Differential Expression Patterns of Rspondin Family and Leucine-Rich Repeat-Containing G-Protein Coupled Receptors in Chondrocytes and Osteoblasts.

OBJECTIVE: Rspondins (RSPOs) are regarded as the significant modulators of WNT signaling pathway and they are expressed dynamically during developmental stages. Since in osteoarthritis (OA) both cartilage and subchondral bone suffer damages and WNT signaling pathway has a crucial role in their maintenance, the objective of the study was to analyze expression profile of RSPO family and its receptors [leucine-rich repeat-containing G-protein coupled receptors (LGRs)] in OA tissue samples as well as in differentiating chondrocytes and osteoblasts. MATERIALS AND METHODS: In this experimental study, human early and advanced stage of OA tissue samples were analyzed for the morphological changes of articular cartilage by hematoxylin and eosin (H and E) staining, safranin-O staining and lubricin immunostaining. RSPOs and LGRs expression were confirmed by immunohistochemistry. Human primary chondrocytes and human osteoblast cell line, SaOS-2, were cultured in differentiation medium till day 14 and they were analyzed in terms of expression of RSPOs, LGRs and specific marker for chondrogenesis and osteogenesis by western blotting and quantitative reverse transcription polymerase chain reaction (qRT-PCR). RESULTS: Advanced stage OA tissue samples showed increased expression of RSPO1 and LGR6 in a region close to subchondral bone. While RSPO2 and LGR5 expression were seen overlapping in the deep region of articular cartilage. Differentiating chondrocytes demonstrated elevated expression of RSPO2 and LGR5 from day 7 to day 14, whereas, osteoblasts undergoing differentiation showed enhanced expression of RSPO1 and LGR6 from day 2 to day 14. Under tumor necrosis factor alpha (TNFα) stimulatory conditions, RSPO2 and RSPO1 recovered the suppressed expression of inflammatory, chondrogenic and osteogenic markers, respectively. A recovery in the stability of ß-catenin was also noticed in both cases. CONCLUSION: Spatial expression of RSPOs during progression of OA might be dynamically controlled by cartilage and subchondral bone. Interplay amid chondrocytes and osteoblasts, via RSPOs, might provide probable mechanisms for treating inflammatory pathogenic conditions like OA.

Kaempferol stimulates WNT/ß-catenin signaling pathway to induce differentiation of osteoblasts.

Flavonoids, a group of natural compounds found in a variety of vegetables and herbal medicines, have been intensively reported on stimulating bone mineral density and bone formation. Among them, kaempferol has been reported to assist bone formation in vitro and in vivo, but its precise mechanism of action for stimulating bone forming abilities of osteoblasts remained elusive. In SaOS-2 osteoblasts, treatment of kaempferol increased early and late osteogenic parameters significantly, including alkaline phosphatase (ALP) activity, collagen synthesis, and mRNA expression levels of Runx2, osterix, osteopontin and bone sialoprotein. Interestingly, kaempferol promoted osteoblastic differentiation via the activation of the WNT signaling pathway. The stimulation of SaOS-2 cells by kaempferol resulted in an increased activity of WNT signaling responsive reporter construct, Axin-2, and, subsequently, stabilization of WNT signaling mediated transcription factor ß-catenin, probably leading to the activation of WNT-targeted genes for osteogenesis. In corroboration, the kaempferol-induced ALP activity was fully abolished by FH 535, an inhibitor of WNT signaling pathway. Kaempferol mediated activation of WNT signaling pathway through estrogen signaling pathway, as the application of ICI 182,780 (an inhibitor for estrogen receptors) markedly inhibited kaempferol-induced WNT signaling activation and osteogenic marker like ALP activity in SaOS-2 cells. Immunohistochemical studies in drill-hole defect model showed increased expression of Runx2 and ß-catenin staining after kaempferol treatment. Thus, it may be concluded that kaempferol stimulates estrogen signaling followed by WNT signaling pathway activation to achieve its potential for bone-sparing effects.

G2A Protects Mice against Sepsis by Modulating Kupffer Cell Activation: Cooperativity with Adenosine Receptor 2b.

