Incadronate amplifies prostaglandin F2 alpha-induced vascular endothelial growth factor synthesis in osteoblasts. Enhancement of MAPK activity

Pregnane X receptor (PXR) deficiency promotes hepatocarcinogenesis via induction of Akr1c18 expression and prostaglandin F2α (PGF2α) levels

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. Pregnane X receptor (PXR), a xenobiotic-sensing nuclear receptor, plays a critical role in the metabolism of endogenous and exogenous substances in the liver. Here, we investigate whether PXR plays a role in pathogenesis of HCC. We show that liver tumors were developed in diethylnitrosamine (DEN)-treated in PXR knockout (KO) mice. Hepatic levels of prostaglandin F2α (PGF2α) and aldo-keto reductase family 1 member C18 (Akr1c18), a prostaglandin synthase of catalyzing reduction of PGH2 to PGF2α, were significantly elevated in DEN-treated PXR KO mice. Hepatic mRNA levels of alpha fetoprotein (AFP), cyclin D1 (Ccnd1), fibroblast growth factor 21 (FGF21), and inflammatory cytokine interleukin 6 (IL-6) were significantly increased in DEN-treated PXR KO mice. Other members of Akr1c family, liver metabolizing enzymes including Cyp1a2, Cyp2b10 and Cyp3a11, and bile acid synthesis enzyme Cyp7a1 mRNA levels were significantly decreased in DEN-treated PXR KO mice. Our findings revealed that PXR deficiency promoted DEN-induced HCC in mice via induction of Akr1c18 expression and PGF2α levels and the increased PGF2α levels synthetized by Akr1c18 enhanced hepatocytes proliferation and induced inflammatory cytokine production, which accelerated liver tumor development after DEN treatment, suggesting that PXR deficiency may create a microenvironment that is more prone to DEN-induced liver tumors and targeting PXR and Akr1c18 to reduce PGF2α biosynthesis may be a potential and novel therapeutic strategy for HCC.

Serous Retinal Detachment in a Patient With a Port-Wine Birthmark Associated With Prostaglandin Analog Therapy

An 11-year-old girl with a port-wine birthmark (PWB), diffuse choroid hemangioma (DCH), and glaucoma experienced decreased vision upon starting treatment with bimatoprost. The patient was switched to latanoprostene bunod. Her vision remained reduced. Shortly after, she was diagnosed with serous retinal detachment (SRD). Both SRD and vision improved following prostaglandin analog (PGA) cessation. Patients with PWB are likely to have DCH and glaucoma. DCH itself poses a risk factor for SRD. Certain glaucoma management modalities may further increase this risk. This report highlights the importance of regular surveillance for SRD in patients with DCH who are receiving PGA. [Ophthalmic Surg Lasers Imaging Retina 2023;54:723-729.].

HSP22 (HSPB8) positively regulates PGF2α-induced synthesis of interleukin-6 and vascular endothelial growth factor in osteoblasts

Background

Heat shock protein 22 (HSP22) belongs to class I of the small HSP family that displays ubiquitous expression in osteoblasts. We previously demonstrated that prostaglandin F2α (PGF2α), a potent bone remodeling factor, induces the synthesis of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) via p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether HSP22 is implicated in the PGF2α-induced synthesis of IL-6 and VEGF and the mechanism of MC3T3-E1 cells.

Methods

MC3T3-E1 cells were transfected with HSP22-siRNA. IL-6 and VEGF release was assessed by ELISA. Phosphorylation of p44/p42 MAP kinase and p38 MAP kinase was detected by Western blotting.

Results

The PGF2α-induced release of IL-6 in HSP22 knockdown cells was significantly suppressed compared with that in the control cells. HSP22 knockdown also reduced the VEGF release by PGF2α. Phosphorylation of p44/p42 MAP kinase and p38 MAP kinase was attenuated by HSP22 downregulation.

