CircRNA_28313/miR-195a/CSF1 axis modulates osteoclast differentiation to affect OVX-induced bone absorption in mice

CircRNA Arf3 suppresses glomerular mesangial cell proliferation and fibrosis in diabetic nephropathy via miR-107-3p/Tmbim6 axis

Diabetic nephropathy (DN) is one of microvascular complication associated with diabetes. Circular RNAs (circRNAs) have been shown to be involved in DN pathogenesis. Hence, this work aimed to explore the role and mechanism of circ_Arf3 in DN. Mouse mesangial cells (MCs) cultured in high glucose (HG) condition were used for functional analysis. Cell proliferation was determined using 5-ethynyl-2'-deoxyuridine (EdU) and cell counting kit-8 assays. Western blotting was used to measure the levels of proliferation indicator PCNA and fibrosis-related proteins α-smooth muscle actin (α-SMA), collagen I (Col I), fibronectin (FN), and collagen IV (Col IV). The binding interaction between miR-107-3p and circ_Arf3 or Tmbim6 (transmembrane BAX inhibitor motif containing 6) was confirmed using dual-luciferase reporter and pull-down assays. Circ_Arf3 is a stable circRNA, and the expression of circ_Arf3 was decreased after HG treatment in MCs. Functionally, ectopic overexpression of circ_Arf3 protected against HG-induced proliferation and elevation of fibrosis-related proteins in MCs. Mechanistically, circ_Arf3 directly bound to miR-107-3p, and Tmbim6 was a target of miR-107-3p. Further rescue assay showed miR-107-3p reversed the protective action of circ_Arf3 on MCs function under HG condition. Moreover, inhibition of miR-107-3p suppressed HG-induced proliferation and fibrosis, which were attenuated by Tmbim6 knockdown in MCs. CircRNA Arf3 could suppress HG-evoked mesangial cell proliferation and fibrosis via miR-107-3p/Tmbim6 axis, indicating the potential involvement of this axis in DN progression.

CircZfp644-205 inhibits osteoblast differentiation and induces apoptosis of pre-osteoblasts via sponging miR-455-3p and promoting SMAD2 expression

BACKGROUND

Circular RNAs (circRNAs) are involved in the progression of osteoporosis; however, their impact on osteogenic differentiation has yet to be fully elucidated. In this study, we identified a novel circRNA known as circZfp644-205 and investigated its effect on osteogenic differentiation and apoptosis in osteoporosis.

METHODS

CircZfp644-205, miR-445-3p, and SMAD2 levels were measured using quantitative real-time polymerase chain reaction (qRT-PCR). MC3T3-E1 cells were subjected to microgravity (MG) to establish a cell model. Osteogenic differentiation was assessed using qRT-PCR, Alizarin Red S staining, alkaline phosphatase staining, and western blot. The apoptosis was evaluated using flow cytometry. The relationship between miR-445-3p and circZfp644-205 or SMAD2 was determined using bioinformatics, RNA pull-down, and luciferase reporter assay. Moreover, a hindlimb unloading mouse model was generated to investigate the role of circZfp644-205 in vivo using Micro-CT.

RESULTS

CircZfp644-205 expression was up-regulated significantly in HG-treated MC3T3-E1 cells. Further in vitro studies confirmed that circZfp644-205 knockdown inhibited the osteogenic differentiation and induced apoptosis of pre-osteoblasts. CircZfp644-205 acted as a sponge for miR-455-3p, which reversed the effects of circZfp644-205 on pre-osteoblasts. Moreover, miR-455-3p directly targeted SMAD2, thus inhibiting the expression of SMAD2 to regulate cellular behaviors. Moreover, circZfp644-205 alleviated the progression of osteoporosis in mice.

CONCLUSIONS

This study provides a novel circRNA that may serve as a potential therapeutic target for osteoporosis and expands our understanding of the molecular mechanism underlying the progression of osteoporosis.

Exploring the Role of Circular RNA in Bone Biology: A Comprehensive Review

Circular RNAs (circRNAs) have emerged as pivotal regulators of gene expression with diverse roles in various biological processes. In recent years, research into circRNAs' involvement in bone biology has gained significant attention, unveiling their potential as novel regulators and biomarkers in bone-related disorders and diseases. CircRNAs, characterized by their closed-loop structure, exhibit stability and resistance to degradation, underscoring their functional significance. In bone tissue, circRNAs are involved in critical processes such as osteogenic differentiation, osteoclastogenesis, and bone remodeling through intricate molecular mechanisms including microRNA regulation. Dysregulated circRNAs are associated with various bone disorders, suggesting their potential as diagnostic and prognostic biomarkers. The therapeutic targeting of these circRNAs holds promise for addressing bone-related conditions, offering new perspectives for precision medicine. Thus, circRNAs constitute integral components of bone regulatory networks, impacting both physiological bone homeostasis and pathological conditions. This review provides a comprehensive overview of circRNAs in bone biology, emphasizing their regulatory mechanisms, functional implications, and therapeutic potential.

Research progress of circRNA as a biomarker of osteoporosis

Osteoporosis, as a chronic metabolic bone disease, has the characteristic of insidious disease progression, which often leads to relatively delayed disease diagnosis. Therefore, early screening for osteoporosis has become a major public health challenge. The latest research indicates that circRNA is widely involved in the regulation of bone metabolism and is closely related to the occurrence and development of osteoporosis. Based on its high degree of sequence conservation and stability, circRNA has the potential to become a new clinical biomarker. The study of biomarkers is generally based on body fluid samples or adjacent tissue samples, with blood being the most commonly used, which can be divided into sources such as serum, plasma, peripheral blood monocytes, and plasma exosomes. Therefore, this article aims to review the research status of circRNA as a biomarker of osteoporosis.

Subchondral osteoclasts and osteoarthritis: new insights and potential therapeutic avenues

Osteoarthritis (OA) is the most common joint disease, and good therapeutic results are often difficult to obtain due to its complex pathogenesis and diverse causative factors. After decades of research and exploration of OA, it has been progressively found that subchondral bone is essential for its pathogenesis, and pathological changes in subchondral bone can be observed even before cartilage lesions develop. Osteoclasts, the main cells regulating bone resorption, play a crucial role in the pathogenesis of subchondral bone. Subchondral osteoclasts regulate the homeostasis of subchondral bone through the secretion of degradative enzymes, immunomodulation, and cell signaling pathways. In OA, osteoclasts are overactivated by autophagy, ncRNAs, and Rankl/Rank/OPG signaling pathways. Excessive bone resorption disrupts the balance of bone remodeling, leading to increased subchondral bone loss, decreased bone mineral density and consequent structural damage to articular cartilage and joint pain. With increased understanding of bone biology and targeted therapies, researchers have found that the activity and function of subchondral osteoclasts are affected by multiple pathways. In this review, we summarize the roles and mechanisms of subchondral osteoclasts in OA, enumerate the latest advances in subchondral osteoclast-targeted therapy for OA, and look forward to the future trends of subchondral osteoclast-targeted therapies in clinical applications to fill the gaps in the current knowledge of OA treatment and to develop new therapeutic strategies.

Osteoclasts and osteoarthritis: Novel intervention targets and therapeutic potentials during aging

Osteoarthritis (OA), a chronic degenerative joint disease, is highly prevalent among the aging population, and often leads to joint pain, disability, and a diminished quality of life. Although considerable research has been conducted, the precise molecular mechanisms propelling OA pathogenesis continue to be elusive, thereby impeding the development of effective therapeutics. Notably, recent studies have revealed subchondral bone lesions precede cartilage degeneration in the early stage of OA. This development is marked by escalated osteoclast-mediated bone resorption, subsequent imbalances in bone metabolism, accelerated bone turnover, and a decrease in bone volume, thereby contributing significantly to the pathological changes. While the role of aging hallmarks in OA has been extensively elucidated from the perspective of chondrocytes, their connection with osteoclasts is not yet fully understood. There is compelling evidence to suggest that age-related abnormalities such as epigenetic alterations, proteostasis network disruption, cellular senescence, and mitochondrial dysfunction, can stimulate osteoclast activity. This review intends to systematically discuss how aging hallmarks contribute to OA pathogenesis, placing particular emphasis on the age-induced shifts in osteoclast activity. It also aims to stimulate future studies probing into the pathological mechanisms and therapeutic approaches targeting osteoclasts in OA during aging.

