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Seminar 08-10-2008 - wnt signaling system
- 1. J. Coen NetelenbosJ. Coen Netelenbos 8 oktober 2008, IWO, Utrecht8 oktober 2008, IWO, Utrecht Wnt Signaling SystemWnt Signaling System *Wat moeten we weten?*Wat moeten we weten? *Nieuwe medicijnen tegen*Nieuwe medicijnen tegen OsteoporoseOsteoporose
- 2. Wnt signalingWnt signaling WWg (wingless)g (wingless) IntInt(egration)(egration) The Wnt Homepage: http://www.stanford.edu/~rnusse/wntwindow.html o.l.v. Roel Nusse de ontdekker 1982 en naamgever Wnt in 1992 The Wnt Homepage: http://www.stanford.edu/~rnusse/wntwindow.html o.l.v. Roel Nusse de ontdekker 1982 en naamgever Wnt in 1992
- 3. plasterk Nature 425, 633-637Nature 425, 633-637 (9 October 2003)(9 October 2003) The Wnt/ -catenin pathwayThe Wnt/ -catenin pathway regulates cardiac valveregulates cardiac valve formationformation Adam F. L. Hurlstone…….Adam F. L. Hurlstone……. RonaldRonald H. A. PlasterkH. A. Plasterk11 andand Hans CleversHans Clevers11 Wnt pathway componentsWnt pathway components `` Wnt &Wnt &
- 4. Wnt & heart diseaseWnt & heart disease • Wound healing response after myocardial infarction in ratsWound healing response after myocardial infarction in rats and mice (and mice (Cardiovascular Research 2002 55(1):16-24)Cardiovascular Research 2002 55(1):16-24) • Cardiac Hypertrophy and the Wnt PathwayCardiac Hypertrophy and the Wnt Pathway (Cingolani OH et al. (Hypertension.(Cingolani OH et al. (Hypertension. 2007;49:427.)2007;49:427.) .
- 5. Boyden LM et al. N Engl J Med 2002;346:1513-21Boyden LM et al. N Engl J Med 2002;346:1513-21 High bone density due to a gain-of-function mutationHigh bone density due to a gain-of-function mutation inin LDL-Receptor Related Protein 5 (LRP5)LDL-Receptor Related Protein 5 (LRP5) Wnt pathway speelt rolWnt pathway speelt rol bij stimulatie humanebij stimulatie humane osteoblasten met LRP5osteoblasten met LRP5 als co-receptor!als co-receptor!
- 6. Gong Y et al. Cell 2001;107:513-23Gong Y et al. Cell 2001;107:513-23 OsteoPorosis-PseudoGlioma syndrome (OPPG) due toOsteoPorosis-PseudoGlioma syndrome (OPPG) due to a loss-of-function mutation in LDL-Receptor Relateda loss-of-function mutation in LDL-Receptor Related Protein 5 (LRP5)Protein 5 (LRP5)
- 7. Wnt Signaling by Low-Density LipoproteinWnt Signaling by Low-Density Lipoprotein Receptor-Related Protein 5 (LRP5),Receptor-Related Protein 5 (LRP5), a coreceptor in Wnt signaling systema coreceptor in Wnt signaling system LRP5(-/-) KO muis:LRP5(-/-) KO muis: osteoporose enosteoporose en pseudoglioom (OPPG)pseudoglioom (OPPG) LRP5 gain of functionLRP5 gain of function muation: hoge bot massamuation: hoge bot massa
- 8. Central Role of Canonical Wnt SignalingCentral Role of Canonical Wnt Signaling Khosla S et al. JCI 2008;118:421-8
- 9. List target genes of Wnt/List target genes of Wnt/ßß-catenin signaling-catenin signaling sept 2008sept 2008
- 10. Regulation Canonical Wnt SignalingRegulation Canonical Wnt Signaling Piters E et al. Arch Biochem Biophysics 2008;473:112-6
- 11. Regulation Canonical Wnt Signaling (A)Regulation Canonical Wnt Signaling (A) Frizzeld baconFrizzeld bacon Low densityLow density lipoproteinlipoprotein Receptor-Receptor- Related ProteinRelated Protein =coreceptor=coreceptor CatenaCatena T-Cell-specificT-Cell-specific transcriptiontranscription FactorFactor •ProliferatieProliferatie •DifferentiatieDifferentiatie •ApoptosisApoptosis Dvl DishevelledDishevelled protein (Dvl)protein (Dvl) Osteoblasten
- 12. Regulation Canonical Wnt Signaling (A)Regulation Canonical Wnt Signaling (A) Dvl GlycogeenGlycogeen Synthetase KinaseSynthetase Kinase LithiumLithium && Small moleculesSmall molecules met zelfde effectmet zelfde effect op bot bij OVX-op bot bij OVX- rat als PTH!rat als PTH! •ProliferatieProliferatie •DifferentiatieDifferentiatie •ApoptosisApoptosis Osteoblasten
- 13. Regulation Canonical Wnt Signaling (B)Regulation Canonical Wnt Signaling (B) Piters E et al. Arch Biochem Biophysics 2008;473:112-6 DickkopfDickkopf (Dkk)(Dkk) Dkk-1 InhibitorDkk-1 Inhibitor (mAb) met(mAb) met zelfde effectzelfde effect op bot bij OVX-op bot bij OVX- muis als PTH!muis als PTH!
