Anti-Inflammatory Heat Shock Protein 70 Genes are Positively Associated with Human Survival

1, 2 3 4 5 3 6 7 R. Singh *, S. Kølvraa , P. Bross , K. Christensen , L. Bathum , N. Gregersen , Q. Tan and S. I. S. Rattan

1FCMB, Vejle, Denmark; 2Department of Clinical Genetics, Vejle Hospital, Denmark; 3Research Unit for Molecular Medicine, Aarhus University Hospital, Denmark; 4Institute of Public Health, University of Southern Denmark, Denmark; 5Department of Epidemiology, Odense University Hospital, Denmark; 6Department of Clinical Biochemistry and Genetics, Odense University Hospital, Denmark; 7Department of Molecular Biology, Aarhus University, Denmark

Abstract: A positive relationship between stress tolerance and longevity has been observed in several model systems. That the same correlation is applicable in humans and that it may be open to experimental manipulation for extending human lifespan requires studies on association of stress genes with longevity. The involvement of heat shock protein 70 (Hsp70) in cellular maintenance and repair mechanisms, including its role as an anti-inflammatory protein, makes it a suitable candidate for studying such associations. We have studied the association of three single nucleotide polymorphisms, HSPA1A (-110A>C), HSPA1B (1267A>G), and HSPA1L (2437T>C), present in the three HSP70 genes, with human survival, in a cohort of individuals born in the year 1905. This population cohort is a part of the longitudinal study of Danish nonagenarians. Since DNA samples were already collected in 1998, this gave us the opportunity to perform survival analysis on these subjects. Haplotype relative risk, and genotype relative risk were calculated to measure the effects of haplotypes and genotypes on human survival in a sex-specific manner. A significant association of HSPA1A-AA (RR=3.864; p=0.016) and HSPA1B-AA (RR=2.764; p=0.039) genotypes with poor survival was observed in female subjects. Also the female carriers of haplotype G-C-T had longer survival than the non-carriers (HRR=0.550; p=0.015). On an average, female carriers of the G-C-T haplotype live about one year longer than non-carriers. This result corroborates our previous observations from heat shock response (HSR) study where we had shown that after heat stimulation, mononuclear cells from the carriers of genotype HSPA1L-TT had better

Keywords: HSP70, HSR, aging, longevity, survival, haplotype, polymorphisms.

INTRODUCTION

association studies, where the frequencies of alleles and genotypes generated from a single locus candidate marker are compared between old cases and young controls [19,20]. This approach has certain drawbacks and is prone to false positive results due to sampling bias and potential secular trend in gene-environment interaction [21]. An alternative to this approach is the cohort based human survival study, where a group of individuals are genotyped for a candidate gene and then followed-up over the years to analyze their survival. This approach, though ideal, is expensive in terms of time and money, and hence rare. However, with the increase in the number of elderly, particularly in the developed world, and with the well established and extensive population based registries, it has been possible to perform cohort based survival studies in the old individuals [22].

At the cellular level, all organisms respond to stress by synthe- sizing specific stress proteins, the so-called heat shock proteins (Hsp), at the expense of other proteins. This phenomenon known as the heat shock response (HSR) protects the cells from subsequent damage and aids them to counteract the adverse effects of the stress [1-4]. Hsp are ubiquitous, cytoprotective, highly conserved cha- perone proteins, which are a part of cellular safety and rescue mechanisms, preventing proteins from misfolding, permitting unfolded proteins to cross biological membranes and then allowing them to fold properly [1], or targeting the damaged proteins for degradation and removal through proteolytic pathways [5]. Furthermore, Hsp are also known to have anti-inflammatory effects by acting on NF-(cid:1)B pathways [6-8].

Another drawback in the conventional genes-for-longevity studies is that, single locus marker are tested for their association with human longevity. Since lifespan is a complex trait where, along with the environment, a network of genes and genetic vari- ables play a critical role, it is prudent to study genetic variations in a group (haplotype), rather than single polymorphisms for mapping longevity determinant genes. In this context recently a lot of atten- tion has been focused on the effects of haplotypes on human longevity [23,24].

This ability to respond rapidly to stress at the gene level determines the adaptive and, therefore, the survival capacity and longevity of the organism [9]. Genes involved in HSR have recently been studied with respect to their role in human survival, aging and longevity [10-14] Of the various stress proteins, Hsp70 is the highly inducible, most prominent and best characterised in the stress protein families [15]. In humans there are 11 isoforms of Hsp70 encoded by different genes located at dispersed loci. Three of the HSP70 genes are mapped within the major histocompatibility complex (MHC) class III region at position 6p21.3 [16]. These are intron-less HSPA1A (HSP70-1), HSPA1B (HSP70-2) and HSPA1L (HSP70-Hom) [17], which have highly similar gene sequence but differ in their regulation. These genes are highly polymorphic [18]. Independent SNPs in these three HSP70 genes have been found to be associated with human longevity [11,12] and certain parameters of aging, such as self rated health [13].