GSK-3beta in mouse fibroblasts controls wound healing and fibrosis through an endothelin-1-dependent mechanism.

Glycogen synthase kinase-3 (GSK-3) is a widely expressed and highly conserved serine/threonine protein kinase encoded by 2 genes, GSK3A and GSK3B. GSK-3 is thought to be involved in tissue repair and fibrogenesis, but its role in these processes is currently unknown. To investigate the function of GSK-3beta in fibroblasts, we generated mice harboring a fibroblast-specific deletion of Gsk3b and evaluated their wound-healing and fibrogenic responses. We have shown that Gsk3b-conditional-KO mice (Gsk3b-CKO mice) exhibited accelerated wound closure, increased fibrogenesis, and excessive scarring compared with control mice. In addition, Gsk3b-CKO mice showed elevated collagen production, decreased cell apoptosis, elevated levels of profibrotic alpha-SMA, and increased myofibroblast formation during wound healing. In cultured Gsk3b-CKO fibroblasts, adhesion, spreading, migration, and contraction were enhanced. Both Gsk3b-CKO mice and fibroblasts showed elevated expression and production of endothelin-1 (ET-1) compared with control mice and cells. Antagonizing ET-1 reversed the phenotype of Gsk3b-CKO fibroblasts and mice. Thus, GSK-3beta appears to control the progression of wound healing and fibrosis by modulating ET-1 levels. These results suggest that targeting the GSK-3beta pathway or ET-1 may be of benefit in controlling tissue repair and fibrogenic responses in vivo.

Integrin ß1 is necessary for the maintenance of corneal structural integrity.

PURPOSE: The precise role of a normal keratocyte in maintaining corneal structural integrity is unclear; it is generally considered to remain quiescent at the end of cell division. Given that integrins are essential for cell/extracellular matrix interactions, the authors tested the hypothesis that integrin expression by keratocytes is essential for corneal structure and function. METHODS: Using a tamoxifen-dependent cre recombinase expressed under the control of a fibroblast-specific promoter/enhancer, the authors conditionally deleted the integrin ß1 (Itgb1) gene in mouse keratocytes during the postnatal matrix maturation phase of the cornea. The effects of this deletion were monitored histologically and by macroscopic observation of the cornea. RESULTS: The resultant cornea shows an initial thinning of the stroma, reduced space between collagen fibrils, loss of epithelial layers and subsequent edema, thickening of Descemet's membrane, and degenerative changes in the endothelial cell layer, with eventual scarring. These pathologic changes have some similarities to human corneal disease keratoconus. The phenotype did not develop when Itgb1 was deleted after complete corneal maturation. CONCLUSIONS: Loss of integrin ß1 expression in keratocytes during the phase of stromal maturation results in corneal thinning and edema. Keratocyte-ECM interaction is essential for matrix maturation and thus in the maintenance of corneal structural integrity. This model has relevance in understanding corneal diseases such as keratoconus.

Loss of peroxisome proliferator-activated receptor gamma in mouse fibroblasts results in increased susceptibility to bleomycin-induced skin fibrosis.

OBJECTIVE: There is increasing evidence that the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) plays an important role in controlling cell differentiation, and that PPARgamma ligands can modify inflammatory and fibrotic responses. The aim of the present study was to examine the role of PPARgamma in a mouse model of skin scleroderma, in which mice bearing a fibroblast-specific deletion of PPARgamma were used. METHODS: Cutaneous sclerosis was induced by subcutaneous injection of bleomycin, while untreated control groups were injected with phosphate buffered saline. Mice bearing a fibroblast-specific deletion of PPARgamma were investigated for changes in dermal thickness, inflammation, collagen content, and the number of alpha-smooth muscle actin-positive cells. The quantity of the collagen-specific amino acid hydroxyproline was also measured. In addition, the effect of PPARgamma deletion on transforming growth factor beta1 (TGFbeta1) signaling in the fibroblasts was investigated. RESULTS: Bleomycin treatment induced marked cutaneous thickening and fibrosis in all treated mice. Deletion of PPARgamma resulted in enhanced susceptibility to bleomycin-induced skin fibrosis, as indicated by increases in all measures of skin fibrosis and enhanced sensitivity of fibroblasts to TGFbeta1 in PPAR-deficient mice. CONCLUSION: These results indicate that PPARgamma suppresses fibrogenesis. Specific agonists of PPARgamma may therefore alleviate the extent of the development of cutaneous sclerosis.

Connective tissue growth factor promoter activity in normal and wounded skin.

In skin, connective tissue growth factor (CTGF/CCN2) is induced during tissue repair. However, what the exact cell types are that express CTGF in normal and wounded skin remain controversial. In this report, we use transgenic knock-in mice in which the Pacific jellyfish Aequorea victoria enhanced green fluorescent protein (E-GFP) gene has been inserted between the endogenous CTGF promoter and gene. Unwounded (day 0) and wounded (days 3 and 7) skin was examined for GFP to detect cells in which the CTGF promoter was active, alpha-smooth muscle actin (alpha-SMA) to detect myofibroblasts, and NG2 expression to detect pericytes. In unwounded mice, CTGF expression was absent in epidermis and was present in a few cells in the dermis. Upon wounding, CTGF expression was induced in the dermis. Double immunolabeling revealed that CTGF-expressing cells also expressed alpha-SMA, indicating the CTGF was expressed in myofibroblasts. A subset (approximately 30%) of myofibroblasts were also NG2 positive, indicating that pericytes significantly contributed to the number of myofibroblasts in the wound. Pericytes also expressed CTGF. Collectively, these results indicate that CTGF expression in skin correlates with myofibroblast induction, and that CTGF-expressing pericytes are significant contributors to myofibroblast activity during cutaneous tissue repair.