- 14. Regulation Canonical Wnt Signaling (B)Regulation Canonical Wnt Signaling (B) Piters E et al. Arch Biochem Biophysics 2008;473:112-6 DickkopfDickkopf (Dkk)(Dkk) KringleKringle containingcontaining transmembranetransmembrane protein;protein; KremenKremen (Krm)(Krm)
- 15. ** SFRP KO (-/-) muisSFRP KO (-/-) muis:: O-blast ontwikkeling en functieO-blast ontwikkeling en functie Apoptosis O-blast en O-cyteApoptosis O-blast en O-cyte ** rat met GIOP:rat met GIOP: SFRP-1 expressieSFRP-1 expressie Secreted Frizzled Related Protein-1 (sFRP-1) isSecreted Frizzled Related Protein-1 (sFRP-1) is inhibitor of Wnt andinhibitor of Wnt and Key Regulator Survival O-blast & O-cyteKey Regulator Survival O-blast & O-cyte
- 16. Sclerostin and Wnt SignalingSclerostin and Wnt Signaling Buchem diseaseBuchem disease && Sclerostosis metSclerostosis met mutaties SOST gene,mutaties SOST gene, waardoor tekort aanwaardoor tekort aan sclerostinsclerostin toename botvormingtoename botvorming First Case (1955)First Case (1955) Antilichamen tegenAntilichamen tegen Sclerostin (Scl-Ab)Sclerostin (Scl-Ab) Phase 1 studyPhase 1 study:: BMD , BFR , BRRBMD , BFR , BRR =
- 17. Weekly s.c. antibody to sclerostin elevates BMDWeekly s.c. antibody to sclerostin elevates BMD reversibly in OVX rats (1211 ASBMR 2008)reversibly in OVX rats (1211 ASBMR 2008) Ab-Scerostin
- 19. LRP5 in MechanotransductionLRP5 in Mechanotransduction Sawakami K et al. J Biol Chem 2006;281:23698-711Sawakami K et al. J Biol Chem 2006;281:23698-711
- 20. Anabolic effects PTHAnabolic effects PTH Khosla S et al. JCI 2008;118:421-8
- 21. PTHR1 Signaling in OsteocytesPTHR1 Signaling in Osteocytes O’Brien CA et al. Plos ONE 2008;3:e Bij LRP5-/- muisBij LRP5-/- muis geen effect vangeen effect van intermitt. PTH op HBMintermitt. PTH op HBM Bij LRP5-/- transgeneBij LRP5-/- transgene PTHR1 muis: geenPTHR1 muis: geen verhoogde BM maarverhoogde BM maar wel verhoogdewel verhoogde remodeling dus andereremodeling dus andere routeroute Bij PTHR1- (gain ofBij PTHR1- (gain of function) muis:function) muis: verhoogde botmassaverhoogde botmassa
- 22. Wnt signaling: eating bone or adding it!Wnt signaling: eating bone or adding it! Goldring SR et al. Nat Med 2007:13:133Goldring SR et al. Nat Med 2007:13:133
- 23. Wnt/Wnt/ß-catenin signaling systeem remt ontwikkelingß-catenin signaling systeem remt ontwikkeling van mesenchymale stamcel tot kraakbeen en vetcelvan mesenchymale stamcel tot kraakbeen en vetcel Baron R et al. Endocrinology 2008:148:2635-43Baron R et al. Endocrinology 2008:148:2635-43
- 24. PPARPPARγγ remt osteoblastgenesis &remt osteoblastgenesis & bevordert osteoclastgenesisbevordert osteoclastgenesis Takada I et al. IBMSBoneKEy 2008;5:258-61Takada I et al. IBMSBoneKEy 2008;5:258-61 ThiazolidinesThiazolidines Role for SPPARMS: good for bone and fat?
