This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Scar tissue is a problem of great importance in many areas of medicine and health. Skin regeneration is known to occur in amphibians, but not in mammals. The exceptions in mammals are fetuses and FOXN1 deficient (nude) mice. Our long-range objective is to understand the mechanisms of scar formation and how these can be controlled to improve healing of the skin and other organs in adult mammals. Matrix metalloproteinases (MMPs) are implicated in regeneration and in scarless healing: MMPs are indispensable to the regeneration in amphibians. Scarless skin healing in mammalian fetuses is associated with higher levels of MMPs expression. We have found that intact skin tissues from nude mice express higher levels of MMPs relative to wild type mice;and we have shown that post-injury skin tissues in nude mice have distinctive, bimodal patterns of MMP9 and MMP13 activity during early and late stages of healing. These patterns of MMPs expression in nude mice strongly resemble those found to occur in amphibians during regeneration. Our working model is that the absence of functional FOXN1 in nude mice removes the transcriptional suppression of MMPs and leads to high levels of MMPs, an essential, necessary condition for scarless repair that mimics regeneration in amphibians. This models leads to the following testable hypothesis: Hypothesis: FOXN1 suppresses MMP9 and MMP13 expression during normal skin repair and scar formation. Corollaries: (a) Absence of FOXN1 expression in nude mice allows upregulation of MMP9 and MMP13 with concomitant scarless repair of skin. (b) Inhibition of FOXN1 will allow MMP9 and MMP13 expression and result in scarless skin healing. We will test this hypothesis and its corollaries in nude mice. Our goals are to determine how a deficiency in FOXN1 regulates Mmp9 and Mmp13 gene expression, and whether MMP9 and MMP13 are necessary for scarless skin repair.
Specific Aim 1 will test mechanisms of interaction between FOXN1 and MMP9/MMP13 expression. Prediction 1: FOXN1 represses MMP9/MMP13 expression through release of soluble factors from keratinocytes that repress MMP13/MMP9 expression in dermal fibroblasts (intercellular mechanism). Prediction 2: FOXN1 represses MMP9 expression in keratinocytes through direct action between FOXN1 binding domain and responsive elements in the promoter region of MMP9 and/or through transcriptional suppression of PKC signaling (intracellular mechanism).
Specific Aim 2 will test the hypothesis that MMP13 and MMP9 expression are a necessary condition for scarless skin wound repair. Prediction 1: Suppression of MMPs activities abrogates nude mouse ability for scar-free healing. Prediction 2: Double mutant mice FOXN1/MMP-9 and FOXN1/ MMP13 will heal skin injuries with scar formation.
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