Myoepithelial cells actively proliferate during atrophy of rat parotid gland

Salivary parameters alterations after early exposure to environmental methylmercury: A preclinical study in offspring rats

BACKGROUND

Methylmercury (MeHg) is still considered a global pollutant of major concern; thus, it becomes relevant to investigate and validate alternative diagnostic methods to track early-life human exposure. This study aimed to evaluate the salivary parameters and to characterize potential mechanisms of oxidative damage on the salivary glands (SG) of offspring rats after pre- and postnatal environmental-experimental MeHg exposure.

METHODS

Pregnant Wistar rats were daily exposed to 40 μg/kg MeHg during both gestational and lactation periods. Then, the saliva of offspring rats was analyzed in terms of flow rate, amylase activity, and total protein concentration. The SG of the offspring rats were dissected to perform the oxidative biochemistry analyses of antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (LPO), and nitrite levels.

RESULTS

Exposure to MeHg significantly decreased the ACAP, increased LPO and nitrite levels, decreased salivary flow rate, amylase activity, and total protein concentration.

CONCLUSION

Saliva analyses can predict damages induced by early-life MeHg exposure and may be used as an auxiliary diagnostic method.

Origin and Lineage Plasticity of Endogenous Lacrimal Gland Epithelial Stem/Progenitor Cells

The lacrimal gland (LG) is an exocrine organ responsible for the secretion of aqueous tear film. Regenerative and stem cell therapies that target LG repair are coming to the fore, although our understanding of LG cell lineage hierarchy is still incomplete. We utilize the analysis of label-retaining cells (LRCs) and genetic lineage tracing to define LG cell lineage hierarchy. Our study suggests that embryonic LG contains unique long-lived multipotent stem cells that give rise to all postnatal epithelial cell types. Following birth, lineages become established and the fate of progenitor cell descendants becomes restricted. However, some cell lineages retain plasticity after maturation and can trans-differentiate into other cell types upon injury. The demonstration that the LG contains progenitor cells with different levels of plasticity has profound implications for our understanding of LG gland function in homeostasis and disease and will be helpful for developing stem cell-based therapies in the future.

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Multipotent stem cells differentiate into distal Sox10+ and proximal Sox10− lineages

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Lineage-restricted progenitor cells sustain the long-term lacrimal gland maintenance

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Label-retaining cells are localized in the intercalated ducts and excretory ducts

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Some cell lineages in the adult lacrimal gland retain plasticity

Establishment of long-term serum-free culture for lacrimal gland stem cells aiming at lacrimal gland repair

BACKGROUND

Aqueous-deficient dry eye disease (ADDED) resulting from dysfunction of the lacrimal gland (LG) is currently incurable. Although LG stem/progenitor cell-based therapy is considered to be a promising strategy for ADDED patients, the lack of a reliable serum-free culture method to obtain enough lacrimal gland stem cells (LGSCs) and the basic standard of LGSC transplantation are obstacles for further research.

METHODS

Adult mouse LGSCs were cultured in Matrigel-based 3D culture under serum-free culture condition, which contained EGF, FGF10, Wnt3A, and Y-27632. LGSCs were continuously passaged over 40 times every 7 days, and the morphology and cell numbers were recorded. LGSCs were induced to differentiate to ductal cells by reducing Matrigel rigidity, while fetal bovine serum was used for the induction of acinar cells. RT-PCR or qRT-PCR analysis, RNA-sequence analysis, H&E staining, and immunofluorescence were used for characterization and examining the differentiation of LGSCs. LGSCs were allotransplanted into diseased LGs to examine the ability of repairing the damage. The condition of eye orbits was recorded using a camera, the tear production was measured using phenol red-impregnated cotton threads, and the engraftments of LGSCs were examined by immunohistochemistry.

RESULTS

We established an efficient 3D serum-free culture for adult mouse LGSCs, in which LGSCs could be continuously passaged for long-term expansion. LGSCs cultured from both the healthy and ADDED mouse LGs expressed stem/progenitor cell markers Krt14, Krt5, P63, and nestin, had the potential to differentiate into acinar or ductal-like cells in vitro and could engraft into diseased LGs and relieve symptoms of ADDED after orthotopic injection of LGSCs.

CONCLUSION

We successfully established an efficient serum-free culture for adult mouse LGSCs aiming at LG repair for the first time. Our approach provides an excellent theoretical and technical reference for future clinical research for ADDED stem cell therapy.

Distribution of aquaporin-5, transforming growth factor-β1 and laminin during regeneration of atrophic rat submandibular glands after duct ligation

The aim of this study was to determine the localization of aquaporin-5 (AQP5), transforming growth factor-β₁ (TGF-β₁) and laminin during regeneration of the rat submandibular gland. After duct ligation for 7 days, the regenerating glands were collected on days 0, 1, 3, 7, and 14 after ligation release to study the process of regeneration. Immunohistochemical staining revealed apical expression of AQP5 in many acinar cells, strong expression in intercalated ducts (ICDs) of the normal submandibular gland at Day 14, and strong expression in duct-like structures (DLSs) during regeneration from Day 0 to 7. However, a few AQP5-negative acinar cells were detected during regeneration. At Day 0, immunopositivity for TGF-β₁ was detected in connective tissue. At Days 3 and 7 during regeneration, TGF-β₁ immunostaining was observed in DLSs, which were surrounded by α-smooth muscle actin-positive thickened myoepithelial cells. Laminin staining was strong in the thickened basement membrane of DLSs at Day 3 during regeneration, but weak around acinar cells at Day 14. These findings suggest that TGF-β₁ is involved in the environment around DLSs, myoepithelial cells and laminin, that DLSs have the same functional properties as ICDs, and that AQP5-negative acinar cells may be mucous cells.

