Histochemical assessment on the cellular interplay of vascular endothelial cells and septoclasts during endochondral ossification in mice

This study was aimed to verify the cellular interplay between vascular endothelial cells and surrounding cells in the chondro-osseous junction of murine tibiae. Many CD31-positive endothelial cells accompanied with Dolichos Biflorus Agglutinin lectin-positive septoclasts invaded into the hypertrophic zone of the tibial epiphyseal cartilage. MMP9 immunoreactive cytoplasmic processes of vascular endothelial cells extended into the transverse partitions of cartilage columns. In contrast, septoclasts included several large lysosomes which indicate the incorporation of extracellular matrices despite no immunopositivity for F4/80—a hallmark of macrophage/monocyte lineage. In addition, septoclasts were observed in c-fos-/- mice but not in Rankl-/- mice. Unlike c-fos-/- mice, Rankl-/- mice showed markedly expanded hypertrophic zone and the irregular shape of the chondro-osseous junction. Immunoreactivity of platelet-derived growth factor-bb, which involved in angiogenic roles in the bone, was detected in not only osteoclasts but also septoclasts at the chondro-osseous junction. Therefore, septoclasts appear to assist the synchronous vascular invasion of endothelial cells at the chondro-osseous junction. Vascular endothelial cells adjacent to the chondro-osseous junction possess endomucin but not EphB4, whereas those slightly distant from the chondro-osseous junction were intensely positive for both endomucin and EphB4, while being accompanied with ephrinB2-positive osteoblasts. Taken together, it is likely that vascular endothelial cells adjacent to the chondro-osseous junction would interplay with septoclasts for synchronous invasion into the epiphyseal cartilage, while those slightly distant from the chondro-osseous junction would cooperate with osteoblastic activities presumably by mediating EphB4/ephrinB2. Mini-abstract: Our original article demonstrated that vascular endothelial cells adjacent to the chondro-osseous junction would interplay with septoclasts for synchronous invasion into the epiphyseal cartilage, while those slightly distant from the chondro-osseous junction would cooperate with osteoblastic activities presumably by mediating EphB4/ephrinB2.(A figure that best represents your paper is Fig. 5c)

NF-κB Signaling Regulates Physiological and Pathological Chondrogenesis

The nuclear factor-κB (NF-κB) is a transcription factor that regulates the expression of genes that control cell proliferation and apoptosis, as well as genes that respond to inflammation and immune responses. There are two means of NF-κB activation: the classical pathway, which involves the degradation of the inhibitor of κBα (IκBα), and the alternative pathway, which involves the NF-κB-inducing kinase (NIK, also known as MAP3K14). The mouse growth plate consists of the resting zone, proliferative zone, prehypertrophic zone, and hypertrophic zone. The p65 (RelA), which plays a central role in the classical pathway, is expressed throughout the cartilage layer, from the resting zone to the hypertrophic zone. Inhibiting the classical NF-κB signaling pathway blocks growth hormone (GH) or insulin-like growth factor (IGF-1) signaling, suppresses cell proliferation, and suppresses bone morphogenetic protein 2 (BMP2) expression, thereby promoting apoptosis. Since the production of autoantibodies and inflammatory cytokines, such as tumor necrosis factor-α (TNFα), interleukin (IL)-1β, IL-6, and IL-17, are regulated by the classical pathways and are increased in rheumatoid arthritis (RA), NF-κB inhibitors are used to suppress inflammation and joint destruction in RA models. In osteoarthritis (OA) models, the strength of NF-κB-activation is found to regulate the facilitation or suppression of OA. On the other hand, RelB is involved in the alternative pathway, and is expressed in the periarticular zone during the embryonic period of development. The alternative pathway is involved in the generation of chondrocytes in the proliferative zone during physiological conditions, and in the development of RA and OA during pathological conditions. Thus, NF-κB is an important molecule that controls normal development and the pathological destruction of cartilage.

Local Changes to the Distal Femoral Growth Plate Following Injury in Mice

Injury to the growth plate is associated with growth disturbances, most notably premature cessation of growth. The goal of this study was to identify spatial changes in the structure and composition of the growth plate in response to injury to provide a foundation for developing therapies that minimize the consequences for skeletal development. We used contrast-enhanced microcomputed tomography (CECT) and histological analyses of a murine model of growth plate injury to quantify changes in the cartilaginous and osseous tissue of the growth plate. To distinguish between local and global changes, the growth plate was divided into regions of interest near to and far from the injury site. We noted increased thickness and CECT attenuation (a measure correlated with glycosaminoglycan (GAG) content) near the injury, and increased tissue mineral density (TMD) of bone bridges within the injury site, compared to outside the injury site and contralateral growth plates. Furthermore, we noted disruption of the normal zonal organization of the physis. The height of the hypertrophic zone was increased at the injury site, and the relative height of the proliferative zone was decreased across the entire injured growth plate. These results indicate that growth plate injury leads to localized disruption of cellular activity and of endochondral ossification. These local changes in tissue structure and composition may contribute to the observed retardation in femur growth. In particular, the changes in proliferative and hypertrophic zone heights seen following injury may impact growth and could be targeted when developing therapies for growth plate injury.

