Deleting Mitochondrial Superoxide Dismutase 2 in Salivary Gland Ductal Epithelial Cells Recapitulates Non-Sjögren's Sicca Syndrome.

Elevated oxidative stress can play a pivotal role in autoimmune diseases by exacerbating inflammatory responses and tissue damage. In Sjögren's disease (SjD), the contribution of oxidative stress in the disease pathogenesis remains unclear. To address this question, we created mice with a tamoxifen-inducible conditional knockout (KO) of a critical antioxidant enzyme, superoxide dismutase 2 (Sod2), in the salivary glands (i-sg-Sod2 KO mice). Following tamoxifen treatment, Sod2 deletion occurred primarily in the ductal epithelium, and the salivary glands showed a significant downregulation of Sod2 expression. At twelve weeks post-treatment, salivary glands from the i-sg-Sod2 KO mice exhibited increased 3-Nitrotyrosine staining. Bulk RNA-seq revealed alterations in gene expression pathways related to ribosome biogenesis, mitochondrial function, and oxidative phosphorylation. Significant changes were noted in genes characteristic of salivary gland ionocytes. The i-sg-Sod2 KO mice developed reversible glandular hypofunction. However, this functional loss was not accompanied by glandular lymphocytic foci or circulating anti-nuclear antibodies. These data demonstrate that although localized oxidative stress in salivary gland ductal cells was insufficient for SjD development, it induced glandular dysfunction. The i-sg-Sod2 KO mouse resembles patients classified as non-Sjögren's sicca and will be a valuable model for deciphering oxidative-stress-mediated glandular dysfunction and recovery mechanisms.

Anti-vimentin antibodies are associated with higher severity of Sjögren's disease.

Vimentin is a ubiquitously present Type III intermediate filament protein, often targeted by autoimmune responses in multiple rheumatic disorders. Although previous studies have reported anti-vimentin antibodies in Sjögren's disease (SjD) patients, the clinical significance of such antibodies is unknown. To address this issue, the presence of anti-vimentin antibodies was determined in serum samples from a well-characterized cohort of primary SjD patients, non-SjD Sicca, and healthy controls. The occurrence of anti-vimentin antibodies and their association with different clinical features of the disease were evaluated. Anti-vimentin antibodies were detected in 24% of primary SjD patients, compared to 4% in non-SjD sicca patients and 3% in healthy controls. In primary SjD patients, higher levels of anti-vimentin antibodies were significantly associated with reduced saliva and tear flow and severe ocular surface damage indicators. The anti-vimentin antibody levels did not show significant associations with the presence or absence of other autoantibodies like ANA, RF, and anti-Ro/La. Our data suggest that the anti-vimentin antibody specificity arises in a subset of primary SjD patients and is associated with oral and ocular features of the disease. Anti-vimentin can potentially serve as a novel biomarker for evaluating the severity of salivary and lacrimal gland dysfunction in primary SjD.

STING Agonist-Induced Skin Inflammation Is Exacerbated with Prior Systemic Innate Immune Activation.

Activation of the Stimulator of Interferon Genes (STING) protein has paradoxical outcomes in skin disease. STING activation exacerbates psoriatic skin disease and delays wound healing in diabetic mice, yet it also facilitates wound healing in normal mice. To address the role of localized STING activation in the skin, mice were injected subcutaneously with a STING agonist, diamidobenzimidazole STING Agonist-1 (diAbZi). The effect of a prior inflammatory stimulus on STING activation was addressed by pre-treating mice intraperitoneally with poly (I:C). The skin at the injection site was evaluated for local inflammation, histopathology, immune cell infiltration, and gene expression. Serum cytokine levels were measured to assess systemic inflammatory responses. Localized diABZI injection induced severe skin inflammation with erythema, scaling, and induration. However, the lesions were self-limiting and resolved within 6 weeks. At the peak of inflammation, the skin showed epidermal thickening, hyperkeratosis, and dermal fibrosis. Neutrophils, CD3 T cells, and F4/80 macrophages were present in the dermis and subcutaneous layers. Gene expression was consistent with increased local interferon and cytokine signaling. Interestingly, the poly (I:C)-pre-treated mice showed higher serum cytokine responses and developed worse inflammation with delayed wound resolution. Our study demonstrates that prior systemic inflammation amplifies STING-mediated inflammatory responses and skin disease.

