4. Discussion

Although the mechanism by which mtDNA variation influences mitochondrial function, longevity and successful aging is unknown, the present study provides evidence of association between mtDNA haplogroups and longevity. At present, there are three methods in longevity studies (Christensen et al., 2006), i.e., case-control studies (KHaplogroup F was widespread in Southeast Asia and at moderate frequencies in Northeast Asia (Li et al., 2007). Alternatively, to explain the difference, we hypothesize certain interactions between mitochondrial haplogroups and nuclear polymorphisms and/or environmental factors. Second, the association of haplogroup F with longevity might be specific in the isolated Bama population. Bama is surrounded by steep mountains, resulting in poor transportation and communication with outside territories throughout history. These external factors resulted in social isolation. And it is quite likely that this haplogroup has had few opportunities for gene flow. In the isolated population, haplogroup F might be a protective factor for successful aging. The present results need to be replicated in additional populations.

Third, there were three mtSNPs (3970CNT, 13928GNC, and 10310GNA) in haplogroup F that were consistently associated with longevity in the women of the Bama Zhuang population. Among haplogroup F-specific mtSNPs, m.13928GNC, which causes an amino acid change Ser531Thr in the MT-ND5 protein, would potentially seem to be a functionally relevant polymorphism (see Supplementary Table 4).

Table 3 shows the distribution of mtDNA haplogroups and variants between long-lived subjects and controls in female and male Chuang populations. C is a subhaplogroup of M8, M7bc and M7b12 are subhaplogroups of M7, D4 and D4a are subhaplogroups of D, F3 is a subhaplogroup of F. #Others haplogroup categories include all other haplotypes except four haplogroups (M8, M7, D and F).

Table 5 shows the metabolism phenotype based on mtDNA haplogroups F in Chuang population. All Women Men F+ F p value F+ F p value F+ F p value FBG (mmol/l) Long-lived 5.30 1.65 5.35 1.52 0.82 5.40 1.71 5.27 1.48 0.63 4.97 1.39 5.56 1.63 0.22 Younger 4.77 0.55 4.86 0.57 0.20 4.78 0.63 4.81 0.54 0.75 4.77 0.52 4.90 0.60 0.16 TG (mmol/l) Long-lived 1.37 1.03 1.37 0.91 0.99 1.29 0.93 1.45 0.95 0.27 1.67 1.35 1.14 0.75 0.19 Younger, etc.

Note: Data in italics indicates p<0 .05, OR=odds ratio, and a confidence interval of95%."F+" indicates subjects with haplogroup F, and "F-" suggests subjects without haplogroup F. FBG refers to fasting blood glucose, TG to serum total triglyceride, TC to serum total cholesterol, HDL-c to high-density lipoprotein-cholesterol, and LDL-c to low-density lipoprotein-cholesterol. Further study of these factors could be important to obtain a clearer relationship between mtDNA variations and longevity. Supplementary materials related to this article can be found online. The successful aging of individuals may be explained by decreased production of ROS from mitochondria. Further studies are needed to examine whether the production of superoxides or ROS from cybrids carrying mtDNA of haplogroup F is lower than that in cybrids carrying mtDNA of other haplogroups. However, the actual effect of the mtSNP m.13928GNC on mitochondrial function remains to be examined. The present study showed that haplogroup F was associated with longevity only in females, whereas no significant association was found in males. Although the male group is small in size in the gender-stratified analyses, previous studies have shown that women live longer than men and the effect of genetics on successful aging differs between females and males (et al., 2010). The gender difference in the association of the haplogroup with longevity may be attributable to differences in biological background such as sex hormones and extrinsic factors like smoking (Candore et al., 2006; Ordovas, 2007). These differences might explain the present observation that women but not men were distinctly influenced by the differences among mitochondrial haplogroups. Therefore, our results suggest that haplogroup F has a protective effect only on women and not on men. In addition, our analysis indicated that subhaplogroup F3 at the branch level of haplogroup F was associated with longevity and successful aging in female subjects. However, in the present study, the frequency of subhaplogroup F3 is very low (4.9% in long-lived populations and 3.0% in controls), and the power in genetic association would fall off for this low frequency. Therefore, the association of subhaplogroup F3 with longevity needs to be ascertained by replication in larger sample sizes. None of the authors have a conflict of interest. The authors thank the subjects for donating DNA samples. The study is partly supported by the National Scientific Foundation of China (30972709, 30671110) and the National Basic Research Program of China (973 Program) (2006CB503901) grants to Z.Y.