Nitric oxide synthase I and VIP-activated signaling are affected in salivary glands of NOD mice

Potential immunomodulatory role of VIP in the implantation sites of prediabetic nonobese diabetic mice

Among several factors known to modulate embryo implantation and survival, uterine quiescence and neovascularization, maternal immunotolerance through the Th1/Th2 cytokine balance towards a Th2 profile, local regulatory T-cell (Treg) activation, and high levels of progesterone were assigned a prominent role. Vasoactive intestinal peptide (VIP) is a neuroimmunopeptide that has anti-inflammatory effects, promotes Th2 cytokines and CD4+CD25+FOXP3+Treg activation, and stimulates exocrine secretion, smooth muscle relaxation, and vasodilatation favoring uterus quiescence. The goal of the present work was to explore the participation of VIP in the implantation sites of normal and pregnant prediabetic nonobese diabetic (NOD) females, a mouse strain that spontaneously develops an autoimmune exocrinopathy similar to Sjögren's syndrome. Our results indicate a reduction in litter size from the third parturition onwards in the NOD female lifespan with increased resorption rates. Progesterone systemic levels were significantly decreased in pregnant NOD mice compared with BALB/c mice, although the allogeneic response to progesterone by spleen cells was not impaired. VIP receptors,Vipr1andVipr2(Vpac1andVpac2), were expressed at the implantation sites and VIP induced leukemia inhibitory factor (LIF) and Treg marker expression in both strains; however, a reducedVipexpression was found in NOD implantation sites. We conclude that the reduced birth rate at 16-week-old NOD mice with a Th1 systemic cytokine profile involves resorption processes with a lower expression of VIP at the sites of implantation, which acts as a local inducer of pro-implantatory LIF and Treg activation.

Reduced nitric oxide synthase and cyclo-oxygenase activity in the uterus of non-obese diabetic mice

A functional interaction between progesterone, Th2 cytokines and a suitable balance between nitric oxide and prostaglandins in the uterus is considered to have a major role in the success of embryo implantation and pregnancy. Non-obese diabetic (NOD) mice offer a suitable model to study the modulatory role of Th1 cytokines on uterus signalling and function, since at the prediabetic stage they develop a spontaneous Th1 autoimmune response against exocrine glands similar to Sjögren's syndrome. Vasoactive intestinal peptide (VIP) is a vasoactive neuro- and immunopeptide that promotes Th2 profiles and contributes to the smooth muscle relaxation and vasodilation. The aim of the present study was to investigate the activities of nitric oxide synthase and cyclo-oxygenase and the effect of VIP in the uterus of NOD mice with an emerging Th1 cytokine response. We present evidence of a reduced basal and VIP-stimulated activity of both enzymes in the uterus of NOD mice compared with normal BALB/c mice in proestrus. An altered functional interaction between both enzymes is also present in NOD mice at the time when increased levels of serum interleukin (IL)-12 and tumour necrosis factor-alpha but not interferon (IFN)-gamma or IL-10 were detected. We conclude that signalling alterations in uteri of NOD mice are simultaneous to the onset of a systemic Th1 cytokine response.

VIP limits LPS-induced nitric oxide production through IL-10 in NOD mice macrophages

The spontaneous non obese diabetic (NOD) mouse model of Sjögren's syndrome provides a valuable tool to study the onset and progression of both autoimmune response and secretory dysfunction. Vasoactive intestinal peptide (VIP) is a neuro and immunopeptide with prosecretory effect in salivary glands and anti-inflammatory actions in various models of autoimmune disease. Our purpose was to analyze the response of peritoneal macrophages to an inflammatory stimulus during the decline of salivary secretion in NOD mice and the potential anti-inflammatory effect of VIP. We present evidence of an increased nitric oxide production by peritoneal macrophages of NOD mice in basal and lipopolysaccharide (LPS)+IFN-gamma-stimulated conditions and a lower IL-10 response to LPS compared with normal BALB/c mice. VIP inhibited LPS-induced TNF-alpha, IL-12 and nitrites accumulation in NOD macrophages while it increased IL-10 production. VIP effect was prevented by an anti-IL-10 monoclonal antibody and it showed an additive effect on exogenously added IL-10 only in NOD mice. The inhibitory effect of VIP-induced IL-10 on nitrites was mediated by COX metabolites mostly in NOD cells as indomethacine inhibited both the increase in IL-10 and the reduction of nitrites exerted by VIP. We conclude that both PGE2 and VIP inhibit nitric oxide production and increase IL-10 induced by LPS in NOD macrophages and VIP effect is mediated through an increase of COX metabolites and IL-10.