Antibody deposition on vascular endothelial cells contributes to localized inflammation in salivary glands.

BACKGROUND: Oral and ocular dryness due to reduced saliva and tear production, exocrine gland inflammation, and autoantibodies to multiple cellular proteins are the cardinal features of Sjögren's Disease. Among the autoantibody specificities, anti-Ro52 is linked with higher disease severity. We have previously reported that mice immunized with recombinant Ro52 developed IgG deposits in salivary and lacrimal glands and showed reduced saliva and tear production. Furthermore, passive transfer of sera from Ro52-immunized mice rapidly induced glandular dysfunction without immune cell infiltration in recipient mice. METHODS: To identify mechanisms driving antibody-mediated salivary gland dysfunction, hyperimmune rabbit antiserum to mouse Ro52 was passively transferred into NZM2758 female mice, pretreated with alum adjuvant. Alum-pretreated mice given hyperimmune rabbit antiserum to maltose-binding protein served as controls. Antibody deposition and its distribution in the salivary glands were studied by immunofluorescence staining for rabbit IgG, nerve fibers, and endothelial cells. The nCounter inflammation panel was used to determine differentially expressed genes in the salivary gland. RESULTS: Rabbit IgG deposits were detected in salivary glands of anti-Ro52 immune sera recipients. The rabbit IgG was present on the endothelial cells in small blood vessels, and it did not co-localize with nerve fibers. Ingenuity pathway analysis of the gene expression dataset predicted the canonical vascular endothelial growth factor (VEGF) pathway as the most activated and Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) as the most inhibited pathway in the salivary glands of anti-Ro52 sera recipients. CONCLUSION: Our study suggests that autoantibody deposition on salivary gland endothelial cells might play a critical role in the pathogenesis of Sjögren's Disease.

Pulmonary Involvement in a Mouse Model of Sjögren's Syndrome Induced by STING Activation.

Sjögren's Syndrome (SS), a chronic autoimmune disorder affecting multiple organ systems, is characterized by an elevated type I interferon (IFN) response. Activation of Stimulator of Interferon Genes (STING) protein induces type I IFN and in mice, several features of SS, including anti-nuclear antibodies, sialadenitis, and salivary gland dysfunction. Since lung involvement occurs in one-fifth of SS patients, we investigated whether systemic activation of STING also leads to lung inflammation. Lungs from female C57BL/6 mice injected with the STING agonist 5, 6-Dimethylxanthenone-4-acetic acid (DMXAA), were evaluated for acute and chronic inflammatory responses. Within 4h of DMXAA injection, the expression of Ifnb1, Il6, Tnf, Ifng, and Mx1 was significantly upregulated. At 1 and 2 months post-treatment, lungs showed lymphocytic infiltration in the peri-bronchial regions. The lungs from DMXAA treated mice showed an increased expression of multiple chemokines and an increase in lymphatic endothelial cells. Despite STING expression in bronchial epithelium and cells lining the alveolar wall, bone marrow chimeras between STING knockout and wild type mice showed that STING expression in hematopoietic cells was critical for lung inflammation. Our results suggest that activation of the STING pathway might be involved in SS patients with concomitant salivary gland and lung disease.

Antibodies to periodontogenic bacteria are associated with higher disease activity in lupus patients.

OBJECTIVES: Microbial infections and mucosal dysbiosis influence morbidity in patients with systemic lupus erythematosus (SLE). In the oral cavity, periodontal bacteria and subgingival plaque dysbiosis provide persistent inflammatory stimuli at the mucosal surface. This study was undertaken to evaluate whether exposure to periodontal bacteria influences disease parameters in SLE patients. METHODS: Circulating antibodies to specific periodontal bacteria have been used as surrogate markers to determine an ongoing bacterial burden, or as indicators of past exposure to the bacteria. Banked serum samples from SLE patients in the Oklahoma Lupus Cohort were used to measure antibody titres against periodontal pathogens (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Treponema denticola) and commensals (Capnocytophaga ochracea, and Streptococcus gordonii) by ELISA. Correlations between anti-bacterial antibodies and different clinicalparameters of SLE including, autoantibodies (anti-dsDNA, anti-SmRNP, anti-SSA/Ro and anti-SSB/La), complement, and disease activity (SLEDAI and BILAG) were studied. RESULTS: SLE patients had varying amounts of antibodies to different oral bacteria. The antibody titres against A. actinomycetemcomitans, P. gingivalis, T. denticola, and C. ochracea were higher in patients positive for anti-dsDNA antibodies, and they showed significant correlations with anti-dsDNA titres and reduced levels of complement. Among the periodontal pathogens, only antibodies to A. actinomycetemcomitans were associated with higher disease activity. CONCLUSIONS: Our results suggest that exposure to specific pathogenic periodontal bacteria influences disease activity in SLE patients. These findings provide a rationale for assessing and improving periodontal health in SLE patients, as an adjunct to lupus therapies.

