Mapping Data

Experiment

• Experiment
  TEXT-QTL-Candidate Genes
• Chromosome
  3
• Reference
  J:290574 Nicolaou A, et al., Quantitative trait locus mapping in mice identifies phospholipase Pla2g12a as novel atherosclerosis modifier. Atherosclerosis. 2017 Oct;265:197-206
• ID
  MGI:6446989

Genes

Gene
Pla2g12a
Vcam1

Notes

• Experiment
  In a previous work (Teupser, 2006), a female-specific atherosclerosis risk locus on Chr 3 (Ascla3; MGI:3613542) was identified in an intercross of atherosclerosis-resistant FVB and atherosclerosis-susceptible C57BL/6 (B6) mice on the LDL-receptor deficient (Ldlr^-/-) background (B6.129S7-Ldlr^tm1Her/J). It was the aim of the current study to identify causative genes at this locus.
  
  The authors established a congenic mouse model, where heterozygous FVB.Chr3^FVB/B6 (carrying an interval from megabases (Mb) 80 to 160 from Chr 3 of B6 mice in an otherwise FVB background) were intercrossed to generate FVB.Chr3^B6/B6, FVB.Chr3^FVB/B6 and wild-type FVB.Chr3^FVB/FVB control mice, to validate the Chr 3 locus. Candidate genes were identified using genome-wide expression analyses. Differentially expressed genes were validated using quantitative PCRs in F0 and F2 mice and their functions were investigated in pathophysiologically relevant cells.
  
  To fine-map the two previously identified female-specific atherosclerosis risk subloci within the Chr 3 QTL (Teupser, 2006), the authors genotyped 6 additional SNPs in 107 female mice of cross A and in 120 female mice of cross B (Fig. 1). QTL analysis revealed LOD score maxima for atherosclerosis at the initially identified markers d3mit45 (LOD 3.3, cross A) and d3mit57 (LOD 4.1, cross B), where homozygosity for the B6 alleles correlated with 2.3-fold and 2.2-fold more atherosclerosis (Teupser, 2006). Applying a conservative cutoff of 1.5 LOD when defining the confidence intervals, the authors narrowed down the genetic regions potentially containing candidate genes of atherosclerosis risk from 44 to 37 Mb in cross A and 55 to 44 Mb in cross B, respectively. The two loci now spanned from SNP rs36523879 to rs31598641 (Fig. 1A) and from SNP rs4224041 to d3mit254 (Fig. 1B), containing 221 genes (cross A) and 593 genes (cross B), respectively.
  
  The two QTL are defined as follows:
  
  Ascla3a (atherosclerotic lesion area 3a) maps to Chr 3: 37 - 44 Mb (rs36523879 - rs31598641) with a peak LOD score of 3.3 at d3mit45.
  
  Ascla3b (atherosclerotic lesion area 3b) maps to Chr 3: 44 - 55 Mb (rs4224041 - d3mit254) with a peak LOD score of 4.1 at d3mit57.
  
  Clinical chemistry parameters and plasma lipid levels showed no differences between FVB.Chr3^B6/B6, FVB.Chr3^B6/FVB and FVB.Chr3^FVB/FVB mice. Yet, the authors found that female homozygous FVB.Chr3^B6/B6 mice showed robustly enhanced 2.5-fold larger atherosclerotic lesions in the aortic root compared to heterozygous FVB.Chr3^B6/FVB (p = 0.02) or control FVB.Chr3^FVB/FVB mice (p = 0.039). These data confirmed that atherosclerosis susceptibility was contained within the 80 Mb of genomic DNA from Chr 3 of B6 mice, and that atherogenesis was likely triggered independent of cholesterol and triglyceride metabolism.
  
  Fine-mapping of the Chr 3 locus revealed two overlapping, yet independent subloci for female atherosclerosis susceptibility: when transmitted by grandfathers to granddaughters, the B6 risk allele increased atherosclerosis and downregulated the expression of the secreted phospholipase Pla2g12a (2.6 and 2.2 fold, respectively); when inherited by grandmothers, the B6 risk allele induced vascular cell adhesion molecule 1 (Vcam1).
  
  Down-regulation of Pla2g12a and up-regulation of Vcam1 were validated in female FVB.Chr3^B6/B6 congenic mice, which developed 2.5 greater atherosclerotic lesions compared to littermate controls (p = 0.039). Pla2g12a was highly expressed in aortic endothelial cells in vivo, and knocking-down Pla2g12a expression by RNAi in cultured vascular endothelial cells or macrophages increased their adhesion to ECs in vitro.