Aquaporins in Salivary Glands: From Basic Research to Clinical Applications

Morphology, glicohistochemistry and immunolocalization of Aquaporin 5 in the mandibular gland of the giant anteater (Myrmecophaga tridactyla)

BACKGROUND

The giant anteater (Myrmecophaga tridactyla) is a toothless mammal that feeds mainly on termites and ants. Therefore, like other toothless mammals, this species has morphological and physiological adaptations of the salivary glands related to eating habits. Saliva is essential for the health of the oral cavity, chewing and lubrication of the mouth and it is constituted by an aqueous fluid containing electrolytes, enzymes, and glycoproteins which play an important role in modulating the oral microbiota. The present study investigated the morphology, glycan pattern and the aquaporin 5 (AQP5) expression in the giant anteater mandibular gland.

METHODS

The morphology of the mandibular gland was studied by gross and microscopic anatomy; the glycopattern was characterized using PAS, Alcian blue, and lectin histochemistry; AQP5 was localized immunohistochemically.

RESULTS

The mandibular gland had big dimensions, irregular shape and showed the classic morphology of the salivary glands. The gland parenchyma consisted of secretory acini, containing acinar cells and demilune cells, and intercalated, striated and interlobular ducts. Secretory acini secrete both neutral and acidic glycans (PAS and AB 2.5 positivity) and expressed a glycopattern characterized by O-linked glycans terminating with Galβl,3GalNAc (PNA affinity) and GalNAc (DBA and SBA positivity) and few N-linked glycans (Con A staining) containing also terminal lactosamine (RCA120 reactivity). Demilune cells contained Con A and RCA120 binding sites as well as α2,6-sialoglycans (SNA binders). The epithelium lining of the striated and interlobular ducts displayed α1,6/ α1,4-fucosylated and α2,3sialoglycoproteins (AAL and MAL II affinity) in addition to the aforementioned glycans. The lumen of the secretory acini contained high-mannosylated and lactosamine-terminating glycans, fucosylated and α2,6-sialoglycans. The presence of α2,6-sialoglycans indicates the role of demilune cells in the production and acidification of saliva. Along the ductal system the saliva enriched with O-linked glycans terminating with Galβl,3GalNAc, GalNAc, and α2,3-linked sialic. As for AQP5, it was detected in the acinar and demilune cells but not in the ductal epithelium.

CONCLUSIONS

These results demonstrate that the saliva secreted by mandibular gland of the giant anteater contains a complex pattern of glycoproteins whose glycosylation also occurs in the ductal system. Lastly, AQP5 of the secretory acini is involved in the production and regulation of saliva viscosity in this toothless and myrmecophagous mammal. Overall, these findings may represent a benchmark for future studies of mandibular glands of other toothless animals.

Autoantibody against aquaporin-5 may be a new diagnostic biomarker for primary Sjögren's syndrome

The study aims to assess the diagnostic and clinical significance of autoantibodies against aquaporin-1 (anti-AQP1) and aquaporin-5 (anti-AQP5) in primary Sjögren's syndrome (pSS). A total of 163 participants were categorized into three groups: pSS group, other connective tissue diseases (CTD) group, and healthy control (HC) group. The levels of anti-AQP1 and anti-AQP5 autoantibodies in serum were determined using enzyme-linked immunosorbent assay (ELISA), and clinical data from patients were collected for statistical analysis. Our results showed that the level of anti-AQP1 in the pSS group was higher than in the HC group (P < 0.05), and no significant difference was observed between the pSS group and the CTD group (P > 0.05). ROC showed that the anti-AQP1 had no diagnostic value for pSS (P > 0.05). The anti-AQP5 level of 39 healthy adults was all below the cut-off value (14.10 ng/ml) (P < 0.05). The level of anti-AQP5 in the pSS group was higher than the CTD group (P < 0.05), the AUC was 0.86 (95% CI 0.80-0.93), with a sensitivity of 0.95 (95% CI 0.87-0.99) and a specificity of 0.70 (95% CI 0.58-0.84). No correlation was found between anti-AQP5 levels and the EULAR primary Sjögren's syndrome disease activity index score, anti-SSA, anti-SSB, antinuclear antibodies, rheumatoid factor, anti-ds-DNA, salivary gland flow rate, complement 3, and lymphocyte count in pSS samples (P > 0.05), respectively. Therefore, the elevated anti-AQP5 may emerge as a novel diagnostic biomarker for pSS patients due to high sensitivity and specificity.

ARL13B controls male reproductive tract physiology through primary and Motile Cilia

ARL13B is a small regulatory GTPase that controls ciliary membrane composition in both motile cilia and non-motile primary cilia. In this study, we investigated the role of ARL13B in the efferent ductules, tubules of the male reproductive tract essential to male fertility in which primary and motile cilia co-exist. We used a genetically engineered mouse model to delete Arl13b in efferent ductule epithelial cells, resulting in compromised primary and motile cilia architecture and functions. This deletion led to disturbances in reabsorptive/secretory processes and triggered an inflammatory response. The observed male reproductive phenotype showed significant variability linked to partial infertility, highlighting the importance of ARL13B in maintaining a proper physiological balance in these small ducts. These results emphasize the dual role of both motile and primary cilia functions in regulating efferent duct homeostasis, offering deeper insights into how cilia related diseases affect the male reproductive system.

Melatonin improves salivary gland damage and hypofunction in pSS by inhibiting IL-6/STAT3 signaling through its receptor-dependent manner

OBJECTIVE

Primary Sjogren's syndrome (pSS) is an autoimmune disease of the exocrine glands with no specific or efficient treatments. Melatonin, a natural hormone, is revealed to show multiple biological functions, both receptor-dependent and independent effects, including anti-apoptotic, antioxidant, and anti-inflammatory activities. However, the potential mechanism by which melatonin protects salivary glands (SGs) of pSS from damage needs to be clarified. The purpose of current study was to explore the role and receptor-related mechanisms of melatonin in pSS-induced glandular damage.

METHODS AND RESULTS

NOD/Ltj mice were used to spontaneously mimic pSS-induced glandular hypofunction in vivo and primary human salivary gland epithelial (HSGE) cells were stimulated by interferon-γ (IFN-γ) to mimic pSS-induced inflammation in SGs cells in vitro. Melatonin-treated mice exhibited a significant reduction in SG injury of NOD/Ltj mice, which was accompanied by an increase in salivary flow rate, a decrease in inflammatory infiltration within the gland, and a suppression of oxidative stress indicators as well as cell apoptosis. Notably, both melatonin membrane receptors and nuclear receptors played an important role in the anti-apoptotic effects of melatonin on the SGs of NOD/Ltj mice. Furthermore, melatonin blocked the IL-6/STAT3 pathway through receptor-dependent manners in IFN-γ-stimulated HSGE cells. However, it was evident that the anti-oxidative and anti-apoptotic properties of melatonin on IFN-γ-stimulated HSGE cells were diminished by IL-6 treatment.

CONCLUSION

Melatonin had the potential to mitigate inflammation, oxidative stress, and apoptosis in SGs of pSS by inhibiting the IL-6/STAT3 pathway through receptor-dependent mechanisms. This intervention effectively prevented glandular damage and preserved functional integrity.

Reversal of Valproate-Induced Major Salivary Gland Changes By Moringa Oleifera Extract in Rats

This study aimed to explore the potential protective impacts of Moringa oleifera extract on major alteration in salivary glands of rats exposed to sodium valproate (VA). Groups were defined as control, control+moringa extract, sodium valproate, and sodium valproate+moringa extract. Antioxidant and oxidant status, activities of digestive and metabolic enzymes were examined. VA treatment led to various biochemical changes in the salivary glands, including decreased levels of antioxidants like glutathione, glutathione-S-transferase, and superoxide dismutase (except for sublingual superoxide dismutase). Conversely, a decrease in alpha-amylase, alkaline and acid phosphatase, lactate dehydrogenase, protease, and maltase activities were observed. The study also demonstrated that VA induces oxidative stress, increases lipid peroxidation, sialic acid, and nitric oxide levels in the salivary glands. Total oxidant capacity was raised in all glands except in the sublingual gland. The electrophoretic patterns of proteins were similar. Moringa oleifera extract exhibited protective properties, reversing these VA-induced biochemical changes due to its antioxidant and therapeutic attributes. This research suggests that moringa extract might serve as an alternative treatment approach for individuals using VA and experiencing salivary gland issues, although further research is necessary to confirm these findings in human subjects.

