Makoto Hirata

GSK-3β Controls Osteogenesis through Regulating Runx2 Activity

Despite accumulated knowledge of various signalings regulating bone formation, the molecular network has not been clarified sufficiently to lead to clinical application. Here we show that heterozygous glycogen synthase kinase-3β (GSK-3β)-deficient mice displayed an increased bone formation due to an enhanced transcriptional activity of Runx2 by suppressing the inhibitory phosphorylation at a specific site. The cleidocranial dysplasia in heterozygous Runx2-deficient mice was significantly rescued by the genetic insufficiency of GSK-3β or the oral administration of lithium chloride, a selective inhibitor of GSK-3β. These results establish GSK-3β as a key attenuator of Runx2 activity in bone formation and as a potential molecular target for clinical treatment of bone catabolic disorders like cleidocranial dysplasia.

C/EBPβ and RUNX2 cooperate to degrade cartilage with MMP-13 as the target and HIF-2α as the inducer in chondrocytes

To elucidate the molecular mechanism underlying the endochondral ossification process during the skeletal growth and osteoarthritis (OA) development, we examined the signal network around CCAAT/enhancer-binding protein-β (C/EBPβ, encoded by CEBPB), a potent regulator of this process. Computational predictions and a C/EBP motif-reporter assay identified RUNX2 as the most potent transcriptional partner of C/EBPβ in chondrocytes. C/EBPβ and RUNX2 were induced and co-localized in highly differentiated chondrocytes during the skeletal growth and OA development of mice and humans. The compound knockout of Cebpb and Runx2 in mice caused growth retardation and resistance to OA with decreases in cartilage degradation and matrix metalloproteinase-13 (Mmp-13) expression. C/EBPβ and RUNX2 cooperatively enhanced promoter activity of MMP13 through specific binding to a C/EBP-binding motif and an osteoblast-specific cis-acting element 2 motif as a protein complex. Human genetic studies failed to show the association of human CEBPB gene polymorphisms with knee OA, nor was there a genetic variation around the identified responsive region in the human MMP13 promoter. However, hypoxia-inducible factor-2α (HIF-2α), a functional and genetic regulator of knee OA through promoting endochondral ossification, was identified as a potent and functional inducer of C/EBPβ expression in chondrocytes by the CEBPB promoter assay. Hence, C/EBPβ and RUNX2, with MMP-13 as the target and HIF-2α as the inducer, control cartilage degradation. This molecular network in chondrocytes may represent a therapeutic target for OA.

Notch signaling in chondrocytes modulates endochondral ossification and osteoarthritis development

Here we examined the involvement of Notch signaling in the endochondral ossification process, which is crucial for osteoarthritis (OA) development. Intracellular domains of Notch1 and -2 were translocated into the nucleus of chondrocytes with their differentiation in mouse limb cartilage and in mouse and human OA articular cartilage. A tissue-specific inactivation of the Notch transcriptional effector recombination signal binding protein for Ig kappa J (RBPjκ) in chondroprogenitor cells of SRY-box containing gene 9 (Sox9)-Cre;Rbpjfl/fl mouse embryos caused an impaired terminal stage of endochondral ossification in the limb cartilage. The RBPjκ inactivation in adult articular cartilage after normal skeletal growth using type II collagen (Col2a1)-CreERT;Rbpjfl/fl mice by tamoxifen injection caused resistance to OA development in the knee joint. Notch intracellular domain with the effector RBPjκ stimulated endochondral ossification through induction of the target gene Hes1 in chondrocytes. Among the Notch ligands, Jagged1 was strongly induced during OA development. Finally, intraarticular injection of N-[N-(3,5-diflurophenylacetate)-l-alanyl]-(S)-phenylglycine t-butyl ester (DAPT), a small compound Notch inhibitor, to the mouse knee joint prevented OA development. The RBPjκ-dependent Notch signaling in chondrocytes modulates the terminal stage of endochondral ossification and OA development, representing an extracellular therapeutic target of OA.

C/EBPβ Promotes Transition from Proliferation to Hypertrophic Differentiation of Chondrocytes through Transactivation of p57Kip2