NOD and NOR mice exhibit comparable development of lacrimal gland secretory dysfunction but NOD mice have more severe autoimmune dacryoadenitis

The male Non-Obese Diabetic (NOD) mouse is an established model of autoimmune dacryoadenitis characteristic of Sjögren's Syndrome (SS), but development of diabetes may complicate studies. The Non-Obese Diabetes Resistant (NOR) mouse is a MHC-II matched diabetes-resistant alternative, but development of autoimmune dacryoadenitis is not well-characterized. We compare features of SS in male NOD and NOR mice at 12 and 20 weeks. Stimulated tear secretion was decreased in 12 week NOD relative to BALB/c mice (p < 0.05), while by 20 weeks both NOD and NOR showed decreased stimulated tear secretion relative to BALB/c mice (p < 0.001). Tear CTSS activity was elevated in NOD and NOR relative to BALB/c mice (p < 0.05) at 12 and 20 weeks. While NOD and NOR lacrimal glands (LG) showed increased LG lymphocytic infiltration at 12 and 20 weeks relative to BALB/c mouse LG (p < 0.05), the percentage in NOD was higher relative to NOR at each age (p < 0.05). Gene expression of CTSS, MHC II and IFN-γ in LG were significantly increased in NOD but not NOR relative to BALB/c at 12 and 20 weeks. Redistribution of the secretory effector, Rab3D in acinar cells was observed at both time points in NOD and NOR, but thinning of myoepithelial cells at 12 weeks in NOD and NOR mice was restored by 20 weeks in NOR mice. NOD and NOR mice share features of SS-like autoimmune dacryoadenitis, suggesting common disease etiology. Other findings suggest more pronounced lymphocytic infiltration in NOD mouse LG including increased pro-inflammatory factors that may be unique to this model.

Lacrimal Gland Repair after Short-term Obstruction of Excretory Duct in Rabbits

Aqueous tear-deficient dry eye is a multifactorial chronic disorder in which the lacrimal glands fail to produce enough tears to maintain a healthy ocular surface. The existence of lacrimal gland stem/progenitor cells was proposed in several species, yet their origin and characteristics are not very clear. Here, we investigated the presence of resident progenitor cells and their regenerative potential in a rabbit model with lacrimal gland main excretory duct ligation-induced injury. The ligation-injured lacrimal glands temporarily decreased in weight and had impaired tear secretion. Protein expression profiles and transcriptional profiles were obtained from injured tissue. Isolated lacrimal gland progenitor cells were tested and characterized by stem cell-related marker evaluation, single cell clonal assay and three-dimensional (3-D) culture. The results of our study indicate that lacrimal glands are capable of tissue repair after duct ligation-induced injury, likely involving resident stem/progenitor cells and epithelial-mesenchymal transitions. Lacrimal gland progenitor cells isolated from ligated tissue can differentiate in 3-D culture. The results provide further insights into lacrimal gland stem/progenitor cell physiology and their potential for treating severe cases of tear deficiency.

Does laser phototherapy influence the proliferation of myoepithelial cells in the salivary gland of hypothyroid rats?

Thyroid hormones influence both development and growth of organs and tissues and guarantee metabolic demands that interfere with the quality of digestive secretions, including those of the salivary glands. Laser phototherapy - LPT can modulate various biological phenomena and its diverse effects permit the action on different cell types. The aim of this study was to evaluate the influence of laser phototherapy on myoepithelial cells of salivary glands of hypothyroid rats. Forty-two albino Wistar rats were divided into two main groups: euthyroid (EU) and hypothyroid (HYPO). Hypothyroidism was induced using propylthiouracil (PTU) for 4weeks. Each group was divided into subgroups: control (without laser) and laser groups (Red/infrared - IR). LPT was used on the submandibular gland and was carried out using a diode laser (λ660 or λ780nm, 40mW, spot size 0.04cm², irradiation area 1cm², 300s, 6J/cm² per gland, 12J/cm² per session) and started two weeks after PTU treatment. LPT was repeated every other day for two weeks. After animal death, the glands were removed, dissected and processed for immunohistochemical analysis. It was observed an increase in the number of myoepithelial cells of hypothyroid control rats in comparison to euthyroid controls (p=0.001). Visible LPT (λ660nm) caused significant higher proliferation of myoepithelial cells in EU rats when compared to IR LPT (λ 780nm)(p≤0.001).It is concluded that, despite the LPT protocol used did not influence myoepithelial proliferation on hypothyroid rats it significantly increased the proliferation on euthyroid animals.

