TET1 Directs Chondrogenic Differentiation by Regulating SOX9 Dependent Activation of Col2a1 and Acan In Vitro

Influence of DNA-methylation at multiple stages of limb chondrogenesis

Precise regulation of gene expression is of utmost importance during cell fate specification. DNA methylation is a key epigenetic mechanism that plays a significant role in the regulation of cell fate by recruiting repression proteins or inhibiting the binding of transcription factors to DNA to regulate gene expression. Limb development is a well-established model for understanding cell fate decisions, and the formation of skeletal elements is coordinated through a sequence of events that control chondrogenesis spatiotemporally. It has been established that epigenetic control participates in cartilage maturation. However, further investigation is required to determine its role in the earliest stages of chondrocyte differentiation. This study investigates how the DNA methylation environment affects cell fate divergence during the early chondrogenic events. Our research has shown for the first time that inhibiting DNA methylation in interdigital tissue with 5-azacytidine results in the formation of an ectopic digit. This discovery suggested that DNA methylation dynamics could regulate the fate of cells between chondrogenesis and cell death during autopod development. Our in vitro findings indicate that DNA methylation at the early stages of chondrogenesis is integral in regulating condensation by controlling cell adhesion and proapoptotic genes. As a result, the dynamics of methylation and demethylation are crucial in governing chondrogenesis and cell death during different stages of limb chondrogenesis.

TET1 Regulates Skeletal Stem-Cell Mediated Cartilage Regeneration

OBJECTIVE

Adult skeletal stem cells (SSCs) that give rise to chondrocytes, osteocytes, and stromal cells as progeny have been shown to contribute to cartilage regeneration in osteoarthritis (OA). Understanding extrinsic and intrinsic regulators of SSC fate and function can therefore identify putative candidate factors to enhance cartilage regeneration. This study explores how the DNA hydroxymethylase Tet1 regulates SSC function in OA.

METHODS

We investigated the differences in the SSC lineage tree and differentiation potential in neonatal and adult Tet1+/+ and Tet1-/- mice with and without injury and upon OA induction and progression. Using RNA sequencing, the transcriptomic differences between SSCs and bone cartilage stroma progenitor cells (BCSPs) were identified in Tet1+/+ mice and Tet1-/- mice.

RESULTS

Loss of Tet1 skewed the SSC lineage tree by expanding the SSC pool and enhanced the chondrogenic potential of SSCs and BCSPs. Tet1 inhibition led to enhanced chondrogenesis in human SSCs and chondroprogenitors isolated from human cartilage. Importantly, TET1 inhibition in vivo in late stages of a mouse model of OA led to increased cartilage regeneration. Transcriptomic analyses of SSCs and BCSPs lacking Tet1 revealed pathway alterations in transforming growth factor β signaling, melatonin degradation, and cartilage development-associated genes. Lastly, we report that use of the hormone melatonin can dampen inflammation and improve cartilage health.

CONCLUSION

Although Tet1 is a broad epigenetic regulator, melatonin can mimic the inhibition ability of TET1 to enhance the chondrogenic ability of SSCs. Melatonin administration has the potential to be an attractive stem cell-based therapy for cartilage regeneration.

Cranial Neural Crest Cells Contribution to Craniofacial Bone Development and Regeneration

PURPOSE OF REVIEW

This review aims to summarize (i) the latest evidence on cranial neural crest cells (CNCC) contribution to craniofacial development and ossification; (ii) the recent discoveries on the mechanisms responsible for their plasticity; and (iii) the newest procedures to ameliorate maxillofacial tissue repair.

RECENT FINDINGS

CNCC display a remarkable differentiation potential that exceeds the capacity of their germ layer of origin. The mechanisms by which they expand their plasticity was recently described. Their ability to participate to craniofacial bone development and regeneration open new perspectives for treatments of traumatic craniofacial injuries or congenital syndromes. These conditions can be life-threatening, require invasive maxillofacial surgery and can leave deep sequels on our health or quality of life. With accumulating evidence showing how CNCC-derived stem cells potential can ameliorate craniofacial reconstruction and tissue repair, we believe a deeper understanding of the mechanisms regulating CNCC plasticity is essential to ameliorate endogenous regeneration and improve tissue repair therapies.