Improvement effect of gemigliptin on salivary gland dysfunction in exogenous methylglyoxal-injected rats

The symptom of hyposalivation associated with hypofunction of the salivary glands is a common feature of diabetes. Inadequate saliva production can cause tissue damage in the mouth, making it susceptible to infections and leading to oral health diseases. Previous studies have highlighted the harmful effects of methylglyoxal (MGO) and MGO-derived advanced glycation end products (AGEs) in diabetes. In this study, we investigated the protective effects of gemigliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, against MGO-induced salivary gland dysfunction. MGO treatment of immortalized human salivary gland acinar cells induced apoptosis via reactive oxygen species (ROS)-mediated pathways, but this effect was mitigated by gemigliptin. In vivo experiments involved the simultaneous administration of MGO (17.25 mg/kg) with aminoguanidine (100 mg/kg) and gemigliptin (10 and 100 mg/kg) daily to rats for two weeks. Gemigliptin increased the saliva volume and amylase levels in MGO-injected rats. Gemigliptin reduced the DPP-4 activity in both the salivary glands and serum of MGO-injected rats. Furthermore, gemigliptin exerted anti-glycation effects by reducing the accumulation of AGEs in the saliva, salivary glands, and serum and suppressing the expression of the receptor for AGEs. These actions protected the salivary gland cells from ROS-mediated apoptosis. Overall, gemigliptin protected the salivary gland cells from ROS-mediated cell death, reduced the accumulation of amylase and mucins in the salivary glands, and enhanced the salivary function by upregulating aquaporin 5 expression, and it exerted protective effects against MGO-induced salivary gland dysfunction by enhancing the anti-glycation, antioxidant, and salivary secretion activities. Our findings suggest gemigliptin as a potential therapeutic for patients with salivary gland dysfunction caused by the complications of diabetes.

Molecular mechanisms of saliva secretion and hyposecretion

The exocrine salivary gland secretes saliva, a fundamental body component to maintain oral homeostasis. Saliva is composed of water, ions, and proteins such as amylase, mucins, and immunoglobulins that play essential roles in the digestion of food, lubrication, and prevention of dental caries and periodontitis. An increasing number of people experience saliva hyposecretion due to aging, medications, Sjögren's syndrome, and radiation therapy for head and neck cancer. However, current treatments are mostly limited to temporary symptomatic relief. This review explores the molecular mechanisms underlying saliva secretion and hyposecretion to provide insight into putative therapeutic targets for treatment. Proteins implicated in saliva secretion pathways, including Ca2+ -signaling proteins, aquaporins, soluble N-ethylmaleimide-sensitive factor attachment protein receptors, and tight junctions, are aberrantly expressed and localized in patients with saliva hyposecretion, such as Sjögren's syndrome. Analysis of studies on the mechanisms of saliva secretion and hyposecretion suggests that crosstalk between fluid and protein secretory pathways via Ca2+ /protein kinase C and cAMP/protein kinase A regulates saliva secretion. Impaired crosstalk between the two secretory pathways may contribute to saliva hyposecretion. Future research into the detailed regulatory mechanisms of saliva secretion and hyposecretion may provide information to define novel targets and generate therapeutic strategies for saliva hyposecretion.

Gemigliptin Improves Salivary Gland Dysfunction in D-Galactose-Injected Aging Rats

Oral dryness is among the most common conditions experienced by the elderly. As saliva plays a crucial role in maintaining oral health and overall quality of life, the condition is increasingly taking its toll on a rapidly growing aging population. D-galactose (D-gal) stimulates their formation, which in turn cause oxidative stress and accelerate age-related decline in physical function. In this study, we observed a reduction in salivary secretion and amylase levels in aged rats injected with D-gal, confirming salivary gland dysfunction. Treatment with gemigliptin increased DPP-4 inhibition and GLP-1 levels in the salivary glands of aging rats and reduced the expression of AGEs and receptors for advanced glycation end products (RAGE). This effect was caused by the presence of additional reactive oxygen species (ROS) in the salivary glands of the examined rats. Gemigliptin's cytoprotective effect reduced amylase and mucin accumulation and increased AQP5 expression, which are important indicators of salivary gland function. In sum, gemigliptin was shown to improve D-gal-induced decline in the salivary gland function of aged rats through its anti-glycation and antioxidant activities. Gemigliptin shows promise as a treatment strategy for patients experiencing decreased salivary function associated with their advancing age.

Plant molecular farming-derived epidermal growth factor revolutionizes hydrogels for improving glandular epithelial organoid biofabrication

Epidermal growth factor (EGF) is a known signaling cue essential towards the development and organoid biofabrication particularly for exocrine glands. This study developed an in vitro EGF delivery platform with Nicotiana benthamiana plant-produced EGF (P-EGF) encapsulated on hyaluronic acid/alginate (HA/Alg) hydrogel to improve the effectiveness of glandular organoid biofabrication in short-term culture systems. Primary submandibular gland epithelial cells were treated with 5 - 20 ng/mL of P-EGF and commercially available bacteria-derived EGF (B-EGF). Cell proliferation and metabolic activity were measured by MTT and luciferase-based ATP assays. P-EGF and B-EGF 5 - 20 ng/mL promoted glandular epithelial cell proliferation during 6 culture days on a comparable fashion. Organoid forming efficiency and cellular viability, ATP-dependent activity and expansion were evaluated using two EGF delivery systems, HA/Alg-based encapsulation and media supplementation. Phosphate buffered saline (PBS) was used as a control vehicle. Epithelial organoids fabricated from PBS-, B-EGF-, and P-EGF-encapsulated hydrogels were characterized genotypically, phenotypically and by functional assays. P-EGF-encapsulated hydrogel enhanced organoid formation efficiency and cellular viability and metabolism relative to P-EGF supplementation. At culture day 3, epithelial organoids developed from P-EGF-encapsulated HA/Alg platform contained functional cell clusters expressing specific glandular epithelial markers such as exocrine pro-acinar (AQP5, NKCC1, CHRM1, CHRM3, Mist1), ductal (K18, Krt19), and myoepithelial (α-SMA, Acta2), and possessed a high mitotic activity (38-62% Ki67 cells) with a large epithelial progenitor population (∼70% K14 cells). The P-EGF encapsulation strikingly upregulated the expression of pro-acinar AQP5 cells through culture time when compared to others (B-EGF, PBS). Thus, the utilization of Nicotiana benthamiana in molecular farming can produce EGF biologicals amenable to encapsulation in HA/Alg-based in vitro platforms, which can effectively and promptly induce the biofabrication of exocrine gland organoids.

Dental pulp stem cell-derived exosomes revitalize salivary gland epithelial cell function in NOD mice via the GPER-mediated cAMP/PKA/CREB signaling pathway

BACKGROUND

Restoration of salivary gland function in Sjogren's syndrome (SS) is still a challenge. Dental pulp stem cells (DPSCs) derived exosomes had shown anti-inflammatory, anti-oxidative, immunomodulatory, and tissue function restorative abilities. However, the salivary gland function restoration potential of DPSCs-derived exosomes (DPSC-Exos) during SS has not been investigated yet.

METHODS

DPSC-Exos was isolated by ultracentrifugation methods and characterized. Salivary gland epithelial cells (SGEC) were treated with interferon-gamma (IFN-γ) to mimic SS in vitro and cultured with or without DPSC-Exos. SGEC survival and aquaporin 5 (AQP5) expression were analyzed. mRNA sequencing and bioinformatics analysis were performed in IFN-γ vs. DPSC-Exos+ IFN-γ treated SGEC. Non-obese diabetic (NOD)/ltj female mice (SS model), were intravenously administered with DPSC-Exos, and salivary gland functions and SS pathogenicity were analyzed. Furthermore, the mRNA sequencing and bioinformatics predicted mechanism of the therapeutic effect of DPSC-Exos was further investigated both in vitro and in vivo using RT-qPCR, Western blot, immunohistochemistry, immunofluorescence, flowcytometry analysis.

RESULTS

DPSC-Exos partially rescued IFN-γ triggered SGEC death. IFN-γ inhibited AQP5 expression in SGEC and DPSC-Exos reversed this effect. Transcriptome analysis showed GPER was the upregulated DEG in DPSC-Exos-treated SGEC with a positive correlation with salivary secretion-related DEGs. Pathway enrichment analysis revealed that DEGs were mainly attributed to estrogen 16 alpha-hydroxylase activity, extracellular exosome function, cAMP signaling, salivary secretion, and estrogen signaling. Intravenous injection of DPSC-Exos in NOD/ltj mice alleviated the SS syndrome as indicated by the increased salivary flow rate, attenuated glandular inflammation, and increased AQP5 expression. GPER was also upregulated in the salivary gland of DPSC-Exos-treated NOD/ltj mice compared with the PBS-treated NOD/ltj mice. IFN-γ+DPSC-Exos-treated SGEC showed higher expression of AQP5, p-PKA, cAMP, and intracellular Ca²⁺ levels compared with IFN-γ-treated SGEC. These effects were reversed by the inhibition of GPER.

CONCLUSIONS

Our results showed that DPSC-Exos revitalize salivary gland epithelial cell function during SS via the GPER-mediated cAMP/PKA/CREB pathway suggesting the possible therapeutic potential of DPSC-Exos in SS-treatment.