Conclusions

Our results strongly suggest that HSP22 acts as a positive regulator in the PGF2α-induced synthesis of IL-6 and VEGF in osteoblasts.

Identification of miR-200c-3p as a major regulator of SaoS2 cells activation induced by fluoride

The skeletal lesion of fluoride has become a major concern in many countries due to its damage to bone and joints and even leading to disability. Skeletal fluorosis is characterized by disturbance of bone metabolism, aberrant proliferation and activation of osteoblasts is critical for the pathogenesis. However, the mechanism underlying the osteotoxicity of fluoride has not been clearly illustrated and there is still limited information on the role of miRNAs in skeletal fluorosis. In this study, we found that NaF promoted SaoS2 proliferation and activation by activating BMP4/Smad pathway. NaF increased expression of miR-200c-3p and miR-200c-3p inhibitor reduced activation of SaoS2 induced by NaF via targeting Noggin to repress BMP4/Smad. These findings suggested an important regulatory role of miR-200c-3p on BMP4/Smad pathway during skeletal fluorosis. MiR-200c-3p might be a novel therapeutic target for skeletal fluorosis.

Resveratrol suppresses prostaglandin F(2α)-induced osteoprotegerin synthesis in osteoblasts: inhibition of the MAP kinase signaling

Resveratrol, a natural polyphenol abundantly found in grape skins and red wine, possesses various beneficial properties for human health. In the present study, we investigated the mechanism underlying the effects of prostaglandin F2α (PGF2α) on osteoprotegerin (OPG) synthesis and of resveratrol on the OPG synthesis in osteoblast-like MC3T3-E1 cells. PGF2α stimulated both the release of the OPG protein and the expression of OPG mRNA. Treatment with PD98059, SB203580 and SP600125, specific inhibitors of MEK1/2, p38 mitogen-activated protein (MAP) kinase and stress-activated protein kinase/c-jun N-terminal kinase (SAPK/JNK) all suppressed the OPG release induced by PGF2α. Resveratrol also significantly reduced the PGF2α-stimulated OPG release and the mRNA levels of OPG. Similarly, treatment with SRT1720, an activator of SIRT1, also suppressed the PGF2α-stimulated OPG release. Resveratrol and SRT1720 both attenuated the phosphorylation of p44/p42 MAP kinase, MEK1/2, Raf-1, p38 MAP kinase and SAPK/JNK induced by PGF2α. These findings strongly suggest that resveratrol suppresses PGF2α-stimulated OPG synthesis by inhibiting the MAP kinase pathways in osteoblasts, and that the effect is mediated via SIRT1 activation.

Prostaglandin F2α: a bone remodeling mediator

Prostaglandin F2α (PGF2α) plays multiple roles on bone metabolism by regulating a wide range of signaling pathways. PGF2α, via activation of PKC, stimulates Na-dependent inorganic phosphate (Pi) transport system in osteoblasts; up-regulates interleukin (IL)-6 synthesis; increases vascular endothelial growth factor (VEGF). In addition, PGF2α acts as a strong mitogenic and survival agent on osteoblasts, and these effects are, at least in part, mediated by the binding of fibroblast growth factor-2 (FGF-2) to the specific receptor FGFR1. The understanding of PGF2α intracellular network, albeit complex to clarify, provides molecular bases useful to identify the players of osteoblast proliferation, apoptosis, and the associated angiogenic processes. Indeed, the molecular mechanism that underline PGF2α-regulated bone metabolism may be a promising platform for the development of novel targeted therapies in the treatment of bone disorders and disease.

