Epidermal keratinocytes are vital to normal wound healing by restoring the epidermal barrier and secreting paracrine factors that govern diverse processes including wound angiogenesis. In pathogenic settings, impaired epidermal function results in chronically insufficient (e.g., diabetic ulcers) or over-exuberant healing (e.g., hypertrophic scars). Our long-term goal is to develop therapeutic paradigms through which integrins can be manipulated to modulate pathogenic keratinocyte function. While it is well established that integrins regulate proliferation, migration and growth factor signaling, their rols in orchestrating wound keratinocyte functions remain enigmatic. Moreover, while normal and wound keratinocytes express integrin a9b1, in vivo, upon explanation integrin a9b1 is lost, confounding observations made in previous studies, in vitro. Using genetically defined, virally transduced keratinocytes that express integrins a3b1 and/or a9b1 in different combinations, we discovered that a9b1 exerts a cross-suppressive effect on cell functions and gene expression that is governed by a3b1, including paracrine signals that promote endothelial cell function. Moreover, we have derived genetically defined mice that express a3b1 and/or a9b1 in epidermis in different combinations. Strikingly, deletion of a9b1 from epidermis enhances wound contraction and angiogenesis, two functions that are attributed to paracrine signaling directed by a3b1. Based on our foundation data, we hypothesize that a9b1 suppresses a3b1-dependent paracrine signals from the epidermis that control wound closure and angiogenesis. We further hypothesize that the regulation of a9b1-mediated suppression of a3b1, perhaps through ligand-dependent activation of a9b1 at key stages of wound healing, is critical for proper temporal and spatial orchestration of epidermal functions that promote wound healing. This hypothesis will be tested in three Aims using a combination of genomics, bioinformatics, peptide biochemistry, cell biology, and defined genetic mouse models of wound healing. At the end of this project period, we will have provided the first analyses of keratinocyte a9b1 functions, determined how a3b1 and a9b1 coordinately regulate wound repair, identified molecular mechanisms through which a9b1 exerts cross- suppressive regulation over a3b1, and tested the concept that a9b1-targeting peptides can be used to control certain epidermal wound healing functions. In doing so, we will have developed the basis for novel integrin- targeting therapeutics to modulate keratinocyte functions and wound outcome.
Keratinocyte adhesion receptors are critical to regenerating a functional epidermis after injury. These receptors regulate important keratinocyte functions in part by communicating with each other. The goal of the proposed work is to elucidate their mechanisms of communication and the keratinocyte functions that they impact during wound healing.
|Longmate, Whitney M; Monichan, Ruby; Chu, Mon-Li et al. (2014) Reduced fibulin-2 contributes to loss of basement membrane integrity and skin blistering in mice lacking integrin ?3?1 in the epidermis. J Invest Dermatol 134:1609-17|