Assessment of Mitochondrial DNA Polymorphisms in Salt-Sensitive Hypertension in Dahl Salt-Sensitive Rats

107 Hypertens Res Vol.31 (2008) No.1 p.107-115 Original Article Assessment of Mitochondrial DNA Polymorphisms in Salt-Sensitive Hypertension in Dahl Salt-Sensitive Rats Chu-Shih CHEN1),*, Yumiko HIURA1),*, Chun-Shen SHEN1), and Naoharu IWAI1) The Dahl salt-sensitive (DS) rat is the most prevalently used animal model of salt-sensitive hypertension. The purpose of the present study was to test the hypothesis that mitochondrial DNA (mtDNA) polymorphisms influence blood pressure in DS rats. We produced two strains of female F1 rats, one from female DS and male Lewis rats (DL) and the other from Lewis female and DS male rats (LD). These two strains had the same autosomal genetic background, but their mitochondria had different origins. The DL and LD rats had DS and Lewis mitochondria, respectively. A high-salt diet was started at 4 weeks of age. Radiotelemetry devices were implanted into the lower abdominal aorta of these F1 rats at 9 weeks of age. Blood pressure was monitored for 24 h at 11, 12, 13, 14, and 19 weeks of age. No significant differences were observed in blood pressure levels between the strains. Although more than 100 polymorphisms were detected between DS and Lewis rats, it is unlikely that polymorphisms in mtDNA contribute to hypertension in DS rats. Moreover, we found no difference between DS and Lewis rats in the mtDNA copy number in the kidneys, the liver, and the ventricles of the heart before and after salt loading. Thus, it is unlikely that mitochondrial dysfunction due to high blood pressure exacerbated target organ damage. Intriguingly, the time course of body weight gain differed significantly between DL and LD F1 rats, suggesting the influence of mitochondrial polymorphisms on body composition. (Hypertens Res 2008; 31: 107–115) Key Words: mitochondrial DNA, hypertension, Dahl salt-sensitive rat Introduction The Dahl salt-sensitive (DS) rat is the most prevalently used animal model of salt-sensitive hypertension. When started on an 8.0% NaCl diet, DS rats rapidly develop low-renin hypertension and renal failure resembling hypertensive nephrosclerosis (1, 2). Although more than 16 genomic regions have been reported to be responsible for this salt-sensitive hypertension, only a few genes have been identified as likely causative ones (3–7). Accumulating evidence suggests that mitochondrial dys- function is associated with the metabolic syndrome (8–11). Statistical tests developed to assess the involvement of mitochondrial DNA (mtDNA) mutation in a disease demonstrated the contributions of mtDNA mutations in hypertension and diabetes (10). Furthermore, a mutation in the mitochondrial transfer RNA has been reported to cause a syndrome including hypertension, hypercholesterolemia, and hypomagnesemia (11). Maternal transmission of mutant mtDNA resulted in the death of most mice within 200 days of birth due to renal failure (12). In that study, blood pressure was not monitored. It can be speculated that the renal failure induced by a high-salt diet in DS rats is exacerbated by some defects From the 1)Department of Epidemiology, Research Institute, National Cardiovascular Center, Suita, Japan. *These two authors contributed equally to this work. The present study was supported by research grants from the Salt Science Research Foundation 06C5 and the Program for the Promotion of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovation, Japan. Address for Reprints: Naoharu Iwai, M.D., Department of Epidemiology, Research Institute, National Cardiovascular Center, 5–7–1 Fujishirodai, Suita 565–8565, Japan. E-mail: Received April 23, 2007; Accepted in revised form July 25, 2007. 