Green tea and bone health: Evidence from laboratory studies

Osteoporosis is a major health problem in the elderly. Epidemiological evidence has shown an association between tea consumption and the prevention of bone loss in the elderly population. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea with its bioactive components on bone health with an emphasis on the following: (i) the etiology of osteoporosis, (ii) evidence of osteo-protective impacts of green tea on bone mass and microarchitecture in various bone loss models in which induced by aging, sex hormone deficiency, and chronic inflammation, (iii) discussion of impacts of green tea on bone mass in two obesity models, (iv) observation of short-term green tea supplementation given to postmenopausal women with low bone mass, (v) possible mechanisms for the osteo-protective effects of green tea bioactive compounds, and (vi) a summary and future research direction of green tea and bone health.

Prostaglandin expression profile in hypoxic osteoblastic cells

Conditions such as fracture and unloading have been shown to be associated with tissue and cellular hypoxia in bone. The effects of hypoxia on bone cell physiology and ultimately its impact on bone tissue repair and remodeling are not well understood. In this study, we investigated the role of hypoxia on prostaglandin release from osteoblastic cells cultured in 2% (hypoxia), 5% (potentially cellular normoxia), and 21% (normoxia for standard cell culture conditions) oxygen for up to 24 h. We quantified the effects of reduced oxygen tension on the release of prostaglandin (PG)E(2), PGF(2alpha), PGD(2), and PGI(2). The mechanism by which hypoxia increases PG production was investigated by examining the various regulatory components of the PG biosynthetic pathway. Our data show that PGE(2) levels alone are significantly elevated under hypoxic conditions. Also, we show that cyclooxygenase (COX)-1 and COX-2 play an important role in hypoxia-induced PGE(2) production, possibly via a mechanism involving changes in their respective activity levels under low oxygen conditions. The effect of hypoxia on PGE(2) levels was mimicked by dimethyloxaloglycine, a known activator of the HIF pathway. In addition, we confirmed that HIF-1alpha was stabilized in osteoblastic cells under hypoxia. Taken together these data suggest a role for the HIF pathway in regulation of PGE(2) levels under hypoxic conditions. Previous studies have detected release of prostaglandins from areas of damaged bone, such as a fracture site, and our data may contribute to an understanding of how this release is regulated.

Green tea and bone metabolism

Osteoporosis is a major health problem in both elderly women and men. Epidemiological evidence has shown an association between tea consumption and the prevention of age-related bone loss in elderly women and men. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea or its bioactive components on bone health, with an emphasis on (i) the prevalence and etiology of osteoporosis; (ii) the role of oxidative stress and antioxidants in osteoporosis; (iii) green tea composition and bioavailability; (iv) the effects of green tea and its active components on osteogenesis, osteoblastogenesis, and osteoclastogenesis from human epidemiological, animal, as well as cell culture studies; (v) possible mechanisms explaining the osteoprotective effects of green tea bioactive compounds; (vi) other bioactive components in tea that benefit bone health; and (vii) a summary and future direction of green tea and bone health research and the translational aspects. In general, tea and its bioactive components might decrease the risk of fracture by improving bone mineral density and supporting osteoblastic activities while suppressing osteoclastic activities.

Delineation of VEGF-regulated genes and functions in the cervix of pregnant rodents by DNA microarray analysis

BACKGROUND

VEGF-regulated genes in the cervices of pregnant and non-pregnant rodents (rats and mice) were delineated by DNA microarray and Real Time PCR, after locally altering levels of or action of VEGF using VEGF agents, namely siRNA, VEGF receptor antagonist and mouse VEGF recombinant protein.

METHODS

Tissues were analyzed by genome-wide DNA microarray analysis, Real-time and gel-based PCR, and SEM, to decipher VEGF function during cervical remodeling. Data were analyzed by EASE score (microarray) and ANOVA (Real Time PCR) followed by Scheffe's F-test for multiple comparisons.