[Research Progress in the Regulatory Role of circRNA-miRNA Network in Bone Remodeling]

The dynamic balance between bone formation and bone resorption is a critical process of bone remodeling. The imbalance of bone formation and bone resorption is closely associated with the occurrence and development of various bone-related diseases. Under both physiological and pathological conditions, non-coding RNAs (ncRNAs) play a crucial regulatory role in protein expression through either inhibiting mRNAs translation or promoting mRNAs degradation. Circular RNAs (circRNAs) are a type of non-linear ncRNAs that can resist the degradation of RNA exonucleases. There is accumulating evidence suggesting that circRNAs and microRNAs (miRNAs) serve as critical regulators of bone remodeling through their direct or indirect regulation of the expression of osteogenesis-related genes. Additionally, recent studies have revealed the involvement of the circRNAs-miRNAs regulatory network in the process by which mesenchymal stem cells (MSCs) differentiate towards the osteoblasts (OB) lineage and the process by which bone marrow-derived macrophages (BMDM) differentiate towards osteoclasts (OC). The circRNA-miRNA network plays an important regulatory role in the osteoblastic-osteoclastic balance of bone remodeling. Therefore, a thorough understanding of the circRNA-miRNA regulatory mechanisms will contribute to a better understanding of the regulatory mechanisms of the balance between osteoblastic and osteoclastic activities in the process of bone remodeling and the diagnosis and treatment of related diseases. Herein, we reviewed the functions of circRNA and microRNA. We also reviewed their roles in and the mechanisms of the circRNA-miRNA regulatory network in the process of bone remodeling. This review provides references and ideas for further research on the regulation of bone remodeling and the prevention and treatment of bone-related diseases.

Thiram exposure induces tibial dyschondroplasia in broilers via the regulation effect of circ_003084/miR-130c-5p/BMPR1A crosstalk on chondrocyte proliferation and differentiation

Thiram, an agricultural insecticide, has been demonstrated to induce tibial dyschondroplasia (TD) in avian species. Circular RNA (circRNAs), a novel class of functional biological macromolecules characterized by their distinct circular structure, play crucial roles in various biological processes and diseases. Nevertheless, the precise regulatory mechanism underlying non-coding RNA involvement in thiram-induced broiler tibial chondrodysplasia remains elusive. In this study, we established a broiler model of thiram exposure for 10 days to assess TD and obtain a ceRNA network by RNA sequencing. By analyzing the differentially expressed circRNAs network, we id entify that circ_003084 was significantly upregulated in TD cartilage. Elevated circ_003084 inhibited TD chondrocytes proliferation and differentiation in vitro but promote apoptosis. Mechanistically, circ_003084 competitively binds to miR-130c-5p and prevents miR-130c-5p to decrease the level of BMPR1A, which upregulates the expression of apoptosis genes Caspase 3, Caspase 9, Bax and Bcl2, and finally facilitates cell apoptosis. Taken together, these findings imply that circ_003084/miR-130c-5p/BMPR1A interaction regulated TD chicken chondrocyte proliferation, apoptosis, and differentiation. This is the first work to reveal the mechanism of regulation of circRNA-related ceRNA on thiram-induced TD, offering a key reference for environmental toxicology.

circ_0029463 promotes osteoclast differentiation by mediating miR-134-5p/Rab27a axis

OBJECTIVE

Osteoporosis is the imbalance in bone homeostasis between osteoblasts and osteoclasts. In this study, we investigated the effects of the circ_0029463/miR-134-5p/Rab27a axis on RANKL-induced osteoclast differentiation.

METHODS

RT-qPCR and western blotting were used to detect the expression of circ_0029463, miR-134-5p, and Rab27a in tissues from patients with osteoporosis and in RANKL-induced osteoclasts. Osteoclast differentiation was verified by TRAP staining. Osteoclast biomarkers, including NFATc1, TRAP, and CTSK, were measured. The target and regulatory relationships between circ_0029463, miR-134-5p, and the Rab27a axis were verified using RIP, dual-luciferase reporter gene, and RNA pull-down assays.

RESULTS

Elevated expression of circ_0029463 and Rab27a and decreased miR-134-5p expression were observed in the tissues of patients with osteoporosis, and a similar expression pattern was observed in RANKL-induced osteoclasts. Suppression of circ_0029463 expression or miR-134-5p overexpression curbed RANKL-induced osteoclast differentiation, whereas such an effect was abolished by Rab27 overexpression. circ_0029463 sponges miR-134-5p to induce Rab27a expression.

CONCLUSION

circ_0029463 sponges miR-134-5p to abolish its suppressive effect of miR-134-5p on Rab27a expression, thereby promoting osteoclast differentiation.

Alterations in Alzheimer's disease microglia transcriptome might be involved in bone pathophysiology

Aging is a major risk factor for multiple chronic disorders in the elderly population, including Alzheimer's disease (AD) and Osteoporosis. AD is a progressive neurodegenerative disease characterized by memory loss. In addition to dementia, several studies have shown that AD patients experience an increased rate of musculoskeletal co-morbidities, such as osteoporosis. Since tissue-specific macrophages contribute to both diseases, this study analyzed the microglia transcriptome of AD mice to determine a common gene signature involved in osteoclast biology. After comparing differentially regulated genes from GEO data sets (GSE93824 and GSE212277), there were 35 common upregulated genes and 89 common downregulated genes. Of these common genes, seven genes are known to play an important role in bone homeostasis. CSF1, SPP1, FAM20C, and Cst7 were upregulated and are associated with osteoclastogenesis and inflammation. Among the downregulated genes, LILRA6, MMP9, and COL18A1 are involved in bone formation and osteoclast regulation. We further validated some of these genes (CSF1, Cst7, and SPP1) in the cortex and the bone of AD mice models. The dysregulation of these microglial genes in AD might provide insights into the co-occurrence of AD and osteoporosis and offer potential therapeutic targets to combat disease progression.

Highlights on the Effects of Non-Coding RNAs in the Osteonecrosis of the Jaw

Osteonecrosis of the jaw is the progressive loss and destruction of bone affecting the maxilla or mandible in patients treated with antiresorptive and antiangiogenic agents without receiving prior radiation therapy. The pathogenesis involves the inflammatory pathway of receptor activator of nuclear factor NF-kB ligand and the macrophage colony-stimulating factor, essential for osteoclast precursors survival and proliferation and acting through its receptor c-Fms. Evidence has shown the role of non-coding RNAs in the pathogenesis of osteonecrosis of the jaw and this finding might be useful in diagnosis since these small RNAs could be considered as biomarkers of apoptotic activity in bone. Interestingly, it has been proved that miR-29 and miR-31-5p, acting on specific targets such as CALCR and RhoA, promote programmed-cell death and consequently the necrosis of bone tissue. Specific long non-coding RNAs, instead, have been detected both at reduced levels in patients with multiple myeloma and osteonecrosis, and associated with suppression of osteoblast differentiation, with consequences in the progression of mandible lesions. Among non-coding genic material, circular RNAs have the capability to modify the expression of specific mRNAs responsible for the inhibition of bisphosphonates activity on osteoclastogenesis.

Circ_0027885 sponges miR-203-3p to regulate RUNX2 expression and alleviates osteoporosis progression

BACKGROUND

Osteoporosis (OP) is a progressive metabolic disorder that is difficult to cure clinically. The molecular mechanisms of OP urgently need to be further examined. This study was designed to explore the potential function of circ_0027885 during osteogenic differentiation, as well as the systematic interactions among circ_0027885, miR-203-3p and runt-related transcription factor 2 (RUNX2).

