Genetic and biochemical studies of SNPs of the mitochondrial A beta-degrading protease, hPreP.

Several studies suggest mitochondrial dysfunction as a possible mechanism underlying the development of Alzheimer disease (AD). There is data showing that amyloid-beta (A beta) peptide is present in AD brain mitochondria. The human presequence protease (hPreP) was recently shown to be the major mitochondrial A beta-degrading enzyme. We investigated if there is an increased susceptibility to AD, which can be attributed to genetic variation in the hPreP gene PITRM1 and if the proteolytic efficiency of recombinant hPreP variants is affected. When a total of 673 AD cases and 649 controls were genotyped for 18 single nucleotide polymorphisms (SNPs), no genetic association between any of the SNPs and the risk for AD was found. In contrast, functional analysis of four non-synonymous SNPs in hPreP revealed a decreased activity compared to wild type hPreP. Using A beta, the presequence of ATP synthase F(1)beta subunit and a fluorescent peptide as substrates, the lowest activity was observed for the hPreP(A525D) variant, corresponding to rs1224893, which displayed only 20-30% of wild type activity. Furthermore, the activity of all variants was restored by the addition of Mg(2+), suggesting an important role for this metal during proteolysis. In conclusion, our data suggest that genetic variation in the hPreP gene PITRM1 may potentially contribute to mitochondrial dysfunctions.