Characterization of the chondrocyte actin cytoskeleton in living three-dimensional culture: response to anabolic and catabolic stimuli.

Division of Arthritis Research, Department of Molecular and Experimental Medicine, The Scripps Research Institute 10550 North Torrey Pines Road, La Jolla CA 92037, USA.
Molecular & cellular biomechanics: MCB 10/2009; 6(3):135-44.
Source: PubMed

ABSTRACT The actin cytoskeleton is a dynamic network required for intracellular transport, signal transduction, movement, attachment to the extracellular matrix, cellular stiffness and cell shape. Cell shape and the actin cytoskeletal configuration are linked to chondrocyte phenotype with regard to gene expression and matrix synthesis. Historically, the chondrocyte actin cytoskeleton has been studied after formaldehyde fixation--precluding real-time measurements of actin dynamics, or in monolayer cultured cells. Here we characterize the actin cytoskeleton of living low-passage human chondrocytes grown in three-dimensional culture using a stably expressed actin-GFP construct. GFP-actin expression does not substantially alter the production of endogenous actin at the protein level. GFP-actin incorporates into all actin structures stained by fluorescent phalloidin, and does not affect the actin cytoskeleton as seen by fluorescence microscopy. GFP-actin expression does not significantly change the chondrocyte cytosolic stiffness. GFP-actin does not alter the gene expression response to cytokines and growth factors such as IL-1beta and TGF-beta. Finally, GFP-actin does not alter production of extracellular matrix as measured by radiosulfate incorporation. Having established that GFP-actin does not measurably affect the chondrocyte phenotype, we tested the hypothesis that IL-1beta and TGF-beta differentially alter the actin cytoskeleton using time-lapse microscopy. TGF-beta increases actin extensions, and lamellar ruffling indicative of Rac/CDC42 activation, while IL-1beta causes cellular contraction indicative of RhoA activation. The ability to visualize GFP-actin in living chondrocytes in 3D culture without disrupting the organization or function of the cytoskeleton is an advance in chondrocyte cell biology and provides a powerful tool for future studies in actin-dependent chondrocyte differentiation and mechanotransduction pathways.


Available from: Dominik R Haudenschild, Apr 25, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cell adhesion is a key phenomenon that affects fundamental cellular processes such as morphology, migration, and differentiation. In the current study, an active modelling framework incorporating actin cytoskeleton remodelling and contractility, combined with a cohesive zone model to simulate debonding at the cell-substrate interface, is implemented to investigate the increased resistance to detachment of highly spread chondrocytes from a substrate, as observed experimentally by Huang et al. (J. Orthop. Res. 21: 88-95, 2003). 3D finite element meshes of the round and spread cell geometries with the same material properties are created. It is demonstrated that spread cells with a flattened morphology and a larger adhesion area have a more highly developed actin cytoskeleton than rounded cells. Rounded cells provide less support for tension generated by the actin cytoskeleton; hence, a high level of dissociation is predicted. It is revealed that the more highly developed active contractile actin cytoskeleton of the spread cell increases the resistance to shear deformation, and subsequently increases the shear detachment force. These findings provide new insight into the link between cell geometry, cell contractility, and cell-substrate detachment.
    Annals of Biomedical Engineering 12/2013; DOI:10.1007/s10439-013-0965-5 · 3.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study examined actin regulation of fibroblast matrix genes in dedifferentiated chondrocytes. We demonstrated that dedifferentiated chondrocytes exhibit increased actin polymerization, nuclear localization of myocardin related transcription factor (MRTF), increased type I collagen (Col1) and tenascin C (Tnc) gene expression, and decreased Sox9 gene expression. Induction of actin depolymerization by latrunculin treatment or cell rounding, reduced MRTF nuclear localization, repressed Col1 and Tnc expression, and increased Sox9 gene expression in dedifferentiated chondrocytes. Treatment of passaged chondrocytes with MRTF inhibitor repressed Col1 and Tnc expression, but did not affect Sox9 expression. Our results show that actin polymerization regulates fibroblast matrix gene expression through MRTF in passaged chondrocytes.
    FEBS Letters 08/2014; 588(20). DOI:10.1016/j.febslet.2014.08.012 · 3.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Importance of actin organization in control of chondrocyte phenotype is well established, but little is known about the role of transforming growth factor-β1 (TFGβ1) in regulating of ROCK I signal pathway. Here, we investigated the role of the TGFβ1, a well-studied member of the TGF-β superfamily, in chondrogenesis. Newborn Rats were randomly assigned to developmental dysplasia of the hip (DDH) group and control group. The isolated hips were performed with HE staining and immunohistochemistry. The chondrocytes was isolated and stained by immunofluorescence. The relative quantification of TGFβ1 on mRNA level was determined using real-time RT-PCR, and its secretion in culture supernatant in each well was detected by means of ELISA. The expression of ROCK I and ROCK II was detected by means of Western Blot. The relative amounts of actin in detergent-soluble and insoluble fractions were determined. Furthermore, TGFβ1 were employed to stimulate normal primary culture chondrocytes in vitro. We found TFGβ1 significantly changed in acetabulum chondrocytes after mechanical overloading. Over expression of TFGβ1 was observed by means of RT-PCR and ELISA assay. The expression of ROCK I was significantly increased in DDH acetabulum chondrocytes compared with normal cells. The detergent-soluble actin was confirmed reorganization in DDH chondrocytes. Furthermore, TFGβ1 can stimulate the ROCK I signaling to modulate actin location in vitro. In conclusion, our data suggested that TFGβ1 expression suppresses chondrogenesis through the control of ROCK signaling and actin organization.
    Molecular and Cellular Biochemistry 02/2014; 391(1-2). DOI:10.1007/s11010-014-1980-z · 2.39 Impact Factor