Usefulness of mouse models to study the pathogenesis of Sjögren's syndrome

The involvement of aquaporin 5 in the inflammatory response of primary Sjogren's syndrome dry eye: potential therapeutic targets exploration

Sjogren's syndrome (SS) is a chronic autoimmune disease. Mainly due to the infiltration of lymphoplasmic cells into the exocrine glands, especially the salivary glands and lacrimal glands, resulting in reduced tear and saliva secretion. Reduced tear flow can trigger Sjogren's syndrome dry eye (SSDE). Although the pathophysiology of SSDE xerosis remains incompletely understood, recent advances have identified aquaporin-5 (AQP5) as a critical factor in dysregulation of the exocrine gland and epithelium, influencing the clinical presentation of SSDE through modulation of inflammatory microenvironment and tear secretion processes. This review aims to explore AQP5 regulatory mechanisms in SSDE and analyze its potential as a therapeutic target, providing new directions for SSDE treatment.

Involvement of aquaporin 5 in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease with the pathological hallmark of lymphoplasmacytic infiltration of exocrine glands - more specifically salivary and lacrimal glands - resulting in a diminished production of tears and saliva (sicca syndrome). The pathophysiology underscoring the mechanisms of the sicca symptoms in SS has still yet to be unraveled but recent advances have identified a cardinal role of aquaporin-5 (AQP5) as a key player in saliva secretion as well as salivary gland epithelial cell dysregulation. AQP5 expression and localization are significantly altered in salivary glands from patients and mice models of the disease, shedding light on a putative mechanism accounting for diminished salivary flow. Furthermore, aberrant expression and localization of AQP5 protein partners, such as prolactin-inducible protein and ezrin, may account for altered AQP5 localization in salivary glands from patients suffering from SS and are considered as new players in SS development. This review provides an overview of the role of AQP5 in SS salivary gland epithelial cell dysregulation, focusing on its trafficking and protein-protein interactions.

TAZ inhibits acinar cell differentiation but promotes immature ductal cell proliferation in adult mouse salivary glands

There are currently no treatments for salivary gland diseases, making it vital to understand signaling mechanisms operating in acinar and ductal cells so as to develop regenerative therapies. To date, little work has focused on elucidating the signaling cascades controlling the differentiation of these cell types in adult mammals. To analyze the function of the Hippo-TAZ/YAP1 pathway in adult mouse salivary glands, we generated adMOB1DKO mice in which both MOB1A and MOB1B were TAM-inducibly deleted when the animals were adults. Three weeks after TAM treatment, adMOB1DKO mice exhibited smaller submandibular glands (SMGs) than controls with a decreased number of acinar cells and an increased number of immature dysplastic ductal cells. The mutants suffered from reduced saliva production accompanied by mild inflammatory cell infiltration and fibrosis in SMGs, similar to the Sjogren's syndrome. MOB1-deficient acinar cells showed normal proliferation and apoptosis but decreased differentiation, leading to an increase in acinar/ductal bilineage progenitor cells. These changes were TAZ-dependent but YAP1-independent. Biochemically, MOB1-deficient salivary epithelial cells showed activation of the TAZ/YAP1 and β-catenin in ductal cells, but reduced SOX2 and SOX10 expression in acinar cells. Thus, Hippo-TAZ signaling is critical for proper ductal and acinar cell differentiation and function in adult mice.

Studying Sjögren's syndrome in mice: What is the best available model?

Sjögren's syndrome (SS) is a common autoimmune disease characterized by lymphocytic infiltration and destruction of exocrine glands. The disease manifests primarily in the salivary and lacrimal glands, but other organs are also involved, leading to dry mouth, dry eyes, and other extra-glandular manifestations. Studying the disease in humans is entailed with many limitations and restrictions; therefore, the need for a proper mouse model is mandatory. SS mouse models are categorized, depending on the disease emergence into spontaneous or experimentally manipulated models. The usefulness of each mouse model varies depending on the SS features exhibited by that model; each SS model has advanced our understanding of the disease pathogenesis. In this review article, we list all the available murine models which have been used to study SS and we comment on the characteristics exhibited by each mouse model to assist scientists to select the appropriate model for their specific studies. We also recommend a murine strain that is the most relevant to the ideal SS model, based on our experience acquired during previous and current investigations.

