Effects of bradykinin on Ca2+ mobilization and prostaglandin E2 release in human periodontal ligament cells

Periodontal ligament cells regulate osteogenesis via miR-299-5p in mesenchymal stem cells

BACKGROUND

The periodontal ligament contains periodontal ligament cells, which is a heterogeneous cell population, and includes progenitor cells that can differentiate into osteoblasts/cementoblasts. Mesenchymal stem cells (MSCs) can differentiate into various cells and can be used for periodontal regenerative therapy. Therefore, transplanted MSCs can be affected by humoral factors from periodontal ligament cells via the transcription factors or microRNAs (miRNAs) of MSCs. In addition, periostin (POSTN) is secreted from HPL cells and can regulate periodontal regeneration and homeostasis. To clarify the regulatory mechanism of humoral factors from periodontal ligament cells, we attempted to identify key genes, specifically microRNAs, involved in this process.

METHODS

Human MSCs (hMSCs) were indirectly co-cultured with human periodontal ligament cells (HPL cells) and then evaluated for osteogenesis, undifferentiated MSCs markers, and miRNA profiles. Furthermore, hMSCs were indirectly co-cultured with HPL cells in the presence of anti-POSTN monoclonal antibody (anti-POSTN Ab) to block the effect of POSTN from HPL cells, and then evaluated for osteogenesis or undifferentiated MSC markers. Moreover, hMSCs showed alterations in miRNA expression or cultured with HPL were challenged with POSTN during osteogenesis, and cells were evaluated for osteogenesis or undifferentiated MSC markers.

RESULTS

hMSCs co-cultured with HPL cells showed suppressed osteogenesis and characteristic expression of SOX11, an undifferentiated MSC marker, as well as miR-299-5p. Overexpression of miR-299-5p regulated osteogenesis and SOX11 expression as observed with indirect co-culture with HPL cells. Furthermore, MSCs co-cultured with HPL cells were recovered from the suppression of osteogenesis and SOX11 mRNA expression by anti-POSTN Ab. However, POSTN induced miR-299-5p and SOX11 expression, and enhanced osteogenesis.

CONCLUSION

Humoral factors from HPL cells suppressed osteogenesis in hMSCs. The suppressive effect was mediated by miR-299-5p and SOX11 in hMSCs.

Hypotonic stress induces RANKL via transient receptor potential melastatin 3 (TRPM3) and vaniloid 4 (TRPV4) in human PDL cells

Bone remodeling occurs in response to various types of mechanical stress. The periodontal ligament (PDL) plays an important role in mechanical stress-mediated alveolar bone remodeling. However, the underlying mechanism at the cellular level has not been extensively studied. In this study, we investigated the effect of shear stress on the expression of bone remodeling factors, including receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL) and osteoprotegerin (OPG), as well as its upstream signaling pathway in primary human PDL cells. We applied hypotonic stress to reproduce shear stress to PDL cells. Hypotonic stress induced the messenger RNA (mRNA) and protein expression of RANKL but not OPG. It also increased intracellular Ca(2+) concentration ([Ca(2+)]i). Extracellular Ca(2+) depletion and nonspecific plasma membrane Ca(2+) channel blockers completely inhibited the increase in both [Ca(2+)]i and RANKL mRNA expression. We identified the expression and activation of transient receptor potential melastatin 3 (TRPM3) and vaniloid 4 (TRPV4) channels in PDL cells. Pregnenolone sulfate (PS) and 4α-phorbol 12, 13-didecanoate (4α-PDD), which are agonists of TRPM3 and TRPV4, augmented Ca(2+) influx and RANKL mRNA expression. Both pharmacological (2-aminoethoxydiphenyl borate [2-APB], ruthenium red [RR], ononetin [Ono], and HC 067047 [HC]) and genetic (small interfering RNA [siRNA]) inhibitors of TRPM3 and TRPV4 reduced the hypotonic stress-mediated increase in [Ca(2+)]i and RANKL mRNA expression. Our study shows that hypotonic stress induced RANKL mRNA expression via TRPM3- and TRPV4-mediated extracellular Ca(2+) influx and RANKL expression. This signaling pathway in PDL cells may play a critical role in mechanical stress-mediated alveolar bone remodeling.

4-Bromophenacyl bromide induces Ca2+ influx in human gingival fibroblasts

4-Bromophenacyl bromide (BPB) is generally used as a phospholipase A(2) (PLA2) inhibitor. In the present study, we demonstrate that BPB induces Ca2+ influx in human gingival fibroblasts. In fura-2-loaded human gingival fibroblasts, BPB evoked a transient increase in intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner. The BPB-induced Ca2+ mobilization was also shown in a single fluo-3-loaded-fibroblast. The BPB-induced increase in [Ca2+]i was completely abolished by the elimination of the external Ca2+. Ca2+ influx induced by the Ca2+-mobilizing agonist histamine was markedly enhanced in the presence of BPB. These suggest that the BPB-induced Ca2+ mobilization is due to the influx of extracellular Ca2+. However, it is unlikely that the effect of BPB is dependent on the inhibition of PLA2 activity, because other PLA2 inhibitors, such as AACOCF3, quinacrine dihydrochloride and manoalide, failed to induce Ca2+ mobilization. Chemical compounds similar to BPB, but which have no -CH2-Br at position 1 in the benzene ring failed to evoke Ca2+ mobilization, indicating that the position of -CH2--Br in BPB is important for causing the Ca2+ influx.

