TGF-ß1 Triggers Salivary Hypofunction via Attenuating Protein Secretion and AQP5 Expression in Human Submandibular Gland Cells.

Aging-related salivary gland degeneration usually causes poor oral health. Periductal fibrosis frequently occurs in the submandibular gland of the elderly. Transforming growth factor ß1 (TGF-ß1) is the primary driving factor for fibrosis, which exhibits an increase in the fibrotic submandibular gland tissue. This study aimed to investigate the effects of TGF-ß1 on the human submandibular gland (HSG) cell secretory function and its influences on aquaporin 5 (AQP5) expressions and distribution. We found that TGF-ß1 reduces the protein secretion amount of HSG and leads to the abundance alteration of 151 secretory proteins. Data are available via ProteomeXchange with the identifier PXD043185. The majority of HSG secretory proteins (84.11%) could be matched to the human saliva proteome. Meanwhile, TGF-ß1 enhances the expression of COL4A2, COL5A1, COL7A1, COL1A1, COL2A1, and α-SMA, hinting that TGF-ß1 possesses the potential to drive HSG fibrosis-related events. Besides, TGF-ß1 also attenuates the AQP5 expression and its membrane distribution in HSGs. The percentage for TGF-ß1-induced AQP5 reduction (52.28%) is much greater than that of the TGF-ß1-induced secretory protein concentration reduction (16.53%). Taken together, we concluded that TGF-ß1 triggers salivary hypofunction via attenuating protein secretion and AQP5 expression in HSGs, which may be associated with TGF-ß1-driven fibrosis events in HSGs.

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.

Molecular and Physiological Functions of PACAP in Sweat Secretion.

Sweat plays a critical role in human body, including thermoregulation and the maintenance of the skin environment and health. Hyperhidrosis and anhidrosis are caused by abnormalities in sweat secretion, resulting in severe skin conditions (pruritus and erythema). Bioactive peptide and pituitary adenylate cyclase-activating polypeptide (PACAP) was isolated and identified to activate adenylate cyclase in pituitary cells. Recently, it was reported that PACAP increases sweat secretion via PAC1R in mice and promotes the translocation of AQP5 to the cell membrane through increasing intracellular [Ca2+] via PAC1R in NCL-SG3 cells. However, intracellular signaling mechanisms by PACAP are poorly clarified. Here, we used PAC1R knockout (KO) mice and wild-type (WT) mice to observe changes in AQP5 localization and gene expression in sweat glands by PACAP treatment. Immunohistochemistry revealed that PACAP promoted the translocation of AQP5 to the lumen side in the eccrine gland via PAC1R. Furthermore, PACAP up-regulated the expression of genes (Ptgs2, Kcnn2, Cacna1s) involved in sweat secretion in WT mice. Moreover, PACAP treatment was found to down-regulate the Chrna1 gene expression in PAC1R KO mice. These genes were found to be involved in multiple pathways related to sweating. Our data provide a solid basis for future research initiatives in order to develop new therapies to treat sweating disorders.

Dynamics of Salivary Gland AQP5 under Normal and Pathologic Conditions.

AQP5 plays an important role in the salivary gland function. The mRNA and protein for aquaporin 5 (AQP5) are expressed in the acini from embryonic days E13-16 and E17-18, respectively and for entire postnatal days. Ligation-reopening of main excretory duct induces changes in the AQP5 level which would give an insight for mechanism of regeneration/self-duplication of acinar cells. The AQP5 level in the submandibular gland (SMG) decreases by chorda tympani denervation (CTD) via activation autophagosome, suggesting that its level in the SMG under normal condition is maintained by parasympathetic nerve. Isoproterenol (IPR), a ß-adrenergic agonist, raised the levels of membrane AQP5 protein and its mRNA in the parotid gland (PG), suggesting coupling of the AQP5 dynamic and amylase secretion-restoration cycle. In the PG, lipopolysaccharide (LPS) is shown to activate mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signalings and potentially downregulate AQP5 expression via cross coupling of activator protein-1 (AP-1) and NF-κB. In most species, Ser-156 and Thr-259 of AQP5 are experimentally phosphorylated, which is enhanced by cAMP analogues and forskolin. cAMP-dependent phosphorylation of AQP5 does not seem to be markedly involved in regulation of its intracellular trafficking but seems to play a role in its constitutive expression and lateral diffusion in the cell membrane. Additionally, Ser-156 phosphorylation may be important for cancer development.

