Bradykinin Mediates Phosphorylation of eNOS in Odontoblasts

Inflammation of the Human Dental Pulp Induces Phosphorylation of eNOS at Thr495 in Blood Vessels

The activity of endothelial nitric oxide synthase (eNOS) in endothelial cells increased with the phosphorylation of the enzyme at Ser1177 and decreased at Thr495. The regulation of the phosphorylation sites of eNOS at Ser1177 and Thr495 in blood vessels of the healthy and inflamed human dental pulp is unknown. To investigate this, healthy and carious human third molars were immersion-fixed and decalcified. The localization of eNOS, Ser1177, and Thr495 in healthy and inflamed blood vessels was examined in consecutive cryo-sections using quantitative immunohistochemical methods. We found that the staining intensity of Ser1177 in healthy blood vessels decreased in inflamed blood vessels, whereas the weak staining intensity of Thr495 in healthy blood vessels strongly increased in inflamed blood vessels. In blood vessels of the healthy pulp, eNOS is active with phosphorylation of the enzyme at Ser1177. The phosphorylation of eNOS at Thr495 in inflamed blood vessels leads to a decrease in eNOS activity, contributing to eNOS uncoupling and giving evidence for a decrease in NO and an increase in O2− production. Since the formation of the tertiary dentin matrix depends on intact pulp circulation, eNOS uncoupling and phosphorylation of eNOS at Thr495 in the inflamed pulp blood vessels should be considered during caries therapy.

The Role of microRNAs in Pulp Inflammation

The dental pulp can be affected by thermal, physical, chemical, and bacterial phenomena that stimulate the inflammatory response. The pulp tissue produces an immunological, cellular, and vascular reaction in an attempt to defend itself and resolve the affected tissue. The expression of different microRNAs during pulp inflammation has been previously documented. MicroRNAs (miRNAs) are endogenous small molecules involved in the transcription of genes that regulate the immune system and the inflammatory response. They are present in cellular and physiological functions, as well as in the pathogenesis of human diseases, becoming potential biomarkers for diagnosis, prognosis, monitoring, and safety. Previous studies have evidenced the different roles played by miRNAs in proinflammatory, anti-inflammatory, and immunological phenomena in the dental pulp, highlighting specific key functions of pulp pathology. This systematized review aims to provide an understanding of the role of the different microRNAs detected in the pulp and their effects on the expression of the different target genes that are involved during pulp inflammation.

Nitric Oxide in Dental Pulp Tissue: From Molecular Understanding to Clinical Application in Regenerative Endodontic Procedures

Nitric oxide (NO), which is synthesized by the enzyme NO synthase (NOS), is a versatile endogenous molecule with multiple biological effects on many tissues and organs. In dental pulp tissue, NO has been found to play multifaceted roles in regulating physiological activities, inflammation processes, and tissue repair events, such as cell proliferation, neuronal degeneration, angiogenesis, and odontoblastic differentiation. However, there is a deficiency of detailed discussion on the NO-mediated interactions between inflammation and reparative/regenerative responses in wounded dental pulp tissue, which is a central determinant of ultimate clinical outcomes. Thus, the purpose of this review is to outline the current molecular understanding on the roles of Janus-faced molecule NO in dental pulp physiology, inflammation, and reparative activities. Based on this knowledge, advanced physicochemical techniques designed to manipulate the therapeutic potential of NOS and NO production in endodontic regeneration procedures are further discussed. Impact statement The interaction between inflammation and reparative/regenerative responses is very important for regenerative endodontic procedures, which are biologically based approaches intended to replace damaged tissues. Inside dental pulp tissue, endogenous nitric oxide (NO) is generated mainly by immunocompetent cells and dental pulp cells and mediates not only inflammatory/immune activities but also signaling cascades that regulate tissue repair and reconstruction, indicating its involvement in both tissue destruction and regeneration. Thus, it is feasible that NO acts as one of the indicators and modulators in dental pulp repair or regeneration under physiological and pathological conditions.

Potassium Currents Activated by Depolarization in Odontoblasts

Increased intracellular free Ca²⁺ concentrations elicit plasma membrane depolarization, which leads to the activation of K⁺ currents. However, the precise properties of K⁺ currents activated by depolarization in odontoblasts remain to be elucidated. The present study identified biophysical and pharmacological characteristics of time-dependent and voltage-activated K⁺ currents in freshly dissociated rat odontoblasts using patch-clamp recordings in a whole-cell configuration. Using a holding potential of −70 mV, outwardly rectifying time- and voltage-dependent currents were activated by depolarizing voltage. To record pure K⁺ conductance, we substituted Cl⁻ in both the extracellular and intracellular solutions with gluconate⁻. Under these conditions, observation of K⁺ concentration changes in the extracellular solution showed that reversal potentials of tail currents shifted according to the K⁺ equilibrium potential. The activation kinetics of outward K⁺ currents were relatively slow and depended on the membrane potential. Kinetics of steady-state inactivation were fitted by a Boltzmann function. The half-maximal inactivation potential was −38 mV. Tetraethylammonium chloride, 4-aminopyridine, and α-dendrotoxin inhibited outward currents in odontoblasts in a concentration-dependent manner, suggesting that rat odontoblasts express the α-subunit of the time- and voltage-dependent K⁺ channel (Kv) subtypes Kv1.1, 1.2, and/or 1.6. We further examined the effects of Kv activity on mineralization by alizarin red and von Kossa staining. Continuous application of tetraethylammonium chloride to human odontoblasts grown in a mineralization medium over a 21-day period exhibited a dose-dependent decrease in mineralization efficiency compared to cells without tetraethylammonium chloride. This suggests that odontoblasts functionally express voltage-dependent K⁺ channels that play important roles in dentin formation.