Bradykinin potentiates prostaglandin E(2) release in the human gingival fibroblasts pretreated with interleukin-1beta via Ca(2+) mobilization

Interleukin-1beta, a proinflammatory cytokine, causes a slow increase in prostaglandin E(2) release. On the other hand, bradykinin, a chemical mediator for inflammation, induces a rapid prostaglandin E(2) release. Simultaneous stimulation with interleukin-1beta (200 pg/ml) and bradykinin (1 microM) evoked a moderately synergistic increase in prostaglandin E(2) release in human gingival fibroblasts. However, in the human gingival fibroblasts pretreated with interleukin-1beta, bradykinin drastically enhanced prostaglandin E(2) release. NS-398, a specific inhibitor of cyclooxygenase-2, inhibited not only interleukin-1beta-induced prostaglandin E(2) release but also bradykinin-induced prostaglandin E(2) release in the human gingival fibroblasts pretreated with interleukin-1beta. Transcriptional and translational inhibitors such as actinomycin D, cycloheximide, and dexamethasone also suppressed the interleukin-1beta-induced prostaglandin E(2) release and the bradykinin-induced prostaglandin E(2) release in interleukin-1beta-pretreated human gingival fibroblasts. In the fibroblasts pretreated with interleukin-1beta, Ca(2+)-mobilizing reagents such as ionomycin and thapsigargin mimicked the potentiating effect of bradykinin on prostaglandin E(2) release. These results suggest that interleukin-1beta- and bradykinin-induced prostaglandin E(2) release is dependent on cyclooxygenase-2 and the potentiated effect of bradykinin in the human gingival fibroblasts primed with interleukin-1beta is caused by Ca(2+) mobilization.

Intracellular measurement of prostaglandin E2: effect of anti-inflammatory drugs on cyclooxygenase activity and prostanoid expression

Cyclooxygenase (COX) converts arachidonic acid to prostaglandin (PG) H2, which is further metabolized to various prostaglandins, prostacyclin and thromboxane A2. COX exists in at least two different isoforms. COX-1 is constitutively expressed, whereas COX-2 is induced by proinflammatory stimuli. Prostaglandin E2 is a major metabolite of COX activation. In order to compare the activity of target ligands and COX inhibitors on PGE2 synthesis and release, the responsiveness of several cell lines to the calcium ionophore A23187, bacterial lipopolysaccharide (LPS), nonsteroidal anti-inflammatory drugs (NSAIDs), and the glucocorticoid, dexamethasone, were investigated. For intracellular measurements, the culture supernatant was aspirated, and the cells were thoroughly washed and lysed with dodecyltrimethylammonium bromide. Intracellular and secreted PGE2 were measured with an enzyme immunoassay. A23187 and LPS increased intracellular PGE2 in a dose-dependent manner. Kinetic experiments with A23187-stimulated mouse 3T3 fibroblast cells revealed a distinct biphasic response in COX activity. In the presence of NSAIDs or dexamethasone, there was a dose-dependent inhibition in intracellular PGE2 with A23187-stimulated 3T3 cells. Inhibitory studies demonstrated an apparent increased sensitivity of COX activity to the action of inhibitors when measuring intracellular PGE2 compared with using cell culture supernatants. Indeed, intracellular PGE2 levels were comprehensively reduced in the presence of low concentrations of inhibitor. The utilization of cell culture lysates and, in particular, measurement of intracellular PGE2 should prove useful for identifying new COX inhibitors.

Medium change amplifies mitogen-activated protein kinase-mediated prostaglandin E2 synthesis in Swiss 3T3 fibroblasts

In Swiss 3T3 fibroblasts, changing the culture medium prior to stimulation resulted in an augmentation of bradykinin-induced prostaglandin E2 synthesis. The augmentation depended on the duration of the exposure to the fresh medium, with a maximum effect at 1 h. Fetal calf serum in the fresh medium was essential for augmented prostaglandin E2 synthesis. The medium change slightly augmented the bradykinin-induced increase in intracellular free Ca2+ concentration and phosphoinositide hydrolysis with a different time course from that for prostaglandin E2 synthesis. 4',5,7-Trihydroxyisoflavone (genistein) and 3,4-dihydroxybenzylidene-malononitrile (tyrphostin 23), inhibitors of tyrosine kinases, and 2'-amino-3'-methoxyflavone (PD98059), an inhibitor of mitogen-activated protein kinase (MAPK) kinase, attenuated the increase in prostaglandin E2 synthesis. Bradykinin caused phosphorylation of cytosolic phospholipase A2 and p42/p44 MAPK, which was augmented by the medium change. From the results, it is concluded that activation of MAPK and cytosolic phospholipase A2 is involved in the augmentation of prostaglandin E2 synthesis produced by the medium change.

