TGF‐β1 drives partial myofibroblastic differentiation in chondromyxoid fibroma of bone

Abstract

Chondromyxoid fibroma (CMF) is a rare benign cartilaginous bone tumour with a lobular architecture containing stellate and myofibroblast-like spindle cells. The aim of this study was to investigate the presence, spatial distribution, and extent of myoid differentiation in CMF and to evaluate a possible causative role for TGF-beta1 signalling, which is known to promote smooth muscle actin (SMA) expression. Twenty cases were studied for immunoreactivity for muscle-specific actin (MSA), SMA, desmin, h-caldesmon, calponin, TGF-beta1, and plasminogen activator inhibitor type 1 (PAI-1). The extent of myofibroblastic differentiation was further investigated ultrastructurally, including immuno-electron microscopy using antibodies against MSA and SMA, focusing upon the different cell types in CMF. The expression of potential genes driving this process was quantified by Q-RT-PCR (TGF-beta1, fibronectin, its EDA splice variant, and PAI-1). Tumour cells, especially those with a spindled morphology, showed diffuse immunoreactivity for MSA, SMA, TGF-beta1, and PAI-1, while desmin, h-caldesmon, and calponin were absent. Ultrastructurally, neoplastic cells showed the presence of myofilaments and rare dense bodies, which were more prominent in spindle cells and less so in chondroblast-like cells. Immuno-electron microscopy confirmed the actin nature of these myofilaments. No fibronexus was identified. The functional activity of TGF-beta1 was demonstrated by the identification of PAI-1, a related downstream molecule both immunohistochemically as well as by Q-RT-PCR. There was a linear correlation between TGF-beta1 and PAI-1 expression. Fibronectin-EDA levels were low. We have therefore substantiated the presence of morphological, immunohistochemical, and immuno-electron microscopic partial myofibroblastic differentiation in CMF, driven by TGF-beta1 signalling.

Heterogeneous and Complex Rearrangements of Chromosome Arm 6q in Chondromyxoid Fibroma

“…Genes for normalization were previously identified. 4,5 Normalization was based on geometric averaging of these normalization genes. 19 We compared the level of expression in the CMF samples to five samples of articular cartilage and seven samples of growth plate cartilage.…”

“…Four m sections of formalin-fixed paraffin-embedded material were used according to standard laboratory procedures. 4 Antigen retrieval was performed by boiling tissue sections in citrate buffer pH 6 in a microwave oven for 10 minutes. Sections from 22 CMFs were then incubated overnight with either anti-BCLAF1 (mouse, monoclonal, clone 5, BD transduction laboratories, Franklin Lakes, NJ, dilution 1:1000) or utrophin (clone 8A4, Novus Biologicals, Littleton, CO, dilution 1:10).…”

“…Quantitative RT-PCR was performed as described previously. 4 For each gene a 3 log dilution curve using cDNA isolated from placenta as a positive control was included to calculate the relative gene expression levels. Relative expression levels were used in the normalization and statistical analysis.…”

The role of noncartilage‐specific molecules in differentiation of cartilaginous tumors

“…6 ECM genes, such as collagen 4A2 (COL4A2), versican, perlecan, and procollagen-lysine 2-oxoglutarate 5-dioxygenase 2 (PLOD2), which is involved in posttranslational modification of ECM, were investigated further because of their more likely causative role in determining the spectrum of differentiation. Primers are described in Table 2.…”

“…3 We demonstrated previously that, within the histology of CMF, the different steps of in vitro chondrogenesis are reflected by the presence of round cells that are more similar to mature chondrocytes and the presence of less differentiated spindle-cell precursors that show partial myofibroblastic transdifferentiation. 6,7 The polygonal-atypical cells in CMF sometimes closely resemble the cells of highgrade central chondrosarcoma (HGCCS). This can make the differential diagnosis difficult in clinical practice, especially in biopsy specimens.…”