Epigenetic Crosstalk between Malignant Plasma Cells and the Tumour Microenvironment in Multiple Myeloma

In multiple myeloma, cells of the bone marrow microenvironment have a relevant responsibility in promoting the growth, survival, and drug resistance of multiple myeloma plasma cells. In addition to the well-recognized role of genetic lesions, microenvironmental cells also present deregulated epigenetic systems. However, the effect of epigenetic changes in reshaping the tumour microenvironment is still not well identified. An assortment of epigenetic regulators, comprising histone methyltransferases, histone acetyltransferases, and lysine demethylases, are altered in bone marrow microenvironmental cells in multiple myeloma subjects participating in disease progression and prognosis. Aberrant epigenetics affect numerous processes correlated with the tumour microenvironment, such as angiogenesis, bone homeostasis, and extracellular matrix remodelling. This review focuses on the interplay between epigenetic alterations of the tumour milieu and neoplastic cells, trying to decipher the crosstalk between these cells. We also evaluate the possibility of intervening specifically in modified signalling or counterbalancing epigenetic mechanisms.

Disrupting mechanotransduction decreases fibrosis and contracture in split-thickness skin grafting

Burns and other traumatic injuries represent a substantial biomedical burden. The current standard of care for deep injuries is autologous split-thickness skin grafting (STSG), which frequently results in contractures, abnormal pigmentation, and loss of biomechanical function. Currently, there are no effective therapies that can prevent fibrosis and contracture after STSG. Here, we have developed a clinically relevant porcine model of STSG and comprehensively characterized porcine cell populations involved in healing with single-cell resolution. We identified an up-regulation of proinflammatory and mechanotransduction signaling pathways in standard STSGs. Blocking mechanotransduction with a small-molecule focal adhesion kinase (FAK) inhibitor promoted healing, reduced contracture, mitigated scar formation, restored collagen architecture, and ultimately improved graft biomechanical properties. Acute mechanotransduction blockade up-regulated myeloid CXCL10-mediated anti-inflammation with decreased CXCL14-mediated myeloid and fibroblast recruitment. At later time points, mechanical signaling shifted fibroblasts toward profibrotic differentiation fates, and disruption of mechanotransduction modulated mesenchymal fibroblast differentiation states to block those responses, instead driving fibroblasts toward proregenerative, adipogenic states similar to unwounded skin. We then confirmed these two diverging fibroblast transcriptional trajectories in human skin, human scar, and a three-dimensional organotypic model of human skin. Together, pharmacological blockade of mechanotransduction markedly improved large animal healing after STSG by promoting both early, anti-inflammatory and late, regenerative transcriptional programs, resulting in healed tissue similar to unwounded skin. FAK inhibition could therefore supplement the current standard of care for traumatic and burn injuries.

MicroRNA Regulation of Bone Marrow Mesenchymal Stem Cell Chondrogenesis: Toward Articular Cartilage

The production of a clinically useful engineered cartilage is an outstanding and unmet clinical need. High-throughput RNA sequencing provides a means of characterizing the molecular phenotype of populations of cells and can be leveraged to better understand differences among source cells, derivative engineered tissues, and target phenotypes. In this study, small RNA sequencing is utilized to comprehensively characterize the microRNA transcriptomes (miRNomes) of native human neonatal articular cartilage and human bone marrow-derived mesenchymal stem cells (hBM-MSCs) differentiating into cartilage organoids, contrasting the microRNA regulation of engineered cartilage with that of a promising target phenotype. Five dominant microRNAs are upregulated during cartilage organoid differentiation and disproportionately regulate transcription factors: miR-148a-3p, miR-140-3p, miR-27b-3p, miR-140-5p, and miR-181a-5p. Two microRNAs that dominate the miRNomes of hBM-MSCs, miR-21-5p and miR-143-3p, persist throughout the differentiation process and may limit the ability of these cells to differentiate into an engineered cartilage resembling target native articular cartilage. By using predictive bioinformatics tools and antagomir inhibition, these persistent microRNAs are shown to destabilize the mRNA of genes with known or potential roles in cartilage biology including FGF18, TGFBR2, TET1, STOX2, ARAP2, N4BP2L1, LHX9, NFIA, and RPS6KA5. These results shed light on the extent to which only a few microRNAs contribute to the complex regulatory environment of hBM-MSCs for engineered tissues. Impact statement MicroRNAs are emerging as important controlling elements in the differentiation of human bone marrow-derived mesenchymal stem cells (hBM-MSCs). By using a robust bioinformatic approach and further validation in vitro, here we provide a comprehensive characterization of the microRNA transcriptomes (miRNomes) of a commonly studied and clinically promising source of multipotent cells (hBM-MSCs), a gold standard model of in vitro chondrogenesis (hBM-MSC-derived cartilage organoids), and an attractive in vivo target phenotype for clinically useful engineered cartilage (neonatal articular cartilage). These analyses highlighted a specific set of microRNAs involved in the chondrogenic program that could be manipulated to acquire a more robust articular cartilage-like phenotype. This characterization provides researchers in the cartilage tissue engineering field a useful atlas with which to contextualize microRNA involvement in complex differentiation pathways.