Regenerative capacity of allogenic gingival margin- derived stem cells with fibrin glue on albino rats' partially dissected submandibular salivary glands

OBJECTIVE

To evaluate the possible regenerative effect of allogenic gingival margin-derived stem cells (GMSCs) with or without autologous fibrin glue on partially dissected submandibular salivary glands of albino rats.

METHODS

Forty rats were randomly divided into four equal groups. Group I, where no operation was performed, was considered the negative control. Group II rats were considered the positive control and were subjected to a rectangular cut on the outer surface of the center right of the submandibular salivary gland and received no other treatment. Groups III and IV rats were handled as those in group II, but the cut areas of group III were filled with fibrin glue and the cut borders of group IV were injected with 1×10⁵cell/ml GMSCs and then glued with fibrin glue. Five animals from each group were euthanized at the end of the first postoperative week, while the remaining animals were euthanized at the end of the second postoperative week, i.e., end of the experiment.

RESULTS

Regeneration of ductal, acinar, and myoepithelial cells was better in group IV. A two-way ANOVA for proliferating cell nuclear antigen and α-smooth muscle actin revealed an overall significant difference between the different groups (P<0.05). In addition, an LSD post hoc test for multiple comparisons revealed a significant difference between each two groups. An independent sample t-test revealed significant differences between time periods for groups II, III, and IV, but there were no significant differences between the time periods for group I.

CONCLUSION

Injecting GMSCs at the cut borders and gluing the cut area with autologous fibrin glue ameliorates the regeneration of partially dissected submandibular salivary gland better than using fibrin glue alone.

Lacrimal Gland Repair Using Progenitor Cells

In humans, the lacrimal gland (LG) is the primary contributor to the aqueous layer of the tear film. Production of tears in insufficient quantity or of inadequate quality may lead to aqueous‐deficiency dry eye (ADDE). Currently there is no cure for ADDE. The development of strategies to reliably isolate LG stem/progenitor cells from the LG tissue brings great promise for the design of cell replacement therapies for patients with ADDE. We analyzed the therapeutic potential of epithelial progenitor cells (EPCPs) isolated from adult wild‐type mouse LGs by transplanting them into the LGs of TSP‐1^−/− mice, which represent a novel mouse model for ADDE. TSP‐1^−/− mice are normal at birth but progressively develop a chronic form of ocular surface disease, characterized by deterioration, inflammation, and secretory dysfunction of the lacrimal gland. Our study shows that, among c‐kit‐positive epithelial cell adhesion molecule (EpCAM⁺) populations sorted from mouse LGs, the c‐kit⁺dim/EpCAM⁺/Sca1⁻/CD34⁻/CD45⁻ cells have the hallmarks of an epithelial cell progenitor population. Isolated EPCPs express pluripotency factors and markers of the epithelial cell lineage Runx1 and EpCAM, and they form acini and ducts when grown in reaggregated three‐dimensional cultures. Moreover, when transplanted into injured or “diseased” LGs, they engraft into acinar and ductal compartments. EPCP‐injected TSP‐1^−/− LGs showed reduction of cell infiltration, differentiation of the donor EPCPs within secretory acini, and substantial improvement in LG structural integrity and function. This study provides the first evidence for the effective use of adult EPCP cell transplantation to rescue LG dysfunction in a model system. Stem Cells Translational Medicine2017;6:88–98

Effects of Benzodiazepines on Acinar and Myoepithelial Cells

Background: Benzodiazepines (BZDs), the most commonly prescribed psychotropic drugs with anxiolytic action, may cause hyposalivation. It has been previously shown that BZDs can cause hypertrophy and decrease the acini cell number. In this study, we investigated the effects of BZDs and pilocarpine on rat parotid glands, specifically on acinar, ductal, and myoepithelial cells.

Methods: Ninety male Wistar rats were divided into nine groups. Control groups received a saline solution for 30 days (C30) and 60 days (C60), and pilocarpine (PILO) for 60 days. Experimental groups received lorazepam (L30) and midazolam (M30) for 30 days. Another group (LS60 or MS60) received lorazepam or midazolam for 30 days, respectively, and saline for additional 30 days. Finally, other groups (LP60 or MP60) received either lorazepam or midazolam for 30 days, respectively, and pilocarpine for additional 30 days. The expression of calponin in myoepithelial cells and the proliferating cell nuclear antigen (PCNA) in acinar and ductal cells were evaluated.

Results: Animals treated with lorazepam showed an increase in the number of positive staining cells for calponin as compared to control animals (p < 0.05). Midazolam administered with pilocarpine (MP60) induced an increase in the proliferation of acinar and ductal cells and a decrease in the positive staining cells for calponin as compared to midazolam administered with saline (MS60).

Conclusion: We found that myoepithelial cells might be more sensitive to the effects of BZD than acinar and ductal cells in rat parotid glands.

