Quantitative immunocytochemical study of secretory protein expression in parotid glands of rats chronically treated with isoproterenol

Immunocytochemical Localization of Histatins in Human Salivary Glands

Histatins are a family of salivary proteins with bactericidal and fungicidal activities that contribute to the innate defense of the oral cavity. Histatins are present in the serous granules of the parotid and submandibular glands. The important role of histatins in saliva, and the limited information on their cellular and subcellular distribution, prompted us to further define the localization of histatins in the major salivary glands. Immunogold-silver staining of 1-μm sections of plastic-embedded tissue with anti-histatin antibody revealed histatin immunoreactivity in the serous acinar cells of the parotid and submandibular glands, the serous demilune cells of the submandibular and sublingual glands, and in occasional intercalated duct cells. No reactivity was seen in mucous cells or in striated or excretory duct cells. Electron microscopic observations of thin sections labeled with anti-histatin and gold-labeled secondary antibodies revealed immunoreactivity associated with the rough endoplasmic reticulum and Golgi complex and in secretory granules of serous acinar and demilune cells. The granules of parotid acinar cells exhibited relatively uniform labeling of their content, whereas the granules of serous cells in the submandibular and sublingual glands showed variable labeling of the dense and light regions of their content. A few intercalated duct cells adjacent to the acinar cells also exhibited labeled granules. These results suggest that the serous cells of the major glands are the main source of histatins in human saliva. They are also consistent with several previous studies demonstrating the variable distribution of different proteins within the granule content.

Functional Histology of Salivary Gland Pleomorphic Adenoma: An Appraisal

The complex microstructure of salivary gland pleomorphic adenoma is examined in relation to function. Events related to secretion of macromolecules and absorption, responses to the altered microenvironment and controversies concerning epithelial-mesenchymal transition versus modified myoepithelial differentiation are explored. Their effects on tumor cell phenotypes and arrangements are emphasized. Heterotopic differentiation and attempts at organogenesis are also considered. The approach allows interpreting microstructure independently of histogenetic perceptions, envisaging the tumor cells as a continuum, endorsing luminal structures as the principal components, and defining pleomorphic adenoma as a benign epithelial tumour characterized by variable epithelial-mesenchymal transition, secretion/differentiation and metaplasia.

Localization of hsp27 in the rat submandibular gland following the application of various surgical treatments

Salivary glands repair and regenerate following various types of injuries and surgical procedures. However, the tissue responses induced in the contralateral glands have yet to be elucidated in detail. Hsp27, a member of the heat-shock protein (Hsp) family, is strongly expressed in physiological environments, particularly during development. Hsp27 was previously shown to play a role in the regulation of acinar cell proliferation and differentiation in the rat submandibular gland. The present study performed the following surgical treatments on the right submandibular glands of adult rats: 1) duct ligation followed by unligation after one week; 2) partial sialoadenectomy; and 3) total sialoadenectomy. Immunohistochemistry for Hsp27 and Ki67 was performed in the experimental and normal contralateral glands, and localization was histologically and morphometrically analyzed. The results obtained revealed the localization of Hsp27 to the intercalated duct in the submandibular glands of non-treated rats. The expression of Hsp27 was strongly induced in both the uninjured contralateral control glands as well as treated glands of experimental rats regardless of the surgical procedure performed. The number of Hsp27-immunopositive cells increased rapidly following surgery, and subsequently returned to the same level as that in non-treated rats after 4 weeks. However, no marked changes were observed in the number of Ki67-immunopositive proliferating cells. Therefore, the change in the number of Hsp27-immunopositive cells may have contributed to compensatory hypertrophy. The results of the present study indicate that the expression of Hsp27 in the intercalated duct in the submandibular gland may play a role in the differentiation of acinar cells.

A perspective of comparative salivary and breast pathology. Part I: microstructural aspects, adaptations and cellular events

This is the first part of a review comparing the pathology of salivary and mammary glands. Here, less obvious similarities and differences in functional histology and their influences on pathology are examined with emphasis on myoepithelial cells, stromal components, analogues of mucosa-associated lymphoid tissue, steroid receptors, and intraparenchymal cells of monocytic lineage. Particular cell phenotypes (oncocytic, apocrine, neuroendocrine and clear) are critically evaluated and responses to atrophy, infarction and fine-needle aspiration biopsy procedures are highlighted together with aspects of metaplasia, regeneration, ageing and microcalcification. Areas of controversy or uncertainty which may benefit from further investigations are also discussed.

