Cyclic AMP enhances Smad-mediated BMP signaling through PKA-CREB pathway

Acetyltransferases CBP/p300 Control Transcriptional Switch of β-Catenin and Stat1 Promoting Osteoblast Differentiation

CREB-binding protein (CBP) (CREBBP) and p300 (EP300) are multifunctional histone acetyltransferases (HATs) with extensive homology. Germline mutations of CBP or p300 cause skeletal abnormalities in humans and mice. However, the precise roles of CBP/p300 in bone homeostasis remain elusive. Here, we report that conditional knockout of CBP or p300 in osteoblasts results in reduced bone mass and strength due to suppressed bone formation. The HAT activity is further confirmed to be responsible for CBP/p300-mediated osteogenesis using A-485, a selective inhibitor of CBP/p300 HAT. Mechanistically, CBP/p300 HAT governs osteogenic gene expression in part through transcriptional activation of β-catenin and inhibition of Stat1. Furthermore, acetylation of histone H3K27 and the transcription factor Foxo1 are demonstrated to be involved in CBP/p300 HAT-regulated β-catenin and Stat1 transcription, respectively. Taken together, these data identify acetyltransferases CBP/p300 as critical regulators that promote osteoblast differentiation and reveal an epigenetic mechanism responsible for maintaining bone homeostasis. © 2023 American Society for Bone and Mineral Research (ASBMR).

Myostatin silencing inhibits podocyte apoptosis in membranous nephropathy through Smad3/PKA/NOX4 signaling pathway

This article focuses on deciphering the effect of myostatin (MSTN) on podocyte apoptosis in membranous nephropathy (MN) and fathoming out its underlying mechanism. Rats received the intravenous injection of cationized-bovine serum albumin to induce MN in vivo, while angiotensin II (Ang II) was exposed to AB8/13 cells to induce MN model in vitro. The mRNA expression of MSTN was detected by qRT-PCR. The effects of MSTN silencing on MN model rats and cells were assessed by cell counting kit-8 assay, flow cytometry, hematoxylin and eosin staining, and TUNEL assay. The expressions of proteins related to apoptosis and Smad3/protein kinase A (PKA)/NADPH oxidase 4 (NOX4) signaling pathway were examined by western blot. As a result, MSTN was highly expressed in MN cell and rat models. Besides, knockdown of MSTN elevated the MN cell viability and dwindled apoptosis rate, as well as attenuated kidney injury in MN rats. Meanwhile, MSTN silencing lessened the expressions of phosphorylated (p)-Smad3 and Nox4, while boosting the p-PKA expression in MN rats and cells. Additionally, Smad3 overexpression reversed the above effects of MSTN silencing on Ang II-induced podocytes. In conclusion, MSTN knockdown restrains the podocyte apoptosis through regulating Smad3/PKA/NOX4 signaling pathway.

Dynamics and Mechanisms of ERK Activation after Different Protocols that Induce Long-Term Synaptic Facilitation in Aplysia

Phosphorylation of the MAPK family member extracellular signal-regulated kinase (ERK) is required to induce long-term synaptic plasticity, but little is known about its persistence. We examined ERK activation by three protocols that induce long-term synaptic facilitation (LTF) of the Aplysia sensorimotor synapse - the standard protocol (five 5-min pulses of 5-HT with interstimulus intervals (ISIs) of 20 min), the enhanced protocol (five pulses with irregular ISIs, which induces greater and longer-lasting LTF) and the two-pulse protocol (two pulses with ISI 45 min). Immunofluorescence revealed complex ERK activation. The standard and two-pulse protocols immediately increased active, phosphorylated ERK (pERK), which decayed within 5 h. A second wave of increased pERK was detected 18 h post-treatment for all protocols. This late phase was blocked by inhibitors of protein kinase A, TrkB and TGF-β. These results suggest that complex interactions among kinase pathways and growth factors contribute to the late increase of pERK. ERK activity returned to basal 24 h after the standard or two-pulse protocols, but remained elevated 24 h for the enhanced protocol. This 24-h elevation was also dependent on PKA and TGF-β, and partly on TrkB. These results begin to characterize long-lasting ERK activation, plausibly maintained by positive feedback involving growth factors and PKA, that appears essential to maintain LTF and LTM. Because many processes involved in LTF and late LTP are conserved among Aplysia and mammals, these findings highlight the importance of examining the dynamics of kinase cascades involved in vertebrate long-term memory.

Glycochenodeoxycholate Affects Iron Homeostasis via Up-Regulating Hepcidin Expression

Increasing hepcidin expression is a vital factor in iron homeostasis imbalance among patients with chronic kidney disease (CKD). Recent studies have elucidated that abnormal serum steroid levels might cause the elevation of hepcidin. Glycochenodeoxycholate (GCDCA), a steroid, is significantly elevated in patients with CKD. However, the correlation between GCDCA and hepcidin has not been elucidated. Decreased serum iron levels and increased hepcidin levels were both detected in patients with CKD in this study. Additionally, the concentrations of GCDCA in nephropathy patients were found to be higher than those in healthy subjects. HepG2 cells were used to investigate the effect of GCDCA on hepcidin in vitro. The results showed that hepcidin expression increased by nearly two-fold against control under 200 μM GCDCA treatment. The phosphorylation of SMAD1/5/8 increased remarkably, while STAT3 and CREBH remained unchanged. GCDCA triggered the expression of farnesoid X receptor (FXR), followed with the transcription and expression of both BMP6 and ALK3 (upward regulators of SMAD1/5/8). Thus, GCDCA is a potential regulator for hepcidin, which possibly acts by triggering FXR and the BMP6/ALK3-SMAD signaling pathway. Furthermore, 40 C57/BL6 mice were treated with 100 mg/kg/d, 200 mg/kg/d, and 300 mg/kg/d GCDCA to investigate its effect on hepcidin in vivo. The serum level of hepcidin increased in mice treated with 200 mg/kg/d and 300 mg/kg/d GCDCA, while hemoglobin and serum iron levels decreased. Similarly, the FXR-mediated SMAD signaling pathway was also responsible for activating hepcidin in liver. Overall, it was concluded that GCDCA could induce the expression of hepcidin and reduce serum iron level, in which FXR activation-related SMAD signaling was the main target for GCDCA. Thus, abnormal GCDCA level indicates a potential risk of iron homeostasis imbalance.

