Association of Mitochondrial DNA Polymorphisms And/Or Haplogroups with Elite Japanese Athlete Status

J Phys Fitness Sports Med, 2(1): 17-27 (2013)

JPFSM: Review Article Association of mitochondrial DNA polymorphisms and/or haplogroups with elite Japanese athlete status

Noriyuki Fuku1*, Eri Mikami1-3 and Masashi Tanaka1

1 Department of Genomics for Longevity and Health, Tokyo Metropolitan Institute of Gerontology, 35-2 Sakae-cho, Itabashi-ku, Tokyo 173-0015, Japan 2 Graduate School of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan 3 Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan

Received: November 8, 2012 / Accepted: January 21, 2013

Abstract A number of familial and twin studies have assessed the relative contribution of genetic and environmental factors to physical performance or its-related traits and have estimated that there is a significant genetic component to their phenotypes. In addition, aerobic capacity has been found to have stronger maternal inheritance than paternal. This finding implies that functional differences in maternally inherited mtDNA-encoded proteins involved in oxidative phosphorylation affect aerobic performance. In this article, therefore, we focus on associations between mtDNA polymorphisms/haplogroups and elite Japanese athlete status. From sequencing analysis of the control region in the mtDNA, certain mtDNA polymorphisms and haplogroups were shown to be associated with elite Japanese endurance athlete status, probably due to enhanced ATP production by mitochondria in the cardiac and skeletal muscles or both. This phenomenon is in agreement with several previous reports on Caucasian and African populations. It should be noted that certain mtDNA polymorphisms or haplogroups are also associated with elite Japanese sprint athlete/power status, probably due to enhanced calcium dynamics in the skeletal muscle. Thus, mtDNA polymorphisms/haplogroups influence not only aerobic performance but also anaerobic performance. Keywords : mitochondrial DNA, haplogroup, polymorphism, athlete status, physical performance, endurance, sprint

