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

TLDR

Mechanical factors are critical to articular cartilage physiology and pathology, yet the mechanisms of mechanical signal transduction remain incompletely understood. The study tests whether type VI collagen is required for mechanotransduction by evaluating TRPV4 activation, chondrocyte swelling, and PCM mechanical properties in type VI collagen knockout mice. Immunofluorescence‑guided atomic force microscopy mapped PCM stiffness, while confocal microscopy measured TRPV4‑mediated calcium signaling and cell swelling in femora from WT and Col6a1(-/-) mice. Type VI collagen knockout reduced PCM stiffness and increased chondrocyte swelling and TRPV4 signaling, demonstrating that PCM alterations can modulate mechanotransduction and may influence aging or osteoarthritis.

Abstract

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 undertook this study to test 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 TRPV4 (transient receptor potential vanilloid channel 4) as well as on osmotically induced chondrocyte swelling and pericellular matrix (PCM) mechanical properties.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.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.In contrast to our original hypothesis, type VI collagen was not required for TRPV4-mediated Ca(2+) 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 they suggest that alterations in PCM properties, as may occur with aging or osteoarthritis, can influence mechanotransduction via TRPV4 or other ion channels.