Pathophysiologic role of Interleukin-33/ST2 in Sjögren's syndrome

Interleukin-33 (IL-33) is a member of the IL-1 family and has dual functions as a nuclear factor as well as a cytokine. The pivotal role of IL-33 as an active player contributing to aberrant local and systemic damage has been highlighted in several inflammatory and autoimmune diseases. Primary Sjögren's syndrome (pSS) is an autoimmune disease characterized by dry eyes and mouth syndrome due to local dysfunctions of exocrine glands, but also accompanied with systemic manifestations. The pathophysiology of pSS has been advocated as a conjecture of activated B and T cells as well as the production of inflammatory cytokines and autoantibodies, driving epithelial tissue damage and disease progression. In pSS, IL-33 is released in the extracellular space from damaged salivary cells upon pro-inflammatory stimuli and/or dysfunction of epithelial barrier. Counter-regulatory mechanisms are initiated to limit the pro-inflammatory actions of IL-33 as portrayed by an increase in the decoy receptor for IL-33, the soluble form of ST2 (sST2). In pSS and associated diseases, the levels of IL-33 are significantly elevated in the serum or tears of patients. Mechanistically, IL-33 acts in synergy with IL-12 and IL-23 on NK and NKT cells to boost the production of IFN-γ contributing to inflammation. TNF-α, IL-1β and IFN-γ in turn further increase the activation of IL-33/ST2 pathway, thereby constituting a vicious inflammatory loop leading to disease exacerbation. IL-33/ST2 axis is involved in Sjögren's syndrome and opens new perspectives as therapeutic target of one of the culprits in the inflammatory perpetuation.

The parotid secretory protein BPIFA2 is a salivary surfactant that affects lipopolysaccharide action

NEW FINDINGS

What is the central question of this study? The salivary protein BPIFA2 binds lipopolysaccharide, but its physiological function is not known. This study uses a new knockout mouse model to explore the physiological role of BPIFA2 in the oral cavity and systemic physiology. What is the main finding and its importance? BPIFA2 is a crucial surfactant in mouse saliva. In its absence, saliva exhibits the surface tension of water. Depletion of BPIFA2 affects salivary and ingested lipopolysaccharide and leads to systemic sequelae that include increased insulin secretion and metabolomic changes. These results suggest that the lipopolysaccharide-binding activity of BPIFA2 affects the activity of ingested lipopolysaccharide in the intestine and that BPIFA2 depletion causes mild metabolic endotoxaemia.

ABSTRACT

Saliva plays important roles in the mastication, swallowing and digestion of food, speech and lubrication of the oral mucosa, antimicrobial and anti-inflammatory activities, and the control of body temperature in grooming animals. The salivary protein BPIFA [BPI fold containing family A member 2; former names: parotid secretory protein (PSP), SPLUN2 and C20orf70] is related to lipid-binding and lipopolysaccharide (LPS)-binding proteins expressed in the mucosa. Indeed, BPIFA2 binds LPS, but the physiological role of BPIFA2 remains to be determined. To address this question, Bpifa2 knockout (Bpifa2^{tm1(KOMP)Vlcg} ) (KO) mice were phenotyped, with emphasis on the saliva and salivary glands. Stimulated whole saliva collected from KO mice was less able to spread on a hydrophobic surface than wild-type saliva, and the surface tension of KO saliva was close to that of water. These data suggest that BPIFA2 is a salivary surfactant that is mainly responsible for the low surface tension of mouse saliva. The reduced surfactant activity of KO saliva did not affect consumption of dry food or grooming, but saliva from KO mice contained less LPS than wild-type saliva. Indeed, mice lacking BPIFA2 responded to ingested LPS with an increased stool frequency, suggesting that BPIFA2 plays a role in the solubilization and activity of ingested LPS. Consistent with these findings, BPIFA2-depleted mice also showed increased insulin secretion and metabolomic changes that were consistent with a mild endotoxaemia. These results support the distal physiological function of a salivary protein and reinforce the connection between oral biology and systemic disease.

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.

MyD88 signaling causes autoimmune sialadenitis through formation of high endothelial venules and upregulation of LTβ receptor-mediated signaling

Autoimmune sialadenitis (AS), chronic inflammation of the salivary glands (SGs) with focal lymphocyte infiltration, appears in autoimmune diseases such as Sjӧgren’s syndrome. The pathological role of MyD88-dependent innate immune signaling in autoimmune diseases including AS has been studied using mouse models, such as NOD mice. Although AS development in NOD mice was reported to be suppressed by Myd88 deficiency, its specific role remains unclear. Here, we determined the potent suppressive effects of Myd88 deficiency on AS development in lupus-prone B6/lpr mice, which have lymphoproliferation abnormalities, and also in NOD mice, which have no lymphoproliferation abnormalities. This indicates that MyD88 signaling triggers AS through both lymphoproliferation-dependent and -independent mechanisms. To address the MyD88-dependent lymphoproliferation-independent AS manifestation, SGs from C57BL/6 mice were analyzed. Remarkable upregulation of Glycam1 and high endothelial venule (HEV)-associated changes were unexpectedly found in Myd88^+/+ mice, compared with Myd88^−/− mice. MyD88-dependent HEV-associated changes were also observed in NOD mice. Additionally, Lta, Ltb, and Ltbr in SGs of NOD mice were lowered by Myd88 deficiency. Interestingly, LTβR-induced HEV-associated gene expression in cultured cells was impaired by Myd88 deficiency. Our findings highlight novel roles for MyD88 in AS development, which imply the existence of MyD88-dependent HEV formation in ectopic lymphoid neogenesis.