Human salivary gland cells express bradykinin receptors that modulate the expression of proinflammatory cytokines

Bradykinin is an important peptide modulator that affects the function of neurons and immune cells. However, there is no evidence of the bradykinin receptors and their functions in human salivary glands. Here we have identified and characterized bradykinin receptors on human submandibular gland cells. Both bradykinin B1 and B2 receptors are expressed on human submandibular gland cells, A253 cells, and HSG cells. Bradykinin increased the intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) in a concentration-dependent manner. Interestingly, a specific agonist of the B1 receptor did not have any effect on [Ca²⁺ ]_i in HSG cells, whereas specific agonists of the B2 receptor had a Ca²⁺ mobilizing effect. Furthermore, application of the B1 receptor antagonist, R715, did not alter the bradykinin-mediated increase in cytosolic Ca²⁺ , whereas the B2 receptor antagonist, HOE140, showed a strong inhibitory effect, which implies that bradykinin B2 receptors are functional in modulating the concentration of cytosolic Ca²⁺ . Bradykinin did not affect a carbachol-induced rise of [Ca²⁺ ]_i and did not modulate translocation of aquaporin-5. However, bradykinin did promote the expression of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), implying the role of bradykinin in salivary gland inflammation. These data suggest that bradykinin receptors are involved in Ca²⁺ signaling in human submandibular gland cells and serve a unique role, which is separate from that of other salivary gland G protein-coupled receptors.

Regulator of Calcineurin 1 in Periodontal Disease

Nuclear factor of activated T-cells (NFAT) and NF-kB pathway associated processes are involved in the pathogenesis of various inflammatory disorders, for example, periodontal disease. The activation of these pathways is controlled by the regulator of calcineurin 1 (RCAN1). The aim of this study was to elucidate the role of RCAN1 in periodontal disease. Healthy and inflamed periodontal tissues were analyzed by immunohistochemistry and immunofluorescence using specific rabbit polyclonal anti-RCAN1 antibodies. For expression analysis human umbilical vein endothelial cells (HUVEC) were used. HUVEC were incubated for 2 h with Vascular Endothelial Growth Factor (VEGF) or with wild type and laboratory strains of Porphyromonas gingivalis (P. gingivalis). Expression analysis of rcan1 and cox2 was done by real time PCR using specific primers for rcan1.4 and cox2. The expression of rcan1 was found to be significantly suppressed in endothelial cells of chronically inflamed periodontal tissues compared to healthy controls. Rcan1 and cox2 were significantly induced by VEGF and wild type and laboratory P. gingivalis strains. Interestingly, the magnitude of the rcan1 and cox2 induction was strain dependent. The results of this study indicate that RCAN1 is suppressed in endothelial cells of chronically inflamed periodontal tissues. During an acute infection, however, rcan1 seems to be upregulated in endothelial cells, indicating a modulating role in immune homeostasis of periodontal tissues.

Effects of non-steroidal anti-inflammatory drugs on proliferation, differentiation and migration in equine mesenchymal stem cells

In equine medicine, stem cell therapies for orthopaedic diseases are routinely accompanied by application of NSAIDs (non-steroidal anti-inflammatory drugs). Thus, it has to be analysed how NSAIDs actually affect the growth and differentiation potential of MSCs (mesenchymal stem cells) in vitro in order to predict the influence of NSAIDs such as phenylbutazone, meloxicam, celecoxib and flunixin on MSCs after grafting in vivo. The effects of NSAIDs were evaluated regarding cell viability and proliferation. Additionally, the multilineage differentiation capacity and cell migration was analysed. NSAIDs at lower concentrations (0.1-1 μM for celecoxib and meloxicam and 10-50 μM for flunixin) exert a positive effect on cell proliferation and migration, while at higher concentrations (10-200 μM for celecoxib and meloxicam and 100-1000 μM for flunixin and phenylbutazone), there is rather a negative influence. While there is hardly any influence on the adipogenic as well as on the chondrogenic MSC differentiation, the osteogenic differentiation potential, as demonstrated with the von Kossa staining, is significantly disturbed. Thus, it can be concluded that the effects of NSAIDs on MSCs are largely dependent on the concentrations used. Additionally, for some differentiation lineages, also the choice of NSAID is critical.

