Lysosomal acid lipase (LAL), encoded by the LIPA gene, is the key lysosomal hydrolase that cleaves cholesteryl esters (CE) and triglycerides (TG). Loss-of-function (LOF) mutations in LIPA result in cholesteryl ester storage disease (CESD), which manifests with hyperlipidemia, hepatic and macrophage CE accumulation, and atherosclerosis. Recently, genome-wide association studies (GWASs) identified LIPA as a novel locus for coronary artery disease (CAD). Surprisingly, LIPA CAD-GWAS risk alleles do not associate with altered plasma lipids or hepatic LIPA mRNA levels but actually relate to higher monocyte LIPA mRNA expression. Our preliminary data also reveal a coincident increase in both LIPA mRNA and LAL enzymatic activity in monocyte-derived macrophages (HMDM) of CAD risk allele carriers, suggesting that monocyte/macrophage-specific gain-of-function (GOF) of LIPA may explain the GWAS CAD risk alleles. LIPA mRNA and LAL activity were markedly induced upon HMDM differentiation and mature HMDM secrets LAL. Extracellular LAL is abundant in the neointima of advanced human atherosclerotic lesions where LAL can remain enzymatically active in the lesion acidic microenvironment. Thus, macrophage LIPA GOF may aggravate atherosclerosis through accelerating intracellular LAL-induced lysosomal free cholesterol (FC) toxicity and extracellular LAL actions on low-density lipoprotein (LDL). My working hypotheses are that LIPA CAD risk alleles encode for macrophage-specific LIPA GOF, and therefore CAD risk alleles or macrophage LIPA overexpression will (i) increase intracellular LAL activity resulting in a shift toward greater lysosomal CE hydrolysis and FC accumulation and thus accelerate macrophage lysosomal dysfunction during modified-LDL loading; (ii) increase macrophage LAL secretion and extracellular LAL-mediated LDL modification driving atherogenic phenotypes in vascular smooth muscle cells (VSMC) and endothelial cells (EC); and (iii) macrophage LIPA overexpression will accelerate atherogenesis in ApoE-/- and Ldlr-/- mice. These hypotheses will be addressed in primary HMDM of specific LIPA genotype, through causal modeling in a novel human iPSC- differentiated macrophage (IPSDM) system utilizing CRISPR/Cas knock-in of risk alleles, in HMDM with lentivirus-mediated LIPA overexpression (Lenti-LIPA), and in murine models with macrophage-specific Lipa overexpression by lentivirus-infected bone marrow (BM) transplantation driven by macrophage-specific promoter. These will be accomplished by pursuing the following three aims:
Aim 1. K99 Phase: Determine the effects of LIPA CAD risk alleles and LIPA overexpression on intracellular macrophage LIPA expression, LAL activity, and phenotype of human macrophages.
Aim 2. R00 Phase: Determine the effects of LIPA CAD risk alleles and LIPA overexpression on macrophage LAL secretion, extracellular LAL-modification of LDL and on atherogenic phenotypes in EC and VSMC.
Aim 3. R00 Phase: Determine if macrophage Lipa overexpression accelerates atherosclerosis in ApoE-/- and Ldlr-/- mice.
Recent genome-wide association studies (GWAS) identified lysosomal acid lipase (LIPA) as a susceptibility gene for coronary artery disease (CAD). The research outlined in this proposal has broad significance for better understanding of the novel mechanisms of GWAS CAD-associated LIPA in atherosclerosis, and in translational research exploring the therapeutic opportunities to prevent and treat CAD.
| Zhang, Hanrui (2018) Lysosomal acid lipase and lipid metabolism: new mechanisms, new questions, and new therapies. Curr Opin Lipidol 29:218-223 |
