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The NLRP3 inflammasome has important roles in the pathogenesis of various inflammatory diseases. However, the regulatory mechanisms of the NLRP3 inflammasome are not fully understood. In this study, we attempted to identify molecules that interact with NLRP3 upon its activation. We identified G protein subunit β 1 (GNB1), a downstream molecule of G protein-coupled receptors (GPCRs), which regulates the NLRP3 inflammasome activation. GNB1 was physically associated with NLRP3 via the pyrin domain of NLRP3. Activation of the NLRP3 inflammasome was enhanced in GNB1-knockdown or GNB1-deficient murine macrophages, although a lack of GNB1 did not affect activation of the AIM2 inflammasome. ASC oligomerization induced by NLRP3 was enhanced by GNB1 deficiency. Conversely, NLRP3-dependent ASC oligomerization was inhibited by the overexpression of GNB1. This study indicates that GNB1 negatively regulates NLRP3 inflammasome activation by suppressing NLRP3-dependent ASC oligomerization, and it provides a regulatory mechanism of the NLRP3 inflammasome. The Journal of Immunology, 2019, 202: 1942-1947. [ABSTRACT FROM AUTHOR]

Biomineralization is the process by which living organisms generate organized mineral crystals. In human cells, this phenomenon culminates with the formation of hydroxyapatite, which is a naturally occurring mineral form of calcium apatite. The mechanism that explains the genesis within the cell and the propagation of the mineral in the extracellular matrix still remains largely unexplained, and its characterization is highly controversial, especially in humans. In fact, up to now, biomineralization core knowledge has been provided by investigations on the advanced phases of this process. In this study, we characterize the contents of calcium depositions in human bone mesenchymal stem cells exposed to an osteogenic cocktail for 4 and 10 days using synchrotron-based cryo-soft-X-ray tomography and cryo-XANES microscopy. The reported results suggest crystalline calcite as a precursor of hydroxyapatite depositions within the cells in the biomineralization process. In particular, both calcite and hydroxyapatite were detected within the cell during the early phase of osteogenic differentiation. This striking finding may redefine most of the biomineralization models published so far, taking into account that they have been formulated using murine samples while studies in human cell lines are still scarce. [ABSTRACT FROM AUTHOR]

ABSTRACT The growth plate is the primary site of longitudinal bone growth with chondrocytes playing a pivotal role in endochondral bone development. Chondrocytes undergo a series of differentiation steps, resulting in the formation of a unique hierarchical columnar structure comprising round, proliferating, pre‐hypertrophic, and hypertrophic chondrocytes. Pre‐hypertrophic chondrocytes, which exist in the transitional stage between proliferating and hypertrophic stages, are a critical cell population in the growth plate. However, the molecular basis of pre‐hypertrophic chondrocytes remains largely undefined. Here, we employed scRNA‐seq analysis on fluorescently labeled growth plate chondrocytes for their molecular characterization. Serine incorporator 5 (Serinc5) was identified as a marker gene for pre‐hypertrophic chondrocytes. Histological analysis revealed that Serinc5 is specifically expressed in pre‐hypertrophic chondrocytes, overlapping with Indian hedgehog (Ihh). Serinc5 represses cell proliferation and Col2a1 and Acan expression by inhibiting the transcriptional activity of Sox9 in primary chondrocytes. Chromatin profiling using ChIP‐seq and ATAC‐seq revealed an active enhancer of Serinc5 located in intron 1, with its chromatin status progressively activated during chondrocyte differentiation. Collectively, our findings suggest that Serinc5 regulates sequential chondrocyte differentiation from proliferation to hypertrophy by inhibiting Sox9 function in pre‐hypertrophic chondrocytes, providing novel insights into the mechanisms underlying chondrocyte differentiation in growth plates. [ABSTRACT FROM AUTHOR]

Background: Embryonic craniofacial development involves several cellular and molecular events that are evolutionarily conserved among vertebrates. Vertebrate models such as mice and zebrafish have been used to investigate the molecular and cellular etiologies underlying human craniofacial disorders, including orofacial clefts. However, the molecular mechanisms underlying embryonic development in these two species are unknown. Therefore, elucidating the shared mechanisms of craniofacial development between disease models is crucial to understanding the underlying mechanisms of phenotypes in individual species., Results: We selected mice and zebrafish as model organisms to compare various events during embryonic craniofacial development. We identified genes (Sox9, Zfhx3 and 4, Cjun, and Six1) exhibiting similar temporal expression patterns between these species through comprehensive and stage-matched gene expression analyses. Expression analysis revealed similar gene expression in hypothetically corresponding tissues, such as the mice palate and zebrafish ethmoid plate. Furthermore, loss-of-function analysis of Zfhx4/zfhx4, a causative gene of human craniofacial anomalies including orofacial cleft, in both species resulted in deformed skeletal elements such as the palatine and ethmoid plate in mice and zebrafish, respectively., Conclusions: These results demonstrate that these disease models share common molecular mechanisms, highlighting their usefulness in modeling craniofacial defects in humans., (© 2024 Kao Corporation and The Author(s). Developmental Dynamics published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