Rickets: Historical, Epidemiological, Pathophysiological, and Pathological Perspectives

Rickets was a common metabolic disease of bone a century ago in Europe, North America, and East Asia (mainly due to vitamin D deficiency) but was largely eradicated in growing children by use of cod liver oil and the introduction of vitamin D fortification of milk in the 1930s in the United States. Vitamin D deficiency (VDD) remains the most common form of metabolic bone disease that is entirely preventable and treatable. Historically, rickets has appeared in sporadic epidemics and, despite the introduction of numerous preventive strategies, VDD has remained a global health problem amongst children. Moreover, developed countries such as Canada, Australia, the United Kingdom, and the United States have not been exempt from this. The radiological and histological features of rickets are both distinctive and characteristic and they reflect the underlying pathophysiological issue of decreased mineralization of bone as a result of VDD. The radiological features include 1) metaphyseal cupping and fraying, 2) poor mineralization of epiphyseal centers, 3) irregular and widened epiphyseal plates, 4) increased distance between the end of shaft and epiphyseal center, 5) cortical spurs at right angles to the metaphysis, 6) coarse trabeculation, and 7) periosteal reactions. Fractures may also be evident. The histological features of rickets reflect the failure of cartilage to mineralize and undergo resorption. This results in 1) disordered proliferation of chondrocytes in the hypertrophic zone secondary to a lack of apoptosis, 2) loss of the columnar arrangement of chondrocytes that results in thickening and disorganization of the hypertrophic zone, 3) tongue-like projections of cartilage that extend into the spongiosa, 4) irregularity of the limit between the proliferative and hypertrophic zones, and 5) penetration of blood vessels into the hypertrophic zone. The case of a premature 3-month-old female infant, born in the winter months in the arctic region of Canada who died from a lobar pneumonia with an incidental finding of radiological and pathological evidence of rickets, is presented. The case is used to review the entity of rickets from historical, pathophysiological, radiological, and histological perspectives.

Chondrocyte-Specific Modulation of Cyp27b1 Expression Supports a Role for Local Synthesis of 1,25-Dihydroxyvitamin D3 in Growth Plate Development

The Cyp27b1 enzyme (25-hydroxyvitamin D-1α-hydroxylase) that converts 25-hydroxyvitamin D into the active metabolite, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], is expressed in kidney but also in other cell types such as chondrocytes. This suggests that local production of 1,25(OH)2D3 could play an important role in the differentiation of these cells. To test this hypothesis, we engineered mutant mice that do not express the Cyp27b1 gene in chondrocytes. Inactivation of both alleles of the Cyp27b1 gene led to decreased RANKL expression and reduced osteoclastogenesis, increased width of the hypertrophic zone of the growth plate at embryonic d 15.5, increased bone volume in neonatal long bones, and increased expression of the chondrocytic differentiation markers Indian Hedgehog and PTH/PTHrP receptor. The expression of the angiogenic marker VEGF was decreased, accompanied by decreased platelet/endothelial cell adhesion molecule-1 staining in the neonatal growth plate, suggesting a delay in vascularization. In parallel, we engineered strains of mice overexpressing a Cyp27b1 transgene in chondrocytes by coupling the Cyp27b1 cDNA to the collagen α1(II) promoter. The transgenic mice showed a mirror image phenotype when compared with the tissue-specific inactivation, i.e. a reduction in the width of the hypertrophic zone of the embryonic growth plate, decreased bone volume in neonatal long bones, and inverse expression patterns of chondrocytic differentiation markers. These results support an intracrine role of 1,25(OH)2D3 in endochondral ossification and chondrocyte development in vivo.

Valgus slipped capital femoral epiphysis: Case report and review of the literature

Slipped capital femoral epiphysis (SCFE) usually occurs in children around the time of the growth spurt. There is a shearing force across the epiphysis at the hypertrophic zone allowing the slip. In the vast majority of cases, the slip occurs in the varus direction. Valgus slipped capital femoral epiphysis (SCFE) is an uncommon entity. Although there are a few isolated cases reported in the literature, to date this entity has not been sufficiently reviewed and understood. Such a case is presented and a review of the published literature on this subject is carried out.

The Somatostatin Analog Octreotide Inhibits GH-Stimulated, But Not IGF-I-Stimulated, Bone Growth in Hypophysectomized Rats

IGF-I mediates growth-promoting actions of GH. In the present study we investigated whether the somatostatin analog octreotide blunts the stimulatory effects of GH and/or IGF-I on bone growth in hypophysectomized rats infused for 6 d with vehicle, GH, or IGF-I. We found that octreotide significantly suppressed the GH-induced rise in liver IGF-I mRNA (−27%) and peptide (−32%) and the serum IGF-I level (−26%) and concomitantly inhibited GH-stimulated, but not IGF-I-stimulated, body weight gain (−31%), tibial epiphyseal width (−14%), and bone growth rate (−24%). Furthermore, octreotide significantly reduced the GH-induced increase in the number of IGF-I immunoreactive chondrocytes in all layers (except in the upper hypertrophic zone) of the tibial growth plate cartilage (P < 0.0001 for stem cell and proliferative zone; P < 0.0005 for lower hypertrophic zone). These findings demonstrate that octreotide does not interfere with IGF-I action, but does interfere with local GH-stimulated IGF-I production in the growth plate. Thus, besides inhibiting pituitary GH secretion, octreotide exerts inhibitory peripheral effects on GH-stimulated longitudinal bone growth.