Immunohistochemical and Immunocytochemical Localization of Amylase in Rat Parotid Glands and von Ebner's Glands by Ion Etching-Immunoscanning Electron Microscopy

The distribution of amylase in rat parotid glands and von Ebner’s glands was examined using ion etching-immunoscanning electron microscopy, which enables both light and electron microscopic observations of identical semi-thin resin sections immunolabeled with anti-α-amylase and immunogold in association with silver enhancement. At the light microscopic level, most acinar secretory granules (SG) and striated duct secretions of parotid glands were strongly stained dark brown. In von Ebner’s glands, acinar SG and duct secretions were weakly to strongly stained light to dark brown. At the electron microscopic level, labeling was observed as bright gold-silver particles. The labeling intensity of acinar SG of parotid glands was higher than that of von Ebner’s glands. In parotid glands, weak labeling of SG in transitional cells between acini and intercalated ducts, very weak labeling of SG in intercalated ducts, and strong labeling of striated duct secretions were observed. In von Ebner’s glands, the secretions and some SG of interlobular ducts were strongly labeled compared to those of intralobular ducts and SG of acini. Less amylase was synthesized in von Ebner’s acini compared to parotid acini, whereas von Ebner’s ducts may secrete significantly more amylase to modify saliva than parotid ducts.

Morphological alterations in salivary glands of mice (Mus musculus) submitted to tannin enriched diets: comparison with sialotrophic effects of sympathetic agonists stimulation

In order to study the effects of tannins at histomorphological level, mice were either fed with three structurally different types of tannins (tannic acid, chestnut, and quebracho) or treated with isoproterenol, during 10 days. Acini of parotid and submandibular glands increased significantly, being the increase higher for parotid compared to submandibular glands, and higher in the quebracho compared with the other tannin groups. Sublingual acinar size also increased after tannin consumption, by opposition to isoproterenol-treated animals. The results present evidences that the effects produced by tannins are dependent on their structure.

Protein expression in salivary glands of rats with streptozotocin diabetes

Diabetes mellitus (DM) is a widespread disease with high morbidity and health care costs. An experimental animal model was employed, using morphological and biochemical methods, to investigate the effects of DM on the expression and compartmentation of salivary gland proteins. The distribution of proline-rich proteins (PRP), submandibular mucin (Muc10) and the regulatory (RI and RII) subunits of cyclic AMP-dependent protein kinase type I and type II was determined in the parotid and submandibular (SMG) glands of rats treated with streptozotocin. Quantitative immunocytochemistry of secretory granules in diabetic glands revealed decreases of 30% for PRP in both the parotid and SMG, and a 40% decrease in Muc10 in the SMG. Immunogold labelling showed that RII decreased in nuclei and the cytoplasm in diabetic acinar cells while labelling of secretory granules was similar in control and diabetic parotid. Electrophoresis and Western blotting of tissue extracts of two secretory proteins showed that the response to DM and insulin treatment was gland specific: PRP showed little change in the SMG, but decreased in the parotid in DM and was partially restored after insulin treatment. Photoaffinity labelling showed only RI present in the SMG and mainly RII in the parotid. The results of this and previous studies demonstrating highly specific changes in salivary protein expression indicate that the oral environment is significantly altered by DM, and that oral tissues and their function can be compromised. These findings may provide a basis for future studies to develop tests using saliva for diabetic status or progression in humans.

Sympathetic outflow activates the venom gland of the snakeBothrops jararacaby regulating the activation of transcription factors and the synthesis of venom gland proteins

The venom gland of viperid snakes has a central lumen where the venom produced by secretory cells is stored. When the venom is lost from the gland,the secretory cells are activated and new venom is produced. The production of new venom is triggered by the action of noradrenaline on bothα 1- and β-adrenoceptors in the venom gland. In this study, we show that venom removal leads to the activation of transcription factors NFκB and AP-1 in the venom gland. In dispersed secretory cells,noradrenaline activated both NFκB and AP-1. Activation of NFκB and AP-1 depended on phospholipase C and protein kinase A. Activation of NFκB also depended on protein kinase C. Isoprenaline activated both NFκB and AP-1, and phenylephrine activated NFκB and later AP-1. We also show that the protein composition of the venom gland changes during the venom production cycle. Striking changes occurred 4 and 7 days after venom removal in female and male snakes, respectively. Reserpine blocks this change,and the administration of α1- and β-adrenoceptor agonists to reserpine-treated snakes largely restores the protein composition of the venom gland. However, the protein composition of the venom from reserpinized snakes treated with α1- or β-adrenoceptor agonists appears normal, judging from SDS-PAGE electrophoresis. A sexual dimorphism in activating transcription factors and activating venom gland was observed. Our data suggest that the release of noradrenaline after biting is necessary to activate the venom gland by regulating the activation of transcription factors and consequently regulating the synthesis of proteins in the venom gland for venom production.