Quantitative description of the interactions among kinase cascades underlying long-term plasticity of Aplysia sensory neurons

Kinases play critical roles in synaptic and neuronal changes involved in the formation of memory. However, significant gaps exist in the understanding of how interactions among kinase pathways contribute to the mechanistically distinct temporal domains of memory ranging from short-term memory to long-term memory (LTM). Activation of protein kinase A (PKA) and mitogen-activated protein kinase (MAPK)-ribosomal S6 kinase (RSK) pathways are critical for long-term enhancement of neuronal excitability (LTEE) and long-term synaptic facilitation (LTF), essential processes in memory formation. This study provides new insights into how these pathways contribute to the temporal domains of memory, using empirical and computational approaches. Empirical studies of Aplysia sensory neurons identified a positive feedforward loop in which the PKA and ERK pathways converge to regulate RSK, and a negative feedback loop in which p38 MAPK inhibits the activation of ERK and RSK. A computational model incorporated these findings to simulate the dynamics of kinase activity produced by different stimulus protocols and predict the critical roles of kinase interactions in the dynamics of these pathways. These findings may provide insights into the mechanisms underlying aberrant synaptic plasticity observed in genetic disorders such as RASopathies and Coffin-Lowry syndrome.

CREB Non-autonomously Controls Reproductive Aging through Hedgehog/Patched Signaling

Evolutionarily conserved signaling pathways are crucial for adjusting growth, reproduction, and cell maintenance in response to altered environmental conditions or energy balance. However, we have an incomplete understanding of the signaling networks and mechanistic changes that coordinate physiological changes across tissues. We found that loss of the cAMP response element-binding protein (CREB) transcription factor significantly slows Caenorhabditis elegans' reproductive decline, an early hallmark of aging in many animals. Our results indicate that CREB acts downstream of the transforming growth factor β (TGF-β) Sma/Mab pathway in the hypodermis to control reproductive aging, and that it does so by regulating a Hedgehog-related signaling factor, WRT-10. Overexpression of hypodermal wrt-10 is sufficient to delay reproductive decline and oocyte quality deterioration, potentially acting via Patched-related receptors in the germline. This TGF-β-CREB-Hedgehog signaling axis allows a key metabolic tissue to communicate with the reproductive system to regulate oocyte quality and the rate of reproductive decline.

ID1-Mediated BMP Signaling Pathway Potentiates Glucagon-Like Peptide-1 Secretion in Response to Nutrient Replenishment

Glucagon-like peptide-1 (GLP-1) is a well-known incretin hormone secreted from enteroendocrinal L cells in response to nutrients, such as glucose and dietary fat, and controls glycemic homeostasis. However, the detailed intracellular mechanisms of how L cells control GLP-1 secretion in response to nutrients still remain unclear. Here, we report that bone morphogenetic protein (BMP) signaling pathway plays a pivotal role to control GLP-1 secretion in response to nutrient replenishment in well-established mouse enteroendocrinal L cells (GLUTag cells). Nutrient starvation dramatically reduced cellular respiration and GLP-1 secretion in GLUTag cells. Transcriptome analysis revealed that nutrient starvation remarkably reduced gene expressions involved in BMP signaling pathway, whereas nutrient replenishment rescued BMP signaling to potentiate GLP-1 secretion. Transient knockdown of inhibitor of DNA binding (ID)1, a well-known target gene of BMP signaling, remarkably reduced GLP-1 secretion. Consistently, LDN193189, an inhibitor of BMP signaling, markedly reduced GLP-1 secretion in L cells. In contrast, BMP4 treatment activated BMP signaling pathway and potentiated GLP-1 secretion in response to nutrient replenishment. Altogether, we demonstrated that BMP signaling pathway is a novel molecular mechanism to control GLP-1 secretion in response to cellular nutrient status. Selective activation of BMP signaling would be a potent therapeutic strategy to stimulate GLP-1 secretion in order to restore glycemic homeostasis.

Synergistic stimulating effect of 2-hydroxymelatonin and BMP-4 on osteogenic differentiation in vitro

2-Hydroxymelatonin is a metabolite produced when melatonin 2-hydroxylase catalyzes melatonin. Recent studies have reported the important roles of melatonin in bone metabolism. However, the roles of 2-hydroxymelatonin in bone metabolism remains poorly understood. The purpose of this study is to present evidence of the effect of 2-hydroxymelatonin on osteogenic differentiation in C2C12 cells. In this study, we demonstrated the synergistic stimulating effect of 2-hydroxymelatonin and bone morphogenetic protein (BMP)-4 on osteogenic differentiation in vitro, using alkaline phosphatase (ALP) staining, Alizarin red S (ARS) staining, qPCR, and luciferase reporter assay. The combination of 2-hydroxymelatonin and BMP-4 revealed a synergistic effect on osteogenic differentiation in vitro. This finding provides evidence that optimal concentrations of both 2-hydroxymelatonin and BMP-4 are beneficial for anabolic effects on bone in vitro.

Bone morphogenetic protein signaling regulates Id1-mediated neural stem cell quiescence in the adult zebrafish brain via a phylogenetically conserved enhancer module

In the telencephalon of adult zebrafish, the inhibitor of DNA binding 1 (id1) gene is expressed in radial glial cells (RGCs), behaving as neural stem cells (NSCs), during constitutive and regenerative neurogenesis. Id1 controls the balance between resting and proliferating states of RGCs by promoting quiescence. Here, we identified a phylogenetically conserved cis-regulatory module (CRM) mediating the specific expression of id1 in RGCs. Systematic deletion mapping and mutation of conserved transcription factor binding sites in stable transgenic zebrafish lines reveal that this CRM operates via conserved smad1/5 and 4 binding motifs under both homeostatic and regenerative conditions. Transcriptome analysis of injured and uninjured telencephala as well as pharmacological inhibition experiments identify a crucial role of bone morphogenetic protein (BMP) signaling for the function of the CRM. Our data highlight that BMP signals control id1 expression and thus NSC proliferation during constitutive and induced neurogenesis.

Cyclic adenosine monophosphate-dependent activation of transient receptor potential vanilloid 4 (TRPV4) channels in osteoblast-like MG-63 cells

Parathyroid hormone (PTH) directly interacts with bone remodeling osteoblasts and osteocytes expressing the G-protein coupled receptor PTH receptor 1 (PTH1R), and its osteoanabolic effects mostly involve the cAMP/PKA signaling cascade. Considering that PTH-dependent calcium entry in rat enterocytes is reproduced by the adenylate cyclase agonist forskolin or by cAMP analogues, possible involvement of calcium as a second messenger in PTH-dependent cAMP signaling was investigated in MG-63 cells. First, Ca²⁺ influx was confirmed in Fluo3-loaded MG-63 cells treated with a cell-permeable cAMP analog. Second, PTH (1-34) and forskolin promoted calcium influxes that were completely abrogated by the PKA inhibitor H-89. Ca²⁺ entry was not reproduced when PTH (1-34) was combined with the PKC-activating competitor PTH (3-34). Vanilloid transient potential (TRPV) channel inhibitor Ruthenium Red, but not a voltage-dependent calcium channel (VDCC) inhibitor nifedipine, efficiently stunted Ca²⁺ entry, and comparable abrogation was reproduced in cells treated with TRPV4-selective inhibitor RN-1734 or transfected with TRPV4-specific siRNA. Interestingly, PTH-driven Ca²⁺ through TRPV4 significantly inhibited MG63 cell migration through a mechanism requiring extracellular Ca²⁺. In contrast, the inhibitory effects of forskolin on migration were refractory to TRPV4 silencing or to RN-1734. Altogether, our results indicate that single treatment with PTH (1-34) promotes extracellular calcium entry through TRPV4 channels in MG-63 cells through a cAMP/PKA-dependent mechanism, and that this influx affects cell migration.

