Nerve growth factor and burn wound healing: Update of molecular interactions with skin cells.

Burn wound healing is a very intricate and complex process that conventionally includes three interrelated and overlapping stages of hemostasis/inflammation, proliferation and remodeling. This review aims to explore the molecular interactions of NGF with the most prominent cell types in the skin and their respective secretory products during wound healing, particularly burn wound healing. Different types of cells such as, nerve cells, endothelial cells, mast cells, macrophages, neutrophils, keratinocytes and fibroblasts all come into play through a plethora of cytokines and growth factors including nerve growth factor (NGF). NGF is a pleiotropic molecule that exerts its effects on all the aforementioned cells using two types of receptors (TrkA and p75) and affects wound healing by decreasing healing time and improving the quality of the scar. Both receptors mediate cellular proliferation, survival and apoptosis through complex signaling molecules. During the inflammatory phase, macrophages and mast cells secrete ample cytokines and growth factors, including NGF, which participate in the inflammatory reaction and induction of other cells targeting a homeostatic state. The proliferative phase follows, and NGF promotes angiogenesis through VEGF and FGF expression in endothelial cells. NGF also stimulates keratinocyte proliferation and neurite extension through the TrkA-PI3K/Akt pathway. Other molecules such as TGF-ß1, IL-1ß and TNF-α increase NGF expression in fibroblasts through dynamic interactions with Smads and MAPK molecules. Stimulated fibroblasts induce new collagen production to form the granulation tissue. In the remodeling phase, NGF regulates fibroblasts and induces their differentiation into myofibroblasts ultimately leading to wound contracture. In addition, NGF stimulates melanocytes and enhances hair growth and pigmentation. Such data depict the mechanisms of action of NGF implicated in the various stages of the healing process and support its applicability as a new targeted therapeutic molecule effective in burn wound healing but with some limitations.

Pharmacological modulation of wound healing in experimental burns.

Factors involved in wound healing and their interdependence are not yet fully understood; nevertheless, new prospects for therapy to favor speedy and optimal healing are emerging. Reports about wound healing modulation by local application of simple and natural agents abound even in the recent literature, however, most are anecdotal and lack solid scientific evidence. We describe the effect of silver sulfadiazine and moist exposed burn ointment (MEBO), a recently described burn ointment of herbal origin, on mast cells and several wound healing cytokines (bFGF, IL-1, TGF-beta, and NGF) in the rabbit experimental burn model. The results demonstrate that various inflammatory cells, growth factors and cytokines present in the wound bed may be modulated by application of local agents with drastic effects on their expression dynamics with characteristic temporal and spatial regulation and changes in the expression pattern. Such data are likely to be important for the development of novel strategies for wound healing since they shed some light on the potential formulations of temporally and combinatory optimized therapeutic regimens.