Differentiation of primary human submandibular gland cells cultured on basement membrane extract

There is no effective treatment for the loss of functional salivary tissue after irradiation for head and neck cancer or the autoimmune disease Sjögren's syndrome. One possible approach is the regeneration of salivary glands from stem cells. The present study aimed to investigate whether small pieces of human submandiblar gland tissue contain elements necessary for the reconstruction of salivary rudiments in vitro via acinar and ductal cell differentiation. Primary submandibular gland (primary total human salivary gland; PTHSG) cells were isolated from human tissue and cultured in vitro using a new method in which single cells form an expanding epithelial monolayer on plastic substrates. Differentiation, morphology, number, and organization of these cells were then followed on basement membrane extract (BME) using RNA quantitation (amylase, claudin-1 (CLN1), CLN3, kallikrein, vimentin), immunohistochemistry (amylase and occludin), viability assay, and videomicroscopy. On the surface of BME, PTHSG cells formed acinotubular structures within 24 h, did not proliferate, and stained for amylase. In cultures derived from half of the donors, the acinar markers amylase and CLN3 were upregulated. The PTHSG culture model suggests that human salivary gland may be capable of regeneration via reorganization and differentiation and that basement membrane components play a crucial role in the morphological and functional differentiation of salivary cells.

Morphological and functional differentiation of HSG cells: role of extracellular matrix and trpc 1

A human salivary intercalated duct cell line (HSG) is capable of morphological change to acinar-type cells, and of salivary amylase (AMY1) expression, by culturing on basement membrane extracts (BME). The aim of this study was to determine the critical conditions for functional and morphological differentiation of HSG cells and to establish if the processes are related. Cells were grown on BMEs that had different protein concentrations and growth factor content, and then examined with respect to morphology and AMY1 expression. To investigate the role of intracellular calcium in amylase expression, a pcDNA3.1-TRPC1alpha construct was used to overexpress htrp1alpha, which mediates the store-operated calcium entry in HSG cells. Expression of the AMY1, TRPC1alpha and beta genes was quantified by means of real time RT-PCR. Growth factor-reduced BME (12.8 mg/ml) induced multicellular acinar structures with lumen formation but without stimulation of either AMY1 or TRPC1. HSG cells cultured on higher concentration BME (17.5 or 16.4 mg/ml) formed reticular networks. AMY1 expression increased both on growth factor-reduced BME (17.5 mg/ml: 3.0-fold, P < 0.001) and on regular BME (16.4 mg/ml: 3.7-fold, P < 0.001) accompanied by a slight increase in expression of TRPC1alpha and TRPC1beta. Overexpression of htrp1alpha did not cause any significant changes in AMY expression, though it attenuated the BME (17.5 mg/ml)-induced AMY1 upregulation. Overall, the higher protein concentration BME favors amylase expression in HSG cells, whereas the lower concentration causes marked morphological changes.

Isoproterenol increases sorting of parotid gland cargo proteins to the basolateral pathway

Exocrine cells have an essential function of sorting secreted proteins into the correct secretory pathway. A clear understanding of sorting in salivary glands would contribute to the correct targeting of therapeutic transgenes. The present work investigated whether there is a change in the relative proportions of basic proline-rich protein (PRP) and acidic PRPs in secretory granules in response to chronic isoproterenol treatment, and whether this alters the sorting of endogenous cargo proteins. Immunoblot analysis of secretory granules from rat parotids found a large increase of basic PRP over acidic PRPs in response to chronic isoproterenol treatment. Pulse chase experiments demonstrated that isoproterenol also decreased regulated secretion of newly synthesized secretory proteins, including PRPs, amylase and parotid secretory protein. This decreased efficiency of the apical regulated pathway may be mediated by alkalization of the secretory granules since it was reversed by treatment with mild acid. We also investigated changes in secretion through the basolateral (endocrine) pathways. A significant increase in parotid secretory protein and salivary amylase was detected in sera of isoproterenol-treated animals, suggesting increased routing of the regulated secretory proteins to the basolateral pathway. These studies demonstrate that shifts of endogenous proteins can modulate regulated secretion and sorting of cargo proteins.

Matrigel-induced acinar differentiation is followed by apoptosis in HSG cells

It has been shown that a human salivary gland cell line (HSG) is capable of differentiation into gland-like structures, though little is known of how morphological features are formed or controlled. Here we investigated the changes in cell proliferation and apoptosis upon terminal differentiation of HSG cells in Matrigel, an extracellular matrix derivative. Changes in the expression of survivin, a prominent anti-apoptotic factor, and caspase-3, a key apoptotic factor were also measured. In order to better understand the involvement of key signal transduction pathways in this system we pharmacologically blocked the activity of tyrosine kinase, nuclear factor kappa B(NF kappa B), protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3K) and matrix metalloproteases (MMP). Results of these studies demonstrate that cytodifferentiation of HSG cells to an acinar phenotype is accompanied first by a decrease of cell proliferation and then by a massive programmed cell death, affected by multiple signal transduction pathways. Thus, Matrigel alone is insufficient for the full maturation and long term survival of the newly formed acini: the presence of other factors is necessary to complete the acinar differentiation of HSG cells.