Vasoactive Intestinal Peptide Protects Salivary Glands against Structural Injury and Secretory Dysfunction via IL-17A and AQP5 Regulation in a Model of Sjögren Syndrome

OBJECTIVE

Sjögren syndrome (SS) is an autoimmune disease involving exocrine glands. Currently, drugs that can improve both abnormal immunity and exocrine gland function are needed. The study aimed to investigate the effect and mechanism of vasoactive intestinal peptide (VIP) on the immune response and exocrine gland function in SS.

METHODS

We investigated the effects of VIP on the immune response and secretory function of submandibular glands using NOD mice, and analyzed the expression of IL-17A and AQP5 (aquaporin 5). The submandibular gland cells from healthy 8-day-old Sprague-Dawley rats were used to observe the influence of VIP on AQP5 expression.

RESULTS

Our study shows that treatment with VIP in an SS mouse model could not only reduce the immune injury to exocrine glands but also improve the secretory function of these glands. Furthermore, VIP was shown to improve the abnormal immune status by downregulating IL-17A expression in the exocrine glands. It also enhanced the secretory function of exocrine glands by upregulating AQP5 expression.

CONCLUSIONS

Using a model of SS, we found that VIP could not only modulate the immune response but also affect exocrine gland function, and that these therapeutic effects were associated with IL-17A and AQP5 regulation.

Mouse Models of Primary Sjogren's Syndrome

Sjogren's syndrome (SjS) is a chronic autoimmune disorder characterized by immune cell infiltration and progressive injury to the salivary and lacrimal glands. As a consequence, patients with SjS develop xerostomia (dry mouth) and keratoconjunctivitis sicca (dry eyes). SjS is the third most common rheumatic autoimmune disorder, affecting 4 million Americans with over 90% of patients being female. Current diagnostic criteria for SjS frequently utilize histological examinations of minor salivary glands for immune cell foci, serology for autoantibodies, and dry eye evaluation by corneal or conjunctival staining. SjS can be classified as primary or secondary SjS, depending on whether it occurs alone or in association with other systemic rheumatic conditions, respectively. Clinical manifestations typically become apparent when the disease is relatively advanced in SjS patients, which poses a challenge for early diagnosis and treatment of SjS. Therefore, SjS mouse models, because of their close resemblance to the human SjS, have been extremely valuable to identify early disease markers and to investigate underlying biological and immunological dysregulations. However, it is important to bear in mind that no single mouse model has duplicated all aspects of SjS pathogenesis and clinical features, mainly due to the multifactorial etiology of SjS that includes numerous susceptibility genes and environmental factors. As such, various mouse models have been developed in the field to try to recapitulate SjS. In this review, we focus on recent mouse models of primary SjS xerostomia and describe them under three categories of spontaneous, genetically engineered, and experimentally induced models. In addition, we discuss future perspectives highlighting pros and cons of utilizing mouse models and current demands for improved models.

Cutting Edge: Nonobese Diabetic Mice Deficient in Chromogranin A Are Protected from Autoimmune Diabetes

T cells reactive to β cell Ags are critical players in the development of autoimmune type 1 diabetes. Using a panel of diabetogenic CD4 T cell clones derived from the NOD mouse, we recently identified the β cell secretory granule protein, chromogranin A (ChgA), as a new autoantigen in type 1 diabetes. CD4 T cells reactive to ChgA are pathogenic and rapidly transfer diabetes into young NOD recipients. We report in this article that NOD.ChgA(-/-) mice do not develop diabetes and show little evidence of autoimmunity in the pancreatic islets. Using tetramer analysis, we demonstrate that ChgA-reactive T cells are present in these mice but remain naive. In contrast, in NOD.ChgA(+/+) mice, a majority of the ChgA-reactive T cells are Ag experienced. Our results suggest that the presence of ChgA and subsequent activation of ChgA-reactive T cells are essential for the initiation and development of autoimmune diabetes in NOD mice.