Parasympathectomy increases resting secretion of the submandibular gland in minipigs in the long term.

Parasympathectomy leads to retrogressive alteration and dysfunction of the submandibular gland (SMG) within 1 month, but its long-term effect is unclear. Excessive secretion is observed in half of the patients 4-6 months after SMG transplantation, which completely denervates the gland. Here, we investigated the long-term effect of parasympathectomy on the secretion of SMGs in minipigs. The results showed that the resting salivary secretion of SMGs decreased by 82.9% of that in control at 2 months after denervation, but increased by 156% at 6 months. Although experiencing an atrophic period, the denervated glands regained their normal morphology by 6 months. The expression of the function-related proteins, including muscarinic acetylcholine receptor (mAChR) 3, aquaporin 5 (AQP5), tight junction protein claudin-3, and claudin-4 was decreased at 2 months after denervation. Meanwhile, the protein expression of stem cell markers, including sex-determining region Y-box 2 and octamer-binding transcription factor 4, and the number of Ki67+ cells were significantly increased. However, at 6 months after denervation, the expression of mAChR3, AQP5, claudin-1, claudin-3, and claudin-4 was significantly raised, and the membrane distribution of these proteins was increased accordingly. The autonomic axonal area of the glands was reduced at 2 months after denervation but returned to the control level at 6 months, suggesting that reinnervation took place in the long term. In summary, parasympathectomy increases resting secretion of the SMGs in the long term with a possible mechanism involving improved transepithelial fluid transport. This finding may provide a new strategy for xerostomia treatment.

Dachengqi decoction alleviates acute lung injury and inhibits inflammatory cytokines production through TLR4/NF-κB signaling pathway in vivo and in vitro.

BACKGROUND AND OBJECTIVES: Sepsis that arises from uncontrolled pulmonary inflammation could induce acute lung injury (ALI), leading to the high death rate. Dachengqi decoction (DCQD) is a common traditional Chinese herbal medicine with strong anti-inflammatory effects. The current study aimed to explore the effect of DCQD on the inflammatory cytokines production, the aquaporin-1 (AQP-1) and AQP-5 protein expression in lipopolysaccharide (LPS)-induced ALI models, and the potential mechanisms underlying its effects. METHODS: Sprague-Dawley rats and HULEC-5a cells were used as study models in the research. To detect related molecules in the study, the real-time polymerase chain reaction analysis, cell counting kit-8 assay, Western blot analysis, and enzyme-linked immunosorbent assay were performed. RESULTS: DCQD could inhibit the expression of LPS-induced inflammatory cytokines, including interleukin-6 (IL-6), IL-8, and tumor necrosis factor-α (TNF-α), in lung tissues and could reduce pulmonary edema by upregulating the expression of AQP-1 and AQP-5 in rats with LPS-induced ALI. Moreover, the results suggested that the toll-like receptor 4 (TLR4)/NF-κB signaling is indispensable for DCQD to increase the expression of AQP-1 and AQP-5 and inhibits the production of IL-6, IL-8, and TNF-α in LPS-induced HULEC-5a cells. CONCLUSION: The results of our study suggested that DCQD suppresses the TLR4/NF-κB signaling pathway, increases the protein expression of AQP-1 and AQP-5, and inhibits the production of inflammatory cytokines, by which it may alleviate the inflammatory reactions in ALI and benefit the treatments.