METHODS

Relative levels of circ_0027885, miR-203-3p and RUNX2 were analyzed with RT-qPCR and western blotting. Alizarin red staining was performed to detect the mineralization ability under the control of circ_0027885 and miR-203-3p. Dual-luciferase reporter gene assay was conducted to examine the combination among circ_0027885, miR-203-3p and RUNX2.

RESULTS

Our research demonstrated that circ_0027885 was significantly increased during hBMSCs differentiation. Overexpression of circ_0027885 notably facilitated osteogenic differentiation and upregulated RUNX2 expression, while knockdown of circ_0027885 reversed the above results. Through prediction on bioinformatics analysis, miR-203-3p was the target binding circ_0027885, and RUNX2 was the potential target of miR-203-3p. Subsequently, these changes induced by the overexpression of circ_0027885 were reversed upon addition of miR-203-3p mimic.

CONCLUSIONS

Circ_0027885 could sponge miR-203-3p to regulate RUNX2 expression and alleviate osteoporosis progression.

Regulatory mechanisms of circular RNAs during human mesenchymal stem cell osteogenic differentiation

Human osteogenic differentiation is a complex and well-orchestrated process which involves a plethora of molecular players and cellular processes. A growing number of studies have underlined that circular RNAs (circRNAs) play an important regulatory role during human osteogenic differentiation. CircRNAs are single-stranded, covalently closed non-coding RNA molecules that are acquiring increased attention as epigenetic regulators of gene expression. Given their intrinsic high conformational stability, abundance, and specificity, circRNAs can undertake various biological activities in order to regulate multiple cellular processes, including osteogenic differentiation. The most recent evidence indicates that circRNAs control human osteogenesis by preventing the inhibitory activity of miRNAs on their downstream target genes, using a competitive endogenous RNA mechanism. The aim of this review is to draw attention to the currently known regulatory mechanisms of circRNAs during human osteogenic differentiation. Specifically, we provide an understanding of recent advances in research conducted on various human mesenchymal stem cell types that underlined the importance of circRNAs in regulating osteogenesis. A comprehensive understanding of the underlying regulatory mechanisms of circRNA in osteogenesis will improve knowledge on the molecular processes of bone growth, resulting in the potential development of novel preclinical and clinical studies and the discovery of novel diagnostic and therapeutic tools for bone disorders.

A novel link between melatonin and circ_0005753/PTBP1/TXNIP regulatory network in the modulation of osteogenic potential in mesenchymal stem cells

Labeled with pluripotent potential, the transplantation of bone marrow mesenchymal stem cells (BMSCs) is considered as a promising strategy for treating osteoporosis (OP). Melatonin (MEL) has been investigated to be an essential regulator involved in bone metabolism, as well as BMSCs differentiation. Circular RNAs (circRNAs) are a unique kind of non-coding RNA and play an important regulatory role in OP. However, whether circRNAs are implicated in the effects of MEL on BMSCs osteogenic differentiation remains largely indeterminate. Expression of circ_0005753 in human BMSCs with MEL treatment, clinical specimens diagnosed with OP, either with ovariectomy (OVX)-induced mice, was measured by RT-qPCR. Western blot was conducted to analyze protein levels of osteogenesis-related molecules (Opg, RUNX2, ALP, BMP4) and TXNIP. RNA immunoprecipitation (RIP) and RNA pull-down assays were performed to validate the binding relationship among circ_0005753, PTBP1, and TXNIP. Alkaline phosphatase (ALP) and alizarin red staining (ARS) were performed to evaluate osteogenic capacity of BMSCs. OP mouse model was established by ovariectomy, as evaluated pathologic changes via hematoxylin-eosin (HE), Masson, and Immunohistochemistry (IHC) staining. Expression of circ_0005753 was remarkably decreased during MEL-induced osteogenic differentiation of BMSCs. Interestingly, not only circ_0005753 knockdown significantly promoted osteogenic differentiation of BMSCs, but circ_0005753 overexpression also weakened osteogenic differentiation induced by MEL treatment. Mechanistically, circ_0005753 maintained the stabilization of TXNIP mRNA via recruiting PTBP1. Additionally, reinforced circ_0005753 abrogated MEL-mediated protective effects on OP pathogenesis in a mouse model. This work shows that MEL facilitates osteogenic differentiation of BMSCs via the circ_0005753/PTBP1/TXNIP axis, which may shed light on the development of a novel therapeutic strategy to prevent OP.

hsa_circ_0037722 Drives Keloid Formation by Interacting with miR-140-3p and NR2F2

Keloids can invade normal skin tissues to lead to itching, pain, hemorrhaging and suppuration, thereby affecting the mental health of patients. circRNAs can participate in keloids formation, but the role of hsa_circ_0037722 in keloids is still unknown. The goal of our study was to reveal the role of hsa_circ_0037722 in keloids. The levels of hsa_circ_0037722, miR-140-3p and NR2F2 in keloids was confirmed by qRT-PCR. Cell experiments were applied to assess the effect of hsa_circ_0037722/miR-140-3p/NR2F2 axis on keloids formation. In addition, the correlation among hsa_circ_0037722, miR-140-3p and NR2F2 was confirmed by luciferase assay. hsa_circ_0037722 and NR2F2 were upregulated in keloids tissues and keloids fibroblasts, whereas miR-140-3p was downregulated in keloids tissues and keloids fibroblasts. The abilities of proliferation and metastasis of keloids fibroblasts were impaired by silencing hsa_circ_0037722. However, miR-140-3p inhibitor or NR2F2 overexpression could restore the inhibitory function of hsa_circ_0037722 knockdown in keloid fibroblasts due to their targeting relationship. Taken together, hsa_circ_0037722 can facilitate keloids formation by interacting with miR-140-3p to relieve the suppression of miR-140-3p for NR2F2. The findings of this study may provide a novel idea for developing molecular targeted therapies for keloid.

Roles of circular RNAs in osteogenic/osteoclastogenic differentiation

The process of bone remodeling occurs and is regulated through interactions between osteoclasts, which resorb bone, and osteoblasts, which generate bone tissue. When the homeostatic balance between these two cell types is dysregulated, this can contribute to abnormal bone remodeling resulting in a loss of bone mass as is observed in osteoporosis (OP) and other forms of degenerative bone metabolic diseases. At present, details of molecular mechanism underlying the development of bone metabolic diseases such as OP remain to be elucidated. Circular RNAs (circRNAs) are small non-coding RNA molecules with a closed-loop structure that can regulate the differentiation of osteoclasts and osteoblasts. The present review provides a systematic overview of recent literature on the processes through which circRNAs regulate the dynamic balance between osteoblasts and osteoclasts that ultimately preserve bone homeostasis. It will also give insight that can shape current understanding of the pathogenesis of OP and other bone metabolic diseases to better guide diagnostic and treatment strategies for affected patients.

Role of non-coding RNAs in osteoporosis

Osteoporosis, a prevalent bone disorder influenced by genetic and environmental elements, significantly increases the likelihood of fractures and bone weakness, greatly affecting the lives of those afflicted. Yet, the exact epigenetic processes behind the onset of osteoporosis are still unclear. Growing research indicates that epigenetic changes could act as vital mediators that connect genetic tendencies and environmental influences, thereby increasing the risk of osteoporosis and bone fractures. Within these epigenetic factors, certain types of RNA, such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), have been recognized as key regulatory elements. These RNA types wield significant influence on gene expression through epigenetic regulation, directing various biological functions essential to bone metabolism. This extensive review compiles current research uncovering the complex ways in which miRNAs, lncRNAs, and circRNAs are involved in the development of osteoporosis, especially in osteoblasts and osteoclasts. Gaining a more profound understanding of the roles these three RNA classes play in osteoporosis could reveal new diagnostic methods and treatment approaches for this incapacitating condition. In conclusion, this review delves into the complex domain of epigenetic regulation via non-coding RNA in osteoporosis. It sheds light on the complex interactions and mechanisms involving miRNAs, lncRNAs, and circRNAs within osteoblasts and osteoclasts, offering an in-depth understanding of the less explored aspects of osteoporosis pathogenesis. These insights not only reveal the complexity of the disease but also offer significant potential for developing new diagnostic methods and targeted treatments. Therefore, this review marks a crucial step in deciphering the elusive complexities of osteoporosis, leading towards improved patient care and enhanced quality of life.

