The role of synovial fibroblasts in tissue mineralization during chondrocalcinosis

 

Franziska I. Kosslowski, Sina Stücker, Prof. Dr. Christoph H. Lohmann, Prof. Dr. Rer. Nat. Jessica Bertrand

Otto-Von-Guericke University Magdeburg, Magdeburg

 

Status: The most common calcium-containing crystals that have been associated with arthropathies are basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP). Both crystals result from an imbalance in the pyrophosphate metabolism. CPP deposition has been linked to genetic mutations in the ankh gene and different comorbidities such as hemochromatosis and hypomagnesaemia. The most important risk factor, however, remains aging. The pathogenic mechanisms resulting in CPP crystal formation and the effect of those on the cells are not fully understood, yet requiring further investigations. Whereas osteoarthritis (OA) is linked to BCP deposition, induction of the canonical wnt-signaling-pathway and hypertrophic differentiation of chondrocytes, chondrocalcinosis (CC) is linked to CPP deposition and a higher expression of senescence markers in chondrocytes.

Objective: The aim of this study is to investigate the role of synovial fibroblasts in tissue calcification during CC.

Methodology: Synovial membrane samples were taken from CC and OA patients undergoing total knee replacement. CC was diagnosed by evaluating the anterior-posterior x-ray pictures. OA severity was described using the kellgren-lawrence score. In order to quantify calcification, the synovial membrane was embedded in paraffin and tissue sections were stained with a von-kossa staining. Furthermore, primary fibroblasts were isolated from the synovial membrane samples. Fibroblast differentiation was analyzed in vitro by staining for the senescence marker β-galactosidase. Therefore, synovial fibroblasts were cultured on glass-bottom wells for 1, 5 and 10 days. OA severity, degree of calcification and the amount of ss-galactosidase were correlated.

Findings: 6 CC and 11 OA patients were included in this study. Both, 3 OA and 3 CC patients, exhibited mineralization of the synovial membrane using the von-kossa staining. However, CC synovial membrane showed an increased amount of von kossa staining (mean OA area fraction: 13,28% ±11,19%, mean CC area fraction: 31,36% ±12,39%, p value: 0,1339). The radiological severity of OA in both groups was comparable (mean OA: 3,364 ±0,636; mean CC: 3,167 ±0,0,753; p-value: 0,5751). Synovial fibroblasts from 1 CC and 1 OA, both displayed an increase in β-galactosidase positive cells over 10 days. However, CC patient showed slightly more β-galactosidase positive cells in comparison to OA fibroblasts.

Conclusion: These finding indicate that CC is associated with a more severe mineralization of the synovial membrane, along with the induction of senescent differentiation in synovial fibroblasts, compared with OA. Further investigations need to be carried out to corroborate these observations.

 

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