Myoepithelial Cells: Their Origin and Function in Lacrimal Gland Morphogenesis, Homeostasis, and Repair

Lacrimal gland (LG) is an exocrine tubuloacinar gland that secretes the aqueous layer of the tear film. LG epithelium is composed of ductal, acinar, and myoepithelial cells (MECs) bordering the basal lamina and separating the epithelial layer from the extracellular matrix. Mature MECs have contractile ability and morphologically resemble smooth muscle cells; however, they exhibit features typical for epithelial cells, such as the presence of specific cytokeratin filaments. Increasing evidence supports the assertion that myoepithelial cells (MECs) play key roles in the lacrimal gland development, homeostasis, and stabilizing the normal structure and polarity of LG secretory acini. MECs take part in the formation of extracellular matrix gland and participate in signal exchange between epithelium and stroma. MECs have a high level of plasticity and are able to differentiate into several cell lineages. Here, we provide a review on some of the MEC characteristics and their role in LG morphogenesis, maintenance, and repair.

Bioengineered Lacrimal Gland Organ Regeneration in Vivo

The lacrimal gland plays an important role in maintaining a homeostatic environment for healthy ocular surfaces via tear secretion. Dry eye disease, which is caused by lacrimal gland dysfunction, is one of the most prevalent eye disorders and causes ocular discomfort, significant visual disturbances, and a reduced quality of life. Current therapies for dry eye disease, including artificial tear eye drops, are transient and palliative. The lacrimal gland, which consists of acini, ducts, and myoepithelial cells, develops from its organ germ via reciprocal epithelial-mesenchymal interactions during embryogenesis. Lacrimal tissue stem cells have been identified for use in regenerative therapeutic approaches aimed at restoring lacrimal gland functions. Fully functional organ replacement, such as for tooth and hair follicles, has also been developed via a novel three-dimensional stem cell manipulation, designated the Organ Germ Method, as a next-generation regenerative medicine. Recently, we successfully developed fully functional bioengineered lacrimal gland replacements after transplanting a bioengineered organ germ using this method. This study represented a significant advance in potential lacrimal gland organ replacement as a novel regenerative therapy for dry eye disease. In this review, we will summarize recent progress in lacrimal regeneration research and the development of bioengineered lacrimal gland organ replacement therapy.

Immunolocalization of FGF-2, -7, -8, -10 and FGFR-1-4 during regeneration of the rat submandibular gland

Fibroblast growth factors (FGFs) and their receptors (FGFRs) play important roles in the development of the submandibular gland. Although regeneration of submandibular glands follows a similar process to their development, it is unknown how FGFs and FGFRs are distributed during regeneration of submandibular gland. The aim of this study was to determine the localization of FGFs and FGFRs during such regenerative processes. After 7 days' obstruction, the submandibular glands were collected at days 0, 1, 3, 7, 11 and 14 after duct release to study regeneration. The regenerative processes of the submandibular gland were investigated by immunohistochemistry for FGF-2, 7, 8, 10 and FGFR-1-4. Immunohistochemical staining revealed that FGF-2 was moderately expressed in the epithelial cells of duct-like structures (DLS) and newly formed acinar cells (NFAC) at days 0-7, and strongly in intercalated duct (ICD) at control gland and Day 7-14. FGF-7 was localized moderately in NFAC and DLS. FGF-8 was localized moderately in the epithelial cells of DLS during regeneration. Strong positive immunoreactions for FGF-10 were found in NFAC and the epithelial cells of DLS during regeneration, as well as the ICD and lateral surfaces of the maturing acinar cells (MAC). FGFR-1 was expressed moderately in the ICD, and weakly in the NFAC and MAC. Positive immunoreactions for FGFR-2 were not observed during regeneration. Additionally, FGFR-4 was detected strongly in the ICD and slightly in NFAC. These findings suggest that FGF-2, -7, -8 and -10 play important roles in NFAC, MAC, and DLS through FGFR-1 and -4 during regeneration of submandibular gland.

Transcription factors Runx1 to 3 are expressed in the lacrimal gland epithelium and are involved in regulation of gland morphogenesis and regeneration

PURPOSE

Lacrimal gland (LG) morphogenesis and repair are regulated by a complex interplay of intrinsic factors (e.g., transcription factors) and extrinsic signals (e.g., soluble growth/signaling factors). Many of these interconnections remain poorly characterized. Runt-related (Runx) factors belong to a small family of heterodimeric transcription factors known to regulate lineage-specific proliferation and differentiation of stem cells. The purpose of this study was to define the expression pattern and the role of Runx proteins in LG development and regeneration.

METHODS

Expression of epithelial-restricted transcription factors in murine LG was examined using immunostaining, qRT-PCR, and RT(2)Profiler PCR microarrays. The role of Runx transcription factors in LG morphogenesis was studied using siRNA and ex vivo LG cultures. Expression of Runx transcription factors during LG regeneration was assessed using in vivo model of LG regeneration.

RESULTS

We found that Runx factors are expressed in the epithelial compartment of the LG; in particular, Runx1 was restricted to the epithelium with highest level of expression in ductal and centroacinar cells. Downregulation of Runx1 to 3 expression using Runx-specific siRNAs abolished LG growth and branching and our data suggest that Runx1, 2, and 3 are partially redundant in LG development. In siRNA-treated LG, reduction of branching correlated with reduction of epithelial proliferation, as well as expression of cyclin D1 and the putative epithelial progenitor cell marker cytokeratin-5. Runx1, Runx3, and cytokeratin-5 expression increased significantly in regenerating LG and there was modest increase in Runx2 expression during LG differentiation.

