Wound healing in the transforming growth factor-beta-deficient mouse

To investigate the role of transforming growth factor-beta(1) in tissue repair, we performed wound healing studies in the transforming growth factor-beta(1)-deficient mouse with targeted disruption of the transforming growth factor-beta(1) gene. Transforming growth factor-beta(1)-deficient mice exhibit no obvious developmental defects and are phenotypically normal until approximately 3 weeks of age when a severe wasting syndrome develops, accompanied by an overwhelming inflammatory response resulting in multisystem organ failure and death. Full-thickness 0.5 x 0.5 cm skin wounds were created on the backs of 10-day-old mice (wild type or heterozygous controls versus homozygous transforming growth factor-beta(1)-deficient mutants) and covered with a nonabsorbent dressing (OpSite). Serial wound measurements were made, and percentage of wound closure over time was determined. On day 10, wounds and liver were harvested for histologic and molecular analysis. Histologic scores were assigned (1 [no healing] to 12 [complete healing]) on the basis of granulation tissue formation, vascularity, collagen deposition, and epithelialization. Reverse transcription-polymerase chain reaction was performed to detect messenger RNA transcripts for transforming growth factor-beta(1), transforming growth factor-beta(2), platelet-derived growth factor A-chain and B-chain, interleukin-1beta and -6, and tumor necrosis factor-alpha in unwounded skin, day 10 wounds, and liver. No significant differences in wound closure were observed until day 10. Weight gain, however, was significantly decreased in the mutant animals as early as day 6. Histologic scores were significantly lower in the transforming growth factor-beta(1)-deficient mutants (5.4 +/- 0.6 versus 11.1 +/- 0.3, p < 0.01, Wilcoxon rank-sum test) and showed decreased granulation tissue formation, vascularity, collagen deposition, and epithelialization and a marked inflammatory infiltrate. As expected, transforming growth factor-beta(1) was expressed in controls but not mutants. Transforming growth factor-beta(2), platelet-derived growth factor A-chain and B-chain, and tumor necrosis factor-alpha were constitutively expressed in unwounded skin, day 10 wounds, and liver of both controls and mutants. Interleukin-1beta and -6, however, were induced after wounding. Early wound healing in the transforming growth factor-beta(1)-deficient mouse proceeds relatively normally because of upregulation or functional redundancy of other growth factors or possibly because of maternal rescue by means of transforming growth factor-beta(1) transmitted in milk. Loss of transforming growth factor-beta(1) regulation ultimately results in a marked inflammatory response, as evidenced by the histologic appearance of the wound and increased expression of the inflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta and 6). The severe wasting syndrome (marked by weight loss) undoubtedly has an adverse effect on wound healing.