AQP5 promotes hepatocellular carcinoma metastasis via NF-κB-regulated epithelial-mesenchymal transition.

Aquaporin 5 (AQP5), a transmembrane protein, is known for its involvement in the progress of many diseases such as chronic kidney disease and systemic disease. Recently, AQP5 has been reported to play an important role in cancer progression. However, little is known about its precise functions in hepatocellular carcinoma (HCC). This study aimed to investigate the specific role of AQP5 in HCC. The results showed that AQP5 was highly expressed in HCC cell lines and its down-regulation inhibited HCC cell invasion and tumor metastasis in vitro and in vivo. In addition, down-regulation of AQP5 suppressed the epithelial-mesenchymal transition (EMT) process in HCC cells by modulating EMT-related molecules such as E-cadherin, α-catenin, N-cadherin and Vimentin. Further studies on corresponding mechanisms indicated that AQP5 down-regulation inhibited HCC metastasis and EMT partly via inactivation of the NF-κB signaling pathway. Taken together, these findings suggest that AQP5 may be a potential therapeutic target for HCC.

Down-regulated expression of AQP5 on lung in rat DIC model induced by LPS and its effect on the development of pulmonary edema.

Disseminated intravascular coagulation (DIC) is an acquired syndrome characterized by the widespread activation of coagulation, which leads to failure of multiple organs in the body. DIC of rat with lipopolysaccharide (LPS) is associated with subsequent pulmonary edema. Lung tissue is highly water permeable and expresses several aquaporins (AQPs). We therefore explored whether AQP5 involved in the pathogenesis of LPS-induced lung edema. The rats were intravenously infused with LPS (30 mg/kg) for 4 h, 6 h, 8 h, 10 h, and 12 h to induce DIC. Platelets count (PLT), D-Dimer (DD), fibrinogen (FIB), prothrombin time (PT), and activated partial thromboplastin time (APTT) were determined. Real-time quantitative PCR and Western blot were used to analyze the mRNA and protein expression of AQP5. Lung samples were stained with hematoxylin-eosin and lung wet/dry weight (W/D) ratios were measured. Here, we demonstrated that PLT and FIB values were significant decreased, the values for DD, PT, and APTT were marked increased, microthrombus was observed in lung specimens, and simultaneously with the AQP5 showed down-regulated expression following LPS infused from 4 h to 12 h. However, histopathological changes such as pulmonary edema and the increased lung W/D weight ratio were observed after LPS infused from 6 h to 12 h. These results indicated that the decreased expression of AQP5 maybe induce liquid transport obstacles between alveolar and capillary, and provides the report of AQP5 gene regulation, revealing the pathogenesis of pulmonary edema in DIC model of rat.

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.

Integrated Single-Cell RNA-Sequencing Analysis of Aquaporin 5-Expressing Mouse Lung Epithelial Cells Identifies GPRC5A as a Novel Validated Type I Cell Surface Marker.

Molecular and functional characterization of alveolar epithelial type I (AT1) cells has been challenging due to difficulty in isolating sufficient numbers of viable cells. Here we performed single-cell RNA-sequencing (scRNA-seq) of tdTomato+ cells from lungs of AT1 cell-specific Aqp5-Cre-IRES-DsRed (ACID);R26tdTomato reporter mice. Following enzymatic digestion, CD31-CD45-E-cadherin+tdTomato+ cells were subjected to fluorescence-activated cell sorting (FACS) followed by scRNA-seq. Cell identity was confirmed by immunofluorescence using cell type-specific antibodies. After quality control, 92 cells were analyzed. Most cells expressed 'conventional' AT1 cell markers (Aqp5, Pdpn, Hopx, Ager), with heterogeneous expression within this population. The remaining cells expressed AT2, club, basal or ciliated cell markers. Integration with public datasets identified three robust AT1 cell- and lung-enriched genes, Ager, Rtkn2 and Gprc5a, that were conserved across species. GPRC5A co-localized with HOPX and was not expressed in AT2 or airway cells in mouse, rat and human lung. GPRC5A co-localized with AQP5 but not pro-SPC or CC10 in mouse lung epithelial cell cytospins. We enriched mouse AT1 cells to perform molecular phenotyping using scRNA-seq. Further characterization of putative AT1 cell-enriched genes revealed GPRC5A as a conserved AT1 cell surface marker that may be useful for AT1 cell isolation.

