Loss of keratinocyte focal adhesion kinase stimulates dermal proteolysis through upregulation of MMP9 in wound healing.
OBJECTIVE
To investigate how epithelial mechanotransduction pathways impact wound repair.


BACKGROUND
Mechanical forces are increasingly recognized to influence tissue repair, but their role in chronic wound pathophysiology remains unknown. Studies have shown that chronic wounds exhibit high levels of matrix metalloproteinase 9 (MMP9), a key proteolytic enzyme that regulates wound remodeling. We hypothesized that epithelial mechanosensory pathways regulated by keratinocyte-specific focal adhesion kinase (FAK) control dermal remodeling via MMP9.


METHODS
A standard wound model was applied to keratinocyte-specific FAK knockout (KO) and control mice. Rates of wound healing were measured and tissue was obtained for histologic and molecular analyses. Transcriptional and immunoblot assays were used to assess the activation of FAK, intracellular kinases, and MMP9 in vitro. A cell suspension model was designed to validate the importance of FAK mechanosensing, p38, and MMP9 secretion in human cells. Biomechanical testing was utilized to evaluate matrix tensile properties in FAK KO and control wounds.


RESULTS
Wound healing in FAK KO mice was significantly delayed compared with controls (closure at 15 days compared with 20 days, P = 0.0003). FAK KO wounds demonstrated decreased dermal thickness and collagen density. FAK KO keratinocytes exhibited overactive p38 and MMP9 signaling in vitro, findings recapitulated in human keratinocytes via the deactivation of FAK in the cell suspension model. Functionally, FAK KO wounds were significantly weaker and more brittle than control wounds, results consistent with the histologic and molecular analyses.


CONCLUSIONS
Keratinocyte FAK is highly responsive to mechanical cues and may play a critical role in matrix remodeling via regulation of p38 and MMP9. These findings suggest that aberrant epithelial mechanosensory pathways may contribute to pathologic dermal proteolysis and wound chronicity.
*Department of Surgery, Stanford University School of Medicine, Stanford, CA; and †Department of Materials Science and Engineering, Stanford University, Stanford, CA.
Victor W
VW
Wong
Ravi K
RK
Garg
Michael
M
Sorkin
Kristine C
KC
Rustad
Satoshi
S
Akaishi
Kemal
K
Levi
Emily R
ER
Nelson
Misha
M
Tran
Robert
R
Rennert
Wei
W
Liu
Michael T
MT
Longaker
Reinhold H
RH
Dauskardt
Geoffrey C
GC
Gurtner
D000818:Animals; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007231:Infant, Newborn; D015603:Keratinocytes / Q000378:metabolism / Q000648:ultrastructure*; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D059748:Proteolysis; D012313:RNA / Q000235:genetics*; D012867:Skin / Q000293:injuries*; D015854:Up-Regulation; D014945:Wound Healing; D014947:Wounds and Injuries / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
D012313:RNA; D051416:Focal Adhesion Protein-Tyrosine Kinases