Ontogenetic development of the water channel protein AQP5 in mouse salivary gland tissue

Aquaporins (AQP) are a family of channel proteins expressed in the cell membranes of many tissue types. As water channels, they enable the selective permeation of water molecules and thus play an important role in water transport through the plasma membrane. There are numerous AQP sub-types, among which AQP5 is expressed in the salivary glands. The expression and localization of AQP5 in different salivary gland cells of animal models during fetal development and after birth have enabled the physiological functions of AQP5 to be elucidated, but subsequent changes in the adult phase are unknown. It is known that saliva production tends to decrease with age, but it is unclear how AQP5 activity and function changes developmentally, from young to old including gender differences. In the present study, we sampled the parotid, submandibular, and sublingual glands from young (8 weeks old) and aged (12 months old) mice of both sexes to study the effects of age- and sex-related differences in AQP5 expression. Positive fluorescence immunostaining was detected in the membranes of cells from all gland types, and this was enhanced in juvenile mice from both sexes. Western blot analyses revealed that AQP5 expression levels tended to decrease with age in both male and female animals. Conversely, AQP5 gene expression levels did not change significantly with aging, but were found to be high in submandibular gland cells of both sexes, in parotid gland cells of older female mice, and in the sublingual gland cells of young male mice.

Developmental function of Piezo1 in mouse submandibular gland morphogenesis

Mechanically activated factors are important in organogenesis, especially in the formation of secretory organs, such as salivary glands. Piezo-type mechanosensitive ion channel component 1 (Piezo1), although previously studied as a physical modulator of the mechanotransduction, was firstly evaluated on its developmental function in this study. The detailed localization and expression pattern of Piezo1 during mouse submandibular gland (SMG) development were analyzed using immunohistochemistry and RT-qPCR, respectively. The specific expression pattern of Piezo1 was examined in acinar-forming epithelial cells at embryonic day 14 (E14) and E16, which are important developmental stages for acinar cell differentiation. To understand the precise function of Piezo1 in SMG development, siRNA against Piezo1 (siPiezo1) was employed as a loss-of-function approach, during in vitro organ cultivation of SMG at E14 for the designated period. Alterations in the histomorphology and expression patterns of related signaling molecules, including Bmp2, Fgf4, Fgf10, Gli1, Gli3, Ptch1, Shh, and Tgfβ-3, were examined in acinar-forming cells after 1 and 2 days of cultivation. Particularly, altered localization patterns of differentiation-related signaling molecules including Aquaporin5, E-cadherin, Vimentin, and cytokeratins would suggest that Piezo1 modulates the early differentiation of acinar cells in SMGs by modulating the Shh signaling pathway.

Aquaporin5 Deficiency Aggravates ROS/NLRP3 Inflammasome-Mediated Pyroptosis in the Lacrimal Glands

Purpose

The pathogenesis of the lacrimal glands (LGs) is facilitated by inflammation mediated by the NACHT, LRR, and NLRP3 inflammasomes in dry eye disease. This research aimed to explore the protective effects of Aquaporin 5 (AQP5) on LGs by inhibiting reactive oxygen species (ROS) and the NLRP3 inflammasome.

Methods

AQP5 knockout (AQP5-/-) mice were used to evaluate pathological changes in LGs. ROS generation was detected with a dichlorodihydro-fluorescein diacetate assay. Lipid metabolism was assessed by Oil Red O staining. The reversal of the mitochondrial membrane potential was detected using a JC-1 fluorescent probe kit. The effect of AQP5 on NLRP3/caspase-1/Gasdermin-D (GSDMD)-mediated pyroptosis was examined using pharmacological treatment of N-acetyl L-cysteine or MCC950.

Results

AQP5 loss significantly increased ROS generation, lipid metabolism disorders, TUNEL-positive cells, and reversal of the mitochondrial membrane potential in the AQP5-/- LGs. NLRP3 upregulation, increased caspase-1 and GSDMD activity, and enhanced IL-1β release were detected in the AQP5-/- mouse LGs and primary LG epithelial cells. MCC950 significantly suppressed NLRP3 inflammasome-related pyroptosis induced by AQP5 deficiency in LGs and primary LG epithelial cells. Furthermore, we discovered that prestimulating the AQP5-/- primary LG epithelial cells with N-acetyl L-cysteine decreased NLRP3 expression, caspase-1 and GSDMD activity levels, and IL-1β release.

Conclusions

Our results revealed that AQP5 loss promoted NLRP3 inflammasome activation through ROS generation. Inhibiting the ROS or NLRP3 inflammasome significantly alleviated the damage and pyroptosis of AQP5-deficient LG epithelial cells, which could provide new insights into dry eye disease.

A novel association of osmotic demyelination in Sjögren's syndrome prompts revisiting role of aquaporins in CNS demyelinating diseases: A literature review

BACKGROUND

Primary Sjögren's syndrome (SS) is a chronic systemic autoimmune disease with varied neurological manifestations. SS is associated with anti-aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD), a demyelinating autoimmune disorder of the central nervous system (CNS). Intriguingly, there are reports of osmotic demyelinating syndrome (ODS), a supposedly non-inflammatory disorder, in the context of SS and renal tubular acidosis (RTA), both of which are not yet established risk factors for ODS.

METHODS

A literature search was undertaken to identify case reports of ODS in patients with SS. Details of the clinical and laboratory features of these patients were compiled. Additionally, we searched for NMOSD in patients with SS. We looked for co-existing RTA in patients with SS-ODS as well as SS-NMOSD. We also screened for reports of ODS in RTA without underlying SS.

RESULTS & DISCUSSION

We identified 15 patients (all women, median age 40 years) with ODS in SS, and all of these patients had comorbid RTA. There were only three reported cases of ODS in RTA without underlying SS. We identified a total of 67 patients with SS-NMOSD, of whom only 3 (4.5%) had RTA. Hence, unlike NMOSD, the development of ODS in SS requires a prolonged osmotic or electrolyte abnormality caused by the comorbid RTA. The 15 patients with ODS and SS -RTA, showed heterogeneous clinical manifestations and outcomes. The most common symptom was quadriparesis, seen in 14 of the 15 patients. Eleven of the 15 patients had one of the following features, either alone or in combination: worsening of the sensorium, extensor plantar response, dysphagia/dysarthria, and facial palsy. The latter four manifestations were present at the onset in 7 patients and later in the course of the illness in the remaining 4 patients. Ocular palsy was seen in only four of the 15 patients and was a late manifestation. One patient who had extensive long-segment myelitis and subsequent ODS died, but most patients recovered without significant sequelae. None had hyponatremia, while all patients had hypokalemia and/or hypernatremia. Hypokalemia causing nephrogenic diabetes insipidus (NDI) followed by rapid rise in sodium and the resultant osmotic stress could potentially explain the occurrence of ODS in SS-RTA. Aquaporin (AQP) in astrocytes is implicated in ODS, and renal AQP is downregulated in NDI. Antibodies against AQPs are present in some patients with SS. Defective AQP is therefore a common link underlying all the connected diseases, namely SS, NDI, and ODS, raising the possibility of immune-mediated AQP dysfunction in the pathogenesis.

CONCLUSION

The hitherto unreported association between SS-RTA and ODS may implicate SS and/or RTA in the development of ODS. In the setting of SS-RTA, ODS must be suspected when a patient with flaccid quadriparesis does not respond to the correction of potassium or develops additional neurological features along with a rise in sodium. Defective functions of AQPs may be a possible mechanism linking demyelinating CNS lesions, SS, and RTA. Studies evaluating AQP functions and serum antibodies against AQPs in these conditions are warranted.

Molecular Mechanisms Linking Inflammation to Autoimmunity in Sjögren's Syndrome: Identification of New Targets

Sjögren's syndrome (SS) is a systemic autoimmune rheumatic disorder characterized by the lymphocytic infiltration of exocrine glands and the production of autoantibodies to self-antigens. The involvement of the exocrine glands drives the pathognomonic manifestations of dry eyes (keratoconjunctivitis sicca) and dry mouth (xerostomia) that define sicca syndrome. To date, the molecular mechanisms mediating pathological salivary gland dysfunction in SS remain to be elucidated, despite extensive studies investigating the underlying cause of this disease, hampering the development of novel therapeutic strategies. Many researchers have identified a multifactorial pathogenesis of SS, including environmental, genetic, neuroendocrine, and immune factors. In this review, we explore the latest developments in understanding the molecular mechanisms involved in the pathogenesis of SS, which have attracted increasing interest in recent years.

A Mathematical Model of Salivary Gland Duct Cells

Saliva is produced in two stages in the salivary glands: the secretion of primary saliva by the acinus and the modification of saliva composition to final saliva by the intercalated and striated ducts. In order to understand the saliva modification process, we develop a mathematical model for the salivary gland duct. The model utilises the realistic 3D structure of the duct reconstructed from an image stack of gland tissue. Immunostaining results show that TMEM16A and aquaporin are expressed in the intercalated duct cells and that ENaC is not. Based on this, the model predicts that the intercalated duct does not absorb Na\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^+$$\end{document}+ and Cl\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^-$$\end{document}- like the striated duct but secretes a small amount of water instead. The input to the duct model is the time-dependent primary saliva generated by an acinar cell model. Our duct model produces final saliva output that agrees with the experimental measurements at various stimulation levels. It also shows realistic biological features such as duct cell volume, cellular concentrations and membrane potentials. Simplification of the model by omission of all detailed 3D structures of the duct makes a negligible difference to the final saliva output. This shows that saliva production is not sensitive to structural variation of the duct.

