LRP5

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LRP5
Identifiers
Aliases LRP5, BMND1, EVR1, EVR4, HBM, LR3, LRP-5, LRP7, OPPG, OPS, OPTA1, VBCH2, LDL receptor related protein 5
External IDs MGI: 1278315 HomoloGene: 1746 GeneCards: LRP5
RNA expression pattern
PBB GE LRP5 209468 at tn.png
More reference expression data
Orthologs
Species Human Mouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_001291902
NM_002335

NM_008513

RefSeq (protein)

NP_001278831
NP_002326

NP_032539.2
NP_032539

Location (UCSC) Chr 11: 68.31 – 68.45 Mb Chr 19: 3.58 – 3.69 Mb
PubMed search [1] [2]
Wikidata
View/Edit Human View/Edit Mouse

Low-density lipoprotein receptor-related protein 5 is a protein that in humans is encoded by the LRP5 gene.[3][4][5] LRP5 is a key component of the LRP5/LRP6/Frizzled co-receptor group that is involved in canonical Wnt pathway. Mutations in LRP5 can lead to considerable changes in bone mass. A loss-of-function mutation causes osteoporosis-pseudoglioma (decrease in bone mass), while a gain-of-function mutation causes drastic increases in bone mass.

Structure[edit]

LRP5 is a transmembrane low-density lipoprotein receptor that shares a similar structure with LRP6. In each protein, about 85% of its 1600-amino-acid length is extracellular. Each has four β-propeller motifs at the amino terminal end that alternate with four epidermal growth factor (EGF)-like repeats. Most extracellular ligands bind to LRP5 and LRP6 at the β-propellers. Each protein has a single-pass, 22-amino-acid segment that crosses the cell membrane and a 207-amino-acid segment that is internal to the cell.[6]

Function[edit]

LRP5 acts as a co-receptor with LRP6 and the Frizzled protein family members for transducing signals by Wnt proteins through the canonical Wnt pathway.[6] This protein plays a key role in skeletal homeostasis.[5]

Transcription[edit]

The LRP5 promoter contains binding sites for KLF15 and SP1.[7] In addition, 5' region region of the LRP5 gene contains four RUNX2 binding sites.[8] LRP5 has been shown in mice and humans to inhibit expression of TPH1, the rate-limiting biosynthetic enzyme for serotonin in enterochromaffin cells of the duodenum[9][10][11][12][13][14] and that excess plasma serotonin leads to inhibition in bone. On the other hand, one study in mouse has shown a direct effect of Lrp5 on bone.[15]

Interactions[edit]

LRP5 has been shown to interact with AXIN1.[16][17]

Canonical WNT signals are transduced through Frizzled receptor and LRP5/LRP6 coreceptor to downregulate GSK3beta (GSK3B) activity not depending on Ser-9 phosphorylation.[18] Reduction of canonical Wnt signals upon depletion of LRP5 and LRP6 results in p120-catenin degradation.[19]

Clinical Significance[edit]

The Wnt signaling pathway was first linked to bone development when a loss-of-function mutation in LRP5 was found to cause osteoporosis-pseudoglioma syndrome.[20] Shortly thereafter, two studies reported that gain-of-function mutations in LRP5 caused high bone mass.[21][22] Many bone density related diseases are caused by mutations in the LRP5 gene. There is controversy whether bone grows through Lrp5 through bone or the intestine.[23] The majority of the current data supports the concept that bone mass is controlled by LRP5 through the osteocytes.[24] Mice with the same Lrp5 gain-of-function mutations as also have high bone mass.[25] The high bone mass is maintained when the mutation only occurs in limbs or in cells of the osteoblastic lineage.[15] Bone mechanotransduction occurs through Lrp5[26] and is suppressed if Lrp5 is removed in only osteocytes.[27] There are promising osteoporosis clinical trials targeting sclerostin, an osteocyte-specific protein which inhibits Wnt signaling by binding to Lrp5.[24][28] An alternative model that has been verified in mice and in humans is that Lrp5 controls bone formation by inhibiting expression of TPH1, the rate-limiting biosynthetic enzyme for serotonin, a molecule that regulates bone formation, in enterochromaffin cells of the duodenum[9][10][11][12][13][14] and that excess plasma serotonin leads to inhibition in bone. Another study found that a different Tph1-inhibitor decreased serotonin levels in the blood and intestine, but did not affect bone mass or markers of bone formation.[15]