Cadherin-11 promotes the mechanical strength of engineered elastic cartilage by enhancing extracellular matrix synthesis and microstructure

Limitations of current treatments for auricular cartilage defects have prompted the field of auricular cartilage tissue engineering. To date, inducing the formation of cartilaginous constructs with biochemical and biomechanical properties of native tissue is the final aim. Through hematoxylin-eosin and immunohistochemistry staining, Cadherin-11(CDH11) was confirmed highly expressed in the auricular cartilage tissue and chondrocytes. In vitro, by knockdown and overexpression of CDH11 in chondrocytes, CDH11 was demonstrated to promote the expression of collagen type II (COL2A), elastin (ELN), aggrecan (ACAN), and cartilage oligomeric matrix protein (COMP). In addition, the CDH11 overexpressed chondrocytes promoted neo-cartilage formation and its biomechanical property by increasing the key transcription factor of chondrogenesis SOX9 expression and cartilage extracellular matrix (ECM) production. The young's modulus and yield stress of the neo-cartilage in CDH11 overexpression group were about 1.7 times (p = 0.0152) and 2 times (p = 0.0428) higher than those in control group, respectively. Then, the immunohistochemistry staining, qRT-PCR and western blot examination results showed that the expression of COL2A and ELN were significantly increased. Notably, the electron microscopy results showed that the collagen and elastic fibers of the neo-cartilage in CDH11-OV group arranged in bunches and were more uniform and compact compared to the control group. Furthermore, CDH11 promoted elastic fiber assembly by increasing lysyl oxidase (LOX), fibrillin-1 (FBN1) expression. Taken together, our results demonstrated that CDH11 improves the mechanical strength of tissue-engineered elastic cartilage by promoting ECM synthesis and elastic fiber assembly.

Analysis of Gene Expression Patterns of Epigenetic Enzymes Dnmt3a, Tet1 and Ogt in Murine Chondrogenic Models

We investigated the gene expression pattern of selected enzymes involved in DNA methylation and the effects of the DNA methylation inhibitor 5-azacytidine during in vitro and in vivo cartilage formation. Based on the data of a PCR array performed on chondrifying BMP2-overexpressing C3H10T1/2 cells, the relative expressions of Tet1 (tet methylcytosine dioxygenase 1), Dnmt3a (DNA methyltransferase 3), and Ogt (O-linked N-acetylglucosamine transferase) were further examined with RT-qPCR in murine cell line-based and primary chondrifying micromass cultures. We found very strong but gradually decreasing expression of Tet1 throughout the entire course of in vitro cartilage differentiation along with strong signals in the cartilaginous embryonic skeleton using specific RNA probes for in situ hybridization on frozen sections of 15-day-old mouse embryos. Dnmt3a and Ogt expressions did not show significant changes with RT-qPCR and gave weak in situ hybridization signals. The DNA methylation inhibitor 5-azacytidine reduced cartilage-specific gene expression and cartilage formation when applied during the early stages of chondrogenesis. In contrast, it had a stimulatory effect when added to differentiated chondrocytes, and quantitative methylation-specific PCR proved that the DNA methylation pattern of key chondrogenic marker genes was altered by the treatment. Our results indicate that the DNA demethylation inducing Tet1 plays a significant role during chondrogenesis, and inhibition of DNA methylation exerts distinct effects in different phases of in vitro cartilage formation.