Salt-inducible kinase 1 regulates bone anabolism via the CRTC1-CREB-Id1 axis

New bone anabolic agents for the effective treatment of bone metabolic diseases like osteoporosis are of high clinical demand. In the present study, we reveal the function of salt-inducible kinase 1 (SIK1) in regulating osteoblast differentiation. Gene knockdown of SIK1 but not of SIK2 or SIK3 expression in primary preosteoblasts increased osteoblast differentiation and bone matrix mineralization. SIK1 also regulated the proliferation of osteoblastic precursor cells in osteogenesis. This negative control of osteoblasts required the catalytic activity of SIK1. SIK1 phosphorylated CREB regulated transcription coactivator 1 (CRTC1), preventing CRTC1 from enhancing CREB transcriptional activity for the expression of osteogenic genes like Id1. Furthermore, SIK1 knockout (KO) mice had higher bone mass, osteoblast number, and bone formation rate versus littermate wild-type (WT) mice. Preosteoblasts from SIK1 KO mice showed more osteoblastogenic potential than did WT cells, whereas osteoclast generation among KO and WT precursors was indifferent. In addition, bone morphogenic protein 2 (BMP2) suppressed both SIK1 expression as well as SIK1 activity by protein kinase A (PKA)–dependent mechanisms to stimulate osteogenesis. Taken together, our results indicate that SIK1 is a key negative regulator of preosteoblast proliferation and osteoblast differentiation and that the repression of SIK1 is crucial for BMP2 signaling for osteogenesis. Therefore, we propose SIK1 to be a useful therapeutic target for the development of bone anabolic strategies.

Icariin Promotes the Osteogenic Action of BMP2 by Activating the cAMP Signaling Pathway

Icariin (ICA) is the main active flavonoid glucoside from herbs of the genus Epimedium; in traditional Chinese medicine, these herbs have long been prescribed for the treatment of bone fractures and osteoporosis. Several studies have shown that treatment with ICA can increase osteogenic differentiation and reduce bone loss in vivo and in vitro. However, the definite signaling pathway of this osteogenic effect remains unclear. In this study, we selected bone morphogenetic protein 2 (BMP2)-induced osteoblastic differentiation of multipotent mesenchymal progenitor C2C12 cells as a model of osteoblast differentiation. We investigated the effects of ICA on C2C12 cells osteogenic differentiation and the underlying molecular mechanisms. We found that ICA could enhance BMP2-mediated osteoblastic differentiation of C2C12 cells in a dose-dependent manner. Treatment with ICA activated the cAMP/PKA/CREB signaling axis in a time-dependent manner. Blocking cAMP signaling using the PKA selective inhibitor H89 significantly inhibited the stimulatory effect of ICA on osteogenesis. Therefore, the osteoinductive potential and the low cost of ICA indicate that it is a promising alternative treatment or promoter for enhancing the therapeutic effects of BMP2.

Pinoresinol promotes MC3T3‑E1 cell proliferation and differentiation via the cyclic AMP/protein kinase A signaling pathway

Estradiol (E2) is a first‑line drug for osteoporosis (OP) treatment via promotion of osteoblastic proliferation and differentiation. However, a long‑term use of E2 would produce side effects thus, it is imperative to discover safer and more effective drugs. Pinoresinol (PINO) has a similar chemical structure to E2. The present study aimed to investigate whether PINO could promote osteoblastic proliferation and differentiation and the potential mechanisms. After treatment with 0.1 µg/l PINO for 2 days, MC3T3‑E1 cell migration was assessed by wound healing assay. Estrogen (E2) treatment served as a positive control. RT‑qPCR and western blotting were used for mRNA and protein expression analyses. Alkaline phosphatase (ALP) activity assay and Alizarin red staining were performed to investigate the calcification and mineralization, and the cyclic AMP (cAMP) level was detected by enzyme‑linked immunosorbent assay (ELISA). H89, an inhibitor of protein kinase A (PKA), was introduced to verify the role of cAMP/PKA in the effect of PINO on MC3T3‑E1 cells. Cell viability was the highest under 48 h of 0.1 µg/l PINO treatment. After treatment with PINO, a significant increase was observed in the migration rate and the expression of collagen type I (Col‑I), ALP, osteopontin (OPN), runt‑related transcription factor 2 (Runx2) and bone morphogenetic protein‑2 (BMP‑2) (P<0.01). The ALP activity and Alizarin red size in PINO and E2 groups were notably increased. The increased cAMP, PKA and phosphorylated cAMP response element‑binding protein (CREB) levels were also observed in the PINO group. Furthermore, H89 co‑treatment abolished the positive effects of PINO on cell viability and migration. PINO had similar effects to E2 on the osteoblastic proliferation and differentiation, and these positive effects may be attributed to the regulation of the cAMP/PKA signaling pathway.

Non-canonical cyclic AMP SMAD1/5/8 signalling in human granulosa cells

Development of mammalian ovarian follicles is promoted by the combined action of endocrine cues and paracrine factors. Follicle stimulating hormone (FSH), through the action of cAMP drives follicular growth and development. The oocyte secretes powerful growth factors such as bone morphogenetic protein 15 (BMP15) to regulate granulosa cell proliferation, metabolism, steroidogenesis and differentiation through the activation of SMAD1/5/8. This study investigated the role of the cAMP signalling pathway on SMAD1/5/8 action in human granulosa cells. Cyclic AMP enhanced BMP15-induction of a SMAD1/5/8-specific BRE reporter. Moreover, in the absence of BMP ligand, cAMP also activated SMAD1/5/8-induced BRE activity. Cyclic AMP increased canonical downstream targets of BMP signalling such as inhibitor of differentiation (ID) mRNA expression. The observed effects were not mediated by secretion of BMPs as cAMP did not promote BMP ligand mRNA expression and a BMP extracellular antagonist, the BMP type II receptor ectodomain, did not affect cAMP-induced ID mRNA expression. Finally, the ERK1/2 pathway was shown to be required for the maintenance of cAMP-induced SMAD1/5/8 activity. Together our results suggest a novel and non-canonical pathway for cAMP signalling in human granulosa cells. Cyclic AMP appears to promote SMAD1/5/8 pathway activity intracellularly and has the ability to activate canonical SMAD1/5/8 downstream targets. Our results add another layer of complexity to the interactions between endocrine signalling and oocyte-secreted BMP ligands during folliculogenesis. Given the importance of both cAMP and SMAD1/5/8 pathways in follicular development, these interactions are likely required for the fine-tuning of oocyte paracrine signalling by endocrine stimuli.

