Diversity of collagen expression in the pleomorphic adenoma of the parotid gland

Heterogeneity and versatility of the extracellular matrix during the transition from pleomorphic adenoma to carcinoma ex pleomorphic adenoma: cumulative findings from basic research and new insights

Pleomorphic adenoma (PA) is the most common salivary gland tumor, accounting for 50%-60% of these neoplasms. If untreated, 6.2% of PA may undergo malignant transformation to carcinoma ex-pleomorphic adenoma (CXPA). CXPA is a rare and aggressive malignant tumor, whose prevalence represents approximately 3%-6% of all salivary gland tumors. Although the pathogenesis of the PA-CXPA transition remains unclear, CXPA development requires the participation of cellular components and the tumor microenvironment for its progression. The extracellular matrix (ECM) comprises a heterogeneous and versatile network of macromolecules synthesized and secreted by embryonic cells. In the PA-CXPA sequence, ECM is formed by a variety of components including collagen, elastin, fibronectin, laminins, glycosaminoglycans, proteoglycans, and other glycoproteins, mainly secreted by epithelial cells, myoepithelial cells, cancer-associated fibroblasts, immune cells, and endothelial cells. Like in other tumors including breast cancer, ECM changes play an important role in the PA-CXPA sequence. This review summarizes what is currently known about the role of ECM during CXPA development.

Zebrafish Model of Stickler Syndrome Suggests a Role for Col2a1a in the Neural Crest during Early Eye Development

Most cases of Stickler syndrome are due to autosomal-dominant COL2A1 gene mutations leading to abnormal type II collagen. Ocular findings include axial eye lengthening with vitreal degeneration and early-onset glaucoma, which can result in vision loss. Although COL2A1 is a major player in cartilage and bone formation, its specific role in eye development remains elusive. We investigated the role of Col2a1a in neural crest migration and differentiation during early zebrafish eye development. In situ hybridization, immunofluorescence, live imaging, exogenous treatments [10 μM diethylaminobenzaldehyde (DEAB), 100 nM all-trans retinoic acid (RA) and 1-3% ethanol (ETOH)] and morpholino oligonucleotide (MO) injections were used to analyze wildtype Casper (roy-/-;nacre-/-), TgBAC(col2a1a::EGFP), Tg(sox10::EGFP) and Tg(foxd3::EGFP) embryos. Col2a1a colocalized with Foxd3- and Sox10-positive cells in the anterior segment and neural crest-derived jaw. Col2a1a expression was regulated by RA and inhibited by 3% ETOH. Furthermore, MO knockdown of Col2a1a delayed jaw formation and disrupted the ocular anterior segment neural crest migration of Sox10-positive cells. Interestingly, human COL2A1 protein rescued the MO effects. Altogether, these results suggest that Col2a1a is a downstream target of RA in the cranial neural crest and is required for both craniofacial and eye development.

Current Approaches for Improving Intratumoral Accumulation and Distribution of Nanomedicines

The ability of nanoparticles and macromolecules to passively accumulate in solid tumors and enhance therapeutic effects in comparison with conventional anticancer agents has resulted in the development of various multifunctional nanomedicines including liposomes, polymeric micelles, and magnetic nanoparticles. Further modifications of these nanoparticles have improved their characteristics in terms of tumor selectivity, circulation time in blood, enhanced uptake by cancer cells, and sensitivity to tumor microenvironment. These "smart" systems have enabled highly effective delivery of drugs, genes, shRNA, radioisotopes, and other therapeutic molecules. However, the resulting therapeutically relevant local concentrations of anticancer agents are often insufficient to cause tumor regression and complete elimination. Poor perfusion of inner regions of solid tumors as well as vascular barrier, high interstitial fluid pressure, and dense intercellular matrix are the main intratumoral barriers that impair drug delivery and impede uniform distribution of nanomedicines throughout a tumor. Here we review existing methods and approaches for improving tumoral uptake and distribution of nano-scaled therapeutic particles and macromolecules (i.e. nanomedicines). Briefly, these strategies include tuning physicochemical characteristics of nanomedicines, modulating physiological state of tumors with physical impacts or physiologically active agents, and active delivery of nanomedicines using cellular hitchhiking.

Pleomorphic adenomas of the parotid express different mesenchymal phenotypes: demonstration of matrix gene expression products characteristic of the fibroblastic and chondrocytic cell lineages

AIMS

Pleomorphic adenomas of the salivary glands are characterized by their high tissue diversity. Many studies have explored the derivation and differentiation of the neoplastic cells. We investigated the composition of the collagenous extracellular tumour matrix and could show a specific biochemical composition pattern in the different tumour areas.