Loss of mucin-type O-glycans impairs the integrity of the glomerular filtration barrier in the mouse kidney.

The kidney's filtration activity is essential for removing toxins and waste products from the body. The vascular endothelial cells of the glomerulus are fenestrated, flattened, and surrounded by podocytes, specialized cells that support glomerular endothelial cells. Mucin-type core 1-derived O-glycans (O-glycans) are highly expressed on both glomerular capillary endothelial cells and their supporting podocytes, but their biological role is unclear. Biosynthesis of core 1-derived O-glycans is catalyzed by the glycosyltransferase core 1 ß1,3-galactosyltransferase (C1galt1). Here we report that neonatal or adult mice with inducible deletion of C1galt1 (iC1galt1-/-) exhibit spontaneous proteinuria and rapidly progressing glomerulosclerosis. Ultrastructural analysis of the glomerular filtration barrier components revealed that loss of O-glycans results in altered podocyte foot processes. Further analysis indicated that O-glycan is essential for the normal signaling function of podocalyxin, a podocyte foot process-associated glycoprotein. Our results reveal a new function of O-glycosylation in the integrity of the glomerular filtration barrier.

Immune response against the coiled coil domain of Sjögren's syndrome associated autoantigen Ro52 induces salivary gland dysfunction.

OBJECTIVES: The structural domains of Ro52, termed the RING, B-box, coiled coil (CC) and B30.2/SPRY are targets of anti-Ro52 in multiple autoimmune disorders. In Sjögren's syndrome patients, the presence of anti-Ro52 is associated with higher disease severity, and in mice, they induce salivary gland hypofunction. This study was undertaken to investigate whether immune responses against different domains of Ro52, influences salivary gland disease in mice. METHODS: Female NZM2758 mice were immunised with Ro52 domains expressed as recombinant fusion proteins with maltose binding protein (MBP) [MBP-RING-B-box, MBP-CC, MBP-CC(ΔC19), MBP-B30.2/SPRY]. Sera from immunised mice were studied for IgG antibodies to Ro52 by immunoprecipitation, and to salivary gland cells by immunofluorescence. Pilocarpine-induced saliva production was measured to evaluate salivary gland function. Submandibular glands were investigated by histopathology for inflammation and by immune-histochemistry for IgG deposition. RESULTS: Mice immunised with different Ro52-domains had comparable reactivity to Ro52 and to salivary gland cells. However, only mice immunised with the CC domain and its C-terminal truncated version CC(ΔC19) showed a significant drop in saliva production. None of the mice developed severe salivary gland inflammation. The salivary gland hypofunction significantly correlated with increased intra-lobar IgG deposits in the submandibular salivary glands. CONCLUSIONS: Our data demonstrate that epitope specificity of anti-Ro52 antibodies plays a critical role in the induction of glandular dysfunction. Clearly, screening Sjögren's syndrome patients for relative levels of Ro52 domain specific antibodies will be more informative for associating anti-Ro52 with clinical measures of the disorder.

Immune Response Targeting Sjögren's Syndrome Antigen Ro52 Suppresses Tear Production in Female Mice.