CONCLUSIONS

Runx1 and 2 are new markers of the LG epithelial lineage and Runx factors are important for normal LG morphogenesis and regeneration.

Alteration of the actin cytoskeleton and localisation of the α6β1 and α3 integrins during regeneration of the rat submandibular gland

OBJECTIVES

Actin filaments, which are regulated by signal transduction via integrins, play important roles in the regulation of cell differentiation and polarity. The aim of this study was to assess alterations in the cytoskeleton and the localisation of integrins during regeneration of the rat submandibular gland.

DESIGN

After obstruction for 7 days, the regenerating glands were collected at days 0, 1, 3, 7, 14 after duct release for analysis of regeneration. Alterations in the actin filaments were examined using phalloidin, which specifically binds to filamentous actin (F-actin), and the distributions of the α6β1 and α3 integrins were examined immunohistochemically.

RESULTS

F-actin was strongly localised at the apical region in the intercalated ducts of normal and day-14 glands and in duct-like structures during the regenerative process. Thereafter, actin accumulated at the basement membrane in mature acinar cells. A temporo-spatial correlation was found between the apical distribution of F-actin and α3 integrin staining. Diffuse α6β1 integrin staining, which occurred at a distal site in α3 integrin-positive cells, was observed in immature cells at day 3. At day 14, α6β1 integrin was detected at the basement membrane in terminal differentiated acinar cells.

CONCLUSION

These findings suggest that duct-like structures have the same properties as intercalated ducts, that alterations in α3 to α6β1 integrins regulate the generation of acinar cells from duct-like structures, and that the α6β1 integrin is involved in the differentiation of acinar cells during regeneration of the rat submandibular gland.

The effects of antidepressants and pilocarpine on rat parotid glands: an immunohistochemical study

OBJECTIVES

To evaluate the effects of antidepressants and pilocarpine on the quantity of myoepithelial cells and on the proliferation index of the epithelial cells of rat parotid glands.

INTRODUCTION

Hyposalivation, xerostomia, and alterations in saliva composition are important clinical side effects related to the use of antidepressants.

METHODS

Ninety male Wistar rats were allocated to nine groups. The control groups received saline for 30 (group C30) or 60 days (group C60) or pilocarpine for 60 days (group Pilo). The experimental groups were administered fluoxetine (group F30) or venlafaxine for 30 days (group V30); fluoxetine (group FS60) or venlafaxine (group VS60) with saline for 60 days; or fluoxetine (group FP60) or venlafaxine (group VP60) with pilocarpine for 60 days. Parotid gland specimens were processed, and the immunohistochemical expression of calponin and proliferating cell nuclear anti-antigen on the myoepithelial and parenchymal cells, respectively, was evaluated. Analysis of variance (ANOVA), Tukey HSD and Games-Howell tests were applied to detect differences among groups (p<0.05).

RESULTS

Compared with the controls, chronic exposure to antidepressants was associated with an increase in the number of positively stained cells for calponin. In addition, venlafaxine administration for 30 days was associated with an increase in the number of positively stained cells for proliferating cell nuclear anti-antigen. Fluoxetine and pilocarpine (group FP60) induced a significant decrease in the number of positively stained cells for calponin compared with all other groups.

CONCLUSIONS

The number of positively stained cells for calponin increased after chronic administration of antidepressants. The proliferation index of the epithelial cells of rat parotid glands was not altered by the use of antidepressants for 60 days.

Pathogenesis of sialadenosis: possible role of functionally deficient myoepithelial cells

OBJECTIVES

The pathogenesis of acinar enlargement in sialadenosis is obscure. As myoepithelial cells had been reported to show degenerative changes, we decided to investigate the possible role of functionally deficient myoepithelial cells in the development of sialadenosis.

STUDY DESIGN

This study was a morphometric analysis of glands immunohistochemically stained for CK14, alpha-actin, and Ki67 in 10 cases of sialadenosis and 11 normal parotids.

RESULTS

In sialadenosis, acini were much larger; there was a minor decrease in the density of the distribution of myoepithelial cells stained for CK14 and a major decrease in the density of the distribution and thickness of the myofilament component of myoepithelial cells stained for alpha-actin; and the proliferation of acinar and myoepithelial cells was reduced.

CONCLUSIONS

Our results demonstrate a major loss and thinning of the myofilament component of the myoepithelial cells and thereby a loss of mechanical support for the acini in sialadenosis. This possibly allows acinar cells to expand as secretory granules accumulate intracellularly to produce the great acinar enlargement. This functional myoepithelial insufficiency is possibly a consequence of an autonomic neuropathy secondary to severe metabolic or hormonal disorders.