Defective signalling in salivary glands precedes the autoimmune response in the non-obese diabetic mouse model of sialadenitis

The spontaneous non-obese diabetic (NOD) mouse model of Sjögren's syndrome provides a valuable tool to study the onset and progression of both the autoimmune response and secretory dysfunction. Our purpose was to analyse the temporal decline of salivary secretion in NOD mice in relation to the autoimmune response and alterations in various signalling pathways involved in saliva secretion within each salivary gland. A progressive loss of nitric oxide synthase activity in submandibular and parotid glands started at 12 weeks of age and paralleled the decline in salivary secretion. This defect was associated with a lower response to vasoactive intestinal peptide in salivary flow rate, cAMP and nitric oxide/cGMP production. No signs of mononuclear infiltrates or local cytokine production were detectable in salivary glands in the time period studied (10-16 weeks of age). Our data support a disease model for sialadenitis in NOD mice in which the early stages are characterized by defective neurotransmitter-mediated signalling in major salivary glands that precedes the autoimmune response.

Lack of nitric oxide-mediated regulation of amylase secretion stimulated by VIP in parotid glands of NOD mice

The non-obese diabetic (NOD) mouse is chosen among other experimental models to study autoimmune sialadenitis resembling Sjögren's syndrome (SS), because of its unique characteristic of developing salivary dysfunction. Based on the deep loss of nitric oxide synthase (NOS) activity in parotid glands of NOD mice observed from early stages of disease and the inhibitory effect of nitric oxide (NO) donors on amylase secretion in normal salivary glands, our goal was to investigate whether parotid glands from NOD mice lacking NOS activity presented this regulatory mechanism of amylase secretion. We found that parotid glands from NOD mice lack nitric oxide-mediated regulation of amylase secretion in response to VIP stimulation. The lack of regulation might be assigned to the loss of NOS activity as derived from the results with NOS inhibitors and increasing concentrations of VIP. These functional differences observed in NOD vs. BALB/c parotid glands occur in the absence of immune infiltrates in exocrine tissue, and it is not related to cAMP accumulation. NO-mediated regulation of amylase secretion was not observed in BALB/c submandibular glands to the same extent as described in parotid glands and was absent in submandibular glands of NOD mice.

Inhibition of calcium-calmodulin kinase restores nitric oxide production and signaling in submandibular glands of a mouse model of salivary dysfunction

Nitric oxide is an intracellular and diffusible messenger of neurotransmitters involved in salivary secretion, as well as an inflammatory mediator in salivary gland diseases. It is synthesized by three different isoforms of nitric oxide synthase (NOS), each subject to a fine transcriptional, post-transcriptional and/or post-translational regulation. Our purpose was to study the possible mechanisms leading to NOS downregulation in submandibular glands of normal mice and in the nonobese diabetic (NOD) mouse model of salivary dysfunction with lower NOS activity. NOS activity and cGMP accumulation were determined by radioassays in submandibular glands of both mice in the presence of the protein kinase inhibitors KN-93 and bisindolylmaleimide. NOS I mRNA and protein expression and localization were assessed by RT-PCR, Western blot and immunohistochemistry. A downregulatory effect of calcium-calmodulin kinase II (CaMK II) on NOS activity in submandibular glands of both NOD and BALB/c mice was observed. Our results are consistent with a physiological regulation of NOS activity by this kinase but not by PKC in normal BALB/c mice. They are also supportive of a role for CaMK II in the lack of detectable NOS activity in submandibular glands of NOD mice. KN-93 also restored cGMP accumulation in NOD submandibular glands. The downregulation of NOS in NOD mice seems to be mainly mediated by this kinase rather than the result of a lower expression or different cellular localization of the enzyme. It was not related to different substrate or cofactors availability either.