METHODS AND RESULTS

In epithelially differentiated acinar and ductal areas there was positive staining for basement membrane collagen type IV and no, or only scarce, staining for collagen types I, II, III, or VI. Solid areas mostly lacked any extracellular matrix. In areas with fibrous tissue-like appearance, the fibroblast-typical interstitial collagen types I, III and VI were seen. Chondroid areas showed abundantly the characteristic cartilage components, collagen type II and, pericellularly, type VI collagen.

CONCLUSIONS

Our data show the presence of fibroblastic and chondrocytic cell differentiation in pleomorphic adenomas. Thus, they confirm that these neoplasms display, besides epithelial cell types, also real mesenchymal cell and tissue types. Differences in the abundance and the biochemical composition of the extracellular tumour matrix account largely for the morphological heterogeneity of pleomorphic adenomas of the salivary glands.

Immunohistochemical evaluation of the small and large proteoglycans in pleomorphic adenoma of salivary glands

This study investigated the immunolocalization of small and large proteoglycans (PGs), including decorin, biglycan, PG-M/versican and aggrecan, in salivary pleomorphic adenoma (PA) using monoclonal and polyclonal antibodies. In addition, a polyclonal antibody, A0082, recognizing blood vessels was also used to help identify truly mesenchymal tissues in PA. Decorin reactivity was detected only in tumor capsule and interstitial tissue of non-neoplastic salivary gland, but not in the tumor tissue. Biglycan was frequently revealed throughout the matrix of small chondroid regions and in the peripheral portion of larger chondroid regions. PG-M/versican was mainly localized to the truly mesenchymal tissues in PA and the innermost portion of tumor capsule. On the contrary, aggrecan was extensively expressed in the non-luminal epithelial areas as well as in the myxoid and chondroid areas, but not in the truly mesenchymal tissues. These findings suggest that aggrecan is the most widely distributed PG in PA and may be produced mainly by non-luminal tumor cells. The absence of aggrecan from the truly mesenchymal tissues argues against its origin from this source. Both aggrecan and biglycan may play important roles in the chondroid differentiation and morphogenesis of PA.

Immunohistochemical demonstration of bone morphogenetic protein-2 and type II collagen in pleomorphic adenoma of salivary glands

Immunohistochemical investigation of bone morphogenetic protein-2 (BMP-2) and type II collagen, two cartilage-associated proteins, was undertaken using monoclonal antibodies in 20 cases of salivary pleomorphic adenoma (PA) in order to explore their possible roles in chondroid differentiation of this tumor. Other salivary gland tumors, including adenoid cystic carcinoma (17 cases), polymorphous low-grade adenocarcinoma (10 cases), basal cell adenoma (3 cases), basal cell adenocarcinoma (1 case), and epithelial-myoepithelial carcinoma (2 cases), were also examined for comparison. In PA, BMP-2 immunoreactivity was detected in the luminal and non-luminal cells of the tubulo-ductal structures, plasmacytoid cells, and other scattered tumor cells in solid areas. In addition, tumor cells in chondroid areas in most cases (14/15), and stellate cells in myxoid areas in many cases (7/19), were also intensely labeled for BMP-2. Furthermore, BMP-2 was also detected in the non-neoplastic ductal cells in salivary glands, whereas no other salivary gland tumors were positively stained for this protein. Type II collagen was localized in the intercellular matrix of chondroid areas and in a few chondroid differentiating cells in myxoid areas, confirming its cartilage-specificity. A proportional relationship was observed between BMP-2 expression and chondroid formation, although BMP-2 was also stained in occasional PAs without chondroid formation. It is speculated that BMP-2 might be secreted by tumor cells and play a role in chondroid formation in PA by inducing some tumor cells to produce type II collagen and other chondroid matrical substances, like glycosaminoglycans. The expression of BMP-2 is specific to PA and may possibly be used as a useful marker in differentiating PA from other salivary gland tumors.

Expression of collagen and elastic fibers in duct-ligated submandibular glands of mice

Atrophy of salivary glands may occur by ductal obstruction caused by calculus, infection or neoplastic processes, or as consequence of systemic diseases and aging. In the present work, we have used histochemical methods to study the expression of elastic and collagen fibers during experimental atrophy of the submandibular gland of mice. Glandular atrophy was accompanied by a rapid increase in collagen deposition in both septal and intralobular regions. The expression of elastic fibers was not significantly altered during atrophy: a discrete increase of elastic fibers was noted only around ductal structures. The results showed that experimental ductal obstruction is a useful in vivo model to study molecular events that take part in the remodeling of the extracellular matrix during atrophy of salivary glands.