The Hippo signaling pathway is required for salivary gland development and its dysregulation is associated with Sjogren's syndrome

Sjogren's syndrome (SS) is a complex autoimmune disease that primarily affects salivary and lacrimal glands and is associated with high morbidity. Although the prevailing dogma is that immune system pathology drives SS, increasing evidence points to structural defects, including defective E-cadherin adhesion, to be involved in its etiology. We have shown that E-cadherin has pivotal roles in the development of the mouse salivary submandibular gland (SMG) by organizing apical-basal polarity in acinar and ductal progenitors and by signaling survival for differentiating duct cells. Recently, E-cadherin junctions have been shown to interact with effectors of the Hippo signaling pathway, a core pathway regulating the organ size, cell proliferation, and differentiation. We now show that Hippo signaling is required for SMG-branching morphogenesis and is involved in the pathophysiology of SS. During SMG development, a Hippo pathway effector, TAZ, becomes increasingly phosphorylated and associated with E-cadherin and α-catenin, consistent with the activation of Hippo signaling. Inhibition of Lats2, an upstream kinase that promotes TAZ phosphorylation, results in dysmorphogenesis of the SMG and impaired duct formation. SMGs from non-obese diabetic mice, a mouse model for SS, phenocopy the Lats2-inhibited SMGs and exhibit a reduction in E-cadherin junctional components, including TAZ. Importantly, labial specimens from human SS patients display mislocalization of TAZ from junctional regions to the nucleus, coincident with accumulation of extracellular matrix components, fibronectin and connective tissue growth factor, known downstream targets of TAZ. Our studies show that Hippo signaling has a crucial role in SMG-branching morphogenesis and provide evidence that defects in this pathway are associated with SS in humans.

Temporal histological changes in lacrimal and major salivary glands in mouse models of Sjogren's syndrome

Background

Evidence in imaging studies suggests that there may be differences in glandular involvement in Sjogren’s syndrome (SS) depending on the stage of the disease. No detailed histological studies are available to show if there are any such difference in glandular involvement at various time periods and stages of SS. This cross sectional study examines the inflammatory changes in mouse models of SS at various ages.

Methods

The histological changes in major salivary and lacrimal glands were studied at ages of 3, 6, 9, 12, 15 and 18 months in both sexes in well characterized mouse models of SS, non-obese diabetes mouse and Interleukin-14 alpha-transgenic mice.

Results

Our results indicate that early inflammation concurrently occur in submandibular and lacrimal glands around the age of 6 weeks. Parotid glands are involved much later in the course of SS with less severe inflammation. Sublingual glands are rarely involved.

Conclusions

Our conclusions are that SS may be an organ specific disease with early inflammation occurring in submandibular and lacrimal glands, followed by the parotid. Non organ specific events occur in later courses of the disease. The understanding of the disease progression is important in tailoring early local therapeutic interventions before complete destruction of salivary and lacrimal glands.

Transient depletion of CD4+ CD25+ regulatory T cells results in multiple autoimmune diseases in wild-type and B-cell-deficient NOD mice

Approximately 80% of female wild-type non-obese diabetic (WT NOD) mice spontaneously develop diabetes, whereas B-cell-deficient (B(-/-)) NOD mice are resistant to diabetes. B(-/-) mice are also resistant to other spontaneous and experimentally induced autoimmune diseases, including arthritis, systemic lupus erythematosus, Sjögren syndrome and thyroiditis. Under normal conditions, activation of self-reactive T cells in the periphery is limited by CD4(+) CD25(+) natural regulatory T (Treg) cells. B(-/-) NOD.H-2h4 mice, normally resistant to spontaneous autoimmune thyroiditis (SAT), develop SAT when Treg cells are depleted, suggesting that Treg cells are preferentially activated when autoantigen is initially presented by non-B-cell antigen-presenting cells. To test the hypothesis that increased Treg cell activity in B(-/-) mice contributes to their resistance to other autoimmune diseases, WT and B(-/-) NOD mice were given anti-CD25 to transiently deplete CD4(+) CD25(+) Treg cells. The WT and B(-/-) NOD mice given anti-CD25 developed diabetes much earlier than WT mice given rat IgG, whereas rat IgG-treated B(-/-) mice did not develop diabetes. Treg-cell-depleted mice had increased lymphocyte infiltration of the pancreas, salivary glands and thyroid compared with controls given rat IgG. These results are consistent with the hypothesis that resistance of B-cell-deficient NOD mice to several autoimmune diseases is due to the activity of Treg cells.

Sjögren's syndrome-like autoimmune sialadenitis in MRL-Faslpr mice is associated with expression of glucocorticoid-induced TNF receptor-related protein (GITR) ligand and 4-1BB ligand

