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Osteogenesis requires FAK‐dependent collagen synthesis by fibroblasts and osteoblasts
Author(s) -
Rajshankar Dhaarmini,
Wang Yongqiang,
McCulloch Christopher A.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.201600645r
Subject(s) - focal adhesion , runx2 , chemistry , gene knockdown , conditional gene knockout , osteoblast , microbiology and biotechnology , kinase , knockout mouse , wild type , mutant , phosphorylation , biology , phenotype , in vitro , receptor , biochemistry , gene , apoptosis
Focal adhesion kinase (FAK) is critical in adhesion‐dependent signaling, but its role in osteogenesis in vivo is ill defined. We deleted Fak in fibroblasts and osteoblasts in Floxed‐Fak mice bred with those expressing Crerecombinase driven by 3.6‐kb α1(I)‐collagen promoter. Compared with wild‐type (WT), conditional FAK‐knockout (CFKO) mice were shorter (2‐fold; P < 0.0001) and had crooked, shorter tails (50%; P < 0.0001). Microcomputed tomography analysis showed reduced bone volume (4‐fold in tails; P < 0.0001; 2‐fold in mandibles; P < 0.0001), whereas bone surface area/bone volume increased (3‐fold in tails; P < 0.0001; 2.5‐fold in mandibles; P < 0.001). Collagen density and fiber alignment in periodontal ligament were reduced by 4‐fold ( P < 0.0001) and 30% ( P < 0.05), respectively, in CFKO mice. In cultured CFKO osteoblasts, mineralization at d 7 and mineralizing colony‐forming units at d 21 were 30% ( P < 0.0001) and >3‐fold less than WT, respectively. Disruptions of FAK function in osteoblasts by conditional knockout, siRNA‐knockdown, or FAK inhibitor reduced mRNA and protein expression of Runx2 (>30%), Osterix (>25%), and collagen‐1 (2‐fold). Collagen synthesis was abrogated in WT osteoblasts with Runx2 knockdown and in Fak ‐null fibroblasts transfected with an FAK kinase domain mutant or a kinase‐impaired mutant (Y397F). These data indicate that FAK regulates osteogenesis through transcription factors that regulate collagen synthesis.—Rajshankar, D., Wang, Y., McCulloch, C. A. Osteogenesis requires FAK‐dependent collagen synthesis by fibroblasts and osteoblasts. FASEB J. 31, 937–953 (2017). www.fasebj.org