- 25. RANKL in osteoclastogenesis in InflammationRANKL in osteoclastogenesis in Inflammation Lorenzo J et al. Endocr Rev 2008;29:403-440Lorenzo J et al. Endocr Rev 2008;29:403-440 Wnt?
- 26. DKK-1 in Osteoarthritis (OA),Rheumatoid ArthritisDKK-1 in Osteoarthritis (OA),Rheumatoid Arthritis (RA) and Ankylosing Spondylitis (AS)(RA) and Ankylosing Spondylitis (AS) Diarra D et al. Nat.Med 2007;13:156 Dickkopf-1 is a master regulator of joint remodeling Effect anti-TNFEffect anti-TNF on DKK-1on DKK-1 Effect disease activityEffect disease activity on DKK-1on DKK-1 in RA and ASin RA and AS Synovial tissueSynovial tissue
- 27. RANKL & Wnt in Rheumatoid ArthritisRANKL & Wnt in Rheumatoid Arthritis Diarra D et al. Nat.Med 2007;13:156 Dickkopf-1 is a master regulator of joint remodeling normaal rheum.arthritis toepassen vantoepassen van anti-DKK-1:
- 28. Role DDK1 Osteolysis in MyelomaRole DDK1 Osteolysis in Myeloma Pinzone JJ et al. Blood 2008 sept on linePinzone JJ et al. Blood 2008 sept on line KAHLER:KAHLER: * Bortezomib* Bortezomib remt DDK-1remt DDK-1 * Antistoffen* Antistoffen tegen DDK1tegen DDK1 therapeutischtherapeutisch op bot- enop bot- en tumorlesietumorlesie •DenosumabDenosumab (Ab-RANKL)(Ab-RANKL) alleen effectiefalleen effectief op botlesiesop botlesies
- 29. Putative model involving Wnt/Putative model involving Wnt/ßcatenin in cancer cells;ßcatenin in cancer cells; Kremen as possible gatekeeperKremen as possible gatekeeper Nakamura T et al. J Cell Mol Med 2008;12:391-408Nakamura T et al. J Cell Mol Med 2008;12:391-408
- 30. Dank voor uw aandacht
- 32. Putative model involving Wnt/Putative model involving Wnt/ßcatenin in cancer cellsßcatenin in cancer cells Nakamura T et al. J Cell Mol Med 2008;12:391-408Nakamura T et al. J Cell Mol Med 2008;12:391-408
- 33. Wnt in Prostate CancerWnt in Prostate Cancer Hall CL et al. JCB 2006;97:661-72Hall CL et al. JCB 2006;97:661-72 • osteolytic phaseosteolytic phase: mediated by RANKL, PTHRP, and: mediated by RANKL, PTHRP, and DKK-1DKK-1 • transitional phasetransitional phase: expression Wnts and decrease: expression Wnts and decrease DKK-1DKK-1 • osteoblastic phaseosteoblastic phase: VEGF, endothelin-1: VEGF, endothelin-1
- 34. Dickkopf-1 [ DDK1]Dickkopf-1 [ DDK1] • Remmer van Wnt/catenin signaling systeemRemmer van Wnt/catenin signaling systeem (bindt aan LRPF5)(bindt aan LRPF5) • Ontwikkeling skeletOntwikkeling skelet • Homeostasis skeletHomeostasis skelet • Hematopoeitische stamcel ?Hematopoeitische stamcel ? • Osteolytische metastaseringOsteolytische metastasering • Betrokken bij - botverlies door oestrogeentekortBetrokken bij - botverlies door oestrogeentekort - GIOP- GIOP - erosieve artritis- erosieve artritis - teratogene effecten thalidomide- teratogene effecten thalidomide
- 35. Role DDK1 in boneRole DDK1 in bone Pinzone JJ et al. Blood 2008 sept on linePinzone JJ et al. Blood 2008 sept on line