Cementum, root dentin and bone extracts stimulate chemotactic behavior in cells from periodontal tissue

In this paper, we used the extracts from cementum, bone, dentin and enamel, and compared the chemotactic behavior of human periodontal ligament (HPDL) cells, human gingival fibroblasts (HGF) and human alveolar bone (HAB) cells using modified Boyden chambers. The extracts, obtained using 4 M guanidine HCl ("G" extract), from cementum, root dentin, and bone had greater chemotactic effects than all the 4 M guanidine HCl/0.5 M EDTA extracts ("E" extract). HPDL cells and HGF exhibited higher chemotactic behavior than osteoblast-like HAB cells in response to cementum and root dentin "G" extracts. On the other hand, HAB cells showed the highest migratory activity in response to the bone "G" extract. The chemotactic activities of these extracts were reduced by heat- and trypsin-treatment. These results suggest that proteinaceous chemotactic factors exist in the cementum, root dentin and bone, and they appear to regulate the migration and orientation of HPDL cells, HGF and HAB cells during periodontal wound healing.

Histamine H1 receptor-induced Ca2+ mobilization and prostaglandin E2 release in human gingival fibroblasts. Possible role of receptor-operated Ca2+ influx

Stimulation of human gingival fibroblasts with histamine elicited an increase in the intracellular concentration of free calcium ([Ca2+]i) and the formation of inositol 1,4,5-trisphosphate (InsP3) in a concentration- and time-dependent manner. The histamine-induced increase in [Ca2+]i was attenuated completely by chlorpheniramine, an H1 antagonist, but not by cimetidine, an H2 antagonist. The histamine-induced Ca2+ response consisted of an initial transient peak response and a subsequent sustained increase. The transient phase can be largely attributed to Ca2+ release from intracellular InsP3-sensitive stores since the increased [Ca2+]i effect of histamine completely disappeared after depletion of intracellular Ca2+ stores with thapsigargin in the absence of extracellular Ca2+. The sustained phase was due to Ca2+ influx which was attenuated in the absence of extracellular Ca2+. The Ca2+ influx required the continuous binding of histamine to the receptor, since chlorpheniramine attenuated the increase in [Ca2+]i observed when extracellular Ca2+ was re-applied to the cells after stimulation with histamine in the absence of extracellular Ca2+. Pretreatment with the Ca2+ channel blocker SK&F96365 inhibited the Ca2+ influx component, suggesting that histamine stimulates Ca2+ influx through an H1 receptor-operated Ca2+ channel. Histamine also evoked a concentration- and time-dependent release of prostaglandin E2 (PGE2). The histamine-evoked PGE2 release was reduced markedly by exclusion of extracellular Ca2+ or pretreatment with SK&F96365 or an H1 antagonist. These results indicate that histamine stimulates both the intracellular Ca2+ release from InsP3-sensitive stores and the H1 receptor-operated Ca2+ influx from extracellular sites. The increased [Ca2+]i due to the Ca2+ influx causes PGE2 release in human gingival fibroblasts.

Comparison of the characteristics of human gingival fibroblasts and periodontal ligament cells

To elucidate the characteristics of human periodontal ligament cells, we compared these cells with gingival fibroblasts isolated from the periodontal tissues of female human subjects. Human periodontal ligament (HPDL) cells had a sharper spindle shape and exhibited a higher growth rate than human gingival fibroblasts (HGF). HPDL cells had a high level of alkaline phosphatase (ALPase) activity, whereas HGF had a low level of such activity. Northern blot analysis demonstrated that HPDL cells produced ALPase mRNA. Decorin and biglycan mRNA were detected in both HPDL cells and HGF, whereas osteocalcin and bone sialoprotein mRNA was not detected in either cells. Both HPDL cells and HGF responded to prostaglandin E2 (PGE2) and isoproterenol, and produced cyclic AMP (cAMP), but did not respond to human 1-34 parathyroid hormone (PTH). Intracellular Ca2+ ([Ca2+]i) was measured in HPDL cells and HGF, using Fura 2-AM. Bradykinin (BK) and histamine (HIS), which are major chemical mediators, caused a transient rise of [Ca2+]i in the presence of extracellular Ca2+. In HGF, but not HPDL cells, HIS induced a biphasic transient peak in [Ca2+]i. BK and HIS increased PGE2 release in both HPDL cells and HGF. However, HGF released a larger amount of PGE2 than HPDL cells. These results demonstrate that HPDL cells have quite different characteristics from HGF. HPDL cells proliferate at a higher rate than HGF, show higher levels of cAMP production and greater ALPase activity, and respond in a different fashion to chemical mediators (BK and HIS) compared with HGF.