Protein kinase C expression in salivary gland acinar epithelial cells in Sjögren's syndrome

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.

Localization of cystic fibrosis transmembrane conductance regulator signaling complexes in human salivary gland striated duct cells

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-dependent protein kinase (PKA)-regulated Cl(-) channel, crucial for epithelial cell regulation of salt and water transport. Previous studies showed that ezrin, an actin binding and A-kinase anchoring protein (AKAP), facilitates association of PKA with CFTR. We used immunohistochemistry and immunogold transmission electron microscopy to localize CFTR, ezrin, and PKA type II regulatory (RII) and catalytic (C) subunits in striated duct cells of human parotid and submandibular glands. Immunohistochemistry localized the four proteins mainly to the apical membrane and the apical cytoplasm of striated duct cells. In acinar cells, ezrin localized to the luminal membrane, and PKA RII subunits were present in secretory granules, as previously described. Immunogold labeling showed that CFTR and PKA RII and C subunits were localized to the luminal membrane and associated with apical granules and vesicles of striated duct cells. Ezrin was present along the luminal membrane, on microvilli and along the junctional complexes between cells. Double labeling showed specific protein associations with apical granules and vesicles and along the luminal membrane. Ezrin, CFTR, and PKA RII and C subunits are co-localized in striated duct cells, suggesting the presence of signaling complexes that serve to regulate CFTR activity.

Urban legends series: Sjögren's syndrome

Sjögren's syndrome (SjS) is one of the most common autoimmune rheumatic diseases, clinically characterized by xerostomia and keratoconjunctivitis sicca. We investigated the following controversial topics: (i) Do we have reliable ways of assessing saliva production? (ii) How important are the quantity and quality of saliva? (iii) Are only anti-SSA/Ro and anti-SSB/La relevant for the diagnosis of SjS? (iv) Are the American-European Consensus criteria (AECC) the best way to diagnose SjS? Results from literature searches suggested the following: (i) Despite the fact that numerous tests are available to assess salivation rates, direct comparisons among them are scarce with little evidence to suggest one best test. (ii) Recent developments highlight the importance of investigating the composition of saliva. However, more research is needed to standardize the methods of analysis and collection and refine the quality of the accumulating data. (iii) In addition to anti-Ro/La autoantibodies, anti α-fodrin IgA and anti-MR3 autoantibodies seem to be promising diagnostic markers of SjS, but more studies are warranted to test their sensitivity and specificity. (iv) AECC are classification, not diagnostic criteria. Moreover, recent innovations have not been incorporated into these criteria. Consequently, treatment directed to patients diagnosed using the AECC might exclude a significant proportion of patients with SjS.

Muscarinic type 3 receptor induces cytoprotective signaling in salivary gland cells through epidermal growth factor receptor transactivation

Muscarinic type 3 receptor (M3R) plays a pivotal role in the induction of glandular fluid secretions. Although M3R is often the target of autoantibodies in Sjögren's syndrome (SjS), chemical agonists for M3R are clinically used to stimulate saliva secretion in patients with SjS. Aside from its activity in promoting glandular fluid secretion, however, it is unclear whether activation of M3R is related to other biological events in SjS. This study aimed to investigate the cytoprotective effect of chemical agonist-mediated M3R activation on apoptosis induced in human salivary gland (HSG) cells. Carbachol (CCh), a muscarinic receptor-specific agonist, abrogated tumor necrosis factor α/interferon γ-induced apoptosis through pathways involving caspase 3/7, but its cytoprotective effect was decreased by a M3R antagonist, a mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) inhibitor, a phosphatidylinositol 3-kinase/Akt inhibitor, or an epidermal growth factor receptor (EGFR) inhibitor. Ligation of M3R with CCh transactivated EGFR and phosphorylated ERK and Akt, the downstream targets of EGFR. Inhibition of intracellular calcium release or protein kinase C δ, both of which are involved in the cell signaling of M3R-mediated fluid secretion, did not affect CCh-induced ERK or Akt phosphorylation. CCh stimulated Src phosphorylation and binding to EGFR. A Src inhibitor attenuated the CCh/M3R-induced cytoprotective effect and EGFR transactivation cascades. Overall, these results indicated that CCh/M3R induced transactivation of EGFR through Src activation leading to ERK and Akt phosphorylation, which in turn suppressed caspase 3/7-mediated apoptotic signals in HSG cells. This study, for the first time, proposes that CCh-mediated M3R activation can promote not only fluid secretion but also survival of salivary gland cells in the inflammatory context of SjS.

