Deletion of the Transforming Growth Factor β Receptor Type II Gene in Articular Chondrocytes Leads to a Progressive Osteoarthritis‐like Phenotype in Mice

Abstract

Objective While transforming growth factor β (TGFβ) signaling plays a critical role in chondrocyte metabolism, the TGFβ signaling pathways and target genes involved in cartilage homeostasis and the development of osteoarthritis (OA) remain unclear. Using an in vitro cell culture method and an in vivo mouse genetic approach, we undertook this study to investigate TGFβ signaling in chondrocytes and to determine whether Mmp13 and Adamts5 are critical downstream target genes of TGFβ signaling. Methods TGFβ receptor type II (TGFβRII)–conditional knockout (KO) (TGFβRIICol2ER) mice were generated by breeding TGFβRIIflox/flox mice with Col2-CreER–transgenic mice. Histologic, histomorphometric, and gene expression analyses were performed. In vitro TGFβ signaling studies were performed using chondro-genic rat chondrosarcoma cells. To determine whether Mmp13 and Adamts5 are critical downstream target genes of TGFβ signaling, TGFβRII/matrix metalloproteinase 13 (MMP-13)– and TGFβRII/ADAMTS-5–double-KO mice were generated and analyzed. Results Inhibition of TGFβ signaling (deletion of the Tgfbr2 gene in chondrocytes) resulted in up-regulation of Runx2, Mmp13, and Adamts5 expression in articular cartilage tissue and progressive OA development in TGFβRIICol2ER mice. Deletion of the Mmp13 or Adamts5 gene significantly ameliorated the OA-like phenotype induced by the loss of TGFβ signaling. Treatment of TGFβRIICol2ER mice with an MMP-13 inhibitor also slowed OA progression. Conclusion Mmp13 and Adamts5 are critical downstream target genes involved in the TGFβ signaling pathway during the development of OA.

TAK1 regulates SOX9 expression in chondrocytes and is essential for postnatal development of the growth plate and articular cartilages

“…As described in detail above, chondrocyte-specific deletion of Tak1 closely resembles that of other chondrocyte-specific BMP loss-of-function models. Chondrocyte-specific loss of TGF-b signaling, however, has little effect on long bone development, but results in an osteoarthritis-like phenotype postnatally as a result of excessive articular chondrocyte hypertrophy (Baffi et al, 2004;Shen et al, 2013). Here, we observed no changes indicative of excessive chondrocyte hypertrophy.…”

“…Indeed, mice with postnatal disruption of components from either the TGF-b or BMP signaling pathways develop phenotypes reminiscent of osteoarthritis. For example, global deletion of Smad3, expression of a dominant-negative TGF-b type II receptor (TbRII) in skeletal tissue, and chondrocyte-specific loss of TbRII (Col2a1-CreER T2 ; Tgfbr2 f/f ) all result in osteoarthritis due to aberrant hypertrophy of articular chondrocytes evident by ectopic expression of Col10a1 in the articular cartilage (Serra et al, 1997;Shen et al, 2013;Yang et al, 2001). Additionally, loss of Bmpr1a expression in developing synovial joints leads to erosion of the articular cartilage with loss of Col2a1 and Acan gene expression (Rountree et al, 2004).…”

The chondrocyte clock gene Bmal1 controls cartilage homeostasis and integrity

“…Ingenuity analysis predicted that the two most significant upstream regulators of the differential genes were TGF-β (inhibited) and TP53 (inhibited). TGF-β signaling plays critical roles in maintaining cartilage metabolic homeostasis and structural integrity (29)(30)(31)(32)(33). TGF-β functions via both the ALK5/SMAD-2/3 and the ALK1/SMAD-1/5/8 signaling pathways, which often ures 7 and 8; and Table 1).…”

Osteoarthritis Pathogenesis: A Review of Molecular Mechanisms

“…In order to overcome embryonic lethality and redundancy, we generated chondrocyte-specific Tgfbr2 conditional knockout mice (Tgfbr2 cKO or Tgfbr2Col2CreER mice) in which deletion of the Tgfbr2 gene is mediated by Cre recombinase driven by the chondrocyte-specific Col2a1 promoter in a tamoxifen (TM)-inducible manner [45, 46]. These mice exhibit typical clinical features of OA, including cell cloning, chondrocyte hypertrophy, cartilage surface fibrillation, vertical clefts, and severe articular cartilage damage as well as the formation of chondrophytes and osteophytes [47]. In addition, the relationship between TGF-β and OA is strengthened by the discovery that a single nucleotide polymorphism (SNP) in the human Smad3 gene is linked to the incidence of hip and knee OA in a 527 patient cohort [48].…”