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

Primary Sjögren's syndrome: new perspectives on salivary gland epithelial cells

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease primarily affecting exocrine glands such as the salivary glands, leading to impaired secretion and sicca symptoms. As the mainstay of salivation, salivary gland epithelial cells (SGECs) have an important role in the pathology of pSS. Emerging evidence suggests that the interplay between immunological factors and SGECs may not be the initial trigger or the sole mechanism responsible for xerostomia in pSS, challenging conventional perceptions. To deepen our understanding, current research regarding SGECs in pSS was reviewed. Among the extensive aberrations in cellular architecture and function, this review highlighted certain alterations of SGECs that were identified to occur independently of or in absence of lymphocytic infiltration. In particular, some of these alterations may serve as upstream factors of immuno-inflammatory responses. These findings underscore the significance of introspecting the pathogenesis of pSS and developing interventions targeting SGECs in the early stages of the disease.

Efficient generation of a stable CHO-K1 cell line overexpressing the human water channel aquaporin-5 as tool to generate therapeutic antibodies

Aquaporins (AQPs) are a family of water permeable channels expressed on the plasma membrane with AQP5 being the major channel expressed in several human tissues including salivary and lacrimal glands. Anti-AQP5 autoantibodies have been observed in patients with Sjögren's syndrome who are characterised by dryness of both salivary and lacrimal glands, and they have been implicated in the underlying mechanisms of glandular dysfunction. AQP5 is formed by six transmembrane helices linked with three extracellular and two intracellular loops. Develop antibodies against membrane protein extracellular loops can be a challenge due to the difficulty in maintaining these proteins as recombinant in their native form. Therefore, in this work we aimed to generate an efficient stable-transfected cell line overexpressing human AQP5 (CHO-K1/AQP5) to perform primarily cell-based phage display biopanning experiments to develop new potential recombinant antibodies targeting AQP5. We also showed that the new CHO-K1/AQP5 cell line can be used to study molecular mechanisms of AQP5 sub-cellular trafficking making these cells a useful tool for functional studies.

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.

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.

Botulinum toxin type a blocks aquaporin 5 trafficking by decreasing synaptosomal-associated protein 23 in submandibular acinar cells

The trafficking of aquaporin 5 (AQP5) is critical for salivary secretion. Synaptosomal-associated protein 23 (SNAP23) is an important regulator in the process of membrane fusion. However, the role of SNAP23 on AQP5 trafficking has not been explored. Botulinum toxin type A (BoNT/A) is a bacterial toxin that effectively treats sialorrhea. We previously reported that BoNT/A induced AQP5 redistribution in cultured acinar cells, but the mechanism remained unclear. In this study, SNAP23 was predominantly localized to the plasma membrane of acinar cells in the rat submandibular gland (SMG) and colocalized with AQP5 at the apical membrane of acinar cells. In stable GFP-AQP5-transfected SMG-C6 cells, the acetylcholine receptor agonist carbachol (CCh) induced trafficking of AQP5 from intracellular vesicles to the apical membrane. Furthermore, SNAP23 knockdown by siRNA significantly inhibited CCh-induced AQP5 trafficking, whereas this inhibitory effect was reversed by SNAP23 re-expression, indicating that SNAP23 was essential in AQP5 trafficking. More importantly, BoNT/A inhibited salivary secretion from SMGs, and the underlying mechanism involved that BoNT/A blocked CCh-triggered AQP5 trafficking by decreasing SNAP23 in acinar cells. Taken together, these results identified a crucial role for SNAP23 in AQP5 trafficking and provided new insights into the mechanism of BoNT/A in treating sialorrhea and thereby a theoretical basis for clinical applications.

Associations between neuromyelitis optica spectrum disorder, Sjögren's syndrome, and conditions with electrolyte disturbances

OBJECTIVE

Electrolyte disorders are among the important conditions negatively affecting the disease course of neuromyelitis optica spectrum disorder (NMOSD). Possible mechanisms may include renal tubular acidosis (RTA) accompanying Sjögren's syndrome (SS), syndrome of inappropriate antidiuretic hormone secretion (SIADH), and central diabetes insipidus (DI). Currently, the overlap profiles between these conditions remain uncertain.

METHODS

This cross-sectional study collected data from the nationwide administrative Diagnosis Procedure Combination (DPC) database and evaluated the overlap profiles.

