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1 REVIEW ARTICLE Vol. 19, No. 1, 2012 LRP5 와골량획득의새로운지평 경북대학교의학전문대학원생화학 - 세포생물학교실 최제용 * = Abstract = New Avenues in the LRP5-mediated Bone Mass Acquisition Je-Yong Choi * Department of Biochemistry and Cell Biology, Skeletal Diseases Genome Research Center, School of Medicine, Kyungpook National University, Daegu, Korea Lipoprotein receptor-related protein (LRP5) signaling is well correlated with the bone mass in both human and mice. Loss-of-function mutations of LRP5 result in osteopenia or osteoporosis. In contrast, gain-of-function mutations show high bone mass phenotype. To elucidate the molecular mechanism of the LRP5-mediated bone mass acquisition, several groups have genetically dissected the Wingless and Int-1 (Wnt) -catenin signaling pathway using osteoblast-lineage specific Cre mice. Key players for LRP5-mediated bone mass acquisition turn out to be different molecules with respect to the expressing tissue and action mode of these molecules. One is serotonin, a tryptophan metabolite that originates from duodenum, which acts as a negative regulator for bone formation. LRP5 suppresses serotonin biosynthesis by inhibiting the expression of tryptophan hydroxylase 1 in the gut. The other is sclerostin, an osteocyteproducing antagonist for LRP5 signaling. Here is a summary of recent findings about these two molecules, providing a chance to speculate new avenues in the LRP5-mediated bone mass acquisition. [Korean Journal of Bone Metabolism, 19(1): 1-9, 2012] Key Words: Bone mass, LRP5, Sclerostin, Serotonin, Wnt signaling 서론골량이부족하여골절이잘생기는골다공증은일반적으로여성호르몬부족으로발생한다. 성인의골량은골흡수와골형성이잘균형을이루어골재형성이유지되는데, 여러가지원인으로여성호르몬이부족하게되면파골세포의골 흡수에대한뼈모세포의골형성이부족하여골량이감소하게된다. 1 포유류는골재형성을조화롭게조절하여골량을유지하는데, 이조절에는특정유전자들이관여하고있으며, 이들중암과같은특별한질병을야기시키지않고뼈강도만올릴수있는유전자는골다공증치료제개발에이상적인타깃이될수있다. 지금까지밝혀진유전자가운데이상적 Received: May 1, 2012, Revised: May 2, 2012, Accepted: May 4, 2012 * Address for Correspondence: Je-Yong Choi, Department of Biochemistry and Cell Biology, Skeletal Diseases Genome Research Center, School of Medicine, Kyungpook National University, Daegu , Korea. Tel: , Fax: , jechoi@knu.ac.kr ** This study was supported by a grant of the Korea Health Technology R&D Project, Ministry of Health & Welfare, Republic of Korea (A010252) and WCU program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (R ). CC This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( 1