Irreversible inflammation is associated with decreased levels of the alpha1-, beta1-, and alpha2-subunits of sGC in human odontoblasts

The nitric oxide (NO) receptor enzyme soluble guanylate cyclase (sGC) contains one prosthetic heme group as an αβ heterodimer, and two heterodimer isoforms (α(1)β(1), α(2)β(1)) were characterized to have enzyme activity. To test the irreversible inflammation-dependent regulation of sGC in odontoblasts, we incubated decalcified frozen sections of healthy and inflamed human third molars with antibodies against β-actin, nitrotyrosine, inducible nitric oxide synthase (iNOS), α(1)-, β(1)-, and α(2)-subunits of sGC and analyzed them at protein levels by quantitative immunohistochemistry. The irreversible inflammation induced an increase in the signal intensities for nitrotyrosine and iNOS and a decrease for the α(1)-, β(1)-, and α(2)-subunits of sGC in odontoblasts. Inflammatory mediators, reactive oxygen, and nitrogen species may impair the expression of the α(1)-, β(1)-, and α(2)-subunits in odontoblasts. The decrease of sGC at the protein level in inflamed odontoblasts is compatible with a critical role for sGC to mediate biological effects of NO in health.

The mechanism of (R,R) ZX-5 on increasing NO release

(R,R) ZX-5 has been proven to have positive effects on choroidal blood flow without affecting the sclera and ciliary bodies in New Zealand white rabbits. This study was designed to investigate the mechanisms of (R,R) ZX-5 on improving the choroidal blood flow and promoting NO production. HUVECs (human umbilical vein endothelial cells) were used to determine the production of eNOS, p-eNOS, AKT and Erk1/2 by Western blot analysis. iNOS and eNOS mRNA levels were investigated by RT-PCR and the effect of (R,R) ZX-5 on NO production were determined by eNOS activity assay. We found (R,R) ZX-5 upregulated protein expression of eNOS and iNOS, increased NO production, and reduced ERK and Akt protein level. Therefore, (R,R) ZX-5 may promote the choroidal blood flow in New Zealand white rabbits without affecting the blood flow in the iris or ciliary bodies via increasing NO production. These results suggest that (R,R) ZX-5 may function to cure and prevent Age-related macular degeneration (AMD).

Role of protease-activated receptor-1 in endothelial nitric oxide synthase-Thr495 phosphorylation

Protease activated receptors (PARs) are G protein-coupled receptors that are known to regulate endothelial nitric oxide synthase (eNOS) activity in part by phosphorylating the enzyme at various sites. Ser1177 is a positive regulatory site, which leads to the enhanced production of nitric oxide (NO), a vasodilator of arteries. Thr495 is a negative regulatory site, which inhibits NO production. We have shown that thrombin, a PAR agonist, mediates eNOS-Ser1177 phosphorylation through Gq and a calcium and protein kinase C (PKC)-delta sensitive, but phosphatidylinositol 3-kinase (PI3K)/Akt-independent pathway. However, the mechanism for eNOS-Thr495 phosphorylation by PAR agonists is unknown. We used a specific synthetic PAR-1 activating peptide, TFLLR, and thrombin to assess the role of PAR-1 involvement in the phosphorylation of eNOS-Thr495 in human umbilical vein endothelial cells (HUVECs). Using Western blot analysis and the Griess Reagent assay, we found that both agonists phosphorylated Thr495 in a time- and dose-dependent manner and significantly decreased nitrite production, respectively. Pretreatment of cells with the PAR-1 inhibitor, SCH-79797, resulted in a significant decrease in thrombin- and TFLLR-induced phosphorylation of eNOS-Thr495 and an increase in nitrite production. We further demonstrated that inhibition of Rho with C3 exoenzyme or dominant negative (dn) RhoA, and inhibition of Rho-Kinase (ROCK) with Y-27632 caused a significant decrease in thrombin and TFLLR-induced Thr495 phosphorylation. Blockade of the Rho/ROCK pathway also caused an increase in nitrite production. This suggests that PAR-1 regulates eNOS activity via phosphorylation of eNOS-Thr495, which is dependent upon activation of the Rho/ROCK pathway. These findings will be beneficial in further understanding the signaling pathways that regulate eNOS-induced NO production, which plays an important role in endothelial dysfunction associated with cardiovascular disease.

Time-dependent Activation of ERK1/2 in Nerve Terminals of the Dentin-Pulp Complex following Bradykinin Treatment

The extracellular signal-regulated kinases 1 and 2 (ERK1/2) have been implicated in the inflammation-dependent sensitization of nociceptors, and the inflammatory mediator bradykinin (BK) led to a reduced threshold in the nociceptor terminals, activating intracellular signaling by phosphorylating receptors and ion channels. The effects of BK on the non-transcriptional modulation of the ERK1/2 in the peripheral nociceptor terminals, including in nerve endings of the dentin-pulp complex, are unknown. The time-dependent effects of BK (10−7 M) on the ERK1/2 phosphorylation in nerve terminals of the dentin-pulp complex were investigated by quantitative and double immunolabeling with organ bath experiments. In nerve terminals, total and p-ERK1/2 were detected. In comparison with the controls, the numbers of p-ERK1/2-positive nerve endings increased after 1 and 3 min and decreased after 10 min of BK treatment. Analysis of the data indicates that BK induces phosphorylation-mediated local activation of ERK1/2 in nerve terminals modulating nociception in the dentin-pulp complex.