G2A is a GPCR abundantly expressed in immune cells. G2A-/- mice showed higher lethality, higher plasma cytokines, and an impaired bacterial clearance in response to a murine model of sepsis (cecal ligation and puncture), which were blocked by GdCl3, an inhibitor of Kupffer cells. Anti-IL-10 Ab reversed the impaired bacterial clearance in G2A-/- mice. Indomethacin effectively blocked both the increased i.p. IL-10 levels and the impaired bacterial clearance, indicating that disturbed PG system is the proximal cause of these phenomena. Stimulation with LPS/C5a induced an increase in Escherichia coli phagocytosis and intracellular cAMP levels in G2A+/+ peritoneal macrophages but not G2A-/- cells, which showed more PGE2/nitrite release and intracellular reactive oxygen species levels. Heterologous coexpression of G2A and adenosine receptor type 2b (A2bAR) induced a synergistic increase in cAMP signaling in a ligand-independent manner, with the evidence of physical interaction of G2A with A2bAR. BAY 60-6583, a specific agonist for A2bAR, increased intracellular cAMP levels in Kupffer cells from G2A+/+ but not from G2A-/- mice. Both G2A and A2bAR were required for antiseptic action of lysophosphatidylcholine. These results show inappropriate activation of G2A-/- Kupffer cells to septic insults due to an impaired cAMP signaling possibly by lack of interaction with A2bAR.

Lysophosphatidic acid enhances breast cancer cells-mediated osteoclastogenesis.

Lysophosphatidic acid (LPA) is known to play a critical role in breast cancer metastasis to bone. In this study, we tried to investigate any role of LPA in the regulation of osteoclastogenic cytokines from breast cancer cells and the possibility of these secretory factors in affecting osteoclastogenesis. Effect of secreted cytokines on osteoclastogenesis was analyzed by treating conditioned media from LPA-stimulated breast cancer cells to differentiating osteoclasts. Result demonstrated that IL-8 and IL-11 expression were upregulated in LPA-treated MDA-MB-231 cells. IL-8 was induced in both MDA-MB-231 and MDA-MB-468, however, IL-11 was induced only in MDA-MB-231, suggesting differential LPARs participation in the expression of these cytokines. Expression of IL-8 but not IL-11 was suppressed by inhibitors of PI3K, NFkB, ROCK and PKC pathways. In the case of PKC activation, it was observed that PKCδ and PKCµ might regulate LPA-induced expression of IL-11 and IL-8, respectively, by using specific PKC subtype inhibitors. Finally, conditioned Medium from LPA-stimulated breast cancer cells induced osteoclastogenesis. In conclusion, LPA induced the expression of osteolytic cytokines (IL-8 and IL-11) in breast cancer cells by involving different LPA receptors. Enhanced expression of IL-8 by LPA may be via ROCK, PKCu, PI3K, and NFkB signaling pathways, while enhanced expression of IL-11 might involve PKCδ signaling pathway. LPA has the ability to enhance breast cancer cells-mediated osteoclastogenesis by inducing the secretion of cytokines such as IL-8 and IL-11.

Anti-inflammatory effects of traditional mixed extract of medicinal herbs (MEMH) on monosodium urate crystal-induced gouty arthritis.

Korean oriental medicine prescription is widely used for the treatment of gouty diseases. In the present study, we investigated anti-inflammatory effects of modified Korean herbal formulation, mixed extract of medicinal herbs (MEMH), and its modulatory effects on inflammatory mediators associated with gouty arthritis. Both in vitro and in vivo studies were carried out to assess the anti-inflammatory efficacy of MEMH on monosodium urate (MSU) crystals-induced gouty inflammation. MSU crystals stimulated human chondrosarcoma cell line, SW1353, and human primary chondrocytes were treated with MEMH in vitro. The expression levels of pro-inflammatory mediators and metalloproteases were analyzed. The effect of MEMH on NFκB signaling pathway in SW1353 cells was examined. Effect of MEMH on the mRNA expression level of pro-inflammatory mediators and chemotactic factor from human monocytic cell line, THP-1, was also analyzed. The probable role of MEMH in the differentiation process of osteoblast like cells, SaOS-2, after MSU treatment was also observed. To investigate the effects of MEMH in vivo, MSU crystals-induced ankle arthritic model was established. Histopathological changes in affected joints and plasma levels of pro-inflammatory mediators (IL-1ß and TNFα) were recorded. MEMH inhibited NFκB signaling pathway and COX-2 protein expression in chondrocytes. MSU-induced mRNA expressions of pro-inflammatory mediators and chemotactic cytokines were suppressed by MEMH. In MSU crystals-induced ankle arthritic mouse model, administration of MEMH relieved inflammatory symptoms and decreased the plasma levels of IL-1ß and TNFα. The results indicated that MEMH can effectively inhibit the expression of inflammatory mediators in gouty arthritis, demonstrating its potential for treating gouty arthritis.

