Suppression of mammalian bone growth by membrane transport inhibitors

Roles of Sodium Hydrogen Exchanger (NHE1) and Anion Exchanger (AE2) across Chondrocytes Plasma Membrane during Longitudinal Bone Growth

Mammalian long bone growth occurs through endochondral ossification, majorly regulated by the controlled enlargement of chondrocytes at the growth plate (GP). This study aimed to investigate the roles of Na+/H+ (sodium hydrogen exchanger (NHE1)) and HCO3− (anion exchanger [AE2]) during longitudinal bone growth in mammals. Bones from P10 SpragueDawley rat pups were cultured exvivo in the presence or absence of NHE1 and AE2 inhibitors to determine their effect on long bone growth. Gross morphometry, histomorphometry, and immunohistochemistry were used to assess the bone growth. The results revealed that the culture of the bones in the presence of NHE1 and AE2 inhibitors reduces bone growth significantly (p < 0.05) by approximately 11%. The inhibitor significantly (p < 0.05) reduces bone growth velocity and the length of the hypertrophic chondrocyte zone without any effect on the total GP length. The total GP chondrocyte density was significantly (p < 0.05) reduced, but hypertrophic chondrocyte densities remained constant. NHE1 fluorescence signaling across the GP length was higher than AE2, and their localization was significantly (p < 0.05) inhibited at the hypertrophic chondrocytes zone. The GP lengthening was majorly driven by an increase in the overall GP chondrocyte and hypertrophic chondrocyte densities apart from the regulatory volume phenomenon. This may suggest that NHE1 and AE2 could have a regulatory role in long bone growth.

A simple method based on confocal microscopy and thick sections recognizes seven subphases in growth plate chondrocytes

This manuscript reports a novel procedure to imaging growth plate chondrocytes by using confocal microscopy. The method is based on fixed undecalcified bone samples, in-block staining with eosin, epoxy resin embedding and grinding to obtain thick sections. It is simple, inexpensive and provides three-dimensional images of entire chondrocytes inside their native lacunae. Quantitative analysis of volume, shape and cytoplasm density of chondrocytes at different strata of the growth plate allowed to objectively grade chondrocytes of the growth plate in seven different clusters. These seven categories of chondrocytes were subsequently evaluated by immunohistochemistry of some well-defined molecular landmarks of chondrocyte differentiation. Furthermore, immunohistochemical analysis of proteins responsible for ionic changes and water transport allowing chondrocyte swelling during hypertrophy was also performed. Results obtained indicate that four subphases can be defined in the pre-hypertrophic zone and three subphases in the hypertrophic zone, a fact that raises that chondrocytes of the growth plate are less homogeneous than usually considered when different zones are defined according to subjective cell morphological criteria. Results in the present study provide a technological innovation and gives new insights into the complexity of the process of chondrocyte differentiation in the growth plate.

Postnatal ex vivo rat model for longitudinal bone growth investigations

BACKGROUND

Chondrocytes in the growth plate (GP) undergo increases in volume during different cascades of cell differentiation during longitudinal bone growth. The volume increase is reported to be the most significant variable in understanding the mechanism of long bone growth.

METHODS

Forty-five postnatal Sprague-Dawley rat pups, 7-15 days old were divided into nine age groups (P7-P15). Five pups were allocated to each group. The rats were sacrificed and tibia and metatarsal bones were harvested. Bone lengths were measured after 0, 24, 48, and 72 hours of ex vivo incubation. Histology of bones was carried out, and GP lengths and chondrocyte densities were determined.

RESULTS

There were significant differences in bone length among the age groups after 0 and 72 hours of incubation. Histological sectioning was possible in metatarsal bone from all age groups, and in tibia from 7- to 13-day-old rats. No significant differences in tibia and metatarsal GP lengths were seen among different age groups at 0 and 72 hours of incubation. Significant differences in chondrocyte densities along the epiphyseal GP of the bones between 0 and 72 hours of incubation were observed in most of the age groups.

