Parathyroid hormone 7-34 (IGI)

Endochondral ossification is tightly controlled by a coordinated network of signaling cascades including parathyroid hormone (PTH). Pleckstrin homology (PH) domain and leucine rich repeat phosphatase 1 (Phlpp1) affects endochondral ossification by suppressing chondrocyte proliferation in the growth plate, longitudinal bone growth, and bone mineralization. As such, Phlpp1−/− mice have shorter long bones, thicker growth plates, and proportionally larger growth plate proliferative zones. The goal of this study was to determine how Phlpp1 deficiency affects PTH signaling during bone growth. Transcriptomic analysis revealed greater PTH receptor 1 (Pth1r) expression and enrichment of histone 3 lysine 27 acetylation (H3K27ac) at the Pth1r promoter in Phlpp1-deficient chondrocytes. PTH (1-34) enhanced and PTH (7-34) attenuated cell proliferation, cAMP signaling, cAMP response element-binding protein (CREB) phosphorylation, and cell metabolic activity in Phlpp1-inhibited chondrocytes. To understand the role of Pth1r action in the endochondral phenotypes of Phlpp1-deficient mice, Phlpp1−/− mice were injected with Pth1r ligand PTH (7-34) daily for the first 4 weeks of life. PTH (7-34) reversed the abnormal growth plate and long-bone growth phenotypes of Phlpp1−/− mice but did not rescue deficits in bone mineral density or trabecular number. These results show that elevated Pth1r expression and signaling contributes to increased proliferation in Phlpp1−/− chondrocytes and shorter bones in Phlpp1-deficient mice. Our data reveal a novel molecular relationship between Phlpp1 and Pth1r in chondrocytes during growth plate development and longitudinal bone growth. © 2021 American Society for Bone and Mineral Research (ASBMR).

A backbone-modified peptide derived from parathyroid hormone (PTH) is shown to function as an inhibitor and inverse agonist of parathyroid hormone receptor-1 (PTHR1) signaling. This receptor acts to regulate calcium and phosphate homeostasis, as well as bone turnover and development. PTH is a natural agonist of PTHR1, and PTH(1-34) displays full activity relative to the natural 84-residue hormone. PTH(1-34) is used clinically to treat osteoporosis. N-terminally truncated derivatives of PTH(1-34), such as PTH(7-34), are known to bind to PTHR1 without initiating intracellular signaling and can thus act as competitive antagonists of PTH-induced signaling at PTHR1. In some cases, N-terminally truncated PTH derivatives also act as inverse agonists of PTHR1 variants that display pathologically high levels of signaling in the absence of PTH. Many analogues of PTH, however, are rapidly degraded by proteases, which may limit biomedical application. We show that backbone modification via periodic replacement of α-amino acid residues with homologous β-amino acid residues leads to an α/β-PTH(7-34) peptide that retains the antagonist and inverse agonist activities of the prototype α-peptide while exhibiting enhanced stability in the presence of aggressive proteases. These findings highlight the value of backbone-modified peptides derived from PTH as tools for investigating determinants of PTH metabolism and provide guidance for designing therapeutic agents for diseases arising from excessive ligand-dependent or ligand-independent PTHR1 activity.