Quercetin induces apoptosis and cell cycle arrest in triple-negative breast cancer cells through modulation of Foxo3a activity.

Quercetin, a plant-derived flavonoid found in fruits, vegetables and tea, has been known to possess bioactive properties such as anti-oxidant, anti-inflammatory and anti-cancer. In this study, anti-cancer effect of quercetin and its underlying mechanisms in triple-negative breast cancer cells was investigated. MTT assay showed that quercetin reduced breast cancer cell viability in a time and dose dependent manner. For this, quercetin not only increased cell apoptosis but also inhibited cell cycle progression. Moreover, quercetin increased FasL mRNA expression and p51, p21 and GADD45 signaling activities. We also observed that quercetin induced protein level, transcriptional activity and nuclear translocation of Foxo3a. Knockdown of Foxo3a caused significant reduction in the effect of quercetin on cell apoptosis and cell cycle arrest. In addition, treatment of JNK inhibitor (SP 600125) abolished quercetin-stimulated Foxo3a activity, suggesting JNK as a possible upstream signaling in regulation of Foxo3a activity. Knockdown of Foxo3a and inhibition of JNK activity reduced the signaling activities of p53, p21 and GADD45, triggered by quercetin. Taken together, our study suggests that quercetin induces apoptosis and cell cycle arrest via modification of Foxo3a signaling in triple-negative breast cancer cells.

Application of Bioactive Quercetin in Oncotherapy: From Nutrition to Nanomedicine.

Phytochemicals as dietary constituents are being explored for their cancer preventive properties. Quercetin is a major constituent of various dietary products and recently its anti-cancer potential has been extensively explored, revealing its anti-proliferative effect on different cancer cell lines, both in vitro and in vivo. Quercetin is known to have modulatory effects on cell apoptosis, migration and growth via various signaling pathways. Though, quercetin possesses great medicinal value, its applications as a therapeutic drug are limited. Problems like low oral bioavailability and poor aqueous solubility make quercetin an unreliable candidate for therapeutic purposes. Additionally, the rapid gastrointestinal digestion of quercetin is also a major barrier for its clinical translation. Hence, to overcome these disadvantages quercetin-based nanoformulations are being considered in recent times. Nanoformulations of quercetin have shown promising results in its uptake by the epithelial system as well as enhanced delivery to the target site. Herein we have tried to summarize various methods utilized for nanofabrication of quercetin formulations and for stable and sustained delivery of quercetin. We have also highlighted the various desirable measures for its use as a promising onco-therapeutic agent.

Methoxy poly(ethylene glycol)-poly(lactide) nanoparticles encapsulating quercetin act as an effective anticancer agent by inducing apoptosis in breast cancer.

PURPOSE: To overcome the therapeutic restrictions offered by hydrophobic quercetin (Qu), this study aims to synthesize MPEG-PLA encapsulated Qu nanoparticle and to evaluate their anticancer efficacy. MATERIALS AND METHODS: In vitro anticancer potential and apoptotic studies were done by cell cytotoxicity assay and flow cytometry, respectively. MPEG-PLA-Qu nanoparticles were evaluated for anticancer efficacy in vivo using xenograft mice model. TUNEL assay was performed to observe the frequency of apoptotic cells in vivo. RESULTS: The hydrodynamic particle size, polydispersity index, zeta potential and drug loading % of MPEG-PLA-Qu nanoparticle was 155.3 ± 3.2 nm, 0.2 ± 0.05, -3.14 mV and 5.3 ± 1.1%, respectively. Also, MPEG-PLA-Qu showed sustained drug release for 10 days. In vitro results showed that MPEG-PLA-Qu could efficiently induce apoptosis in triple negative breast cancer cell line (MDA-MB-231) with higher amount of quercetin in cell lysate treated with MPEG-PLA-Qu in comparison to free quercetin. In xenograft model for breast cancer, peritumorally injected MPEG-PLA-Qu significantly inhibited the tumor growth. Moreover, TUNEL assay showed more occurrence of apoptotic cells in MPEG-PLA-Qu treated tumors compared to free quercetin at similar dose. CONCLUSION: Our data suggest that MPEG-PLA-Qu nanoparticle can have a promising clinical potential for the treatment of breast cancer.

