No abstract

II.

Differences in cellular competence offer explanation of differences in the healing capacity of tissues of various ages and conditions. The homeobox family of genes plays key roles in governing cellular competence. Of these, we hypothesize that Msx2 is a strong candidate regulator of competence in skin wound healing because it is expressed in the skin during fetal development at stage of scarless healing, affects postnatal digit regeneration, and is re-expressed transiently during postnatal skin wound repair. To address if Msx2 affects cellular competence in injury repair, three millimeter full thickness excisional wounds were created on the back of C.Cg-Msx2tm1Rilm/Mmcd (Msx2 null) mice and the healing pattern was compared with that of the WT mice. Results show that Msx2 null mice exhibited faster wound closure with accelerated re-epithelialization plus earlier appearance of keratin markers for differentiation and increased level of smooth muscle actin and tenascin in the granulation tissue. In vitro, keratinocytes of Msx2 null mice exhibit increased cell migration and the fibroblasts stronger collagen gel contraction. Thus, our results suggest that Msx2 regulates cellular competence of keratinocytes and fibroblasts in skin injury repair.

Keloids are tumor-like skin scars that grow as a result of the aberrant healing of skin injuries, with no effective treatment. We provide new evidence that both overexpression of plasminogen activator inhibitor-1 (PAI-1) and elevated collagen accumulation are intrinsic features of keloid fibroblasts and that these characteristics are causally linked. Using seven strains each of early passage normal and keloid fibroblasts, the keloid strains exhibited inherently elevated collagen accumulation and PAI-1 expression in serumfree, 0.1% ITS؉ culture; larger increases in these parameters occurred when cells were cultured in 3% serum. To demonstrate a causal relationship between PAI-1 overexpression and collagen accumulation, normal fibroblasts were infected with PAI-1-expressing adenovirus. Such cells exhibited a two-to fourfold increase in the accumulation of newly synthesized collagen in a viral dose-dependent fashion in both monolayers and fibrin gel, provisional matrix-like cultures. Three different PAI-1-targeted small interfering RNAs, alone or in combination, produced greater than an 80% PAI-1 knockdown and reduced collagen accumulation in PAI-1-overexpressing normal or keloid fibroblasts. A vitronectin-binding mutant of PAI-1 was equipotent with wild-type PAI-1 in inducing collagen accumulation, whereas a complete protease inhibitor mutant retained approximately 50% activity. Thus, PAI-1 may use more than its protease inhibitory activity to control keloid collagen accumulation. PAI-1-targeted interventions , such as small interfering RNA and lentiviral short hairpin RNA-containing microRNA sequence suppression reported here , may have therapeutic utility in the prevention of keloid scarring.