RESULTS

Of the 30,000 genes analyzed, about 4,200 genes were altered in expression by VEGF, i.e., expression of about 2,400 and 1,700 genes were down- and up-regulated, respectively. Based on EASE score, i.e., grouping of genes according to their biological process, cell component and molecular functions, a number of vascular- and non-vascular-related processes were found to be regulated by VEGF in the cervix, including immune response (including inflammatory), cell proliferation, protein kinase activity, and cell adhesion molecule activity. Of interest, mRNA levels of a select group of genes, known to or with potential to influence cervical remodeling were altered. For example, real time PCR analysis showed that levels of VCAM-1, a key molecule in leukocyte recruitment, endothelial adhesion, and subsequent trans-endothelial migration, were elevated about 10 folds by VEGF. Further, VEGF agents also altered mRNA levels of decorin, which is involved in cervical collagen fibrillogenesis, and expression of eNO, PLC and PKC mRNA, critical downstream mediators of VEGF. Of note, we show that VEGF may regulate cervical epithelial proliferation, as revealed by SEM.

CONCLUSION

These data are important in that they shed new insights in VEGF's possible roles and mechanisms in cervical events near-term, including cervical remodeling.

PEG-derivative effectively modifies the characteristics of indomethacin-PLGA microspheres destined to intra-articular administration

The aim of this study was to obtain biodegradable indomethacin microspheres for intra-articular administration in rheumatoid arthritis, where angiogenic processes are involved. Indomethacin concentrations to achieve an anti-angiogenic effect would be five-times higher than an anti-inflammatory. Microspheres were prepared by solvent evaporation using PLGA. Indomethacin is a poor water-soluble drug with it being possible that dissolved and non-dissolved drug co-exist within the polymeric matrix resulting in rapid release. To control this release, an oil-PEG-derivative was incorporated, producing changes in morphology, crystallinity and indomethacin release. To minimize the amount of microspheres administered, a two-factor five-level central rotable composite 2(2)+star design was employed with two independent variables: indomethacin percentage and PEG-derivative percentage. The optimum formulation showed mean encapsulation efficiency of 94.3+/-2.2% and released 7.99+/-0.25 microg indomethacin/day/mg microspheres for 21 days. A dose of 20-50 mg of this formulation could be appropriate to achieve both anti-angiogenic and anti-inflammatory effects. Preliminary cytotoxicity studies performed in rat splenocytes showed an adequate cell viability.

Platelet-derived growth factor-BB amplifies PGF2alpha-stimulated VEGF synthesis in osteoblasts: function of phosphatidylinositol 3-kinase

We have reported that prostaglandin F2alpha (PGF2alpha) stimulates the synthesis of vascular endothelial growth factor (VEGF) via p44/p42 mitogen-activated protein (MAP) kinase in osteoblast-like MC3T3-E1 cells. In addition, we recently showed that phosphatidylinositol 3 (PI3)-kinase activated by platelet-derived growth factor-BB (PDGF-BB) negatively regulates the interleukin-6 synthesis in these cells. In the present study, we investigated the effect of PDGF-BB on the PGF2alpha-induced VEGF synthesis in MC3T3-E1 cells. PDGF-BB, which alone did not affect the levels of VEGF, significantly enhanced the PGF2alpha-stimulated VEGF synthesis. The amplifying effect of PDGF-BB was dose dependent in the range between 10 and 70 ng/ml. LY294002 or wortmannin, specific inhibitors of PI3-kinase, which by itself failed to affect the PGF2alpha-stimulated VEGF synthesis, significantly suppressed the amplification by PDGF-BB. PD98059, a specific inhibitor of MEK1/2, suppressed the amplification by PDGF-BB of the PGF2alpha-stimulated VEGF synthesis similar to the levels of PGF2alpha with PD98059. PDGF-BB itself induced the phosphorylation of p44/p42 MAP kinase in these cells, and the effects of PDGF-BB and PGF2alpha on the phosphorylation of p44/p42 MAP kinase were additive. Moreover, LY294002 had little effect on the phosphorylation of p44/p42 MAP kinase induced by PGF2alpha with PDGF-BB. These results strongly suggest that PGF2alpha-stimulated VEGF synthesis is amplified by PI3-kinase-mediating PDGF-BB signaling in osteoblasts, and that the effect is exerted at a point downstream from p44/p42 MAP kinase.

