TITLE:
Intra-Articular Cartilage Calcification Associated with Type II Pro-Collagen Accumulation in Chondrocytes and Abnormal Fibrils in the Extra Cellular Matrix (ECM): Case Report
AUTHORS:
Peter Storgaard Skagen, Tom Nicolaisen
KEYWORDS:
Calcification, Collagen Bundles, Endoplasmic Reticulum Storage Disease (ERSD)
JOURNAL NAME:
Case Reports in Clinical Medicine,
Vol.8 No.4,
April
18,
2019
ABSTRACT: Objective: The purpose of this
case-study was to perform morphological and molecular analysis of articular
cartilage biopsies from the femoral condyle of a 33 year old woman with
intra-articular calcification in the right knee joint and compare the findings
with those of normal cartilage. Methods: Femural condyle cartilage
biopsies were used for Light Microscopy (LM), Transmission Electron Microscopy
(TEM), explant culturing and DNA mutation analysis
of the COL2A1 gene. Results: X-ray of the affected knee joint showed intra-articular calcifications on the
femur condyle, tibia and meniscus. Pathological LM and TEM examination
of cartilage biopsies revealed calcified islands
morphologically identical to calcium pyro-phosphate
dehydrate (CPPD) and hydroxyapatite (HA)-like crystals. In addition, chondrocytes
showed accumulation of pro-collagen molecules. With explant culturing and
immunochemistry, it was
confirmed that matrix calcification correlated with high intracellular matrix
accumulation and expression of type X collagen. The induction of hypertrophy in
chondrocytes was further associated with matrix vesicle (MV) release and a
prominent calcification zone. Surprisingly, TEM showed crystal development on
thick abnormal type II collagen fibrils suggesting that these ECM components
might nucleate and contribute to calcification. Conclusions: We suggest
that intra-articular calcification may be associated with type II pro-collagen
accumulation in chondrocytes. In particular, we hypothesize that matrix
accumulation may induce hypertrophy and type X collagen expression in cartilage
cells and release of MV’s into the ECM, which together with thick abnormal type
II collagen hetero-fibrils, are responsible for crystal deposition in the ECM.