LRP5 may be essential for the development of retinal vasculature, and may play a role in capillary maturation.[29] Mutations in this gene also cause familial exudative vitreoretinopathy.[5]

A glial-derived extracellular ligand, Norrin, acts on a transmembrane receptor, Frizzled4, a coreceptor, Lrp5, and an auxiliary membrane protein, TSPAN12, on the surface of developing endothelial cells to control a transcriptional program that regulates endothelial growth and maturation.[30]

LRP5 knockout in mice led to increased plasma cholesterol levels on a high-fat diet because of the decreased hepatic clearance of chylomicron remnants. When fed a normal diet, LRP5-deficient mice showed a markedly impaired glucose tolerance with marked reduction in intracellular ATP and Ca2+ in response to glucose, and impairment in glucose-induced insulin secretion. IP3 production in response to glucose was also reduced in LRP5—islets possibly caused by a marked reduction of various transcripts for genes involved in glucose sensing in LRP5—islets. LRP5-deficient islets lacked the Wnt-3a-stimulated insulin secretion. These data suggest that WntLRP5 signaling contributes to the glucose-induced insulin secretion in the islets.[31]

In osteoarthritic chondrocytes the Wnt/beta-catenin pathway is activated with a significant up-regulation of beta-catenin mRNA expression. LRP5 mRNA and protein expression are also significantly up-regulated in osteoarthritic cartilage compared to normal cartilage, and LRP5 mRNA expression was further increased by vitamin D. Blocking LRP5 expression using siRNA against LRP5 resulted in a significant decrease in MMP13 mRNA and protein expressions. The catabolic role of LRP5 appears to be mediated by the Wnt/beta-catenin pathway in human osteoarthritis.[32]

The polyphenol curcumin increases the mRNA expression of LRP5.[33]

Mutations in LRP5 cause polycystic liver disease .[34]

References[edit]

