Mutations in mitochondrial aldehyde dehydrogenase (ALDH2) change cofactor affinity and segregate with voluntary alcohol consumption in rats

Abstract

Genetic factors influence alcohol consumption and alcoholism. A number of groups have bred alcohol drinker and non drinker rat strains, but genetic determinants remain unknown. The University of Chile rat lines UChA (low drinkers) and UChB (high drinkers) display differences in the relative K-m for NAD(+) of mitochondrial aldehyde dehydrogenase (ALDH2) but no V-max differences. The relative K-m differences may be due to mitochondrial changes or to genetic differences coding for ALDH2. We investigated whether there are differences in the coding regions of ALDH2 cDNA in these lines and whether the AIdh2 genotype predicts the phenotype of alcohol consumption and the K-m of ALDH2 for NAD(+). Liver cDNA was prepared, and the Aldh2 transcript was amplified, cloned and sequenced. Genotyping was conducted by DNA amplification and restriction enzyme digestion. When compared to Aldh2(1) of Sprague-Dawley, 94% of the UChA (low drinker) rats (n = 61), presented a mutation that changes Gln(67) to Arg in the mature enzyme (allele referred to as Aldh2(2)). In UChB (high drinker) rats (n = 69), 58% presented the Aldh2(1) allele, while 42% presented the Gln(67)Arg change plus a second mutation that changed GIu(479) to Lys (allele Aldh2(3)). The Aldh2(2) allele was absent in high drinker rats. Rats of different AIdh2 genotypes displayed marked phenotypic differences in both ethanol consumption (g/kg/day; means +/- SE): (AIdh2(1)/ Aldh2(1)) = 5.7 +/- 0.2, (Aldh2(2)/Aldh2(2)) = 0.9 +/- 0.2 and (Aldh2(3)/Aldh2(3)) = 4.6 +/- 0.2; and K(m)s for NAD(+) of 43 +/- 3 muM, 132 +/- 13 muM and 41 +/- 2 mum, respectively (Aldh2(2) versus Aldh2(1) or Aldh2(3); P < 0.0001 for both phenotypes). Overall, the data show that alleles of Aldh2 strongly segregate with the phenotype of ethanol consumption and the relative K-m for NAD(+) of ALDH2. Bases mutated suggest that non drinker Aldh2(2) is ancestral with regard to the coding changes in either Aldh2(1) or Aldh2(3), variants which would allow ethanol consumption and may provide an evolutionary advantage by promoting calorie intake from fermented products along with carbohydrates.