Although costimulatory molecules have been shown to play crucial roles in the immune response, their involvement in the pathogenesis of Sjögren's syndrome is incompletely understood. In this study, we evaluated the relationship between the severity of spontaneous Sjögren's syndrome-like autoimmune sialadenitis in MRL/MpJ-lpr/lpr (MRL-Fas(lpr)) mice and the expression of 6 costimulatory molecules that play important roles in the immune response: CD80, CD86, OX40 ligand (OX40L), 4-1BB ligand (4-1BBL), glucocorticoid-induced TNF receptor-related protein ligand (GITRL), and B cell-activating factor of the tumor necrosis factor family (BAFF). Expression of the costimulatory molecules in the submandibular salivary glands of age-matched autoimmune MRL-Fas(lpr) mice and non-autoimmune MRL/MpJ-+/+(MRL/+) and C3H/HeJ-lpr/lpr (C3H-Fas(lpr)) mice was examined immunohistochemically and scored on a scale of 0 to 3. The severity of sialadenitis was evaluated histologically and scored on a scale of 0 to 3. We found that all of the costimulatory molecules were expressed in duct epithelial cells of salivary glands from MRL-Fas(lpr) mice, whereas immunoreactivity was absent or weak in the MRL/+ mice. The staining intensity for all 6 costimulatory molecules was significantly higher in the MRL-Fas(lpr) than in the MRL/+ mice. Partial correlation analysis was performed to assess the degree of association between costimulatory molecule staining scores and disease scores, which clearly revealed a significant correlation for only GITRL and 4-1BBL. These molecules showed negligible immunoreactivity in the submandibular glands of C3H-Fas(lpr) mice, suggesting that their expression was independent of the Fas(lpr) mutation. In conclusion, the expression of GITRL and 4-1BBL in salivary gland duct epithelial cells is associated with background genes in the MRL strain, but not with the Fas(lpr) mutation itself, and contributes significantly to the pathogenesis of autoimmune sialadenitis in MRL-Fas(lpr) mice. These results suggest that GITRL and 4-1BBL may be effective targets for the development of therapies for Sjögren's syndrome.

Systems analysis of primary Sjögren's syndrome pathogenesis in salivary glands identifies shared pathways in human and a mouse model

Introduction

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease with complex etiopathogenesis. Despite extensive studies to understand the disease process utilizing human and mouse models, the intersection between these species remains elusive. To address this gap, we utilized a novel systems biology approach to identify disease-related gene modules and signaling pathways that overlap between humans and mice.

Methods

Parotid gland tissues were harvested from 24 pSS and 16 non-pSS sicca patients and 25 controls. For mouse studies, salivary glands were harvested from C57BL/6.NOD-Aec1Aec2 mice at various times during development of pSS-like disease. RNA was analyzed with Affymetrix HG U133+2.0 arrays for human samples and with MOE430+2.0 arrays for mouse samples. The images were processed with Affymetrix software. Weighted-gene co-expression network analysis was used to identify disease-related and functional pathways.

Results

Nineteen co-expression modules were identified in human parotid tissue, of which four were significantly upregulated and three were downregulated in pSS patients compared with non-pSS sicca patients and controls. Notably, one of the human disease-related modules was highly preserved in the mouse model, and was enriched with genes involved in immune and inflammatory responses. Further comparison between these two species led to the identification of genes associated with leukocyte recruitment and germinal center formation.

Conclusion

Our systems biology analysis of genome-wide expression data from salivary gland tissue of pSS patients and from a pSS mouse model identified common dysregulated biological pathways and molecular targets underlying critical molecular alterations in pSS pathogenesis.

Destruction of salivary and lacrimal glands by Th1-polarized reaction in a model of secondary Sjögren's syndrome in lupus-prone female NZB × NZWF(1) mice

T helper (Th)1/Th2 balance determines the direction of some kinds of autoimmune diseases. The involvement of acini areas by CD4(+) helper T(Th) cell subset in submandibular and lacrimal glands are largely unknown in secondary Sjögren's syndrome (sSjS) with systemic lupus erythematosus (SLE). Submandibular and lacrimal glands were examined immunopathologically in lupus-prone female NZB × NZW(B/W)F(1) mice, model for human sSjS with SLE. Dacryoadenitis and sialoadenitis with renal failure developed with age. Infiltration of lymphoid cells (lymphocytes and plasma cells) expanded from the periductal areas in striated ducts to the acini, and the isolated foci in the acini were observed in those organs. The destruction of duct and acini epithelium, including the myoepithelium, was induced by interferon (IFN)-γ(+) and IgG2a(+) lymphoid cells, but not by interleukin(IL)-4(+), IL-5(+), IL-13(+), and IgG1(+) lymphoid cells. Compared with IL-5 and IL-13, high values of IFN-γ were produced systemically at various ages. Also local expression of IFN-γ mRNA was higher than that of IL-4 mRNA. The result suggests that the acini destruction in submandibular and lacrimal glands may be induced by systemic and local Th1 cell dominant reactions in lupus-prone B/WF(1) mice with sSjS.