polymorphisms that relate to physical performance and Introduction response to physical training. In 2009, over 200 genes Background. Human physical performance is essen- in both nuclear DNA and mitochondrial DNA (mtDNA) tially multifactorial and is determined by a range of envi- have been reported to be associated with physical perfor- ronmental (i.e., physical training, nutrition, and techno- mance and health-related fitness6,7). The number of genes logical aids) and genetic factors. De Moor et al.1) studied associated with physical performance-related phenotypes 4488 British adult monozygotic and dizygotic female is expected to increase dramatically with the application twins and estimated that the heritability of athletic status of genome-wide methods to elite athlete cohorts; albeit is 66%. It has also been reported that genetic factors are such studies are only in their infancy8). major determinants of physical performance-related traits Mitochondria are essential to all higher organisms for ・ 2,3) such as maximal oxygen uptake (VO2max) and muscle sustaining life, and are extremely important in energy strength4,5). The strong genetic contributions to physical metabolism, providing 36 molecules of ATP per glucose performance and/or its-related traits indicate the possibil- molecule in contrast to the 2 ATP molecules produced by ity of using genetic approaches to individualize training glycolysis. It is reasonable to hypothesize that mitochon- approaches for enhancing competitive abilities in sports dria play an important role in setting aerobic performance, or even to help select appropriate athletic events through because mitochondria supply the majority of cellular ATP the use of genetic screening for extending the personal by the process of oxidative phosphorylation (OXPHOS), limit of athletes (i.e., talent identification). These pos- which is the main source of energy for endurance exer- sibilities provide the rationale and motivation for genetic cise. Although most DNA is packaged in chromosomes studies of physical performance or its-related traits. To within the nucleus, mitochondria also possess their own date, numerous studies have attempted to identify genetic circular DNA, designated as mtDNA. The 16,569-base pair (bp) human mtDNA contains 13 genes for mitochon- *Correspondence: [email protected] drial OXPHOS, as well as 2 rRNA and 22 tRNA genes 18 JPFSM: Fuku N, et al. that are necessary for protein synthesis within mitochon- ies. The mode of inheritance of the mtDNA is unique, dria9,10). Therefore, mtDNA diversity is likely to be in- because it is inherited maternally. The entire sequence of volved in determining elite endurance athlete status or its- human mtDNA has been determined9,10), and the length ・ related phenotype such as VO2max. of this mtDNA is 16,569 bp, sufficient for 13 messenger In this article, we discuss the polymorphisms and/or RNA (mRNA)-producing genes of the OXPHOS system, haplogroups of the mtDNA reported to date in association 2 ribosomal RNA (rRNA) genes, and 22 transfer RNA with elite athlete status and its-related traits, especially, in (tRNA) genes (Fig. 2-A). mtDNA and its encoded prod- the Japanese population. ucts are important regulators of aerobic ATP production via the mitochondrial OXPHOS system (Fig. 2-B). The Mitochondrial structure and mitochondrial genetics. Mi- mitochondrial electron-transfer chain is composed of 4 tochondria are membrane-enclosed organelles that are enzyme complexes (Complexes I-IV). Three of them (I, found in most eukaryotic cells. These organelles range III, and IV) contain subunits encoded by mtDNA (Table from 0.5 to 1.0 μm in diameter. Mitochondria are some- 1). The other one, namely, Complex II, contains only times described as “cellular power plants”, because they nuclear DNA-encoded subunits. Mitochondrial ATP provide 36 molecules of adenosine triphosphate (ATP) synthase (Complex V) comprises 2 subunits encoded by per glucose molecule in contrast to the 2 ATP molecules mtDNA (ATP6 and 8), as well as 10-16 subunits encoded produced by glycolysis. Mitochondria are also involved by nuclear DNA. Mitochondrial cytochrome b (Cytb) is in other functions such as cell growth, cell differentiation, the only mtDNA-encoded subunit of respiratory Complex cell death, and so on. A mitochondrion contains inner and III (ubiquinol: ferrocytochrome c oxidoreductase or cyto- outer membranes composed of phospholipid bilayers (Fig. chrome bc1 complex. 1). These membranes create two compartments, i.e., ma- mtDNA also contains major and minor non-coding re- trix (large space) and inter-membrane space (small space) gions11). The major non-coding region is located between within the organelle, and they have different functions and the genes for tRNA-Phe and tRNA-Pro, and is called the structures. The inner membrane of the mitochondrion has control region. This region is about 1.1 kb long (m.16024- numerous folds called cristae, which expand the surface 16569 plus m.1-576 = 1,122 bp) in humans and contains area of the inner membrane and thus enhance the ability the main regulatory elements for mtDNA transcrip- of the organelle to produce ATP. The matrix contains the tion and replication. This is also the region that is most enzymes that are associated with the citric acid cycle and variable in sequence and size among different species, beta-oxidation systems. The inner membrane is the site of although it contains several conserved elements with pos- all of the complexes of the OXPHOS system (i.e., elec- sible regulatory functions. tron transport chain and ATP synthase). Although most DNA is packaged in chromosomes with- Mitochondrial haplogroup. The term ‘haplotype’ is a in the nucleus, mitochondria also have a small amount of contraction of the term ‘haploid genotype’. In genetics, their own circular DNA, which is called mtDNA. Each a haplotype is a combination of alleles at multiple loci mitochondrion is estimated to contain 2-10 mtDNA cop- that are transmitted together on the same chromosome.

OXPHOS

Inter membrane space Matrix

Cristae Ribosome

Granules

Inner membrane Outer membrane mtDNA

Fig. 1 Mitochondrial structure. OXPHOS: Oxidative phosphorylation; mtDNA: mitochondrial DNA. JPFSM: mtDNA and physical performance 19

