Estrogen deficiency induces bone loss by increasing bone resorption, in part through upregulation of receptor activator of nuclear factor-kappa B ligand (RANKL). RANKL is secreted by osteoblasts... Show moreEstrogen deficiency induces bone loss by increasing bone resorption, in part through upregulation of receptor activator of nuclear factor-kappa B ligand (RANKL). RANKL is secreted by osteoblasts and osteocytes, but more recently bone marrow (pre)adipocytes have also been shown to express RANKL. Estrogen deficiency increases bone marrow adipose tissue (BMAT). The aim of this study was to determine the effect of ovariectomy (OVX) on RANKL protein expression by bone marrow adipocytes in C3H/HeJ mice. Fourteen-week-old female C3H/HeJ mice (n = 20) were randomized to sham surgery (Sham) or OVX. After 4 wk animals were euthanized. BMAT volume fraction (BMAT volume/marrow volume) was quantified by polyoxometalate-based contrast-enhanced nano-computed tomography. The percentage of RANKL-positive bone marrow adipocytes (RANKL-positive bone marrow adipocytes/total adipocytes) and the percentage of RANKL-positive osteoblasts covering the bone surface (bone surface covered in RANKL-positive osteoblasts/total bone surface) were quantified in the distal metaphysis of immunohistochemically stained sections of the left femur. The effects of OVX were analyzed by Student's t test or Mann-Whitney U test. RANKL was detected in osteoblasts, osteocytes, and bone marrow adipocytes. OVX significantly increased mean percentage of RANKL-positive bone marrow adipocytes [mean (SD): Sham 42 (18)%; OVX 64 (12)%; P = 0.029] as well as BMAT volume/marrow volume [median (interquartile range): Sham 1.4 (4.9)%; OVX 7.2 (7.3)%; P = 0.008] compared with Sham. We show that OVX increased both the percentage of RANKL-positive bone marrow adipocytes and the total BMAT volume fraction in C3H/HeJ mice. Therefore, RANKL produced by bone marrow adipocytes could be an important contributor to OVX-induced bone loss in C3H/HeJ mice. Show less
Sanchez Duffhues, G.; Mikkers, H.; Jong, D. de; Szuhai, K.; Vries, T.J. de; Freund, C.; ... ; Dijke, P. ten 2019
Fibrodysplasia ossificans progressiva (FOP) is a very rare devastating heterotopic ossification disorder, classically caused by a heterozygous single point mutation (c.617G>A) in the ACVR1gene,... Show moreFibrodysplasia ossificans progressiva (FOP) is a very rare devastating heterotopic ossification disorder, classically caused by a heterozygous single point mutation (c.617G>A) in the ACVR1gene, encoding the Bone morphogenetic protein (BMP) type I receptor, also termed activin receptor-like kinase (ALK)2. FOP patients develop heterotopic ossification episodically in response to inflammatory insults, thereby compromising tissue sampling and the development of in vitro surrogate models for FOP. Here we describe the generation and characterization of a control and a classical FOP induced pluripotent stem cell (iPSC) line derived from periodontal ligament fibroblast cells using Sendai virus vectors. Show less
Purpose of ReviewOsteocytes are responsible for mechanosensing and mechanotransduction in bone and play a crucial role in bone homeostasis. They are embedded in a calcified collagenous matrix and... Show morePurpose of ReviewOsteocytes are responsible for mechanosensing and mechanotransduction in bone and play a crucial role in bone homeostasis. They are embedded in a calcified collagenous matrix and connected with each other through the lacuno-canalicular network. Due to this specific native environment, it is a challenge to isolate primary osteocytes without losing their specific characteristics in vitro. This review summarizes the commonly used and recently established models to study the function of osteocytes in vitro.Recent FindingsOsteocytes are mostly studied in monolayer culture, but recently, 3D models of osteocyte-like cells and primary osteocytes in vitro have been established as well. These models mimic the native environment of osteocytes and show superior osteocyte morphology and behavior, enabling the development of human disease models.SummaryOsteocyte-like cell lines as well as primary osteocytes isolated from bone are widely used to study the role of osteocytes in bone homeostasis. Both cells lines and primary cells are cultured in 2D-monolayer and 3D-models. The use of these models and their advantages and shortcomings are discussed in this review. Show less