CREB/Wnt10b mediates the effect of COX-2 on promoting BMP9-induced osteogenic differentiation via reducing adipogenic differentiation in mesenchymal stem cells

Bone morphogenetic protein 9 (BMP9) is one of the most potent osteogenic factors, which may be a potential candidate for bone tissue engineering. However, the osteogenic capacity of BMP9 still need to be further enhanced. In this study, we determined the effect of Wnt10b on BMP9-induced osteogenic differentiation in mesenchymal stem cell (MSCs) and the possible mechanism underlying this process. We introduced the polymerase chain reaction (PCR), Western blot analysis, histochemical stain, ectopic bone formation, and microcomputed tomography analysis to evaluate the effect of Wnt10b on BMP9-induced osteogenic differentiation. Meanwhile, PCR, Western blot analysis, chromatin immunoprecipitation, and immunoprecipitation were used to analyze the possible relationship between BMP9 and Wnt10b. We found that BMP9 upregulates Wnt10b in C3H10T1/2 cells. Wnt10b increases the osteogenic markers and bone formation induced by BMP9 in C3H10T1/2 cells, and silencing Wnt10b decreases these effects of BMP9. Meanwhile, Wnt10b enhances the level of phosphorylated Smad1/5/8 (p-Smad1/5/8) induced by BMP9, which can be reduced by silencing Wnt10b. On the contrary, Wnt10b inhibits adipogenic markers induced by BMP9, which can be decreased by silencing Wnt10b. Further analysis indicated that BMP9 upregulates cyclooxygenase-2 (COX-2) and phosphorylation of cAMP-responsive element binding (p-CREB) simultaneously. COX-2 potentiates the effect of BMP9 on increasing p-CREB and Wnt10b, while silencing COX-2 decreases these effects. p-CREB interacts with p-Smad1/5/8 to bind the promoter of Wnt10b in C3H10T1/2 cells. Our findings suggested that Wnt10b can promote BMP9-induced osteogenic differentiation in MSCs, which may be mediated through enhancing BMP/Smad signal and reducing adipogenic differentiation; BMP9 may upregulate Wnt10b via the COX-2/p-CREB-dependent manner.

Adenine alleviates iron overload by cAMP/PKA mediated hepatic hepcidin in mice

Hemochromatosis is prevalent and often associated with high rates of morbidity and mortality worldwide. The safe alternative iron-reducing approaches are urgently needed in order to better control iron overload. Our unbiased vitamin screen for modulators of hepcidin, a master iron regulatory hormone, identifies adenine (vitamin B4) as a potent hepcidin agonist. Adenine significantly induced hepcidin mRNA level and promoter activity activation in human cell lines, possibly through BMP/SMAD pathway. Further studies in mice validated the effect of adenine on hepcidin upregulation. Consistently, adenine dietary supplement in mice led to an increase of hepatic hepcidin expression compared with normal diet-fed mice via BMP/SMAD pathway. Notably, adenine-rich diet significantly ameliorated iron overload accompanied by the enhanced hepcidin expression in both high iron-fed mice and in Hfe^-/- mice, a murine model of hereditary hemochromatosis. To further validate this finding, we selected pharmacological inhibitors against BMP (LDN193189). We found LDN193189 strongly blocked the hepcidin induction by adenine. Moreover, we uncovered an essential role of cAMP/PKA-dependent axis in triggering adenine-induced hepcidin expression in primary hepatocytes by using 8 br cAMP, a cAMP analog, and H89, a potent inhibitor for PKA signaling. These findings suggest a potential therapeutic role of adenine for hereditary hemochromatosis.

The crucial role of the TRPM7 kinase domain in the early stage of amelogenesis

Transient receptor potential melastatin-7 (TRPM7) is a bi-functional protein containing a kinase domain fused to an ion channel. TRPM7 is highly expressed in ameloblasts during tooth development. Here we show that TRPM7 kinase-inactive knock-in mutant mice (TRPM7 KR mice) exhibited small enamel volume with opaque white-colored incisors. The TRPM7 channel function of ameloblast-lineage cells from TRPM7 KR mice was normal. Interestingly, phosphorylation of intracellular molecules including Smad1/5/9, p38 and cAMP response element binding protein (CREB) was inhibited in ameloblasts from TRPM7 KR mice at the pre-secretory stage. An immunoprecipitation assay showed that CREB was bound to TRPM7, suggesting that direct phosphorylation of CREB by TRPM7 was inhibited in ameloblast-lineage cells from TRPM7 KR mice. These results indicate that the function of the TRPM7 kinase domain plays an important role in ameloblast differentiation, independent of TRPM7 channel activity, via phosphorylation of CREB.

Aryl Hydrocarbon Receptor-Interacting Protein (AIP) N-Terminus Gene Mutations Identified in Pituitary Adenoma Patients Alter Protein Stability and Function

Mutations spanning the entire aryl hydrocarbon receptor-interacting protein (AIP) gene have been found in isolated familial cases of pituitary adenomas (PA). Missense mutations located in the N-terminus of the gene have been identified in several patients. However, the functional significance of these mutations remains a matter of controversy. In most studies, the N-terminus of AIP has been shown to regulate protein stability and subcellular localization of the AIP-AHR-HSP90 complex but not to be involved in protein-protein interactions. Other studies found that the N-terminal domain interacts directly with other proteins. The aim of this study was to analyze whether specific N-terminus AIP mutations identified in PA patients would be functionally different from wild-type (WT) AIP. In vitro analyses were used to assess the role of known N-terminus variants, a locally identified mutant, R9Q, and three other commonly genotyped N-terminus mutations R16H, V49M and K103R are found in PA patients. Given the functional effect of WT AIP on cAMP signalling alterations caused by N-terminus mutants on this pathway were also analyzed in GH3 cells. Results indicate that N-terminus mutations lead to de-regulation of the effect of WT AIP on cAMP signalling and increased cAMP thresholds in GH3 cells resulting in increased growth hormone (GH) secretion. Cycloheximide chase analysis identified a variation in protein degradation patterns between WT and N-terminus variants. Therefore, both functional and structural studies reveal that N-terminus mutations in the AIP gene alter protein behaviour significantly and hence can truly be pathogenic in nature.