Therefore, the hereditary mode of mtDNA is haplotypic mtDNA have resulted from the sequential addition of new because mtDNA is inherited maternally. A mitochondrial mutations during the expansion of Homo sapiens from haplogroup is defined by the presence of a characteris- Africa to Asia and Europe over the last 200,000 years12). tic cluster of tightly linked mtDNA polymorphisms. In Because the mutational rate of the mtDNA is 10 times modern humans, maternally inherited substitutions in the higher than that of the nuclear DNA, the ancient mitochondrial polymorphisms that have accumulated during the relatively short history of Homo sapiens may have A D-loop contributed to the metabolic characteristics of modern hu- 12S Cytb mans13). Each of the African haplogroups (mainly, L0-L3), determined by mtDNA sequence analysis, has deeper ge- ND6 16S netic roots than those haplogroups in European and Asian populations14). Mitochondrial haplogroup L3 is proposed 15) ND5 to be the ancestor of all non-African populations . Euro- ND1 pean haplogroups (H, I, J, K, S, T, U, V, W, etc.) belong to mtDNA: 16,569 bp macrohaplogroup N16), whereas Asian haplogroups belong to both macrohaplogroups N and M (haplogroups A, B, F, and N9a to macrohaplogroup N; and haplogroups M7a, ND2 17) ND4 M7b, M8, D, and G to macrohaplogroup M) . Both macrohaplogroups N and M have haplogroup L3 as a com- ND4L mon root (Fig. 3). ND3 COI COIII COII ATP6 ATP8 Table 1. Respiratory chain subunits encoded by mtDNA72) Fig. 2 The human mitochondrial DNA (A) and mitochondrial Complex Enzyme No. of subunits mtDNA-encoded subunits oxidative phosphorylation system (B). Human mtDNA encodes 13 polypeptides: 7 subunits shown in orange I NADH reductase 43 7 (ND1, 2, 3, 4, 4L, 5, and 6) (ND1, ND2, ND3, ND4, ND4L, ND5, and ND6) of Complex I; 1 subunit shown in green (cytochrome b) II Succinate reductase 4 -

of Complex III, 3 subunits shown in pink (COI, COII, III Cytochrome c reductase 11 1 (Cytb) and COIII) of Complex IV, and 2 subunits (ATP6 and ATP8) of Complex V. mtDNA: mitochondrial DNA; IV Cytochrome c oxidase 13 3 (CO1, 2, and 3) ND: NADH dehydrogenase; ND1: NADH dehydroge- V ATP synthase 17 2 (ATP6, and 8) nase subunit 1; CO: Cytochrome c oxidase; ATP: ATP synthase; 12S: 12S rRNA; 16S: 16S rRNA.

B 20 JPFSM: Fuku N, et al.

N Macrohaplogroup M

L3 F B A N9a N9b M7a M7b G2 G1 D5 D4 African Haplogroup

Fig. 3 Japanese major mitochondrial haplogroups. The Japanese population based on mtDNA sequences is classfied into two groups, namely, macrohaplogroups N and M. Macrohaplogroup N comprises haplogroups F, B, A, N9a, and N9b; and macrohaplogroup M comprises haplogroups M7a, M7b, G2, G1, D4, and D4.

