Investigating the epidermal Notch activation during wound healing and the consequences of prolonged Notch activity during skin wound healing

The Notch signaling pathway is critically involved in cell fate decisions during skin development and homeostasis. In the present study an in vivo model (seven-week-old male, C57BL/6) was used to elucidate the role of epidermal Notch activation in the healing of full-thickness dermal wound. Immunolocalization of activated Notch1, Notch2 and Jagged1 was performed during skin wound healing in vivo in mice. The expression level of Notch1, Notch 2 and Jagged1 in the C57BL/6 skin was examined by quantitative PCR (qPCR). This study shows that skin injury rapidly actives Notch signaling in the epidermis. Epidermal forced Notch1 activation results in a Jagged1 dependent Notch2 activation in epidermis. Data presented in this thesis also demonstrate that the prolonged epidermal Notch activation via a 4-hydroxy-tamoxifen-inducible transgene before and after wounding caused an over-activation of Notch during early stages of the healing of full-thickness dermal wounds. The expression level of Notch1, Notch2 and the inflammatory Notch related genes, in the transgenic wounded skin was examined by quantitative PCR (qPCR). The phenotypes and morphology of the transgenic skin were compared with that of wild type (WT) controls. The skin response to wound healing was studied by H&E staining at the microscopic level at 2, 5 and 8 days post injury. These data show that the prolonged epidermal Notch activity may do more harm than good in terms of an increased inflammatory response at the wound site. These data suggest that Notch plays an important role in the early stages of the skin wound healing process, a finding that has implications in wound inflammatory responses. This thesis also examines skin wound healing in different anatomical locations on seven-week-old male, C57BL/6 mice model. 4mm full thickness dermal wounds were made at different anatomic regions; upper posterior, middle to posterior and posterior-most (caudal). These data showed that lower body wounds healed significantly better than those in the upper posterior, or middle to posterior of the mouse back skin. The data presented here show that anatomical location is important in wound healing responses, as reflected by differences in keratinocyte proliferation and differentiation.