2 β-catenin β-catenin Fig. 1. Lipoprotein receptor-related protein 5 (LRP5) and Wingless and Int-1 (Wnt) signaling pathway. Wnt signaling pathway consists of -catenin-dependent canonical and noncanonical pathways (not shown). Binding of Wnt to its receptor (Fz) and coreceptor (LRP) allows recruiting of Dishevelled (DV) and Axin (AX) to Fz and LRP5/6/4, respectively, and results in stabilization of -catenin. Extracellular portion of LRP5/6 can bind to various proteins like Sclerostin (Sost), Wise, R-spondin (Rspo) and Dickkopf (Dkk). Complex formation of Dkk with Kremen and LRP5/6 allow to internalization of complex into cells. 이라여겨지는것중하나는 Wingless and Int-1 (Wnt) 신호계의공동수용체인 lipoprotein receptor-related protein (LRP)5이다. LRP5는기능이증가되면높은골량을나타내고, 기능이소실되면낮은골량을보여골감소증이나골다공증이된다. 2 LRP5 유전자에나타나는돌연변이의위치에따라골량이현저히차이나는점은매우흥미로운현상이다. LRP5와골량의상관관계기전을자세히규명하면새로운골량조절방식을알고또골다공증을치료할수있는신약개발에좋은목표가될수있을것이다. 여기서는 LRP5 신호가골량조절과어떤연관성이있는지그동안의연구를요약해보고자한다. Wnt/Frizzled (Fz)/LRP5 신호계 2000년이후골생물학분야의커다란발전중하나는 bone morphogenetic protein (BMP) 신호못지않게 Wnt 신호계가뼈형성에중요하다는사실을규명한점이다. 현재까지 Wnt 신호계는 19가지리간드가있고, 11개의 Fz 수용체와 LRP4/5/6 공동수용체로구성되어있다 (Fig. 1). 3,4 많 은 Wnt 신호는 Fz와 LRP4/5/6 공동수용체를활성화시켜 β-catenin의안정화를유도하는 Wnt/β-catenin 신호또는 canonical Wnt 신호경로를통하여일어난다. 그러나일부 Wnt는다른수용체와결합하여신호를전달하는데이를 noncanonical Wnt 신호경로라한다. 예로서 Wnt5a가 receptor tyrosine kinase-like orphan receptor (Ror)2 수용체및 Fz와함께결합하여오히려 Wnt/β-catenin 신호를억제하기도한다. 5 LRP5는 Wnt 뿐아니라다른여러단백질과결합하여 Wnt 신호를조절하는데, 골량과밀접한관계가있는결합단백질로 Sclerostin (SOST) 과 Dickkopf (Dkk)1 등이잘알려져있다. 3 여기서는 Wnt 리간드나 Fz 그리고 noncanonical Wnt 신호계수용체등은제외하고 LRP5를중심으로살펴보고자한다. LRP5는염색체 11번에위치하고, 1,615개아미노산으로구성된단백질로대부분세포외부위, 하나의막통과부위, 그리고세포내부위로구성된 low density lipoprotein receptor (LDLR) 패밀리의한군에속한다 (Fig. 2). 세포외부위는 4개의베타프로펠러와 epidermal growth factor (EGF)-like repeat가존재한다. 6 LRP5의세포질부위는 207개의아미노산으로구성되어있고독특한모티프는 Pro-Pro- 2

3 A B C Fig. 2. Comparision of Lipoprotein receptor-related protein (LRP)4/5/6 amino acid sequences. LRP5 has a putative transmembrane sequence as signal peptide by search program (see in the text), which was not revealed in LRP4 and LRP6 (A). LRP5/6/4 show similar structure with 4 propellers in extracellular portion (B). Analyses of amino acid sequences of LRP5/6/4 show a high identity and similarity between LRP5 and LRP6 (C). LRP5, LRP6 and LRP4 belong to low density lipoprotein receptor (LDLR). Although LRP5/6/4 show similar structure and function, knockout of each gene reveals different phenotypes, which indicates that there is no compensatory function among them. Pro-Ser/Thr-Pro (PPPS/TP) 로 Wnt나 parathyroid hormone (PTH) 같은외부자극에의하여인산화된다. Canonical Wnt 신호계를 Wnt3a로자극하면 PPPS/TP 부위가인산화되고 Axin이결합하여 ras-related C3 botulinum toxin substrate (Rac)1, c-jun N-terminal kinase (JNK)2 등을통해그다음일련의과정들이일어나결국 β-catenin이파괴되지않고핵으로들어가잘작용하도록한다. 