Novel biomarker for prostate cancer diagnosis by MRS.

Magnetic resonance spectroscopy (MRS) is a prospective tool for characterization of the chemical composition of tissues. In vivo MRS can be used for metabolite profiling in the prostate tissue to discriminate non-invasively carcinomas and healthy prostate. In this article different prostate metabolites have been discussed and how to exploit the MRS technique for the estimation of metabolites in prostate tissue quantitatively is elucidated. Choline, citrate, creatine, myo-inositol metabolites can be considered as biomarker for localization of malignancy in the prostate and their ratio can be used for the determination of cancer tissue in the prostate gland.

Effect of Wnt3a on keratinocytes utilizing in vitro and bioinformatics analysis.

Wingless-type (Wnt) signaling proteins participate in various cell developmental processes. A suppressive role of Wnt5a on keratinocyte growth has already been observed. However, the role of other Wnt proteins in proliferation and differentiation of keratinocytes remains unknown. Here, we investigated the effects of the Wnt ligand, Wnt3a, on proliferation and differentiation of keratinocytes. Keratinocytes from normal human skin were cultured and treated with recombinant Wnt3a alone or in combination with the inflammatory cytokine, tumor necrosis factor α (TNFα). Furthermore, using bioinformatics, we analyzed the biochemical parameters, molecular evolution, and protein-protein interaction network for the Wnt family. Application of recombinant Wnt3a showed an anti-proliferative effect on keratinocytes in a dose-dependent manner. After treatment with TNFα, Wnt3a still demonstrated an anti-proliferative effect on human keratinocytes. Exogenous treatment of Wnt3a was unable to alter mRNA expression of differentiation markers of keratinocytes, whereas an altered expression was observed in TNFα-stimulated keratinocytes. In silico phylogenetic, biochemical, and protein-protein interaction analysis showed several close relationships among the family members of the Wnt family. Moreover, a close phylogenetic and biochemical similarity was observed between Wnt3a and Wnt5a. Finally, we proposed a hypothetical mechanism to illustrate how the Wnt3a protein may inhibit the process of proliferation in keratinocytes, which would be useful for future researchers.

Lys1110 of TRPM2 is critical for channel activation.

TRPM2 (transient receptor potential melastatin 2) is a non-selective Ca2+-permeable cation channel activated by ADPR (adenosine diphosphoribose) and H2O2. It is widely expressed in mammalian cells and plays an important role in the regulation of various cell functions. However, the mechanisms of TRPM2 channel activation are not fully understood. Previously, we reported that TRPM2 channel activation is induced by high intracellular Cl- concentration. In the present study, we investigated the functional role of Lys1110 in the membrane-proximal C-terminal region by site-directed mutagenesis. Replacement of the positively charged amino acid lysine (Lys1110) with the neutrally charged amino acid asparagine (K1110N) or the negatively charged amino acid glutamic acid (K1110E) generated mutants that failed to induce an increase in free cytosolic calcium concentration ([Ca2+]i) not only by intracellular injection of Cl-, but also by H2O2 or ADPR. However, a mutant generated by replacing the lysine residue with a positively charged amino acid arginine (K1110R) displayed channel activity similar to wild-type TRPM2. Interestingly, in the K1107N/K1110N double-point mutant, the impaired function of the K1110N mutant in response to ADPR and H2O2, but not to Cl-, was recovered. There were no changes in protein expression, membrane trafficking and oligomerization of the mutant channels. The extent of [Ca2+]i increase by H2O2 in HEK (human embryonic kidney)-293 cells expressing TRPM2 mutants was well correlated with the degree of susceptibility to H2O2-induced cell death. These results display the crucial role of a positively charged amino acid residue at position 1110 for TRPM2 channel activity.

