How do macrophages sense modified low-density lipoproteins?

In atherosclerosis, serum lipoproteins undergo various chemical modifications that impair their normal function. Modification of low density lipoprotein (LDL) such as oxidation, glycation, carbamylation, glucooxidation, etc. makes LDL particles more proatherogenic. Macrophages are responsible for clearance of modified LDL to prevent cytotoxicity, tissue injury, inflammation, and metabolic disturbances. They develop an advanced sensing arsenal composed of various pattern recognition receptors (PRRs) capable of recognizing and binding foreign or altered-self targets for further inactivation and degradation. Modified LDL can be sensed and taken up by macrophages with a battery of scavenger receptors (SRs), of which SR-A1, CD36, and LOX1 play a major role. However, in atherosclerosis, lipid balance is deregulated that induces inability of macrophages to completely recycle modified LDL and leads to lipid deposition and transformation of macrophages to foam cells. SRs also mediate various pathogenic effects of modified LDL on macrophages through activation of the intracellular signaling network. Other PRRs such Toll-like receptors can also interact with modified LDL and mediate their effects independently or in cooperation with SRs.