7,8 반면에 Wnt5a로 noncanonical Wnt 신호를자극하면 LRP5는관여하지않고 Ror2나 Fz 자체가 G-protein을경유해서활성화된다. 최근 Wnt5a로자극하면간엽줄기세포가뼈모세포로잘전환되는데, 이것은 peroxisome proliferator-activated receptor-γ (PPAR-γ) 의발현이억제되어일어난다. 9 또한동물모델에서뼈모세포에서발현되는 Wnt5a가파골전구세포의 Ror2에작용하면파골세포분화증가로골량이감소된다. 10 LRP5의세포외부위에는여러가지단백질들이결합할수있다. 먼저 Dkk로척추동물에서 4종류가있고그중 3가지 (Dkk1, 2, 4) 만 LRP5에결합하는것으로알려져있다. 11 Dkk는 β-프로펠러모티프에결합하여 Wnt 리간드가붙지못하게방해하거나 Dkks, LRP5, Kremens 등이복합체를이루어쉽게세포내로들어가세포막에존재하는 LRP5 의수를감소시켜 Wnt 신호전달을방해하기도한다. 11 다른결합단백질로는분비단백질인 R-spondin, Wise, (SOST) 등이있다. 아직각각에대하여정확한작용기전은잘알려져있지않지만, 그중에서도 SOST이가장활발히연구되고있다. LRP5의돌연변이와골량 LRP5가뼈분야에서지대한관심을받게된것은 Osteoporosis-pseudoglioma (OPPG) syndrome의원인유전자이기때문인데, OPPG는근육이급격히줄고, 점차실명되며, 뼈도잘부러지는질환이다. 12 OPPG는 LRP5가기능이 3

4 소실되어일어나는현상으로상염색체열성으로유전되고이종접합 (heterozygous) 인경우에도골절에취약하다. 12 반대로높은골량을보이는경우는상염색체우성으로같은 LRP5 유전자이지만돌연변이위치만다른곳이다 즉, LRP5에일어나는돌연변이위치에따라골량이반대로나타나는데 LRP5 기능이높아지면골량증가, 낮아지면골량감소를보인다. 이것은 LRP5의기능조절을통하여뼈의골량을제어할수있다는점을시사한다. 또다른중요한점은 LRP5가비교적널리발현되는유전자임에도불구하고기능 -증가돌연변이는골조직에골량을증가시키는것외엔별다른증상이없다. Wnt 신호가증가하면암이생긴다는것은비교적잘규명된상황인데도 LRP5 돌연변이에서는암이보고되지않았다. 16 이런사실들은 LRP5 신호를적절히조절한다면새로운골량제어기전을이해하게되고, 좋은골다공증치료제개발도가능할수있음을시사한다. β-catenin 을통한 canonical Wnt pathway 와골량과의관계 LRP5의기능-증가돌연변이로높은골량을보였다면 canonical Wnt 신호계가관여되었을것이고, 이 canonical Wnt 신호계가실제골량조절과어떻게연관되는지먼저잘살펴볼필요가있다. Canonical Wnt 신호전달계에서리간드, 수용체, 공동수용체의유전자들이많아분석하기가쉽지않다. 하지만확실하게관여여부를알수있는방법은단일유전자로존재하는 β-catenin이골량조절에어떻게작용하는지판정하는것이다. 먼저 canonical Wnt 신호가뼈발생초기에어떤작용이있는지알아보기위하여초기미분화간엽전구세포 (mesenchymal progenitor cells) 에서발현이강한 Prx1-Cre 나 Dermo-Cre 또는연골세포에특이적인 α1(ii) collagen-cre로 β-catenin을제거하여확인한결과 β-catenin은간엽전구세포에서뼈모세포로전환되기위해서는필수적으로존재해야하는것으로밝혀졌다 β-catenin이없으면간엽세포로부터뼈모세포가생기지않고모두연골세포로존재하게된다. 반대로 β-catenin을증가시키면빨리뼈가생성되어오히려생쥐가죽게된다. 17,20,21 이는간엽전구세포에서뼈모세포가되기위해서는 β-catenin을통한적절한 canonical Wnt 신호가있어야한다는것을의미한다. 그러나 β-catenin의활성을 2.3 kb 1(I) collagen-cre 생쥐를이용하여뼈모세포에서높이면뼈는높은골량을보이고 치아는붕출이되지않는다. 이것은뼈모세포에서발현되는 Osteoprotegerin (OPG) 이증가되어파골세포수와기능이감소되어나타난결과이다. 20 반대로 β-catenin을뼈모세포특이적으로제거하면낮은골량을보이는데, 이는뼈모세포의수와기능에는차이없으나 OPG가감소되어파골세포의수와기능이증가했기때문이다. 20 좀더성숙한뼈모세포와초기뼈세포에발현되는 Osteocalcin-Cre (OC-Cre) 로 β-catenin 을제거하면쥐가 5주에죽고해면골과막골모두에서골량이감소된다. 22 또한성숙뼈모세포에서제거했을때와비슷하게파골세포수가증가된다. 뼈세포에서 β-catenin을 Dmp1-Cre로제거하면마찬가지로일찍죽고골량도적어진다. 23 즉, canonical Wnt 신호는간엽줄기세포로부터초기뼈모세포분화에중요하고, 뼈모세포의수나기능에는큰영향없이, 성숙뼈모세포가 OPG 생성조절을통하여파골세포의수와기능을조절한다. 최근 noncanonical Wnt 신호계에서도흥미로운점은뼈모세포에서발현되는 Wnt5a가파골전구세포의 Ror2와작용하여 RANK 발현이증가되고파골세포분화가촉진된다는것이다. 10 LRP5 knockout (KO) 된생쥐는 OPPG 증상처럼골량이감소된다. 