Regulation of Wnt signaling activity for growth suppression induced by quercetin in 4T1 murine mammary cancer cells.

Quercetin is a promising chemopreventive agent against cancer that inhibits tumor progression by inducing cell cycle arrest and promoting apoptotic cell death. Recently, the Wnt/ß-catenin signaling pathway has been implicated in mammary tumorigenesis, where its abnormal activation is associated with the development of breast cancer. Thus, the objective of this study was to examine the biological activities of quercetin against mammary cancer cells, and to determine whether quercetin could regulate the Wnt/ß-catenin signaling pathway. Quercetin showed dose-dependent inhibition of cell growth and induced apoptosis in 4T1 cells. Treatment of 20 µM quercetin suppressed ~50% of basal TopFlash luciferase activity. Moreover, the inhibitory effect of quercetin on the Wnt/ß-catenin signaling pathway was confirmed by the reduced stabilization of the ß-catenin protein. Among various antagonists screened for the Wnt/ß-catenin signaling pathway, the expression of DKK1, 2 and 3 was induced after treatment with 20 µM of quercetin. Stimulation with recombinant DKK1 protein, showed suppressive cell growth of mammary cancer cells instead of quercetin. When 4T1 cells were treated with recombinant Wnt3a or LiCl along with quercetin, both stimulators for the Wnt/ß-catenin signaling pathway were able to restore the suppressed cell viability by quercetin. Thus, our data suggest that quercetin exerts its anticancer activity through the downregulation of Wnt/ß-catenin signaling activity. These results indicate for the first time that quercetin decreases cell viability and induces apoptosis in murine mammary cancer cells, which is possibly mediated by DKK-dependent inhibition of the Wnt/ß-catenin signaling pathway. In conclusion, our findings suggest that quercetin has great potential value as chemotherapeutic agent for cancer treatment, especially in breast cancer controlled by Wnt/ß-catenin signaling activity.

Osteogenic activity of silymarin through enhancement of alkaline phosphatase and osteocalcin in osteoblasts and tibia-fractured mice.

Bone-remodeling imbalance induced by increased bone resorption and osteoclast formation is known to cause skeletal diseases such as osteoporosis. There has been growing interest in the anabolic natural agents that enhance bone formation. Silymarin is flavonolignans extracted from blessed milk thistle. Several studies suggest that silymarin possesses antihepatotoxic properties and anticancer effects against carcinoma cells. This study investigated promoting effects of silymarin on differentiation and mineralization of osteoblastic MC3T3-E1 mouse cells and on bone mineral density (BMD) by in vivo fracture experiments. Osteoblasts were treated with 1-20 µmol/L silymarin for 15 days in a differentiating medium. In addition, this study explored signaling pathways implicated in the osteoblastogenesis of silymarin. It was found that silymarin stimulated alkaline phosphatase (ALP) activity and calcium nodule formation in a dose-dependent manner with a substantial effect on osteoblast proliferation. Silymarin treatment enhanced collagen secretion, osteocalcin transcription and bone morphogenetic protein (BMP) expression. The BMP inhibitor noggin suppressed the silymarin-promoted ALP activity in differentiated osteoblasts, suggesting that its osteoblastogenic actions entail the BMP pathway. This was proved by increased SMAD1/5/8 phosphorylation and runt-related transcription factor 2 (Runx2) expression in the presence of silymarin. In 21-day fracture-healing experiments, fractured and silymarin (10 mg/kg)-treated C57BL/6 mice showed better bone healing than fractured mice. Silymarin supplementation improved tibial bone strength with elevated BMD and serum levels of osteogenic ALP and osteocalcin. Taken together, these results demonstrate, for the first time, that silymarin has a potential to enhance osteoblastogenesis through accelerating BMP/SMAD/Runx2 signal pathways and to improve fracture healing and bone strength in mouse tibiae.

The effect of TNFα secreted from macrophages activated by titanium particles on osteogenic activity regulated by WNT/BMP signaling in osteoprogenitor cells.

