Changes in stiffness and biochemical composition of the pericellular matrix as a function of spatial chondrocyte organisation in osteoarthritic cartilage

Abstract

Objective: During osteoarthritis (OA), chondrocytes seem to change their spatial arrangement from single to double strings, small and big clusters. Since the pericellular matrix (PCM) appears to degrade alongside this reorganisation, it has been suggested that spatial patterns act as an image-based biomarker for OA. The aim of this study was to establish the functional relevance of spatial organisation in articular cartilage. Method: Cartilage samples were selected according to their predominant spatial cellular pattern. Young's modulus of their PCM was measured by atomic force microscopy (AFM) (~500 measurements/pattern). The distribution of two major PCM components (collagen type VI and perlecan) was analysed by immunohistochemistry (8 patients) and protein content quantified by enzyme-linked immunosorbent assay (ELISA) (58 patients). Results: PCM stiffness significantly decreased with the development from single to double strings (p ¼ 0.030), from double strings to small clusters (p ¼ 0.015), and from small clusters to big clusters (p < 0.001). At the same time, the initially compact collagen type VI and perlecan staining progressively weakened and was less focalised. The earliest point with a significant reduction in protein content as shown by ELISA was the transition from single strings to small clusters for collagen type VI (p ¼ 0.016) and from double strings to small clusters for perlecan (p ¼ 0.008), with the lowest amounts for both proteins seen in big clusters. Conclusions: This study demonstrates the functional relevance of spatial chondrocyte organisation as an image-based biomarker. At the transition from single to double strings PCM stiffness decreases, followed by protein degradation from double strings to small clusters.

Biochemical changes of the pericellular matrix and spatial chondrocyte organization—Two highly interconnected hallmarks of osteoarthritis

“…In a previous study, we had already shown that the PCM progressively loses its characteristic biomechanic properties alongside cellular rearrangement 39 . We had further demonstrated that, accompanying these pattern changes, the two main PCM components—collagen type VI and perlecan—undergo progressive destruction 39 . In the present study, the current knowledge of PCM degradation on the basis of cellular spatial organization is further expanded upon by additionally investigating its components collagen type III, biglycan, and fibrillin‐1.…”

“…Discs of articular cartilage from 127 patients (approximately 30 discs per target analysis) were cut, sorted, and assigned to their predominant cellular pattern organization as described previously 39 . Using a custom‐fabricated device, cartilage was cut in the horizontal plane (ie, parallel to the superficial zone) to obtain discs of 300 µm in thickness and 4 mm in diameter.…”

“…For biglycan (BIOZOL Diagnostica Vertrieb GmbH, Eching, Germany) and fibrillin‐1 (LifeSpan Biosciences Inc., Seattle), 30 µg was used following the manufacturer's protocol. For collagen type VI and perlecan, the data from a previous publication were used 39 . While collagen type VI, perlecan, collagen type III and biglycan absorbance was measured with an EL 800 reader (BioTek Instruments GmbH, Bad Friedrichshall, Germany), a chemiluminescent plate reader (Infinite 200 PRO; Tecan Group Ltd., Männedorf, Switzerland) was used for fibrillin‐1 ELISA.…”

“…In order to paint the big picture with respect to PCM degradation and to better understand the underlying mechanisms, these minor and often overlooked PCM components and the synergetic role they play in the degradative process of the pericellular region need to be elucidated. In a previous study, we had already shown that the PCM progressively loses its characteristic biomechanic properties alongside cellular rearrangement 39 . We had further demonstrated that, accompanying these pattern changes, the two main PCM components—collagen type VI and perlecan—undergo progressive destruction 39 .…”

Biological Properties and Pathological Stages of Chondrocyte Colony-like Clusters in Osteoarthritic Cartilage Tissue

“…12,16,17,[20][21][22][23][24][25] Only at certain stages during the progression of OA can rapid colony-like proliferation of chondrocytes occur in cartilage tissue,which we call chondrocyte colony-like clusters. [26][27][28][29][30][31][32] However, the signi cance of chondrocyte colony-like cluster formation in cartilage during OA progression remains unclear. 27,33,34 Some studies have suggested that chondrocyte colony-like cluster formation in cartilage is a compensatory response by which the body compensates for the decrease in the number of chondrocytes during the development of OA.…”