24,25 LRP5KO 생쥐의골량감소는뼈모세포의사멸이나파골세포에는관련없이뼈모세포의증식과골형성속도가감소되어일어난현상이다. 24 또한흥미롭게도 LRP5 가없어도 Wnt와 lymphoid enhancer factor (Lef)1 매개신호는여전히일부존재하는것으로알려져있다. 아마뼈모세포에 LRP4나 LRP6가존재하기때문일것이다. 최근 LRP4 의 hypomorphic한경우나 LRP6 KO heterozygous 생쥐를조사한결과모두골량이감소되었다. 26,27 그러나 LRP4, LRP5, LRP6 KO 결과가모두다르고서로보완되지않는점은흥미로운사실이다. 이부분에대해서는더많은연구가진행되어야할것이다. 종합하면 canonical pathway를담당하는 β-catenin을뼈모세포계에제거하면주로 OPG 발현의감소로파골세포수와기능이강화되어골흡수가진행되고 LRP5 공동수용체를제거하거나기능을변화시키면주로뼈모세포의수나기능에영향을미친다. 즉, LRP5와 β-catenin은같은 canonical Wnt 신호전달계를담당하지만실제골조직에서작용하는기전은다르게나타나좀더다양한시각에서골량조절기전을살펴봐야된다는사실을암시한다. 4

5 LRP5 높은골량돌연변이와 Serotonin 연관성뼈모세포및뼈세포특이적으로제거한 β-catenin의결과와 LRP5KO, Dermo-Cre, 또는 2.3 kb α1(i) collagen-cre로제거한결과가다르기때문에 Karsenty 그룹은 LRP5의기능-증가돌연변이에의한골량증가는 Wnt가리간드인전형적인 Wnt/β-catenin 신호전달계가아닌새로운 LRP5 리간드가있을것으로추정하였다. 28 이그룹은다음과같은이유를들어 LRP5가단순히 canonical Wnt 신호계로골량을조절하는것이아니라고주장한다. 29 1) LRP5는매우복잡한단백질로여러가지리간드가있을가능성이있다. 2) LRP5KO 생쥐나 OPPG 또는 LRP5 골량증가돌연변이환자에는태어난후뼈패턴의이상은없다. 이것은모든 Wnt 신호계관련유전자들이발생기에중요한역할이있다는기존결과와상반된다. 3) LRP5의기능-증가돌연변이환자에서암이발생되지않았는데, Wnt 신호계가증가되면암이잘생긴다는사실과상반된다. 4) 뼈모세포에서 β-catenin으로 canonical Wnt 신호전달을제거하면태어난후뼈형성에는문제없고뼈모세포에의존하여뼈흡수가증가될뿐이다. LRP5KO 쥐는 OPPG 환자처럼골량이감소되는데, 세포증식관련유전자들 (Cyclin D1, D2, E1) 이감소된다. 뼈모세포분화에관련된전사인자들 (runt-related transcription factor [RUNX]2, osterix [OSX], activating transcription factor [ATF]4) 과파골세포분화에중요한 OPG, receptor activator of NF-κB ligand (RANKL) 발현에는변화가없다. 흥미로운것은 LRP5KO 유래뼈모세포가 in vivo에서는그수가감소되었지만 in vitro에서는정상군과차이가없어뼈모세포자체의문제라기보다뼈모세포외다른세포에의해뼈형성이조절된다는점이다. 심지어 Dermo1-Cre로 LRP5를제거해도뼈모세포의수, 뼈형성속도, 골량에는큰차이가없다. 30 따라서 LRP5 기능-증가돌연변이에서보이는골량증가는 Wnt 신호계가아닐가능성이높고또한뼈모세포외다른세포에의하여일어난현상이라고할수있다. LRP5와 Serotonin의연결고리는 LRP5KO 생쥐유래뼈의 DNA microarray 분석에서찾은흥미로운유전자때문이다. 정상과비교했을때 LRP5KO 생쥐의뼈에서현저히높은값으로나온유전자는 Serotonin 합성과연관있는 tryptophan hydroxylase (TPH)1이었다. TPH1은십이지장에서 Serotonin 합성에관여하는중요한효소인데 LRP5KO 생쥐의십이지장에서 3배증가하였다. LRP5 유전자를 α1(i) collagen-cre 와 Villin-Cre로각각제거하는 Conditional KO (CKO) 생쥐와 (LRP5-G171V) 와같은 LRP5 Conditional Knock-in (CKI) 생쥐를제작하여여러가지 Cre 생쥐로조직별로조사하였는데, 이 CKO나 CKI 생쥐에서 Dermo1-Cre나 α1(i) collagen-cre로제거해도골량이나뼈모세포수, 골형성속도에는차이가없었다. 29 심지어 Dmp1-Cre로 LRP5를제거하여도변화가없었다. 그러나 LRP5를 Villin-Cre 생쥐로제거시골량, 골형성속도, 뼈모세포수가감소되었고, LRP5- G171V CKI 생쥐를 Villin-Cre 생쥐로활성화하면반대로골량과골형성이증가되어, LRP5로인한골량은장에서만들어지는 Serotonin과역상관관계가있다고보고하였다. 29 또한 OPPG 환자에서 Serotonin 농도가높고, 높은골량을보이는 LRP5 기능-증가돌연변이경우는낮고, 31 실제여성에서혈중 Serotonin 농도는골량과역상관관계를보였다. 32 즉, LRP5 기능-증가돌연변이에의한골량증가는뼈모세포자체가아닌장관세포에서만드는 Serotonin이혈류를타고뼈조직에작용하여일어난현상임을나타낸다. Serotonin이골량이미치는영향십이지장유래 Serotonin은골량을줄이고뇌유래 Serotonin은골량을증가시킨다. 같은화학물질인데왜골량이상반되게조절되는가? 이는 Serotonin의작용장소가어디냐에따라뼈에미치는영향이다르다고한다. 