PDGF β-Receptor Kinase Activity and ERK1/2 Mediate Glycosaminoglycan Elongation on Biglycan and Increases Binding to LDL

Abstract

The initiation of atherosclerosis involves the subendothelial retention of lipoproteins by proteoglycans (PGs). Structural characteristics of glycosaminoglycan (GAG) chains on PGs influence lipoprotein binding and are altered adversely by platelet-derived growth factor (PDGF). The signaling pathway for PDGF-mediated GAG elongation via the PDGF receptor (PDGFR) was investigated. In human vascular smooth muscle cells, PDGF significantly increased 35S-sulfate incorporation into PGs and GAG chain size. PGs from PDGF-stimulated cells showed increased binding low-density lipoprotein (P < 0.001) in gel mobility shift assays. Knockdown of PDGFRβ using small interfering RNA demonstrated that PDGF mediated changes in PGs via PDGFRβ. GAG synthesis and hyperelongation was blocked by inhibition of receptor tyrosine kinase autophosphorylation site Tyr857 activity using Ki11502 or imatinib. Downstream signaling to GAG hyperelongation was mediated through ERK MAPK and not phosphatidylinositol-3 kinase or phospholipase Cγ. In high-fat-fed apolipoprotein E−/− mice, inhibition of PDGFRβ activity by imatinib reduced aortic total lipid staining area by 35% (P < 0.05). Inhibition of PDGFRβ tyrosine kinase activity leads to inhibition of GAG synthesis on vascular PGs and aortic lipid area in vivo. PDGFRβ and its signaling pathways are potential targets for novel therapeutic agents to prevent the earliest stages atherosclerosis.