MATERIALS AND METHODS: Thirty-nine formalin-fixed paraffin-embedded ameloblastoma cases comprising unicystic ameloblastoma (n=19) and solid/multicystic ameloblastoma (n=20) were subjected to IHC staining for IL-1α, IL-1β, IL-6 and IL-8. A semi-quantitative method was used to evaluate the expression levels of these cytokines according to cell types in the tumoural parenchyma and stroma.
RESULTS: Major findings were upregulations of IL-1α and IL-6 in SMA compared to UA. Both cytokines were heterogeneously detected in the tumoural parenchyma and stroma. Within the neoplastic epithelial compartment, IL-1α expression was more frequently detected in PA-like cells in UA whereas it was more frequently encountered in SR-like cells in SMA. IL-6 demonstrated higher expression levels in the stromal compartment of SMA. IL-1β and IL-8 were markedly underexpressed in both tumour subsets.
CONCLUSIONS: Overexpression of IL-1α in SMA suggests that this growth factor might play a role in promoting bone resorption and local invasiveness in this subtype. The expression levels of IL-1α and IL-6 in three cellular localizations indicate that parenchymal-stromal components of ameloblastoma interact reciprocally via IL-1α and IL-6 to create a microenvironment conducive for tumour progression.
MATERIALS AND RESULTS: Thirty-five paraffin-embedded ameloblastoma cases, ameloblastoma-derived cell lines (AM-1), and primary cultures of ameloblastoma stromal fibroblasts (ASF) were used. Immunohistochemistry, MTT assay, Western blotting, and RT-PCR were performed on these samples. Parenchyma-stromal CCN2 overexpression correlated significantly with fibrous-type stroma, but not with myxoid-type stroma, suggesting a role of CCN2 in fibrosis (P < 0.05). Recombinant CCN2 induction of enhanced ASF proliferation in AM-1 medium supports this view. Conversely, BMP4 and TGF-β were expressed in myxoid-type fibroblasts, but little expression was found in parenchyma. RANKL-positive and CD68-positive stromal cell populations were significantly greater in myxoid-type tumor areas than in fibrous-type tumor areas, while a higher Ki-67 labeling index was recorded in ameloblastoma with fibrous-type stroma. These data suggest that stromal properties influence bone resorption-related activities and growth rates, respectively.
CONCLUSIONS: These results suggest that the effects of secreted growth factors are governed by ameloblastoma parenchyma-stromal interactions. CCN2 promotes fibrogenesis independent of TGF-β signaling. Absence of CCN2 expression is associated with a phenotypic switch to a myxoid-type microenvironment that is conducive for TGF-β/BMP4 signaling to promote osteoclastogenesis.