- 36. 19 Human Wnt Genes19 Human Wnt Genes Link toLink to GeneGene cardscards SOURCESOURCE linklink HUGO linkHUGO link DiseaseDisease WNT1 WNT1 WNT1 WNT2 WNT2 WNT2 WNT2B/13 WNT2B WNT2B WNT3 WNT3 Tetra-Amelia (Niemann 2004) WNT3A WNT3A WNT4 WNT4 Mullerian-duct regression and virilization (Biason-Lauber 2004) SERKAL syndrome (Mandel, 2008) WNT5A WNT5A WNT5A WNT5B WNT5B Associated with Susceptibility to type 2 diabetes (Kanazawa 2004) WNT6 WNT6 WNT7A WNT7A WNT7A Fuhrmann syndrome WNT7B WNT7B WNT8A WNT8A WNT8B WNT8B WNT8B WNT9A (previously WNT14) WNT9A WNT9A WNT9B Previously WNT15) WNT9B WNT10A WNT10A Odonto-onycho-dermal dysplasia Adaimy , 2007 WNT10B WNT10B WNT10B Â Mutations in Obesity patients Christodoulides 2006 Split-Hand/Foot Malformation (Ugur 2008 ) WNT11 WNT11 WNT11 WNT16 WNT16
- 37. Human Diseases Caused by Abnormality Wnt SignalingHuman Diseases Caused by Abnormality Wnt Signaling Nakamura T et al. J Cell Mol Med 2008;12:391-408Nakamura T et al. J Cell Mol Med 2008;12:391-408
- 38. Different Wnt signaling PathwaysDifferent Wnt signaling Pathways
- 39. DDK1 & Wnt Signaling in MSC differentiationDDK1 & Wnt Signaling in MSC differentiation Pinzone JJ et al. Blood 2008 sept on linePinzone JJ et al. Blood 2008 sept on line
- 40. Biology of the Osteoclast in Bone MetabolismBiology of the Osteoclast in Bone Metabolism Deftos LJ. NEJM 2005;353:872-5Deftos LJ. NEJM 2005;353:872-5 DenosDenosuumab OdanaOdanacatib Freedom TrialFreedom Trial:: 3jaar bij 7868 PMP3jaar bij 7868 PMP osteopor. vrouwenosteopor. vrouwen •wervelFx 68%wervelFx 68% •heupFx 40%heupFx 40% •nonVertFX 20%nonVertFX 20%
- 41. Wnt & heart diseaseWnt & heart disease • Wound healing response after myocardial infarction in rats and miceWound healing response after myocardial infarction in rats and mice ((Cardiovascular Research 2002 55(1):16-24)Cardiovascular Research 2002 55(1):16-24) • Cardiac Hypertrophy and the Wnt/Frizzled PathwayCardiac Hypertrophy and the Wnt/Frizzled Pathway (Cingolani OH et al. (Hypertension. 2007;49:427.)(Cingolani OH et al. (Hypertension. 2007;49:427.) • LRP6 mutation in a family with early coronary disease and metabolicLRP6 mutation in a family with early coronary disease and metabolic risk factors.risk factors. (Ani A et al.(Ani A et al. Science. 2007 MarScience. 2007 Mar 2;315(5816):1278-82 )2;315(5816):1278-82 ) .
Notas do Editor
- opening
- C elegans, rondworm nematode
- Figure 1. Clinical and Radiographic Features of Affected Members of the Kindred. Photographs of an affected member at the ages of 12 years (Panel A) and 45 years (Panel B) show the development of the wide, deep mandible that was characteristic of all affected members of the kindred. A large, lobulated torus palatinus in an affected member (Panel C, arrow) was also characteristic of all affected kindred members. Characteristic radiographic findings included an abnormally thick mandibular ramus (arrow, Panel D); a markedly thickened cortex and narrowed medullary cavity (arrow) in the femur (Panel E), which was otherwise normal; and dense but otherwise normal- appearing vertebrae (Panel F).
