In the response-to-retention hypothesis of atherosclerosis, which lipoprotein modification within the subendothelial intima is the critical initial pro-atherogenic step that precedes oxidation?

• A HDL reverse cholesterol transport failure causing intimal macrophage foam cell accumulation as the primary initiating event
• B VLDL hydrolysis by lipoprotein lipase generating IDL that directly enters macrophages via SR-BI and SR-BII
• C Endothelial expression of LOX-1 receptor that captures circulating oxidized LDL before its entry into the subendothelial space
• D LDL retention via ionic interaction between apoB-100 and proteoglycans (biglycan, versican) in the intimal extracellular matrix, with subsequent enzymatic and non-enzymatic modification ✓

Explanation

The response-to-retention hypothesis proposes that LDL accumulation in the arterial intima is the initiating event in atherosclerosis. The key step is the binding of apolipoprotein B-100 (apoB-100) — the structural protein of LDL — to proteoglycans in the intimal extracellular matrix, principally biglycan and versican (chondroitin sulfate proteoglycans) and to a lesser extent perlecan (heparan sulfate proteoglycan). This retention concentrates LDL in focal areas prone to low shear stress, facilitating subsequent enzymatic modification (lipolysis by SMase, PLA2) and oxidative modification by reactive oxygen species and enzymes (15-LOX, myeloperoxidase), converting LDL into minimally modified and then fully oxidized LDL (oxLDL) — the form recognized by macrophage scavenger receptors SR-A and CD36 leading to foam cell formation.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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