sports. They estimated the heritability of athlete status at Heritability of physical performance 66%. This proportion of genetic factors regarding athlete Heritability is defined as the additive proportion of ob- status seems to be reasonable in terms of the heritability served total phenotypic variation in a particular trait (e.g., estimates for aerobic performance from large cohorts as physical performance) that can be attributed to inherited mentioned above (approximately 50-60%)2,21). ・ genetic factors in contrast to environmental ones. In ge- Interestingly, the data on VO2max in the HERITAGE netics, it is the relative importance of genetics versus the Family Study, mentioned above, also indicated that ma- environment that determines the phenotype. The values of ternal influence, i.e., mitochondrial inheritance, accounts heritability estimates can range from 0 (0%) to 1 (100%). for as much as 30% of familial transmission, in which This heritability is a function of genetic and environmen- inheritance constitutes well more than half of the genetic tal factors, and the interaction between them; e.g., mono- factors2). Lesage et al.22) also reported stronger maternal ・ genic traits usually have a high heritability estimate (al- inheritance (than paternal) for VO2max in their familial most 100%), whereas only a relatively smaller proportion study. These results suggest a possible mitochondrial ge- of multifactorial disorders can be explained by genetic netic component active in athletic performance. factors alone. The topic of the role of genetic and environmental Association study on physical performance factors in the manifestation of physical performance- ・ related phenotypes, such as VO2max, was first addressed Restriction fragment length polymorphisms. RFLP (re- 18) ・ by Klissouras in 1971. He showed that the VO2max of striction fragment length polymorphism) is an old tech- monozygotic twins is more alike than that of dizygotic nique (but still useful) for detecting variation in DNA twins, and concluded a heritability estimate of 91% of sequences. A restriction enzyme cuts double- stranded the total phenotype diversity, although the sample size of DNA at a specific sequence, which is usually from 4 to 6 his study was small. Subsequent examination of moder- base pairs in length. The restricted DNA fragments, i.e., ate19,20) or large2,21) sample sizes has indicated a smaller polymorphisms, are usually separated by agarose gel elec- ・ effect of heritability estimates on VO2max. Among large- trophoresis. Analysis of DNA variation by RFLP has been scale studies, Sundet et al.21) reported that the heritability an important tool for genome mapping, identification of estimate accounts for approximately 60% of maximum disease-related genes, genetic fingerprinting, and so on. aerobic power based on data obtained from 436 monozy- The first report to address the association between mtD- gotic and 622 dizygotic male twin pairs registered with NA variations and a physical performance-related trait ・ 23) the Norwegian Army Draft Board. Similarly, Bouchard et (VO2max) was made by Dionne et al. They assessed 2) ・ al. reported that the heritability estimate of VO2max in the relationship between mtDNA RFLPs and baseline ・ the sedentary state, adjusted for age, sex, and body mass, VO2max, and its response to 20-week endurance training, is approximately 50% based on data from 429 individu- by examining 15 mtDNA RFLPs generated by 22 restric- als from 86 nuclear families in the HERITAGE Family tion enzymes in 46 sedentary North Americans of Quebec Study. Relatively recently, De Moor et al.1) provided indi- City. These 22 RFLP sites had been generated by base rect support for these observations in their study on 4488 substitutions located in protein-coding regions as well as adult female twins from the TwinsUK Adult Registry, in non-coding regions. They found that carriers of 3 mtD- which employed the first genome-wide linkage scan for NA RFLPs, 2 in the ND5 gene and 1 in the tRNA-Thr JPFSM: mtDNA and physical performance 21

・ gene, have a VO2max in the untrained state significantly pairs) of the mtDNA control region, which is a mutational higher than the non-carriers; whereas carriers of 1 mtDNA hotspot26). This matrilineal pattern of descent means that ・ RFLP in the ND2 gene have a lower initial VO2max. Car- individual haplotypes share linked complexes of poly- riers of 3 RFLPs in the ND5 gene are also associated with morphisms common to all sequences in a haplogroup. ・ 24) a lower VO2max. Subsequently, Rivera et al. examined We sequenced HVS1 and the C>A polymorphism at 125 Caucasian male elite endurance athletes and 65 sed- m.5178 within the ND2 gene of the mtDNA by use of entary controls for a possible association between elite an automated DNA sequencing machine from Applied endurance athlete status and 4 mtDNA RFLPs (3 in the Biosystems, and compared the percent frequency of mito- ND5 and 1 in the control region), which were previously chondrial haplogroups found in 141 Japanese Olympians, ・ 27) reported to be associated with VO2max as mentioned from various sports, with 672 Japanese controls . These above23). They found no significant associations between athletes were classified as endurance/middle-power ath- mtDNA RFLPs and elite endurance athlete status. In the letes (EMA=81) or sprint/power athletes (SPA=60). Sub- 1990’s, RFLP technology was generally considered the jects were classified into 12 major Japanese mitochondrial gold standard for genotyping, etc. Although it has been haplogroups (i.e., F, B, A, N9a, N9b, M7a, M7b, M*, G2, the most accurate method for gene typing, it has some G1, D5 or D4) on the basis of the presence of HVS1 poly- drawbacks, namely, sample size, sample quality, specific morphisms and several protein-coding region polymor- restriction enzyme (cannot be used for all sequence varia- phisms. The distribution of mitochondrial haplogroups in tions), and the length of time for analysis. Currently, the EMA and SPA, relative to that in the controls, is shown RFLP method is becoming less used for genotyping due in Fig. 4. When the frequency of each haplogroup versus to the rise of inexpensive DNA sequencing technologies. the sum of all others was compared between EMA or SPA and controls, we found that EMA displays an excess of Mitochondrial haplogroups. As mentioned above, a mi- haplogroup G1 (OR 2.52 [95% CI 1.05-6.02], P=0.032; tochondrial haplogroup is defined by the presence of a Fig. 4), with 8.9% in the EMA group compared with 3.7% characteristic cluster of tightly linked mtDNA polymor- in the control. On the other hand, SPA shows a greater phisms, namely, a set of mtDNA polymorphisms (See proportion of haplogroup F (OR 2.79 [95% CI 1.28-6.07], section 1-3). The matrilineal inheritance of mtDNA and P=0.007; Fig. 4), with 15.0% in the SPA group relative to linear accumulation of polymorphisms have allowed the 6.0% in the control. construction of detailed mtDNA phylogenies25). These Our previous reports also suggested that certain mi- phylogenies display the variation and diversity of hu- tochondrial haplogroups are associated with elite Ke- man mtDNA and allow haplogroup identification through nyan endurance athlete status28) and Jamaican/African- the analysis of a small number of haplogroup-specific American sprint athlete status29). Elite Kenyan endurance polymorphisms, i.e., polymorphisms detected in the hy- athletes display an excess of haplogroup L0 and a dearth pervariable segment 1 (HVS1: approximately 350 base of haplogroup L3 relative to the general Kenyan popula-

