RESUMEN

The cranial base is formed by endochondral ossification and functions as a driver of anteroposterior cranial elongation and overall craniofacial growth. The cranial base contains the synchondroses that are composed of opposite-facing layers of resting, proliferating and hypertrophic chondrocytes with unique developmental origins, both in the neural crest and mesoderm. In humans, premature ossification of the synchondroses causes midfacial hypoplasia, which commonly presents in patients with syndromic craniosynostoses and skeletal Class III malocclusion. Major signaling pathways and transcription factors that regulate the long bone growth plate-PTHrP-Ihh, FGF, Wnt, BMP signaling and Runx2-are also involved in the cranial base synchondrosis. Here, we provide an updated overview of the cranial base synchondrosis and the cell population within, as well as its molecular regulation, and further discuss future research opportunities to understand the unique function of this craniofacial skeletal structure.

Asunto(s)

RESUMEN

The cranial base contains a special type of growth plate termed the synchondrosis, which functions as the growth center of the skull. The synchondrosis is composed of bidirectional opposite-facing layers of resting, proliferating, and hypertrophic chondrocytes, and lacks the secondary ossification center. In long bones, the resting zone of the epiphyseal growth plate houses a population of parathyroid hormone-related protein (PTHrP)-expressing chondrocytes that contribute to the formation of columnar chondrocytes. Whether PTHrP+ chondrocytes in the synchondrosis possess similar functions remains undefined. Using Pthrp-mCherry knock-in mice, we found that PTHrP+ chondrocytes predominantly occupied the lateral wedge-shaped area of the synchondrosis, unlike those in the femoral growth plate that reside in the resting zone within the epiphysis. In vivo cell-lineage analyses using a tamoxifen-inducible Pthrp-creER line revealed that PTHrP+ chondrocytes failed to establish columnar chondrocytes in the synchondrosis. Therefore, PTHrP+ chondrocytes in the synchondrosis do not possess column-forming capabilities, unlike those in the resting zone of the long bone growth plate. These findings support the importance of the secondary ossification center within the long bone epiphysis in establishing the stem cell niche for PTHrP+ chondrocytes, the absence of which may explain the lack of column-forming capabilities of PTHrP+ chondrocytes in the cranial base synchondrosis.

Asunto(s)

RESUMEN

OBJECTIVE: This study aimed to determine the effect of C-type natriuretic peptide (CNP) overexpression on craniofacial growth during the pubertal growth period in mice. DESIGN: Six-week-old C57BL/6 mice were injected with pLIVE-Empty vectors (Control mice) and pLIVE-NPPC vectors (CNP mice) using the hydrodynamic method. Morphological analyses were performed at the age of 12 weeks. RESULTS: Micro-computed tomography (µCT) images showed significant (p < 0.05) hyperplasia in the maxilla along the sagittal plane (CNP mice: 13.754 mm, Control mice: 13.215 mm). Further, the images revealed significant bone overgrowth in the sagittal direction in the sphenoid (CNP mice: 6.936 mm, Control mice: 6.411 mm) and occipital (CNP mice: 4.051 mm, Control mice: 3.784 mm) bones in the CNP mice compared with that in the Control mice. Compared with SAP-Nppc-Tg mice in previous studies, although there was no effect on nose length and nasal bone length, the effect was sufficient to improve craniofacial hypogrowth. Furthermore, CNP promoted sagittal cranial growth by increasing the thickness of the spheno-occipital synchondrosis in organ cultures and nasal septal cartilage in micromass cultures, which were derived from 6-week-old mice. CONCLUSIONS: We have previously shown that the elevated blood levels of CNP from the neonatal period affect midfacial skeletogenesis by promoting endochondral ossification using mice (SAP-Nppc-Tg mice). The overexpression of CNP, even in 6-weeks-old mice, promoted growth in the sagittal direction within the maxillary region. These findings indicate the therapeutic potential of CNP for the treatment of midfacial hypoplasia during the pubertal growth spurt.

