The presence of macrophages is required for the regeneration of many cell types during wound healing. Macrophages have been reported to express a wide range of mitogenic factors and cytokines, but none of these factors has been shown in vivo to sustain all the wound-healing processes. It has been suggested that transforming growth factor-alpha (TGF-alpha) may mediate angiogenesis, epidermal regrowth, and formation of granulation tissue in vivo. Macrophages isolated from a wound site, and not exposed to cell culture conditions, expressed messenger RNA transcripts for TGF-alpha, TGF-beta, platelet-derived growth factor A-chain, and insulin-like growth factor-1. The expression of these transcripts was determined by a novel method for RNA analysis in which low numbers of mouse macrophages were isolated from wound cylinders, their RNA was purified and reverse-transcribed, and the complementary DNA was amplified in a polymerase chain reaction primed with growth factor sequence-specific primers. This single-cell RNA phenotyping procedure is rapid and has the potential for quantification, and mRNA transcripts from a single cell or a few cells can be unambiguously demonstrated, with the simultaneous analysis of several mRNA species. Macrophages from wounds expressed TGF-alpha antigen, and wound fluids contained TGF-alpha. Elicited macrophages in culture also expressed TGF-alpha transcripts and polypeptide in a time-dependent manner after stimulation with modified low-density lipoproteins and lipopolysaccharide endotoxin, which are characteristic of the activators found in injured tissues.

Recent studies have shown that appliaton of basic fibroblast growth factor (basic FGF) to a wound has a beneficial effect. However, it has not been whether endogenous FGF also plays a role in tissue repair. In this study we found a 160-fold induction of mRNA encoding keratinocyte growth factor (KGF) 1 day after skin injury. This large induction was unique within the family of FGFs, since mRNA lvel of acidic FGF, basc FGF, and FGF-5 were only slightly induced (2-to 10-fold) during wound healing, and there was no expression of FGF-3, FGF-4, and FGF-6 deed in normal and wounded skin. gh levels of FGF receptor 1 and FGF receptor 2 mRNA and iow levels ofFGF receptor 3 mRNA were found in both normal and wounded skin. No change in the levels of these transcripts was detected during wound healing. In situ hybridization studies revealed highest levels of KGF mRNA expression in the dermis at the wound edge and in the hypodermis beiow the wound. In contrast, mRNA encoding the receptor of this growth factor (a splice variant of FGF receptor 2) was predominantly expressed in the epidermis. These results suggest that basal keratinocytes are stimulated by dermally derived KGF during wound healing and implte a unique role of this member of the FGF family in wound repair.

When cultured in a hypoxic environment similar to that found in the center of a wound, macrophages secreted active angiogenesis factor into the medium. Under conditions similar to those of well-oxygenated tissue, macrophages did not secrete active angiogenesis factor. Macrophages that secreted the factor at hypoxic conditions stopped secreting it when returned to room air. Thus the control of angiogenesis in wound healing may be the result of macrophages responding to tissue oxygen tension without the necessity of interacting with other cell types or biochemical signals.

Excisional dermal wound healing is impaired in mice with a targeted deletion in the stromelysin-1 gene. Incisional wound healing is not affected. These data implicate stromelysin-1 proteolysis during early wound contraction and indicate that stromelysin-1 is crucial for the organization of a multicellular actin network.