Type VI Collagen Regulates Pericellular Matrix Properties, Chondrocyte Swelling, and Mechanotransduction in Mouse Articular Cartilage

Abstract

Objective Mechanical factors play a critical role in the physiology and pathology of articular cartilage, although the mechanisms of mechanical signal transduction are not fully understood. We examined the hypothesis that type VI collagen is necessary for mechanotransduction in articular cartilage, by determining the effects of type VI collagen knockout on the activation of the mechano-osmosensitive calcium-permeable channel, transient receptor potential vanilloid 4 (TRPV4), osmotically-induced chondrocyte swelling, and pericellular matrix (PCM) mechanical properties. Methods Confocal laser scanning microscopy was used to image TRPV4-mediated calcium signaling and osmotically-induced cell swelling in intact femora from 2 and 9 month old wild type (WT) and type VI collagen deficient (Col6a1−/−) mice. Immunofluorescence-guided atomic force microscopy was used to map PCM mechanical properties based on the presence of perlecan. Results Hypo-osmotic stress induced TRPV4-mediated calcium signaling was increased in Col6a1−/− mice relative to WT controls at 2 months. Col6a1−/− mice exhibited significantly increased osmotically-induced cell swelling and decreased PCM moduli relative to WT controls at both ages. Conclusion In contrast to our original hypothesis, type VI collagen was not required for TRPV4-mediated Ca2+ signaling; however, knockout of type VI collagen altered the mechanical properties of the PCM, which in turn increased the extent of cell swelling and osmotically-induced TRPV4 signaling in an age-dependent manner. These findings emphasize the role of the PCM as a transducer of mechanical and physicochemical signals, and suggest that alterations in PCM properties, as may occur with aging or osteoarthritis, can influence mechanotransduction via TRPV4 or other ion channels.

Induced superficial chondrocyte death reduces catabolic cartilage damage in murine posttraumatic osteoarthritis

“…We are not the first to apply confocal imaging to articular cartilage (10,(32)(33)(34)(35)(36). We believe that the present study is novel in its demonstration of the utility of confocal imaging for quantifying several useful measures of cartilage structure/organization, including cartilage volume, chondrocyte number, cells/volume near the surface, cell division frequency, and nearest neighbor distance.…”

Combining Targeted Metabolomic Data with a Model of Glucose Metabolism: Toward Progress in Chondrocyte Mechanotransduction

“…In vivo chondrocytes reside within a pericellular matrix composed of type VI collagen and perlecan [21] that serves as the primary source for delivering deformational stimuli. Loading chondrocytes in vitro required encapsulating them in a material that successfully emulates how cartilage transmits loads.…”

Collagen VI at a glance

“…Despite a structurally intact PCM in the absence of ColVI, the alterations found in the cartilage were mostly linked to the mechanical properties of the PCM, resulting in decreased stiffness (Alexopoulos et al, 2009). This defect, in turn, increases the extent of chondrocyte swelling and osmosis-induced signaling through transient receptor potential cation channel subfamily V member 4 (TRPV4), which responds to a variety of physical signals at the cell surface (Zelenski et al, 2015). These findings highlight the importance of ColVI in the transmission of mechanical and osmotic stresses from the ECM to the PCM, and thus to the chondrocytes, thereby identifying the importance of the PCM in transducing mechanical and physico-chemical signals (Zelenski et al, 2015).…”

“…This defect, in turn, increases the extent of chondrocyte swelling and osmosis-induced signaling through transient receptor potential cation channel subfamily V member 4 (TRPV4), which responds to a variety of physical signals at the cell surface (Zelenski et al, 2015). These findings highlight the importance of ColVI in the transmission of mechanical and osmotic stresses from the ECM to the PCM, and thus to the chondrocytes, thereby identifying the importance of the PCM in transducing mechanical and physico-chemical signals (Zelenski et al, 2015). In a different context, the use of soluble ColVI has been shown to be an important stimulus for the proliferation of both adult and osteoarthritic chondrocytes.…”