Biology subjects

Uchibe, K.

Publications and source records attributed to Uchibe, K..

3 recordsLinked to original sources

bioRxiv2025

Functional impact of pathogenic Runt domain mutations in Runx2 in vivo: Insights into the skeletal and dental anomalies of cleidocranial dysplasia

Runt-related transcription factor 2 (RUNX2) is essential for skeletogenesis, and mutations in its gene cause cleidocranial dysplasia (CCD), an autosomal dominant skeletal disorder. The evolutionarily conserved 128-amino acid Runt homology domain (RHD) of human RUNX2 is essential for DNA binding and heterodimerization, and serves as a mutation hotspot associated with severe CCD phenotypes. To elucidate the functional impact of pathogenic RHD mutations in vivo, we generated two novel mouse lines: one carrying a missense mutation, c.695G>A (p.R232Q) (Runx2m/+), corresponding to the human RUNX2 c.674G>A (p.R225Q), and the other harboring a frameshift mutation, c.697_698delGA (p.E233TfsTer9) (Runx2112/+), causing a premature stop codon. Homozygous Runx2m/mand Runx2112/112 mice lacked membranous ossification, whereas heterozygous Runx2m/+ and Runx2112/+ mice displayed typical CCD-like skeletal features, including an open anterior fontanelle and clavicle hypoplasia. Unexpectedly, heterozygotes carrying pathogenic mutations in RHD developed an accessory root-like protrusion at the furcation of three-rooted maxillary first molars, representing a previously unrecognized dental phenotype during root development. Dual luciferase assays revealed impaired transactivation of the p.R232Q mutant Runx2 on the osteocalcin enhancer/promoter. Wild-type Runx2 was robustly expressed in osteoblasts and hypertrophic chondrocytes during bone formation, but the mutant Runx2 exhibited reduced expression in hypertrophic chondrocytes and partially impaired nuclear localization, resulting in arrested osteoblast and chondrocyte maturation. Our mutant mouse model provides a valuable in vivo platform to study CCD pathogenesis, mechanisms of tooth root furcation, and therapeutic interventions targeting dysfunctional RHD.

genetics↗

bioRxiv2024

Retinoid-impregnated nanoparticles enable control of bone growth by site-specific modulation of endochondral ossification in mice

Growth-plate (GP) injures in limbs and other sites can impair GP function and cause deceleration of bone growth, leading to progressive bone lengthening imbalance, deformities and/or physical discomfort, decreased motion and pain. At present, surgical interventions are the only means available to correct these conditions by suppressing the GP activity in the unaffected limb and/or other bones in the ipsilateral region. Here, we aimed to develop a pharmacologic treatment of GP growth imbalance that involves local application of nanoparticles-based controlled release of a selective retinoic acid nuclear receptor gamma (RAR{gamma}) agonist drug. When RAR{gamma} agonist-loaded nanoparticles were implanted near the medial and lateral sides of proximal tibial growth plate in juvenile C57BL/6j mice, the GP underwent involution and closure. Overall tibia length was shortened compared to the contralateral element implanted with drug-free control nanoparticles. Importantly, when the RAR{gamma} agonist nanoparticles were implanted on the lateral side only, the adjacent epiphysis tilted toward the lateral site, leading to apical angulation of the tibia. In contrast to the local selectivity of these responses, systemic administration of RAR{gamma} agonists led to GP closure at many sites, inhibiting skeletal growth over time. Agonists for RAR and RAR{beta} elicited no obvious responses over parallel regimens. Our findings provide novel evidence that RAR{gamma} agonist-loaded nanoparticles can control activity, function and directionality of a targeted GP, offering a potential and clinically-relevant alternative or supplementation to surgical correction of limb length discrepancy and angular deformities. Lay summaryGrowth-plates (physes), which are cartilage tissues near the ends of bones, support normal bone growth in children. Growth plate injures in limbs and other sites can impair growth plate function, leading to inhibited or imbalanced bone growth, skeletal deformities, decreased motion, discomfort or pain. At present, surgical interventions are the only means available to correct these conditions. Here, we aimed to develop a pharmacologic treatment for bone growth imbalance. Nanoparticles loaded with a selective agonist for the retinoic acid nuclear receptor gamma were prepared and implanted near the tibial growth plate in juvenile mice. The growth plate underwent involution and closure, and overall tibia length was shortened compared to the contralateral element implanted with drug-free control nanoparticles. Importantly, when the same drug nanoparticles were implanted in only one side of the tibia, the tibia was tilted toward the injection site. Our findings provide novel evidence that retinoic acid receptor gamma agonist-loaded nanoparticles can control activity, function and directionality of a targeted growth plate, offering a potential and clinically-relevant alternative or supplementation to surgical correction of limb length imbalances and deformities.

pharmacology and toxicology↗

bioRxiv2023

Sclerostin modulates the degree of mineralization and the stiffness profile of the fibrocartilaginous enthesis for mechanical tissue integrity

Fibrocartilaginous entheses consist of four graded tissue layers including tendon, the unmineralized and mineralized fibrocartilage, and subchondral bone with varying degrees of stiffness. Here we examined the functional role of sclerostin that is expressed in mature mineralized fibrochondrocytes. Following rapid mineralization of the unmineralized fibrocartilage and parallel replacement of epiphyseal hyaline cartilage by bone, the unmineralized fibrocartilage re-expanded after a decline in alkaline phosphatase activity at the mineralization front. Sclerostin was co-expressed with osteocalcin in the bottom of the mineralized fibrocartilage adjacent to subchondral bone. In Scx deficient mice with less mechanical loading due to defects of the Achilles tendon, the number of sclerostin+ fibrochondrocytes was significantly reduced in the defective enthesis where chondrocyte maturation was markedly impaired in both fibrocartilage and hyaline cartilage. Loss of the Sost gene, coding for sclerostin, caused increased mineral density in the mineralized zones of the fibrocartilaginous enthesis. Atomic force microscopy analysis revealed the higher stiffness of fibrocartilage. These lines of evidence suggest that sclerostin in mature mineralized fibrochondrocytes acts as a modulator for mechanical tissue integrity of the fibrocartilaginous enthesis.

developmental biology↗