Mechanisms involved in injury and repair of the murine lacrimal gland: role of programmed cell death and mesenchymal stem cells

The non-keratinized epithelia of the ocular surface are constantly challenged by environmental insults, such as smoke, dust, and airborne pathogens. Tears are the sole physical protective barrier for the ocular surface. Production of tears in inadequate quantity or of inadequate quality results in constant irritation of the ocular surface, leading to dry eye disease, also referred to as keratoconjunctivitis sicca (KCS). Inflammation of the lacrimal gland, such as occurs in Sjogren syndrome, sarcoidosis, chronic graft-versus-host disease, and other pathological conditions, results in inadequate secretion of the aqueous layer of the tear film and is a leading cause of dry eye disease. The hallmarks of lacrimal gland inflammation are the presence of immune cell infiltrates, loss of acinar epithelial cells (the secreting cells), and increased production of proinflammatory cytokines. To date, the mechanisms leading to acinar cell loss and the associated decline in lacrimal gland secretion are still poorly understood. It is also not understood why the remaining lacrimal gland cells are unable to proliferate in order to regenerate a functioning lacrimal gland. This article reviews recent advances in exocrine tissue injury and repair, with emphasis on the roles of programmed cell death and stem/progenitor cells.

Distribution of tenascin-C, fibronectin and collagen types III and IV during regeneration of rat submandibular gland

The aim of this study was to determine the localization of tenascin-C, fibronectin and collagen types III and IV during regeneration of the rat submandibular gland. After 7 days' obstruction, the regenerating glands were collected at days 0, 1, 3, 5, 7, 11 and 14 after duct release to study regeneration. Immunohistochemical staining revealed that tenascin-C was strongly expressed in the epithelial cells of duct-acinar structures at days 0-3, and down-regulated in its expression from day 5 to 11, though weak expression was detected in the intercalated duct and acinar cells of the normal gland. Strong labeling of fibronectin was detected around duct-acinar structures during days 0-3 of regeneration. Type IV collagen was expressed strongly in the thickened basement membrane of acinar cells and duct-acinar structures during days 0-3, but weakly around large ducts, though type III collagen was expressed at consistent levels. These findings suggest that tenascin-C and fibronectin affect only the duct-acinar structures, and type IV but not type III collagen is involved in the regeneration of acinar cells.

Early markers of regeneration following ductal ligation in rat submandibular gland

Rat submandibular glands can recover their function and secretory protein content following ductal ligation-induced atrophy. Morphological studies have established that following ligation, deligation of the gland allows the regeneration of new salivary gland tissue. However, little is known about changes happening during early regeneration following intra-oral duct ligation, which does not damage the parasympathetic nerves. Glands that had been 2 weeks ligated or 2 weeks ligated + 3 days deligated were compared. Tissue was prepared for histological, immunohistochemical (SMG-B and Ki-67) and immunocytochemical analyses (smooth muscle actin, aquaporin 5). Haematoxylin and eosin staining of deligated glands showed that some acini regained their cytoplasmic volume; moreover, the loss of Alcian blue/periodic acid-Schiff's staining from the lumen of ducts suggested successful deligation. The deligated gland was characterized by atypical acinar-ductal branched structures, which were less frequent in the ligated gland and rarely seen in normal unoperated tissue. Myoepithelial cells were also investigated since changes in their morphology reflected changes in the acini morphology not readily detected by conventional staining. Actin staining revealed the presence of some shrunken acini in the atrophic tissue, whereas they had regained their normal morphology in the deligated gland suggesting that the acini were recovering. Some acini during deligation regained aquaporin 5 expression, which had decreased during atrophy. SMG-B protein, located in the pro-acinar cell during gland development and usually found in the intercalated duct cells in the adult, was detected in the newly formed acini of the deligated gland. This study suggests that morphological markers of regeneration appear as early as 3 days following ligation removal.

A single injection of interleukin-1 induces reversible aqueous-tear deficiency, lacrimal gland inflammation, and acinar and ductal cell proliferation

Emerging studies from our laboratory demonstrate that interleukin-1 (IL-1) family members play a major role in impairing lacrimal gland functions. Here we have extended our investigations to observe the effects of IL-1 on aqueous tear production, lacrimal gland secretion, lacrimal gland histology, and acinar and ductal cell proliferation. We demonstrate that a single injection of IL-1 into the lacrimal glands inhibited neurally- as well as agonist-induced protein secretion resulting in decreased tear output. Meanwhile, IL-1 injection induced a severe, but reversible (7-13 days), inflammatory response that led to destruction of lacrimal gland acinar epithelial cells. Finally, we demonstrate that as the inflammatory response subsided and lacrimal gland secretion and tear production returned to normal levels, there was increased proliferation of acinar and ductal epithelial cells. Our work uncovers novel effects of IL-1 on lacrimal gland functions and the potential regenerative capacity of the mouse lacrimal gland.