108 Hypertens Res Vol. 31, No. 1 (2008) Table 1. Sequence Analyses of mtDNAs of DS and Lewis Rats No. Map position Location 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 935 942 1130 1131 1137 1209 1223 1248 1521 1585 1653–4 1716 1832 2170 2836 2928 2955 3000 3378 3429 3435 3444 4352 4446 4554 4696 4785 4814 4848–50 5200 5202 5237 5269 5559 5709 5742 6012 6174 6312 6438 6600 6624 6663 6768 6786 6825 6852 6978 7206 7227 7401 12S rRNA 12S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA 16S rRNA ND1 ND1 ND1 ND1 ND1 ND1 ND1 ND1 ND2 ND2 ND2 ND2 ND2 ND2 ND2 tRNA-Cys tRNA-Cys tRNA-Cys tRNA-Tyr CO I CO I CO I CO I CO I CO I CO I CO I CO I CO I CO I CO I CO I CO I tRNA-Asp CO II CO II CO II Nucleotide change DS Lewis A C Del A A T A C G T AC T G T T T T T C C T C A C T G T C Del A A T G A T G T A A C T A T G T T T G T T A G T CCCCCC C C A G T A C Del C A C C C C C T T C T G T C A A T CCA G G A C G C A C G G T C G C A C C C A C C G Amino acid change — — — — — — — — — — — — — — syn syn syn syn syn syn syn syn Asn→Ser syn syn Ala→Thr syn Thr→Met Del→His — — — — syn syn syn syn syn syn syn syn syn syn syn syn syn syn — syn syn syn Chen et al: mtDNA Polymorphisms in DS Rats Table 1. Continued No. Map position Location 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 7498 7557 7578 7886 7981 8021 8150 8155 8452 8844 8961 9120 9534 9669 9702 9916 10051 10053 10227 10372 10696 11128 11170 11194 11389 11415 11799 11831 11844 11918 12068 12272 12350 12468 12575 12635 12818 13478 13647 13693 13822 14324 14483 14489 14775 15005 15062 15188 15209 15333 15549 CO II CO II CO II ATP 8 ATP 6 ATP 6 ATP 6 ATP 6 ATP 6 CO III CO III CO III ND 3 ND 3 ND 3 ND 4L ND 4L ND 4L ND 4 ND 4 ND 4 ND 4 ND 4 ND 4 ND 4 ND 4 ND 5 ND 5 ND 5 ND 5 ND 5 ND 5 ND 5 ND 5 ND 5 ND 5 ND 5 ND 5 ND 6 ND 6 ND 6 Cyt b Cyt b Cyt b Cyt b Cyt b Cyt b Cyt b Cyt b tRNA-Thr D-loop Nucleotide change DS Lewis A C A C G G T C C A C T C T C T T A T A T A T T G T C C A C C C C C T C A A T T T C G C G G C T T G C G G G T A A G T T G T G T C T G A T C G C C C C A C T T G T T T T T C T G G C C C T A T A A T C C A T Amino acid change Ile→Val syn syn syn syn Glu→Arg Phe→Val syn syn syn syn syn syn syn syn Leu→Arg Ile→Asn Thr→Ser Ile→Thr syn syn syn syn syn syn syn syn syn Thr→Ala syn syn syn syn syn syn syn syn syn Ile→Val syn syn syn syn syn Asp→Asn syn syn syn syn — — 109 110 Hypertens Res Vol. 31, No. 1 (2008) Table 1. Continued No. Map position Location 103 104 15589 16313 D-loop D-loop Nucleotide change DS Lewis A A G G Amino acid change — — The map position numbers are based on the sequence of Norway rat published on GenBank (AC_000022). ND 1, ND 2, ND 3, ND 4, ND 4L, ND 5, and ND 6 are subunits 1–6 of complex I (NADH dehydrogenase); CO I, CO II, and CO III are subunits 1–3 of complex IV (cytochrome c oxidase); ATP 8 and ATP 6 are subunits of complex V (ATP synthase); and Cyt b is a subunit of complex III (ubiquinol: cytochrome c oxidoreductase). mtDNA, mitochondrial DNA; syn, synonymous; Del, deletion. in the mito (...truncated)