Local co-application of zoledronate promotes long-term maintenance of newly formed bone induced by recombinant human bone morphogenetic protein 2

Bone Morphogenetic Proteins (BMPs) strongly induce the recruitment and differentiation of mesenchymal progenitor cells into mature osteoblasts, but also directly and indirectly stimulate differentiation of osteoclast progenitor cells and acceleration of mature osteoclasts function leading excessive bone resorption. Bisphosphonates, such as zoledronate (ZOL), inhibit osteoclasts function and osteoclasts mediated bone resorption. The short or middle term effect of BMPs and bisphosphonates on bone formation were previously reported, but there was no study that argue about the long term effect of bisphosphonates on BMP-induced bone anabolism. The present study demonstrated that the local administration of ZOL with recombinant human BMP-2 (rh-BMP-2) using beta tricalcium phosphate (β-TCP) as a carrier had superior efficacy not only to augment the BMP-induced new ectopic bone formation but to maintain the trabecular bone structure inside the new bone for long period. Histological analysis showed that rh-BMP-2/β-TCP composite induced trabecular bone resorption especially inside the new bone nodules over time, whereas no trabecular bone resorption was seen in rh-BMP-2/ZOL/β-TCP composite reducing the number of TRAP-positive cells. Thus, inhibition of bone resorption by bisphosphonate, such as ZOL, would be one of the advantageous ways to augment the new bone formation induced by rh-BMP-2, and moreover local co-application of ZOL using β-TCP as a carrier can be a useful material for long term suppression of osteoclastic resorption and thereby maintain the structure of new bone formation induced by rh-BMP-2.

The SMAD Pathway Is Required for Hepcidin Response During Endoplasmic Reticulum Stress

Hepcidin, the iron hormone, is regulated by a number of stimulatory and inhibitory signals. The cAMP responsive element binding protein 3-like 3 (CREB3L3) mediates hepcidin response to endoplasmic reticulum (ER) stress. In this study we asked whether hepcidin response to ER stress also requires the small mother against decapentaplegic (SMAD)-1/5/8 pathway, which has a major role in hepcidin regulation in response to iron and other stimuli. We analyzed hepcidin mRNA expression and promoter activity in response to ER stressors in HepG2 cells in the presence of the bone morphogenetic protein (BMP) type I receptor inhibitor LDN-193189, mutated hepcidin promoter or small interfering RNA against different SMAD proteins. We then used a similar approach in vivo in wild-type, Smad1/5, or Creb3l3^-/- animals undergoing ER stress. In vitro, LDN-193189 prevented hepcidin mRNA induction by different ER stressors. Seemingly, mutation of a BMP-responsive element in the hepcidin promoter prevented ER stress-mediated up-regulation. Moreover, in vitro silencing of SMAD proteins by small interfering RNA, in particular SMAD5, blunted hepcidin response to ER stress. On the contrary, hepcidin induction by ER stress was maintained when using antibodies against canonical BMP receptor ligands. In vivo, hepcidin was induced by ER stress and prevented by LDN-193189. In addition, in Smad1/5 knockout mice, ER stress was unable to induce hepcidin expression. Finally, in Creb3l3 knockout mice, in response to ER stress, SMAD1/5 were correctly phosphorylated and hepcidin induction was still appreciable, although to a lesser extent as compared with the control mice. In conclusion, our study indicates that hepcidin induction by ER stress involves the central regulatory SMAD1/5 pathway.

Porcine oocyte maturation in vitro: role of cAMP and oocyte-secreted factors - A practical approach

Polyspermy or the penetration of more than one sperm cell remains a problem during porcine in vitro fertilization (IVF). After in vitro culture of porcine zygotes, only a low percentage of blastocysts develop and their quality is inferior to that of in vivo derived blastocysts. It is unknown whether the cytoplasmic maturation of the oocyte is sufficiently sustained in current in vitro maturation (IVM) procedures. The complex interplay between oocyte and cumulus cells during IVM is a key factor in this process. By focusing on this bidirectional communication, it is possible to control the coordination of cumulus expansion, and nuclear and cytoplasmic maturation during IVM to some extent. Therefore, this review focuses on the regulatory mechanisms between oocytes and cumulus cells to further the development of new in vitro embryo production (IVP) procedures, resulting in less polyspermy and improved oocyte developmental potential. Specifically, we focused on the involvement of cAMP in maturation regulation and function of oocyte-secreted factors (OSFs) in the bidirectional regulatory loop between oocyte and cumulus cells. Our studies suggest that maintaining high cAMP levels in the oocyte during the first half of IVM sustained improved oocyte maturation, resulting in an enhanced response after IVF and cumulus matrix disassembly. Recent research indicated that the addition of OSFs during IVM enhanced the developmental competence of small follicle-derived oocytes, which was stimulated by epidermal growth factor (EGF) via developing EGF-receptor signaling.

Linarin promotes osteogenic differentiation by activating the BMP-2/RUNX2 pathway via protein kinase A signaling

Linarin (LIN), a flavonoid which exerts both anti-inflammatory and antioxidative effects, has been found to promote osteogenic differentiation. However, the molecular mechanism of its effect on osteoblast differentiation was unclear. In the present study, LIN from Flos Chrysanthemi Indici (FCI) was isolated in order to investigate the underlying mechanisms of LIN on MC3T3-E1 cells (a mouse osteoblastic cell line) and the osteoprotective effect of LIN in mice which had undergone an ovariectomy (OVX). The results revealed that LIN enhanced osteoblast proliferation and differentiation in MC3T3-E1 cells dose-dependently, with enhanced alkaline phosphatase (ALP) activity and mineralization of extracellular matrix. LIN upregulated osteogenesis-related gene expression, including that of ALP, runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), bone sialoprotein (BSP), and type I collagen (COL-I). Pretreatment with noggin, a bone morphogenetic protein-2 (BMP-2) antagonist, meant that LIN-induced gene expression levels of COL-1, ALP, OCN, BSP and RUNX2 were significantly reduced, as shown by RT-qPCR. Western blot analysis showed that LIN dose-dependently increased the protein levels of BMP-2 and RUNX2 and enhanced the phosphorylation of SMAD1/5. In addition, LIN dose-dependently upregulated protein kinase A (PKA) expression. H-89 (a PKA inhibitor) partially blocked the LIN-induced protein increase in BMP-2, p-SMAD1/5 and RUNX2. We noted that LIN preserved the trabecular bone microarchitecture of ovariectomized mice in vivo. Moreover, pretreatment with LIN significantly lowered serum levels of ALP and OCN in ovariectomized mice. Our data indicated that LIN induced the osteogenic differentiation and mineralization of MC3T3-E1 osteoblastic cells by activating the BMP-2/RUNX2 pathway through PKA signaling in vitro and protected against OVX-induced bone loss in vivo. The results strongly suggest that LIN is a useful natural alternative for the management of postmenopausal osteoporosis.

