Faculty Bibliography

Keratinocytes are the major cellular component of epidermis, and they have several critical roles in the wound healing process. They are involved in the intricate mechanisms of initiation, maintenance, and completion of wound healing. The properties of keratinocytes vary depending upon their location and circumstances within chronic wounds. Keratinocytes at the non-healing edges of chronic wounds differ from normal, healthy keratinocytes. The cross-talk between healthy keratinocytes and other cell types participating in wound healing is critical for successful wound closure. This discovery provides the biological foundation for debridement: Removing 'bad' cells from a quiescent wound edge and exposing or even replacing them with 'healthy' cells with a high regenerative potential can enhance epithelialization and healing of chronic wounds. This paper will review the biological and pathological properties of keratinocytes as they relate to wound healing, and the ways in which they may provide highly efficacious therapy for patients with chronic wounds

In silico docking of a chemical library with the ligand binding domain (LBD) of thyroid hormone nuclear receptor-alpha (TRalpha) suggested that farnesyl pyrophosphate (FPP), a key intermediate in cholesterol synthesis and protein farnesylation, might function as an agonist. Surprisingly, addition of FPP to cells activated TR as well as the classical steroid hormone receptors but not peroxisome proliferative activating receptors, farnesol X receptor, liver x receptor, or several orphan nuclear receptors whose ligands are unknown. FPP enhanced receptor-coactivator binding in vitro and in vivo and elevation of FPP levels in cells by squalene synthetase or farnesyl transferase inhibitors leads to activation. The FPP effect was blocked by selective receptor antagonists, and in silico docking with 143 nuclear receptor LBD structures revealed that FPP only docked with the agonist conformation of those receptors activated by FPP. Our results suggest that certain nuclear receptors maintain a common structural feature that may reflect an action of FPP on an ancient nuclear receptor or that FPP could function as a ligand for one of the many orphan nuclear receptors whose ligands have not yet been identified. This finding also has potential interesting implications which may, in part, explain the pleotropic effects of statins as well as certain actions of farnesylation inhibitors in cells

The novel Ca2+-binding protein, Scarf (skin calmodulin-related factor) belongs to the calmodulin-like protein family and is expressed in the differentiated layers of the epidermis. To determine the roles of Scarf during stratification, we set out to identify the binding target proteins by affinity chromatography and subsequent analysis by mass spectrometry. Several binding factors, including 14-3-3s, annexins, calreticulin, ERp72 (endoplasmic reticulum protein 72), and nucleolin, were identified, and their interactions with Scarf were corroborated by co-immunoprecipitation and co-localization analyses. To further understand the functions of Scarf in epidermis in vivo, we altered the epidermal Ca2+ gradient by acute barrier disruption. The change in the expression levels of Scarf and its binding target proteins were determined by immunohistochemistry and Western blot analysis. The expression of Scarf, annexins, calreticulin, and ERp72 were up-regulated by Ca2+ gradient disruption, whereas the expression of 14-3-3s and nucleolin was reduced. Because annexins, calreticulin, and ERp72 have been implicated in Ca2+-induced cellular trafficking, including the secretion of lamellar bodies and Ca2+ homeostasis, we propose that the interaction of Scarf with these proteins might be crucial in the process of barrier restoration. On the other hand, down-regulation of 14-3-3s and nucleolin is potentially involved in the process of keratinocyte differentiation and growth inhibition. The calcium-dependent localization and up-regulation of Scarf and its binding target proteins were studied in mouse keratinocytes treated with ionomycin and during the wound-healing process. We found increased expression and nuclear presence of Scarf in the epidermis of the wound edge 4 and 7 days post-wounding, entailing the role of Scarf in barrier restoration. Our results suggest that Scarf plays a critical role as a Ca2+ sensor, potentially regulating the function of its binding target proteins in a Ca2+-dependent manner in the process of restoration of epidermal Ca2+ gradient as well as during epidermal barrier formation

Both diabetes and advanced age have been implicated in delaying wound repair. However, the contribution of age alone has not been shown clinically to significantly impair the ability to heal. To determine the contribution of age and db/db genotype multiple wound healing parameters were determined in young db/db mice, aged db/db mice, age-matched non-db/db control and wild-type C57BL/6 mice. Biomechanical properties (breaking load and tensile stiffness), epithelialization, and collagen deposition were determined for the four groups of mice 14 days after wounding with suture-closed incisional wounds. While neither hyperglycemia nor age alone caused impairment in biomechanical properties, the combination of age and db/db genotype resulted in a 36% reduction in stiffness and a 42% reduction in breaking load, when compared to young control mice, suggesting poor quality of healing. Statistically significant differences in the volume of granulation tissue deposited within the wound site were also observed, with the aged db/db mice displaying more than any other group, suggesting greater dermal loss from the dermal edges of incisional wounds in aged db/db mice, suggesting that the combination of age and diabetes act synergistically to impair healing in mice with type 2 diabetes. Interestingly, the impairment occurs independently of the prevailing glycemia, supporting the hypothesis that diabetes in synergy with advanced age has downstream effects, leading to further impairment, necessitating initiation of early and aggressive intervention in elderly patients with diabetic foot ulcers

Diabetic foot ulcers (DFUs), a leading cause of amputations, affect 15% of people with diabetes. A series of multiple mechanisms, including decreased cell and growth factor response, lead to diminished peripheral blood flow and decreased local angiogenesis, all of which can contribute to lack of healing in persons with DFUs. In this issue of the JCI, Gallagher and colleagues demonstrate that in diabetic mice, hyperoxia enhances the mobilization of circulating endothelial progenitor cells (EPCs) from the bone marrow to the peripheral circulation (see the related article beginning on page 1249). Local injection of the chemokine stromal cell-derived factor-1alpha then recruits these EPCs to the cutaneous wound site, resulting in accelerated wound healing. Thus, Gallagher et al. have identified novel potential targets for therapeutic intervention in diabetic wound healing