Relationship between the chondrocyte maturation cycle and the endochondral ossification in the diaphyseal and epiphyseal ossification centers

Effects of pseudoephedrine on rat fetal bone development: evaluation by three different methods

Pseudoephedrine (PSE) is an agent that is contained in common cold medications. The agent, which is used to treat cold and cough, is the fourth most prescribed drug group in some countries. During pregnancy, expectant mothers use PSE for colds and other reasons. One out of every four expectant mothers use PSE alone or in combination with other medicines for various reasons. This study was aimed to investigate effects of PSE on long bones development in rat during fetal growth. Pregnant rats were divided into five groups: control and four experimental groups (25 mg/kg, 50 mg/kg, 100 mg/kg, 200 mg/kg PSE). Between 1 and 20 days of pregnancy, PSE was given to them by gavage. Weights and heights of fetuses isolated by cesarean on the 21st day were measured. Ossification of femur and humerus was examined by three different methods mentioned earlier. Depending on the dose increase, all morphometric data, ossification rate and bone length of the fetuses were decreased. Besides, it was determined that the amount of Calcium in the bone tissue decreased in the analyzes made with SEM-EDX Analysis. The data obtained from this study reveal that the use of PSE during pregnancy disrupts the existing balance in the bone and negatively affects ossification due to the dose increase. In conclusion, we present descriptive and novel data on the effects of PSE use during pregnancy on the bone development of rat fetal long bones.

Effects of Development on Bone Mineral Density and Mechanical Properties in the Aquatic Frog, Xenopus Laevis, and a Terrestrial Frog, Lithobates Catesbianus

The limb bones of vertebrates have a critical role in supporting the weight of the body and transmitting forces that power locomotion. The loads that limb bones experience can vary in association with a range of factors, including locomotor environment or developmental stage. Limbed vertebrates that are habitually found in environments with low locomotor loads (e.g., water) might be predicted to also exhibit limb bones with less elevated mechanical properties, such as yield stiffness and yield stress. Frogs provide a distinctive case, in which these ideas can be tested as they experience changes in both locomotor style and habitat as they develop. However, while many frog taxa shift from aquatic to terrestrial habitats as they metamorphose, some lineages, such as pipids, maintain an aquatic lifestyle even after metamorphosis, providing a comparative framework for the effects of habitat shifts on developing limbs in vertebrates. This study compares the material composition and mechanical properties of the femur between frog species that are aquatic specialists (Xenopus laevis) vs generalists that spend considerable time both on land and in water (Lithobates catesbeianus) as they transition from metamorphic tadpoles to fully grown adults. MicroCT scanning was used to determine changes in bone density related to developmental stage and hindlimb use during swimming. Microindentation was then used to collect hardness values from the cortical bone of each femur, which was used to evaluate bone material properties. We found that aquatic frogs had less overall bone mineral density (BMD) than terrestrial frogs and that BMD was more elevated in the cortical region of the diaphysis than trabeculae and distal and proximal epiphyses. Despite its less elevated BMD, bone mechanical properties were not significantly different in aquatic specialist X. laevis than in more terrestrial L. catesbeianus. Our results suggest that the limb bones of aquatic frogs may experience compensatory effects through development to offset their lower BMD. Furthermore, changes in bone density and material properties across development may help to explain some of the differences in locomotor performance found between aquatic and terrestrial metamorphic frogs, providing insight into how environmental factors might correlate with bone ossification.

Exogenous growth hormone functionally alleviates glucocorticoid-induced longitudinal bone growth retardation in male rats by activating the Ihh/PTHrP signaling pathway

Glucocorticoid (GC)-induced longitudinal bone growth retardation is a common and severe adverse effect in pediatric patients receiving GC immunosuppressive therapy. Molecular mechanisms underlying GC-induced growth inhibition are unclear. GC withdrawal following short-term high-dose use is common, including in the immediate post-transplant period. However, whether skeleton growth recovery is sufficient or whether growth-promoting therapy is required following GC withdrawal is unknown. The aim of this study was to investigate the effect of exogenous growth hormone (GH) on growth plate impairment in GC-induced longitudinal bone growth retardation. Here, apoptotic chondrocytes in the hypertrophic layer of growth plates increased whereas Indian Hedgehog (Ihh) and Parathyroid Hormone Related Peptide (PTHrP) protein levels in the growth plate decreased following GC exposure. The hypertrophic zone of the growth plate expanded following GC withdrawal. Subcutaneously injected GH penetrated the growth plate and modified its organization in rats following GC withdrawal. Ihh and PTHrP expression in GC-induced apoptotic chondrocytes decreased in vitro. GH promoted chondrocyte proliferation by activating Ihh/PTHrP signaling. Downregulating Ihh using specific siRNAs increased chondrocyte apoptosis and inhibited PTHrP, Sox9, and type II collagen (Col2a1) protein expression. GH inhibited apoptosis of Ihh-deficient growth plate chondrocytes by upregulating PTHrP, Sox9, and Col2a1 expression. Thus, reversal of the effect of GC on growth plate impairment following its withdrawal is insufficient, and exogenous GH provides growth plate chondral protection and improved longitudinal growth following GC withdrawal by acting on the Ihh/PTHrP pathway.