Beekman, K.M.; Veldhuis-Vlug, A.G.; Veen, A. van der; Heijer, M. den; Maas, M.; Kerckhofs, G.; ... ; Bravenboer, N. 2019
Context: Gaucher disease (GD) is a lysosomal storage disorder characterized by abundant presence of macrophages. Bone complications and low bone density are believed to arise from enhanced bone... Show moreContext: Gaucher disease (GD) is a lysosomal storage disorder characterized by abundant presence of macrophages. Bone complications and low bone density are believed to arise from enhanced bone resorption mediated through macrophage-derived factors. Objective: The objective of the study was to investigate the relationship between bone turnover and bone complications in GD. Design: This was a retrospective cohort study and review of the literature. Patients: Forty adult type I GD patients were included in the study. Outcome Measures: Levels of the bone-resorption marker, type 1 collagen C-terminal telopeptide, and two bone-formation markers, N-terminal propeptide of type 1 procollagen and osteocalcin, were investigated in relation to clinical bone disease, measures of overall disease severity, and imaging data representing bone marrow infiltration. Results: Osteocalcin was decreased in 50% of our patients (median 0.35 nmol/liter, normal 0.4-4.0), indicating a decrease of bone formation. Type 1 collagen C-terminal telopeptide and N-terminal propeptide of type 1 procollagen were within the normal range for most patients. Osteocalcin concentration was negatively correlated to measures of overall disease severity and positively correlated with imaging data (correlation coefficient 0.423; P = 0.025), suggesting a relation with disease severity. A review of the literature revealed variable outcomes on bone resorption markers but more consistent abnormalities in bone formation markers. Two of three reports conclude that bone-formation parameters increase in response to enzyme therapy, but none describes an effect on bone-resorption markers. Conclusions: In contrast to earlier hypotheses, we propose that in GD patients, primarily a decrease in bone formation causes an imbalance in bone remodeling. (J Clin Endocrinol Metab 96: 2194-2205, 2011) Show less
BACKGROUND & AIMS: Crohn's disease (CD) is associated with an increased prevalence of osteoporosis, but the pathogenesis of this bone loss is only partly understood. We assessed bone structure... Show moreBACKGROUND & AIMS: Crohn's disease (CD) is associated with an increased prevalence of osteoporosis, but the pathogenesis of this bone loss is only partly understood. We assessed bone structure and remodeling at the tissue level in patients with quiescent CD. We also investigated the roles of osteocyte density and apoptosis in CD-associated bone loss. METHODS: The study included 23 patients with quiescent CD; this was a subgroup of patients from a large randomized, double-blind, placebo-controlled, multicenter trial. We obtained transiliac bone biopsy samples and performed histomorphometric analysis. Results were compared with data from age-and sex-matched healthy individuals (controls). RESULTS: Trabecular bone volume was decreased among patients with CD compared with controls (18.90% vs 25.49%; P < .001). The low bone volume was characterized by decreased trabecular thickness (120.61 vs 151.42 mu m; P < .01). Bone formation and resorption were reduced, as indicated by a decreased mineral apposition rate (0.671 vs 0.746 mu m/day; P < .01) and a low osteoclast number and surface area compared with controls and published values, respectively. In trabecular bone of patients with CD, osteocyte density and apoptosis were normal. The percentage of empty lacunae among patients was higher than that of published values in controls. CONCLUSIONS: In adult patients with quiescent CD, bone histomorphometric analysis revealed a reduction in bone mass that was characterized by trabecular thinning. The CD-associated bone loss was caused by reduced bone formation, possibly as a consequence of decreased osteocyte viability in the patients' past. Show less