Morphological features of the minor salivary glands

The minor salivary glands are important components of the oral cavity, present in most parts of the mouth, and their secretions directly bathe the tissues. Individual glands are usually in the submucosa between muscle fibres, and consist of groups of secretory endpieces made up of mucous acinar cells and serous or seromucous demilune cells. The ductal systems comprise intercalated ducts, intralobular ducts usually lacking basal striations, and excretory ducts opening directly through the mucosa Minor glands secrete highly glycosylated mucins, containing blood group determinants, and probably active in tissue lubrication and bacterial aggregation. They also secrete several antimicrobial proteins and immunoglobulins, and the lingual serous (von Ebner's) glands secrete digestive enzymes and proteins with possible taste perception functions. Minor gland morphology and function can conveniently be studied in the rat. There are substantial differences between major and minor salivary glands, as well as among the minor glands, in the nature and composition of their mucous and serous secretory products. The role of minor salivary glands in the function and defence of the oral cavity may be better understood as a result of new physiological and molecular methods applicable to samples of limited size and availability.

Secretory protein expression patterns during rat parotid gland development

The rat parotid gland produces a number of well-characterized secretory proteins. Relatively little is known, however, about the onset of their synthesis and cellular localization during gland development. Secretory protein expression was studied in parotid glands of fetal and postnatal rats using light and electron microscopic immunocytochemistry and Northern blotting. Amylase, parotid secretory protein (PSP), common salivary protein-1 (CSP-1), and SMGB were first detected by immunofluorescence in parotid glands of 18 day fetuses. By 5 days after birth, light and electron microscopic immunolabeling localized all of these proteins to the secretory granules of developing acinar cells. Labeling of acinar cells for DNAse I, however, was not observed until 18 days after birth. Between 9 and 25 days, CSP-1 and SMGB reactivity of acinar cells declined, but increased in intercalated duct cells. After 25 days, CSP-1 and SMGB were found only in intercalated ducts, and amylase, PSP, and DNAse I were restricted to acinar cells. Levels of CSP-1 and SMGB mRNA were relatively constant through 21 postnatal days, but declined significantly after that. Amylase and PSP mRNA increased rapidly and continuously from five days after birth to the adult stage. In contrast, DNAse I mRNA was not detectable until 18 days after birth. The immunocytochemical and molecular analyses define three basic patterns of protein expression in the rat parotid gland: proteins whose synthesis is initiated early in development and is maintained in the acinar cells, such as amylase and PSP; proteins that are initially synthesized by immature acinar cells but are restricted to intercalated ducts in the adult gland, such as CSP-1 and SMGB; and proteins that are synthesized only by mature acinar cells and first appear during the third postnatal week, such as DNAse I. The parotid gland exhibits four distinct developmental stages: prenatal, from initiation of the gland rudiment until birth; neonatal, from 1 day up to about 9 days postnatal; transitional, from 9 days to 25 days of age; and adult, from 25 days on. Although differences exist in timing and in the specific proteins expressed, these developmental stages are similar to those seen in the rat submandibular gland. Additionally, the results support the suggestion that intercalated ducts may differentiate from the neonatal acini.

Two regulated secretory pathways for newly synthesized parotid salivary proteins are distinguished by doses of secretagogues

Low doses of the muscarinic agonist pilocarpine (0.1-1 microM) and the beta-adrenergic agonist isoproterenol (0.5-4 nM) stimulate a minor regulated secretory pathway for salivary proteins in rat parotid lobules. Newly synthesized proteins (labeled biosynthetically) are selectively discharged, and they are secreted in the same relative proportions as observed in constitutive-like unstimulated secretion but different from the proportions of older proteins that are discharged by granule exocytosis in response to higher doses of secretagogue. The response to low doses of agonists is transient and involves output of no more than 1–2% of tissue-associated amylase. The same increase in output of pulse-labeled proteins is observed when agonist is added at various chase times (1.5-6 hours), implying that release occurs from a post-Golgi storage pool. Stimulation for 40 minutes significantly depletes the storage pool as a second stimulation elicits smaller output. Stimulation also partially depletes labeled proteins from subsequent constitutive-like secretion after the agonist is removed implying that the constitutive-like and low dose agonist mediated pathways draw on the same pool of secretory proteins. While these results indicate that acinar cells have a second regulated secretory pathway, this new pathway is unlikely to contribute uniquely to the protein composition of parotid secretion. Rather it may serve a different role in secretion at the apical cell surface.