Initiation and progression of dental-stimulated temporomandibular joints osteoarthritis

Temporomandibular joint (TMJ), a site that is often impacted by osteoarthritis (OA), is biomechanically linked with dental occlusion. Tissue responses in TMJ condyle to biomechanical stimulation could be investigated by intervention of the dental occlusion in animals. Unilateral anterior crossbite, an experimental malocclusion, has been demonstrated to induce TMJ-OA lesions, showing primarily as enhanced cartilage calcification and subchondral cortical bone formation at the osteochondral interface, causing the osteochondral interface thickening and stiffening. The changed interface would worsen the local biomechanical environment. At the cartilage side, the matrix degenerates. In the case of insufficient restoration of the matrix, the cells in the deep zone flow into the ones undergoing autophagy, apoptosis, and terminal differentiation while the cells in the superficial zone are promoted to differentiate to supply the loss of the deep zone cells. At the meantime, the bone marrow stromal cells are stimulated to bone formation in the subchondral cortical region which is uncoupled with the sites of the osteoclast-mediated resorption process that is predominantly observed at the subchondral trabecular bone region. Overall, the thickening and stiffening osteochondral interface, due greatly to the enhanced endochondral ossification in deep zone cartilage, should be a central pathological process that links with cartilage decay and subchondral bone remodelling in OA joints. The residual chondrocytes locating in the cartilage superficial zone have the progenitor-like qualities that can proliferate, and also differentiate into the deep zone chondrocytes, thus should be critical in progression and rehabilitation of TMJ-OA.

Craniofacial and Long Bone Development in the Context of Distraction Osteogenesis

BACKGROUND

Bone retains regenerative potential into adulthood, and surgeons harness this plasticity during distraction osteogenesis. The underlying biology governing bone development, repair, and regeneration is divergent between the craniofacial and appendicular skeleton. Each type of bone formation is characterized by unique molecular signaling and cellular behavior. Recent discoveries have elucidated the cellular and genetic processes underlying skeletal development and regeneration, providing an opportunity to couple biological and clinical knowledge to improve patient care.

METHODS

A comprehensive literature review of basic and clinical literature regarding craniofacial and long bone development, regeneration, and distraction osteogenesis was performed.

RESULTS

The current understanding in craniofacial and long bone development and regeneration is discussed, and clinical considerations for the respective distraction osteogenesis procedures are presented.

CONCLUSIONS

Distraction osteogenesis is a powerful tool to regenerate bone and thus address a number of craniofacial and appendicular skeletal deficiencies. The molecular mechanisms underlying bone regeneration, however, remain elusive. Recent work has determined that embryologic morphogen gradients constitute important signals during regeneration. In addition, striking discoveries have illuminated the cellular processes underlying mandibular regeneration during distraction osteogenesis, showing that skeletal stem cells reactivate embryologic neural crest transcriptomic processes to carry out bone formation during regeneration. Furthermore, innovative adjuvant therapies to complement distraction osteogenesis use biological processes active in embryogenesis and regeneration. Additional research is needed to further characterize the underlying cellular mechanisms responsible for improved bone formation through adjuvant therapies and the role skeletal stem cells play during regeneration.

New morphological evidence of the 'fate' of growth plate hypertrophic chondrocytes in the general context of endochondral ossification

The 'fate' of growth plate hypertrophic chondrocytes has been long debated with two opposing theories: cell apoptosis or survival with transformation into osteogenic cells. This study was carried out on the proximal tibial growth plate of rabbits using light microscopy, scanning and transmission electron microscopy. We focused particularly on the orientation of the specimens included in order to define the mineral deposition and the vascular invasion lines and obtain histological and ultrastructural images at the corresponding height of the plate. Chondrocyte morphology transformation through the maturation process (characterized by vesicles and then large cytoplasmic lacunae before condensation, fragmentation and disappearance of the nuclear chromatin) did not correspond to that observed in the 'in vitro' apoptosis models. These findings rather suggested the passage of free water from the cartilage matrix into a still live cell (swelling). The level of these changes suggested a close relationship with the mineral deposition line. Furthermore, the study provided evidence that the metaphyseal capillaries could advance inside the columns of stacked hypertrophic chondrocytes (delimited by the intercolumnar septa) without the need for calcified matrix resorption because the thin transverse septa between the stacked chondrocyte (below the mineral deposition line) were not calcified. The zonal distribution of cell types (hypertrophic chondrocytes, osteoblasts, osteoclasts and macrophages) did not reveal osteoclasts or chondroclasts at this level. Morphological and morphometric analysis recorded globular masses of an amorphous, necrotic material in a zone 0-70 μm below the vascular invasion line occasionally surrounded by a membrane (indicated as 'hypertrophic chondrocyte ghosts'). These masses and the same material not bound by a membrane were surrounded by a large number of macrophages and other blood cell precursors, suggesting this could be the cause of macrophage recall and activation. The most recent hypotheses based on genetic and lineage tracing studies stating that hypertrophic chondrocytes can survive and transform into osteoblasts and osteocytes (trans-differentiation) were not confirmed by the ultrastructural morphology or by the zonal comparative counting and distribution of cell types below the vascular invasion line.