Vasoactive intestinal peptide/vasoactive intestinal peptide receptor relative expression in salivary glands as one endogenous modulator of acinar cell apoptosis in a murine model of Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease characterized by a progressive oral and ocular dryness that correlates poorly with the autoimmune damage of the glands. It has been proposed that a loss of homeostatic equilibrium in the glands is partly responsible for salivary dysfunction with acinar cells involved actively in the pathogenesis of SS. The non-obese diabetic (NOD) mouse model of Sjögren's syndrome develops secretory dysfunction and early loss of glandular homeostatic mechanisms, with mild infiltration of the glands. Based on the vasodilator, prosecretory and trophic effects of the vasoactive intestinal peptide (VIP) on acini as well as its anti-inflammatory properties we hypothesized that the local expression of VIP/vasoactive intestinal peptide receptor (VPAC) system in salivary glands could have a role in acinar cell apoptosis and macrophage function thus influencing gland homeostasis. Here we show a progressive decline of VIP expression in submandibular glands of NOD mice with no changes in VPAC receptor expression compared with normal mice. The deep loss of endogenous VIP was associated with a loss of acinar cells through apoptotic mechanisms that could be induced further by tumour necrosis factor (TNF)-α and reversed by VIP through a cyclic adenosine-5'-monophosphate (cAMP)/protein kinase A (PKA)-mediated pathway. The clearance of apoptotic acinar cells by macrophages was impaired for NOD macrophages but a shift from inflammatory to regulatory phenotype was induced in macrophages during phagocytosis of apoptotic acinar cells. These results support that the decline in endogenous VIP/VPAC local levels might influence the survival/apoptosis intracellular set point in NOD acinar cells and their clearance, thus contributing to gland homeostasis loss.

Mechanisms involved in injury and repair of the murine lacrimal gland: role of programmed cell death and mesenchymal stem cells

The non-keratinized epithelia of the ocular surface are constantly challenged by environmental insults, such as smoke, dust, and airborne pathogens. Tears are the sole physical protective barrier for the ocular surface. Production of tears in inadequate quantity or of inadequate quality results in constant irritation of the ocular surface, leading to dry eye disease, also referred to as keratoconjunctivitis sicca (KCS). Inflammation of the lacrimal gland, such as occurs in Sjogren syndrome, sarcoidosis, chronic graft-versus-host disease, and other pathological conditions, results in inadequate secretion of the aqueous layer of the tear film and is a leading cause of dry eye disease. The hallmarks of lacrimal gland inflammation are the presence of immune cell infiltrates, loss of acinar epithelial cells (the secreting cells), and increased production of proinflammatory cytokines. To date, the mechanisms leading to acinar cell loss and the associated decline in lacrimal gland secretion are still poorly understood. It is also not understood why the remaining lacrimal gland cells are unable to proliferate in order to regenerate a functioning lacrimal gland. This article reviews recent advances in exocrine tissue injury and repair, with emphasis on the roles of programmed cell death and stem/progenitor cells.

Aberrant localization of ezrin correlates with salivary acini disorganization in Sjogren's Syndrome

OBJECTIVES

To analyse whether the alterations in the structure and organization of microvilli in salivary acinar cells from SS patients are linked to changes in the expression and/or cellular localization of ezrin.

METHODS

Salivary gland (SG) acini from controls and SS patients were used to evaluate ezrin expression by western blot and localization of total and activated (phospho-Thr567) ezrin by IF and EM.

RESULTS

In acini from control labial SGs, ezrin was located predominantly at the apical pole and to a lesser extent at the basal region of these cells. Conversely, in acini extracts from SS patients, ezrin showed significantly elevated levels, which were accompanied with localization mostly at the basal region. Moreover, F-actin maintained its distribution in both the apical region and basolateral cortex; however, it was also observed in the acinar cytoplasm. Phospho-ezrin (active form) was located exclusively at the apical pole of acinar cells from control subjects and abundantly located at the basal cytoplasm in SS samples. These results were confirmed by immunogold studies.

CONCLUSIONS

The decrease of ezrin and phospho-ezrin at the apical pole and the cytoplasmic redistribution of F-actin suggest an altered interaction between the F-actin-cytoskeleton and plasma membrane in SS patient acini, which may explain the microvilli disorganization. These alterations could eventually contribute to SG hyposecretion in SS patients.

Vasoactive intestinal peptide inhibits TNF-alpha-induced apoptotic events in acinar cells from nonobese diabetic mice submandibular glands

Introduction

The role of apoptotic secretory epithelium as a pro-inflammatory triggering factor of exocrine dysfunction is currently explored in Sjogren's syndrome patients and in the nonobese diabetic (NOD) mouse model. Vasoactive intestinal peptide (VIP) has anti-inflammatory effects in various models of chronic inflammation. Our goal was to analyse the effect of TNF-α on apoptotic mediators in isolated acinar cells from NOD submandibular gland and their modulation by VIP.

Methods

Acinar cells were isolated from submandibular glands of 16-week-old NOD females with salivary flow decline. Age-matched BALB/c females or eight-week-old NOD females were used as controls. Apoptotic mediators and TNF-α receptor expression were assessed by immunoblotting and RT-PCR, caspase 3 activity was assessed by optical density at 405 nm with Ac-DEVD-pNA as a substrate and chromatin condensation by Hoechst stain. They were evaluated in resting conditions and after a 3.5 or 6 hours of culture with TNF-α. VIP effects in acinar cells were assessed at 100 nM in TNF-α-treated cultures and VIP receptor functional assays by radio immunoassay (cAMP) or enzymatic detection (amylase).

Results

NOD acinar cells at 16 weeks present an increased expression of TNF-α receptor1 together with increased Bax, tumour protein 53-induced nuclear protein1α (TP53INP1α), caspase 3 activity and chromatin condensation. Acini from NOD mice were more sensitive to TNF-α-induced increases of apoptotic mediators than control cells. VIP inhibited TNF-α-induced apoptotic events through functional VPAC1 receptors coupled to the protein kinase A (PKA) signalling pathway.