RESULTS

Among the 28,285,908 individuals from 1203 DPC-covered hospitals, 8477 had NMOSD, 174108 had SS, 4977 had RTA, 7640 had SIADH, and 24,789 had central DI. Of those with NMOSD, 986 (12%) had SS. The odds ratio (OR) for a diagnosis of NMOSD in those with SS compared with those without was 21 [95% confidence interval (CI), 20-23]. Overlap between NMOSD and SS was seen both in males (OR, 28 [95% CI, 23-33]) and females (OR, 16 [15-17]) and was more prominent in the younger population. Among patients with SS, the prevalence of RTA was lower in patients with NMOSD compared with those without NMOSD. Patients with NMOSD showed a higher prevalence of SIADH (OR, 11 [7.5-17]; p < 0.0001) and DI (OR, 3.7 [2.4-5.3]; p < 0.0001). Comorbid SS in NMOSD was associated with a higher prevalence of DI.

CONCLUSIONS

Patients with NMOSD are likely to have SS, SIADH, and central DI. RTA in SS does not facilitate the overlap between NMOSD and SS. SS in NMOSD may predispose patients to DI.

Hyperosmolar environment and salivary gland epithelial cells increase extra-cellular matrix remodeling and lymphocytic infiltration in Sjögren's syndrome

Salivary gland epithelial cells (SGECs) play an active role in primary Sjogren's syndrome (pSS) pathogenesis. Quantitative and qualitative abnormalities of saliva might expose SGECs to chronic hyperosmolarity. We aimed to decipher the links between hyperosmolar stimulation of SGECs and lymphocytic infiltration of the salivary glands (SG) observed in pSS. RNAseq was performed on NS-SV-AC cells stimulated with hyperosmolar media containing NaCl (100 mM) or sucrose (200 mM), or with iso-osmolar (Iso) medium. RNAseq was performed on primary cultured SGECs from pSS and controls, in the presence or not of B cells. Hyperosmolar stimulation of NS-SV-AC-cells identified an upregulation of interferon-induced (MX1, IFIT2) and MMPs genes. Enrichment analysis revealed an over-representation of fibrosis pathway. In parallel, RNAseq of SGECs comparing pSS to controls identified an over-representation of a pathway involving MMPs. Given the unexpected upregulation of collagen (COL3A1, COL1A2) and ADAMTS genes in pSS SGECs, we hypothesized that SGECs might undergo epithelial-mesenchymal transition. ZEB2 was upregulated and SLUG was down regulated in SGECs from pSS versus controls. MMP24 and ZEB2 were higher in SGECs from pSS with a focus score ≥1 versus <1. Lastly, SGECs cocultured with B cells expressed higher levels of COL1A2. These results suggest the existence of a vicious circle. Alteration of SGECs in pSS participates in the establishment of a hyperosmolar microenvironment, which in turn promotes SGECs transcriptomic modifications. These modifications include extracellular matrix remodeling and promote SG lymphocytic infiltration.

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.

Isolated adrenocorticotropic hormone deficiency and sialadenitis associated with nivolumab: a case report

BACKGROUND

Immune checkpoint inhibition with anti-PD(L)1 and anti-CTLA4 antibodies has significantly changed cancer treatment during the last 10 years. Nevertheless, boosting the immune system with immune checkpoint inhibition can result in immune-related adverse events, affecting different organ systems, among which the endocrine system is the most affected. However, there are few descriptions of the association of immune-related adverse events, and the pathophysiology of some is still lacking. Here, we report a 70-year-old Caucasian patient treated with nivolumab (anti-PD1 monoclonal antibody) after resection of a unique relapse of melanoma in the neck region who presented with sicca syndrome, extreme fatigue, and weight loss 6 months after the start of anti-PD1 therapy. Blood tests revealed hypoglycemia and secondary hypocortisolism due to isolated adrenocorticotrophic hormone deficiency. Interestingly, brain methionine positron emission tomography/magnetic resonance revealed physiological metabolism of the pituitary gland, which was not increased in size, and no hypophyseal metastasis was detected. The sicca syndrome investigation revealed the absence of anti-SSA/SSB antibodies, while the labial salivary gland biopsy showed lymphoplasmatocytic infiltrates with a focus score of 1. To provide new insights into the physiopathology of the anti-PD1-related sialadenitis, we investigated the distribution of aquaporins 5 by immunostaining on the labial salivary gland acini, and compared this distribution with the one expressed in the primary Sjögren's syndrome. Contrary to patients with primary Sjögren's syndrome (in whom aquaporins 5 is mainly expressed at the basolateral side), but similar to the patients with no sialadenitis, we observed expression of aquaporins 5 at the apical pole. This new finding deserves to be confirmed in other patients with anti-PD1-related sialadenitis. Owing to these immune-related adverse events, anti-PD1 was stopped; nevertheless, the patient developed a new relapse 1 year later (March 2020) in the neck region, which was treated by radiotherapy. Since then, no relapse of melanoma was seen (1.5 years after radiotherapy), but the patient still requires hypophyseal replacement therapy. The sialoadenitis resolved partially.