Promotion of EGF receptor signaling improves the quality of low developmental competence oocytes

Oocytes acquire developmental competence with progressive folliculogenesis. Cumulus oocyte complexes (COCs) from small antral follicles have inherent low competence and are poorly responsive to amphiregulin (AREG) which normally mediates oocyte maturation and ovulation. Using low competence porcine COCs, in an in vitro AREG-induced oocyte maturation system, the combined exposure to N(6),2'-O-dibutyryladenosine 3':5' cyclic monophosphate (cAMP) and bone morphogenetic protein 15 (B15) and growth differentiation factor 9 (G9) was necessary to enhance the rate of oocyte meiotic maturation and blastocyst formation. Furthermore, the combination of cAMP+B15+G9 enabled AREG-stimulated cumulus expansion and increased expression of the matrix-related genes HAS2, TNFIPA6 and PTGS2. Additionally, the combination enhanced p-ERK1/2 which is downstream of the EGF receptor. The enhanced nuclear maturation and blastocyst formation rates with the combinational treatment were ablated by an EGF receptor phosphorylation inhibitor. These results indicate that cAMP and oocyte-secreted factors cooperate to promote EGF receptor functionality in developing COCs, representing a key component of the acquisition of oocyte developmental competence.

The bone morphogenetic protein system and the regulation of ovarian follicle development in mammals

The bone morphogenetic protein (BMP) family consists of several growth factor proteins that belong to the transforming growth factor-β (TGF-β) superfamily. BMPs bind to type I and type II serine-threonine kinase receptors, and transduce signals through the Smad signalling pathway. BMPs have been identified in mammalian ovaries, and functional studies have shown that they are involved in the regulation of oogenesis and folliculogenesis. This review summarizes the role of the BMP system during formation, growth and maturation of ovarian follicles in mammals.

Molecular profiles of pyramidal neurons in the superior temporal cortex in schizophrenia

Disrupted synchronized oscillatory firing of pyramidal neuronal networks in the cerebral cortex in the gamma frequency band (i.e., 30-100 Hz) mediates many of the cognitive deficits and symptoms of schizophrenia. In fact, the density of dendritic spines and the average somal area of pyramidal neurons in layer 3 of the cerebral cortex, which mediate both long-range (associational) and local (intrinsic) corticocortical connections, are decreased in subjects with this illness. To explore the molecular pathophysiology of pyramidal neuronal dysfunction, we extracted ribonucleic acid (RNA) from laser-captured pyramidal neurons from layer 3 of Brodmann's area 42 of the superior temporal gyrus (STG) from postmortem brains from schizophrenia and normal control subjects. We then profiled the messenger RNA (mRNA) expression of these neurons, using microarray technology. We identified 1331 mRNAs that were differentially expressed in schizophrenia, including genes that belong to the transforming growth factor beta (TGF-β) and the bone morphogenetic proteins (BMPs) signaling pathways. Disturbances of these signaling mechanisms may in part contribute to the altered expression of other genes found to be differentially expressed in this study, such as those that regulate extracellular matrix (ECM), apoptosis, and cytoskeletal and synaptic plasticity. In addition, we identified 10 microRNAs (miRNAs) that were differentially expressed in schizophrenia; enrichment analysis of their predicted gene targets revealed signaling pathways and gene networks that were found by microarray to be dysregulated, raising an interesting possibility that dysfunction of pyramidal neurons in schizophrenia may in part be mediated by a concerted dysregulation of gene network functions as a result of the altered expression of a relatively small number of miRNAs. Taken together, findings of this study provide a neurobiological framework within which specific hypotheses about the molecular mechanisms of pyramidal cell dysfunction in schizophrenia can be formulated.

Aip regulates cAMP signalling and GH secretion in GH3 cells

Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene have been linked to predisposition to pituitary adenomas. However, the mechanism by which this occurs remains unknown. AIP interacts with a number of interesting proteins, including members of the cAMP signalling pathway that has been shown to be consistently altered in pituitary tumours. The functional role of Aip was investigated using both over-expression and knock down of Aip in GH3 cells. cAMP signalling and its downstream effectors, including GH secretion, were then investigated. cAMP signalling was analysed using cAMP assays, cAMP-response element-promoter luciferase reporter assays, real-time PCR and finally secreted GH quantification. Over-expression of wild-type (WT)-Aip reduced forskolin-induced cAMP signalling at the total cAMP level, luciferase reporter activity and target gene expression, when compared with empty vector and the non-functional R304X mutant. Additionally, GH secretion was reduced in WT-Aip over-expressing GH3 cells treated with forskolin. Knock down of endogenous Aip resulted in increased cAMP signalling but a decrease in GH secretion was also noted. Inhibition of phosphodiesterase activity using general and selective inhibitors did not completely ablate the effect of Aip on forskolin-augmented cAMP signalling. A mechanism by which Aip acts as a tumour suppressor, by maintaining a low cAMP signalling and concentration, is suggested. Mutations of Aip render the protein incapable of such activity. This effect appears not to be mediated by the AIP-PDE interaction, suggesting the involvement of other interacting partners in mediating this outcome.

Paternally inherited gsα mutation impairs adipogenesis and potentiates a lean phenotype in vivo

Paternally inherited inactivating mutations of the GNAS gene have been associated with a rare and disabling genetic disorder, progressive osseous heteroplasia, in which heterotopic ossification occurs within extraskeletal soft tissues, such as skin, subcutaneous fat, and skeletal muscle. This ectopic bone formation is hypothesized to be caused by dysregulated mesenchymal progenitor cell differentiation that affects a bipotential osteogenic-adipogenic lineage cell fate switch. Interestingly, patients with paternally inherited inactivating mutations of GNAS are uniformly lean. Using a mouse model of Gsα-specific exon 1 disruption, we examined whether heterozygous inactivation of Gnas affects adipogenic differentiation of mesenchymal precursor cells from subcutaneous adipose tissues (fat pad). We found that paternally inherited Gsα inactivation (Gsα(+/p-) ) impairs adipogenic differentiation of adipose-derived stromal cells (ASCs). The Gsα(+/p-) mutation in ASCs also decreased expression of the adipogenic factors CCAAT-enhancer-binding protein (C/EBP)β, C/EBPα, peroxisome proliferator-activated receptor gamma, and adipocyte protein 2. Impaired adipocyte differentiation was rescued by an adenylyl cyclase activator, forskolin, and provided evidence that Gsα-cAMP signals are necessary in early stages of this process. Supporting a role for Gnas in adipogenesis in vivo, fat tissue weight and expression of adipogenic genes from multiple types of adipose tissues from Gsα(+/p-) mice were significantly decreased. Interestingly, the inhibition of adipogenesis by paternally inherited Gsα mutation also enhances expression of the osteogenic factors, msh homeobox 2, runt-related transcription factor 2, and osteocalcin. These data support the hypothesis that Gsα plays a critical role in regulating the balance between fat and bone determination in soft tissues, a finding that has important implications for a wide variety of disorders of osteogenesis and adipogenesis.