Animal models in autoimmune diseases: lessons learned from mouse models for Sjögren's syndrome

The mouse model is the one of the most frequently used and well-established animal models, and is currently used in many research areas. To date, various mouse models have been utilized to elucidate underlying causes of multifactorial autoimmune conditions, including pathological immune components and specific signaling pathways. This review summarizes the more recent mouse models for Sjögren's syndrome, a systemic autoimmune disease characterized by lymphocytic infiltration in the exocrine glands, such as the salivary and lacrimal glands, and loss of secretory function, resulting in dry mouth and dry eyes in patients. Although every Sjögren's syndrome mouse model resembles the major symptoms or phenotypes of Sjögren's syndrome conditions in humans, the characteristics of each model are variable. Moreover, to date, there is no single mouse model that can completely replicate the human conditions. However, unique features of each mouse model provide insights into the roles of potential etiological and immunological factors in the development and progression of Sjögren's syndrome. Here, we will overview the Sjögren's syndrome mouse models. Lessons from these mouse models will aid us to understand underlying immune dysregulation in autoimmune diseases in general, and will guide us to direct future research towards appropriate diagnostic and therapeutic strategies.

Link between inflammation and aquaporin-5 distribution in submandibular gland in Sjögren's syndrome?

OBJECTIVE

To determine whether a link exists between inflammation and aquaporin-5 distribution in submandibular glands from three animal models for Sjögren's syndrome: IQI/JIC, r1ΔT/r2n and non-obese diabetic mice.

METHODS

Mice of different ages were used. Inflammatory infiltrates were quantified using the focus score. Acinar aquaporin-5 subcellular distribution was determined by immunohistochemistry and quantified using labelling indices.

RESULTS

  Minor inflammatory infiltrates were present in r1f/r2n mice. Massive inflammatory infiltrates and acinar destruction were observed in 24-week-old non-obese diabetic mice, 10-and 13-month-old IQI/JIC mice and some r1ΔT/r2n mice. Aquaporin-5 immunoreactivity was primarily apical in submandibular glands from 8- and 24-week-old Balb/C mice, 8-week-old non-obese diabetic mice, 2-, 4- and 7-month-old IQI/JIC mice and r1f/r2n mice. In contrast, decreased apical aquaporin-5 labelling index with concomitant increased apical-basolateral, apical-cytoplasmic and/or apical-basolateral-cytoplasmic aquaporin-5 labelling indices was observed in 24-week-old non-obese diabetic, 10- and 13-month-old IQI/JIC and r1ΔT/r2n mice with a focus score≥1.

CONCLUSIONS

  Altered aquaporin-5 distribution in submandibular acinar cells from IQI/JIC, non-obese diabetic and r1ΔT/r2n mice with a focus score≥1 appears to be concomitant to the presence of inflammatory infiltrates and acinar destruction.

Activation of the alternative NFκB pathway improves disease symptoms in a model of Sjogren's syndrome

The purpose of our study was to understand if Toll-like receptor 9 (TLR9) activation could contribute to the control of inflammation in Sjogren's syndrome. To this end, we manipulated TLR9 signaling in non-obese diabetic (NOD) and TLR9^−/− mice using agonistic CpG oligonucleotide aptamers, TLR9 inhibitors, and the in-house oligonucleotide BL-7040. We then measured salivation, inflammatory response markers, and expression of proteins downstream to NF-κB activation pathways. Finally, we labeled proteins of interest in salivary gland biopsies from Sjogren's syndrome patients, compared to Sicca syndrome controls. We show that in NOD mice BL-7040 activates TLR9 to induce an alternative NF-κB activation mode resulting in increased salivation, elevated anti-inflammatory response in salivary glands, and reduced peripheral AChE activity. These effects were more prominent and also suppressible by TLR9 inhibitors in NOD mice, but TLR9^−/− mice were resistant to the salivation-promoting effects of CpG oligonucleotides and BL-7040. Last, salivary glands from Sjogren's disease patients showed increased inflammatory and decreased anti-inflammatory biomarkers, in addition to decreased levels of alternative NF-κB pathway proteins. In summary, we have demonstrated that activation of TLR9 by BL-7040 leads to non-canonical activation of NF-κB, promoting salivary functioning and down-regulating inflammation. We propose that BL-7040 could be beneficial in treating Sjogren's syndrome and may be applicable to additional autoimmune syndromes.

Loss of PKCδ results in characteristics of Sjögren's syndrome including salivary gland dysfunction

OBJECTIVES

Chronic infiltration of lymphocytes into the salivary and lacrimal glands of patients with Sjögren's syndrome (SS) leads to destruction of acinar cells and loss of exocrine function. Protein kinase C-delta (PKCδ) is known to play a critical role in B-cell maintenance. Mice in which the PKCδ gene has been disrupted have a loss of B-cell tolerance, multiple organ lymphocytic infiltration, and altered apoptosis. To determine whether PKCδ contributes to the pathogenesis of SS, we quantified changes in indicators of SS in PKCδ-/- mice as a function of age. Salivary gland histology, function, the presence of autoantibodies, and cytokine expression were examined.

MATERIALS AND METHODS

Submandibular glands were examined for the presence of lymphocytic infiltrates, and the type of infiltrating lymphocyte and cytokine deposition was evaluated by immunohistochemistry. Serum samples were tested by autoantibody screening, which was graded by its staining pattern and intensity. Salivary gland function was determined by saliva collection at various ages.