CONCLUSION

We report a combination of sialoadenitis and hypophysitis explaining extreme fatigue in a patient who was treated in the adjuvant setting with anti-PD1 for a melanoma relapse.

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.

Ocular Surface Ion-Channels Are Closely Related to Dry Eye: Key Research Focus on Innovative Drugs for Dry Eye

Abundant ion-channels, including various perceptual receptors, chloride channels, purinergic receptor channels, and water channels that exist on the ocular surface, play an important role in the pathogenesis of dry eye. Channel-targeting activators or inhibitor compounds, which have shown positive effects in in vivo and in vitro experiments, have become the focus of the dry eye drug research and development, and individual compounds have been applied in clinical experimental treatment. This review summarized various types of ion-channels on the ocular surface related to dry eye, their basic functions, and spatial distribution, and discussed basic and clinical research results of various channel receptor regulatory compounds. Therefore, further elucidating the relationship between ion-channels and dry eye will warrant research of dry eye targeted drug therapy.

Recent breakthroughs and future directions in drugging aquaporins

Aquaporins facilitate the passive transport of water, solutes, or ions across biological membranes. They are implicated in diverse pathologies including brain edema following stroke or trauma, epilepsy, cancer cell migration and tumor angiogenesis, metabolic disorders, and inflammation. Despite this, there is no aquaporin-targeted drug in the clinic and aquaporins have been perceived to be intrinsically non-druggable targets. Here we challenge this idea, as viable routes to inhibition of aquaporin function have recently been identified, including targeting their regulation or their roles as channels for unexpected substrates. Identifying new drug development frameworks for conditions associated with disrupted water and solute homeostasis will meet the urgent, unmet clinical need of millions of patients for whom no pharmacological interventions are available.

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.

Tetrahedral Framework Nucleic Acids Reestablish Immune Tolerance and Restore Saliva Secretion in a Sjögren's Syndrome Mouse Model

As one of the most frequent autoimmune diseases, Sjogren's syndrome (SS) is characterized by overactive lymphocytic infiltration in the exocrine glands, with ensuing dry mouth and dry eyes. Unfortunately, so far, there are no appropriate therapies without causing overall immunosuppression. Tetrahedral framework nucleic acids (tFNAs) were regarded as promising nanoscale materials whose immunomodulatory capabilities have already been verified. Herein, we reveal, for the first time, that tFNAs were utilized to treat SS in female nonobese diabetic (NOD) mice, the animal model used for SS. We proved a 250 nM tFNA treatment was successful in suppressing inflammation and stimulating saliva secretion in NOD mice. Specialised proteins for the secretory function and structure of acinar cells in submandibular glands (SMGs) were restored. It has been the permanent goal for SS treatment to establish immune tolerance and stop disease development. Surprisingly, tFNA treatment guided T cells toward regulatory T cells (Tregs), while suppressing T helper (Th) cell responses. Th cells include Th1, Th17, and follicular helper T (Tfh) cells. Tregs are highly significant in immune tolerance. Inducing Tregs is a promising approach to reestablish immune tolerance. Comparable results were also observed in B cell responses. Reductions in the percentage of germinal center (GC) B cells and plasma cells were detected, and a marked increase in the percentage of regulatory B cells (Bregs) was also noticed. The mechanisms of inducing Tregs may associated with cytokine changes. Changes of T cell subsets, especially changes of Tfh, may influence the differentiation of B cells accordingly. Collectively, our results demonstrated the immunomodulatory capacities of tFNAs once again, which may provide a novel, safe, and effective option for the treatment of SS and other autoimmune diseases.