40 EMA 35 Control SPA 30

nt age 20

Perce ** 15

10 *

0 FBAN9a N9bM7a M7bM*G2G1D5D4Others Haplogroup

Fig. 4 Mitochondrial haplogroup distribution in endurance/middle power athletes, sprint/ power athletes, and controls27). Significant differences from Controls (gray bars) are highlighted by asterisks (*P<0.05, **P<0.01). For haplogroup analysis, we compared each haplogroup versus the sum of all other haplogroups. The P value, odds ratio (OR), and 95% confidence intervals (CI) were calculated. A P value < 0.05 was considered statistically significant. 22 JPFSM: Fuku N, et al. tion; and the elite African-American sprint athletes, an obesity. excess of non-African haplogroups relative to the general We have proposed a hypothesis to explain this incon- African-American population. Niemi et al.30) also found sistency (Fig. 5). The main function of mitochondria is differences in mitochondrial haplogroup frequencies be- to produce ATP by OXPHOS; and while the uncoupling tween elite Finnish sprint and endurance athletes, i.e, no of mitochondrial OXPHOS generates heat, it concomi- endurance athletes belong to mitochondrial haplogroup K tantly reduces the production of ATP36). Conversely, more and subhaplogroup J2; although this study did not use a tightly coupled OXPHOS would be expected to decrease control group for comparison. Furthermore, Castro et al.31) heat production and result in higher efficiency of ATP reported that haplogroup T is negatively associated with production. This improved efficiency in ATP production elite Spanish endurance athlete status. Our study, noted could explain, in part at least, the association between above, is the first one to report that “Asian”-specific mito- haplogroup G1 and endurance performance. However, chondrial haplogroups G1 and F are associated with elite this energy conservation by mitochondrial OXPHOS may Japanese EMA and SPA status, respectively. It is very predispose to obesity in sedentary individuals later on in important to examine the association between phenotypic life - a phenomenon commonly referred to as the “thrifty” traits and mtDNA polymorphisms in terms of popula- genotype and/or “thrifty” phenotype37). These hypotheses tion, ethnicity, and/or race, because mtDNA sequences, require further investigation. especially those in the control region, are known to vary among populations32-34). 2. Sprint/power performance-related haplogroup F: Although numerous studies have reported associations 1. Endurance performance-related haplogroup G1: between aerobic performance phenotypes and mitochon- Among the mtDNA polymorphisms characteristic of drial haplogroups, studies on associations between “an- haplogroup G1, the m.15497G>A transition, causing aerobic” performance phenotypes and mitochondrial hap- Gly251Ser replacement in the Cytb gene, seems to be a logroups are lacking. Because “anaerobic” capacity relies functional polymorphism. A previous survey, conducted more heavily upon glycolysis than upon mitochondrial as part of the National Institute for Longevity Longitu- OXPHOS, it is not commonly believed that certain mtD- dinal Study on Aging, revealed that this m.15497G>A NA polymorphisms and/or mitochondrial haplogroups transition is associated with obesity in the middle aged- are related to anaerobic capacity. However, it should be to-elderly Japanese population35). This observation may noted that we found a positive association between mito- indicate increased efficiency of mitochondrial energy chondrial haplogroup F and elite Japanese SPA status. We conservation at the cytochrome bc1 complex, resulting in also examined the effect of mitochondrial haplogroups on decreased energy consumption. As mentioned above, we anaerobic performance phenotypes such as muscle power, recently reported that this obesity-associated mitochon- muscle strength, and muscle mass in 480 healthy Japa- drial haplogroup, namely, haplogroup G1, is also associ- nese non-athlete adults, and found that macrohaplogroup ated with elite Japanese EMA status27). This finding seems N is significantly associated with stronger leg extension to be inconsistent with the association between G1 and power and higher vertical jump performance compared