장유래 Serotonin은뼈모세포에발현되는 human serotonin receptor (Htr)1b 수용체와작용하여 cyclic adenosine monophosphate (camp) responsive element-binding protein (CREB) 의인산화를감소시키고 Cyclin D1의발현을억제하여뼈모세포의수를줄인다. 뼈흡수에대해서는별작용이없는것으로밝혀졌다. TPH2 KO 생쥐경우낮은골량을보여뇌에서만들어지는 Serotonin은뼈형성과흡수모두에영향을주어골량을증가시킨다. 33 흥미롭게도 TPH1/TPH2 double KO 하면골량이감소된다. 이는 5% 정도되는뇌-Serotonin이 95% 나되는장-Serotonin의기능을넘어작용함을알수있다. 장-Serotonin 신호계억제가골다공증치료가가능한지난소절제동물모델을이용하여검증하였는데, TPH1에대한경구용 Serotonin 합성억제제는뼈흡수에대해서는큰작용없이뼈모세포증식과뼈형성의활성화로골량을증가시킨다. 34 이것은장-Serotonin 신호계억제가새로운골다공증치료제개발의작용점이될수있음을보여준다. 5

6 β-catenin Fig. 3. Bone mass regulation in Lipoprotein receptor-related protein (LRP)5 signaling pathway via Serotonin and Sclerostin Regulation of bone mass by LRP5 mutations is not directly correlated with the involvement of -catenin mediated canonical Wnt pathway. High bone mass phenotypes of LRP5 gain-offunction mutations were explained by two different ways. One is local regulatory role of Sclerostin and Dickkopf (Dkk1) which are produced in bone cells and play as strong inhibitors for bone formation. They cannot bind to LRP5 with high bone mass mutations (left panel). Another explanation is systemic regulatory role of Serotonin which is produced in intestine and also play as strong inhibitor for bone formation. LRP5 gain-of-function mutations decreases blood Serotonin level by inhibition of trypthopan hydroxylase 1 expression in enterochromaffiin cells. Serotonin decreases osteoblast number and function through Serotonin receptor (Htr1b) in osteoblasts (right panel). LRP5 돌연변이와 Sclerostin 연관성 Sclerosteosis (SCL; OMIM ) 는 Van Buchem disease (VBD; OMIM ) 와매우유사하나임상적으로약간다르다. SCL은점진적으로뼈의과성장과두께가증가하는데특히두개골, 하악, 그리고장골에서뚜렷하게관찰된다. 환자들은키가크고하악과이마가커지는바람에얼굴에변형과대뇌신경이눌려안면마비, 청각소실, 후각소실등이오며, 뇌압이증가하여두통이나갑자기사망할수도있다. 또한많은경우손에 syndactyly가있다. 이러한특징들은 VBD에서는나타나지않아임상적으로다른상태로분류된다. 그러나두질환의경우모두 SOST이부족하여골량증가가되었다. SOST은 213개아미노산으로구성된 단백질로아미노산서열이쥐, 생쥐각각사람의것과 89%, 88% 정도로높은유사성을보인다. 35,36 사람에서높은골량을보이는 LRP5-G171V 돌연변이를 Rat 3.6 kb α1(i) collagen promoter로과발현시킨형질전환생쥐는사람과같이높은골량과골강도를보였다. 37,38 이러한 LRP5-G171V와같은기능-증가돌연변이는 Dkk1이나 SOST과결합하지못할뿐아니라 Mesd와도결합하지못해세포막으로이동이적어진다. 15,39,40 그러나 Karsenty 그룹에서는높은골량을초래하는 LRP5-G171V나 LRP5 과발현형질전환동물에서골량이증가되지않는다는상반된결과도보고하였다. 28 또다른연구에서는 LRP5를 Dmp1-Cre로제거시골량과골강도가감소되었으나, 장관특이적인 Villin1-Cre로제거시골량이나 Serotonin 혈중농도는변화가없었다. 41 또한 LRP5-G171V를 Dmp1-Cre와 Prx1-Cre 생쥐로활성화시켰을때모두골량이증가되었고, Villin1-Cre 생쥐로활성화시켰을때는차이가없었다. 높은골량을나타내는 LRP5- G171V를같은생쥐에서 Prx1-Cre 생쥐로실험하여척추는차이가없지만사지에서만골량이증가되어 LRP5에의한골량조절은뼈조직자체에서국소적으로일어나는강력한증거를제시하였다. 