Exploration of changes in spatial chondrocyte organisation in human osteoarthritic cartilage by means of 3D imaging

Marina Danalache,Bernd Rolauffs,Kevin Ralf Beutler,Florian Christof Bonnaire,Imke Greving,Stefan Fischer,Julius Michael Wolfgart,Ulf Krister Hofmann

doi:10.1038/s41598-021-89582-w

Abstract

Using two-dimensional top-down view microscopy, researchers have recently described chondrocytes as being spatially arranged in distinct patterns such as strings, double strings, and small and large clusters. Because of the seeming association of these changes with tissue degeneration, they have been proposed as an image-based biomarker for early osteoarthritis (OA) staging. The aim of our study was to investigate the spatial arrangement of chondrocytes in human articular cartilage in a 3D fashion and to evaluate the 3D changes of these patterns in the context of local tissue destruction. Decalcified femoral condyle resections from the load-bearing area were analysed in 3D for their spatial chondrocyte organisation by means of fluorescence microscopy and synchrotron-radiation micro-computed tomography (SR-µCT). In intact cartilage chondrocyte strings can be found in the superficial, transitional and deep zones. The proposed pattern changes accompanying tissue destruction could be located not just along the surface but also through all layers of cartilage. Each spatial pattern was characterised by a different cellular density (the only exception being between single and double strings with p = 0.062), with cellular density significantly increasing alongside the increase in local tissue degeneration as defined by the chondrocyte patterns. We can thus corroborate that the proposed cellular spatial changes are a three-dimensional function of local tissue degeneration, underlining their relevance as an image-based biomarker for the early diagnosis and description of OA.Clinical trial registration number: Project number of the ethics committee of the University of Tübingen:171/2014BO2.

Highlights

Using two-dimensional top-down view microscopy, researchers have recently described chondrocytes as being spatially arranged in distinct patterns such as strings, double strings, and small and large clusters
Articular cartilage is composed of sparsely scattered chondrocytes embedded in an expansive extracellular matrix (ECM)
The aim of our study was to investigate the spatial arrangement of chondrocytes in human articular cartilage in a 3D fashion and to evaluate the 3D changes of these patterns in the context of local tissue destruction

Summary

Introduction

Using two-dimensional top-down view microscopy, researchers have recently described chondrocytes as being spatially arranged in distinct patterns such as strings, double strings, and small and large clusters. We can corroborate that the proposed cellular spatial changes are a three-dimensional function of local tissue degeneration, underlining their relevance as an image-based biomarker for the early diagnosis and description of OA. Abbreviations DS Double strings ECM Extracellular matrix Em Emission Ex Excitation LC Large clusters μCT Micro-computed tomography OA Osteoarthritis SC Small clusters SS Single strings. With initiation and progression of OA, the chondrocytes’ spatial organisation at the cartilage surface changes from strings to double s trings[10], to small or even large clusters[7] (Supplementary Figure 1). Analysing the cartilage surface in a top-down view only might, lead to perceived changes of cellular organisation already as a result of deeper tissue layers made visible to top-down observation by superficial erosion. Since cellular organisation had been shown and validated in the topmost layer of articular cartilage as a 2D phenomenon, we hypothesised that it is a 3D feature of cartilage destruction during OA pathogenesis (Fig. 1)

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