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.

Musculoskeletal Manifestations in Sjogren's Syndrome: An Orthopedic Point of View

Sjogren's syndrome (SS) is a frequent entity with a broad symptomatology spectrum, mainly affecting the salivary and lachrymal glands. The disease also affects the musculoskeletal system targeting bones, specific joints, muscles, and the peripheral nerve system. Disease related clinical manifestations canhave an accumulative impact, as the syndrome is commonly associated with other rheumatic diseases. A literature review was performed with the aim to assess the in-depth association of Sjogren's syndrome and its treatment agents with the musculoskeletal system and further investigate its potential relevance with common orthopedic postoperative complications.

Aquaporins and diseases pathogenesis: From trivial to undeniable involvements, a disease-based point of view

Aquaporins (AQPs), as transmembrane proteins, were primarily identified as water channels with the ability of regulating the transmission of water, glycerol, urea, and other small-sized molecules. The classic view of AQPs involvement in therapeutic plan restricted them and their regulators into managing only a narrow spectrum of the diseases such as diabetes insipidus and the syndrome of inappropriate ADH secretion. However, further investigations performed, especially in the third millennium, has found that their cooperation in water transmission control can be manipulated to handle other burden-imposing diseases such as cirrhosis, heart failure, Meniere's disease, cancer, bullous pemphigoid, eczema, and Sjögren's syndrome.

Insulin on changes in expressions of aquaporin-1, aquaporin-5, and aquaporin-8 in submandibular salivary glands of rats with Streptozotocin-induced diabetes

OBJECTIVE

This study aimed to explore the relationship between diabetic xerostomia and changes in aquaporin-1 (AQP1), aquaporin-5 (AQP5), and aquaporin-8 (AQP8) expression in the submandibular glands (SMGs), to further study the pathogenesis of diabetic xerostomia and to observe the therapeutic effect of insulin (INS).

METHODS

Thirty SD rats were randomized equally into 3 groups: control group, diabetic model (DM) group and insulin (INS) group (n=10, respectively). The control group received no treatment. DM group and INS group were induced by a high-fat diet and streptozotocin intraperitoneal injection. After establishment of a diabetic rat model, the rats in INS group were treated with insulin. Then all rats were fed continuously with ordinary diet for 2 months. H&E staining was used to describe morphologic changes in the SMGs of rats. Immunohistochemistry was used to analyze the expressions and localization of AQP1, AQP5, and AQP8 in the SMGs. Computer image analysis was used to detect the mean optical density (MOD) values of AQP1, AQP5, and AQP8 expression, and changes in the diameters of acini and ducts.

RESULTS

The acini were mildly atrophied and the acinar cells were rearranged in an irregular way. The morphology of insulin-administered diabetic SMGs was similar to that of the control group. The acinar average circumference and GCT average diameter in DM group were significantly reduced (P<0.05). The acinar average circumference and GCT average diameter of INS group were significantly increased (P<0.05). The expressions of AQP1, AQP5, and AQP8 were significantly reduced in DM group (P<0.05). The expressions of AQP1, AQP5, and AQP8 in INS group were significantly increased (P<0.05).

CONCLUSION

The decreased expressions of AQP1, AQP5, and AQP8 led to decreased salivary secretion of SMGs in diabetic rats, which may be involved in the pathogenesis of diabetic xerostomia. Insulin could up-regulate the expressions of AQP1, AQP5 and AQP8, and play a protective role in the secretory function of diabetic SMGs.

Traditional Chinese medicine is a useful and promising alternative strategy for treatment of Sjogren's syndrome: A review

Primary Sjogren's syndrome (pSS) is a chronic autoimmune disease involving exocrine glands. Current studies have found that the occurrence of the disease is closely related to genetic, environmental and neuroendocrine factors, as well as abnormal activation of T and B lymphocytes. The etiology and pathogenesis of pSS is complex, and there is a lack of specific targeted drugs. Traditional Chinese medicines (TCMs) have been comprehensively investigated for their treatment effects on pSS. Through a systematic review of the literature, we summarized the TCMs used to treat pSS, and find that there are four major ways that TCMs are used, including upregulation of aquaporin proteins, suppression of cell apoptosis, suppression of the abnormal activation of B lymphocytes and suppression of the abnormal activation of T lymphocytes (balancing T helper type [Th]1/Th2 & Th17/Treg and suppressing follicular helper T [Tfh] cells). However, there are not enough data about the active constituents, quality control, pharmacokinetics, toxicity and modern preparations of these TCMs; therefore, more investigations are needed. This paper highlights the importance of TCMs for treating pSS and provides guidance for future investigations.