Mitochondria

Haplogroup G1 (Thrifty genotype) Normal genotype

Heat ATP Heat ATP

Energy efficiency Energy efficiency

Sedentary Training Sedentary Training

Obesity Elite endurance athlete Resistance against Normal athlete obesity

Fig. 5 Model to explain effect of “thrifty” genotype and/or “thrifty” phenotype. JPFSM: mtDNA and physical performance 23 with macrohaplogroup M for these Japanese subjects38). Polymorphisms in the control region. We have already Mitochondrial haplogroup F, which is associated with stated that mtDNA contains 37 genes, i.e., 13 mRNAs, 22 elite Japanese SPA status, is one of the major components tRNAs, and 2 rRNAs. The mtDNA also contains major of macrohaplogroup N17), which is associated with muscle non-coding regions43), which include the control region or power in non-athletic Japanese individuals. Although we D-loop. The control region of mtDNA contains the heavy could not demonstrate a significant association between strand origin of replication, the promoters for heavy (H) mitochondrial haplogroup F and anaerobic performance and light (L) strand transcription, and the binding site of phenotypes in the 480 non-athletic individuals, both leg mitochondrial transcriptional factor A (TFAM)44). There- extension power (18.3 ± 1 vs. 17.3 ± 0.3 watts/kg body fore, it is likely that the polymorphisms in these function- weight) and vertical jump performance (38.2 ± 1.9 vs. al regions of mtDNA cause a difference in the sensitivity 36.5 ± 0.5 cm) tended to be higher in subjects with mi- of this TFAM binding site. Thus, the control region may tochondrial haplogroup F than in those with other hap- contain important polymorphisms influencing physical logroups. performance. Previous studies also focused on the roles of mitochon- To examine this hypothesis, we sequenced the entire dria in the regulation of intracellular calcium dynam- control region of mtDNA by use of an automated DNA ics39,40). Kazuno et al.41) previously reported that baseline sequencing machine from Applied Biosystems, and com- mitochondrial calcium levels and peak cytosolic calcium pared the percentage frequencies of polymorphisms found levels after stimulation with histamine, which induces the in 185 Japanese international athletes from various sports, release of calcium from the endoplasmic reticulum, are mainly track & field, with those found in 672 Japanese higher in cybrids with mitochondrial macrohaplogroup controls45). The subjects were comprised of 185 elite N than in those with mitochondrial macrohaplogroup M. Japanese athletes who had represented Japan at interna- Thus, a certain mitochondrial macrohaplogroup might tional competitions (i.e., 100 EMA and 85 SPA) and 672 be related to intracellular calcium dynamics. Calcium Japanese controls. Table 2 displays the results of all poly- regulates muscle contraction. During activation of con- morphisms that reached statistical significance (P<0.05) traction in skeletal muscle, calcium is released from the when the frequencies of polymorphisms were compared sarcoplasmic reticulum, and also activates phosphorylase between the athletes and controls. The EMA group dis- kinase. Interestingly, it has also been reported that certain played an excess of three polymorphisms [m.152T>C, mitochondrial haplogroups affect the expression of com- m.514(CA)n repeat (n≥5), and poly-C stretch at m.568-573 ponents of the glycolysis pathway encoded by nuclear (C≥7)] compared to the controls. On the other hand, the DNA42). This suggests that mtDNA polymorphisms or SPA group showed a greater frequency of the m.204T>C haplogroups can affect the expression of nuclear genes polymorphism compared to the controls. In addition, none regulating mitochondrial functions or cellular energetics. of the SPA individuals had m.16278C>T polymorphism, Thus, a certain mitochondrial haplogroup, which indicates whereas the frequencies of this polymorphism in controls differences in mitochondrial function, may influence an- and EMA were 8.3% and 10.0%, respectively. These find- aerobic performance and its-related phenotypes such as ings imply that several polymorphisms detected in the muscle power. control region of mtDNA may influence physical performance, probably in a functional manner.

