Wound Healing In CD36 Knock-out Mice

CD36, an 88 kD glycosylated, cell surface receptor, has a diverseexpression pattern. It has been identified on platelets, monocytes, macrophages, keratinocytes, immature dendritic cells, erythrocytes, activated B cells, specialized epithelium of the digestive tract, retina, taste buds and mammary gland, adipocytes, skeletal and cardiac myocytes and microvascular endothelium. As a member of the class B scavenger receptor family, CD36 binds to a heterogeneous group of extracellar ligands including collagen types I, IV and V, phosphotidylserine and phosphotidylinositol vesicles, oxidized low density lipoprotein, apoptotic cells, rod outer segments, long chain fatty acids, advanced glycation end products, sickle and plasmodiua falciparuarinfected erythrocytes, and thrombospondin-1. It has been implicated in a varied set of physiological and pathological processes, such as platelet adhesion, antigen cross-presentation, cerebral malaria, lupus, breast cancer progression, fatty acid metabolism, insulin resistance, hypertrophic cardiomyopathy, angiogenesis and atheroscleros i s.The wide range of CD36 expression, ligand interaction and function gives rise to significant complexity in attempts to study CD36.The literature is filled with conflicting data relating to CD36structure, ligand specificity, expression, signaling and cellular effects. At the cellular level, the most accurate conclusions about CD36 biology are generally drawn from experiments using ex vivo cell culture models, as cellular context considerably influences CD36 function. Often studies relying on cell lines or transfection of CD36 produce results contrary to those actually seen for the receptor in vivo. Therefore, CD36 knockout mice provide a powerful tool for the study of CD36 function. This thesis focuses on the study of wound healing.No obvious alterations in phenotype were observed between wild-type and CD36 knock-out mice. Histological analysis of the skin shows no major differences in the thickness and morphology of epidermis and dermis. PECAM immunohistochemistry did not reveal any obvious differences in the branching pattern and structure of blood vessels in the ear skin and skin. Comparable vascular leakage and bleeding time was observed between them. These show CD36 has little impact on the normal structure and function of the skin.In would healing experiments, no major differences were observed of inflammatory cells infiltrating between them by immunofluorescence staining of CD11 and CD45. Cultured keratinocytes and fibroblasts from both types shows no differences of proliferation and migration abilityby using migration assay and BrdU labeling assay. TSP-1 mRNA expression was identical in both types by in situ hybridization. On the other hand, wounds closed faster in CD36 knock-out mice than those of wild-type from day 3 to day 6. After day 7, identical wound areas were observed. Meanwhile, PECAM immunohistochemistry and double immunofluorescence stainings of PECAM and BrdU showed increased blood vessels in the would area of CD36 knock out mice, which suggested CD36 can mediates the anti-angiogenic activity of TSP-1. This results in the faster closing of would healing of CD36 knock-out mice.Apoptosis analysis showed increased apoptotic cells in CD36 knock-out mice which indicates CD36 mediates phagocytosis of apoptotic cells by marcrophages.