Protein kinase C delta regulates the phosphorylation of heat shock protein 27 in human hepatocellular carcinoma

We have recently reported that attenuated phosphorylation of heat shock protein (HSP) 27 correlates with tumor progression in patients with hepatocellular carcinoma (HCC). In the present study, we investigated what kind of kinase regulates phosphorylation of HSP27 in human HCC-derived HuH7 cells. 12-O-tetradecanoylphorbol-13-acetate (TPA) and 1-oleoyl-2-acetylglycerol, direct activators of protein kinase C (PKC), markedly strengthened the phosphorylation of HSP27. Bisindorylmaleimide I, an inhibitor of PKC, suppressed the TPA-induced levels of HSP27 phosphorylation in addition to its basal levels. Knock down of PKCdelta suppressed HSP27 phosphorylation, as well as p38 mitogen-activated protein kinase (MAPK) phosphorylation. SB203580, an inhibitor of p38 MAPK, suppressed the TPA-induced HSP27 phosphorylation. Our results strongly suggest that activation of PKCdelta regulates the phosphorylation of HSP27 via p38 MAPK in human HCC.

(-)-Epigallocatechin gallate suppresses endothelin-1-induced interleukin-6 synthesis in osteoblasts: inhibition of p44/p42 MAP kinase activation

We previously showed that endothelin-1 (ET-1) stimulates the synthesis of interleukin-6 (IL-6), a potent bone resorptive agent, in osteoblast-like MC3T3-E1 cells, and that protein kinase C (PKC)-dependent p44/p42 mitogen-activated protein (MAP) kinase plays a part in the IL-6 synthesis. In the present study, we investigated the effect of (-)-epigallocatechin gallate (EGCG), one of the major flavonoids containing in green tea, on ET-1-induced IL-6 synthesis in osteoblasts and the underlying mechanism. EGCG significantly reduced the synthesis of IL-6 stimulated by ET-1 in MC3T3-E1 cells as well primary cultured mouse osteoblasts. SB203580, a specific inhibitor of p38 MAP kinase, but not SP600125, a specific SAPK/JNK inhibitor, suppressed ET-1-stimulated IL-6 synthesis. ET-1-induced phosphorylation of p38 MAP kinase was not affected by EGCG. On the other hand, EGCG suppressed the phosphorylation of p44/p42 MAP kinase induced by ET-1. Both the IL-6 synthesis and the phosphorylation of p44/p42 MAP kinase stimulated by 12-O-tetradecanoylphorbol 13-acetate (TPA), a direct activator of PKC, were markedly suppressed by EGCG. The phosphorylation of MEK1/2 and Raf-1 induced by ET-1 or TPA were also inhibited by EGCG. These results strongly suggest that EGCG inhibits ET-1-stimulated synthesis of IL-6 via suppression of p44/p42 MAP kinase pathway in osteoblasts, and the inhibitory effect is exerted at a point between PKC and Raf-1 in the ET-1 signaling cascade.

(−)-epigallocatechin gallate enhances prostaglandin F2α-induced VEGF synthesis via upregulating SAPK/JNK activation in osteoblasts