Biological behavior of myoepithelial cells in the regeneration of rat atrophied sublingual glands following release from duct ligation

The present study aimed to clarify how myoepithelial cells behave during regeneration of an atrophied sublingual gland by investigating cell proliferation and ultrastructure. Atrophy of rat sublingual glands was induced by unilateral ligation of the excretory duct near the hilum with metal clips, which were then removed after one week of ligation for regeneration. The sublingual glands 0-14 days after unligation were examined with single immunohistochemistry for actin as a marker of myoepithelial cells, double immunohistochemistry for actin and proliferating cell nuclear antigen (PCNA) as a marker of proliferating cells, and transmission electron microscopy (TEM). The single immunohistochemistry and TEM showed that myoepithelial cells surrounded residual ducts in the atrophied glands and immature and mature acini in the regenerating glands. Although PCNA-positive myoepithelial cells were identified during regeneration, PCNA labeling indices of myoepithelial cells were low at all time points except at day 7. Ultrastructurally, myoepithelial cells showing bizarre shaped structures in the atrophy changed with maturation of differentiating acinar cells and appeared normal in the regenerated glands. There was no differentiation of the remaining duct cells to myoepithelial cells. These observations suggest that proliferation of myoepithelial cells and differentiation to myoepithelial cells do not commonly participate in the regeneration of atrophied sublingual glands and that the bizarre shaped myoepithelial cells in the atrophied sublingual glands recover the original shapes with acinar cell regeneration.

Transglutaminase 2 expression in the salivary myoepithelial cells of mouse embryo

Earlier a strong transient expression of transglutaminase 2 (TGase 2) localized at the anchoring sites of muscle bundles in human embryo was observed. In this study, we report a similar transient expression of the TGase 2 in the salivary myoepithelial cells of mouse embryo by immunohistochemistry, RNA in situ hybridisation, and RT-PCR. From 35 submandibular glands of mouse embryos and postnatal mice, a consistent expression of TGase 2 in the myoepithelial cells via a stage-specific manner was identified by mono-clonal antibody to TGase 2 immunostaining. A similar expression pattern of TGase 2 in the myoepithelial cells was also observed by RNA in situ hybridisation analysis. The expression of TGase 2 in the salivary epithelium and mesenchyme during the prenatal 14.5-15.5 days was found minimally diffusely spread and became intensely focalised in the myoepithelial cells of salivary acini and ducts during the prenatal 16.5-18.5 days but thereafter gradually decreased until postnatal 7 days and remained weak in postnatal 3 weeks. Such transient rise and fall expressions of TGase 2 were also found with the sequential amount of RT-PCR products during the same period. The alpha-smooth muscle actin (alpha-SMA) as a positive control in the myoepithelial cells of mouse submandibular glands was consistently expressed during the prenatal and postnatal period. These results of transient expression of TGase 2 in the myoepithelial cells coincided with the formation of the dendritic basket structure in the periphery of acini and ducts, suggest a possible catalytic role of transglutaminase in a newly formed cellular matrixes during the cytodifferentiating stage of mouse prenatal and neonatal submandibular glands.

Regeneration in chronic sialadenitis: an analysis of proliferation and apoptosis based on double immunohistochemical labelling

The understanding of regeneration in salivary glands as a finely tuned balance of cellular proliferation, differentiation and apoptosis has been limited by the difficulty of identifying proliferating cells. This has been overcome in the present investigation by double immunohistochemical labelling for the proliferation-associated antigen Ki67 and for different cell-type-specific antigens applied to 8 specimens of normal parotids and 16 specimens of chronic parotid sialadenitis with particular reference to acini and intercalated ducts. In comparison with low baseline rates of proliferation in normal parotids, proliferative indices were significantly increased in chronic sialadenitis in mature acinar cells, intercalated ductal cells and myoepithelial cells without evidence of proliferation by an additional population of cells. In accordance with findings in glands of experimental animals, the present data do not support the previously postulated concept of regeneration of acini and intercalated ducts by a hypothetical population of uncommitted ductal stem cells. The demonstration of a profound capacity for intrinsic glandular regeneration from differentiated cells represents a biological basis for the good results obtained from conservative therapy of chronic sialadenitis and offers hope for novel therapies designed to reconstitute impaired salivary flow.

Regenerative Medicine for Diseases of the Head and Neck: Principles ofIn vivoRegeneration

The application of endogenous regeneration in regenerative medicine is based on the concept of inducing regeneration of damaged or lost tissues from residual tissues in situ. Therefore, endogenous regeneration is also termed in vivo regeneration as opposed to mechanisms of ex vivo regeneration which are applied, for example, in the field of tissue engineering. The basic science foundation for mechanisms of endogenous regeneration is provided by the field of regenerative biology. The ambitious vision for the application of endogenous regeneration in regenerative medicine is stimulated by investigations in the model organisms of regenerative biology, most notably hydra, planarians and urodeles. These model organisms demonstrate remarkable regenerative capabilities, which appear to be conserved over large phylogenetical stretches with convincing evidence for a homologue origin of an endogenous regenerative capability. Although the elucidation of the molecular and cellular mechanisms of these endogenous regenerative phenomena is still in its beginning, there are indications that these processes have potential to become useful for human benefit. Such indications also exist for particular applications in diseases of the head and neck region. As such epimorphic regeneration without blastema formation may be relevant to regeneration of sensorineural epithelia of the inner ear or the olphactory epithelium. Complex tissue lesions of the head and neck as they occur after trauma or tumor resections may be approached on the basis of relevant mechanisms in epimorphic regeneration with blastema formation.

Immunocytochemistry of myoepithelial cells in the salivary glands

MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.