Effect of dobutamine on lung aquaporin 5 in endotoxine shock-induced acute lung injury rabbit.

BACKGROUND: Dobutamine, a commonly used vasoactive drug, has been reported to reduce pulmonary edema and protect against acute lung injury (ALI) by up-regulating aquaporin 5 (AQP5) expressions. However, the underlying mechanism is still elusive. METHODS: ALI was induced by intravenous injection of LPS. Seventy male New Zealand white rabbits were randomly divided into seven groups: sham group, ALI group, dobutamine low-dose group [group ALI + Dob (L)], dobutamine medium-dose group [group ALI + Dob (M)], dobutamine high-dose group [group ALI + Dob (H)], ALI + Dob (H) + ICI group and sham + ICI group. ICI 118,551, a potent and specific beta-2 antagonist, could block the effect of dobutamine. The animals were sacrificed at 3 h after endotoxic shock and lungs were removed. The arterial blood gas was analyzed. The lung wet to dry (W/D) ratio was determined. The level of cyclic AMP (cAMP) in lung tissue was assessed by ELISA. The expression of AQP5 protein was determined by western blotting and immunohistochemistry. The pathological alteration in lung tissue was evaluated by optical microscopy and electron microscope, and lung injury score was assessed. RESULTS: Dobutamine increased AQP5 protein expression and cAMP level in a dose-dependent manner. Meanwhile, the degree of lung pathological and ultrastructural lesion was ameliorated and arterial blood gas was improved obviously. Additionally, W/D ratio and histological scores decreased significantly. However, the AQP5 protein expression and cAMP level were significantly decreased in group ALI + Dob (H) + ICI than that in group ALI + Dob (H), the degree of lung pathological and ultrastructural lesion was more serious in group ALI + Dob (H) + ICI than that in group ALI + Dob (H) and the arterial blood gas was not obviously improved. CONCLUSIONS: These results suggested that protective effect of dobutamine against endotoxin shock-induced ALI may be due to its ability of up-regulating AQP5 protein expression via increasing intracellular cAMP concentration.

Effects of repeated administration of pilocarpine and isoproterenol on aquaporin-5 expression in rat salivary glands.

Aquaporins are water channel proteins which enable rapid water movement across the plasma membrane. Aquaporin-5 (AQP5) is the major aquaporin and is expressed on the apical membrane of salivary gland acinar cells. We examined the effects of repeated administration of pilocarpine, a clinically useful stimulant for salivary fluid secretion, and isoproterenol (IPR), a stimulant for salivary protein secretion, on the abundance of AQP5 protein in rat salivary glands by immunofluorescence microscopy and semi-quantitative immunoblotting. Unexpectedly AQP5 was decreased in pilocarpine-administered salivary glands, in which fluid secretion must be highly stimulated, implying that AQP5 might not be required for fluid secretion at least in pilocarpine-administered state. The abundance of AQP5, on the other hand, was found to be significantly increased in IPR-administered submandibular and parotid glands. To address the possible mechanism of the elevation of AQP5 abundance in IPR-administered animals, changes of AQP5 level in fasting animals, in which the exocytotic events are reduced, were examined. AQP5 was found to be decreased in fasting animals as expected. These results suggested that the elevation of cAMP and/or frequent exocytotic events could increase AQP5 protein. AQP5 expression seems to be easily changed by salivary stimulants, although these changes do not always reflect the ability in salivary fluid secretion.