Catechin, one of the major flavonoids presented in plants such as tea, reportedly suppresses bone resorption. We previously reported that prostaglandin F(2alpha) (PGF(2alpha)) stimulates the synthesis of vascular endothelial growth factor (VEGF) via p44/p42 mitogen-activated protein (MAP) kinase in osteoblast-like MC3T3-E1 cells. To clarify the mechanism of catechin effect on osteoblasts, we investigated the effect of (--)-epigallocatechin gallate (EGCG), one of the major green tea flavonoids, on the VEGF synthesis by PGF(2alpha) in MC3T3-E1 cells. The PGF(2alpha)-induced VEGF synthesis was significantly enhanced by EGCG. The amplifying effect of EGCG was dose dependent between 10 and 100 microM. EGCG did not affect the PGF(2alpha)-induced phosphorylation of p44/p42 MAP kinase. SB203580, a specific inhibitor of p38 MAP kinase, and SP600125, a specific inhibitor of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), reduced the PGF(2alpha)-induced VEGF synthesis. EGCG markedly enhanced the phosphorylation of SAPK/JNK induced by PGF(2alpha) without affecting the PGF(2alpha)-induced phosphorylation of p38 MAP kinase. SP600125 markedly reduced the amplification by EGCG of the SAPK/JNK phosphorylation. In addition, the PGF(2alpha)-induced phosphorylation of c-Jun was amplified by EGCG. These results strongly suggest that EGCG upregulate PGF(2alpha)-stimulated VEGF synthesis resulting from amplifying activation of SAPK/JNK in osteoblasts.

Parathyroid hormone induces mitogen-activated kinase phosphatase 1 in murine osteoblasts primarily through cAMP-protein kinase A signaling

BACKGROUND

Parathyroid hormone (PTH) regulates osteoblast function by binding to the PTH receptor 1 (PTHR1) to activate downstream signaling to induce expression of primary response genes (PRGs), which affect various aspects of the osteoblast phenotype. We previously identified PTH-induced PRGs in MC3T3-E1 cells, including mitogen-activated protein kinase (MAPK) phosphatase 1 (mkp1), which dephosphorylates members of the MAPK family. The aim of this study was to explore the molecular mechanisms of PTH's induction of mkp1 in primary mouse osteoblasts.

METHODS

Northern and Western analyses were used to determine mkp1 mRNA and protein expression. In vivo experiments were also performed to determine PTH's effect on mkp1 in mouse calvariae and long bones.

RESULTS

A total of 10 nM PTH and PTH-related protein (PTHrP) maximally induced mkp1 mRNA levels after 1 hour in osteoblasts. PTH also increased mkp1 protein expression, and induced mkp1 mRNA independent of new protein synthesis. PTHR1 triggers protein kinase A (PKA), PKC, and calcium pathways. Although PKA and PKC agonists induced mkp1 mRNA levels, only cyclic adenosine 3':5'-monophosphate (cAMP)-PKA inhibition blocked PTH-induced mkp1 mRNA levels. These data suggest that PTH-induced mkp1 mRNA levels are primarily mediated through the cAMP-PKA pathway. Further, prostaglandin E2 (PGE2), which activates cAMP-PKA and PKC, induced mkp1 mRNA to a greater extent than PGF2alpha and fluprostenol, which activate PKC signaling only. Finally, PTH maximally induced mkp1 mRNA levels in mouse calvariae and long bones in vivo at 0.5 hours.

CONCLUSIONS

mkp1's in vitro and in vivo induction in PTH-target tissues suggests its involvement in some of the effects of PTH on osteoblast function. mkp1 may be an important target gene in the anabolic effect of PTH on osteoblasts.

Tiludronate inhibits prostaglandin F2alpha-induced vascular endothelial growth factor synthesis in osteoblasts

We have previously reported that prostaglandin F2alpha (PGF2alpha) activates p44/p42 mitogen-activated protein (MAP) kinase through protein kinase C (PKC), resulting in the synthesis of vascular endothelial growth factor (VEGF) in osteoblast-like MC3T3-E1 cells, and that incadronate, a bisphosphonate, amplifies the VEGF synthesis. In the present study, we investigated the effects of tiludronate and etidronate, other bisphosphonates, on the PGF2alpha-stimulated VEGF synthesis in these cells. Tiludronate reduced the synthesis of VEGF induced by PGF2alpha. The PGF(2alpha)-stimulated phosphorylation of p44/p42 MAP kinase was suppressed by tiludronate. On the other hand, etidronate affected neither the VEGF synthesis nor the phosphorylation of p44/p42 MAP kinase elicited by PGF2alpha. Tiludronate attenuated the phosphorylation of both Raf-1 and MEK1/2 induced by PGF2alpha. The VEGF synthesis stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA), a direct activator of PKC, was suppressed by tiludronate. The TPA-induced phosphorylations of Raf-1, MEK1/2 and p44/p42 MAP kinase were inhibited by tiludronate. These results strongly suggest that tiludronate but not etidronate suppresses the PGF2alpha-stimulated VEGF synthesis in osteoblasts, and that the effect of tiludronate is exerted at the point between PKC and Raf-1.