Early diagnosis and treatment for Sjögren's syndrome: current challenges, redefined disease stages and future prospects

There are some challenges and unmet needs in the early diagnosis and management of Sjögren's syndrome (SjS) such as prominent glandular dysfunction at diagnosis and long diagnostic delay. Those challenges are partly attributed to the lack of a good knowledge of the early stages of SjS, which is a major obstacle to delivering appropriate care to SjS patients. Findings from both clinical and experimental studies suggest the plausibility of a redefined SjS course consisting of 4 stages, which includes initiation stage, preclinical stage, asymptomatic SjS stage and overt SjS stage. More studies focusing on the pathological processes and changes during the early stages of SjS are needed. To enable early diagnosis and treatment for SjS, more useful biomarkers of the early stages of SjS need to be identified, and individuals at high risk of SjS development need to be identified. Appropriate screening can be performed to facilitate the early diagnosis of SjS among those high-risk individuals.

Can Gut Microbiota Affect Dry Eye Syndrome?

Using metagenomics, continuing evidence has elicited how intestinal microbiota trigger distant autoimmunity. Sjögren's syndrome (SS) is an autoimmune disease that affects the ocular surface, with frequently unmet therapeutic needs requiring new interventions for dry eye management. Current studies also suggest the possible relation of autoimmune dry eye with gut microbiota. Herein, we review the current knowledge of how the gut microbiota interact with the immune system in homeostasis as well as its influence on rheumatic and ocular autoimmune diseases, and compare their characteristics with SS. Both rodent and human studies regarding gut microbiota in SS and environmental dry eye are explored, and the effects of prebiotics and probiotics on dry eye are discussed. Recent clinical studies have commonly observed a correlation between gut dysbiosis and clinical manifestations of SS, while environmental dry eye portrays characteristics in between normal and autoimmune. Moreover, a decrease in both the Firmicutes/Bacteroidetes ratio and genus Faecalibacterium have most commonly been observed in SS subjects. The presumable pathways forming the "gut dysbiosis-ocular surface-lacrimal gland axis" are introduced. This review may provide perspectives into the link between the gut microbiome and dry eye, enhance our understanding of the pathogenesis in autoimmune dry eye, and be useful in the development of future interventions.

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.

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.

Aquaporin3 (AQP3) expression in oral epithelium in oral lichen planus

Lichen Planus is an autoimmune disease of skin and mucous membranes, including oral mucosa and genital organs, with the potential to undergo a malignant transformation. Xerostomia and the salivary gland hypofunction are common manifestations and complications in oral lichen planus (OLP), whose exact cause has not been well defined yet. Aquaporins (AQP) are a family of membrane channel cell proteins which play an important role in the intercellular water permeability. This study for the first time compares the expression of the aquaporin-3 (AQP3) gene in oral tissues of a group of OLP patients and a control group. In this study, 30 OLP patients and 30 healthy individuals were selected. The expression of AQP3 gene was measured using Real-Time PCR method. The expression of the gene in the OLP patients was more than the control group. It could be argued that decreased salivation increases the level of expression of the AQP3 gene in an effort to compensate for this deficiency and prevent the onset of xerostomia (compensatory up-regulation).

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.

Mechanisms of Disease in Sjögren Syndrome-New Developments and Directions

Sjögren Syndrome (SS) is an autoimmune disease that affects the exocrine glands, mainly salivary and lacrimal glands [...].