In Vivo Transfection of Rat Salivary Glands With Fluorescently Tagged Aquaporin-5 Channel DNA

Background 

The acinar cells of salivary glands are responsible for most saliva production and are, unfortunately, h­­ighly radiosensitive. As such, dry mouth or xerostomia is an adverse effect experienced by half of head and neck cancer patients treated with radiation. We evaluate a novel method of gene transfection of aquaporin channels to rat salivary glands.

Materials and methods

A green fluorescent protein (GFP)-tagged human Aquaporin-5 (AQP5) cDNA sequence cloned into a pCMV6-AC-GFP vector was complexed with lipofectamine 2000. One submandibular gland of the anesthetized rats was injected with the complexed cDNA and lipid solution under ultrasound guidance, while the opposite gland was injected with the vehicle control. The animals were sacrificed between 24 to 48 hours post-injection. The salivary glands were removed and evaluated via fluorescence imaging. Western blot assays were also performed to determine AQP5 cDNA expression.

Results 

In the experiments, the submandibular glands were identified and injected under ultrasound guidance. Four control glands and eight experimental glands were evaluated. The cDNA was expressed successfully and variably within the experimental glands, noting greater intensity along the cell surface consistent with appropriate trafficking of the AQP5 channel. Western blot analysis demonstrated variable expression in the experimental sample with no expression in the control sample. Several glands across the groups showed mild to moderate interstitial edema or inflammation.

Conclusion 

In this study, we demonstrate an alternative in vivo transfection method via lipofection and demonstrate the successful expression of the AQP5 channel in rat salivary gland tissue.

Comprehensive Analysis of the Structure and Function of Peptide:N-Glycanase 1 and Relationship with Congenital Disorder of Deglycosylation

The cytosolic PNGase (peptide:N-glycanase), also known as peptide-N4-(N-acetyl-β-glucosaminyl)-asparagine amidase, is a well-conserved deglycosylation enzyme (EC 3.5.1.52) which catalyzes the non-lysosomal hydrolysis of an N(4)-(acetyl-β-d-glucosaminyl) asparagine residue (Asn, N) into a N-acetyl-β-d-glucosaminyl-amine and a peptide containing an aspartate residue (Asp, D). This enzyme (NGLY1) plays an essential role in the clearance of misfolded or unassembled glycoproteins through a process named ER-associated degradation (ERAD). Accumulating evidence also points out that NGLY1 deficiency can cause an autosomal recessive (AR) human genetic disorder associated with abnormal development and congenital disorder of deglycosylation. In addition, the loss of NGLY1 can affect multiple cellular pathways, including but not limited to NFE2L1 pathway, Creb1/Atf1-AQP pathway, BMP pathway, AMPK pathway, and SLC12A2 ion transporter, which might be the underlying reasons for a constellation of clinical phenotypes of NGLY1 deficiency. The current comprehensive review uncovers the NGLY1’ssdetailed structure and its important roles for participation in ERAD, involvement in CDDG and potential treatment for NGLY1 deficiency.

Apigenin, a Single Active Component of Herbal Extract, Alleviates Xerostomia via ERα-Mediated Upregulation of AQP5 Activation

Xerostomia is a common symptom in menopausal women, suggesting the role of sex steroids in disease development. Shreds of literature had reported the potential use of herbal extracts to relieve xerostomia. However, a cocktail of multiple components in herbal extract makes it difficult to understand the exact mechanism of action. Aquaporin5 (AQP5), the specific aquaporin expressed in salivary glands, plays an important role in salivary secretion as a downstream of estrogen signaling. In this study, we aimed to unravel a single active herbal component as a therapeutic for xerostomia and investigate its mechanism of action. The effects of apigenin (flavonoid), dauricine (alkaloids), protopine (alkaloids), and lentinan (polysaccharides) on AQP5 transcription were screened in vitro. Only apigenin robustly induced AQP5 transcription and expression, and this effect was even robust compared to the effect of estradiol (E2, a positive control). Overexpression of estrogen receptor α (ERα) in the human salivary gland cell line (HSG) upregulated the AQP5 transcription and expression and the knockdown ERα reversed this effect, suggesting the role of ERα signaling on AQP5 activation in HSG cells. Docking results showed apigenin-specific binding sites in ERα. We further analyzed the therapeutic effect of apigenin on ovariectomized mice as a xerostomia model. The saliva secretion in the xerostomia group was reduced to one-third of the sham group, whereas the apigenin or E2 treatment for 12 weeks reversed this effect. Meanwhile, the water consumption in the xerostomia group was augmented obviously compared to the sham group, whereas the water consumption in the apigenin and E2 group was declined to the level of the sham group. Immunohistochemistry of submandibular glands revealed the downregulation of AQP5 expression in xerostomia mice compared to control. Apigenin, or E2 treatment, upregulated AQP5 expression in xerostomia mice. In conclusion, apigenin, a single active component of herbal extract, upregulated AQP5 expression in HSG cells via activation of ERα signaling and restored saliva flow rates in OVX mice. These results revealed apigenin as a single active component of herbal extract with the potential to treat xerostomia.

[Effects of acid stimulation on saliva flow rate and compositions of human parotid and submandibular glands]

OBJECTIVE

To investigate the effect of acid stimulation on salivary flow rate and compositions of human parotid and submandibular glands, so as to provide basis for comprehensive evaluation of salivary gland function in both health and disease status.

METHODS

In the study, 210 healthy participants' whole saliva samples were collected under passive drooling, and their parotid gland and submandibular gland secretions were collected by negative pressure suction. 2% citric acid was dropped on the tip of tongue every 1 min for acid stimulation for a total of 5 times to collect stimulated whole saliva, parotid and submandibular gland saliva. The collected saliva was weighed and saliva flow rate was calculated. The K+, Na+, Cl-, Ca2+, total protein, total phosphorus and α-amylase in saliva samples were detected by biochemical analyzer, and the changing features of flow rate and compositions of different kinds of saliva were compared and analyzed.

RESULTS

After acid stimulation, saliva flow rate significantly increased. The increase proportion of parotid gland saliva (10.7 folds) was much higher than that of submandibular gland saliva (2.9 folds). The concentrations of Na+, Cl-, Ca2+, total protein and α-amylase in parotid gland saliva increased significantly (P < 0.05), but there was no significant difference in total phosphorus and K+ (P=0.89, P=0.34). The concentration of Na+ and Ca2+ in saliva of submandibular gland increased significantly(P < 0.05), the concentration of total phosphorus decreased significantly(P < 0.05), and the concentration of Cl- increased, but the difference was not significant(P=0.068). There was no significant difference in total protein, K+ and α-amylase (P=0.85, P=0.07, P=0.95). The compound secretion rate of total phosphorus in saliva of submandibular gland remained unchanged(P=0.066), while the secretion rate of K+, Na+, Cl-, Ca2+, total protein and α-amylase significantly increased(P < 0.01). The compound secretion rate of K+, Na+, Cl-, Ca2+, total protein and total phosphorus and α-amylase in parotid gland saliva increased(P < 0.01). The concentrations of Na+, Cl-, K+, total phosphorus, total protein and α-amylase in parotid were higher than those in submandibular gland (P < 0.01), and the concentration of Ca2+ in submandibular gland saliva was significantly higher than that in parotid (P < 0.001).

CONCLUSION

The response of parotid to acid stimulation is stronger, and the secretion of submandibular gland is more stable. Acid stimulation significantly influences the concentrations of electrolytes in saliva, and the composited secretion rate is an evaluation index to reflect both flow rate and composition concentration of saliva. The parotid gland plays an important role in the secretion of total protein, total phosphorus and α-amylase in saliva, and the submandibular gland is the main source of Ca2+ in saliva.

[Effects of acid stimulation on saliva flow rate and compositions of human parotid and submandibular glands]

OBJECTIVE

To investigate the effect of acid stimulation on salivary flow rate and compositions of human parotid and submandibular glands, so as to provide basis for comprehensive evaluation of salivary gland function in both health and disease status.

METHODS

In the study, 210 healthy participants' whole saliva samples were collected under passive drooling, and their parotid gland and submandibular gland secretions were collected by negative pressure suction. 2% citric acid was dropped on the tip of tongue every 1 min for acid stimulation for a total of 5 times to collect stimulated whole saliva, parotid and submandibular gland saliva. The collected saliva was weighed and saliva flow rate was calculated. The K⁺, Na⁺, Cl^-, Ca²⁺, total protein, total phosphorus and α-amylase in saliva samples were detected by biochemical analyzer, and the changing features of flow rate and compositions of different kinds of saliva were compared and analyzed.

