Abstract 359: The T-Cell Negative Regulator, Lymphocyte Activation Gene-3, is Significantly Associated With SCARB1 Intronic Variant rs10846744 and Small HDL Particles

Abstract

Objective: We previously reported a significant association of SCARB1 intronic rs10846744 in reducing odds ratio for incident coronary heart disease (CHD) within participants of the Multi-Ethnic Study of Atherosclerosis (MESA), which was independent of lipid levels. We have now explored the underlying molecular mechanism for this clinical association. Methods and Results: Adults between 18-80 years of age with fasting HDL-C levels ≥ 60 mg/dl (HALP) donated fasting blood for rs10846744 genotyping, lipid/lipoprotein measurements, and EBV-B cell lymphocyte culture. Using RNA Seq, we found that lymphocytes isolated from HALP carriers homozygous for the risk C allele had significantly lower RNA expression of MHC class II (82-fold lower, p<0.05) and lymphocyte activation gene-3 (LAG3: a negative regulator of T cell activation) (5-fold lower, p<0.05) compared with carriers homozygous for the reference G allele. We next measured plasma soluble LAG3 (sLAG3) and observed that sLAG3 was significantly lower in carriers of the C allele (1722 ± 2983 pg/ml, 6-fold lower, p=0.009) compared with carriers of the G allele (11926 ± 1134). Given that traditional lipid levels did not attenuate the association of rs10846744 with CHD, we next determined whether sLAG3 associated with HDL subfractions as measured by NMR spectroscopy and 2D gel electrophoresis. As compared with GG carriers, CC carriers had significantly higher concentration of small HDL particles by NMR (24.8 ± 1.7 vs. 17.9 ± 0.8 μmol/L, p=0.0009, n=101) and by 2D gel electrophoresis (4.3 ± 0.5 vs. 2.0 ± 0.2, p=0.0002, n=63). For the entire cohort, sLAG2 was negatively associated with small HDL particles by NMR (p=0.02, n=98) and 2D gel electrophoresis (prebeta 2: p=0.04, n=59). Conclusion: This is the first observation that the SCARB1 intronic rs10846744 significantly associates with LAG3, and both are associated with higher concentrations of small HDL particles known to be linked to higher risk of CHD.