Smad7 Ameliorates TGF-ß-Mediated Skin Inflammation and Associated Wound Healing Defects but Not Susceptibility to Experimental Skin Carcinogenesis.

We assessed the roles of Smad7 in skin inflammation and wound healing using genetic and pharmacological approaches. In K5.TGFß1/K5.Smad7 bigenic (double transgenic) mice, Smad7 transgene expression reversed transforming growth factor (TGF)-ß1 transgene-induced inflammation, fibrosis, and subsequent epidermal hyperplasia and molecularly abolished TGF-ß and NF-κB activation. Next, we produced recombinant human Smad7 protein with a Tat-tag (Tat-Smad7) that rapidly enters cells. Subcutaneous injection of Tat-Smad7 attenuated infiltration of F4/80+ and CD11b+ leukocytes and α-smooth muscle actin+ fibroblasts before attenuating epidermal hyperplasia in K5.TGFß1 skin. Furthermore, topically applied Tat-Smad7 on K5.TGFß1 skin wounds accelerated wound closure, with improved re-epithelialization and reductions in inflammation and fibrotic response. A short treatment with Tat-Smad7 was also sufficient to reduce TGF-ß and NF-κB signaling in K5.TGFß1 skin and wounds. Relevant to the clinic, we found that human diabetic wounds had elevated TGF-ß and NF-κB signaling compared with normal skin. To assess the oncogenic risk of a potential Smad7-based therapy, we exposed K5.Smad7 skin to chemical carcinogenesis and found reduced myeloid leukocyte infiltration in tumors but not accelerated carcinogenesis compared with wild-type littermates. Our study suggests the feasibility of using exogenous Smad7 below an oncogenic level to alleviate skin inflammation and wound healing defects associated with excessive activation of TGF-ß and NF-κB.

Topical Application of Tat-Rac1 Promotes Cutaneous Wound Healing in Normal and Diabetic Mice.

The endogenous small GTPase, Rac1, plays a critical role during normal skin wound healing. It remains to be determined whether endogenous Rac1 can be appropriately activated in chronic wounds; if not, whether exogenous Rac1 has therapeutic effects on wound healing. Here we show that Rac1 protein levels were lower in wounds of db/db diabetic mice than wounds in wild type mice during the healing process. To assess the therapeutic potential of exogenous Rac1 in wound healing, we produced a Tat-Rac1 fusion protein that enters into cells through protein transduction. Tat-Rac1 increased proliferation and migration of keratinocytes and dermal fibroblasts in vitro. Topical application of Tat-Rac1 accelerated cutaneous wound closure in vivo in db/db mice as well as wild type mice. Further analyses revealed that Tat-Rac1 had faster re-epithelialization, higher keratinocyte proliferation and migration without an earlier onset of myofibroblast activation than vehicle treated wounds. Tat-Rac1 also reduced inflammation in wounds. Our findings revealed the failure of diabetic wounds to elevate Rac1 expression and suggested a therapeutic strategy utilizing a Rac1-based biologic to compensate for this defect thereby promoting wound healing.