Wear particles are the major cause of osteolysis associated with failure of implant following total joint replacement. During this pathologic process, activated macrophages mediate inflammatory responses to increase osteoclastogenesis, leading to enhanced bone resorption. In osteolysis caused by wear particles, osteoprogenitors present along with macrophages at the implant interface may play significant roles in bone regeneration and implant osteointegration. Although the direct effects of wear particles on osteoblasts have been addressed recently, the role of activated macrophages in regulation of osteogenic activity of osteoblasts has scarcely been studied. In the present study, we examined the molecular communication between macrophages and osteoprogenitor cells that may explain the effect of wear particles on impaired bone forming activity in inflammatory bone diseases. It has been demonstrated that conditioned medium of macrophages challenged with titanium particles (Ti CM) suppresses early and late differentiation markers of osteoprogenitors, including alkaline phosphatase (ALP) activity, collagen synthesis, matrix mineralization and expression of osteocalcin and Runx2. Moreover, bone forming signals such as WNT and BMP signaling pathways were inhibited by Ti CM. Interestingly, TNFα was identified as a predominant factor in Ti CM to suppress osteogenic activity as well as WNT and BMP signaling activity. Furthermore, Ti CM or TNFα induces the expression of sclerostin (SOST) which is able to inhibit WNT and BMP signaling pathways. It was determined that over-expression of SOST suppressed ALP activity, whereas the inhibition of SOST by siRNA partially restored the effect of Ti CM on ALP activity. This study highlights the role of activated macrophages in regulation of impaired osteogenic activity seen in inflammatory conditions and provides a potential mechanism for autocrine regulation of WNT and BMP signaling mediated by TNFα via induction of SOST in osteprogenitor cells.

Lysophosphatidic acid induces upregulation of Mcl-1 and protects apoptosis in a PTX-dependent manner in H19-7 cells.

Lysophosphatidic acid (LPA) is a lipid growth factor known to regulate diverse cell functions, including cell proliferation, survival, and apoptosis. Tight regulation of cell survival in neuronal precursor is essential during neurogenesis in both developing and adult brain. Increasing data show that diverse external factors including LPA play roles in controlling cell survival and apoptosis in early developing neurons. However, the underlying control mechanism remains unclear. To explore how LPA regulates cell survival or apoptosis in a developing neuron, mechanisms for cell survival and signaling cascades by LPA were investigated in H19-7 hippocampal progenitor cells. Here, we showed that LPA promotes cell survival by protection from apoptosis. Mcl-1 was demonstrated to be crucial in LPA-induced cell survival by transfection of the siRNA specific for Mcl-1 and overexpression of Mcl-1. LPA-induced cell survival was critically mediated by the upregulation of Mcl-1 which was regulated not only through a post-translational control but a transcriptional control. Mcl-1 stabilization by LPA-induced inhibitory phosphorylation of GSK-3 contributed predominantly to the Mcl-1 upregulation. Both LPA-induced cell survival and the GSK-3 phosphorylation were attenuated by PTX and by siRNA specific for LPA1 or LPA2 receptor. Taken together, these results showed that Mcl-1 stabilization by inhibitory phosphorylation of GSK-3 through Gi/o coupling of the LPA1 and LPA2 receptors following Mcl-1 upregulation plays a critical role in LPA-induced survival of H19-7 cells. In developing neurons, modulation of Mcl-1 levels may constitute a crucial mechanism for controlling their fates.

Lysophosphatidic acid-induced c-fos up-regulation involves cyclic AMP response element-binding protein activated by mitogen- and stress-activated protein kinase-1.