RESULTS

After acid stimulation, saliva flow rate significantly increased. The increase proportion of parotid gland saliva (10.7 folds) was much higher than that of submandibular gland saliva (2.9 folds). The concentrations of Na⁺, Cl^-, Ca²⁺, total protein and α-amylase in parotid gland saliva increased significantly (P < 0.05), but there was no significant difference in total phosphorus and K⁺ (P=0.89, P=0.34). The concentration of Na⁺ and Ca²⁺ in saliva of submandibular gland increased significantly(P < 0.05), the concentration of total phosphorus decreased significantly(P < 0.05), and the concentration of Cl^- increased, but the difference was not significant(P=0.068). There was no significant difference in total protein, K⁺ and α-amylase (P=0.85, P=0.07, P=0.95). The compound secretion rate of total phosphorus in saliva of submandibular gland remained unchanged(P=0.066), while the secretion rate of K⁺, Na⁺, Cl^-, Ca²⁺, total protein and α-amylase significantly increased(P < 0.01). The compound secretion rate of K⁺, Na⁺, Cl^-, Ca²⁺, total protein and total phosphorus and α-amylase in parotid gland saliva increased(P < 0.01). The concentrations of Na⁺, Cl^-, K⁺, total phosphorus, total protein and α-amylase in parotid were higher than those in submandibular gland (P < 0.01), and the concentration of Ca²⁺ in submandibular gland saliva was significantly higher than that in parotid (P < 0.001).

CONCLUSION

The response of parotid to acid stimulation is stronger, and the secretion of submandibular gland is more stable. Acid stimulation significantly influences the concentrations of electrolytes in saliva, and the composited secretion rate is an evaluation index to reflect both flow rate and composition concentration of saliva. The parotid gland plays an important role in the secretion of total protein, total phosphorus and α-amylase in saliva, and the submandibular gland is the main source of Ca²⁺ in saliva.

The Expression of Aquaporin-1 and Aquaporin-3 in Extrahepatic Cholangiocarcinoma and their Clinicopathological Significance

BACKGROUND

The aim of the study was to evaluate the expression and clinicopathological significance of aquaporin-1 (AQP1) and aquaporin-3 (AQP3) in extrahepatic cholangiocarcinoma (EHCC).

METHODS

Immunostaining of AQP1 and AQP3 was performed by EnVision immunohistochemistry in benign and malignant biliary tract tissues.

RESULTS

The expression of AQP1 and AQP3 protein were significantly higher in EHCC tumor tissues (P < 0.05 or P < 0.01). Adenoma and paracancerous tissues with positive AQP1 and/or AQP3 protein expression exhibited atypical hyperplasia. AQP1 expression was positive correlated with AQP3 expression in EHCC (P < 0.01). TNM I + II stage and radical surgery, the positive expression of AQP1 and AQP3 In patients with well-differentiation, no invasion, no lymph metastasis, is lower (P < 0.05 or P < 0.01). Average overall survival time of those with positive expression of AQP1 and AQP3 was significant shorter (P < 0.01). Both AQP1 and AQP3 positive expressions were proved to be an independent prognostic factors in EHCC by cox multivariate analysis. The AUC calculated for AQP1 was 0.769 (95% confidence interval [CI]: 0.618-0.920), and that for AQP3 was 0.758 (95%CI: 0.605-0.911, while that for AQP1 and AQP3 was 0.825 (95%CI: 0.658-0.991).

CONCLUSIONS

Positive expression of AQP1 and AQP3 is closely related to the pathogenesis, severe clinicopathological characteristics, aggressive biological behaviors, and dismal prognoses in EHCC.

Human dental pulp stem cells attenuate streptozotocin-induced parotid gland injury in rats

OBJECTIVE

Diabetes mellitus causes deterioration in the body, including serious damage of the oral cavity related to salivary gland dysfunction, characterised by hyposalivation and xerostomia. Human dental pulp stem cells (hDPSCs) represent a promising therapy source, due to the easy, minimally invasive surgical access to these cells and their high proliferative capacity. It was previously reported that the trophic support mediated by these cells can rescue the functional and structural alterations of damaged salivary glands. However, potential differentiation and paracrine effects of hDPSCs in diabetic-induced parotid gland damage have not been investigated. Our study aimed to investigate the therapeutic effects of intravenous transplantation of hDPSCs on parotid gland injury in a rat model of streptozotocin (STZ)-induced type 1 diabetes.

METHODS

Thirty Sprague-Dawley male rats were randomly categorised into three groups: control, diabetic (STZ), and transplanted (STZ + hDPSCs). The hDPSCs or the vehicles were injected into the rats' tail veins, 7 days after STZ injection. Fasting blood glucose levels were monitored weekly. A glucose tolerance test was performed, and the parotid gland weight, salivary flow rate, oxidative stress indices, parotid gland histology, and caspase-3, vascular endothelial growth factor, proliferating cell nuclear antigen, neuronal nitric oxide synthase, endothelial nitric oxide synthase, and tetrahydrobiopterin biosynthetic enzyme expression levels in parotid tissues were assessed 28 days post-transplantation.

RESULTS

Transplantation of hDPSCs decreased blood glucose, improved parotid gland weight and salivary flow rate, and reduced oxidative stress. The cells migrated to the STZ-injured parotid gland and differentiated into acinar, ductal, and myoepithelial cells. Moreover, hDPSCs downregulated the expression of caspase-3 and upregulated the expression of vascular endothelial growth factor and proliferating cell nuclear antigen, likely exerting pro-angiogenic and anti-apoptotic effects and promoting endogenous regeneration. In addition, the transplanted cells enhanced the parotid nitric oxide-tetrahydrobiopterin pathway.

CONCLUSIONS

Our results showed that hDPSCs migrated to and survived within the STZ-injured parotid gland, where functional and morphological damage was prevented due to the restoration of normal glucose levels, differentiation into parotid cell populations, and stimulation of paracrine-mediated regeneration. Thus, hDPSCs may have potential in the treatment of diabetes-induced parotid gland injury.

ACE2 and TMPRSS2 in human saliva can adsorb to the oral mucosal epithelium

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) is primarily transmitted through droplets. All human tissues with the angiotensin‐converting enzyme 2 (ACE2) and transmembrane protease serines 2 (TRMPRSS2) are potential targets of SARS‐CoV‐2. The role of saliva in SARS‐CoV‐2 transmission remains obscure. In this study, we attempted to reveal ACE2 and TRMPRSS2 protein expression in human parotid, submandibular, and sublingual glands (three major salivary glands). Then, the binding function of spike protein to ACE2 in three major salivary glands was detected. The expression of ACE2 and TMPRSS2 in human saliva from parotid glands were both examined. Exogenous recombined ACE2 and TMPRSS2 anchoring and fusing to oral mucosal epithelial cells in vitro were also unraveled. ACE2 and TMPRSS2 were found mainly to be expressed in the cytomembrane and cytoplasm of epithelial cells in the serous acinus cells in parotid and submandibular glands. Our research also discovered that the spike protein of SARS‐CoV‐2 binds to ACE2 in salivary glands in vitro. Furthermore, exogenous ACE2 and TMPRSS2 can anchor and fuse to oral mucosa in vitro. Thus, the expression of ACE2 and TMPRSS2 in human saliva might have implications for SARS‐CoV‐2 infection.

Ezrin Is a Novel Protein Partner of Aquaporin-5 in Human Salivary Glands and Shows Altered Expression and Cellular Localization in Sjögren's Syndrome

Sjögren’s syndrome (SS) is an exocrinopathy characterized by the hypofunction of salivary glands (SGs). Aquaporin-5 (AQP5); a water channel involved in saliva formation; is aberrantly distributed in SS SG acini and contributes to glandular dysfunction. We aimed to investigate the role of ezrin in AQP5 mislocalization in SS SGs. The AQP5–ezrin interaction was assessed by immunoprecipitation and proteome analysis and by proximity ligation assay in immortalized human SG cells. We demonstrated, for the first time, an interaction between ezrin and AQP5. A model of the complex was derived by computer modeling and in silico docking; suggesting that AQP5 interacts with the ezrin FERM-domain via its C-terminus. The interaction was also investigated in human minor salivary gland (hMSG) acini from SS patients (SICCA-SS); showing that AQP5–ezrin complexes were absent or mislocalized to the basolateral side of SG acini rather than the apical region compared to controls (SICCA-NS). Furthermore, in SICCA-SS hMSG acinar cells, ezrin immunoreactivity was decreased at the acinar apical region and higher at basal or lateral regions, accounting for altered AQP5–ezrin co-localization. Our data reveal that AQP5–ezrin interactions in human SGs could be involved in the regulation of AQP5 trafficking and may contribute to AQP5-altered localization in SS patients

