Fine mapping of Dyscalc1, the major genetic determinant of dystrophic cardiac calcification in mice

Abstract

Calcification of severely dystrophic muscle is occasionally observed in targeted mouse models of muscular dystrophy and cardiomyopathy. Intracellular calcium deposition occurs in necrotic myocytes in the absence of plasma calcium and phosphate imbalances. In the heart, this recessive trait is referred to as dystrophic cardiac calcinosis (DCC). We identified previously Dyscalc1, a major genetic determinant of DCC, in a 15.2-Mbp region on proximal chromosome 7. We report now further steps toward the identification of the Dyscalc1 gene by reverse genetics. Transferring the Dyscalc1 locus from susceptible mouse strain C3H/He onto a resistant C57BL/6 strain background, we generated congenic inbred strains B6.C3-(D7Mit56-D7Mit230) and B6.C3-(D7Nds5-D7Mit230). Three days after myocardial freeze-thaw injury, both strains exhibited calcification of necrotic lesions, confirming the pathogenetic relevance of Dyscalc1. Analysis of two (129S1 x C57BL/6) x 129S1 backcrosses allowed mapping of Dyscalc1 more precisely to a region spanning 0.76 Mbp between genes Fgf21 (39.70 Mbp) and Myod1 (40.46 Mbp). This interval contains 31 known and putative genes in three large, ancestral haplotypes shared by susceptible strains C3H/He, 129S1, and DBA/2. Thus we were able to exclude previously proposed candidate genes Bax and Hrc. Instead, a potential candidate may be the gene encoding the ATP-binding cassette C6. Mutations in the orthologous human ABCC6 gene cause pseudoxanthoma elasticum, or Gronblad-Strandberg syndrome, an elastic tissue disorder with cardiovascular calcifications.

Ultrafine mapping of Dyscalc1 to an 80-kb chromosomal segment on chromosome 7 in mice susceptible for dystrophic calcification

“…Interestingly, a single major locus appears to determine the phenotype, as a highly conserved region on chromosome 7 is found in practically all mouse strains that develop DCC (4,9,11). The genotypes of these DCC-positive strains can be compared with those that do not display calcifications upon tissue injury.…”

“…Very recently, Korff et al (11) reported fine mapping of the Dyscalc1 region by analysis of novel congenic mouse strains to an interval Ͻ1 million base pairs (Mb) wide and suggested the ATP-binding cassette C6 (Abcc6) as a new candidate gene for DCC.…”

SPP1 Promoter Polymorphisms: Identification of the First Modifier Gene for Pseudoxanthoma Elasticum

“…Altered expression of SPP1 has been found in the dermis of PXE patients analyzed by immunoelectron microscopy (19 ). Recent studies have described strong SPP1 expression due to the Dyscalc1 locus in mice suffering from dystrophic cardiac calcification, with abcc6 gene as a potential candidate gene (20,21 ). The abcc6 gene has just been excluded, however, emphasizing that only the N-terminal part of the gene was screened for sequence variations and that most PXE-associated ABCC6 mutations were found in the C-terminal part (5,6,34 ).…”

“…SPP1 expression is increased in mice suffering from dystrophic cardiac calcification (20 ), leading to the suggestion that high SPP1 expression is influenced by a trans-activator gene, the Dyscalc1 locus on chromosome 7 (20 ). The mouse abcc6 gene was identified as a potential candidate gene in this region (21 ).…”

Chronic Kidney Disease Results in Deficiency of ABCC6, the Novel Inhibitor of Vascular Calcification

“…PXE has a prevalence of 1 in 25,000 [9] and is characterized by ectopic calcification and fragmentation of elastic fibers of connective tissues, including skin, vascular walls and the eyes [10]. ABCC6 has also been identified as the causal gene within the Dyscalc1 locus that predisposes certain mouse strains (such as C3H/HeJ and DBA/2J) to dystrophic cardiac calcinosis and other ectopic soft tissue calcification [11,12]. …”