- Figure 1. Clinical Features of the Osteoporosis- Pseudoglioma Syndrome (A) Lower extremity photograph of a 40-yearold female OPPG patient demonstrating angular deformity of the tibia and fibula, the consequence of multiple fractures occurring during childhood. (B) Lateral lumbar spine radiograph of a 10- year-old male OPPG patient demonstrating abnormal flattening and concavity of the lumbar vertebrae. Affected individuals have normal growth during the first few years of life, but can fall below the normal range for height because of long bone fractures and vertebral collapse. (C) Photograph of the right eye of a 3-monthold male with OPPG demonstrating leukocoria (a white mass behind the pupil resembling retinoblastoma but actually a retrolental membrane). This individual had persistence of the tunica vasculosa partially covering the anterior lens surface, and evaluation of the dense retrolental membrane revealed a vascular central stalk that extended from the optic nerve into the vitreous cavity. (D and E) Iliac crest bone biopsies (both at 40 magnification) from an unaffected 2.5-year-old child (control) and from a 2.5-year-old child with OPPG, respectively. The control biopsy is substantially thicker than the OPPG biopsy. Note that the bone volume in the control (D) allows for only one cortical surface and a substantial trabecular bone network to be contained within the microscopic field. In contrast, both the inner and outer cortices and very little trabecular bone are contained within the field of the OPPG patient (E).
- Figure 1. Prevention of Wnt Signaling by the Binding of Dickkopf (Dkk) Proteins to Low-Density Lipoprotein Receptor-Related Protein 5 (LRP5). In the absence of Dkk proteins, Wnt binding to its receptor and to its coreceptor, LRP5, activates intracellular signaling (Panel A). In the presence of Dkk proteins, the formation of an active signaling complex does not occur (Panel B).
- Figure 2 The central role of canonical Wnt signaling in regulating osteoblast lineage specification, expansion, and terminal differentiation. Osteoblasts are derived from multipotent mesodermal or neural crest progenitors. Activation of the canonical (ca) Wnt signaling pathway, manifest through β-catenin stabilization, prevents the formation of cartilage (chondrogenesis). Wnt10b prevents adipogenesis (40). The canonical Wnt signaling pathway promotes survival of all cells of the osteoblast lineage and induces the proliferation of preosteoblasts. +, canonical Wnt signaling promotes the process; – , canonical Wnt signaling inhibits the process; AP, alkaline phosphatase; Cola1, collagen a1; DMP1, dentin matrix protein 1; OCN, osteocalcin; Osx, osterix; PTHR, receptor for PTH
- Fig. 2. The canonical wnt/b-catenin signaling pathway and its extracellular regulation. (A) Extracellular binding of wnt to the Fz–LRP5/6 receptor complex causes intracellular accumulation of b-catenin that can induce the expression of target genes after translocation to the nucleus. (B) In the presence of Dkk and Krm a tertiary protein complex can be made with LRP5/6 for internalization thus inhibiting wnt signaling as b-catenin will no longer be stabilized but will be phosphorylated and subsequently degraded. (C) The extracellular sclerostin prevents by binding to LRP5/6–Fz further signaling.
- Canonical wnt signaling can be regulated extracellularly, at the cell membrane, in the cytosol as well as in the nucleus. As shown in Fig. 2A, canonical wnt signaling is induced by binding of a wnt molecule to its receptor complex. This complex is composed of a member of the Fz receptor family, seven-transmembrane serpentine receptors, as well as a coreceptor either the LDL receptor related protein-5 (LRP5) or LRP6 [12–15]. Frizzled is a family of G protein-coupled receptor proteins [1] that serve as receptors in the Wnt signaling pathway and other signaling pathways. When activated, Frizzled leads to activation of Dishevelled in the cytosol. Frizzled proteins and the genes that encode them have been identified in an array of animals, from sponges to humans. Frizzled proteins also play key roles in governing cell polarity, embryonic development, formation of neural synapses , cell proliferation, and many other processes in developing and adult organisms. [2] Mutations in the human frizzled-4 receptor have been linked to familial exudative vitreoretinopathy, a rare disease affecting the retina at the back of the eye, and the vitreous, the clear fluid inside the eye.
- Canonical wnt signaling can be regulated extracellularly, at the cell membrane, in the cytosol as well as in the nucleus. As shown in Fig. 2A, canonical wnt signaling is induced by binding of a wnt molecule to its receptor complex. This complex is composed of a member of the Fz receptor family, seven-transmembrane serpentine receptors, as well as a coreceptor either the LDL receptor related protein-5 (LRP5) or LRP6 [12–15]. Frizzled is a family of G protein-coupled receptor proteins[1] that serve as receptors in the Wnt signaling pathway and other signaling pathways. When activated, Frizzled leads to activation of Dishevelled in the cytosol. Frizzled proteins and the genes that encode them have been identified in an array of animals, from sponges to humans. Frizzled proteins also play key roles in governing cell polarity, embryonic development, formation of neural synapses, cell proliferation, and many other processes in developing and adult organisms.[2] Mutations in the human frizzled-4 receptor have been linked to familial exudative vitreoretinopathy, a rare disease affecting the retina at the back of the eye, and the vitreous, the clear fluid inside the eye.