DOT1L decelerates the development of osteoporosis by inhibiting SRSF1 transcriptional activity via microRNA-181-mediated KAT2B inhibition

OBJECTIVE

Our study explored the function of DOT1L in osteoporosis (OP) via the microRNA (miR)-181/KAT2B/SRSF1 axis.

METHODS

Osteoclast (OC) number was evaluated via TRAP staining, and serum CTXI, PINP, and ALP contents were tested by ELISA. Following identification of bone marrow mesenchymal stem cells (BMSCs), OC differentiation was induced by M-CSF and RANKL, followed by the detection of OC differentiation and the expression of bone resorption-related genes, DOT1L, miR-181, KAT2B, and SRSF1.

RESULTS

Overexpressed DOT1L or miR-181 stimulated calcified nodule formation and increased alkaline phosphatase activity and osteogenic marker gene expression. KAT2B knockdown enhanced the osteogenic differentiation of BMSCs by reducing SRSF1 acetylation. The enhancement of OC differentiation induced by overexpressed SRSF1 was inhibited by simultaneous DOT1L or miR-181 overexpression. DOT1L suppressed OP development in vivo via the miR-181/KAT2B/SRSF1 axis.

CONCLUSION

DOT1L overexpression slowed down bone loss and promoted bone formation via the miR-181/KAT2B/SRSF1 axis, thereby alleviating OP development.

Circ_0114581 promotes osteogenic differentiation of BMSCs via the MiR-155-5p/HNRNPA3 axis

Osteoporosis (OP) is a common metabolic bone disease characterized by deterioration of bone tissue structure, reduction of bone mass, and susceptibility to fracture. More and new suitable therapeutic targets need to be discovered. The purpose of this study was to explore the ceRNA mechanisms of circRNAs involved in osteoporosis. In this study, a competing endogenous RNA (ceRNA) regulatory network was obtained through the application of OP-related high throughput data sets. Our results provided evidence that HNRNPA3 was involved in the regulation of osteogenic differentiation in BMSCs. Testing of human bone tissues and ovariectomized mice bones proved that its expression level was negatively correlated with OP. The utilization of miRNA mimic or inhibitor proved that miR-155-5p could negatively regulate the expression of HNRNPA3, while overexpression of hsa_circ_0114581 with a circRNA overexpression vector proved that hsa_circ_0114581 could indirectly promoted HNRNPA3 expression and osteogenic differentiation by sponging hsa-miR-155-5p. A serious of luciferase reporter assay experiments further verified the binding site between miR-155-5p and HNRNPA3 and the binding site between miR-155-5p and hsa_circ_0114581. This study proved that the hsa_circ_0114581/hsa-miR-155-5p/HNRNPA3 axis was related with OP. The results reveal valuable insights into the pathogenesis of OP and noncoding RNA markers that may have a treatment role and will help to provide hypotheses for future studies.

Role and Regulation of Transcription Factors in Osteoclastogenesis

Bones serve mechanical and defensive functions, as well as regulating the balance of calcium ions and housing bone marrow.. The qualities of bones do not remain constant. Instead, they fluctuate throughout life, with functions increasing in some situations while deteriorating in others. The synchronization of osteoblast-mediated bone formation and osteoclast-mediated bone resorption is critical for maintaining bone mass and microstructure integrity in a steady state. This equilibrium, however, can be disrupted by a variety of bone pathologies. Excessive osteoclast differentiation can result in osteoporosis, Paget's disease, osteolytic bone metastases, and rheumatoid arthritis, all of which can adversely affect people's health. Osteoclast differentiation is regulated by transcription factors NFATc1, MITF, C/EBPα, PU.1, NF-κB, and c-Fos. The transcriptional activity of osteoclasts is largely influenced by developmental and environmental signals with the involvement of co-factors, RNAs, epigenetics, systemic factors, and the microenvironment. In this paper, we review these themes in regard to transcriptional regulation in osteoclastogenesis.

Circ_KIAA0922 regulates Saos-2 cell proliferation and osteogenic differentiation by regulating the miR-148a-3p/SMAD5 axis and activating the TGF-β signaling pathway

Circular RNAs (circRNAs) are emerging as important regulators in human disease, but their function in osteoporosis (OP) is not sufficiently known. The aim of this study was to identify the possible molecular mechanism of circ_KIAA0922 in osteogenic differentiation of Saos-2 cells in vitro and the interactions among circ_KIAA0922, miR-148a-3p, and SMAD family member 5 (SMAD5). Circ_ KIAA0922, miR-148a-3p, and SMAD5 were overexpressed by transient transfection. Dual-luciferase reporter assay system was used to analyze the combination among circ_KIAA0922, miR-148a-3p, and SMAD5. In addition, the levels of circ_KIAA0922, miR-148a-3p, SMAD5, osteocalcin (OCN), and runt-related transcription factor 2 (RUNX2) were detected using RT-qPCR or western blot analysis. Alizarin red staining was performed to analyze the degree of osteogenic differentiation under the control of circ_KIAA0922, miR-148a-3p, and SMAD5. We found that circ_KIAA0922 knockdown inhibited the proliferation and osteogenic differentiation of Saos-2 cells. Circ_KIAA0922 directly targeted miR-148a-3p, and miR-148a-3p inhibition reversed the effects of circ_KIAA0922 knockdown on the proliferation and osteogenic differentiation of Saos-2 cells. Overexpression of SMAD5 promoted the proliferation and osteogenic differentiation of Saos-2 cells and attenuated the inhibitory effect of miR-148a-3p on cell proliferation and osteogenic differentiation. In conclusion, circ_ KIAA0922 facilitated Saos-2 cell proliferation and osteogenic differentiation via the circ_KIAA0922/ miR-148a-3p/ SMAD5 axes in vitro, thus providing insights into the mechanism of osteogenic differentiation by circ_ KIAA0922.

Overexpression of SENP3 promotes PPAR-γ transcription through the increase of HIF-1α stability via SUMO2/3 and participates in molecular mechanisms of osteoporosis

Patients with type II diabetes are exposed to a high risk of osteoporosis. The present study sought to exploit the detailed mechanisms of the SENP3/HIF-1α/PPAR-γ axis in osteoporosis. A rat model of type II diabetic osteoporosis was established, followed by the isolation of bone marrow mononuclear macrophages (BMMs). Gain- and loss-of-function assays were conducted in rat models and BMMs from rat models, followed by the evaluation of SENP3, HIF-1α, and PPAR-γ expression and detection of osteoclast differentiation-related indexes. Next, the SUMOylated modification of HIF-1α and the regulation of SENP3 on SUMOylated modification level of HIF-1α were assessed using immunoprecipitation, and the binding of HIF-1α to the PPARγ promoter was identified with ChIP and dual-luciferase reporter assays. SENP3 and HIF-1α expression was down-regulated in tissues of type II diabetes-induced osteoporotic rats and BMMs, with high SUMOylated modification levels of HIF-1α. Mechanically, HIF-1α was modified by SUMO2/3. SENP3 suppressed SUMOylated modification of HIF-1α and enhanced HIF-1α stability. HIF-1α bound to the PPAR-γ promoter and facilitated PPAR-γ transcription. SENP3 overexpression restrained osteoblast differentiation in type II diabetes-induced osteoporotic rats and BMMs from rat models. SENP3 knockdown facilitated osteoclast differentiation in type II diabetes-induced osteoporotic rats and BMMs from rat models, which was neutralized by further HIF-1α overexpression. To sum up, SENP3 overexpression restrained osteoclast differentiation in type II diabetic osteoporosis by increasing HIF-1α stability and expression and thus promoting PPAR-γ expression via de-SUMOylation, which might expand the understanding of the mechanisms of type II diabetes combined with osteoporosis.