Multiple regulatory pathways of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) expression in tumors

VPF/VEGF is a multi-functional cytokine with important roles in both vasculogenesis and angiogenesis. Its production is generally regulated by local oxygen concentration. Hypoxia stimulates VPF/VEGF production by increasing its gene transcription and the stability of its mRNA. The increase in transcription in hypoxia occurs mainly through the stabilization and activation of the transcription factor, Hypoxia Inducible Factor (HIF). Cellular oxygen concentration is not the only regulator of VPF/VEGF synthesis. Some cancer cells can produce high levels of VPF/VEGF even in normoxia. Clear cell renal carcinoma cell line (RCC) like 786-0, pancreatic carcinoma cell line, ASPC-1, fibrocarcinoma cell line, HT1080, ovarian cancer cells, etc. produce an elevated level of VPF/VEGF, which is not dependent on hypoxia. In this article, we discuss different regulatory pathways in tumor cells comprised of oncogenes, tumor suppressor genes etc. that play important roles, in both the transcription and stability of VPF/VEGF mRNA.

Effect of eosinophil adhesion on intracellular signaling in cholinergic nerve cells

Eosinophil localization to cholinergic nerves occurs in a variety of inflammatory conditions, including asthma. This localization is mediated by interactions between eosinophil integrins and neuronal vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). Eosinophil-nerve cell interactions lead to generation of neuronal reactive oxygen species and release of eosinophil proteins. The effects of eosinophil adhesion on neuronal intracellular signaling pathways were investigated. Eosinophil adhesion to IMR32 cholinergic nerves led to a rapid and sustained activation of the nuclear transcription factors nuclear factor (NF)-kappaB and activator protein (AP)-1 in the nerve cells. Eosinophil binding to neuronal ICAM-1 led to a rapid activation of ERK1/2 in nerve cells. Inhibition of ERK1/2 prevented NF-kappaB activation. Eosinophil adhesion to VCAM-1 resulted in AP-1 activation, mediated partially by rapid activation of the p38 mitogen-activated protein kinase. These data show that adhesion of eosinophils induces mitogen-activated protein kinase-dependent activation of the transcription factors NF-kappaB and AP-1 in nerve cells, indicating that eosinophil adhesion may control nerve growth and phenotype.

Enteric nervous system progenitors are coordinately controlled by the G protein-coupled receptor EDNRB and the receptor tyrosine kinase RET

The enteric nervous system (ENS) in vertebrates is derived mainly from vagal neural crest cells that enter the foregut and colonize the entire wall of the gastrointestinal tract. Failure to completely colonize the gut results in the absence of enteric ganglia (Hirschsprung's disease). Two signaling systems mediated by RET and EDNRB have been identified as critical players in enteric neurogenesis. We demonstrate that interaction between these signaling pathways controls ENS development throughout the intestine. Activation of EDNRB specifically enhances the effect of RET signaling on the proliferation of uncommitted ENS progenitors. In addition, we reveal novel antagonistic roles of these pathways on the migration of ENS progenitors. Protein kinase A is a key component of the molecular mechanisms that integrate signaling by the two receptors. Our data provide strong evidence that the coordinate and balanced interaction between receptor tyrosine kinases and G protein-coupled receptors controls the development of the nervous system in mammals.