Background Although transition from proliferation to hypertrophic differentiation of chondrocytes is a crucial step for endochondral ossification in physiological skeletal growth and pathological disorders like osteoarthritis, the underlying mechanism remains an enigma. This study investigated the role of the transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) in chondrocytes during endochondral ossification. Methodology/Principal Findings Mouse embryos with homozygous deficiency in C/EBPβ (C/EBPβ−/−) exhibited dwarfism with elongated proliferative zone and delayed chondrocyte hypertrophy in the growth plate cartilage. In the cultures of primary C/EBPβ−/− chondrocytes, cell proliferation was enhanced while hypertrophic differentiation was suppressed. Contrarily, retroviral overexpression of C/EBPβ in chondrocytes suppressed the proliferation and enhanced the hypertrophy, suggesting the cell cycle arrest by C/EBPβ. In fact, a DNA cell cycle histogram revealed that the C/EBPβ overexpression caused accumulation of cells in the G0/G1 fraction. Among cell cycle factors, microarray and real-time RT-PCR analyses have identified the cyclin-dependent kinase inhibitor p57Kip2 as the transcriptional target of C/EBPβ. p57Kip2 was co-localized with C/EBPβ in late proliferative and pre-hypertrophic chondrocytes of the mouse growth plate, which was decreased by the C/EBPβ deficiency. Luciferase-reporter and electrophoretic mobility shift assays identified the core responsive element of C/EBPβ in the p57Kip2 promoter between −150 and −130 bp region containing a putative C/EBP motif. The knockdown of p57Kip2 by the siRNA inhibited the C/EBPβ-induced chondrocyte hypertrophy. Finally, when we created the experimental osteoarthritis model by inducing instability in the knee joints of adult mice of wild-type and C/EBPβ+/− littermates, the C/EBPβ insufficiency caused resistance to joint cartilage destruction. Conclusions/Significance C/EBPβ transactivates p57Kip2 to promote transition from proliferation to hypertrophic differentiation of chondrocytes during endochondral ossification, suggesting that the C/EBPβ-p57Kip2 signal would be a therapeutic target of skeletal disorders like growth retardation and osteoarthritis.

A novel disease-modifying osteoarthritis drug candidate targeting Runx1

Objectives To identify a new disease-modifying osteoarthritis drug (DMOAD) candidate that can effectively repair cartilage by promoting chondrogenic differentiation and halt osteoarthritis (OA) progression by suppressing aberrant hypertrophy. Methods We screened 2500 natural and synthetic small compounds for chondrogenic agents via four steps using the Col2GFP-ATDC5 system and identified a small thienoindazole derivative compound, TD-198946, as a novel DMOAD candidate. We tested its efficacy as a DMOAD via intra-articular injections directly into the joint space in a surgically-induced mouse model of OA both at the onset (prevention model) and 4   weeks after (repair model) OA induction. The downstream molecules were screened by microarray analysis. We further investigated the mechanism of the drug action and its molecular target using in vitro and in vivo assays. Results TD-198946 strongly induced chondrogenic differentiation without promoting hypertrophy in cell and metatarsal organ cultures. When administered directly into the joint space, TD-198946 successfully prevented and repaired degeneration of the articular cartilage. TD-198946 exerted its effect through the regulation of Runx1 expression, which was downregulated in both mouse and human OA cartilage compared with normal tissue. Conclusions Our data suggest that TD-198946 is a novel class of DMOAD candidate, and that targeting Runx1 will provide a promising new approach in the development of disease-modifying drugs against OA.

Overview of the BioBank Japan Project: Study design and profile

Background The BioBank Japan (BBJ) Project was launched in 2003 with the aim of providing evidence for the implementation of personalized medicine by constructing a large, patient-based biobank (BBJ). This report describes the study design and profile of BBJ participants who were registered during the first 5-year period of the project. Methods The BBJ is a registry of patients diagnosed with any of 47 target common diseases. Patients were enrolled at 12 cooperative medical institutes all over Japan from June 2003 to March 2008. Clinical information was collected annually via interviews and medical record reviews until 2013. We collected DNA from all participants at baseline and collected annual serum samples until 2013. In addition, we followed patients who reported a history of 32 of the 47 target diseases to collect survival data, including cause of death. Results During the 5-year period, 200,000 participants were registered in the study. The total number of cases was 291,274 at baseline. Baseline data for 199,982 participants (53.1% male) were available for analysis. The average age at entry was 62.7 years for men and 61.5 years for women. Follow-up surveys were performed for participants with any of 32 diseases, and survival time data for 141,612 participants were available for analysis. Conclusions The BBJ Project has constructed the infrastructure for genomic research for various common diseases. This clinical information, coupled with genomic data, will provide important clues for the implementation of personalized medicine.

Mutant IDH is sufficient to initiate enchondromatosis in mice.

Significance Current genomic and biochemical analysis revealed mutations in isocitrate dehydrogenase (IDH) genes associated with several neoplasms and a novel enzymatic activity of IDH mutations to catalyze α-ketoglutarate to d-2-hydroxyglutarate, contributing to tumorigenesis. We identified a broad range of IDH1 mutations, including a previously unidentified IDH1-R132Q mutation, in cartilage tumors. Cartilage-specific Col2a1-Cre/ERT2;Idh1-R132 mutant knock-in mice developed multiple enchondroma-like lesions. These data show that mutant Idh in growth-plate cells causes persistence of chondrocytes, giving rise to enchondromas adjacent to the growth cartilage in bone. Enchondromas are benign cartilage tumors and precursors to malignant chondrosarcomas. Somatic mutations in the isocitrate dehydrogenase genes (IDH1 and IDH2) are present in the majority of these tumor types. How these mutations cause enchondromas is unclear. Here, we identified the spectrum of IDH mutations in human enchondromas and chondrosarcomas and studied their effects in mice. A broad range of mutations was identified, including the previously unreported IDH1-R132Q mutation. These mutations harbored enzymatic activity to catalyze α-ketoglutarate to d-2-hydroxyglutarate (d-2HG). Mice expressing Idh1-R132Q in one allele in cells expressing type 2 collagen showed a disordered growth plate, with persistence of type X-expressing chondrocytes. Chondrocyte cell cultures from these animals or controls showed that there was an increase in proliferation and expression of genes characteristic of hypertrophic chondrocytes with expression of Idh1-R132Q or 2HG treatment. Col2a1-Cre;Idh1-R132Q mutant knock-in mice (mutant allele expressed in chondrocytes) did not survive after the neonatal stage. Col2a1-Cre/ERT2;Idh1-R132 mutant conditional knock-in mice, in which Cre was induced by tamoxifen after weaning, developed multiple enchondroma-like lesions. Taken together, these data show that mutant IDH or d-2HG causes persistence of chondrocytes, giving rise to rests of growth-plate cells that persist in the bone as enchondromas.