Autoantibodies reactive against Ro52 are present in 70% of Sjögren's syndrome patients and are associated with higher disease severity. However, their role in causing aqueous deficient dry eye, a major cause for morbidity in Sjögren's syndrome, is unclear. To investigate whether immune responses targeting Ro52 contribute towards the dry eye, male and female NZM2758 mice were immunized with recombinant Ro52. Tear production was measured by the phenol red thread test. Sera were analyzed for anti-Ro52 levels by immunoprecipitation. Lacrimal glands were evaluated for inflammatory foci and IgG deposits. Our results showed that, although all mice generated anti-Ro52 antibodies, only females developed a significant drop in tear production. None of the mice developed severe lacrimal gland inflammation, and female mice with anti-Ro52 showed higher levels of IgG deposits within their glands. Passive transfer of anti-Ro52 sera caused reduced tear production in female mice, but not in males. This study demonstrates for the first time that immune responses initiated by Ro52 induce aqueous dry eye, and this may be driven by anti-Ro52 antibodies. Furthermore, the sexual dimorphism in glandular dysfunction suggests that the lacrimal glands in females are more susceptible to autoantibody-mediated injury.

Anti-La positive, anti-Ro negative subset of primary Sjögren's syndrome: anti-La is a reality but is the disease?

OBJECTIVES: To characterise the serological and clinical findings in primary Sjögren's syndrome in which anti-La was found without anti-Ro. We hypothesised that a significant portion of these are falsely negative for anti-Ro60. METHODS: Twenty-nine sera from primary Sjögren's syndrome patients were tested for antibodies directed against La and Ro. Anti-La was detected using bovine La treated with or without DNAase and RNAase to identify potential false positivity. Anti-Ro60 antibodies were detected using HEp-2000 substrate (in which cells are transfected with human Ro60) and HEp-2 substrate. Anti-Ro60 and Ro-52 were also tested by in vitro transcription/translation followed by immunoprecipitation assay. RESULTS: All 29 sera bound La, even after treatment with DNAase and RNAase. Of the 29 sera, 25 were unequivocally negative on HEp-2000 (1:40 dilution). Four samples were anti-Ro60 positive with a speckled pattern, three of the four at 1:320 dilution. Thus, false negative anti-Ro60 exists in a small fraction (14%) of the Ro-negative/La-positive primary Sjögren's patients. However, all the samples were negative for Ro60 and Ro52 by in vitro immunoprecipitation assay. Clinically these patients tended not to have salivary gland pathology characteristic of Sjögren's syndrome. CONCLUSIONS: We found only a small fraction of Ro negative/La positive sera to show positive HEp-2000 pattern. These subjects did not have characteristic findings on pathological examination of minor salivary glands, suggesting these subjects have a process distinct from Sjögren's syndrome.

Concordance of increased B1 cell subset and lupus phenotypes in mice and humans is dependent on BLK expression levels.

Polymorphisms in the B lymphoid tyrosine kinase (BLK) gene have been associated with autoimmune diseases, including systemic lupus erythematosus, with risk correlating with reduced expression of BLK. How reduced expression of BLK causes autoimmunity is unknown. Using Blk(+/+) , Blk(+/-) , and Blk(-/-) mice, we show that aged female Blk(+/-) and Blk(-/-) mice produced higher anti-dsDNA IgG Abs and developed immune complex-mediated glomerulonephritis, compared with Blk(+/+) mice. Starting at young age, Blk(+/-) and Blk(-/-) mice accumulated increased numbers of splenic B1a cells, which differentiated into class-switched CD138(+) IgG-secreting B1a cells. Increased infiltration of B1a-like cells into the kidneys was also observed in aged Blk(+/-) and Blk(-/-) mice. In humans, we found that healthy individuals had BLK genotype-dependent levels of anti-dsDNA IgG Abs as well as increased numbers of a B1-like cell population, CD19(+)CD3(-)CD20(+)CD43(+)CD27(+), in peripheral blood. Furthermore, we describe the presence of B1-like cells in the tubulointerstitial space of human lupus kidney biopsies. Taken together, our study reveals a previously unappreciated role of reduced BLK expression on extraperitoneal accumulation of B1a cells in mice, as well as the presence of IgG autoantibodies and B1-like cells in humans.

Interaction between innate immunity and Ro52-induced antibody causes Sjögren's syndrome-like disorder in mice.