- One important mechanism of regulation involves Dickkopf (DKK) proteins that are secreted regulators which can bind to the coreceptor LRP5/6 preventing the formation of the LRP–Fz–wnt complex and thus inhibiting the induction of wnt signaling. Furthermore, in the presence of kremen1 or kremen2 (krm1/2), two-transmembrane proteins, a tertiary complex between krm, DKK and LRP5/6 can be formed which can be internalized reducing the availability of this coreceptor for its wnt-ligands (Fig. 2B) [16,17]. Alternative extracellular mechanisms to inhibit wnt signaling involve members of the secreted frizzled-related proteins (sFRPs) which have domains that can bind to wnts and thus prevent the binding of the latter to their receptor complex [18]. In a similar way wnt inhibitory factor-1 (Wif-1) can bind to wnts resulting in suppression of wnt signaling [18,19].
- One important mechanism of regulation involves Dickkopf (DKK) proteins that are secreted regulators which can bind to the coreceptor LRP5/6 preventing the formation of the LRP–Fz–wnt complex and thus inhibiting the induction of wnt signaling. Furthermore, in the presence of kremen1 or kremen2 (krm1/2), two-transmembrane proteins, a tertiary complex between krm, DKK and LRP5/6 can be formed which can be internalized reducing the availability of this coreceptor for its wnt-ligands (Fig. 2B) [16,17]. Alternative extracellular mechanisms to inhibit wnt signaling involve members of the secreted frizzled-related proteins (sFRPs) which have domains that can bind to wnts and thus prevent the binding of the latter to their receptor complex [18]. In a similar way wnt inhibitory factor-1 (Wif-1) can bind to wnts resulting in suppression of wnt signaling [18,19].
- One important mechanism of regulation involves Dickkopf (DKK) proteins that are secreted regulators which can bind to the coreceptor LRP5/6 preventing the formation of the LRP–Fz–wnt complex and thus inhibiting the induction of wnt signaling. Furthermore, in the presence of kremen1 or kremen2 (krm1/2), two-transmembrane proteins, a tertiary complex between krm, DKK and LRP5/6 can be formed which can be internalized reducing the availability of this coreceptor for its wnt-ligands (Fig. 2B) [16,17]. Alternative extracellular mechanisms to inhibit wnt signaling involve members of the secreted frizzled-related proteins (sFRPs) which have domains that can bind to wnts and thus prevent the binding of the latter to their receptor complex [18]. In a similar way wnt inhibitory factor-1 (Wif-1) can bind to wnts resulting in suppression of wnt signaling [18,19].
- Recently, the two members of a gene family (SOST, encoding sclerostin, and WISE) are added to this list of extracellular wnt antagonists. As shown in Fig. 2C and discussed below, they are capable of binding to LRP5/6 and in this way modulating wnt signaling [20–23].
- Recently, the two members of a gene family (SOST, encoding sclerostin, and WISE) are added to this list of extracellular wnt antagonists. As shown in Fig. 2C and discussed below, they are capable of binding to LRP5/6 and in this way modulating wnt signaling [20–23].
- FIGURE 3. Lrp5/ mice have impaired osteogenic responses to mechanical loading. A , diagram of the noninvasive mouse ulna loading model, which applies cyclic compression to the forearm to produce mediolateral bending (due to natural curvature of the ulna) to mechanically stimulate ulnar bone tissue in adult mice in vivo . Midshaft ulnar tissue sections from control and loaded forearms among male Lrp5/ and Lrp5/ mice given fluorochrome injections after loading show a robust bone formation response on the medial ( inset ) and lateral surfaces of the loaded Lrp5/ ulna, yet almost no response can be observed in the loaded Lrp5/ ulna.
- Figure 4 Potential cellular targets for the anabolic effects of PTH. PTH targets multiple cell types to mediate its bone anabolic effects. Specifically, PTH decreases apoptosis and proliferation of osteoblasts (OBs), as well as increasing their differentiation. It can activate bone-lining cells into functioning osteoblasts and decrease sclerostin production by osteocytes, which would be expected to increase Wnt signaling to osteoblasts. Finally, PTH is postulated to stimulate factors produced by osteoclasts (OCs) that stimulate osteoblasts.