FoxO1 as a Regulator of Aquaporin 5 Expression in the Salivary Gland

Forkhead box O1 (FoxO1) is a multifunctional initiator, mediator, and repressor of autoimmune diseases in an organ- or disease-specific manner. However, the role of FoxO1 in the salivary gland has not yet been elucidated. In this study, we discovered that FoxO1 and aquaporin 5 (AQP5) are both significantly downregulated in the patients with primary Sjögren syndrome, an autoimmune disease accompanying salivary gland dysfunction. Pharmacologic or genetic perturbation of FoxO1 in the rat salivary gland acinar cell line, SMG-C6, induced a significant downregulation of AQP5 expression, as observed in clinical specimens. There was a strong correlation between FoxO1 and AQP5 expression because FoxO1 is a direct regulator of AQP5 expression in salivary gland acinar cells through its interaction with the promoter region of AQP5. Serial injection of a FoxO1 inhibitor into mice induced a reduction of AQP5 expression in submandibular glands and, consequently, hyposalivation, which is one of the major clinical symptoms of primary Sjögren syndrome. However, there was no sign of inflammation or cell damage in the submandibular glands harvested from mice treated with the FoxO1 inhibitor. In conclusion, our findings indicate that FoxO1 in salivary gland tissue acts as a direct regulator of AQP5 expression. Thus, downregulation of FoxO1 observed in primary Sjögren syndrome is a putative mechanism for hyposalivation without the involvement of previously reported soluble factors in primary Sjögren syndrome patient sera.

Characteristics of aquaporin 1, 3, and 5 expression during early murine salivary gland development

Aquaporins (AQPs) are essential to coordinate the transit of water and ions through the cell membrane. In salivary glands (SGs), AQPs have been associated with saliva formation, facilitating water absorption through the epithelium during the formation of hypotonic saliva, which is then secreted into the oral cavity. Different members of the AQP family have been suggested to play distinct roles during embryonic development, highlighted by their specific expression patterns. Here, we have investigated the expression patterns of AQP-1, AQP-3 and AQP-5 by immunofluorescence at key stages of salivary gland development, utilising cultured mouse embryonic submandibular (SMG) and sublingual (SLG) glands. The expression of AQPs was compared to a mitotic marker, phospho-histone 3 (PH3), a myoepithelial marker, smooth muscle actin (SMA), and a vascular marker, CD31. Qualitative analysis revealed that AQP-1 and AQP-3 were primarily expressed during the earlier phases of SG morphogenesis and were associated with cells undergoing mitotic processes (PH3-positive). AQP-5, in contrast, was not associated to mitotic figures, but was predominantly expressed during late stages of SG morphogenesis. Our results highlight that AQPs are expressed from early stages of SG morphogenesis and exhibit complimentary expression patterns that may contribute to the morphogenesis of salivary glands.

N-Glycanase 1 Transcriptionally Regulates Aquaporins Independent of Its Enzymatic Activity

Patients with pathogenic mutations in NGLY1 cannot make tears and have global developmental delay and liver dysfunction. Traditionally, NGLY1 cleaves intact N-glycans from misfolded, retrotranslocated glycoproteins before proteasomal degradation. We demonstrate that Ngly1-null mouse embryonic fibroblasts, NGLY1 knockout human cells, and patient fibroblasts are resistant to hypotonic lysis. Ngly1-deficient mouse embryonic fibroblasts swell slower and have reduced aquaporin1 mRNA and protein expression. Ngly1 knockdown and overexpression confirms that Ngly1 regulates aquaporin1 and hypotonic cell lysis. Patient fibroblasts and NGLY1 knockout cells show reduced aquaporin11 mRNA, supporting NGLY1 as regulating expression of multiple aquaporins across species. Complementing Ngly1-deficient cells with catalytically inactive NGLY1 (p.Cys309Ala) restores normal hypotonic lysis and aquaporin1 protein. We show that transcription factors Atf1/Creb1 regulate aquaporin1 and that the Atf1/Creb1 signaling pathway is disrupted in Ngly1-deficient mouse embryonic fibroblasts. These results identify a non-enzymatic, regulatory function of NGLY1 in aquaporin transcription, possibly related to alacrima and neurological symptoms.

Evaluation of Aquaporins 1 and 5 Expression in Rat Parotid Glands After Volumetric Modulated Arc Radiotherapy and Use of Low-Level Laser Therapy at Different Times

Introduction: This experimental study investigated the mRNA expression of aquaporins (AQPs) 1 and 5 in the parotid glands of rats irradiated with volumetric modulated arc therapy (VMAT) and subjected to low-level laser therapy (LLLT) at different time points. Methods: The sample consisted of 30 Wistar rats (Rattus norvegicus) divided into the following groups: control, LLLT alone (LG), radiotherapy alone (RG), and experimental groups that received LLLT at 24 hours (early experimental group [EEG], n=12) and 120 hours (late experimental group [LEG], n=12) after radiotherapy. VMAT was delivered at a single dose (12 Gy) and LLLT was performed with an aluminium-gallium-arsenide diode laser (660 nm, 100 mW), spot area of 0.0028 cm2, energy of 2 J/cm² applied to 3 spots in the region corresponding to the right parotid gland, for 10 consecutive days. The right parotid gland was resected and prepared for RNA extraction. The gene expression of AQPs was evaluated by quantitative polymerase chain reaction (qPCR) using specific TaqMan probes, with the HPRT gene as an internal control. Results: The lowest AQP1 gene expression was 0.83 (0.27) with the use of LLLT 24 hours after radiotherapy (EEG), and the highest was 1.56 (0.80) with the use of LLLT alone (LG). Likewise, the lowest AQP5 gene expression was found in the EEG (mean = 0.88; SD = 0.49) and the highest in the LG (mean = 1.29; SD = 0.33). Conclusion: The use of LLLT after radiotherapy may contribute to the maintenance and an increase of these proteins, even when used at a later time point after radiotherapy.

Current State of Knowledge on Primary Sjögren's Syndrome, an Autoimmune Exocrinopathy

Primary Sjögren's syndrome (pSS) is a chronic systemic autoimmune rheumatic disease characterized by lymphoplasmacytic infiltration of the salivary and lacrimal glands, whereby sicca syndrome and/or systemic manifestations are the clinical hallmarks, associated with a particular autoantibody profile. pSS is the most frequent connective tissue disease after rheumatoid arthritis, affecting 0.3-3% of the population. Women are more prone to develop pSS than men, with a sex ratio of 9:1. Considered in the past as innocent collateral passive victims of autoimmunity, the epithelial cells of the salivary glands are now known to play an active role in the pathogenesis of the disease. The aetiology of the "autoimmune epithelitis" still remains unknown, but certainly involves genetic, environmental and hormonal factors. Later during the disease evolution, the subsequent chronic activation of B cells can lead to the development of systemic manifestations or non-Hodgkin's lymphoma. The aim of the present comprehensive review is to provide the current state of knowledge on pSS. The review addresses the clinical manifestations and complications of the disease, the diagnostic workup, the pathogenic mechanisms and the therapeutic approaches.

Insight into Salivary Gland Aquaporins

The main role of salivary glands (SG) is the production and secretion of saliva, in which aquaporins (AQPs) play a key role by ensuring water flow. The AQPs are transmembrane channel proteins permeable to water to allow water transport across cell membranes according to osmotic gradient. This review gives an insight into SG AQPs. Indeed, it gives a summary of the expression and localization of AQPs in adult human, rat and mouse SG, as well as of their physiological role in SG function. Furthermore, the review provides a comprehensive view of the involvement of AQPs in pathological conditions affecting SG, including Sjögren's syndrome, diabetes, agedness, head and neck cancer radiotherapy and SG cancer. These conditions are characterized by salivary hypofunction resulting in xerostomia. A specific focus is given on current and future therapeutic strategies aiming at AQPs to treat xerostomia. A deeper understanding of the AQPs involvement in molecular mechanisms of saliva secretion and diseases offered new avenues for therapeutic approaches, including drugs, gene therapy and tissue engineering. As such, AQP5 represents a potential therapeutic target in different strategies for the treatment of xerostomia.

Optimization of an oral mucosa in vitro model based on cell line TR146

During the last years, the popularity of saliva has been increasing for its applicability as a diagnostic fluid. Blood biomarker molecules have to cross the blood-saliva barrier (BSB) in order to appear in saliva. The BSB consists of all oral and salivary gland epithelial barriers. Within this context, the optimization of in vitro models for mechanistic studies about the transport of molecules across the oral mucosa is an important task. Here, we describe the optimization and comprehensive characterization of a Transwell model of the oral mucosa based on the epithelial cell line TR146. Through systematic media optimization investigating 12 different set-ups, a significant increase of barrier integrity upon airlift cultivation is described here for TR146 cell layers. The distinct improvement of the paracellular barrier was described by measurements of transepithelial electrical resistance (TEER) and carboxyfluorescein permeability assays. Histological characterization supported TEER data and showed a stratified, non-keratinized multilayer of the optimized TR146 model. High-Throughput qPCR using 96 selected markers for keratinization, cornification, epithelial-mesenchymal transition, aquaporins, mucins, tight junctions, receptors, and transporter proteins was applied to comprehensively characterize the systematic optimization of the cellular model and validate against human biopsy samples. Data revealed the expression of several genes in the oral mucosa epithelium for the first time and elucidated novel regulations dependent on culture conditions. Moreover, functional activity of ABC-transporters ABCB1 and ABCC4 was shown indicating the applicability of the model for drug transport studies. In conclusion, a Transwell model of the oral mucosa epithelium was optimized suitably for transport studies.

