CDC42 regulates the expression of superficial zone molecules in part through the actin cytoskeleton and myocardin‐related transcription factor‐A

Abstract

Osteoarthritis (OA) is a degenerative disease that initially manifests as loss of the superficial zone (SZ) of articular cartilage. SZ chondrocytes (SZC) differ in morphology from other chondrocytes as they are elongated and oriented parallel to the tissue surface. Proteoglycan 4 (PRG4) and tenascin C (TNC) are molecules expressed by SZC, which have been shown to be chondroprotective. Identification of the signalling pathway(s) regulating expression of SZ molecules may lead to a therapeutic target that can be used to delay or prevent the onset of OA. The hypothesis of this study is that expression of SZ molecules are regulated in part, by the CDC42-actin-myocardin-related transcription factor-A (MRTF-A) signaling pathway. SZC from bovine metacarpal-phalangeal joints were isolated and grown in monolayer culture. Each target in the CDC42-actin-MRTF-A pathway was inhibited and the effect on cell shape, actin cytoskeleton status, and expression of PRG4 and TNC were determined. Treatment with the CDC42 inhibitor ML141 decreased PRG4 and TNC expression, and correlated with increased cell circularity and G-/F-actin ratio. PRG4 and TNC expression were differentially regulated by actin depolymerizing agents, latrunculin B and cytochalasin D. Chemical inhibition of MRTF-A resulted in decreased expression of both PRG4 and TNC; however, specific knockdown by small interfering RNA only decreased expression of TNC indicating that TNC, but not PRG4, is regulated by MRTF-A. Although PRG4 and TNC expression are both regulated by CDC42 and actin, it appears to occur through different downstream signaling pathways. Further study is required to elucidate the pathway regulating PRG4. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2421-2430, 2018.

Rho GTPase signaling in rheumatic diseases

“…Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) deletion has been demonstrated to restore the phenotype of chondrocytes, and Cdc42 inhibition can reduce the levels of YAP/TAZ ( Goto et al., 2018 ). Cdc42 increases the level of actin formation, which further enhances myocardin-related transcription factor-A (MRTF-A), and subsequently upregulates tenascin C (TNC) expression, which is chondroprotective ( Delve et al., 2018 ). Proteoglycan 4 (PRG4) is also upregulated by Cdc42 and independent of MRTF-A, thus providing protective effects to cartilage ( Delve et al., 2018 ).…”

“…Cdc42 increases the level of actin formation, which further enhances myocardin-related transcription factor-A (MRTF-A), and subsequently upregulates tenascin C (TNC) expression, which is chondroprotective ( Delve et al., 2018 ). Proteoglycan 4 (PRG4) is also upregulated by Cdc42 and independent of MRTF-A, thus providing protective effects to cartilage ( Delve et al., 2018 ). YAP/TAZ downregulation further leads to the suppression of PRG4 and TNC, indicating that Cdc42 regulates a variety of chondroprotective molecules, which might alleviate OA ( Delve et al., 2020 ).…”

“… / in vitro Upstream inhibition Mutant Fortier and Miller (2006) Cdc42 increases the expressions of TNC and PRG4 in chondrocytes, which are protective to the cartilage. Cdc42–Actin–MRTF-A–TNC Cdc42–PRG4 in vitro Inhibitor Delve et al. (2018) Cdc42 inhibition attenuates OA development.…”

“…(2019) Osteoarthritis Superficial zone chondrocytes Cdc42 ML141 10 μM ( in vitro ) Cdc42 inhibition decreases actin polymerization status and reduces the expression of superficial zone molecules. Delve et al. (2018) Mouse primary articular chondrocytes Mouse embryonic fibroblast C3H10T1/2 cells Mouse chondrogenic ATDC5 cells Cdc42 ZCL278 20 to 50 μM ( in vitro ) 8 μg/knee joint ( in vivo ) Cdc42 inhibition alleviates articular cartilage degeneration and subchondral bone deterioration of osteoarthritis.…”

“…The Cdc42 inhibitor ZCL278, which blocks GEF binding and deactivates Cdc42, alleviates articular cartilage degradation and subchondral bone remodeling via inhibition of Cdc42 ( Friesland et al., 2013 ; Hu et al., 2018 ). ML141, another potent and selective Cdc42 inhibitor via nucleotide-binding blockade, reduces the expression of MRTF-A in superficial zone chondrocytes, which might further decrease the expression of protective molecules for OA, including PRG4 and TNC ( Delve et al., 2018 , 2020 ; Surviladze et al., 2010 ).…”