- Figure 7. PTHR1 Signaling in Osteocytes Leads to Increased Bone Mass and Remodeling via Distinct Mechanisms. In the proposed model, PTHR1 signaling in osteocytes activates at least two distinct pathways: one leading to increased bone mass and the other leading to increased bone remodeling. Suppression of Sost/sclerostin and activation of LRP5 signaling increase osteoblast numbers and are required for the increase in bone mass. The elevation of bone resorption is independent of the Sclerostin/LRP5 pathway. The question mark indicates uncertainty of the cellular source of RANKL and M-CSF (osteocytes versus stromal/osteoblastic cells). doi:10.1371/journal.pone.0002942.g007 PTHR1 Signaling in Osteocytes PLoS
- Figure 1 Bifunctional role of the Wnt signaling pathway in regulation of osteoblast (bone-forming cell) and osteoclast (bone-resorbing cell) differentiation. Wnt signaling diverts the mesenchymal stem cells down the pathway of osteoblast differentiation. DKK-1 binds to the Wnt receptor complex on the surface of the osteoblast lineage cell and blocks Wnt signaling, arresting osteoblast proliferation and differentiation. The precursors of the mature osteoblast enhance bone resorption by boosting RANKLinduced osteoclastogenesis. Blockade of DKK-1 permits progression of osteoblast differentiation. Activation of the Wnt signaling pathway in the mature osteoblast upregulates OPG, which blocks RANKL-induced osteoclastogenesis, resulting in inhibition of bone resorption.
- FIG. 2. Role of Wnt/-catenin signaling in determining the cell fate from mesenchymal progenitor cells. Wnt signaling plays a dual role in regulating chrondrocytic differentiation. The Wnt canonical pathway represses chondrocyte differentiation from progenitor cells, whereas it is required for chondrocyte hypertrophy. Wnt pathway activation also inhibits adipocyte differentiation and promotes osteoblast cell lineages by controlling proliferation, maturation, and terminal differentiation. Differentiated osteoblasts or osteocytes produce Wnt inhibitors such asDkk1 and sclerostin as a negative feedback control of osteoblast differentiation and/or function. Committed osteoblasts produce OPG to increase the OPG/RANKL ratio, thus decreasing osteoclast differentiation and activation
- Fig. 1. PPAR-γ function in osteoclastogenesis and osteoblastogenesis. PPAR-γ inhibits osteoblastogenesis and promotes osteoclastogenesis. Cytokines such as IL-1, TNF-α and Wnt signals (Wnt-5a, Wnt-10b) suppress the transactivation function of PPAR-γ.
- FIG. 3. Regulation of osteoclastogenesis in inflammation. In inflammatory states such as inflammatory arthritis, local production of proinflammatory cytokines (IL-1, IL-6, and TNF) as well as RANKL by inflamed tissues such as the synovium leads to stimulation of osteoclastogenesis and bone destruction. In addition, IL-17-producing TH17 T lymphocytes stimulate local production of RANKL by inflamed tissues and produce RANKL themselves, which enhances resorptive destruction of bone at sites adjacent to the inflammation.
- ( a ) In a physiological state, cortical bone formation and resorption next to joints are in balance. ( b ) Inflammatory arthritis such as rheumatoid arthritis leads to an imbalance between bone formation and resorption. Bone formation is hampered by TNF-mediated expression of DKK-1, which suppresses Wnt signals, whereas bone resorption is enhanced by expression of RANKL. ( c ) Blockade of DKK-1 met anti DKK-1 relieves Wnt signaling from DKK-1–mediated suppression and induces bone formation mirrored by the growth of osteophytes. Moreover, Wnt proteins induce OPG expression, which blocks RANKL-mediated bone resorption.
- Figure 4. Metastatic cancer cells that secrete elevated levels of DKK1 disrupt the balance of osteoblastogenesis and osteoclastogenesis in favor of an osteolytic microenvironment that is conducive to tumor growth. MM has a unique and absolute requirement for the bone marrow microenvironment for its growth and survival and MM plasma cells may cultivate this ‘soil’ by synthesizing and secreting DKK1. The primary effect of DKK1 appears to be the disruption the differention of mesenchymal stem cells (MSC) in the osteoblasts (OB). RANK signaling regulates osteoclast development and Wnt signaling in MSC/OB differentially regulates RANK ligand (RANKL) and OPG, a RANKL decoy, which together modulate osteoclast development. DKK1 suppression of Wnt in MSC/OB leads to increased production of RANKL and IL-6 and decreased production of OPG. The shift in RANKL/OPG ratios leads to increased osteoclastogenesis and IL-6 is a potent survival factor MM cells. The subsequent loss of osteoblasts and increase in osteclasts causes lytic bone destruction, hyercalcemia, and loss of normal bone marrow function. A vicious cycle of bone destruction and tumor growth ensues. The absence of DKK1 in a subset of MM suggests that other soluble factors produced by MM cells may contribute to this process. These include MIP1a, sFRP-2, IL-3, RANKL and possibly sFRP-3. (see text for more details).