Synthesis of elastin by pleomorphic adenomas

Previous morphologic and histochemical studies have documented extracellular elastin and elastic fibers within the matrix of pleomorphic adenomas of the salivary glands. By morphologic criteria, the elastin appeared to be synthesized by the tumor rather than being a consequence of stroma produced in response to the tumor cells. To examine this issue, nine pleomorphic adenomas were studied by immunohistochemistry and in situ hybridization with tropoelastin-specific antibodies and complementary DNAs. Corroborating the previous morphologic studies, immunohistochemistry demonstrated abundant extracellular elastin within the matrix of pleomorphic adenomas. Additionally, both immunohistochemistry and in situ hybridization demonstrated continued synthesis of tropoelastin by the neoplastic cells. Tropoelastin production was seen in neoplastic cells with all morphologies.

Immunohistochemical expression of tenascin in normal human salivary glands and in pleomorphic adenomas

The presence of the extracellular matrix glycoprotein tenascin was studied immunohistochemically in normal human salivary glands and in pleomorphic adenomas. Its expression was compared to that of fibronectin, and type IV collagen. In the normal salivary gland, tenascin was found with interruptions in periductal tissues, and continuously in blood vessels, fat cells and around nerve bundles. In pleomorphic adenoma, tenascin was detected surrounding the clusters of epithelioid cells, in areas with a myxoid and a chondroid matrix, and around some myoepithelial cells as a halo. As compared to fibronectin, there is a similar location of tenascin and fibronectin around tumor cell clusters but not in myxoid and chondroid matrices. Fibronectin was found around the cells in chondroid matrix. In conclusion, tenascin is not only found in malignant tumors but also in benign tumors such as pleomorphic adenoma. The presence of tenascin as a halo around myoepithelial cells suggests a role of these cells in development of myxoid and chondroid matrices.

Comparison of the solophenyl-red polarization method and the immunohistochemical analysis for collagen type III

In the present study, we have compared the staining pattern of the Solophenyl-Red 3 BL-method for the visualization of collagen type III with the immunohistochemical staining in serial sections from 7 skin wounds (wound age 3 days up to 4 weeks) to elucidate the specificity of the histochemical staining method. Large amounts of collagen type III were clearly detectable in the investigated wounds using the immunohistochemical technique. In the sections stained with Solophenyl-Red, however, only 3 out of 7 skin lesions showed a significant positive red staining at the wound margin or in the granulation tissue, while the adjacent normal connective tissue revealed a typical intensive staining. Using polarization microscopy no characteristic bright green fibrils, as reported for collagen type III, could be seen in the wound areas without positive Solophenyl-Red staining. Since the localization of collagen type III detected by immunohistochemistry and the presumed distribution of this collagen type by the Solophenyl-Red method was not identical, the histochemical polarization method has to be regarded as non-specific for visualization of this collagen type.

Mucosubstance histochemistry of pleomorphic adenoma of parotid and submandibular salivary glands of man: light and electron microscopy

Lumina and adluminal cells in human salivary gland pleomorphic adenomas were found to contain neutral, carboxylated, and occasionally sulphated glycoproteins. A variable component of luminal contents and secretory granules did not appear to contain glycoprotein and possibly consisted of protein. Glycosaminoglycans, which appeared to be hyaluronic acid and chondroitin sulphate, were demonstrated rarely in lumina, often between epithelial cells, and forming the matrix of myxoid tissue and, together with collagen, chondroid tissue. No differences were seen between tumours from parotid glands and those from submandibular glands. Glycoproteins demonstrated in the epithelium are similar to those of intercalary ducts of parotid and submandibular glands, and may represent a primitive form of salivary secretion. Glycosaminoglycans secreted intercellularly by epithelial cells cause their increasing separation to form myxoid or chondroid tissue. This stromalization extends to lumina to produce a loss of epithelium. Pleomorphic adenoma appears to be a manifest example of variable derepression of the genotype.

Immunohistochemical demonstration of type II collagen in the chondroid tissue of pleomorphic adenomas of the salivary glands

A study was done to investigate the presence of type II collagen and elastin in the metaplastic chondroid tissue of 21 pleomorphic adenomas of the major and minor salivary glands. Type II collagen was detected with anti-bovine type II collagen antibody after double digestion of histological sections with trypsin and hyaluronidase. The immunoreaction was positive in the chondrocytic cells and intercellular matrix. Elastic fibers in the chondroid tissue were found by orcein staining; they were scarce and randomly distributed. Although the presence of type II collagen and elastin in the metaplastic chondroid tissue is not directly implicated in the genesis of the tumor, it reveals a unique and high grade of cellular differentiation in comparison with true cartilage.