RESULTS

PKCδ-/- mice have reduced salivary gland function, B220+ B-cell infiltration, anti-nuclear antibody production, and elevated IFN-γ in the salivary glands as compared to PKCδ+/+ littermates.

CONCLUSIONS

PKCδ-/- mice have exocrine gland tissue damage indicative of a SS-like phenotype.

Dysfunction of lacrimal and salivary glands in Sjögren's syndrome: nonimmunologic injury in preinflammatory phase and mouse model

Sjögren's syndrome (SjS) is a chronic autoimmune disorder characterized by dry eyes and dry mouth due to dacryoadenitis and sialoadenitis with SS-A/Ro and/or SS-B/La autoantibodies in genetically predisposed individuals. Destruction of lacrimal and salivary glands by autoimmune reactions may lead to clinical manifestation. However, the mechanisms behind the decreased volume of secretions in tears and saliva are complex and are not fully understood. Exocrine gland dysfunction may precede autoimmunity (acquired immunity) or represent a process independent from inflammation in the pathogenesis of SjS. The preceded functional and morphologic changes of those tissues by nonimmunologic injury before the development of inflammation at the sites of target organs have been implicated. This paper focuses on the several factors and components relating to glandular dysfunction and morphologic changes by nonimmunologic injury during the preinflammatory phase in mouse model, including the factors which link between innate immunity and adaptive immunity.

A role for lymphotoxin in primary Sjogren's disease

The etiology of salivary gland injury in primary Sjögren's disease is not well understood. We have previously described a mouse model of Sjögren's disease, IL-14α transgenic (IL14αTG) mice, which reproduces many of the features of the human disease. We now demonstrate a critical role for lymphotoxin α (LTA) in the pathogenesis of Sjögren's disease in IL14αTG mice. IL14αTG mice express LTA mRNA in their salivary glands and spleen and produce soluble LTA protein in their salivary secretions. When IL14αTG mice were crossed with LTA(-/-) mice, the IL14αTG.LTA(-/-) mice retained normal salivary gland secretions and did not develop either lymphocytic infiltration of their salivary glands or secondary lymphomas. However, both IL14αTG and IL14αTG.LTA(-/-) mice produced similar amounts of IFN-α and had similar deposition of autoantibodies in their salivary glands. Both IL14α and IL14α/LTA(-/-) mice had similar B cell responses to T-dependent and T-independent Ags, L-selectin expression, and expression of RelA, RelB, and NF-κB2 in their spleens. These studies suggest that LTA plays a critical role in the local rather than systemic inflammatory process of Sjögren's disease. Furthermore, local production of soluble LTA in the salivary glands of IL14αTG mice is necessary for the development of overt Sjögren's disease. Autoantibody deposition alone is not sufficient to produce salivary gland dysfunction. We also demonstrate that LTA is increased in the salivary gland secretions and sera of patients with Sjögren's disease, further strengthening the biological relevance of the IL14αTG model to understanding the pathogenesis of human disease.

Bone marrow cells are a source of undifferentiated cells to prevent Sjögren's syndrome and to preserve salivary glands function in the non-obese diabetic mice

Non-obese diabetic (NOD) mice develop Sjögren's-like syndrome (Ss) and a gradual loss of saliva secretory function. Our previous study showed that injections of matched normal spleen cells with Complete Freund's Adjuvant (CFA) reversed salivary gland dysfunction in 14-week-old NOD mice, which had established Ss. The spleen and bone marrow are closely related organs, and both are among the first sites of hematopoiesis during gestation. Noticing a rapidly increasing number of clinical trials using bone marrow (BM) cells treatments for autoimmune diseases, we tested if BM cells can prevent Ss and restore salivary glands' function. We injected CFA and MHC class I-matched normal BM cells in 7-week-old NOD mice, which had not yet developed Ss. We found at week 52 post-treatment that all NOD mice receiving BM cells and CFA had a recovery of salivary flow and were protected from Ss and diabetes. BM cells-treated mice had their salivary function restored quantitatively and qualitatively. Saliva flow was higher (p<0.05) in BM cells-transplanted mice when compared to control mice, which continued to deteriorate over time. Total proteins, epidermal growth factor, amylase, and electrolytes concentrations in saliva of BM cells-treated mice were not significantly changed at week 44 and 52 post-therapy when compared to pre-therapy (when the mice did not have Ss). Restoration of salivary flow could have resulted from a combination of rescue and paracrine effects from BM cells. This study suggests that a combined immuno- and cell-based therapy can permanently prevent Ss and restored salivary function in NOD mice.

