The pathobiology of salivary gland. I. Growth and development of rat submandibular gland organoids cultured in a collagen gel matrix

Organoid Models for Salivary Gland Biology and Regenerative Medicine

The salivary gland is composed of an elegant epithelial network that secrets saliva and maintains oral homeostasis. While cell lines and animal models furthered our understanding of salivary gland biology, they cannot replicate key aspects of the human salivary gland tissue, particularly the complex architecture and microenvironmental features that dictate salivary gland function. Organoid cultures provide an alternative system to recapitulate salivary gland tissue in vitro, and salivary gland organoids have been generated from pluripotent stem cells and adult stem/progenitor cells. In this review, we describe salivary gland organoids, the advances and limitations, and the promising potential for regenerative medicine.

Immunoexpression of extracellular matrix proteins in human salivary gland development

Immunoexpression of the extracellular matrix (ECM) proteins laminin, fibronectin, tenascin and types I, III and IV collagen was analyzed in the major and minor salivary glands of seven human fetuses at different gestational ages. The results showed the presence and localization of laminin, collagen IV and fibronectin around glandular structures at all stages of development. Tenascin was only detectable around excretory ducts. In the earliest stages of development, type I and type III collagen were presented as fine fibers delineating the glandular structures and delimiting the extension of the future lobule. As glandular development proceeded, the lobule was gradually filled with collagens and glandular tissue.

A feasibility study of salivary gland autograft transplantation for xerostomia

BACKGROUND

Radiation-induced xerostomia is a frequent sequela in patients treated for cancer of the head and neck. One strategy to treat xerostomia would be to relocate portions of salivary tissue to adjacent submucosal sites that lie outside the radiation portals such as the anterior oral vestibule. It is not known whether salivary tissue transplanted as an autogenous free graft can survive, function adequately, and not produce mucoceles.

METHODS

Salivary gland tissue from the parotid and submandibular glands of the Syrian hamster were transplanted into the submucosal layer of the cheek pouch. After 3 months of observation, looking at graft size, graft extrusion, ulceration, infection, and mucocele formation, the graft sites were harvested. The specimens then underwent pathologic analysis by hematoxylin and eosin staining, as well as immunohistochemical methods to determine positivity for cytokeratin, smooth muscle actin (SMA), and amylase.

RESULTS

Histologic analysis of tissue harvested from Syrian hamsters grafted into the cheek pouch demonstrated intact, viable, organized salivary gland tissue. Eighty percent of the animals in the submandibular group and 63% of the animals in the parotid group had at least 1 graft with viable salivary tissue without undue complications.

CONCLUSIONS

Salivary gland tissue can be transplanted successfully as free autogenous grafts in the Syrian hamster model. Further studies are needed to determine whether the grafts will subsequently become functional and whether growth can be biologically stimulated. This approach may be a useful strategy to protect salivary gland tissue in patients undergoing radiotherapy for head and neck cancer.

Squamous cell Carcinomas of the Head and Neck Cultured in Floating Collagen Gels: 1. The Maintenance of Stromal and Epithelial Elements in Vitro without Fibroblast Overgrowth

The study of the molecular biology of head and neck squamous cell carcinomas has been heavily reliant on the analysis of cell lines. This is largely because the maintenance of primary cell cultures is difficult. However, being monoclonal, cell lines are not representative of the primary tumor because of the loss of tumor cell heterogeneity. We report a technique for primary culture of squamous cell carcinomas with maintenance of epithelial and stromal cell components without overgrowth of the fibroblast cells. Phenotypic markers for fibroblasts and squamous cells were present up to 45 days after initiation of culture, and expression of epidermal growth factor receptor and involucrin in cultures paralleled that in the primary tumor. In vivo, tumor stromal elements are thought to play an important role in the support of epithelial cell growth. In the collagen gel system the preservation of the stromal cell component likely improves culture viability and growth. More importantly, this culture system allows the in vitro tumor to more accurately reflect the tumor from which it was derived, and it permits the study of primary squamous cell carcinomas under in vitro conditions.

Pathology of the salivary glands: the contribution of electron microscopy

Electron microscopy has a limited role in the diagnosis of primary salivary gland tumors, although it can be helpful in metastatic lesions of possible salivary gland origin. The diversity of subtypes in salivary gland tumors, as well as the range of histomorphology within any one subtype, is unparalleled in any other human tumor. This and their relative infrequency causes diagnostic problems for pathologists. Ultrastructural techniques have been of major importance in determining the inter-relationship of these tumors for classification purposes, revealing the subtle variations in common cellular differentiation pathways, determining the organization of tumor cells, and displaying the importance of extracellular matrix materials in establishing diagnostic criteria for each of the many subtypes. Electron microscopy has also been valuable in non-neoplastic salivary gland disease and has an increasing role in experimental studies involving tissue from human and animal salivary parenchyma.

Current status of histogenetic and morphogenetic concepts of salivary gland tumorigenesis

Because of their complexity and relative infrequency, salivary gland tumors commonly result in diagnostic problems. Histogenetic and morphogenetic concepts of tumorigenesis in these glands are reviewed and their relevance to routine diagnosis and classification of salivary gland tumors evaluated. Evidence is presented from animal and human studies that under steady-state and pathophysiological conditions, all cell types present in the normal gland, including acinar cells, are capable of rapidly entering the cell cycle and are, therefore, possible targets for neoplastic transformation.

Pathobiology of salivary glands. IV. Histogenetic concepts and cycling cells in human parotid and submandibular glands cultured in floating collagen gels

Localization of cells with proliferative capacity in human major salivary glands lacks extensive study. Minced fragments of human parotid (n = 3) and submandibular (n = 3) glands embedded in a floating collagen gel matrix and cultured for up to 28 days allowed maintenance of the three-dimensional relationship of the various cell types in these glands. Immunocytochemistry and electron microscopy of a time-dependent series of cultured gland fragments showed gradual cytologic modification of acinar cells so that acini became duct-like but also established that even after 28 days of culture certain cellular features allowed continued identification of acinar cells. Serial section immunostaining for amylase, cytokeratins, and proliferating cell nuclear antigen (a specific marker for cycling cells) revealed that acinar, intercalated duct, and excretory duct (both basal and luminal) cells are all capable of entering the cell cycle. At day 5 of culture, the number of cycling cells increased 16-fold in the parotid gland and 9-fold in the submandibular gland over that in the respective in situ gland. In this in vitro system, which perhaps simulates regenerative processes in human salivary glands, none of the samples showed cycling cells localized only to segments of intercalated duct or the basal cells of excretory duct as suggested by current histogenetic concepts.