Osteoporosis is a disease characterized by a low BMD leading to higher bone fragility, where fractures occur after minimal trauma. Our previous studies in girls and boys, and recent studies in mice, have shown that 40-50% of bone accretion occurs during the period of puberty. Therefore, of considerable importance in the prevention and treatment of osteoporosis are those studies that focus on understanding the mechanisms regulating bone accretion that occurs during puberty. Our recent finding that puberty-induced increases in BMD failed to occur in mice lacking functional IGF-I gene provide direct evidence for a role of IGF-I in the acquisition of peak BMD. Uniquely, IGF-I functions as a local growth factor and as a systemic hormone. The systemic action of IGF-I could be different from that of the local action of IGF-I since (1) the mechanisms involved in regulating the actions of systemic (liver-derived) and local (bone-derived) IGF-I are different, and (2) a deficiency in endocrine IGF-I action failed to reduce peak BMD in mice. Studies of gene function are being advanced by the development of new molecular techniques. One such technique is the Cre/IoxP system, which allows the conditional disruption of gene function (i.e., allows cell specific disruption of IGF-I production). We propose to apply this method to evaluate the effect of IGF-I gene-knock out exclusively in skeletal cells (i.e., osteoblasts (OBs) and also chondroblasts) on skeletal phenotype. The specific hypotheses that we propose to test in this grant proposal are: (1) disruption of the IGF-I gene in OBs will lead to a significant reduction in peak BMD and bone size; and (2) disruption of the IGF-I gene in chondroblasts will lead to reduction in longitudinal growth. In order to evaluate the above hypotheses, transgenic mice expressing Cre recombinase under the direction of osteocalcin promoter, type I collagen promoter (OB-specific), or type II collagen promoter (chondroblast-specific) will be crossed with IoxP IGF-I mice to generate Cre/IoxP IGF-I mice with disruption of IGF-I gene in OBs or chondroblasts. The efficiency of Cre recombinase to cause excision of IGF-I gene in cell types of interest will be evaluated by measurement of IGF-I mRNA by real-time PCR, and by in situ hybridization. The phenotypic manifestations in the skeletal tissues caused by disruption of IGF-I gene specifically in bone during various growth phases will be examined by skeletal phenotypic measurements, including BMD, bone strength, biochemical assays of bone turnover and histomorphometric analyses. If our hypothesis, that locally produced IGFs are more important than systemically produced IGFs, is proven to be correct, this could lead to exploration of mechanisms regulating local production of IGFs as a means to increase bone formation and peak BMD. Since small differences in peak bone mass and BMD at maturity could contribute to substantial difference in osteoporotic fractures, future therapies to increase peak BMD could reduce health care costs by decreasing the incidence of osteoporotic fractures.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR048139-03
Application #
6943182
Study Section
Orthopedics and Musculoskeletal Study Section (ORTH)
Program Officer
Sharrock, William J
Project Start
2003-08-01
Project End
2007-07-31
Budget Start
2005-08-01
Budget End
2006-07-31
Support Year
3
Fiscal Year
2005
Total Cost
$252,801
Indirect Cost
Name
Loma Linda Veterans Assn Research & Education
Department
Type
DUNS #
606630762
City
Redlands
State
CA
Country
United States
Zip Code
92373
Lindsey, Richard C; Aghajanian, Patrick; Mohan, Subburaman (2018) Thyroid Hormone Signaling in the Development of the Endochondral Skeleton. Vitam Horm 106:351-381
Lindsey, Richard C; Rundle, Charles H; Mohan, Subburaman (2018) Role of IGF1 and EFN-EPH signaling in skeletal metabolism. J Mol Endocrinol 61:T87-T102
Cheng, Shaohong; Pourteymoor, Sheila; Alarcon, Catrina et al. (2017) Conditional Deletion of the Phd2 Gene in Articular Chondrocytes Accelerates Differentiation and Reduces Articular Cartilage Thickness. Sci Rep 7:45408
Sanchez, Cheryl P; Mohan, Subburaman (2017) Genetic Knockout and Rescue Studies in Mice Unravel Abnormal Phosphorus Threshold in Hypophosphatemic Rickets. Endocrinology 158:455-457
Cheng, Shaohong; Xing, Weirong; Pourteymoor, Sheila et al. (2016) Conditional Deletion of Prolyl Hydroxylase Domain-Containing Protein 2 (Phd2) Gene Reveals Its Essential Role in Chondrocyte Function and Endochondral Bone Formation. Endocrinology 157:127-40
Lindsey, Richard C; Mohan, Subburaman (2016) Skeletal effects of growth hormone and insulin-like growth factor-I therapy. Mol Cell Endocrinol 432:44-55
Cheng, Shaohong; Aghajanian, Patrick; Pourteymoor, Sheila et al. (2016) Prolyl Hydroxylase Domain-Containing Protein 2 (Phd2) Regulates Chondrocyte Differentiation and Secondary Ossification in Mice. Sci Rep 6:35748
Liu, Zhongbo; Mohan, Subburaman; Yakar, Shoshana (2016) Does the GH/IGF-1 axis contribute to skeletal sexual dimorphism? Evidence from mouse studies. Growth Horm IGF Res 27:7-17
Aghajanian, Patrick; Hall, Susan; Wongworawat, Montri D et al. (2015) The Roles and Mechanisms of Actions of Vitamin C in Bone: New Developments. J Bone Miner Res 30:1945-55
Mohan, Subburaman; Wergedal, Jon E; Das, Subhashri et al. (2015) Conditional disruption of miR17-92 cluster in collagen type I-producing osteoblasts results in reduced periosteal bone formation and bone anabolic response to exercise. Physiol Genomics 47:33-43

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