Anti-PTH1R monoclonal antibody

Parathyroid hormone (PTH) signaling via PTH 1 receptor (PTH1R) involves mitogen-activated protein kinase (MAPK) pathways. MAPK phosphatase 1 (MKP1) dephosphorylates and inactivates MAPKs in osteoblasts, the bone-forming cells. We previously showed that PTH1R activation in differentiated osteoblasts upregulates MKP1 and downregulates pERK1/2-MAPK and cyclin D1. In this study, we evaluated the skeletal phenotype of Mkp1 knockout (KO) mice and the effects of PTH in vivo and in vitro. Microcomputed tomography analysis of proximal tibiae and distal femora from 12-week-old Mkp1 KO female mice revealed osteopenic phenotype with significant reduction (8-46%) in bone parameters compared with wild-type (WT) controls. Histomorphometric analysis showed decreased trabecular bone area in KO females. Levels of serum osteocalcin (OCN) were lower and serum tartrate-resistant acid phosphatase 5b (TRAP5b) was higher in KO animals. Treatment of neonatal mice with hPTH (1-34) for 3 weeks showed attenuated anabolic responses in the distal femora of KO mice compared with WT mice. Primary osteoblasts derived from KO mice displayed delayed differentiation determined by alkaline phosphatase activity, and reduced expressions of Ocn and Runx2 genes associated with osteoblast maturation and function. Cells from KO females exhibited attenuated PTH response in mineralized nodule formation in vitro. Remarkably, this observation was correlated with decreased PTH response of matrix Gla protein expression. Expressions of pERK1/2 and cyclin D1 were inhibited dramatically by PTH in differentiated osteoblasts from WT mice but much less in osteoblasts from Mkp1 KO mice. In conclusion, MKP1 is important for bone homeostasis, osteoblast differentiation and skeletal responsiveness to PTH. Journal of Endocrinology (2011) 211, 145-156

Parathyroid hormone (PTH) binds to its receptor PTH1R ( parathyroid hormone 1 receptor) in osteoblastic cells to regulate bone remodeling and calcium homeostasis. While prolonged exposure to PTH causes increased bone resorption, intermittent injections of PTH have an anabolic effect on bone. The molecular mechanisms regulating these processes are still largely unknown. Here, we present our results on gene expression profile changes in the PTH-treated osteoblastic cell line, UMR 106-01, using DNA microarray analysis. A total of 125 known genes and 30 unknown expressed sequence tags ( ESTs) were found to have at least 2-fold expression changes after PTH treatment at 4, 12, and 24 h. 14 genes were previously known to be PTH-regulated but many were unknown to be regulated by PTH prior to our experiments. Real-time reverse transcriptase-PCR confirmed that 90 and 50% of the genes are regulated more than 2-fold by PTH in UMR 106-01 and rat primary osteoblastic cells, respectively. Most genes belong to the following protein families: hormones, growth factors, and receptors; signal transduction pathway proteins; transcription factors; proteases; metabolic enzymes; structural and matrix proteins; transporters; etc. These results provide a comprehensive and deeper knowledge about PTH regulation of osteoblastic gene expression. Next, we designed a computational method to extract information about transcription factors likely involved in regulating these genes. These factors include those previously known to be involved in PTH signaling (AP-1 and the cAMP response element-binding protein), those that were identified by microarray data (C/EBP), and some novel transcription factors ( AP-2, AP-4, SP1, FoxD3, etc.). Our results suggest that a reliable bioinformatics approach can be easily applied for other systems.