OBJECTIVES: Autoantibodies reactive with Ro52 are often found in sera of patients with Sjögren's syndrome (SS). This study was undertaken to investigate the role of Ro52-induced immune responses in pathogenesis of SS. METHODS: New Zealand Mixed (NZM) 2758 mice were immunised with Ro52 in alum adjuvant. Control mice were immunised either with maltose-binding protein or injected with alum alone. Mice were monitored for anti-Ro52 antibody, sialoadenitis and pilocarpine-induced salivation. Antibody binding to salivary gland (SG) cells was analysed in vivo and in vitro by immunofluorescence. Sera from immunised mice were passively transferred into untreated or alum injected NZM2758 mice. RESULTS: By day 30 post-immunisation, Ro52 immunised mice generated immunoprecipitating anti-Ro52 antibodies and they had the maximum drop in saliva production. Both Ro52 immunised and control mice showed evidence of mild sialoadenitis. However, only Ro52 immunised mice had antibody deposition in their SG. Passive transfer of Ro52-immune sera induced SG dysfunction in recipient mice, only if the recipients were primed with alum. In vitro, antibodies from Ro52-immune sera were internalised by a SG cell line and this uptake was inhibited by cytochalasin D treatment. CONCLUSIONS: Our data show for the first time that antibodies induced by Ro52 are capable of inducing SG dysfunction, and that this phenomenon is dependent on the activation of innate immunity. The mouse model described in this study implies that autoantibody deposition in the SG might be an important step in the induction of xerostomia and pathogenesis of SS.

Influenza A (H1N1) virus infection triggers severe pulmonary inflammation in lupus-prone mice following viral clearance.

Each year, up to one fifth of the United States population is infected with influenza virus. Although mortality rates are low, hundreds of thousands are hospitalized each year in the United States. Specific high risk groups, such as those with suppressed or dysregulated immune systems, are at greater danger for influenza complications. Respiratory infections are a common cause of hospitalizations and early mortality in patients with systemic lupus erythematosus (SLE); however, whether this increased infection risk is a consequence of the underlying dysregulated immune background and/or immunosuppressing drugs is unknown. To evaluate the influenza immune response in the context of lupus, as well as assess the effect of infection on autoimmune disease in a controlled setting, we infected lupus-prone MRL/MpJ-Fas(lpr) mice with influenza virus A PR/8/34 H1N1. Interestingly, we found that Fas(lpr) mice generated more influenza A virus specific T cells with less neutrophil accumulation in the lung during acute infection. Moreover, Fas(lpr) mice produced fewer flu-specific IgG and IgM antibodies, but effectively cleared the virus. Further, increased extrinsic apoptosis during influenza infection led to a delay in autoimmune disease pathology with decreased severity of splenomegaly and kidney disease. Following primary influenza A infection, Fas(lpr) mice had severe complications during the contraction and resolution phase with widespread severe pulmonary inflammation. Our findings suggest that influenza infection may not exacerbate autoimmune pathology in mice during acute infection as a direct result of virus induced apoptosis. Additionally, autoimmunity drives an enhanced antigen-specific T cell response to clear the virus, but persisting pulmonary inflammation following viral clearance may cause complications in this lupus animal model.

T cell epitope mimicry between Sjögren's syndrome Antigen A (SSA)/Ro60 and oral, gut, skin and vaginal bacteria.

This study was undertaken to test the hypothesis that Sjogren's syndrome Antigen A (SSA)/Ro60-reactive T cells are activated by peptides originating from oral and gut bacteria. T cell hybridomas generated from HLA-DR3 transgenic mice recognized 3 regions on Ro60, with core epitopes mapped to amino acids 228-238, 246-256 and 371-381. BLAST analysis identified several mimicry peptides, originating from human oral, intestinal, skin and vaginal bacteria, as well as environmental bacteria. Amongst these, a peptide from the von Willebrand factor type A domain protein (vWFA) from the oral microbe Capnocytophaga ochracea was the most potent activator. Further, Ro60-reactive T cells were activated by recombinant vWFA protein and whole Escherichia coli expressing this protein. These results demonstrate that peptides derived from normal human microbiota can activate Ro60-reactive T cells. Thus, immune responses to commensal microbiota and opportunistic pathogens should be explored as potential triggers for initiating autoimmunity in SLE and Sjögren's syndrome.

Inhibitor of differentiation 3, a transcription factor, regulates hyperlipidemia-associated kidney disease.