CONCLUSION

Ex vivo growth of tibia and metatarsal bones of rats aged 7-15 days old is possible, with percentage growth rates of 23.87 ± 0.80% and 40.38 ± 0.95% measured in tibia and metatarsal bone, respectively. Histological sectioning of bones was carried out without the need for decalcification in P7-P13 tibia and P7-P15 metatarsal bone. Increases in chondrocyte density along the GP influence overall bone elongation.

The use of rats and mice as animal models in ex vivo bone growth and development studies

In vivo animal experimentation has been one of the cornerstones of biological and biomedical research, particularly in the field of clinical medicine and pharmaceuticals. The conventional in vivo model system is invariably associated with high production costs and strict ethical considerations. These limitations led to the evolution of an ex vivo model system which partially or completely surmounted some of the constraints faced in an in vivo model system. The ex vivo rodent bone culture system has been used to elucidate the understanding of skeletal physiology and pathophysiology for more than 90 years. This review attempts to provide a brief summary of the historical evolution of the rodent bone culture system with emphasis on the strengths and limitations of the model. It encompasses the frequency of use of rats and mice for ex vivo bone studies, nutritional requirements in ex vivo bone growth and emerging developments and technologies. This compilation of information could assist researchers in the field of regenerative medicine and bone tissue engineering towards a better understanding of skeletal growth and development for application in general clinical medicine.Cite this article: A. A. Abubakar, M. M. Noordin, T. I. Azmi, U. Kaka, M. Y. Loqman. The use of rats and mice as animal models in ex vivo bone growth and development studies. Bone Joint Res 2016;5:610-618. DOI: 10.1302/2046-3758.512.BJR-2016-0102.R2.

Cysteine induces longitudinal bone growth in mice by upregulating IGF-I

Cysteine (Cys) is known to exert various effects, such as antioxidant, antipancreatitic and antidiabetic effects. However, the effects of Cys on longitudinal bone growth have not been elucidate to date. Thus, the aim of the present study was to evaluate the effects of Cys on bone growth. Growth-plate thickness and bone parameters, such as bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), connectivity density (Conn.D) and total porosity were analyzed by means of micro-computed tomography (μCT). The levels of serum insulin-like growth factor-I (IGF-I) were measured by enzyme-linked immunosorbent assay (ELISA). Hepatic IGF-I mRNA expression was analyzed by quantitative polymerase chain reaction (qPCR). The phosphorylation of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 5 (STAT5) was investigated by western blot analysis. Our results revealed that Cys increased IGF-I mRNA expression in HepG2 cells. The thickness of the growth plates was increased following treatment with Cys. Moreover, BV/TV, Tb.Th, TbN, Conn.D and total porosity were improved following treatment with Cys. Hepatic IGF-I mRNA expression and serum IGF-I levels were increased by Cys. The levels of phosphorylated JAK2 and STAT5 were elevated by Cys. The findings of our study indicate that Cys increases the thickness of growth plates through the upregulation of IGF-I, which results from the phosphorylation of JAK2-STAT5. Thus, our data suggest that Cys may have potential for use as a growth-promoting agent.

Cartilage to bone transitions in health and disease

Aberrant redeployment of the 'transient' events responsible for bone development and postnatal longitudinal growth has been reported in some diseases in what is otherwise inherently 'stable' cartilage. Lessons may be learnt from the molecular mechanisms underpinning transient chondrocyte differentiation and function, and their application may better identify disease aetiology. Here, we review the current evidence supporting this possibility. We firstly outline endochondral ossification and the cellular and physiological mechanisms by which it is controlled in the postnatal growth plate. We then compare the biology of these transient cartilaginous structures to the inherently stable articular cartilage. Finally, we highlight specific scenarios in which the redeployment of these embryonic processes may contribute to disease development, with the foresight that deciphering those mechanisms regulating pathological changes and loss of cartilage stability will aid future research into effective disease-modifying therapies.