41 요약 LRP5의기능-증가및기능-소실돌연변이로인한골량의증감은골생물학자가골다공증치료제개발을위한가장이상적인모델이지만아직여러측면에서명확하지않는점이많다. LRP5의기능-증가돌연변이의주된이유는뼈세포에서발현하는 SOST과 Dkk1이 LRP5에제대로결합하지못해 Wnt 신호가증가되어일어난현상으로요약된다. LRP5 기능-증가돌연변이의 Wnt 신호증가로인한높은골량은뼈조직이라는국소부위에서일어나는현상이라는그룹과, 장에서만들어지는 Serotonin으로인하여전신적으로작용한다는그룹으로나누어져있다. 여성의혈청에서 SOST 과 Serotonin은모두골량과역비례관계가있어현재로서는양쪽모두의주장이유효하다고할수있다 (Fig. 3). 32,42 어느쪽이주된역할을하는지는좀더자세한연구가필요하다. 현재까지 LRP5에의한골량조절에 Serotonin 또는 SOST 에비중을두는각그룹들의비슷한전략의실험들이왜다른결과가나왔는지자세한설명은없다. 여러가지이유중 6

7 하나는 LRP5를제거하기위해사용한 Cre 생쥐가다르기때문일수있다. 이부분또한자세한규명이필요하다. Serotonin/SOST와 LRP5와의연관성을임상결과로증명이되고분자기전이좀더잘규명된다면 LRP5 기능-증가에의한골량조절기전이더욱명확해질것이다. 이미 Dkk1이나 SOST에대한전임상및임상시험결과들은좋은성적을내고있어머지않아좋은골다공증치료제로개발될수있을것이다. 따라서 Wnt 신호계의자세한이해는골다공증치료를위한새로운신약개발에좋은작용점을제공할것이다. 참고문헌 1. Rachner TD, Khosla S, Hofbauer LC. Osteoporosis: now and the future. Lancet 2011;377: Baron R, Rawadi G. Targeting the Wnt/beta-catenin pathway to regulate bone formation in the adult skeleton. Endocrinology 2007;148: Zhu D, Kang Q, Huang PY, He TC, Xie P. Neurogenesisrelated genes expression profiling of mouse fibroblastic stem cells induced by Wnt signaling. Neurol Res 2009;31: Logan CY, Nusse R. The Wnt signaling pathway in development and disease. Annu Rev Cell Dev Biol 2004;20: Mikels A, Minami Y, Nusse R. Ror2 receptor requires tyrosine kinase activity to mediate Wnt5A signaling. J Biol Chem 2009;284: He X, Semenov M, Tamai K, Zeng X. LDL receptor-related proteins 5 and 6 in Wnt/beta-catenin signaling: arrows point the way. Development 2004;131: Pan W, Choi SC, Wang H, et al. Wnt3a-mediated formation of phosphatidylinositol 4,5-bisphosphate regulates LRP6 phosphorylation. Science 2008;321: Wu X, Tu X, Joeng KS, Hilton MJ, Williams DA, Long F. Rac1 activation controls nuclear localization of beta-catenin during canonical Wnt signaling. Cell 2008;133: Takada I, Mihara M, Suzawa M, et al. A histone lysine methyltransferase activated by non-canonical Wnt signalling suppresses PPAR-gamma transactivation. Nat Cell Biol 2007; 9: Maeda K, Kobayashi Y, Udagawa N, et al. Wnt5a-Ror2 signaling between osteoblast-lineage cells and osteoclast precursors enhances osteoclastogenesis. Nat Med 2012;18: Niehrs C. Function and biological roles of the Dickkopf family of Wnt modulators. Oncogene 2006;25: Gong Y, Slee RB, Fukai N, et al. LDL receptor-related protein 5 (LRP5) affects bone accrual and eye development. Cell 2001;107: Little RD, Carulli JP, Del Mastro RG, et al. A mutation in the LDL receptor-related protein 5 gene results in the autosomal dominant high-bone-mass trait. Am J Hum Genet 2002;70: Johnson ML, Gong G, Kimberling W, Reckér