Circ_0001825 promotes osteogenic differentiation in human-derived mesenchymal stem cells via miR-1270/SMAD5 axis

BACKGROUND

The implication of deregulated circular RNAs in osteoporosis (OP) has gradually been proposed. Herein, we aimed to study the function and mechanism of circ_0001825 in OP using osteogenic-induced human-derived mesenchymal stem cells (hMSCs).

METHODS

The content of genes and proteins was tested by quantitative real-time polymerase chain reaction and Western blotting. The osteogenic differentiation in hMSCs were evaluated by ALP activity and Alizarin Red staining, as well as the detection of osteogenesis-related markers. Cell viability and apoptosis were measured by CCK-8 assay and flow cytometry. The binding between miR-1270 and circ_0001825 or SMAD5 (SMAD Family Member 5) was confirmed by using dual-luciferase reporter assay and pull-down assay.

RESULTS

Circ_0001825 was lowly expressed in OP patients and osteogenic induced hMSCs. Knockdown of circ_0001825 suppressed hMSC viability and osteogenic differentiation, while circ_0001825 overexpression showed the exact opposite effects. Mechanistically, circ_0001825/miR-1270/SMAD5 formed a feedback loop. MiR-1270 was increased and SMAD5 was decreased in OP patients and osteogenic induced hMSCs. MiR-1270 up-regulation suppressed hMSC viability and osteogenic differentiation, which was reversed by SMAD5 overexpression. Moreover, miR-1270 deficiency abolished the effects of circ_0001825 knockdown on hMSCs.

CONCLUSION

Circ_0001825 promoted hMSC viability and osteogenic differentiation via miR-1270/SMAD5 axis, suggesting the potential involvement of circ_0001825 in osteoporosis.

Association between circHIPK3/miR-378a-3p/HDAC4 axis and osteoporotic fractures: A comprehensive investigation

BACKGROUND

Osteoporotic fractures (OFs) are a significant public health issue, which can lead to pain and impaired mobility. The underlying mechanisms of OFs remain unclear, but recent studies have suggested that the circRNA-miRNA-mRNA pathway may play a crucial role.

PURPOSE

This study aimed to investigate the potential involvement of the circHIPK3/miR-378a-3p/HDAC4 pathway in the pathogenesis of OFs.

METHODS

We collected tissue and serum samples from 10 patients with OFs and 10 healthy controls. The expression levels of circHIPK3, miR-378a-3p, and HDAC4 were measured by qPCR and WB. Additionally, we quantified the serum levels of bone metabolism-related indicators (ALP, OC, TRAP, OCIF, ODF) using ELISA.

RESULTS

Our results revealed significant upregulation of circHIPK3 and HDAC4 in both tissue and serum samples from OF patients compared with controls. Simultaneously, we detected a lower expression level of miR-378a-3p in OF tissues and serum than that in the control group. Furthermore, the serum levels of bone metabolism-related indicators ALP, TRAP, OCIF, and ODF were significantly higher in OF patients than in the control group. Interestingly, the serum level of OCIF was lower in OF patients than in the control group.

CONCLUSION

Our study provides important evidence for the involvement of the circHIPK3/miR-378a-3p/HDAC4 pathway in the pathogenesis of OFs. The upregulation of circHIPK3 and HDAC4 and downregulation of miR-378a-3p observed in OF patients suggests their potential regulatory effects on bone metabolism. Meanwhile, abnormal expression of serum bone metabolism-related indicators may contribute to the development of OFs by disrupting the balance of bone remodeling.

Research progress on the role of lncRNA-miRNA networks in regulating adipogenic and osteogenic differentiation of bone marrow mesenchymal stem cells in osteoporosis

Osteoporosis (OP) is characterized by a decrease in osteoblasts and an increase in adipocytes in the bone marrow compartment, alongside abnormal bone/fat differentiation, which ultimately results in imbalanced bone homeostasis. Bone marrow mesenchymal stem cells (BMSCs) can differentiate into osteoblasts and adipocytes to maintain bone homeostasis. Several studies have shown that lncRNAs are competitive endogenous RNAs that form a lncRNA-miRNA network by targeting miRNA for the regulation of bone/fat differentiation in BMSCs; this mechanism is closely related to the corresponding treatment of OP and is important in the development of novel OP-targeted therapies. However, by reviewing the current literature, it became clear that there are limited summaries discussing the effects of the lncRNA-miRNA network on osteogenic/adipogenic differentiation in BMSCs. Therefore, this article provides a review of the current literature to explore the impact of the lncRNA-miRNA network on the osteogenic/adipogenic differentiation of BMSCs, with the aim of providing a new theoretical basis for the treatment of OP.

CircZNF367 promotes osteoclast differentiation and osteoporosis by interacting with FUS to maintain CRY2 mRNA stability

BACKGROUND

Osteoporosis, characterized by reduced bone mass and deterioration of bone quality, is a significant health concern for postmenopausal women. Considering that the specific role of circRNAs in osteoporosis and osteoclast differentiation remains poorly understood, this study aims to shed light on their involvement in these processes to enhance our understanding and potentially contribute to improved treatment strategies for osteoporosis.

METHODS

An osteoporotic model was constructed in vivo in ovariectomized mouse. In vitro, we induced osteoclast formation in bone marrow-derived macrophages (BMDMs) using M-CSF + RANKL. To assess osteoporosis in mice, we conducted HE staining. We used MTT and TRAP staining to measure cell viability and osteoclast formation, respectively, and also evaluated their mRNA and protein expression levels. In addition, RNA pull-down, RIP and luciferase reporter assays were performed to investigate interactions, and ChIP assay was used to examine the impact of circZNF367 knockdown on the binding between FUS and CRY2.

RESULTS

We observed increased expression of CircZNF367, FUS and CRY2 in osteoporotic mice and M-CSF + RANKL-induced BMDMs. Functionally, knocking down circZNF367 inhibited osteoporosis in vivo. Furthermore, interference with circZNF367 suppressed osteoclast proliferation and the expression of TRAP, NFATc1, and c-FOS. Mechanistically, circZNF367 interacted with FUS to maintain CRY2 mRNA stability. Additionally, knocking down CRY2 rescued M-CSF + RANKL-induced osteoclast differentiation in BMDMs promoted by circZNF367 and FUS.

CONCLUSION

This study reveals that the circZNF367/FUS axis may accelerate osteoclasts differentiation by upregulating CRY2 in osteoporosis and suggests that targeting circZNF367 may have potential therapeutic effects on osteoporosis.

Global Transcriptomic Study of Circular-RNA Expression Profile in Osteoclasts Infected by Intracellular Staphylococcus aureus

Osteomyelitis is difficult to cure, and the rapidly rising morbidity is a thorny problem accompanied by a large number of joint replacement applications. Staphylococcus aureus is the main pathogen of osteomyelitis. Circular RNAs (circRNAs), as emerging noncoding RNAs, play important roles in multiple physiopathological processes which could provide novel insights into osteomyelitis. However, little is known about the roles of circRNAs in the pathogenesis of osteomyelitis. Osteoclasts, considered bone sentinels, are the resident macrophages in bone and may play the immune defense roles in osteomyelitis. It has been reported that S. aureus can survive in osteoclasts, but the function of osteoclast circRNAs in response to intracellular S. aureus infection remains unclear. In this study, we investigated the profile of circRNAs in osteoclasts infected by intracellular S. aureus through high-throughput RNA sequencing. In total, 24 upregulated and 62 downregulated differentially expressed circRNAs were identified and subsequently analyzed to demonstrate their potential functions. On this basis, three circRNAs (chr4:130718154-130728164+, chr8:77409548-77413627-, and chr1:190871592-190899571-) were confirmed as potential novel biomarkers for the diagnosis of osteomyelitis through the murine model of osteomyelitis. Most importantly, we verified that the circRNA chr4:130718154-130728164+ named circPum1 could regulate the host autophagy to affect the intracellular infection of S. aureus through miR-767. In addition, circPum1 could serve as a promising serum biomarker in osteomyelitis patients caused by S. aureus infection. Taken together, this study provided the first global transcriptomic profile analysis of circRNAs in osteoclasts infected by intracellular S. aureus and first proposed a novel perspective for the pathogenesis and immunotherapy of S. aureus-induced osteomyelitis from the term of circRNAs.

