CD36 participates in a signaling pathway that regulates ROS formation in murine VSMCs

Abstract

CD36 is a membrane glycoprotein expressed on platelets, monocytes, macrophages, and several other cell types that was recently demonstrated to be involved in platelet activation in response to oxidized phospholipids, including oxidized LDL. Although the role of CD36 in other vascular cells has not been well defined, previous studies have demonstrated that cd36-knockout (cd36 -/-) mice have prolonged thrombosis times after vascular injury, which can be protective in the state of hyperlipidemia. Here, we found significantly less ROS in the vessel walls of cd36 -/-mice compared with WT after chemically induced arterial injury, suggesting that CD36 may contribute to ROS generation in the VSMCs themselves. Gene expression analysis revealed that the antioxidant enzymes peroxiredoxin-2 (Prdx2) and heme oxygenase-1 were upregulated in cd36 -/-VSMCs. Molecular dissection of the pathway in isolated mouse VSMCs revealed CD36 ligand-dependent induction of Fyn phosphorylation, with subsequent phosphorylation and degradation of the redox-sensitive transcription factor Nrf2. Chromatin immunoprecipitation experiments further showed that Nrf2 directly occupied the Prdx2 promoter. The importance of this pathway was evidenced by increased ROS generation in prdx2 -/-mice and decreased thrombosis times in both prdx2 -/-and nrf2 -/-mice after vascular injury. These data suggest that CD36-mediated downregulation of antioxidant systems in VSMCs may contribute to its prothrombotic, proinflammatory, and atherogenic effects. Introduction CD36, a class B scavenger receptor, is an 88-kDa membrane glycoprotein expressed on platelets, monocytes, macrophages, and several other cell types (1). It is a multifunctional receptor with independent capacity to bind 3 major classes of ligands: modified phospholipids, long-chain fatty acids, and proteins containing thrombospondin structural homology domains. Although CD36 was first identified on platelets, its role in platelet function remained undefined until recently, when our group showed that CD36 promotes platelet activation in response to oxidized phospholipids, including oxidized LDL (oxLDL) (2). We found that genetic deletion of CD36 in mice protected them from the prothrombotic state associated with hyperlipidemia (2) and oxidant stress and also significantly prolonged thrombotic occlusion times after vascular injury induced by ferric chloride (FeCl 3 ) (3). The mechanisms underlying this phenotype remain incompletely understood, but the antithrombotic effects of CD36 deficiency were dependent on the dose of FeCl 3 used to induce injury (3) and platelet transfusion studies revealed that they were in part platelet dependent. Furthermore, CD36-mediated signaling through specific Src family kinases and MAPKs was shown to promote platelet activation after vascular injury (4). The endogenous CD36 ligands generated during FeCl 3 -induced injury include endothelial cellderived microparticles (EMPs), which we showed bind specifically to platelet CD36 and enhance platelet reactivity (3).

Immune complex formation in human diabetic retina enhances toxicity of oxidized LDL towards retinal capillary pericytes

“…We assessed cell surface expression of the scavenger receptor CD36 ( 28 ) and three IgG Fc receptors: highaffi nity CD64 (Fc ␥ RI), low-affi nity CD32 (Fc ␥ R II), and CD16 (Fc ␥ R III) ( 29 ). Only CD36 and CD64 were detectable in pericytes.…”

Oxidized LDL activates blood platelets through CD36/NOX2–mediated inhibition of the cGMP/protein kinase G signaling cascade

“…In vascular smooth muscle, CD36 ligation activates the multisubunit enzyme complex reduced NAD phosphate oxidase 2 (gp91 phox /NOX2) to produce reactive oxygen species (ROS). 20 Platelet-generated ROS can enhance platelet recruitment by preformed platelet aggregates, 21 although it is unclear if this is important for oxLDL-mediated platelet activation. We hypothesized that oxLDL could induce the generation of platelet ROS through CD36 to promote platelet hyperactivity.…”

The effects of glycemic control on malondialdehyde modified low-density-lipoprotein-immunglobulin G levels in type 2 diabetics

“…The formation of immune complexes of immunoglobulin G (IgG) and malondialdehyde modified LDL (MDA-LDL) increases the proinflammatory immune response and leads to progression of atheroma plaque (19,20,21). Clinical studies on type1-DM have shown that high levels of MDA-LDL and Ig complexes are associated with increased odds for developing diabetic nephropathy and progression of retinopathy (22).…”