Arterial macrophages/foam cells store surplus of lipids in cytoplasmic lipid droplets (LDs). Since cholesterol is the most abundant lipid in atheroma, most studies have focused on cholesterol homeostasis. However, the LD is increasingly seen as a site of storage of esters that are signaling precursors. How bioactive lipids are released is not known, but presumably lipases that associate with LDs should play a central role in the process. We recently identified a novel LD protein with a lipase/esterase sequence that we named LD-associated hydrolase (LDAH). LDAH is highly expressed in mouse and human foam cells, and studies on in vivo models we have generated support an atheroprotective role. LDAH reduces fatty components from lesions and promotes favorable remodeling, with a remarkable increase in collagen. There is a direct correlation between levels of LDAH and ATP-binding cassettes (ABC) A1 and G1, two major cholesterol efflux transporters that are regulated by liver X receptors (LXR). The endogenous LXR ligands are oxysterols. In atheroma some oxysterols are mainly found as esters that because of their hydrophobicity need to be confined in non-polar compartments such as LDs, and pilot lipidomics suggest that LDAH prefers side-chain oxysterols to other sterol substrates. Here we propose 3 aims to elucidate LDAH's mechanisms of atheroprotection and integrative networking in foam cell cholesterol mobilization. Aim 1 will employ targeted and untargeted lipidomics to define LDAH's substrates. Primary macrophages that lack or overexpress LDAH, or that express a catalytically dead enzyme, will be used for these studies. These models will also be used to identify LDAH's interactors that might regulate its activity, or mediate sorting of the signals it produces. Aim 2 will determine LDAH's impact on the transcriptome of lesional macrophages and smooth muscle cells. Aim 3 will explore the synergy between LDAH and plasma cholesterol acceptors in foam cell cholesterol mobilization and atheroprotection. The identification of novel mechanisms of regulation of bioactive lipids with a positive impact on foam cell and plaque biology would represent a tremendous advance in the field, open new avenues of research, and provide a logical foundation to develop novel strategies to exploit the atheroprotective potential of endogenous lipid mediators that traffic through LDs. Thus, this proposal can have a positive and sustained impact on cardiovascular and stroke research.
|Program type||Transformational Project Award|
|Effective start/end date||07/01/2018 → 06/30/2021|