Long bone human anlage longitudinal and circumferential growth in the fetal period and comparison with the growth plate cartilage of the postnatal age

The patterns of longitudinal and peripheral growth were analyzed in human autopod cartilage anlagen (fetal developmental stage 20th-22nd week) through morphometric assessment of chondrocyte parameter size, shape, alignment and orientation between peripheral and central sectors of the anlage transition zone defined by primary ossification center and the epiphyseal basis. The aim was to correlate the chondrocyte dynamics with the longitudinal and peripheral growth. A further comparison was carried out between the corresponding sectors of the postnatal (3-5 months old) growth plate cartilage documenting: (1) the different chondrocyte framework and the new peripheral mechanism; (2) the opposite direction of fetal periosteal ossification versus the Lacroix bone bark. Measurement of multiple parameters (% lac area, % total matrix area, total lac density and mean single lac area), which characterize the cartilage Anlage growth, suggested the following correlations with chondrocyte duplication rate: (a) slow duplication rate ≈ coupled, intralacunar chondrocytes (in central epiphysis); (b) repeated/frequent cell duplications ≈ clusters (in the basal epiphyseal layer); (c) clusters of chondrocytes before becoming hypertrophic were stacked up on the top of each other (both in the Anlage transition zone or in the columns of metaphyseal growth plate); (d) enhanced osteoclastic resorption of the Lacroix bone bark lower end, extended to the more external metaphyseal trabeculae counterbalancing the discrepancy between the epiphyseal and the diaphyseal circumferential growth.

The missing segment of the autopod 1st ray: new insights from a morphometric study of the human hand

Whether the 1st segment of the human autopod 1st ray is a 'true' metapodial with loss of the proximal or mid phalanx or the original basal phalanx with loss of the metacarpal has been a long-lasting discussion. The actual knowledge of the developmental pattern of upper autopod segments at a fetal age of 20-22 weeks, combined with X-ray morphometry of normal long bones of the hand in the growing ages, was used for analysis of the parameters, percentage length, position of epiphyseal ossification centers and proximal/distal growth rate. The symmetric growth pattern in the fetal anlagen changed to unidirectional in the postnatal development in relation to epiphyseal ossification formation. The percentage length assessment, the distribution of the epiphyseal ossification centers, and differential proximal/distal growth rate among the growing hand segments supported homology of most proximal segment of the thumb with the 2nd-5th proximal phalanges and that of the proximal phalanx of the thumb with the 2nd-5th mid phalanges in the same hand. Published case reports of either metanalysis of 'triphalangeal thumb' and 'proximal/distal epiphyseal ossification centers' were used to support the applied morphometric methodology; in particular, the latter did not give evidence of growth pattern inversion of the proximal segment of the thumb. The presented data support the hypothesis that during evolution, the lost segment of the autopod 1st ray is the metacarpal.

Study of Endochondral Ossification in Human Fetalcartilage Anlagen of Metacarpals: Comparative Morphology of Mineral Deposition in Cartilage and in the Periosteal Bone Matrix

The progression of mineral phase deposition in hypertrophic cartilage and periosteal bone matrix was studied in human metacarpals primary ossification centers before vascular invasion began. This study aimed to provide a morphologic/morphometric comparative analysis of the calcification process in cartilage and periosteal osteoid used as models of endochondral ossification. Thin, sequential sections from the same paraffin inclusions of metacarpal anlagen (gestational age between the 20th and 22nd weeks) were examined with light microscopy and scanning electron microscopy, either stained or heat-deproteinated. This process enabled the analysis of corresponding fields using the different methods. From the initial CaPO₄ nucleation in cartilage matrix, calcification progressed increasing the size of focal, globular, randomly distributed deposits (size range 0.5-5 µm), followed by aggregation into polycyclic clusters and finally forming a dense, compact mass of calcified cartilage. At the same time, the early osteoid calcification was characterized by a fine granular pattern (size range 0.1-0.5 µm), which was soon compacted in the layer of the first periosteal lamella. Scanning electron microscopy of heat-deproteinated sections revealed a rod-like hydroxyapatite crystallite pattern, with only size differences between the early globular deposits of the two calcifying matrices. The morphology of the early calcium deposits was similar in both cartilage and osteoid, with variations in size and density only. However, integration of the reported data with the actual hypotheses of the mechanisms of Ca concentration suggested that ion transport was linked to the progression of the chondrocyte maturation cycle (with recall of H₂ O from the matrix) in cartilage, while ions transport was an active process through the cell membrane in osteoid. Other considered factors were the collagen type specificity and the matrix fibrillar texture. Anat Rec, 301:571-580, 2018. © 2017 Wiley Periodicals, Inc.