Genome-wide association study identifies 112 new loci for body mass index in the Japanese population

Obesity is a risk factor for a wide variety of health problems. In a genome-wide association study (GWAS) of body mass index (BMI) in Japanese people (n = 173,430), we found 85 loci significantly associated with obesity (P < 5.0 × 10−8), of which 51 were previously unknown. We conducted trans-ancestral meta-analyses by integrating these results with the results from a GWAS of Europeans and identified 61 additional new loci. In total, this study identifies 112 novel loci, doubling the number of previously known BMI-associated loci. By annotating associated variants with cell-type-specific regulatory marks, we found enrichment of variants in CD19+ cells. We also found significant genetic correlations between BMI and lymphocyte count (P = 6.46 × 10−5, rg = 0.18) and between BMI and multiple complex diseases. These findings provide genetic evidence that lymphocytes are relevant to body weight regulation and offer insights into the pathogenesis of obesity.

Cross-sectional analysis of BioBank Japan clinical data: A large cohort of 200,000 patients with 47 common diseases

Background To implement personalized medicine, we established a large-scale patient cohort, BioBank Japan, in 2003. BioBank Japan contains DNA, serum, and clinical information derived from approximately 200,000 patients with 47 diseases. Serum and clinical information were collected annually until 2012. Methods We analyzed clinical information of participants at enrollment, including age, sex, body mass index, hypertension, and smoking and drinking status, across 47 diseases, and compared the results with the Japanese database on Patient Survey and National Health and Nutrition Survey. We conducted multivariate logistic regression analysis, adjusting for sex and age, to assess the association between family history and disease development. Results Distribution of age at enrollment reflected the typical age of disease onset. Analysis of the clinical information revealed strong associations between smoking and chronic obstructive pulmonary disease, drinking and esophageal cancer, high body mass index and metabolic disease, and hypertension and cardiovascular disease. Logistic regression analysis showed that individuals with a family history of keloid exhibited a higher odds ratio than those without a family history, highlighting the strong impact of host genetic factor(s) on disease onset. Conclusions Cross-sectional analysis of the clinical information of participants at enrollment revealed characteristics of the present cohort. Analysis of family history revealed the impact of host genetic factors on each disease. BioBank Japan, by publicly distributing DNA, serum, and clinical information, could be a fundamental infrastructure for the implementation of personalized medicine.

GSK-3α and GSK-3β Proteins Are Involved in Early Stages of Chondrocyte Differentiation with Functional Redundancy through RelA Protein Phosphorylation

Background: GSK-3α and GSK-3β are crucial kinases that mediate various principal signals. Results: The compound knock-out mice (Gsk3a−/−;Gsk3b+/−) showed impaired skeletal growth with RelA as the key target. Conclusion: Their redundant functions through RelA phosphorylation at Thr-254 regulate chondrocyte differentiation. Significance: This is the first report that shows in vivo evidence of the functional relationship of GSK-3α and GSK-3β and the underlying mechanism. Here we examine the roles of two isoforms of glycogen synthase kinase-3 (GSK-3), GSK-3α and GSK-3β, in skeletal development. Both isoforms were unphosphorylated and active in chondrocyte differentiation stages during SOX9 and type II collagen (COL2A1) expression. Although knock-out of both alleles of Gsk3a (Gsk3a−/−) or a single allele of Gsk3b (Gsk3b+/−) in mice did not significantly affect skeletal development, compound knock-out (Gsk3a−/−;Gsk3b+/−) caused dwarfism with impairment of chondrocyte differentiation. GSK-3α and GSK-3β induced differentiation of cultured chondrocytes with functional redundancy in a cell-autonomous fashion, independently of the Wnt/β-catenin signal. Computational predictions followed by SOX9 and COL2A1 transcriptional assays identified RelA (NF-κB p65) as a key phosphorylation target of GSK-3. Among several phosphorylation residues in RelA, Thr-254 was identified as the critical phosphorylation site for GSK-3 that modulated chondrocyte differentiation. In conclusion, redundant functions of GSK-3α and GSK-3β through phosphorylation of RelA at Thr-254 play a crucial role in early stages of chondrocyte differentiation.