Circ_PIAS1 Promotes the Apoptosis of ALV-J Infected DF1 Cells by Up-Regulating miR-183

(1) Background: circRNAs are closed circular molecules with covalent bonds generated by reverse shearing, which have high stability and have different manifestations in different tissues, cells, or physiological conditions and play important roles in various disease processes and physiological processes. In addition, circ_PIAS1 has been screened out and verified, and the bioinformatics analyzed in previous studies. In this study, we investigated the function of circ_PIAS1 and studied its role in ALV-J infection to provide a basis for the role of circRNA in ALV-J infection. (2) Methods: the effect of circ_PIAS1 on apoptosis during ALV-J infection was studied by flow cytometry and detection of apoptotic gene expression, and miR-183 was screened by a biotin-labeled RNA pull-down technique. After overexpression and inhibition of miR-183, the effect of miR-183 on apoptosis in the process of ALV-J infection was studied by flow cytometry and detection of apoptotic gene expression. (3) Results: after overexpression of circ_PIAS1, flow cytometry and apoptotic gene expression showed that circ_PIAS1 promoted apoptosis. The results of RNA pull-down showed that 173 miRNAs could bind to circ_PIAS1, and circ_PIAS1 up-regulated the expression of miR-183. On the other hand, the same results were obtained whether miR-183 was overexpressed or inhibited that miR-183 affected ALV-J infection by promoting cell apoptosis. (4) Conclusions: circ_PIAS1 up-regulated the expression of miR-183 and influenced ALV-J infection by promoting cell apoptosis.

Role of ceRNA network in inflammatory cells of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease caused by inflammatory cells. Various inflammatory cells involved in RA include fibroblast-like synoviocytes, macrophages, CD4+T-lymphocytes, B lymphocytes, osteoclasts and chondrocytes. The close interaction between various inflammatory cells leads to imbalance of immune response and disorder of the expression of mRNA in inflammatory cells. It helps to drive production of pro-inflammatory cytokines and stimulate specific antigen-specific T- and B-lymphocytes to produce autoantibodies which is an important pathogenic factor for RA. Competing endogenous RNA (ceRNA) can regulate the expression of mRNA by competitively binding to miRNA. The related ceRNA network is a new regulatory mechanism for RNA interaction. It has been found to be involved in the regulation of abnormal biological processes such as proliferation, apoptosis, invasion and release of inflammatory factors of RA inflammatory cells. Understanding the ceRNA network in 6 kinds of RA common inflammatory cells provides a new idea for further elucidating the pathogenesis of RA, and provides a theoretical basis for the discovery of new biomarkers and effective therapeutic targets.

Fine-tuning osteoclastogenesis: An insight into the cellular and molecular regulation of osteoclastogenesis

Osteoclasts, the bone-resorbing cells, are essential for the bone remodeling process and are involved in the pathophysiology of several bone-related diseases. The extensive corpus of in vitro research and crucial mouse model studies in the 1990s demonstrated the key roles of monocyte/macrophage colony-stimulating factor, receptor activator of nuclear factor kappa B ligand (RANKL) and integrin αvβ3 in osteoclast biology. Our knowledge of the molecular mechanisms by which these variables control osteoclast differentiation and function has significantly advanced in the first decade of this century. Recent developments have revealed a number of novel insights into the fundamental mechanisms governing the differentiation and functional activity of osteoclasts; however, these mechanisms have not yet been adequately documented. Thus, in the present review, we discuss various regulatory factors including local and hormonal factors, innate as well as adaptive immune cells, noncoding RNAs (ncRNAs), etc., in the molecular regulation of the intricate and tightly regulated process of osteoclastogenesis. ncRNAs have a critical role as epigenetic controllers of osteoclast physiologic activities, including differentiation and bone resorption. The primary ncRNAs, which include micro-RNAs, circular RNAs, and long noncoding RNAs, form a complex network that affects gene transcription activities associated with osteoclast biological activity. Greater knowledge of the involvement of ncRNAs in osteoclast biological activities will contribute to the treatment and management of several skeletal diseases such as osteoporosis, osteoarthritis, rheumatoid arthritis, etc. Moreover, we further outline potential therapies targeting these regulatory pathways of osteoclastogenesis in distinct bone pathologies.

CircRNAs in osteoarthritis: research status and prospect

Osteoarthritis (OA) is the most common joint disease globally, and its progression is irreversible. The mechanism of osteoarthritis is not fully understood. Research on the molecular biological mechanism of OA is deepening, among which epigenetics, especially noncoding RNA, is an emerging hotspot. CircRNA is a unique circular noncoding RNA not degraded by RNase R, so it is a possible clinical target and biomarker. Many studies have found that circRNAs play an essential role in the progression of OA, including extracellular matrix metabolism, autophagy, apoptosis, the proliferation of chondrocytes, inflammation, oxidative stress, cartilage development, and chondrogenic differentiation. Differential expression of circRNAs was also observed in the synovium and subchondral bone in the OA joint. In terms of mechanism, existing studies have mainly found that circRNA adsorbs miRNA through the ceRNA mechanism, and a few studies have found that circRNA can serve as a scaffold for protein reactions. In terms of clinical transformation, circRNAs are considered promising biomarkers, but no large cohort has tested their diagnostic value. Meanwhile, some studies have used circRNAs loaded in extracellular vesicles for OA precision medicine. However, there are still many problems to be solved in the research, such as the role of circRNA in different OA stages or OA subtypes, the construction of animal models of circRNA knockout, and more research on the mechanism of circRNA. In general, circRNAs have a regulatory role in OA and have particular clinical potential, but further studies are needed in the future.

Circular RNAs: Promising Targets in Osteoporosis

PURPOSE OF REVIEW

Circular RNAs (circRNAs) are RNA transcripts derived from fragments of pre-messenger RNAs through a back-splicing process. An advantage that rises from their circular covalently closed conformation is their high stability, when compared with their linear counterparts. The current review focuses on the emerging roles of circRNAs in osteoporosis, including in osteogenic differentiation and osteoclastogenesis. Their potential as osteoporosis biomarkers will also be discussed.

RECENT FINDINGS

Although firstly described as non-coding, some of these single-stranded RNAs were recently reported to possess protein-coding capacity. On the other hand, the circRNAs exhibit cell and tissue-specific patterns at the transcriptome level in eukaryotes and are regulated throughout the development or disease progression. Even though thousands of these circular transcripts are listed and annotated, only a limited number of studies describe their biological role in bone processes. Recent evidence indicates inhibitory activator roles in both osteoblasts and osteoclasts differentiation and function. Latest screenings in the blood, plasma, or serum of osteoporosis patients support the potential for circRNA signature to be used as biomarkers in osteoporosis, but further validation is required. While intense research into circRNAs has been detailing their biological roles, there remains a need for standardization and further research to fulfil the future potential of this emerging and highly promising class of regulatory molecules.