BACKGROUND: Lipoprotein abnormalities are associated with a rapid decline in renal function in patients of chronic kidney disease. In addition, hyperlipidemia is associated with an increased risk of developing renal insufficiency. The underlying molecular mechanisms for these clinical findings are unclear. We have previously reported a role for inhibitor of differentiation 3 (ID3), a transcription factor, in regulating kidney disease in hyperlipidemia. Introducing a genetic deficiency of Id3 in spontaneously hyperlipidemic apolipoprotein E knockout (Apoe(-/-)) mice led to accelerated mesangioproliferative glomerulonephritis. The present study was carried out to further investigate the contribution of ID3 in hyperlipidemia-associated kidney disease. METHODS: Female C57BL/6 mice that were ID3-sufficient wild-type (WT) or ID3-deficient (Id3(-/-)) were fed a Western diet and evaluated for proteinuria, glomerular pathology, and immune infiltrating cells. Primary mesangial cell lines were generated from both mouse strains and stimulated with oxidized phospholipids. Cytokines and chemokines produced were measured by multiplex assays, ELISA, and QPCR. Glomerular isolates were studied for CXCL1 expression by QPCR. RESULTS: Id3(-/-) mice on a Western diet developed accelerated proteinuria and mesangioproliferative glomerulonephritis compared to WT controls. In vitro, Id3(-/-) glomerular mesangial cell lines produced higher levels of the monocyte chemoattractant CXCL1 in response to oxidized phospholipids. This was consistent with the rapid increase in glomerular CXCL1 expression followed by macrophage infiltration in Id3(-/-) mice fed a Western diet. CONCLUSIONS: A functional ID3 influences susceptibility to kidney disease and prevents glomerular injury by regulating local chemokine production and inflammatory cell recruitment.

Age-associated B cell infiltration in salivary glands represents a hallmark of Sjögren's-like disease in aging mice.

Sjögren's disease (SjD), characterized by circulating autoantibodies and exocrine gland inflammation, is typically diagnosed in women over 50 years of age. However, the contribution of age to SjD pathogenesis is unclear. C57BL/6 female mice at different ages were studied to investigate how aging influences the dynamics of salivary gland inflammation. Salivary glands were characterized for immune cell infiltration, inflammatory gene expression, and saliva production. At 8 months, gene expression of several chemokines involved in immune cell trafficking was significantly elevated. At this age, age-associated B cells (ABCs), a unique subset of B cells expressing the myeloid markers CD11b and/or CD11c, were preferentially enriched in the salivary glands compared to other organs like the spleen or liver. The salivary gland ABCs increased with age and positively correlated with increased CD4 T follicular helper cells. By 14 months, lymphocytic foci of well-organized T and B cells spontaneously developed in the salivary glands. In addition, the mice progressively developed high titers of serum autoantibodies. A subset of aged mice developed salivary gland dysfunction mimicking SjD patients. Our data demonstrates that aging is a significant confounding factor for SjD. Thus, aged female C57BL/6 mice are more appropriate and a valuable preclinical model for investigating SjD pathogenesis and novel therapeutic interventions.

Age-associated B cell infiltration in salivary glands represents a hallmark of Sjögren's-like disease in aging mice.

Sjögren's disease (SjD), characterized by circulating autoantibodies and exocrine gland inflammation, is typically diagnosed in women over 50 years of age. However, the contribution of age to SjD pathogenesis is unclear. C57BL/6 female mice at different ages were studied to investigate how aging influences the dynamics of salivary gland inflammation. Salivary glands were characterized for immune cell infiltration, inflammatory gene expression, oxidative stress, and saliva production. At 8 months, gene expression of several chemokines involved in immune cell trafficking was significantly elevated. At this age, Age-associated B cells (ABCs), a unique subset of B cells expressing the myeloid markers CD11b and/or CD11c, were preferentially enriched in the salivary glands compared to other organs like the spleen or liver. The salivary gland ABCs increased with age and positively correlated with increased CD4 T follicular helper cells. By 14 months, lymphocytic foci of well-organized T and B cells spontaneously developed in the salivary glands. In addition, the mice progressively developed high titers of serum autoantibodies. A subset of aged mice developed salivary gland dysfunction mimicking SjD patients. Our data demonstrates that aging is a significant confounding factor for SjD. Thus, aged female C57BL/6 mice are more appropriate and a valuable preclinical model for investigating SjD pathogenesis and novel therapeutic interventions.