SM, Kimmel DB, Recker RB. Linkage of a gene causing high bone mass to human chromosome 11 (11q12-13). Am J Hum Genet 1997;60: Boyden LM, Mao J, Belsky J, et al. High bone density due to a mutation in LDL-receptor-related protein 5. N Engl J Med 2002;346: Moon RT, Kohn AD, De Ferrari GV, Kaykas A. WNT and beta-catenin signalling: diseases and therapies. Nat Rev Genet 2004;5: Hill TP, Später D, Taketo MM, Birchmeier W, Hartmann C. Canonical Wnt/beta-catenin signaling prevents osteoblasts from differentiating into chondrocytes. Dev Cell 2005;8: Day TF, Guo X, Garrett-Beal L, Yang Y. Wnt/beta-catenin signaling in mesenchymal progenitors controls osteoblast and chondrocyte differentiation during vertebrate skeletogenesis. Dev Cell 2005;8: Hu H, Hilton MJ, Tu X, Yu K, Ornitz DM, Long F. Sequential roles of Hedgehog and Wnt signaling in osteoblast development. Development 2005;132: Glass DA, 2nd, Bialek P, Ahn JD, et al. Canonical Wnt signaling in differentiated osteoblasts controls osteoclast differentiation. Dev Cell 2005;8: Rodda SJ, McMahon AP. Distinct roles for Hedgehog and canonical Wnt signaling in specification, differentiation and maintenance of osteoblast progenitors. Development 2006; 133: Holmen SL, Zylstra CR, Mukherjee A, et al. Essential role of beta-catenin in postnatal bone acquisition. J Biol Chem 2005; 280:

8 23. Kramer I, Halleux C, Keller H, et al. Osteocyte Wnt/betacatenin signaling is required for normal bone homeostasis. Mol Cell Biol 2010;30: Kato M, Patel MS, Levasseur R, et al. Cbfa1-independent decrease in osteoblast proliferation, osteopenia, and persistent embryonic eye vascularization in mice deficient in Lrp5, a Wnt coreceptor. J Cell Biol 2002;157: Fujino T, Asaba H, Kang MJ, et al. Low-density lipoprotein receptor-related protein 5 (LRP5) is essential for normal cholesterol metabolism and glucose-induced insulin secretion. Proc Natl Acad Sci U S A 2003;100: Choi HY, Dieckmann M, Herz J, Niemeier A. Lrp4, a novel receptor for Dickkopf 1 and sclerostin, is expressed by osteoblasts and regulates bone growth and turnover in vivo. PLoS One 2009;4:e Kubota T, Michigami T, Sakaguchi N, et al. Lrp6 hypomorphic mutation affects bone mass through bone resorption in mice and impairs interaction with Mesd. J Bone Miner Res 2008;23: Glass DA, 2nd, Karsenty G. In vivo analysis of Wnt signaling in bone. Endocrinology 2007;148: Yadav VK, Ryu JH, Suda N, et al. Lrp5 controls bone formation by inhibiting serotonin synthesis in the duodenum. Cell 2008;135: Yadav VK, Arantes HP, Barros