Conclusions

Our results indicate that acinar cells isolated from submandibular glands of NOD mice with salivary dysfunction are more sensitive to apoptosis induced by TNF-α which could be prevented by VIP through a PKA-mediated pathway.

Modified aquaporin 5 expression and distribution in submandibular glands from NOD mice displaying autoimmune exocrinopathy

OBJECTIVE

To investigate the expression and localization of aquaporin 5 (AQP5) in salivary glands and salivary gland function in the NOD mouse.

METHODS

All experiments were performed using NOD and BALB/c mice (ages 8 weeks and 24 weeks). Real-time reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemical analysis were used to study the expression and distribution of AQP5 in salivary glands. In addition, salivary gland function was determined.

RESULTS

Compared with the levels in BALB/c mice, relative AQP5 messenger RNA levels were not significantly modified in the parotid glands from NOD mice of both ages but were significantly increased in the submandibular glands from NOD mice of both ages. Western blot analyses of both salivary gland membranes revealed that the level of AQP5 protein was increased in 24-week-old NOD mice. Important inflammatory infiltrates were observed in the submandibular glands, but not in the parotid glands, from 24-week-old NOD mice. The 8-week-old and 24-week-old BALB/c mice and the 8-week-old NOD mice showed AQP5 primarily at the apical membrane of the salivary gland acinus. In contrast, in acini from the submandibular glands (but not the parotid glands) from 24-week-old NOD mice, AQP5 staining was reduced at the apical membrane but was increased at the basal membrane. A moderately statistically significant decrease in pilocarpine-stimulated salivary flow was observed in 24-week-old NOD mice compared with that in age-matched BALB/c mice.

CONCLUSION

Submandibular glands from 24-week-old NOD mice displayed inflammatory infiltrates, increased AQP5 protein expression, and impaired AQP5 distribution. However, the moderately statistically significant decrease in the salivary flow rate in these mice did not match the extent of AQP5 misdistribution.

Inflammation in dry eye

Dry eye is a condition of altered tear composition that results from a diseased or dysfunctional lacrimal functional unit. Evidence suggests that inflammation causes structural alterations and/or functional paralysis of the tear-secreting glands. Changes in tear composition resulting from lacrimal dysfunction, increased evaporation and/or poor clearance have pro-inflammatory effects on the ocular surface. This inflammation is responsible in part for the irritation symptoms, ocular surface epithelial disease, and altered corneal epithelial barrier function in dry eye. Anti-inflammatory therapies for dry eye target one or more of the inflammatory mediators/pathways that have been identified in dry eye.

Pathophysiology of Sjögren's syndrome

The term Sjögren's syndrome refers to keratoconjunctivitis sicca and xerostomia due to lymphocytic infiltrates of lachrymal and salivary glands. The current used criteria for diagnosis of primary Sjögren's syndrome is the American-European consensus. Primary Sjögren's syndrome is an autoimmune disorder characterized by lymphocytic infiltrates and destruction of the salivary and lachrymal glands and systemic production of autoantibodies to the ribonucleoprotein particles SS-A/Ro and SS-B/La. The infiltrating cells (T- and B-cells, dendritic cells) interfere with glandular function at several points: destruction of glandular elements by cell-mediated mechanisms; secretion of cytokines that activate pathways bearing the signature of type 1 and 2 interferons; production of autoantibodies that interfere with muscarinic receptors; and secretion of metalloproteinases (MMPs) that interfere with the interaction of the glandular cell with its extracellular matrix, which is necessary for efficient glandular function. As the process progresses, the mucosal surfaces become sites of chronic inflammation and the start of a vicious circle. Despite extensive study of the underlying cause of Sjögren's syndrome, the pathogenesis remains obscure. In broad terms, pathogenesis is multifactorial; environmental factors are thought to trigger inflammation in individuals with a genetic predisposition to the disorder.

Immunohistopathology of Sjögren's syndrome

Sjögren's syndrome (SS) is characterized by keratoconjunctivitis sicca and xerostomia, which occur in an autoimmune lacrimal and salivary gland disease characterized by lymphocyte infiltrates of exocrine glands and/or Sjögren's syndrome autoantibody production. It has been reported that aquaporin-5 distribution is abnormal in SS, perhaps as a result of paracrine effect of TNF-alpha. Also the neurogenic regulation of the salivary gland is impaired in SS. Apart from functional changes, the syndrome is also characterized by structural abnormalities of the secretory acinar apparatus. The acinar basement membrane is abnormal as it lacks laminin alpha1 chain, which may impair its capability to induce the progenitor cells to differentiate to acinar cells. CRISP-3 and TMPRSS-2 can be used as androgen markers and LIV-1 and Cyr61 as estrogen markers to study the sexual dimorphism of the salivary glands. Patients with SS seem to have low concentrations of dehydroepiandrosterone, which may predispose women and the exocrine glands to this syndrome.