Asunto(s)

RESUMEN

Achondroplasia is the most common genetic form of human dwarfism, characterized by midfacial hypoplasia resulting in occlusal abnormality and foramen magnum stenosis, leading to serious neurologic complications and hydrocephalus. Currently, surgery is the only way to manage jaw deformity, neurologic complications, and hydrocephalus in patients with achondroplasia. We previously showed that C-type natriuretic peptide (CNP) is a potent stimulator of endochondral bone growth of long bones and vertebrae and is also a potent stimulator in the craniofacial region, which is crucial for midfacial skeletogenesis. In this study, we analyzed craniofacial morphology in a mouse model of achondroplasia, in which fibroblast growth factor receptor 3 (FGFR3) is specifically activated in cartilage ( Fgfr3ach mice), and investigated the mechanisms of jaw deformities caused by this mutation. Furthermore, we analyzed the effect of CNP on the maxillofacial area in these animals. Fgfr3ach mice exhibited midfacial hypoplasia, especially in the sagittal direction, caused by impaired endochondral ossification in craniofacial cartilage and by premature closure of the spheno-occipital synchondrosis, an important growth center in craniomaxillofacial skeletogenesis. We crossed Fgfr3ach mice with transgenic mice in which CNP is expressed in the liver under the control of the human serum amyloid-P component promoter, resulting in elevated levels of circulatory CNP ( Fgfr3ach/SAP-Nppc-Tg mice). In the progeny, midfacial hypoplasia in the sagittal direction observed in Fgfr3ach mice was improved significantly by restoring the thickness of synchondrosis and promoting proliferation of chondrocytes in the craniofacial cartilage. In addition, the foramen magnum stenosis observed in Fgfr3ach mice was significantly ameliorated in Fgfr3ach/SAP-Nppc-Tg mice due to enhanced endochondral bone growth of the anterior intraoccipital synchondrosis. These results clearly demonstrate the therapeutic potential of CNP for treatment of midfacial hypoplasia and foramen magnum stenosis in achondroplasia.

Asunto(s)

RESUMEN

Objective To establish the technique of biphasic seeding of articular chondrocyte s in vitro for cartilage engineering in u sing a self designed biological gel a nd the three-dimensional scaffold a nd observe the efficiency of cartilage regeneration in vitro-tissue engin eered articular cartilage from cell scaffold complex.Methods The articular chondrocytes were iso lated enzymatically from the epiphyseal cartilage of young rabbits,and were then plated i nto the tissue culture flasks and were cultivated.The first passage ar-ticular chondrocytes were collecte d and mixed fully with the self-made l iquid biological gel-matrix at appr oxi-mately 2.5?10 7 cells /ml to form cell-gel fluid.The cell-gel fluid was dropped into the p orous CPPf /PLLA(calcium polyphosphate fiber /poly -L -lactic acid)scaffold,and a cell-gel-scaffold c omplex was formed after being solidified.The complexes were cultivated for 4weeks.The changes of complexes in morphology and synthesis of collagen typeⅡandⅠand aggregates were investigated under the gross and the phase and light microscope.The GAG sulfate content in complexes was quantitatively mea sured by the modified dimethyl-methylene blue method.Results1)After feeded,the porous CPPf /PLLA s caffolds were completely filled with the liquid chondrocyte-gel and the chondrocyte-gel-scaffold comp lexes were well formed by solidification.During the cultivation,the complex es could keep its original shape and m aintain the stable homogeneous three-dimensional distribution of chondrocytes in themselves without cell falling.In the same time,the com-plexes were gradually increasing th e consistency with the elasticity an d lubrication surface.2)The chondro-genesis began in the periphery area a nd extended to the central area of the complexes with the passage of cultivation period.After the 2nd we ek,the complexes were gradually reorganized into the mature engineered cartilage with typical cartilaginous histological structure,with ric h typeⅡcollagen and the strong typical het-erochromia to toluidine blue,but wi th gradually fading negative immunological stain of collagen typeⅠ.Meantime,the scaffold was graduall y de-graded in the complexes.The average content of GAG sulfate in the enginee red cartilages at 4th week was(15.70?2.00)mg /g(wet weight ),and was over 30%of the natural articular cartila ge.Conclusion The technique of chondrocytes biphasic seeding for three-dimensional scaffold has advantages of simple manipulation,fix ing cell stably in the scaffold,main-taining the original shape of the com plexes and the stable homogeneous th ree-dimensional distribution of chondrocytes in the scaffold,and ad vancing the regeneration and matura tion of tissue-engineered articula r cartilage.[