Aquaporin 1, 3, and 5 Patterns in Salivary Gland Mucoepidermoid Carcinoma: Expression in Surgical Specimens and an In Vitro Pilot Study

Salivary gland aquaporins (AQPs) are essential for the control of saliva production and maintenance of glandular structure. However, little is known of their role in salivary gland neoplasia. Salivary gland tumors comprise a heterogeneous group of lesions, featuring variable histological characteristics and diverse clinical behaviors. Mucoepidermoid carcinoma (MEC) is the most common salivary gland malignancy. The aim of this study was to evaluate the expression of AQP1, AQP3, and AQP5 in 24 MEC samples by immunohistochemistry. AQP1 expression was observed in vascular endothelium throughout the tumor stroma. AQP3 was expressed in epidermoid and mucosal cells and AQP5 was expressed in mucosal cells of MEC. These proteins were expressed in the human MEC cell line UH-HMC-3A. Cellular ultrastructural aspects were analyzed by electron microscopy to certificate the tumor cell phenotype. In summary, our results show that, despite the fact that these molecules are important for salivary gland physiology, they may not play a distinct role in tumorigenesis in MEC. Additionally, the in vitro model may offer new possibilities to further investigate mechanisms of these molecules in tumor biology and their real significance in prognosis and possible target therapies.

Aquaporins' Influence on Different Dental Erosive Wear Phenotypes in Humans

Dental erosive wear is a multifactorial condition of high prevalence. Nowadays, there is an emphasis on discovering individual genetic predisposition for the development of this condition. Aquaporins (AQPs) are water channel proteins expressed in salivary glands, as well as during tooth development. They are involved in salivary secretion and composition and linked to physiological protection of the oral cavity. The aim of this study was to explore the relationship between different dental erosive wear phenotypes, AQP genes, and selected environmental factors. Data from 705 dental patients were used to investigate the association between dental erosive wear phenotypes and AQPs' single-nucleotide variants. Phenotypes were further analyzed considering diet and oral hygiene data, using logistic regression analysis, as implemented in PLINK, with the assumption that dental erosive wear is a complex gene-environment model. Associations were found between severe erosive tooth wear and rs2878771 (AQP2) for the genotypic (p = 0.02) and dominant (p = 0.03) models, and rs3736309 (AQP5) for the allelic model (p = 0.02). Logistic regression analyses, after implementing the Bonferroni correction, showed that several significant associations were present when covariates were included, suggesting that a strong environmental component is present. Our results show that dental erosive wear establishes under a gene-environmental complex model.

Human umbilical cord mesenchymal stem cells confer potent immunosuppressive effects in Sjögren's syndrome by inducing regulatory T cells

BACKGROUND

Primary Sjögren's syndrome (SS) is a lymphoproliferative disease with a chronic autoimmune disorder characterized by mononuclear cell (MNC) infiltration of notably the lacrimal and salivary glands. As mesenchymal stem cells (MSCs) regulate series of immunological responses partially by regulating proportion of CD4⁺ T cells and inducing an immunosuppressive local milieu, umbilical cord MSCs (UC-MSCs) are being considered as a novel source for cell-based therapies against primary SS. This study aimed to investigate the feasibility of UC-MSCs in treatment of SS and to explore the possible mechanism(s) with the special emphasis on regulatory T cells (Tregs).

METHODS

Potent immunosuppressive effects of human UC-MSCs on SS were explored in vivo and in vitro. To study the effects of human UC-MSCs on the development and progression of SS, human UC-MSCs were administered before disease onset (preventive protocol) and after disease occurrence (therapeutic protocol) in non-obese diabetic (NOD) mice. In human study, the effect of human UC-MSCs on T cells from SS patients was studied.

RESULTS

In both protocols, the histopathology of submandibular and sublingual salivary glands showed decreased inflammatory infiltrates. In vitro, human UC-MSCs exhibited potent suppressive effects on responses of MNCs in NOD mice and T cells in SS patients. Such inhibitory effects were coupled with decreased production of proinflammtory cytokines interferon-γ, interleukin (IL)-6, tumor necrosis factor-α and increased production of IL-10 (n = 10, p < .01). The frequency of CD4⁺Foxp3⁺T cells in the spleen of NOD recipients was elevated (n = 6, p < .05).

CONCLUSION

Human UC-MSCs are capable of inducing CD4⁺Foxp3⁺ T cells in both NOD mice and human in vitro. Human UC-MSCs effectively interfere with the autoimmune attack in the course of SS by inducing an in vivo state of T cell unresponsiveness and the upregulation of Tregs.

Cordycepin attenuates Salivary Hypofunction through the Prevention of Oxidative Stress in Human Submandibular Gland Cells

Xerostomia (dry mouth) is a significant age-related condition. Meanwhile, cordycepin, the natural therapeutic agent, has demonstrated an anti-aging effect. Therefore, the present study aimed to investigate the preventive effects of cordycepin on secretory function in an in vitro model of hydrogen peroxide (H₂O₂)-induced salivary hypofunction. After being exposed to H₂O₂, human submandibular gland (HSG) cells were treated with various concentrations of cordycepin (6.25-50 µM) for 24, 48, and 72h. To evaluate cell proliferation and reactive oxygen species (ROS) generation, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and 2, 7'-dichlorodihydrofluorescein diacetate assays were performed. The amylase activity was kinetically measured by 2-chloro-p-nitrophenol linked with maltotrioside. The expression of salivary, antioxidant and apoptotic markers at mRNA and protein levels were performed by reverse transcriptase polymerase chain reaction (RT-PCR) and immunofluorescence analysis, respectively. We demonstrated that cordycepin (6.25-25 µM) contributed to significant increases in expression of the salivary marker genes, alpha-amylase 1 (AMY1A) and aquaporin-5 (AQP5), and in amylase secretion without changes in cell viability. Under oxidative stress, HSG cells showed remarkable dysfunction. Cordycepin rescued the protective effects partially by decreasing ROS generation and restoring the expression of the salivary proteins, AMY and AQP5 via anti-oxidant and anti-apoptotic activity. In addition, the amount of amylase that was secreted from HSG cells cultured in cordycepin was increased. In conclusion, cordycepin demonstrated a protective effect on H₂O₂ -induced HSG cells by decreasing ROS generation and upregulating the salivary function markers, AMY1A and AQP5, at both the transcriptional and translational levels.

Aquaporins Involvement in Pancreas Physiology and in Pancreatic Diseases

Aquaporins are a family of transmembrane proteins permeable to water. In mammals, they are subdivided into classical aquaporins that are permeable to water; aquaglyceroporins that are permeable to water, glycerol and urea; peroxiporins that facilitate the diffusion of H2O2 through cell membranes; and so called unorthodox aquaporins. Aquaporins ensure important physiological functions in both exocrine and endocrine pancreas. Indeed, they are involved in pancreatic fluid secretion and insulin secretion. Modification of aquaporin expression and/or subcellular localization may be involved in the pathogenesis of pancreatic insufficiencies, diabetes and pancreatic cancer. Aquaporins may represent useful drug targets for the treatment of pathophysiological conditions affecting pancreatic function, and/or diagnostic/predictive biomarker for pancreatic cancer. This review summarizes the current knowledge related to the involvement of aquaporins in the pancreas physiology and physiopathology.

Physiology, Pathology and Regeneration of Salivary Glands

Salivary glands are essential structures in the oral cavity. A variety of diseases, such as cancer, autoimmune diseases, infections and physical traumas, can alter the functionality of these glands, greatly impacting the quality of life of patients. To date, no definitive therapeutic approach can compensate the impairment of salivary glands, and treatment are purely symptomatic. Understanding the cellular and molecular control of salivary glands function is, therefore, highly relevant for therapeutic purposes. In this review, we provide a starting platform for future studies in basic biology and clinical research, reporting classical ideas on salivary gland physiology and recently developed technology to guide regeneration, reconstruction and substitution of the functional organs.