Different roles of GNAS and cAMP signaling during early and late stages of osteogenic differentiation

Progressive osseous heteroplasia (POH) and fibrous dysplasia (FD) are genetic diseases of bone formation at opposite ends of the osteogenic spectrum: imperfect osteogenesis of the skeleton occurs in FD, while heterotopic ossification in skin, subcutaneous fat, and skeletal muscle forms in POH. POH is caused by heterozygous inactivating germline mutations in GNAS, which encodes G-protein subunits regulating the cAMP pathway, while FD is caused by GNAS somatic activating mutations. We used pluripotent mouse ES cells to examine the effects of Gnas dysregulation on osteoblast differentiation. At the earliest stages of osteogenesis, Gnas transcripts Gsα, XLαs and 1A are expressed at low levels and cAMP levels are also low. Inhibition of cAMP signaling (as in POH) by 2',5'-dideoxyadenosine enhanced osteoblast differentiation while conversely, increased cAMP signaling (as in FD), induced by forskolin, inhibited osteoblast differentiation. Notably, increased cAMP was inhibitory for osteogenesis only at early stages after osteogenic induction. Expression of osteogenic and adipogenic markers showed that increased cAMP enhanced adipogenesis and impaired osteoblast differentiation even in the presence of osteogenic factors, supporting cAMP as a critical regulator of osteoblast and adipocyte lineage commitment. Furthermore, increased cAMP signaling decreased BMP pathway signaling, indicating that G protein-cAMP pathway activation (as in FD) inhibits osteoblast differentiation, at least in part by blocking the BMP-Smad pathway, and suggesting that GNAS inactivation as occurs in POH enhances osteoblast differentiation, at least in part by stimulating BMP signaling. These data support that differences in cAMP levels during early stages of cell differentiation regulate cell fate decisions. Supporting information available online at http:/www.thieme-connect.de/ejournals/toc/hmr.

Ascl1-induced neuronal differentiation of P19 cells requires expression of a specific inhibitor protein of cyclic AMP-dependent protein kinase

cAMP-dependent protein kinase (PKA) plays a critical role in nervous system development by modulating sonic hedgehog and bone morphogenetic protein signaling. In the current studies, P19 embryonic carcinoma cells were neuronally differentiated by expression of the proneural basic helix-loop-helix transcription factor Ascl1. After expression of Ascl1, but prior to expression of neuronal markers such as microtubule associated protein 2 and neuronal β-tubulin, P19 cells demonstrated a large, transient increase in both mRNA and protein for the endogenous protein kinase inhibitor (PKI)β. PKIβ-targeted shRNA constructs both reduced the levels of PKIβ expression and blocked the neuronal differentiation of P19 cells. This inhibition of differentiation was rescued by transfection of a shRNA-resistant expression vector for the PKIβ protein, and this rescue required the PKA-specific inhibitory sequence of the PKIβ protein. PKIβ played a very specific role in the Ascl1-mediated differentiation process as other PKI isoforms were unable to rescue the deficit conferred by shRNA-mediated knockdown of PKIβ. Our results define a novel requirement for PKIβ and its inhibition of PKA during neuronal differentiation of P19 cells.

Immune-regulatory transcriptional responses in multiple organs of Atlantic salmon after tributyltin exposure, alone or in combination with forskolin

Tributyltin (TBT) is a widespread marine pollutant that influences physiological conditions of fish and other aquatic organisms. In addition to effects on reproduction, the immune system has been proposed as a possible target for TBT effects. In the present study, the effects of TBT exposure were examined on the expression of genes involved in immune system compentence in liver and head kidney of Atlantic salmon, in the presence and absence of a second-messenger activator (forskolin). Juvenile salmon were force-fed a diet containing TBT (0-solvent control, 0.1, 1, or 10 mg/kg fish) for 72 h. Consequently, fish from the control group and 10-mg/kg TBT group were exposed to the adenylate cyclase (AC) activator forskolin (200 μg/L) for 2 or 4 h. Forskolin was selected for this study because it is known to exhibit potent immune system enhancement by activating macrophages and lymphocytes. After sacrifice, liver and head kidney were sampled and transcript changes for interleukin (IL)-1β, IL-10, transforming growth factor (TGF) β, interferon (INF) α, INFγ, tumor necrosis factor (TNF) α, Mx3, and insulin-like growth factor (IGF)-1 were determined in both tissues by quantitative polymerase chain reaction (qPCR) using gene-specific primers. TBT, when given alone and also in combination with forskolin, decreased IL-1β, TNFα, IFNγ, IFNα, Mx3, and IGF-1 gene expression. In contrast, IL-10 and TGFβ transcripts were increased after TBT exposure alone and also in combination with forskolin. Generally, these effects were largely dependent on TBT dose and time of exposure when given in combination with forskolin. Overall, our findings suggest a possible immunomodulatory effect of TBT, possibly involving cAMP activation.

Epinephrine accelerates osteoblastic differentiation by enhancing bone morphogenetic protein signaling through a cAMP/protein kinase A signaling pathway

Topical effects of a catecholamine on bone morphogenetic protein (BMP)-induced ectopic bone formation were investigated in both in vivo and in vitro experimental systems. Epinephrine enhanced bone induction by BMP-2. Thus, the mass of ossicles ectopically induced by BMP-2 (5 μg) was increased by the addition of a low dose (10, 20, 40, or 80 μg) of epinephrine into a biodegradable BMP-2 carrier, in a dose-dependent manner. To investigate the mechanism by which epinephrine enhances BMP activity, in vitro experiments were carried out using osteogenic cells. The expression level of alkaline phosphatase (ALP) in cells, a marker of osteoblastic differentiation, was consistently elevated by BMP-2 (50 ng/ml) and was further elevated by the addition of epinephrine (10(-8)M). The epinephrine-enhanced ALP elevation was specifically abolished by an antagonist to β2-adrenergic receptors (Butoxamine) and by a protein kinase A inhibitor (H89). Furthermore, BMP-induced mRNA expression of ALP and osteocalcin (marker proteins of osteoblastic differentiation) and of Osterix (a transcription factor essential for terminal differentiation to osteoblasts) in ST2 cells was significantly enhanced by the addition of epinephrine (10(-8)M). In luciferase expression assays using the promoter sequence of the Id1 gene (an immediate early response gene to BMP), luciferase activity was elevated by BMP-2 treatment (50 ng/ml) and this activity was further enhanced by the addition of epinephrine (10(-8)M). Epinephrine-enhanced luciferase activity was abolished by mutation of the cAMP-response element (CRE) sequence in the Id1 promoter, indicating that CRE-binding transcription proteins induced by epinephrine addition may act as enhancers of Smad-mediated BMP signaling.