Distinct expression patterns of aquaporin 3 and 5 in ductal and alveolar epithelial cells in mouse mammary glands before and after parturition

Milk osmolarity maintains an isotonic status for suckling infants during lactation. However, it remains unclear how the water content in milk is regulated in lactating mammary glands. In lactating mammary alveoli and ducts, mammary epithelial cells (MECs) are in direct contact with milk. In this study, we focus on two types of water channels, aquaporin 3 (AQP3) and AQP5, in alveolar and ductal MECs before and after parturition. AQP3 showed diffuse localization in the cytoplasm of ductal MECs but concentrated localization in the basolateral membrane of alveolar MECs during the late pregnancy and lactation periods. Translocation of AQP5 from the cytoplasm toward the apical membrane occurred in ductal MECs immediately before parturition. Subsequently, we examined the hormonal influences on the expression of AQP3 and AQP5 in cultured MECs in vitro. Progesterone and estrogen distinctly increased AQP3 and AQP5 in cultured MECs, respectively. Cotreatment with prolactin and dexamethasone significantly decreased both AQP3 and AQP5. Prolactin also facilitated the translocation of AQP5 into the apical membrane of MECs. In cultured MECs, AQP3 was homogeneously expressed in MECs, whereas AQP5 showed different expression levels between MECs regardless of the hormonal treatment. Different activation states of the prolactin/STAT5 pathway were also observed between ductal and alveolar MECs. These findings suggest that the expression pattern of AQP3 and AQP5 is distinctly regulated by lactogenic hormones in alveolar and ductal MECs before and after parturition. AQP5 expressed in ductal MECs may function as a water channel to regulate milk osmolarity in mice.

Associations of Anti-Aquaporin 5 Autoantibodies with Serologic and Histopathological Features of Sjögren's Syndrome

Biomarkers to stratify the complex and heterogeneous phenotypes of Sjogren's syndrome (SS) are needed. We aimed to validate the prevalence of anti-aquaporin 5 (AQP5) IgG in a non-Korean cohort and to optimize the method to screen the anti-AQP5 IgG. The study cohort included 111 primary SS and 43 non-SS Sjögren's International Collaborative Clinical Alliance (SICCA) controls that were obtained from the Sjögren's International Collaborative Clinical Alliance registry, in addition to 35 systemic lupus erythematosus (SLE) and 35 rheumatoid arthritis (RA) phenotypes. Anti-AQP5 IgG was screened by cell-based immunofluorescence cytochemistry (CB-IFC) assay in the absence or presence of epitope peptides, as well as by ELISA using the epitope peptides as coated antigens. Anti-AQP5 IgG specific to an E1 epitope was best at discriminating between SS and non-SS, and the two different methods (CB-IFC and ELISA) presented comparable performance in diagnostic accuracy (0.690 vs. 0.707). Notably, the SLE and RA groups had substantially lower levels of anti-AQP5 IgG than the SS group. In addition, the presence of anti-AQP5_E1 IgG was associated with serologic and histopathological features of SS. In conclusion, a similar prevalence of anti-AQP5 IgG was confirmed in a non-Korean cohort. Screening anti-AQP5 autoantibodies may help to form subgroups of SS for targeted therapy.

Mesenchymal Stem Cells Extract (MSCsE)-Based Therapy Alleviates Xerostomia and Keratoconjunctivitis Sicca in Sjogren's Syndrome-Like Disease

Sjogren’s syndrome (SS) is an autoimmune disease that manifests primarily in salivary and lacrimal glands leading to dry mouth and eyes. Unfortunately, there is no cure for SS due to its complex etiopathogenesis. Mesenchymal stem cells (MSCs) were successfully tested for SS, but some risks and limitations remained for their clinical use. This study combined cell- and biologic-based therapies by utilizing the MSCs extract (MSCsE) to treat SS-like disease in NOD mice. We found that MSCsE and MSCs therapies were successful and comparable in preserving salivary and lacrimal glands function in NOD mice when compared to control group. Cells positive for AQP5, AQP4, α-SMA, CK5, and c-Kit were preserved. Gene expression of AQP5, EGF, FGF2, BMP7, LYZ1 and IL-10 were upregulated, and downregulated for TNF-α, TGF-β1, MMP2, CASP3, and IL-1β. The proliferation rate of the glands and serum levels of EGF were also higher. Cornea integrity and epithelial thickness were maintained due to tear flow rate preservation. Peripheral tolerance was re-established, as indicated by lower lymphocytic infiltration and anti-SS-A antibodies, less BAFF secretion, higher serum IL-10 levels and FoxP3⁺ T_reg cells, and selective inhibition of B220⁺ B cells. These promising results opened new venues for a safer and more convenient combined biologic- and cell-based therapy.