to different clonal expansions in the CD4+ and CD8+ subsets. Int. Immunol. 10: 1281-1288, 1998. Zerofsky M, Harel E, Silverman N, Tatar M. Aging of the innate immune response in Drosophila melanogaster. Aging Cell 4: 103-108, 2005. 105