Histone methyltransferase SETDB1 promotes osteogenic differentiation in osteoporosis by activating OTX2-mediated BMP-Smad and Wnt/β-catenin pathways

Osteogenic differentiation plays important roles in the pathogenesis of osteoporosis. In this study, we explored the regulatory mechanism of histone methyltransferase SET domain bifurcated 1 (SETDB1) underlying the osteogenic differentiation in osteoporosis. The common osteoporosis-related genes were retrieved from the GeneCards, CTD, and Phenolyzer databases. The enrichment analysis was conducted on the candidate osteoporosis-related genes using the PANTHER software, and the binding site between transcription factors and target genes predicted by hTFtarget. The bioinformatics analyses suggested 6 osteoporosis-related chromatin/chromatin binding protein or regulatory proteins (HDAC4, SIRT1, SETDB1, MECP2, CHD7, and DKC1). Normal and osteoporosis tissues were collected from osteoporosis patients to examine the expression of SETDB1. It was found that SETDB1 was poorly expressed in osteoporotic femoral tissues, indicating that SETDB1 might be involved in the development of osteoporosis. We induced SETDB1 overexpression/knockdown, orthodenticle homeobox 2 (OTX2) overexpression, activation of Wnt/β-catenin or BMP-Smad pathways alone or in combination in osteoblasts or ovariectomized mice. The data indicated that SETDB1 methylation regulated H3K9me3 in the OTX2 promoter region and inhibited the expression of OTX2. Besides, the BMP-Smad and Wnt/β-catenin pathways were inhibited by OTX2, thereby resulting in inhibited osteogenic differentiation. Animal experiments showed that overexpressed SETDB1 could promote the increase of calcium level and differentiation of femoral tissues. In conclusion, upregulation of SETDB1 promotes osteogenic differentiation by inhibiting OTX2 and activating the BMP-Smad and Wnt/β-catenin pathways in osteoporosis.

Comprehensive analysis of epigenetics mechanisms in osteoporosis

Epigenetic modification pertains to the alteration of genetic-expression, which could be transferred to the next generations, without any alteration in the fundamental DNA sequence. Epigenetic modification could include various processes such as DNA methylation, histone alteration, non-coding RNAs (ncRNAs), and chromatin adjustment are among its primary operations. Osteoporosis is a metabolic disorder that bones become more fragile due to the decrease in mineral density, which could result in a higher risk of fracturing. Recently, as the investigation of the causal pathology of osteoporosis has been progressed, remarkable improvement has been made in epigenetic research. Recent literatures have illustrated that epigenetics is estimated to be one of the most contributing factors to the emergence and progression of osteoporosis. This dissertation primarily focuses on indicating the research progresses of epigenetic mechanisms and also the regulation of bone metabolism and the pathogenesis of osteoporosis in light of the significance of epigenetic mechanisms. In addition, it aims to provide new intelligence for the treatment of diseases related to bone metabolism.

Epigenetic regulation in metabolic diseases: mechanisms and advances in clinical study

Epigenetics regulates gene expression and has been confirmed to play a critical role in a variety of metabolic diseases, such as diabetes, obesity, non-alcoholic fatty liver disease (NAFLD), osteoporosis, gout, hyperthyroidism, hypothyroidism and others. The term 'epigenetics' was firstly proposed in 1942 and with the development of technologies, the exploration of epigenetics has made great progresses. There are four main epigenetic mechanisms, including DNA methylation, histone modification, chromatin remodelling, and noncoding RNA (ncRNA), which exert different effects on metabolic diseases. Genetic and non-genetic factors, including ageing, diet, and exercise, interact with epigenetics and jointly affect the formation of a phenotype. Understanding epigenetics could be applied to diagnosing and treating metabolic diseases in the clinic, including epigenetic biomarkers, epigenetic drugs, and epigenetic editing. In this review, we introduce the brief history of epigenetics as well as the milestone events since the proposal of the term 'epigenetics'. Moreover, we summarise the research methods of epigenetics and introduce four main general mechanisms of epigenetic modulation. Furthermore, we summarise epigenetic mechanisms in metabolic diseases and introduce the interaction between epigenetics and genetic or non-genetic factors. Finally, we introduce the clinical trials and applications of epigenetics in metabolic diseases.

CircRNA hsa_circ_0006859 inhibits the osteogenic differentiation of BMSCs and aggravates osteoporosis by targeting miR-642b-5p/miR-483-3p and upregulating EFNA2/DOCK3

Hsa_circ_0006859 has been found as a possible biomarker for postmenopausal osteoporosis (PMOP) with an effect on the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), but the underlying mechanism is unclear. Bioinformatics analysis was used to identify dysregulated RNAs involved in osteoporosis based on public datasets. Function assays were used to determine the functions of hsa_circ_0006859 on cell proliferation and osteogenic differentiation in vitro. It was found that hsa_circ_0006859 was upregulated in OVX mice-derived BMSCs, but lowly expressed during osteogenic differentiation. Overexpressing hsa_circ_0006859 inhibited the cell proliferation and osteogenesis of BMSCs and hFOB 1.19 cells, vice versa. Bilateral ovariectomy (OVX) was used to induce PMOP in mice. The interactions among circ_0006859, miR-642b-5p/miR-483-3p, and EFNA2/DOCK3 were determined using the RIP assay. Silencing circ_0006859 relieved PMOP in mice. Mechanistically, circ_0006859 bound to miR-642b-5p/miR-483-3p directly, while miR-642b-5p and miR-483-3p respectively targeted EFNA2 and DOCK3. Hsa_circ_0006859 downregulated the expression of miR-642b-5p/miR-483-3p to upregulate EFNA2/DOCK3. Additionally, miR-642b-5p/miR-483-3p targeted EFNA2/DOCK3 to inhibit BMSCs osteogenic differentiation and facilitate osteoporosis progression by inactivating the Wnt signaling. In conclusion, hsa_circ_0006859 is involved in PMOP by targeting miR-642b-5p/EFNA2 and miR-483-3p/DOCK3 axes to maintain the Wnt-signaling pathway, which may be a novel possible therapeutic targets and biomarkers for PMOP.

METTL14 alleviates the development of osteoporosis in ovariectomized mice by upregulating m6A level of SIRT1 mRNA

The purpose of this study was to investigate whether METTL14 participated in ovariectomized (OVX)-induced osteoporosis (OP) in mice by regulating the m⁶A level of SIRT1 mRNA. OVX was performed on mice to induce OP, and mouse bone marrow stromal cells (BMSCs) and bone marrow mononuclear macrophages (BMMs) were isolated to induce osteoblast differentiation and osteoclast differentiation, respectively. The morphology of bone trabeculae was evaluated under a micro-CT scanner. The changes in pathology of bone tissues were observed through staining using hematoxylin-eosin. The number of osteoclasts was measured by tartrate-resistant acid phosphatase staining, and the content of serum calcium, PINP, and CTX-I was tested by enzyme-linked immunosorbent assay, accompanied by the measurement of the expression of SIRT1, METTL14, osteogenic marker genes, and osteoclast marker genes. The m⁶A modification level of SIRT1 and the binding between METTL14 and SIRT1 were verified. In OVX mice, SIRT1 and METTL14 were downregulated. Overexpression of SIRT1 or METTL14 increased the expression of osteogenic marker genes but decreased the expression of osteoclast marker genes. Additionally, METTL14 overexpression increased m⁶A level of SIRT1 mRNA. Furthermore, overexpression of METTL14 promoted osteoblast differentiation and suppressed osteoclast differentiation, which were reversed by knockdown of SIRT1. METTL14 promoted osteoblast differentiation and repressed osteoclast differentiation by m⁶A-dependent upregulation of SIRT1 mRNA, thereby alleviating OP development.

Implications and theragnostic potentials of circular RNAs in rheumatic diseases

Circular RNAs (circRNAs), a class of non-coding RNAs (ncRNAs), are highly stable and ubiquitous molecules that exhibit tissue-specific expression. Accumulating evidence has shown that aberrant expression of circRNAs can play a role in the pathogenesis of several diseases. Rheumatic diseases are a varied group of autoimmune and inflammatory disorders affecting mainly the musculoskeletal system. Notably, circRNAs, which are essential immune system gene modulators, are strongly linked to the occurrence and progression of autoimmune disorders. Here, we present and discuss the current findings concerning the roles, implications and theragnostic potentials of circRNAs in common rheumatic diseases, including ankylosing spondylitis (AS), osteoarthritis (OA), osteoporosis (OP), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Crohn's disease (CD), and gout. This review aims to provide new insights to support the development of novel diagnostic and therapeutic strategies for these disabling diseases.