Hyperplasia of myoepithelial cells expressing calponin during atrophy of the rat parotid gland induced by duct ligation

The number and location of myoepithelial cells in the rat parotid gland submitted to surgical ligation of its main excretory duct were studied through immunohistochemical labelling for calponin. These cells were labelled by the streptavidin-biotin method using anti-calponin primary antibody, and their number was determined during each step of glandular atrophy, i.e., at time zero (control) and 1, 7, 15, 21, 30 and 60 days after ligation. Morphological analysis showed a gradual decrease and fibrosis of the glandular lobules accompanied by disappearance of the acini and the occurrence of duct-like structures. The expression of calponin was observed in all specimens analysed, being restricted to myoepithelial cells. Labelling revealed the distribution of myoepithelial cells around the acini and intercalated ducts in the control group and around duct-like structures later during the course of atrophy. Quantitative analysis demonstrated significant increase in the number of myoepithelial cells up to day 7 post-ligation, followed by gradual increases which, however, were not statistically significant. These results suggest that myoepithelial cells proliferate intensely up to day 7 post-ligation, an event that coincides with a higher rate of disappearance of acinar cells. After this period, the elevatednumber of cells observed at the end of the previous period is maintained.

Apoptosis and proliferation of myoepithelial cells in atrophic rat submandibular glands

This study was designed to determine whether apoptosis and proliferation of myoepithelial cells occur in atrophic rat submandibular glands. The excretory duct of the right submandibular gland was doubly ligated with metal clips. The atrophic right submandibular glands removed after 1-28 days of duct ligation were investigated using immunohistochemical double staining for actin as a marker for myoepithelial cells and proliferating cell nuclear antigen (PCNA) as a marker for proliferating cells, double staining for actin immunohistochemistry, nick end-labeling (TUNEL) as a marker for apoptotic cells, and transmission electron microscopy (TEM). A few PCNA- and no TUNEL-positive myoepithelial cells were found in the control submandibular glands taken from animals with no operation. In the experimental glands, PCNA-positive myoepithelial cells were common 2 and 3 days after duct ligation and then decreased in number. TUNEL-positive myoepithelial cells appeared at 2 days and were observed most frequently at 5 days. Apoptotic myoepithelial cells were also identified by TEM. These observations suggest that both apoptosis and proliferation of myoepithelial cells occur, especially in the early phase of atrophy, in the rat submandibular gland.

Changing myoepithelial cell distribution during regeneration of rat parotid glands

The distribution of the myoepithelial cells during regeneration of the rat parotid gland after atrophy induced by one week of parotid duct ligation was investigated by immunohistochemistry for actin and transmission electron microscopy (TEM). Immunohistochemically, residual ducts were surrounded by actin-positive cells when clips were removed from the duct. Three days later, most of the newly formed acini originating from the residual ducts were also embraced by actin-positive cells. After 10 days, actin-positivity tended to be seen as dots around acini that decreased in number day by day. On day 21 actin-positive cells mainly surrounded intercalated ducts with only a few positive reactions identified at the acinar periphery. Electron microscopically, residual ducts and newly formed acini were peripherally embraced by myoepithelial cells before day 5. After day 7, shift of myoepithelial cells from the periphery of acini to the duct-acinar junctional region was identified. Then few myoepithelial cells were identified at the periphery of acini. These observations indicate that myoepithelial cells migrate from the acinar periphery to the duct-acinar junctional region during rat parotid regeneration, and that such behaviour is closely related to that seen during rat parotid development.

Cell population changes during atrophy and regeneration of rat parotid gland

Limited data exist regarding the changes in number and location of myoepithelial cells during salivary gland atrophy and regeneration. Through the use of double immunohistochemical labeling for muscle-specific actin and amylase coupled with morphometric analysis, this study investigated the changes in distribution and proportion of cell types during salivary gland atrophy/regeneration phases in a model previously used to study proliferation in rat parotid gland. The double immunohistochemical labeling clearly showed the changes in proportion of cell types in the atrophying and regenerating glands. The morphometric analysis showed that the relative myoepithelial area increased (as did the intercalated duct and striated duct areas) as the gland atrophied. Myoepithelial cells occupied 19.0% of the total epithelial area by day 7 of atrophy, up from 2.7% in the resting gland. Regeneration of acinar cells was obvious 1 day after duct release. The myoepithelial cell area decreased to 4.3% of the total epithelial area by day 14 of regeneration; this value was higher than the percentage of area in the resting gland (p = 0.02). The relative areas of acinar, striated duct, and intercalated duct cells returned to resting levels after 14 days of regeneration. The morphometric and histologic results of this study show that the parotid gland is capable of regenerating to essentially normal anatomic condition after 7 days of gland atrophy and then 14 days of regeneration. Each type of cell, however, responded to the atrophy and regeneration differently. Atrophy of salivary glands from radiation therapy. Sjögren's syndrome, or sialadenitis is an important clinical problem. Study of the salivary gland response to atrophy and regeneration may provide a framework for designing strategies for the radioprotection of salivary glands or methods by which to treat or reverse the effects of gland atrophy.