Cracking the Pericellular Matrix Code: Exploring how MMP-2, -3, and -7 influence matrix breakdown and biomechanical properties

Introduction: The intricate process of articular cartilage remodeling, pivotal for both physiological functions and osteoarthritis (OA) progression, is orchestrated through a balance of matrix synthesis and breakdown, which is mediated by matrix metalloproteinase enzymes (MMPs). At the heart of this remodeling lies the pericellular matrix (PCM), a specialized microenvironment encapsulating each chondrocyte and composed mainly of collagen type VI and perlecan. The aim of this study was to assess the impact of MMP-2, -3, and -7 on the structural integrity and biomechanical attributes of the PCM. Methods: Human articular cartilage explants (N = 10 patients) were incubated with activated MMP-2, -3, or -7, individually or in combination. Structural alterations in the PCM were evaluated by immunolabeling. The biomechanical properties of the PCM were measured using atomic force microscopy (AFM). Results: Collagen type VI structural integrity and fluorescence intensity uniformly decreased across all enzyme groups, while perlecan was selectively affected by MMP-3 and -7. AFM measurements demonstrated decreased PCM stiffness after incubation with individual MMPs, leading to an overall ∼31% reduction in elastic modulus for each enzyme. Combinations of enzymes induced comparable significant biomechanical alterations (∼35%), except for MMP-2+MMP-7. Discussion: This study highlights the significant influence of MMP-induced alterations in PCM composition on biomechanical properties, mirroring characteristics observed in early OA. Each MMP showed specificity in breaking down PCM, and an intriguing interplay, especially between MMP-2 and -7, indicated reduced efficacy in lowering PCM stiffness. Overall, MMP-2, -3, and -7 directly induce functional and structural PCM modifications.