  1. ^ "Human PubMed Reference:". 
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  3. ^ Hey PJ, Twells RC, Phillips MS, Brown SD, Kawaguchi Y, Cox R, Dugan V, Hammond H, Metzker ML, Todd JA, Hess JF (Aug 1998). "Cloning of a novel member of the low-density lipoprotein receptor family". Gene. 216 (1): 103–11. doi:10.1016/S0378-1119(98)00311-4. PMID 9714764. 
  4. ^ Chen D, Lathrop W, Dong Y (Feb 1999). "Molecular cloning of mouse Lrp7(Lr3) cDNA and chromosomal mapping of orthologous genes in mouse and human". Genomics. 55 (3): 314–21. doi:10.1006/geno.1998.5688. PMID 10049586. 
  5. ^ a b c "Entrez Gene: LRP5 low density lipoprotein receptor-related protein 5". 
  6. ^ a b Williams BO, Insogna KL (Feb 2009). "Where Wnts went: the exploding field of Lrp5 and Lrp6 signaling in bone". Journal of Bone and Mineral Research. 24 (2): 171–8. doi:10.1359/jbmr.081235. PMC 3276354Freely accessible. PMID 19072724. 
  7. ^ Li J, Yang Y, Jiang B, Zhang X, Zou Y, Gong Y (2010). "Sp1 and KLF15 regulate basal transcription of the human LRP5 gene". BMC Genetics. 11: 12. doi:10.1186/1471-2156-11-12. PMC 2831824Freely accessible. PMID 20141633. 
  8. ^ Agueda L, Velázquez-Cruz R, Urreizti R, Yoskovitz G, Sarrión P, Jurado S, Güerri R, Garcia-Giralt N, Nogués X, Mellibovsky L, Díez-Pérez A, Marie PJ, Balcells S, Grinberg D (May 2011). "Functional relevance of the BMD-associated polymorphism rs312009: novel involvement of RUNX2 in LRP5 transcriptional regulation". Journal of Bone and Mineral Research. 26 (5): 1133–44. doi:10.1002/jbmr.293. PMID 21542013. 
  9. ^ a b Yadav VK, Ryu JH, Suda N, Tanaka KF, Gingrich JA, Schütz G, Glorieux FH, Chiang CY, Zajac JD, Insogna KL, Mann JJ, Hen R, Ducy P, Karsenty G (Nov 2008). "Lrp5 controls bone formation by inhibiting serotonin synthesis in the duodenum". Cell. 135 (5): 825–37. doi:10.1016/j.cell.2008.09.059. PMC 2614332Freely accessible. PMID 19041748. 
  10. ^ a b Kode A, Mosialou I, Silva BC, Rached MT, Zhou B, Wang J, Townes TM, Hen R, DePinho RA, Guo XE, Kousteni S (Oct 2012). "FOXO1 orchestrates the bone-suppressing function of gut-derived serotonin". The Journal of Clinical Investigation. 122 (10): 3490–503. doi:10.1172/JCI64906. PMC 3461930Freely accessible. PMID 22945629. 
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  15. ^ a b c Cui Y, Niziolek PJ, MacDonald BT, Zylstra CR, Alenina N, Robinson DR, Zhong Z, Matthes S, Jacobsen CM, Conlon RA, Brommage R, Liu Q, Mseeh F, Powell DR, Yang QM, Zambrowicz B, Gerrits H, Gossen JA, He X, Bader M, Williams BO, Warman ML, Robling AG (Jun 2011). "Lrp5 functions in bone to regulate bone mass". Nature Medicine. 17 (6): 684–91. doi:10.1038/nm.2388. PMC 3113461Freely accessible. PMID 21602802. 
  16. ^ Mao J, Wang J, Liu B, Pan W, Farr GH, Flynn C, Yuan H, Takada S, Kimelman D, Li L, Wu D (Apr 2001). "Low-density lipoprotein receptor-related protein-5 binds to Axin and regulates the canonical Wnt signaling pathway". Molecular Cell. 7 (4): 801–9. doi:10.1016/S1097-2765(01)00224-6. PMID 11336703. 
  17. ^ Kim MJ, Chia IV, Costantini F (Nov 2008). "SUMOylation target sites at the C terminus protect Axin from ubiquitination and confer protein stability". FASEB Journal. 22 (11): 3785–94. doi:10.1096/fj.08-113910. PMC 2574027Freely accessible. PMID 18632848. 
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  19. ^ Hong JY, Park JI, Cho K, Gu D, Ji H, Artandi SE, McCrea PD (Dec 2010). "Shared molecular mechanisms regulate multiple catenin proteins: canonical Wnt signals and components modulate p120-catenin isoform-1 and additional p120 subfamily members". Journal of Cell Science. 123 (Pt 24): 4351–65. doi:10.1242/jcs.067199. PMC 2995616Freely accessible. PMID 21098636. 
  20. ^ Gong Y, Slee RB, Fukai N, Rawadi G, Roman-Roman S, Reginato AM, et al. (Nov 2001). "LDL receptor-related protein 5 (LRP5) affects bone accrual and eye development". Cell. 107 (4): 513–23. doi:10.1016/S0092-8674(01)00571-2. PMID 11719191. 
  21. ^ Little RD, Carulli JP, Del Mastro RG, Dupuis J, Osborne M, Folz C, Manning SP, Swain PM, Zhao SC, Eustace B, Lappe MM, Spitzer L, Zweier S, Braunschweiger K, Benchekroun Y, Hu X, Adair R, Chee L, FitzGerald MG, Tulig C, Caruso A, Tzellas N, Bawa A, Franklin B, McGuire S, Nogues X, Gong G, Allen KM, Anisowicz A, Morales AJ, Lomedico PT, Recker SM, Van Eerdewegh P, Recker RR, Johnson ML (Jan 2002). "A mutation in the LDL receptor-related protein 5 gene results in the autosomal dominant high-bone-mass trait". American Journal of Human Genetics. 70 (1): 11–9. doi:10.1086/338450. PMC 419982Freely accessible. PMID 11741193. 
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Further reading[edit]

External links[edit]

This article incorporates text from the United States National Library of Medicine, which is in the public domain.