Table 2. Polymorphisms in the mtDNA control region associated with SPA or EMA status45)

CON (n=672) EMA (n=100) SPA (n=85) Polymorphism P P % (n) % (n) value OR (95% CI) % (n) value OR (95% CI) For EMA status m.152T>C 㻌 T 81.5 (548) 72.0 (72) 0.025 1.72 (1.07 to 2.77) 75.3 (64) 0.168 1.45 (0.85 to 2.46) 㻌 C 18.5 (124) 28.0 (28) 24.7 (21) m.514(CA)n (CA) 40.6 (273) 27.0 (27) 0.009 1.85 (1.16 to 2.95) 40.0 (34) 0.912 1.03 (0.65 to 1.63) (CA) 59.4 (399) 73.0 (73) 60.0 (51) Poly-C stretch at m.568-573 (C)6 96.0 (645) 89.0 (89) 0.003 2.95 (1.42 to 6.16) 98.8 (84) 0.191 0.28 (0.04 to 2.12) (C)7 4.0 (27) 11.0 (11) 1.2 (1)

For SPA status m.204T>C 㻌 T 95.1 (639) 98.0 (98) 0.192 0.40 (0.09 to 1.67) 88.2 (75) 0.010 2.58 (1.22 to 5.45) 㻌 C 4.9 (33) 2.0 (2) 11.8 (10) m.16278C>T 㻌 C 91.7 (616) 90.0 (90) 0.578 1.22 (0.60 to 2.48) 100.0 (85) 0.006 0.00 - 㻌 T 8.3 (56) 10.0 (10) 0.0 (0) CON: Controls; EMA: endurance/middle-power athletes; SPA: sprint/power athlete; OR: odds ratio; CI: confidence intervals. 24 JPFSM: Fuku N, et al.