Sjögren's syndrome-like ocular surface disease in thrombospondin-1 deficient mice

Thrombospondin-1 (TSP-1) is a major activator of latent transforming growth factor-beta in vitro as well as in vivo. Mice deficient in TSP-1, despite appearing normal at birth, develop a chronic form of ocular surface disease that is marked by increased apoptosis and deterioration in the lacrimal gland, associated dysfunction, and development of inflammatory infiltrates that result in abnormal tears. The increase in CD4(+) T cells in the inflammatory infiltrates of the lacrimal gland, and the presence of anti-Sjögren's syndrome antigen A and anti-Sjögren's syndrome antigen B antibodies in the serum resemble autoimmune Sjögren's syndrome. These mice develop an ocular surface disorder dry eye that includes disruption of the corneal epithelial layer, corneal edema, and a significant decline in conjuctival goblet cells. Externally, several mice develop dry crusty eyes that eventually close. The inflammatory CD4(+) T cells detected in the lacrimal gland, as well as those in the periphery of older TSP-1 null mice, secrete interleukin-17A, a cytokine associated with chronic inflammatory diseases. Antigen-presenting cells, derived from TSP-1 null, but not from wild-type mice, activate T cells to promote the Th17 response. Together, these results indicate that TSP-1 deficiency results in a spontaneous form of chronic dry eye and aberrant histopathology associated with Sjögren's syndrome.

Genes and Sjögren's syndrome

The evidence for a strong genetic component conferring susceptibility to primary Sjögren's syndrome (SS) is mounting. Several associations with SS have been reported and provide evidence that the HLA region harbors important susceptibility loci and that multiple genes outside the HLA region play a role. Genetic discovery lags behind success observed in related autoimmune diseases. Identifying genetic factors that cause SS will allow more precise definition of pathogenic mechanisms leading to the overall SS phenotype and clinically heterogeneous subsets of patients. Critical opportunities are certain to follow for translation into improved diagnosis and therapies for SS and its spectrum diseases.

Aquaporins in secretory glands and their role in Sjögren's syndrome

Salivary, lacrimal and pancreatic secretions are known to account for multiple physiological functions. These exocrine secretions are watery fluids containing electrolytes, and a mixture of proteins, and can be stimulated by a number of agonists. Since water movement is involved in exocrine secretion, aquaporins (AQPs) have been hypothesised to contribute to fluid production in exocrine glands. This chapter will focus on the expression, localisation and function of AQPs in salivary and lacrimal glands and pancreas. The role of multiple water and ion transporters and channels in exocrine fluid secretion will also be reviewed. Finally, this chapter will address the potential role of AQPs in Sjögren's syndrome.

Selecting highly sensitive non-obese diabetic mice for improving the study of Sjögren's syndrome

BACKGROUND

Non-obese diabetic (NOD) mice are a commonly used murine model for the study of Sjögren's syndrome. However, variations in susceptibility to the disease among the mice has often yielded less stable results. Based on the correlation between the pathological changes and the tear tests, we attempt to establish a simple screening procedure to assure the validity of experimental results by excluding those mice with poor susceptibility to dry eyes.

METHODS

Seventy male NOD mice were recruited. The tear film break-up test (BUT) and the phenol red cotton thread test (CTT) were implemented while the mice were under anesthesia. The mice were divided into four groups (grades 1 to 4) based on their BUT readings, and four similar groups based on CTT measurements. Tear samples in each grade were collected for IL-1beta detection with ELISA. The lacrimal glands and conjunctiva of the mice were used to detect the levels of leucocyte common antigen (LCA). LCA-Positive staining was considered as the "gold standard" in the receiver operating characteristic curve (ROC curve) analysis. C57BL/6 mice were used as wild-type controls.

RESULTS

There were 13 (18.57%), 43 (61.43%), 10 (14.29%) and 4 (5.71%) mice in grades 1, 2, 3 and 4 by BUT test, and 34 (48.57%), 15 (21.43%), 14 (20.00%) and 7 (10.00%) in grades 1, 2, 3 and 4 by CTT test respectively. Fifty-one out of the 70 mice (72.86%) were detected LCA-positive, and they were mainly in grades 1 and 2 of both the BUT and CCT grading systems. ELISA showed significant variances of IL-beta levels among the four groups (p < 0.01), with much lower IL-beta levels in group 3 and 4 when both BUT and CTT were used for grouping. The tear IL-beta level in the wild-type mice was similar to those of the grade 4 mice, using either BUT or CTT for grouping. The ROC curve analysis provided optimal cutting lines, which were 2 seconds in BUT readings and 4 mm/min in CTT measurements respectively.

CONCLUSION

BUT and CTT tests are useful methods in screening high susceptible NOD mice. Cutting lines at BUT < or = 2 seconds and CTT < or = 4 mm/min provide a good balance between the assurance of susceptibility and the maximization of use of NOD mice for the study of Sjögren's syndrome.