Lysophosphatidic acid (LPA) is a lipid growth factor that exerts diverse biological effects through its cognate receptor-mediated signaling cascades. Recently, we reported that LPA stimulates cAMP response element-binding protein (CREB) through mitogen- and stress-activated protein kinase-1 (MSK1). Previously, LPA has been shown to stimulate c-fos mRNA expression in Rat-2 fibroblast cells via a serum response element binding protein (SRF). However, involvement of CREB in LPA-stimulated c-fos gene expression is not elucidated yet. To investigate the CREB-mediated c-fos activation by LPA, various c-fos promoter-reporter constructs containing wild-type and mutated SRE and CRE were tested for their inducibility by LPA in transient transfection assays. LPA-stimulated c-fos promoter activation was markedly decreased when SRE and CRE were mutated. A dominant negative CREB significantly down-regulated the LPA-stimulated c-fos promoter activation. Chromatin immunoprecipitation assay revealed that LPA induced an increased binding of phosphorylated CREB and CREB-binding protein (CBP) to the CRE region of the endogenous c-fos promoter. Immunoblot analyses with various pharmacological inhibitors further showed that LPA induces up-regulation of c-fos mRNA level by activation of ERK, p38 MAPK, and MSK1. Taken together, our results suggest that CREB plays an important role in up-regulation of c-fos mRNA level in LPA-stimulated Rat-2 fibroblast cells.

Mouse R-spondin2 is required for apical ectodermal ridge maintenance in the hindlimb.

The R-spondin (Rspo) family of proteins consists of secreted cysteine-rich proteins that can activate beta-catenin signaling via the Frizzled/LRP5/6 receptor complex. Here, we report that targeted inactivation of the mouse Rspo2 gene causes developmental limb defects, especially in the hindlimb. Although the initiation of the expression of apical ectodermal ridge (AER)-specific genes, including fibroblast growth factor 8 (FGF8) and FGF4 occurred normally, the maintenance of these marker expressions was significantly defective in the hindlimb of Rspo2(-/-) mice. Consistent with the ligand role of R-spondins in the Wnt/beta-catenin signaling pathway, expression of Axin2 and Sp8, targets for beta-catenin signaling, within AER was greatly reduced in Rspo2(-/-) embryos. Furthermore, sonic hedgehog (Shh) signaling within the hindlimbs of Rspo2(-/-) mice was also significantly decreased. Rspo2 is expressed in the AER of all limb buds, however the stunted phenotype is significantly more severe in the hindlimbs than the forelimbs and strongly biased to the left side. Our findings strongly suggest that Rspo2 expression in the AER is required for AER maintenance likely by regulating Wnt/beta-catenin signaling.

Lysophosphatidic acid stimulates cAMP accumulation and cAMP response element-binding protein phosphorylation in immortalized hippocampal progenitor cells.

cAMP response element-binding protein (CREB) has been known to play a pivotal role in neuronal differentiation and neuronal plasticity. Lysophosphatidic acid (LPA) was reported to activate CREB in Rat2 fibroblast cells. To study the roles of LPA in neuronal differentiation, we determined whether LPA activates CREB in H19-7, hippocampal progenitor cells. LPA induced three-fold increase in cAMP level in a pertussis toxin-independent manner. Moreover, LPA stimulated CREB phosphorylation, which was inhibited by not only H89 but also Rp-cAMP. In H19-7 cells, high-level expression of lpa1 and moderate-level expression of lpa4 were detected, whereas any detectible expression of lpa2 or lpa3 was not detected by reverse transcription polymerase chain reaction. Together, these data suggested that LPA potentiates cAMP accumulation through activating Gs, and thereby, LPA can stimulate cAMP-CREB signaling cascade.

Therapeutic effects of lysophosphatidylcholine in experimental sepsis.

Sepsis represents a major cause of death in intensive care units. Here we show that administration of lysophosphatidylcholine (LPC), an endogenous lysophospholipid, protected mice against lethality after cecal ligation and puncture (CLP) or intraperitoneal injection of Escherichia coli. In vivo treatment with LPC markedly enhanced clearance of intraperitoneal bacteria and blocked CLP-induced deactivation of neutrophils. In vitro, LPC increased bactericidal activity of neutrophils, but not macrophages, by enhancing H(2)O(2) production in neutrophils that ingested E. coli. Incubation with an antibody to the LPC receptor, G2A, inhibited LPC-induced protection from CLP lethality and inhibited the effects of LPC in neutrophils. G2A-specific antibody also blocked the inhibitory effects of LPC on certain actions of lipopolysaccharides (LPS), including lethality and the release of tumor necrosis factor-alpha (TNF-alpha) from neutrophils. These results suggest that LPC can effectively prevent and treat sepsis and microbial infections.