- Figure 3. DKK1 is both anabolic and anti-catabolic in bone. TNFα enhances DKK1 secretion which inhibits MSC-derived osteoblastogenesis and lowers osteoprotegrin (OPG) levels, resulting in reduced bone accretion. In addition, DKK1 enhances receptor activator of NF-kappa B ligand (RANKL) levels, and the increased RANKL:OPG ratio activates osteoclast activity, leading to bone resorption.
- Fig. 1. Overview of the different wnt signaling pathways. Binding of wnts to their receptor or receptor complex can result in two non-canonical pathways (Ca2+-dependent or the planar cell polarity (PCP) pathway) or the canonical pathway. The canonical or wnt/b-catenin pathway involves the induction of a cascade that results in the translocation of b-catenin to the nucleus where association with the lymphoid-enhancer binding factor (Lef)/T-cell specific transcription factors (Tcf’s) results in the expression of target genes (Fig. 1) [4,5], [http://www.stanford.edu/rnusse/wntwindow.html]. For intracellular accumulation and consecutive translocation to the nucleus, b-catenin needs to be hypophosphorylated. Glycogen synthase kinase 3 (GSK3) is, after complexation with Axin and adenomatous polyposis coli (APC), capable of phosphorylating b-catenin thus labeling it for proteasomal degradation (Fig. 1). However, binding of the wnt-ligand to one of the Frizzled (Fz) receptors results, through the protein Disheveled (Dvl), in inactivation of GSK3 and therefore prevents phosphorylation and consecutive degradation of b-catenin (For review see [4]). An alternative wnt pathway is calcium dependent and plays important roles during dorso-ventral patterning of the embryo, regulating cell migration, as well as heart development, and might play a role during tumor suppression. This wnt/calcium pathway relies on an intracellular release of Ca2+ to activate calcium sensitive enzymes like Ca2+-calmodulin dependent kinase II (CamKII), protein kinase C (PKC) or calcineurin (CaCN). TAK-1 (TGF-b activated kinase-1)/NLK (nemo-like kinase) was identified as a downstream target of CamKII for ventral development. Among the target proteins regulated by CaCN is the transcription factor Elk-1 and NF-AT (nuclear factor of activated T-cells). After activation, NF-AT enters the nucleus to regulate target gene expression [6]. Finally the planar cell polarity (PCP) pathway is also Dvl-dependent and results in coactivation of Rho and Rac, two small GTPases that are able to regulate cytoskeletal architecture. Wnt/Fz activation of Rac is independent of Rho and mediates activation of cjun NH2-terminal kinase (JNK) [7,8]. The JNK pathway is known to be required for embryonic morphogenesis and contributes to the regulation of cell proliferation and apoptosis. JNK also contributes to the functioning of some differentiated cells [9].
- Figure 2. A prevailing model of the role of DKK1 and Wnt signaling in mesenchymal stem cell differentiation. Wnt3a, 5a, 7b and 10b, and Indian hedgehog (Ihh) cooperatively promote osteoblast differentiation, whereas DKK1 inhibits osteoblastogenesis and shifts the use only. From www.bloodjournal.org at VRIJE UNIVERSITEIT Medical Library 34942 on September 24, 2008. For personal 21 developmental program toward adipogenesis. Wnt-5A also inhibits adipogenesis by suppressing of PPAR-γactivation. β-catenin/TCF1 promotes early osteoblast lineage commitment through induction of the master bone development transcription factor Runt-related Transcription Factor 2/Runx2. Runx2 then promotes transcriptional activation of a second master bone development transcription factor Osterix (Osx), which utilizes DKK1 to repress Runx2 expression to further promote osteoblast progenitor maturation. Finally, phenotypic lineage-specific markers for osteoblast maturation are illustrated.