Lrp5 is a positive regulator of bone formation in vertebrates. It is generally assumed that it fulfills this function as a coreceptor for Wnt proteins. However, disrupting canonical Wnt signaling in osteoblasts does not affect bone formation thus raising the testable hypothesis that Lrp5 uses other and/or additional means to regulate bone formation. While testing this hypothesis we have generated a large body of preliminary data indicating that in absence of Lrp5 there is a severe increase in circulating levels of peripherally produced serotonin, which known to be produced by the enterochromaffin cells of the gut (duodenum). Based on this body of preliminary data we hypothesize that, in mice and men, the bone diseases triggered by loss- or gain-of-function mutations in Lrp5 are endocrine diseases originating from the gut and mediated by serotonin. To demonstrate the validity of our hypothesis we propose to pursue the following specific aims: - To generate and analyze mice lacking Lrp5 in either osteoblasts or duodenum to determine the cellular origin of the bone phenotype caused by Lrp5 inactivation. - To generate and analyze mutant mice lacking Tph1 in osteoblasts or duodenum to determine whether serotonin acts on osteoblast in an autocrine or endocrine manner. - To determine through genetic means whether a gain-of-function mutation in Lrp5 affects bone mass in a serotonin-dependent manner. - To use genetic assays to identify serotonin signaling receptors in osteoblasts - To determine genetically whether CREB is the transcription factor acting downstream of serotonin in osteoblasts.

Public Health Relevance

We have identified Tph1, a gene governing serotonin production in gut cells, as the gene most affected by the absence of Lrp5, a major regulator of osteoblast proliferation and bone formation implicated in two human disorders of the skeleton. This project will test whether serotonin is a major mediator of Lrp5'regulation of bone mass, whether this effect has a gut origin i.e. is of endocrine nature or has an osteoblastic origin, and will identify the receptor(s) for serotonin in osteoblasts as well as the transcription factor mediating its effect in these cells.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK067936-09
Application #
8459524
Study Section
Skeletal Biology Structure and Regeneration Study Section (SBSR)
Program Officer
Malozowski, Saul N
Project Start
2004-07-01
Project End
2014-05-31
Budget Start
2013-06-01
Budget End
2014-05-31
Support Year
9
Fiscal Year
2013
Total Cost
$347,953
Indirect Cost
$131,833
Name
Columbia University (N.Y.)
Department
Genetics
Type
Schools of Medicine
DUNS #
621889815
City
New York
State
NY
Country
United States
Zip Code
10032
Kajimura, Daisuke; Lee, Ha Won; Riley, Kyle J et al. (2013) Adiponectin regulates bone mass via opposite central and peripheral mechanisms through FoxO1. Cell Metab 17:901-15
Yadav, Vijay K; Ducy, Patricia (2010) Lrp5 and bone formation : A serotonin-dependent pathway. Ann N Y Acad Sci 1192:103-9
Karsenty, Gerard; Kronenberg, Henry M; Settembre, Carmine (2009) Genetic control of bone formation. Annu Rev Cell Dev Biol 25:629-48
Yadav, Vijay K; Ryu, Je-Hwang; Suda, Nina et al. (2008) Lrp5 controls bone formation by inhibiting serotonin synthesis in the duodenum. Cell 135:825-37