Insulin-like growth factor 1 receptor polymorphism rs2229765 and circulating interleukin-6 level affect male longevity in a population-based prospective study (Treviso Longeva− TRELONG)

Diego albani1, Stefano Mazzuco2, Letizia Polito1,3, Sara Batelli1, Gloria Biella1, Fausta Ongaro2, Deborah r Gustafson4, Piero antuono5, Gianbattista Gajo6,7, elisabetta Durante6, Livio caberlotto8, andrea Zanardo8,7, Marinella Siculi8, Maurizio Gallucci9,7& Gianluigi Forloni1

1Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, via La Masa, Milan, Italy, 2Department Statistics, University of Padova, Via Cesare Battisti, Padova, Italy, 3Golgi Cenci Research Center, P.zza Golgi, Abbiategrasso, 4Neuropsychiatric Epidemiology Unit, Sahlgrenska Academy, University of Gothenburg, Sweden, SUNY-Downstate Medical Center, Brooklyn, NY, USA, 5Dementia Research Center, The Medical College of Wisconsin, West Wisconsin Avenue, Milwaukee, WI, USA, 6Transfusional Department, General Hospital of Treviso, Piazza Ospedale, Treviso, Italy, 7FORGEI, Interdisciplinary Geriatric Research Foundation, Viale Trento Trieste, Treviso, Italy, 8Department of Pathology, and 9Cognitive Impairment General Hospital of Treviso, Piazza Ospedale, Treviso, Italy

longevity is supported in twin-based studies where the individ- ual genome accounted for approximately 25% of lifespan [5,6].

The biochemical basis of longevity has been explored in model organisms like Caenorhabditis elegans, Drosophila and the mouse, leading to the identification of key cell pathways (oxidative stress response, DNA repair, inflammation and energy metabolism) related to successful aging [7,8]. The insulin/insulin like-growth factor 1 (IGF-1) pathway and the pro-inflammatory cytokine network seem to have an impor- tant role in modulating longevity [9–11].

Insulin/IGF-1 signaling (IIS) triggers intracellular down- stream transcription factors as a consequence of a cascade starting from the membrane receptors of insulin and IGF-1 [12]. Biochemical or genetic attenuation of IIS has been associated with increased lifespan, probably due to slow cell growth rate and metabolism [13–15]. In humans, circulating IGF-1 decreases with age and is also modified by sex hor- mones [16–18]. A synonymous polymorphism (rs2229765) on the IGF-1 receptor gene (IGF-1R) [GenBank:NM_000875] consisting of G to A transition at nucleotide 3174 leading to the amino acid change Glu->Glu at position 1043 (E1043E) [GenBank:NP_000876], has been positively associated with longevity in the Italian population [19].

Keywords: IGF-1, IL-6, aging, longevity, inflammation, male genetics

Introduction

Inflammation has a significant and dual role in aging physiology, both as an acute inflammatory response that is beneficial for survival, but also as a chronic inflamma- tory state that often parallels neurodegenerative disorders,

Genetics and the environment influence human longevity. Several works have addressed the role of genetics in excep- tional longevity [1–4], while the influence of genetics on

Correspondence: Diego Albani, MSc, Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, via La Masa, Milan, Italy. Tel: +390239014594. Fax: +3902 3546277. E-mail: diego.albani@marionegri.it

Plasma IGF-1 and IL-6 assays

autoimmunity and cancer [20,21]. A key pro-inflammatory molecule is interleukin-6 (IL-6) whose circulating level in humans tends to rise over time [22]. IL-6 transcription rate is slowed by the single nucleotide polymorphism (SNP) rs1800795(C/T) located in the IL-6 gene promoter region [GenBank: NM_000600] [23]. The role of rs1800795 in lon- gevity has been explored in the Italian population, with con- troversial results [24–27]. However, a higher IL-6 circulating level is almost invariably a negative predictor of survival [22–28].

Plasma IGF-1 was assayed by sandwich-type enzyme-linked immunosorbent assay (ELISA) (Diagnostic System Laborato- ries, Inc, Webster, TX, USA), according to the manufacturer’s instructions. The kit sensitivity was 10 ng/mL and intra- assay %CV was <10%. Plasma IL-6 was measured by another sandwich-type ELISA (Ultra Sensitive ELISA Kit, Biosource, Camarillo, CA, USA), according to the manufacturer’s instruc- tions. The kit sensitivity was 0.10 pg/mL and intra-assay %CV was between 5 and 10%. Each plasma sample was tested in duplicate.

We assessed the influence of IGF-1R rs2229765, IL-6 rs1800795, circulating IGF-1 and IL-6 on survival curves in a sample of elderly people from Treviso (Italy) who were fol- lowed for seven years from baseline (TRELONG Study), with particular attention to sex-specific patterns.

Statistics

The curves reported in Figures 1 and 2 were plotted by the Kaplan-Meier method. Survival curves were plotted separately by sex and by IL-6 or IGF-1 level. Odds ratios and 95% confidence intervals (CI) were calculated using sex-stratified Cox proportional hazard models, adjusted for age. Multivariate regression analysis was done considering mortality as a dependent outcome. Participants who died within the first three years were excluded from the analyses to control for reverse causality bias. Statistics were obtained by using the “survival” package of R software. Results were considered significant at p < 0.05, using two-tailed tests of significance.

Methods

Population sample recruitment and ethics