Transforming Growth Factor-β ReceptoreMediated, p38 Mitogen-Activated Protein KinaseeDependent Signaling Drives Enhanced Myofibroblast Differentiation during Skin Wound Healing in Mice Lacking Hyaluronan Synthases 1 and 3

Normal myofibroblast differentiation is critical for proper skin wound healing. Neoexpression of alpha-smooth muscle actin (alpha-SMA), a marker for myofibroblast differentiation, is driven by transforming growth factor (TGF)-beta receptoremediated signaling. Hyaluronan and its three synthesizing enzymes, hyaluronan synthases (Has 1, 2, and 3), also participate in this process. Closure of skin wounds is significantly accelerated in Has1/3 double-knockout (Has1/3-null) mice. Herein, TGF-beta activity and dermal collagen maturation were increased in Has1/3-null healing skin. Cultures of primary skin fibroblasts isolated from Has1/3-null mice had higher levels of TGF-beta activity, alpha-SMA expression, and phosphorylation of p38 mitogen-activated protein kinase at Thr180/Tyr182, compared with wild-type fibroblasts. p38a mitogen-activated protein kinase was a necessary element in a noncanonical TGF-beta receptor signaling pathway driving alpha-SMA expression in Has1/3-null fibroblasts. Myocardin-related transcription factor (MRTF), a cofactor that binds to the transcription factor serum response factor (SRF), was also critical. Nuclear localization of MRTF was increased, and MRTF binding to SRF was enhanced in Has1/3-null fibroblasts. Inhibition of MRTF or SRF expression by RNA interference suppresses alpha-SMA expression at baseline and diminished its overexpression in Has1/3-null fibroblasts. Interestingly, total matrix metalloproteinase activity was increased in healing skin and fibroblasts from Has1/3-null mice, possibly explaining the increased TGF-beta activation.

Automated summary

Deletion of hyaluronan-related genes accelerates skin wound healing, increases TGF-β activity and dermal collagen maturation. α-SMA expression in Has1/3-null fibroblasts is associated with increased phosphorylation of p38 MAPK, and p38 MAPK is involved in the noncanonical TGF-β signaling pathway driving α-SMA expression. Additionally, enhanced binding and nuclear localization of MRTF in Has1/3-null fibroblasts play a critical role in baseline and overexpression of α-SMA. Increased total matrix metalloproteinase activity in healing skin may explain the increased activation of TGF-β.