ER, Lazaretti-Castro M, Ducy P. Genetic analysis of Lrp5 function in osteoblast progenitors. Calcif Tissue Int 2010;86: Frost M, Andersen TE, Yadav V, Brixen K, Karsenty G, Kassem M. Patients with high-bone-mass phenotype owing to Lrp5-T253I mutation have low plasma levels of serotonin. J Bone Miner Res 2010;25: Mödder UI, Achenbach SJ, Amin S, Riggs BL, Melton LJ, 3rd, Khosla S. Relation of serum serotonin levels to bone density and structural parameters in women. J Bone Miner Res 2010;25: Yadav VK, Oury F, Suda N, et al. A serotonin-dependent mechanism explains the leptin regulation of bone mass, appetite, and energy expenditure. Cell 2009;138: Yadav VK, Balaji S, Suresh PS, et al. Pharmacological inhibition of gut-derived serotonin synthesis is a potential bone anabolic treatment for osteoporosis. Nat Med 2010;16: Brunkow ME, Gardner JC, Van Ness J, et al. Bone dysplasia sclerosteosis results from loss of the SOST gene product, a novel cystine knot-containing protein. Am J Hum Genet 2001;68: Balemans W, Ebeling M, Patel N, et al. Increased bone density in sclerosteosis is due to the deficiency of a novel secreted protein (SOST). Hum Mol Genet 2001;10: Akhter MP, Wells DJ, Short SJ, et al. Bone biomechanical properties in LRP5 mutant mice. Bone 2004;35: Babij P, Zhao W, Small C, et al. High bone mass in mice expressing a mutant LRP5 gene. J Bone Miner Res 2003;18: Ellies DL, Viviano B, McCarthy J, et al. Bone density ligand, Sclerostin, directly interacts with LRP5 but not LRP5G171V to modulate Wnt activity. J Bone Miner Res 2006;21: Zhang Y, Wang Y, Li X, et al. The LRP5 high-bone-mass G171V mutation disrupts LRP5 interaction with Mesd. Mol Cell Biol 2004;24: Cui Y, Niziolek PJ, MacDonald BT, et al. Lrp5 functions in bone to regulate bone mass. Nat Med 2011;17: Modder UI, Hoey KA, Amin S, et al. Relation of age, gender, and bone mass to circulating sclerostin levels in women and men. J Bone Miner Res 2011;26:

9 = 국문초록 = LRP5 신호는사람이나쥐에서골량획득과잘일치한다. LRP5 의기능 - 소실돌연변이는골감소나골다공증을초래하고기능 - 증가돌연변이는높은골량을나타낸다. LRP5 로인한골량조절기전은뼈모세포계특이적으로 -catenin 이나 LRP5 를제거하여평가한결과두유전자가중요하게관여한다고알려졌다. 하나는 LRP5 로인한골량은골조직이아닌십이지장에서발현되는 Serotonin 이호르몬처럼작용하여조절된다는것이고, 다른하나는뼈세포에서발현하는 Sclerostin 이뼈조직에서국소적으로작용하여조절된다는것이다. 여기서는이두분자에대한최근결과들을요약하고 LRP5 에의한골량획득의새로운기전에대하여알아보고자한다. 중심단어 : 골량, LRP5, Sclerostin, Serotonin, Wnt signaling 9

2016 학년도약학대학면접문제해설 문제 2 아래의질문에 3-4분이내로답하시오. 표피성장인자수용체 (epidermal growth factor receptor, EGFR) 는수용체티로신인산화효소군 (receptor tyrosine kinases, RTKs) 의일종으로서세

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