Dysregulated Ca2+ signaling, fluid secretion, and mitochondrial function in a mouse model of early Sjögren's syndrome.

Saliva is essential for oral health. The molecular mechanisms leading to physiological fluid secretion are largely established, but factors that underlie secretory hypofunction, specifically related to the autoimmune disease Sjögren's syndrome (SS) are not fully understood. A major conundrum is the lack of association between the severity of inflammatory immune cell infiltration within the salivary glands and glandular hypofunction. In this study, we investigated in a mouse model system, mechanisms of glandular hypofunction caused by the activation of the stimulator of interferon genes (STING) pathway. Glandular hypofunction and SS-like disease were induced by treatment with 5,6-Dimethyl-9-oxo-9H-xanthene-4-acetic acid (DMXAA), a small molecule agonist of murine STING. Contrary to our expectations, despite a significant reduction in fluid secretion in DMXAA-treated mice, in vivo imaging demonstrated that neural stimulation resulted in greatly enhanced spatially averaged cytosolic Ca2+ levels. Notably, however, the spatiotemporal characteristics of the Ca2+ signals were altered to signals that propagated throughout the entire cytoplasm as opposed to largely apically confined Ca2+ rises observed without treatment. Despite the augmented Ca2+ signals, muscarinic stimulation resulted in reduced activation of TMEM16a, although there were no changes in channel abundance or absolute sensitivity to Ca2+. However, super-resolution microscopy revealed a disruption in the intimate colocalization of Inositol 1,4,5-trisphosphate receptor Ca2+ release channels in relation to TMEM16a. TMEM16a channel activation was also reduced when intracellular Ca2+ buffering was increased. These data are consistent with altered local coupling between the channels contributing to the reduced activation of TMEM16a. Appropriate Ca2+ signaling is also pivotal for mitochondrial morphology and bioenergetics and secretion is an energetically expensive process. Disrupted mitochondrial morphology, a depolarized mitochondrial membrane potential, and reduced oxygen consumption rate were observed in DMXAA-treated animals compared to control animals. We report that early in SS disease, dysregulated Ca2+ signals lead to decreased fluid secretion and disrupted mitochondrial function contributing to salivary gland hypofunction and likely the progression of SS disease.

Salivary gland hypofunction induced by activation of innate immunity is dependent on type I interferon signaling.

BACKGROUND: Activation of innate immunity through polyinosinic:polycytidylic acid [poly(I:C)] causes acute salivary gland hypofunction. As a major consequence of poly(I:C) treatment is type I interferon (IFN) production, this study was undertaken to investigate their role in salivary gland dysfunction. METHODS: Different strains of mice deficient in either interferon alpha receptor (IFNAR1(-/-)) or IL-6(-/-), or IL-10(-/-), or EBI3(-/-) were treated with poly(I:C). Salivary gland function was determined by measuring pilocarpine-induced saliva volume. Gene expression levels were measured by real-time PCR. Ca(2+) mobilization studies were performed using ex-vivo acinar cells. RESULTS: A single injection of poly(I:C) rapidly induced salivary gland hypofunction in wild-type B6 mice (41% drop in saliva volumes compared to PBS-treated mice). In contrast, the loss of function in poly(I:C)-treated IFNAR(-/-) mice was only 9.6%. Gene expression analysis showed reduced levels of Il-6, Il-10, and Il-27 in submandibular glands of poly(I:C)-treated IFNAR(-/-) mice. While salivary gland dysfunction in poly(I:C)-treated IL-10(-/-) and EBI3(-/-) mice was comparable to wild-type mice, the IL-6(-/-) mice were more resistant, with only a 21% drop in function. Pilocarpine-induced Ca(2+) flux was significantly suppressed in acinar cells obtained from poly(I:C)-treated wild-type mice. CONCLUSIONS: Our data demonstrate that a combined action of type I IFNs and IL-6 contributes toward salivary gland hypofunction. This happens through interference with Ca(2+) mobilization within acinar cells. Thus, in acute viral infections and diseases like Sjögren's syndrome, elevated levels of type I IFNs and IL-6 can directly affect glandular function.