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DOI: 10.1055/s-0031-1278523
The increased frequency of epithelial to myofibroblast transition during colorectal adenoma-dysplasia-carcinoma sequence
Introduction: The epithelial to myofibroblast transition (EMyT) is fundamental in the building of abnormal stromal microenvironment of colorectal cancer (CRC). The main regulator of EMyT is transforming growth factor (TGF)-β via its receptor (TGF-βRII) activation. During adenoma-dysplasia-carcinoma sequence (ADCS) the enhanced stromal TGF-β level may associate with Toll-like receptor (TLR)-9 activation by increased CRC-originated circulating free DNA motifs. Aims: Our aim was to examine myofibroblast-like differentiation events by detecting the frequency of intrapithelial α-smooth muscle actin (SMA)+/cytokeratin (CK)+ cells, in relation to TLR-9 and TGF-βRII expression with the help of immunohistochemistry during ADCS. Our further aim was to determine the mRNA expression levels of TGF-β as well.
Materials and methods: Histologically healthy (n=8), adenoma (n=8), and CRC (n=8) biopsy samples were taken during routine colonoscopy and included into tissue microarrays. Slides were immunostained for α-SMA, CK, TLR9, TGF-βRII antibodies, then were digitalized and analyzed with digital microscopy. We also performed whole-genome gene expression microarrays using independent samples to define TGF-β expression levels.
Results: The intraepithelial α-SMA showed dot-like expression patterns mainly in perinuclear localization. The proportion of intraepithelial α-SMA+/CK+ cells was significantly higher in CRC samples (3.34±1.01%) as compared to healthy (1.94±0.69%) or adenoma (1.62±0.78%) samples (p<0.01). This change was closely correlated with TGF-βRII expression, but the level of intraepithelial TGF-β were similar in all histological stages. We found significantly increased (p<0.05) cytoplasmic TLR-9 expression both in CRC epithelium (68.25±24.33%) and adenoma (70.34±2.49%) as compared to healthy samples (32.92±8.314%).
Conclusion: During tumor progression we found an increased appearance of EMT events parallel with enhanced intraepithelial TGF-βRII expression, but the activating TGF-β ligand originated mainly from stromal cells. The dot-like α-SMA staining in CK positive cells may refer to the initial phase of EMyT, and it suggests that this process does not require active motility. The increased expression of TLR-9 in adenoma was not followed by increased number of intraepithelial α-SMA+/CK+ cells, probably due to deficiency of TLR-9 ligands.