Systems Biology Approaches and Precision Oral Health: A Circadian Clock Perspective

A vast majority of the pathophysiological and metabolic processes in humans are temporally controlled by a master circadian clock located centrally in the hypothalamic suprachiasmatic nucleus of the brain, as well as by specialized peripheral oscillators located in other body tissues. This circadian clock system generates a rhythmical diurnal transcriptional-translational cycle in clock genes and protein expression and activities regulating numerous downstream target genes. Clock genes as key regulators of physiological function and dysfunction of the circadian clock have been linked to various diseases and multiple morbidities. Emerging omics technologies permits largescale multi-dimensional investigations of the molecular landscape of a given disease and the comprehensive characterization of its underlying cellular components (e.g., proteins, genes, lipids, metabolites), their mechanism of actions, functional networks and regulatory systems. Ultimately, they can be used to better understand disease and interpatient heterogeneity, individual profile, identify personalized targetable key molecules and pathways, discover novel biomarkers and genetic alterations, which collectively can allow for a better patient stratification into clinically relevant subgroups to improve disease prediction and prevention, early diagnostic, clinical outcomes, therapeutic benefits, patient's quality of life and survival. The use of “omics” technologies has allowed for recent breakthroughs in several scientific domains, including in the field of circadian clock biology. Although studies have explored the role of clock genes using circadiOmics (which integrates circadian omics, such as genomics, transcriptomics, proteomics and metabolomics) in human disease, no such studies have investigated the implications of circadian disruption in oral, head and neck pathologies using multi-omics approaches and linking the omics data to patient-specific circadian profiles. There is a burgeoning body of evidence that circadian clock controls the development and homeostasis of oral and maxillofacial structures, such as salivary glands, teeth and oral epithelium. Hence, in the current era of precision medicine and dentistry and patient-centered health care, it is becoming evident that a multi-omics approach is needed to improve our understanding of the role of circadian clock-controlled key players in the regulation of head and neck pathologies. This review discusses current knowledge on the role of the circadian clock and the contribution of omics-based approaches toward a novel precision health era for diagnosing and treating head and neck pathologies, with an emphasis on oral, head and neck cancer and Sjögren's syndrome.

Effects of herbal medicine for xerostomia in head and neck cancer patients: an observational study in a tertiary cancer hospital

PURPOSE

More than 80% head and neck cancer patients endured radiotherapy-induced xerostomia which impacts their quality of life (QoL). This observational study evaluated the effect of herbal treatment on head and neck cancer patients' xerostomia and QoL.

METHODS

Head and neck cancer patients were recruited from July 2016 till March 2017 at National Cancer Institute, Ministry of Health, Malaysia. All study participants continued their standard oncology surveillance. Treatment group participants additionally received Chinese herbal treatment. The assessments included unstimulated salivary flow rate (USFR), stimulated salivary flow rate (SSFR), and QoL questionnaire.

RESULTS

Of 42 recruited participants, 28 were in the treatment group and 14 were in the control group. Participants were mainly Chinese (71.4%), stage III cancer (40.5%), and had nasopharynx cancer (76.2%). The commonly used single herbs were Wu Mei, San Qi, and Tian Hua Fen. Sha Shen Mai Dong Tang, Liu Wei Di Huang Wan, and Gan Lu Yin were the frequently prescribed herbal formulas. The baseline characteristics, USFR, SSFR, and QoL between control and treatment groups were comparable (p > 0.05). USFR between control and treatment groups were similar throughout the 6-month study period. SSFR for the treatment group significantly improved from 0.15 ± 0.28 ml/min (baseline) to 0.32 ± 0.22 ml/min (p = 0.04; at the 3rd month) and subsequently achieved 0.46 ± 0.23 ml/min (p = 0.001; at the 6th month). The treatment group had better QoL in terms of speech (p = 0.005), eating (p = 0.02), and head and neck pain (p = 0.04) at the 6th month.

CONCLUSION

Herbal treatment may improve xerostomia and QoL in post-radiotherapy head and cancer patients.

Aquaporin water channels: New perspectives on the potential role in inflammation

Aquaporins (AQPs) are a family of membrane water channel proteins that osmotically modulate water fluid homeostasis in several tissues; some of them also transport small solutes such as glycerol. At the cellular level, the AQPs regulate not only cell migration and transepithelial fluid transport across membranes, but also common events that are crucial for the inflammatory response. Emerging data reveal a new function of AQPs in the inflammatory process, as demonstrated by their dysregulation in a wide range of inflammatory diseases including edematous states, cancer, obesity, wound healing and several autoimmune diseases. This chapter summarizes the discoveries made so far about the structure and functions of the AQPs and provides updated information on the underlying mechanisms of AQPs in several human inflammatory diseases. The discovery of new functions for AQPs opens new vistas offering promise for the discovery of mechanisms and therapeutic opportunities in inflammatory disorders.

Carbonic anhydrase 12 mutation modulates membrane stability and volume regulation of aquaporin 5

Patients carrying the carbonic anhydrase12 E143K mutation showed the dry mouth phenotype. The mechanism underlying the modulation of aquaporin 5 and function in the salivary glands by carbonic anhydrase12 remains unknown. In this study, we identified the mislocalised aquaporin 5 in the salivary glands carrying the E143K. The intracellular pH of E143K cells was more acidic than that of the cells carrying wild type. To evaluate the role of carbonic anhydrase12 on the volume regulation of aquaporin 5, the submandibular gland cells were subjected to hypotonic stimuli. E143K enhanced the extent of swelling of cells on hypotonicity. Aquaporin 5 modulates water influx through ion transporters to prevent osmotic imbalance. These results suggest that the carbonic anhydrase12 E143K, including acidification or inflammation, mediates volume dysregulation by the loss of aquaporin 5. Thus, carbonic anhydrase12 may determine sensible effects on the cellular osmotic regulation by modulating aquaporin 5.

Involvement of Aquaporins in the Pathogenesis, Diagnosis and Treatment of Sjögren's Syndrome

Sjögren’s syndrome (SS) is a chronic autoimmune disease characterized by lymphocytic infiltration of salivary and lacrimal glands resulting in diminished production of saliva and tears. The pathophysiology of SS has not yet been fully deciphered. Classically it has been postulated that sicca symptoms in SS patients are a double step process whereby lymphocytic infiltration of lacrimal and salivary glands (SG) is followed by epithelial cell destruction resulting in keratoconjunctivitis sicca and xerostomia. Recent advances in the field of the pathophysiology of SS have brought in new players, such as aquaporins (AQPs) and anti AQPs autoantibodies that could explain underlying mechanistic processes and unveil new pathophysiological pathways offering a deeper understanding of the disease. In this review, we delineate the link between the AQP and SS, focusing on salivary glands, and discuss the role of AQPs in the treatment of SS-induced xerostomia.

Tanshinol upregulates the expression of aquaporin 5 in lung tissue of rats with sepsis

Aquaporin 5 (AQP-5) is a water channel protein that is closely associated with non-small cell lung cancer tissues. The present study aimed to investigate the mechanism of tanshinol treatment on AQP-5 in the lung tissue of rats with sepsis. Animals in a rat sepsis model were randomly divided into six groups including blank control (ctrl), sham operation (SO), model (sepsis), low dose tanshinol (5 mg/kg/day; Tan-L), moderate dose tanshinol (10 mg/kg/day; Tan-M) and high dose tanshinol (20 mg/kg/day; Tan-H) groups. After 7 days of administration, the expression level of AQP-5 mRNA was detected by reverse transcription-quantitative polymerase chain reaction. The levels of interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α) were measured by ELISA. Hematoxylin and eosin staining was used for histopathological observation. The expression levels of AQP-5, P38 and phosphorylated (P)-P38 protein in lung tissues were detected by western blot analysis. The expression levels of AQP-5 in the sepsis group were significantly decreased compared with those in ctrl and SO groups (P<0.01), while the levels of TNF-α, IL-6 and p-P38 were significantly increased in sepsis group compared with those in ctrl and SO groups (P<0.01). Following tanshinol intervention, the expression levels of AQP-5 were significantly increased, while the levels of TNF-α, IL-6 and p-P38 were decreased compared with those in sepsis group. Tanshinol may upregulate the expression of AQP-5 by inhibiting the inflammatory cytokines and phosphorylation of P38, therefore protecting the lung tissue of rats with sepsis.

The Emerging Role of microRNAs in Aquaporin Regulation

Aquaporins (AQPs) are membrane channels widely distributed in human tissues. AQPs are essential for water and energy homeostasis being involved in a broad range of pathophysiological processes such as edema, brain injury, glaucoma, nephrogenic diabetes insipidus, salivary and lacrimal gland dysfunction, cancer, obesity and related metabolic complications. Compelling evidence indicates that AQPs are targets for therapeutic intervention with potential broad application. Nevertheless, efficient AQP modulators have been difficult to find due to either lack of selectivity and stability, or associated toxicity that hamper in vivo studies. MicroRNAs (miRNAs) are naturally occurring small non-coding RNAs that regulate post-transcriptional gene expression and are involved in several diseases. Recent identification of miRNAs as endogenous modulators of AQP expression provides an alternative approach to target these proteins and opens new perspectives for therapeutic applications. This mini-review compiles the current knowledge of miRNA interaction with AQPs highlighting miRNA potential for regulation of AQP-based disorders.