A gender–dependent genetic predisposition to produce high levels of IL-6 is detrimental for longevity

Massimiliano Bonafe`1, Fabiola Olivieri2, Luca Cavallone2, Simona Giovagnetti2, Francesca Marchegiani2, Maurizio Cardelli2, Carlo Pieri2, Maurizio Marra2, Roberto Antonicelli2, Rosmarie Lisa2, Maria Rosaria Rizzo3, Giuseppe Paolisso3, Daniela Monti4 and Claudio Franceschi1,

1 Department of Experimental Pathology, Bologna University, Bologna, Italy 2 Italian National Research Centers on Aging, Ancona, Italy 3 Department of Geriatric Medicine and Metabolic Disease, II University of Naples, Naples, Italy 4 Department of Experimental Pathology and Oncology, University of Florence, Florence, Italy

Current literature indicates that elevated IL-6 serum levels are associated with diseases, dis- ability and mortality in the elderly. In this paper, we studied the IL-6 promoter genetic vari- ability at –174 C/G locus and its effect on IL-6 serum levels in a total of 700 people from 60 to 110 years of age, including 323 centenarians. We found that the proportion of homozy- gotes for the G allele at –174 locus decreases in centenarian males, but not in centenarian females. Moreover, we found that, only among males, homozygotes for the G allele at –174 locus have higher IL-6 serum levels in comparison with carriers of the C allele. On the whole, our data suggest that those individuals who are genetically predisposed to produce high levels of IL-6 during aging, i.e. –174 locus GG homozygous men, are disadvantaged for

Key words: IL-6 / Aging / Centenarians / Polymorphism

1 Introduction

able marker for functional disability, and as a predictor of disability and mortality among elderly [8, 9]. IL-6 dysre- gulation has been thought to be involved in the patho- genesis of a variety of age-related diseases, such as dia- betes and atherosclerosis, which have a substantial inflammatory pathogenesis [10, 11]. A C/G polymor- phism located at 5’-upstream of IL-6 (–174 C/G locus) has been identified [12]: this base transition is associated with different IL-6 plasma levels in healthy subjects, and affects the rate of IL-6 gene transcription [12, 13]. In the present investigation, a total of 700 subjects ranging from 60 to 110 years of age (including 323 centenarians) was genotyped for –174 C/G locus variability to obtain information on the age-related changes in the proportion of people carrying different –174 C/G alleles. Moreover, 269 of these subjects (from 60 to 110 years of age) were studied to assess the impact of –174 C/G locus on IL-6 serum levels.

An age-related increase of IL-6 concentration has been found in serum, plasma, and supernatants of mononu- clear blood cell cultures from elderly people and cente- narians [1–3]. IL-6 is a pleiotropic cytokine capable of regulating proliferation, differentiation and activity of a variety of cell types [3], and plays a pivotal role in neuro- endocrine and immune system homeostasis [4]. In par- ticular, IL-6 plays a major role in acute phase response and in the balancing of the pro-inflammatory/anti- inflammatory pathways [5]. An age-related increase of IL-6 serum level among elderly people devoid of any overt age-related disease [3], beginning as early as 30–40 years of age [6], and being prominent among men [7], has been observed. Recent population-based stud- ies identified the magnitude of IL-6 serum level as a reli-

2 Results

A total of 700 individuals (482 women and 218 men), ranging from 60 to 110 years of age was subdivided into three age-groups (60–80, 81–99 and G 99 years of age), and was assessed for –174 C/G locus variability. CC and

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Table 1. Percentages of the C allele and C+ / C– individuals in mena)

Table 2. Percentages of the C allele and C+ / C– individuals in womena)

Elderly Long-lived Centenarians (n=101) (n=126) (n=255) % % % C allele 24a 30b 27c C + subjects 46d 48e 49f C – subjects 54 52 51

Elderly Long-lived Centenarians (n=93) (n=57) (n=68) % % % C allele 24a 24b 35c C + subjects 42d 42e 62f C – subjects 58 58 38

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CG genotypes were grouped and indicated as “C+”, and GG genotype was named as “C–”. The female to male ratio in centenarians was 3.75, in agreement with that reported in a recent nationwide study on Italian centenar- ians [14]. Due to the heterogeneity of male to female pro- portions in the three age groups, genders were analyzed separately. Genotype distributions fitted with the expec- tations of Hardy-Weinberg equilibrium (p G 0.05). As shown in Table 1, elderly and long-lived men had similar

C allele frequency (24% in both groups), whilst the fre- quency of C allele was increased in centenarian men (35%). Accordingly, C– individuals were significantly under-represented among centenarian men (38%), whilst no difference was found between elderly and long- lived men (58% in both groups). As shown in Table 2, no difference was found when the frequency of the C allele and the percentage of C+ / C– individuals were analyzed in the three age groups of women.

IL-6 (pg/ml)7.394.482.721.641.000.610.370.220.140.08WomenWomenMenWomen