The sulfate transporter gene SLC26A2 is crucial for skeletal formation, as evidenced by its role in diastrophic dysplasia, a type of skeletal dysplasia in humans. Although SLC26A2-related chondrodysplasia also affects craniofacial and tooth development, its specific role in these processes remains unclear. In this study, we explored the pivotal roles of SLC26A2-mediated sulfate metabolism during tooth development. We found that Slc26a2 was predominantly expressed in dental tissues, including odontoblasts and ameloblasts. Slc26a2 knockout (Slc26a2-KO-Δexon2) mice exhibited distinct craniofacial abnormalities, such as a retrognathic upper jaw, small upper incisors and upper molar hypoplasia. These mice also showed flattened odontoblasts and loss of nuclear polarity in upper incisors and molars, with significant reductions in odontoblast differentiation markers Dspp and Dmp1. Ex vivo and in vitro studies further revealed dentin matrix hypoplasia, tooth root shortening and downregulation of Wnt signaling in Slc26a2-deficient cells. These findings highlight the crucial role of SLC26A2-mediated sulfate metabolism in tooth development and offer insights into the mechanisms underlying dental abnormalities in patients with SLC26A2-related chondrodysplasias., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Osteoarthritis is a common disease in joint cartilages. Because the molecular pathogenesis of osteoarthritis remains elusive, early diagnostic markers and effective therapeutic agents have not been developed. To understand the molecular mechanisms, we attempted to identify transcription factors involved in the onset of osteoarthritis. Microarray analysis of mouse articular cartilage cells indicated that retinoic acid, a destructive stimulus in articular cartilage, up-regulated expression of sex-determining region Y-box (Sox)4, a SoxC family transcription factor, together with increases in Adamts4 and Adamts5, both of which are aggrecanases of articular cartilages. Overexpression of Sox4 induced a disintegrin-like and metallopeptidase with thrombospondin type 4 and 5 motif (ADAMTS4 and ADAMTS5, respectively) expression in chondrogenic cell lines C3H10T1/2 and SW1353. In addition, luciferase reporter and chromatin immunoprecipitation assays showed that Sox4 up-regulated ADAMTS4 and Adamts5 gene promoter activities by binding to their gene promoters. Another SoxC family member, Sox11, evoked similar effects. To evaluate the roles of Sox4 and Sox11 in articular cartilage destruction, we performed organ culture experiments using mouse femoral head cartilages. Sox4 and Sox11 adenovirus infections caused destruction of articular cartilage associated with increased Adamts5 expression. Finally, SOX4 and SOX11 mRNA expression was increased in cartilage of patients with osteoarthritis compared with nonosteoarthritic subjects. Thus, Sox4, and presumably Sox11, are involved in osteoarthritis onset by up-regulating ADAMTS4 and ADAMTS5.-Takahata, Y., Nakamura, E., Hata, K., Wakabayashi, M., Murakami, T., Wakamori, K., Yoshikawa, H., Matsuda, A., Fukui, N., Nishimura, R. Sox4 is involved in osteoarthritic cartilage deterioration through induction of ADAMTS4 and ADAMTS5.

Wnt plays important roles in regulation of differentiation of osteoblast and chondrocyte and their function. Wnt family members ingeniously utilize canonical Wnt signaling pathway through β-catenin and non-canonical Wnt signaling pathway independent of β-catenin, consequently regulating development, formation and homeostasis of bone and cartilage. Recent studies revealed that canonical Wnt signal activates transcriptional regulator, TAZ, in addition to transcription factors, LEF and TCF. Canonical Wnt signal crosstalks with BMP signal by stimulating complex formation of LEF1, TAZ and Runx2. Although molecular mechanism of non-canonical Wnt signal is getting clearer, the precise role of non-canonical Wnt signal in bone and cartilage seems still elusive.

One of the major topics of ASBMR in this year was progress in research on "Bone and muscle crosstalk". It has been practically and clinically known that appropriate exercise has good effects on bones strength, however the mechanism is still elusive. In this ASBMR meeting, there were many reports that muscle-derived hormones, e.g. Irisin, β-aminoisobutyric acid(BAIBA)or Myostatin interact with skeletal cells. Especially, the report regarding Irisin was impressive. Moreover, several reports regarding new aspects of osteoblasts and bone formation were also interesting. In this report, we would like to introduce these interesting abstracts.

Chondrocytes, which are originated from undifferentiated mesenchymal stem cells, play roles in skeletal development and growth in mammal, and smooth movement of joints. Endochondral ossification is necessary for skeletal development, and the multiple and complex biological events are precisely regulated by several hormones, cytokines, and their downstream signaling and transcriptional regulation. On the other hands, articular chondrocytes physiologically retains their features during a lifetime. Numerous molecules involved in endochondral ossification have been identified and investigation of the molecular mechanisms have amazingly progressed. Although GDF5 and Prg4 were identified as important molecules associated with articular cartilage development and its homeostasis, the molecular mechanisms are very unclear to date.