Laboratory findings in tear fluid analysis

The tear film, composed of the lipid, aqueous and mucin layers, has many functions including defending the ocular surface. The tear film covering the ocular surface presents a mechanical and antimicrobial barrier and ensures an optical refractive surface. The lipid component originates from the meibomian glands of the tarsus and forms the superficial layer of the tear film. The aqueous component contains electrolytes, water, and a large variety of proteins, peptides and glycoproteins, and is primarily secreted by the lacrimal gland. Mucins are glycoproteins expressed by epithelial tissues of mucous surfaces. They protect tissues by functioning as antioxidants, providing lubrication, and inhibiting bacterial adherence. Quantitatively and qualitatively, its composition must be maintained within the fairly narrow limits to maintain a healthy and functional visual system. Abnormalities of the tear film, affecting the constituents or the volume, can rapidly result in serious dysfunction of the eyelids and conjunctiva and ultimately affect the transparency of the cornea. Many ocular surface tests have been developed for the clinical diagnosis of dry eye syndromes. This paper provides an overview on laboratory methods for the analysis of the tear film. Understanding the components of the tear film will aid in the treatment of dry eye syndromes and the ocular surface diseases.

Effect of inflammation on lacrimal gland function

The lacrimal gland is the main contributor to the aqueous layer of the tear film. It secretes proteins, electrolytes and water, which helps to nourish and protect the ocular surface. Lacrimal gland secretion is primarily under neural control, which is achieved through a neural reflex arc. Stimuli to the ocular surface activate afferent sensory nerves in the cornea and conjunctiva. This in turn activates efferent parasympathetic and sympathetic nerves in the lacrimal gland to stimulate secretion. Sex steroid hormones are also important regulators of lacrimal gland functions. A decrease or lack of lacrimal gland secretion is the leading cause of aqueous tear deficient dry eye syndrome (DES). It has been suggested that DES is an inflammatory disorder that affects the ocular surface and the lacrimal gland. In several pathological instances, the lacrimal gland can become a target of the immune system and show signs of inflammation. This can result from autoimmune diseases (Sjögren's syndrome), organ transplantation (graft versus host disease), or simply as a result of aging. The hallmarks of lacrimal gland inflammation are the presence of focal lymphocytic infiltrates and increased production of proinflammatory cytokines. The mechanisms leading to lacrimal gland dysfunction are still poorly understood. Apoptosis, production of autoantibodies, hormonal imbalance, alterations in signaling molecules, neural dysfunction, and increased levels of proinflammatory cytokines have been proposed as possible mediators of lacrimal gland insufficiency in disease states.

The protein kinase C system in focal adenitis of the lacrimal gland in the non-obese diabetic mouse model for Sjögren's syndrome

PURPOSE

Non-obese diabetic (NOD) mice develop an autoimmune exocrinopathy characterized by hyposecretion of saliva and acinar cell atrophy. As the protein kinase C (PKC) system is involved in the signal transduction pathways associated with primary secretion and acinar cell differentiation and growth, the PKC profile was analysed in NOD mice.

METHODS

Lacrimal glands from BALB/c, NOD, NOD scid and transgenic NOD x interferon-gamma (IFN-gamma) mice were analysed for their PKC profiles using antibodies against several conventional (alpha, beta, gamma), novel (delta, epsilon, theta) and atypical (iota, lambda) PKC isoforms using the Streptavidin/HRP (horseradish peroxidase) method.

RESULTS

Acinar cells in BALB/c control mice expressed two conventional (alpha, beta) and two atypical (iota, lambda) PKC isoforms. In NOD and transgenic NOD x IFN-gamma mice the same isoforms were more strongly expressed. NOD scid mice lacked all other PKC isoforms except PKC lambda.

CONCLUSIONS

Co-expression of several PKC isoforms in single cell type may be necessary for transcriptional activation and agonist-induced secretory responses. Hyposecretion in NOD mice was paradoxically associated with up-regulation of the PKC system. This may be associated with a deranged signal transduction per se rather than with the immune-inflammation, as the transgenic NOD x IFN-gamma mice showed similar PKC profiles. The NOD model does not reproduce lack/consumption of PKC II and PKC as in Sjögren's syndrome. This may be because the receptor autoantibodies in mice are directed against the adrenergic, not muscarinic, receptors. Lack and/or low level PKC expression in NOD scid mouse may explain the excessive acinar cell apoptosis in this model.

Altered traffic to the lysosome in an ex vivo lacrimal acinar cell model for chronic muscarinic receptor stimulation

