Regulation of wound angiogenesis: Role of VEGF and VEGF receptor

Angiogenesis, or blood vessel formation, plays an essential role in tissue repair, giving rise to the formation of normal cutaneous scar or its extreme variants, hypertrophic scar and keloid. The characteristic feature of tissue hypoxia frequently reported in both hypertrophic scar and keloid might attribute to an aberrant angiogenic process which takes place in the early granulation tissue phase of wound healing and is further perpetuated in the process of scar remodeling and maturation. The regulation of wound angiogenesis is not well-understood at present time; however, recent studies on animal wound model suggest a possible role of vascular endothelial growth factor (VEGF) in neovessel formation as well as increase in vascular permeability at the wound site. The proposed study will examine whether or not VEGF and its receptor play a role in the remodeling and maintenance of dermal microvasculature in both normal dermal tissue (defined as normal skin and normal scar) and abnormal scar (keloid scar). The specific aims of this thesis are: (1) To isolate microvascular endothelial cells derived from normal human dermal tissue and abnormal scar tissue. (2) To confirm that vascular endothelial growth factor receptors, Flt and KDR, are expressed on human microvascular endothelium of normal dermal tissues and abnormal scar tissues and to establish whether such expression is altered as a function of the tissue of origin. (3) To examine the biologic effects exerted by VEGF on human microvascular endothelial cells in terms of ligand-induced protein phosphorylation, growth proliferation and in vitro angiogenic activity.; The results of the study indicate that: (1) Both VEGF receptors, KDR and Flt, are expressed by cultured dermal microvascular endothelial cells derived from normal skin, normal scar, and keloid scar. (2) KDR is the major form of VEGF receptors expressed in cultured dermal microvascular endothelial cells. (3) Phosphorylation of the 210 kDa and 170-175 kDa molecules, likely to be KDR and its cleavage product, is specifically induced by VEGF. (4) VEGF is an extremely sensitive angiogenic growth factor for cultured dermal microvascular endothelial cells derived from either normal skin/normal scar or keloid scar, stimulating an average of 5-10 fold cell proliferation and inducing an increase in tubular branching in Matrigel matrix. (5) Dermal microvascular endothelial cells derived from keloid scar exhibit a slower growth rate than those harvested from normal skin/normal scar and appear to reach the aging/apoptotic phase more prematurely, a characteristic degenerative feature commonly described by other investigators. (6) All sources of dermal microvascular endothelial cells are capable of tubular formation in 3-dimensional Matrigel matrix, an in vitro basement membrane model.