1. Endurance performance-related m.152T>C polymor- in Table 2, the frequencies of m.204T>C and m.16278C>T phism polymorphisms in SPA and EMA deviated in opposite The m.152T>C polymorphism is located next to the directions from the controls (P=0.013 and P=0.003, re- second heavy-strand replication origin (m.146-151). spectively). Opposite effects on elite SPA and EMA status Although there is no direct evidence explaining an asso- of different genotypes at a single locus have also been ciation between endurance performance and m.152T>C observed in studies on the genes encoding angiotensin- polymorphism of the mtDNA control region, some inter- converting enzyme (ACE)54), α-actinin-3 (ACTN3)55,56), esting findings have been reported to explain this associa- and peroxisome proliferator-activated receptor-alpha tion. Fish et al.46) suggested that the nucleotide position (PPARA)57). These genes and/or genotype regulate, at m.151 in the mtDNA is important for accelerating mtD- least in part, muscle properties such as fiber-type compo- NA replication in response to physiological demands. An- sition and metabolic dynamics in the skeletal muscle58). other polymorphism, the m.150C>T polymorphism adja- Sprint/power athletes obviously require a proliferation cent to m.151, is reportedly associated with longevity and of fast-twitch muscle fibers, and 70-80% of the skeletal remodeling of the replication-origin site47). We previously muscle fibers in elite-level SPA individuals are fast-twitch reported that mitochondrial haplogroups N9a, G1, and D5 muscle fibers59). Sprint performance also relies more on are associated with resistance against the metabolic syn- anaerobic ATP production by glycolysis than on aerobic drome in Japanese women48,49), and that haplogroup N9a ATP production by mitochondrial OXPHOS. Possible is also associated with resistance against type 2 diabetes mechanisms underlying the results presented here explain mellitus in an Asian population48,50). Interestingly, all of why the mtDNA control region polymorphisms are as- these haplogroups are accompanied by the 150C>T poly- sociated with elite-status Japanese athletes whether they morphism. These findings suggest the importance of the are of EMA or SPA status. Mitochondria play an impor- region around the heavy-strand replication-origin site, and tant role in determining muscle fiber-type composition, consequently allow the prediction that polymorphisms because it was previously reported that PPAR gamma near this site are functional to some extent. The m.152T>C coactivator 1-alpha (PPARGC1A) and/or PPAR-delta polymorphism, which is associated with endurance per- (PPARD), which are regulators of mitochondrial biogen- formance, seems to be one of the potentially functional esis, drive the ratio of slow/fast-twitch muscle fibers60,61). polymorphisms influencing mtDNA replication and/or If certain control-region polymorphisms, e.g., m.204T>C mitochondria biogenesis. or m.16278C>T, in mtDNA down- or up-regulate mtDNA replication and/or transcription by PPARs or a variation, 2. Endurance performance-related m.514(CA)n length muscle composition can be changed to fast- or slow- polymorphism twitch muscle fiber. In addition, decreased ATP genera- Another EMA status-related polymorphism, i.e., the tion from mitochondrial OXPHOS, due to mitochondrial m.514(CA)n repeat, displays variation in length. The dysfunction by mtDNA mutation, induces compensatory 62) frequency of m.514(CA)≤4 is significantly lower in EMA up-regulation of the cytoplasmic glycolysis process , 63) individuals than in controls, whereas that of m.514(CA)≥5 which is called the Warburg effect . Therefore, decreased is higher in the former than in the latter. It should be mitochondrial function contributes to enhanced capacity noted that Murakami et al.51) reported that the mtDNA content in the vastus lateralis muscle is higher in healthy sedentary Japanese males with m.514(CA)≥5 than in those with m.514(CA)4 (Fig. 6). mtDNA content is significantly associated with citrate synthase activity and VO2peak52). This apparent link between the long m.514(CA)n repeat (n≥5) in the mtDNA control region and enhanced aerobic capacity, due to an increase in mtDNA content in the skeletal muscle (or cardiac muscle), may explain why this polymorphism is associated with elite EMA status.

3. Sprint/power performance-related m.204T>C and m.16278C>T polymorphisms The nucleotide position at m.204 is located 9 bp up- stream of the conserved sequence block 1 (CSB1: m.213- 235), a region associated with RNA priming of mtDNA replication. On the other hand, the nucleotide position at m.16278 is located in the 7S DNA (m.16106-191), which Fig. 6 Relationship between mtDNA content in the skeletal is also called the short single-stranded DNA fragment, a muscle and m.514(CA)n length polymorphism of 53) region associated with mtDNA copy number . As shown the control region in mtDNA51). JPFSM: mtDNA and physical performance 25 for generation of ATP by glycolysis. This effect can, at phisms detected in both mtDNA and nuclear DNA, e.g., least in part, explain why athletes with certain polymor- whole genome sequencing for mtDNA and genome-wide phisms in the mtDNA control region associated with mi- association studies (GWAS) for nuclear DNA70), even tochondrial function, such as mtDNA replication and/or though GWAS may not be able to find genetic polymor- transcription, have an advantage or disadvantage in terms phisms with a large effect that explain the overall genetic of sprint/power performance. factors predicted by heritability estimates71).

Conclusions and future directions References

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