Smad-dependent and smad-independent induction of id1 by prostacyclin analogues inhibits proliferation of pulmonary artery smooth muscle cells in vitro and in vivo

RATIONALE

Mutations in the bone morphogenetic protein type II receptor (BMPR-II) are responsible for the majority of cases of heritable pulmonary arterial hypertension (PAH). Mutations lead to reduced Smad1/5-driven expression of inhibitor of DNA binding protein 1 (Id1) and loss of the growth suppressive effects of BMPs. The impact of existing PAH therapies on BMP signaling is lacking.

OBJECTIVE

Because prostacyclin analogues are effective treatments for clinical PAH, we hypothesized that these agents enhance Smad1/Id1 signaling.

METHODS AND RESULTS

Iloprost alone induced Id1 expression in human pulmonary artery smooth muscle cells (PASMCs), an effect that was independent of Smad1/5 activation but dependent on a cAMP-responsive element in the Id1 promoter. In addition, iloprost and treprostinil enhanced BMP-induced phosphorylation of Smad1/5 and Id1 expression in a cAMP-dependent manner. The mechanism involved suppression of inhibitory Smad, Smad6. Furthermore, iloprost rescued the deficit in Smad1/5 phosphorylation and Id gene expression in PASMCs harboring mutations in BMPR-II and restored growth suppression to BMP4 in mutant PASMCs. We confirmed a critical role for Id1 in PASMC proliferation. Reduced expression of Id1 was observed in concentric intimal lesions of heritable PAH cases. In the monocrotaline rat model of PAH, associated with reduced BMPR-II expression, we confirmed that treprostinil inhibited smooth muscle cell proliferation and prevented progression of PAH while enhancing Smad1/5 phosphorylation and Id1 gene expression.

CONCLUSIONS

Prostacyclin analogues enhance Id1 expression in vitro and in vivo and restore deficient BMP signaling in BMPR-II mutant PASMCs.

Analysis of gene expression in PTHrP-/- mammary buds supports a role for BMP signaling and MMP2 in the initiation of ductal morphogenesis

Parathyroid hormone-related protein (PTHrP) acts on the mammary mesenchyme and is required for proper embryonic mammary development. In order to understand PTHrP's effects on mesenchymal cells, we profiled gene expression in WT and PTHrP(-/-) mammary buds, and in WT and K14-PTHrP ventral skin at E15.5. By cross-referencing the differences in gene expression between these groups, we identified 35 genes potentially regulated by PTHrP in the mammary mesenchyme, including 6 genes known to be involved in BMP signaling. One of these genes was MMP2. We demonstrated that PTHrP and BMP4 regulate MMP2 gene expression and MMP2 activity in mesenchymal cells. Using mammary bud cultures, we demonstrated that MMP2 acts downstream of PTHrP to stimulate ductal outgrowth. Future studies on the functional role of other genes on this list should expand our knowledge of how PTHrP signaling triggers the onset of ductal outgrowth from the embryonic mammary buds.

Successful spinal fusion by E. coli-derived BMP-2-adsorbed porous beta-TCP granules: a pilot study

Bone morphogenetic proteins (BMPs) were originally identified as osteoinductive proteins. With cloning of BMP genes, studies of BMPs and their clinical application have advanced. However, with increasing clinical applications, drug delivery systems and production costs have become more important issues. To address these issues, we asked whether E. coli-derived rhBMP-2 (E-BMP-2)-adsorbed porous beta-TCP granules could achieve posterolateral lumbar fusion in a rabbit model similar to autogenous bone grafts. Lumbar spinal fusion masses were evaluated by 3-D computed tomography, mechanical testing, and histological analyses 8 weeks after surgery. By these measures E-BMP-2-adsorbed beta-TCP granules achieved lumbar spinal fusion in dose-dependent fashion in a rabbit model as well as autogenous bone graft. Our preliminary findings suggest E-BMP-2-adsorbed porous beta-TCP could be a novel, effective alternative to autogenous bone grafting for generating new bone and promoting regenerative repair of bone, and potentially utilizable in the clinical setting for treating spinal disorders.

Parathyroid hormone enhances bone morphogenetic protein activity by increasing intracellular 3', 5'-cyclic adenosine monophosphate accumulation in osteoblastic MC3T3-E1 cells

Intermittent subcutaneous injections of parathyroid hormone (PTH) increase bone mass in a variety of animal models and humans. The anabolic actions of PTH on osteogenic cells are mainly mediated through the protein kinase A (PKA) signaling pathway via PTH receptor 1 (PTHR1). We have already reported 3', 5'-cyclic adenosine monophosphate (cAMP)/PKA-mediated enhancement of bone morphogenetic protein (BMP) signaling. Herein, we focused on the involvement of PTH in BMP signaling pathways in the MC3T3-E1 mouse osteoblastic cell line, to elucidate a potential mechanism of the anabolic actions of PTH on bone formation. Elevation of intracellular cAMP level in MC3T3-E1 cells by addition of PTH (10(-7) M) to culture media was transient without significant effect on biological actions of BMP. Cyclic addition of PTH (10 cyclic additions of 10(-8) M PTH at 3-min intervals) maintained a high intracellular cAMP level for about 2 h and mRNA expression and enzymatic activity of alkaline phosphatase (ALP) by BMP was enhanced by this addition. Relative luciferase expression assay in MC3T3-E1 cells using the Id1 promoter, an early response gene to BMPs, enhanced elevation of transcriptional activity in response to recombinant human BMP-2 by concomitant addition of PTH and BMP. Furthermore, cyclic PTH treatment significantly further suppressed BMP-induced inhibitory Smad6 expression. H89 (PKA inhibitor) almost completely abolished PTH actions on BMP signaling. IBMX (phosphodiesterase inhibitor) enhanced PTH actions. These results suggest that PTH enhances BMP signaling when PTH-induced intracellular cAMP level is maintained for a few hours, accelerating BMP actions to promote osteoblastic function and anabolic actions of new bone formation.