Evidence suggests that lacrimal and salivary epithelial cells constitutively expose potentially pathogenic autoantigens, but that active regulatory networks normally suppress pathological autoimmune responses . Events that potentially disrupt the regulatory networks include increased exposure of constitutive autoantigens and induced exposure of previously cryptic autoantigen epitopes. Chronic muscarinic receptor (MAChR) stimulation in an ex vivo rabbit lacrimal acinar cell model induces functional and biochemical alterations reminiscent of the functional quiescence associated with Sjogren's syndrome . Chronic MAChR stimulation also elicits changes in the compartmental distribution of beta-hexosaminidase, a product that normally is dually targeted into the lysosomal pathway and the regulated apical secretory pathway. Here, we use subcellular fractionation analyses to further explore the nature of the stimulation-induced traffic changes and to identify effectors that might mediate this change. Overnight stimulation of primary cultured rabbit lacrimal gland acinar cells with 10 microM carbachol (CCh) significantly decreased the abundance of mature cathepsin B in the pre-lysosome and lysosome; decreased the abundance of preprocathepsin B in fractions containing the TGN and late endosome; increased the abundance of procathepsin B in fractions containing the basal-lateral membrane; and increased the accumulation of endocytosed [(125)I]-EGF in the recycling endosome. Alterations in distribution or abundance of traffic effectors included: increased abundances of rab5A and rab6 in the TGN; decreased overall abundance of gamma-adaptin; remarkably increased relative abundance of membrane phase-associated actin; redistribution of cytoplasmic dynein from biosynthetic and proximal endocytic compartments to the lysosome; and redistribution of p150(Glued) from the lysosome to biosynthetic or proximal endocytic compartments. We conclude that chronic MAChR stimulation blocks traffic from the early endosome and the TGN to the lysosome, causing lysosomal proteins to reflux to the TGN, endosomes, and basal-lateral membrane. These traffic alterations may be mediated through action on one or more of the effectors noted.

Recent advances in understanding molecular mechanisms in the pathogenesis and antibody profile of Sjögren's syndrome

Sjögren's syndrome is a chronic autoimmune and rheumatic disorder of the mucous membranes caused by a lack of proper exocrine secretions, with prominent sicca complaints. The molecular mechanisms of the pathogenesis are virtually unknown, although progress has been made with regard to chemokines, B cell activating factor, and apoptosis. A large number of autoantibodies have been reported in Sjögren's syndrome, some of which relate to impairment of glandular function. Sjögren's syndrome is a female-dominant disease with a late age of onset; most patients contract the disease at the age of 40 to 50 years. Lately, attention has been drawn to the effects of adrenopause in Sjögren's syndrome and on dehydroepiandrosterone and its intracrine metabolism in target tissues. This can influence the maintenance and remodeling of exocrine glands and may explain, in part, another important disease symptom--fatigue.

Biochemical changes contributing to functional quiescence in lacrimal gland acinar cells after chronic ex vivo exposure to a muscarinic agonist

Profound secretory dysfunction can be associated with relatively modest lymphocytic infiltration of the lacrimal and salivary glands of Sjögren's syndrome (SjS) patients. SjS patients' sera contain autoantibodies to M3 muscarinic acetylcholine receptors (MAChR) that have variously been reported to have agonistic and antagonistic effects. We sought to identify consequences of chronic agonist stimulation by maintaining acinar cells from rabbit lacrimal glands for 20 h in the presence or absence of 10 microM carbachol (CCh). Exposure to CCh diminished the cells' ability to elevate cytosolic Ca2+ and secrete beta-hexosaminidase in response to acute stimulation with 100 microM CCh, but it enhanced their secretory responses to phenylephrine and ionomycin. Secretory vesicles appeared normal by electron microscopy, but confocal fluorescence microscopy revealed depletion of the secretory vesicle membrane marker, rab3D, and decreased ability to recruit secretory transport vesicles in response to acute 100 microM CCh. Additionally, the apical cortical actin cytoskeleton was disrupted and diminished compared to the basal-lateral cortical network. Subcellular fractionation analyses revealed that total membrane phase protein content was increased. The contents of beta-hexosaminidase and MAChR relative to total protein were not significantly altered, and MAChR abundance in the plasma membrane fraction was increased as the result of redistribution from endomembrane pools. However, relative cellular contents of the heterotrimeric guanosine triphosphate (GTP)-binding proteins, Gq and G11, were decreased. Additional biochemical changes included decreased contents of 47 kDa Gs and Gi3, protein kinase Calpha and rab3D and polymeric immunoglobulin (Ig) receptors; internalization of Na,K-ATPase from the plasma membranes to endomembrane compartments and decreased content of beta-hexosaminidase in the lysosomes. The observations demonstrate that chronic exposure to a MAChR agonist induces refractoriness to optimal stimulation, without causing receptor downregulation, by downregulating postreceptor-signalling mediators and effectors. The cells' secretory mechanisms for IgA and electrolytes also appear to be impaired, as does their ability to properly sort proteins to the lysosomes.

Salivary gland scintigraphy in Sjögren's syndrome and patients with sicca symptoms but without Sjögren's syndrome: the psychological profiles and predictors for salivary gland dysfunction

OBJECTIVE

To characterise the psychological profiles of Sjögren's syndrome (SS) and patients with sicca symptoms but without SS; to find predictors for salivary gland function; to evaluate salivary scintigraphy as a method to differentiate between SS and patients with sicca symptoms but without SS.

PATIENTS AND METHODS

Psychological tests (Medical Outcomes Study Short Form General Health Survey (SF-36), Jenkins Activity Survey, Toronto Alexithymia Scale, and Maastricht Questionnaire for vital exhaustion) were performed and assessment of the function of the salivary glands made in 26 patients with primary SS, 8 with secondary SS, and 9 with sicca symptoms but without SS. Data were analysed with BMDP new system version 1.0 statistical program.

