Statistical analysis was performed and P-values were calculated using 2 £ 2 contingency tables and the chi-squared ðx2Þ test with Yate’s correction Fisher’s exact probability tests. Those frequency differences that are observed to be statistically significant at p , 0:05 are highlighted with an asterix. The frequency of the heterozygote TC genotype was significantly ðx2 ¼ 6:366; p ¼ 0:01Þ decreased within the aged group. The TT genotype was significantly increased ðx2 ¼ 4:672; p ¼ 0:03Þ in the cohort of aged individuals.

O.A. Ross et al. / Experimental Gerontology 38 (2003) 561–565

decrease in the aged females (27%) in comparison to the younger control females (44%) and these results were also reflected in the males (28% vs 44%). The TT genotype was significantly increased ðx2 ¼ 4: 672; p ¼ 0: 03Þ in the cohort of aged individuals (70%) in comparison to the younger control group (55%). This increase was confirmed when the data was analysed with respect to females (69 vs 56%) and males (72 vs 54%).

Increased expression of HSP 70-Hom or increased functionality of this chaperone protein may provide better protection against oxidative stress and prevent the accumu- lation of abnormal proteins within the cell. There appears to be an age-related decrease in the frequency of the variant HSP 70-Hom C allele, a significant increase in the HSP 70- Hom TT genotype ðp ¼ 0: 03Þ; and a significant decrease in the frequency of the HSP 70-Hom heterozygote TC genotype ðp ¼ 0: 01Þ; independent of gender. The highly significant p-value obtained for the TC genotype would suggest that the heterogeneity may play a role in affecting the lifespan of the subjects in this study. The possible presence of two isoforms of the HSP 70-Hom protein, one containing a Met residue at position 493 and the other containing a Thr residue, may decrease the functionality of this chaperone protein restricting its ability in alleviating the effects of oxidative stress.

4. Discussion

HSPs act as molecular chaperones and are induced in response to elevated temperatures and a variety of cellular stresses, including oxidative stress. Oxidative damage generates inactive or altered proteins, e.g. abnormal enzymes, which are reported to accumulate within humans as they age (Lee and Wei, 2001; Stadtman, 2001). It is proposed that following oxidative stress or heat shock the partially altered proteins expose hydrophobic regions on their surface, and it is these regions that the majority of HSPs recognise and bind to, facilitating refolding and preventing irreversible aggregation.

These results would lead one to conclude that this polymorphism, 2437T allele resulting in the Met residue, allows the HSP 70-Hom protein to function with greater efficiency than if the Thr residue is present. The distribution of the T and C alleles in the normal population is already highly skewed towards T (TT: 55%, TC: 44%, CC: 1%), suggesting that the homozygous CC is almost incompatible with life. One postulates that the presence of the Met residue results in individuals, who are less susceptible to disease, while more resistant to cellular stresses and ageing. If the polymorphic nucleotide T2437C is demonstrated to affect expression or functionality of the protein it may account for the significant association of the TT genotype (and decrease of the TC genotype) with the Irish aged population investigated in this study.

Due to the role of HSP 70 in protection against stresses, HSP 70 polymorphisms are thought to be involved in diseases or the conditions associated with an oxidant/an- tioxidant imbalance, such as inflammation, cancer and ageing. The HSP 70 family is particularly implicated in the defence against oxidative stress but virtually no studies exist aimed at correlating resistance to oxidative stress with genetically determined overexpression, or increased func- tionality, of HSP 70.

To begin to address this lack of knowledge, this study focussed on the analysis of a polymorphism of the HSP 70- Hom gene (position 2437, T ! C transition) that results in a methionine (Met) to threonine (Thr) amino acid substitution at position 493. Pociot et al., 1993 hypothesised that this alteration from a non-polar and hydrophobic Met residue to the polar and neutral Thr residue may disrupt the peptide- bindingspecificityofHSP70-Homandhaveaneffectuponits functional efficiency.

This study investigated polymorphism of the HSP 70- Hom gene located in the class III region of the HLA complex and it has also been postulated that HSPs are involved in antigen presentation and are a central link between the innate and adaptive immune responses (Arnold et al., 1995; Multhoff and Botzler, 1998; Anderson and Srivastava, 2000; Wallin et al., 2002). The genes of the class III region display strong linkage disequilibrium with HLA class I and II genes, and it is important to point out that any polymorphic association with ageing observed within the HSP genes may be a result of closely linked polymorphism elsewhere within the HLA region (Fig. 1).

III region display strong linkage disequilibrium with HLA class I and II genes, and it is important to point out that any polymorphic association with ageing observed within the HSP genes may be a result of closely linked polymorphism elsewhere within the HLA region (Fig. 1).