Begun, Dana L.

Abstract Studies on human and animal models have demonstrated a complex molecular regulatory network between the dental mesenchyme and epithelium governing tooth development. However, epigenetic regulation of tooth development is largely unexplored. This study aimed to elucidate the relationship between epigenetic modifiers and dental root development using mice deficient in histone deacetylase 3 (Hdac3) under the control of the osterix promoter (Osx-Cre/Hdac3fl/fl or Hdac3-CKOosx). We observed tooth root size and histology in Hdac3-CKOosx mice. Dental pulp progenitor cells (DPCs) were isolated from lower incisors, and calcification and gene expression were assessed. Hdac3 depletion in osterix-expressing dental pulp stem cells, including odontoblasts, caused a progressive postnatal obstruction, resulting in relatively short roots and small root apices of the first molar. Mild degeneration was observed during the development of dentin and cementum structures. Dentin and cementum had uneven borders and showed disordered H&E staining in Hdac3-CKOosx mice that had a thin cementum compared to that of WT mice. Hdac3 inhibition/deletion in dental pulp stem cells probably influenced Msh homeobox 1 (Msx1) and Col1a1 expression in the early developmental stage, thereby driving differentiation in DPCs. Subsequently, Msx1, Col1a1, and osteocalcin expression were remarkably downregulated during calcification. Deletion or inhibition of Hdac3 in conditional KO dental pulp stem cells cultured in mineralization medium resulted in aberrant cell cycle control, and the early stages of maturation of DPCs and odontoblasts were inhibited. Inhibition of Hdac3 in cementocytes also restricted their proliferation and calcification. These results suggested that the deletion or inhibition of Hdac3 in the dental mesenchyme may cause development and maturation deficiency of tooth root.

Excess fat within bone marrow is associated with lower bone density. Metabolic stressors such as chronic caloric restriction (CR) can exacerbate marrow adiposity, and increased glucocorticoid signaling and adrenergic signaling are implicated in this phenotype. The current study tested the role of glucocorticoid signaling in CR-induced stress by conditionally deleting the glucocorticoid receptor ( Nr3c1 ; hereafter abbreviated as GR) in bone marrow osteoprogenitors (Osx1-Cre) of mice subjected to CR and ad libitum diets. Conditional knockout of the GR (GR-CKO) reduced cortical and trabecular bone mass as compared to WT mice under both ad libitum feeding and CR conditions. No interaction was detected between genotype and diet, suggesting that the GR is not required for CR-induced skeletal changes. The lower bone mass in GR-CKO mice, and the further decrease in bone by CR, resulted from suppressed bone formation. Interestingly, treatment with the β-adrenergic receptor antagonist propranolol mildly but selectively improved metrics of cortical bone mass in GR-CKO mice during CR, suggesting interaction between adrenergic and glucocorticoid signaling pathways that affects cortical bone. GR-CKO mice dramatically increased marrow fat under both ad libitum and CR-fed conditions, and surprisingly propranolol treatment was unable to rescue CR-induced marrow fat in either WT or GR-CKO mice. Additionally, serum corticosterone levels were selectively elevated in GR-CKO mice with CR, suggesting the possibility of bone–hypothalamus–pituitary–adrenal crosstalk during metabolic stress. This work highlights the complexities of glucocorticoid and β-adrenergic signaling in stress-induced changes in bone mass, and the importance of GR function in suppressing marrow adipogenesis while maintaining healthy bone mass.

ABSTRACTPhlpp protein phosphatases are abnormally abundant within human osteoarthritic articular chondrocytes and may contribute to the development of osteoarthritis. Mice lacking Phlpp1 were previously shown to be resistant to post‐traumatic osteoarthritis. Here a small molecule with therapeutic properties that inhibits Phlpp1 and Phlpp2 was tested for its ability to slow post‐traumatic OA in mice and to stimulate anabolic pathways in human articular cartilage from OA joints. PTOA was induced in male C57Bl/6 mice by surgically destabilizing the meniscus. Seven weeks after surgery, mice received a single intra‐articular injection of the Phlpp inhibitor NSC117079 or saline. Mechanical allodynia was measured with von Frey assays, mobility was tracked in an open field system, and cartilage damage was assessed histologically. A single intra‐articular injection of the Phlpp inhibitor NSC117079 attenuated mechanical allodynia and slowed articular cartilage degradation in joints with a destabilized meniscus. Animals treated with the Phlpp inhibitor 7 weeks after injury maintained normal activity levels, while those in the control group traveled shorter distances and were less active 3 months after the joint injury. NSC117079 also increased production of cartilage extracellular matrix components (glycosaminoglycans and aggrecan) in over 90% of human articular cartilage explants from OA patients and increased phosphorylation of Phlpp1 substrates (AKT2, ERK1/2, and PKC) in human articular chondrocytes. Our results indicate that Phlpp inhibitor NSC117079 is a novel osteoarthritis disease modifying drug candidate that may have palliative affects. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1487–1497, 2018.