RESULTS

Psychological profiles were similar in all groups. Hb, RF, ANA, and SSA differentiated between the groups. Results of salivary scintigraphy were predicted to 51% by ANA, SSA, SSB, IgG, IgA, diagnosis, vitality, and role limitations due to emotional problems. No predictors were found for the resting salivary flow. Salivary scintigraphy was pathological in 21/26 (81%) and in 8/8 (100%) patients with secondary SS, but only in 2/9 (22%) patients with sicca symptoms without SS (p=0.002) (sensitivity 85.3%, specificity 77.8%).

CONCLUSIONS

Patients with sicca symptoms but without SS have sickness behaviour similar to that of patients with SS. The results of salivary scintigraphy can be predicted by diagnosis and autoimmune findings; psychological characteristics added 20% to this predictive value. Distinction between SS and patients with sicca symptoms but without SS is difficult, but in addition to autoantibodies, salivary scintigraphy can be used for this purpose.

Protein kinase C expression in salivary gland acinar epithelial cells in non-obese diabetic mice, an experimental model for Sjögren's syndrome

We planned to investigate the expression of protein kinase C (PKC) isoforms in acinar epithelial cells of salivary glands in the non-obese diabetic (NOD) mouse to find out if they develop changes of the PKC system like those seen in the human counterpart, i.e. in Sjögren's syndrome. Parotid, submandibular, and sublingual glands from NOD and control BALB/c mice were stained with a panel of monoclonal antibodies directed against conventional (alpha, beta, and gamma), novel (delta, epsilon, and theta), and atypical (lambda and iota) PKC isoforms using the streptavidin/HRP method. Similarly to human labial salivary glands, acinar epithelial cells of the healthy control BALB/c mice contained two of the conventional PKC isoforms, alpha and beta. Acinar and ductal epithelial cells also contained the atypical PKC isoforms lambda and iota. PKC isoforms gamma, delta, epsilon, and theta were not found. NOD mice which displayed focal sialadenitis contained the same conventional and atypical PKC isoforms. The acinar cells in NOD mice, in contrast to the Sjögren's syndrome patients, did not lack PKC alpha or beta. On the contrary, PKC alpha and beta staining was stronger than in the control BALB/c mice. The present results demonstrate that both conventional and atypical PKC isoforms participate in the salivary epithelial cell biology and that there are mouse strain-associated and/or disease state-associated changes in their expression. The lack of PKC alpha and beta isoforms found in Sjögren's syndrome was not reproduced in NOD mice, which discloses one more difference between the human disease and its NOD mouse model.

Parasympathetic nervous system dysfunction in primary Sjögren's syndrome

In the past sicca syndromes were attributed to destruction of glandular tissue. It is now thought that cytokines, autoantibodies, and parasympathetic nervous system dysfunction all have an important role in the xerostomia and xerophthalmia in Sjögren's syndrome.

Primary Sjögren's syndrome: oral aspects on pathogenesis, diagnostic criteria, clinical features and approaches for therapy

Primary Sjögren's syndrome (pSS) is a chronic inflammatory systemic autoimmune disease affecting the exocrine glands and predominantly the salivary and lacrimal glands. The impaired gland function is assumed to be a result of progressive lymphocyte-mediated destruction of the exocrine gland tissue leading to the cardinal manifestations, hyposalivation and keratoconjunctivitis sicca (KCS), as well as devastating symptoms of oral and ocular dryness. Although primarily characterised as an exocrine dysfunction, non-exocrine organs may also be affected. The onset and course of pSS is usually insidious but may develop into a disabling disease, which profoundly affects the patient's general well being and quality of life. Moreover, pSS may even evolve into a lymphoid malignancy. The aetiology of pSS remains unknown but the pathogenesis of exocrine cell damage is apparently multi-factorial, including immunological, genetic, hormonal and viral components. Recent research also includes neurogenic aspects of exocrine gland dysfunction, including the interference of immune mediators with glandular response to neurotransmitters released from nerve fibres. pSS usually affects middle-aged women and the female:male ratio is 9:1. The prevalence varies from 0.29-4.8%, depending on the population sampled and the diagnostic criteria used. At present, there are no specific diagnostic tests for pSS and no universally accepted diagnostic criteria. The current therapy is primarily symptomatic. This review focuses on the current oral clinical, diagnostic, pathogenic and therapeutic aspects of pSS.

Ku protein and DNA strand breaks in lip glands of normal and primary Sjögren's syndrome subjects: lack of correlation with apoptosis

The aim was to examine tissue expression of Ku protein in lower lip salivary gland (LSG) biopsies from cases of primary Sjögren's syndrome (SS) and from normal subjects.

METHODS

immunohistochemistry was used with antibodies to Ku70/86 and also Ki67, PCNA and p53. In addition, the Klenow method was applied in order to detect evidence of apoptosis. Sections of hyperplastic tonsil served as additional controls.

RESULTS

in normal controls, LSG acinar cells stained negatively whereas LSG excretory duct cell nuclei stained positively with Ku and Klenow and occasionally with PCNA but negatively with Ki67 and p53. In LSG focal sialadenitis of SS cases, some lymphocytic cells showed staining with Ku, Ki67, PCNA, Klenow and p53. In addition to duct cell Ku and Klenow as well as PCNA staining which was not much different from normals, a few ductal epithelial and also mononuclear cells stained with p53. In focal sialadenitis, some acinar cells showed staining with PCNA as well as with Klenow.

