PTH and Vitamin D Repress DMP1 in Cementoblasts

Area of Science:

• Mineral and bone metabolism
• Endocrinology
• Molecular biology

Background:

• Mineral homeostasis is tightly regulated by parathyroid hormone (PTH), 1,25-dihydroxyvitamin D3 (1,25D), and FGF-23.
• 1,25D regulates mineral homeostasis by repressing dentin matrix protein 1 (DMP1) through the vitamin D receptor.
• The mechanism by which PTH influences DMP1 and mineral homeostasis remains to be elucidated.

Purpose of the Study:

• To investigate the effect of PTH on DMP1 expression in cementoblasts.
• To elucidate the signaling pathway involved in PTH-mediated DMP1 regulation.
• To identify shared and distinct gene expression patterns regulated by PTH and 1,25D in mineral homeostasis.

Main Methods:

• Treatment of immortalized murine cementoblasts (OCCM.30) with PTH (1-34).
• Real-time quantitative PCR and Western blot analysis to assess DMP1 gene and protein expression.
• In vivo immunohistochemistry in mice treated with PTH.
• RNA-sequencing (RNA-seq) to analyze global gene expression changes.
• Validation of RNA-seq data using PCR array.

Main Results:

• PTH significantly decreased DMP1 gene transcription (85%) and protein expression (30%) in OCCM.30 cells.
• PTH-induced DMP1 downregulation occurred via the cAMP/protein kinase A (PKA) pathway.
• In vivo studies confirmed reduced DMP1 localization in cementum and alveolar bone after PTH administration.
• RNA-seq revealed 36 mutually upregulated and 27 mutually downregulated genes between PTH and 1,25D treatments (≥2-fold, P ≤ 0.05).
• Shared gene expression patterns were associated with bone/tooth homeostasis, cell signaling, and mineral metabolism.

Conclusions:

• PTH downregulates DMP1 expression through the cAMP/PKA pathway, contributing to phosphate homeostasis.
• PTH and 1,25D exhibit complementary roles in mineral homeostasis through mutual regulation of shared genes.
• Distinct roles of PTH and 1,25D in modulating mineral metabolism factors exist.
• Targeting genes regulated by both PTH and 1,25D may offer therapeutic strategies for mineralized tissue health.