CONCLUSIONS

our findings in LSG biopsies of SS cases added little to an increased understanding about the pathogenetic mechanisms in the development of focal sialadenitis in SS. However, in normal LSG, ductal epithelial but not acinar cells seem to express a constitutively specific Ku protein and Klenow profile, suggestive of DNA strand breaks but not clearly associated with ongoing apoptotic events. It may reflect an enhanced stress response, which may be pathogenetically important in the early events of focal sialadenitis development in primary Sjögren's syndrome.

Abnormal distribution of aquaporin-5 water channel protein in salivary glands from Sjögren's syndrome patients

Patients with Sjögren's syndrome (SS) suffer from deficient secretion of saliva due to an autoimmune destruction of salivary glands, however, glandular dysfunction also occurs without destruction. Based upon its abnormal distribution in SS salivary glands, a potential role for the water channel protein aquaporin-5 (AQP5) is proposed in the pathogenesis of SS. The immunohistochemical distribution of AQP5 was compared in minor salivary gland biopsies obtained from women after informed consent: primary SS (53.2 +/- 14 years old, n = 10), healthy volunteers (46.2 +/- 17 years old, n = 10), patients with sarcoidosis (37 and 48 years old), and patients with non-specific sialoadenitis (54 and 61 years old). Biopsies from normal subjects revealed AQP5 primarily at the apical membrane of the salivary gland acinus. In contrast, biopsies from SS patients revealed AQP5 primarily at the basal membranes of the acinus. The AQP5 distribution in biopsies from patients with other dry mouth disorders, such as non-specific sialoadenitis or sarcoidosis, was similar to biopsies from control subjects. Computer-assisted microscopy was performed to quantitatively evaluate AQP5 distribution in the immunoreactive acini of both SS and control subjects. Biopsies from SS patients had higher labeling indices (percentage of acinus area immunoreactive for AQP5) at the basal membrane when compared with biopsies from control subjects. In contrast, biopsies of SS patients exhibited lower labeling indices at the apical membrane when compared with biopsies from control subjects. To verify the specificity of the AQP5 antibody, Western blot analysis was performed on membranes from Xenopus oocytes injected with AQP5 cRNA or on membranes from minor salivary glands of control subjects and SS patients. In each case, the immunoblots had a 27 kd band, corresponding to the expected molecular weight of AQP5. Abnormal distribution of AQP5 in salivary gland acini is likely to contribute to the deficiency of fluid secretion, which is a defining feature of Sjögren's syndrome.

Impaired microvascular response to cholinergic stimuli in primary Sjögren's syndrome

OBJECTIVE

Signs of a parasympathetic dysfunction have been revealed in primary Sjögren's syndrome (SS). Its role in the pathogenesis and the clinical picture of the disease is not clear. To investigate the responsiveness of SS patients to a cholinergic agonist, a model was used involving examination of the cutaneous microcirculation. The microvascular response to the administration of carbachol was measured, a muscarinic cholinergic agonist.

METHODS

Twenty two SS patients and 12 controls were examined. Carbachol and 0.9% saline solution were administered intracutaneously into the forearm skin at two distinct places. Skin blood flow (SBF) in the injected areas was measured continuously before and for 10 minutes after the injections by means of a laser Doppler perfusion monitor. The increase in SBF in response to carbachol (dSBF), reflecting vasodilatation, was calculated by a formula including the baseline and the maximum SBF values after the injections of carbachol and saline solution.

RESULTS

The vasodilatation was significantly lower in SS patients than in the controls (mean dSBF: 2.1 (range: 1.0-4.5) versus 3.3 (range: 1.7-7.6), p=0.02). With non-responder patients defined as those in whom a smaller response was observed than in any of the controls, 11 of the 22 SS patients proved to be non-responders to carbachol. Comparisons of demographic, clinical and laboratory characteristics and HLA class II genotypes between responder and non-responder SS patients did not show any significant differences.

CONCLUSIONS

A diminished or absent response to carbachol indicates a cholinergic dysfunction in SS patients. A disturbance in the neurotransmission at a receptorial or postreceptorial level is hypothesised. Unresponsiveness to cholinergic stimuli may contribute to exocrine insufficiency.

Sjögren autoantibodies modify neonatal cardiac function via M1 muscarinic acetylcholine receptor activation

Isolated congenital heart block may be associated with primary Sjögren syndrome. In this work we describe circulating antibodies in the sera of primary Sjögren syndrome patients that are able to interact with neonatal myocardium by activating muscarinic acetylcholine receptors of M1 subtype. We report on the presence of autoantibodies against the second extracellular loop of human M1 muscarinic acetylcholine receptors in primary Sjögren syndrome mothers whose children have congenital heart block using a synthetic peptide in indirect immunofluorescence technique. Autoantibodies from primary Sjögren syndrome patients gave positive image on neonatal atria but not on adult atria slices. The synthetic M1 peptide selectively abrogated indirect immunofluorescence recognition. The primary Sjögren syndrome-immunoglobulin G also displayed an 'agonist like' activity modifying the intracellular events associated with muscarinic acetylcholine receptor activation. The mechanism appears to occur secondarily to stimulation of phosphoinositides turnover via phospholipase C activation. This, in turn, triggers cascade reactions involving calcium/calmodulin and leads to activation of nitric oxide synthase and soluble guanylate cyclase. All of these effects were selectively blunted by pirenzepine and neutralized by M1 synthetic peptide. These biological effects were not obtained using adult instead of neonatal rat atria and neither occurred with the sera of normal healthy women of childbearing age. It could be concluded that antibodies against neonatal M1 muscarinic acetylcholine receptor may be another serum factor to be considered in the pathophysiology of the development of congenital heart block associated with primary Sjögren syndrome mothers.

An alternative perspective to the immune response in autoimmune exocrinopathy: induction of functional quiescence rather than destructive autoaggression

Sjögren's syndrome is characterized by dryness of the eyes and the mouth due to mononuclear cell infiltration of the lacrimal and salivary glands. The aetiology is unknown but autoimmunity is considered to play a significant role in the pathogenesis. Recent studies have focused on the fact that tear and salivary flow involves an entire functional system that includes the mucosal surfaces with adnexes (the site of inflammation), efferent nerve signals sent to the midbrain (lacrimal and salivary response region), and afferent neural signals from the brain to the acinar/ductal epithelial structures in the gland. Mononuclear cell infiltration in exocrine glands can lead to glandular destruction, suggested to be mediated through apoptosis. However, the functional impairment of exocrine glands could be regulated by cytokines and/or antibodies against the muscarinic M3 receptor by inhibiting the neural stimulation of the residual glands. This review discusses the possibility that the pathogenesis of Sjögren's syndrome comprises aberrant immune-mediated neuro-hormonal events.

Matrix metalloproteinase (MMP)-9 type IV collagenase/gelatinase implicated in the pathogenesis of Sjögren's syndrome

Type IV collagenases/gelatinases (matrix metalloproteinases MMP-2 and MMP-9) in labial salivary glands (LSG) and saliva in Sjögren's syndrome (SS) and healthy controls were studied. Zymograms and Western blots disclosed that SS saliva contained 92/82 kD MMP-9/type IV collagenase duplex. Specific activity measurement disclosed 53.1+/-9.8 U/mg protein MMP-9 in SS compared to 16.5+/-2.6 U/mg in healthy controls (p=0.01). MMP-2 did not differ between SS and controls. In SS salivary glands, MMP-2 and MMP-9 were also expressed, in addition to stromal fibroblasts and occasional infiltrating neutrophils, respectively, in acinar end piece cells. In addition, an effective proMMP-9 activator, human trypsin-2 (also known as tumor-associated trypsin-2 or TAT-2), was found in acinar end piece cells and in saliva. Interestingly, proteolytically processed MMP-9 was found in saliva (vide supra), and in vivo activated MMP-9 was significantly higher in SS than in controls (p=0.002). LSGs, particularly in SS, were characterized ultrastructurally by areas containing small cytoplasmic vesicles in the basal parts of the epithelial cells associated with areas of disordered and thickened basal lamina. Based on our results, we conclude here that SS saliva contains increased concentrations of MMP-9, which is of glandular origin in part. Pro MMP-9 is to a large extent proteolytically activated. This is probably mediated by the most potent pro MMP-9 activator found in vivo thus far, namely trypsin-2. Therefore, the MMP 9/trypsin-2 cascade may be responsible for the increased remodelling and/or structural destruction of the basement membrane scaffolding in salivary glands in SS. Due to the role of basal lamina as an important molecular sieve and extracellular matrix-cell signal, these pathological changes may contribute to the pathogenesis of the syndrome.

Neuropeptides of the autonomic nervous system in Sjögren's syndrome

OBJECTIVE

To assess the activity level of the autonomic nervous system in Sjögren's syndrome (SS) and to correlate this with stress.

METHODS

Patients with SS (n = 12) and healthy controls (n = 10) were analysed for the content of vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) in their stimulated saliva by radioimmunoassays and for stress by the use of a modified Jenkins Activity Survey (JAS).

RESULTS

The data are expressed as median (interquartile range). Salivary VIP output (pg/min) and NPY output (pg/min) were high in SS compared with healthy controls (30.0 (15.6, 36.6) versus 12.3 (9.2, 24.0), p = 0.045, 4.8 (0.6, 24.1) versus 0.7 (0.0, 2.4), p = 0.038, respectively). Patients experienced only a little, but not significantly, more stress than the healthy controls (stress index -2.8 (-7.7, 6.9) versus -5.2 (-12.9, 2.7), p > 0.05). Stress in general was associated with high salivary VIP concentrations (r = 0.41, p = 0.05).

CONCLUSIONS

These findings show that adequately processed saliva (containing aprotinin and EDTA as neuropeptidase inhibitors) contains measurable amounts of marker peptides of the autonomic nervous system. Secondly, VIP concentration but not output may be affected by stress, which may act by decreasing watery salivary flow. In patients with SS, VIP and NPY outputs are increased. This may indicate increased leakage into saliva or efforts to compensate for the diminished salivary flow, or both.