Epigenetic Regulations in Autoimmunity and Cancer: from Basic Science to Translational Medicine

Epigenetics, as a discipline that aims to explain the differential expression of phenotypes arising from the same gene sequence and the heritability of epigenetic expression, has received much attention in medicine. Epigenetic mechanisms are constantly being discovered, including DNA methylation, histone modifications, noncoding RNAs and m6A. The immune system mainly achieves an immune response through the differentiation and functional expression of immune cells, in which epigenetic modification will have an important impact. Because of immune infiltration in the tumor microenvironment, immunotherapy has become a research hotspot in tumor therapy. Epigenetics plays an important role in autoimmune diseases and cancers through immunology. An increasing number of drugs targeting epigenetic mechanisms, such as DNA methyltransferase inhibitors, histone deacetylase inhibitors, and drug combinations, are being evaluated in clinical trials for the treatment of various cancers (including leukemia and osteosarcoma) and autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis). This review summarizes the progress of epigenetic regulation for cancers and autoimmune diseases to date, shedding light on potential therapeutic strategies.

Exosomal circ_0091741 promotes gastric cancer cell autophagy and chemoresistance via the miR-330-3p/TRIM14/Dvl2/Wnt/β-catenin axis

The importance of cancer cell-released exosomes in the treatment of various cancers has been well-characterized. The current study aims to examine the potential biological functions of gastric cancer (GC) cell-released exosomes delivering a novel circRNA circ_0091741 in GC and the underlying molecular mechanism. Expression of circ_0091741 was examined in the GC cells, (OXA)-resistant HGC-27 (HGC-27/OXA) cells, and isolated exosomes, after which its downstream miRNA was analyzed. The role and mechanism of the circ_0091741 transmitted by GC cells-derived exosomes in GC cell autophagy and chemoresistance were assessed using various molecular biological methods. A mouse tumor xenograft model was prepared to discern the effect of circ_0091741 on tumorigenesis in vivo. GC cells and their exosomes were characterized by upregulated circ_0091741 expression. circ_0091741 transferred by GC cell-derived exosomes induced the autophagy and OXA resistance of GC cells. circ_0091741 obstructed the binding of miR-330-3p to TRIM14 and increased the expression of TRIM14. TRIM14 could cause activation of the Wnt/β-catenin signaling pathway by stabilizing Dvl2. By this mechanism, the autophagy and OXA resistance of GC cells were augmented. In vivo assay unfolded that orthotopic implantation of exosomal circ_0091741 overexpressed GC cells into nude mice enhanced tumorigenesis. In conclusion, our study emphasized the promotive role of exosomal circ_0091741 in autophagy and chemoresistance of GC cells, thus laying the basis for the development of novel therapeutic targets for GC treatment.

Circular RNAs: typical biomarkers for bone-related diseases

Bone is a connective tissue that has important functions in the human body. Cells and the extracellular matrix (ECM) are key components of bone and are closely related to bone-related diseases. However, the outcomes of conventional treatments for bone-related diseases are not promising, and hence it is necessary to elucidate the exact regulatory mechanisms of bone-related diseases and identify novel biomarkers for diagnosis and therapy. Circular RNAs (circRNAs) are single-stranded RNAs that form closed circular structures without a 5' cap or 3' tail and polycyclic adenylate tails. Due to their high stability, circRNAs have the potential to be typical biomarkers. Accumulating evidence suggests that circRNAs are involved in bone-related diseases, including osteoarthritis, osteoporosis, osteosarcoma, multiple myeloma, intervertebral disc degeneration, and rheumatoid arthritis. Herein, we summarize the recent research progress on the characteristics and functions of circRNAs, and highlight the regulatory mechanism of circRNAs in bone-related diseases.

Tetrandrine inhibits RANKL-induced osteoclastogenesis by promoting the degradation of TRAIL

Background

Tetrandrine, a bisbenzylisoquinoline (BBI) alkaloid extracted from Stephania tetrandra (S. Moore), and is widely used in several diseases such as tuberculosis, hyperglycemia, malaria, and tumors. Tetrandrine was recently shown to prevent bone loss in ovariectomized mice. However, the specific mechanism underlying osteoclastogenesis inhibition remains unclear.

Methods

Tetrandrine’s cytotoxicity to cells was determined using the Cell Counting Kit-8 assay. Tartrate-resistant acid phosphatase staining, immunofluorescence and bone resorption assay were performed to evaluate osteoclasts’ differentiation and absorption capacity. The bone-forming capacity was assessed using alkaline phosphatase and Alizarin red S staining. qPCR and Western blotting were applied to assess the related genes and protein expression. Tetrandrine’s impact on TRAIL was demonstrated through a co-immunoprecipitation assay. Animal experiments were performed for the detection of the therapeutic effect of Tetrandrine on osteoporosis.

Results

Tetrandrine attenuated RANKL-induced osteoclastogenesis and decreased the related gene expression. The co-immunoprecipitation assay revealed that Tetrandrine administration accelerated the ubiquitination of TNF-related apoptosis-inducing ligand (TRAIL), which was subsequently degraded. Moreover, TRAIL overexpression was found to partially reverse the Tetrandrine-induced inhibition of osteoclastogenesis. Meanwhile, Tetrandrine significantly inhibited the phosphorylation of p38, p65, JNK, IKBα and IKKα/β, while the TRAIL overexpression weakened this effect. In addition, Tetrandrine promoted osteogenesis and inhibited the TRAIL expression in osteoblasts. Tetrandrine consistently improved bone destruction by stimulating bone formation and inhibiting bone resorption in an OVX-induced mouse model.

Conclusion

Tetrandrine inhibits RANKL-induced osteoclastogenesis by promoting TRAIL degradation and promotes osteoblast differentiation, suggesting its potential in antiosteopenia pharmacotherapy.

Serum hsa_circ_0000615 is a prognostic biomarker of sorafenib resistance in hepatocellular carcinoma

BACKGROUND

Circular RNAs (circRNAs) can shape tumor progression and chemoresistance. How specific circRNAs shape hepatocellular carcinoma (HCC) chemoresistance, however, remains to be fully elucidated.

METHODS

In total, serum samples were collected from 202 HCC patients that had completed four sorafenib chemotherapy cycles. Serum hsa_circ_0000615 levels in these patients were quantified via quantitative real-time polymerase chain reaction (qRT-PCR), with demographic details and survival outcomes being recorded for subsequent analyses.

RESULTS

We found hsa_circ_0000615 to be significantly upregulated in chemoresistant HCC patients relative to chemosensitive patients, with such upregulation being positively correlated with disease stage. Moreover, the area under the curve (AUC) value for hsa_circ_0000615 was moderately good, and high levels of hsa_circ_0000615 expression were associated with shorter overall survival among chemoresistant HCC patients.

CONCLUSION

Our results highlight hsa_circ_0000615 as a promising driver of sorafenib resistance in HCC patients, highlighting it as a promising target for the treatment of this deadly cancer type.

MCU Inhibitor Ruthenium Red Alleviates the Osteoclastogenesis and Ovariectomized Osteoporosis via Suppressing RANKL-Induced ROS Production and NFATc1 Activation through P38 MAPK Signaling Pathway

Osteoporosis is a disorder of bone metabolism that is extremely common in elderly patients as well as in postmenopausal women. The main manifestation is that the bone resorption capacity is greater than the bone formation capacity, which eventually leads to a decrease in bone mass, increasing the risk of fracture. There is growing evidence that inhibiting osteoclast formation and resorption ability can be effective in treating and preventing the occurrence of osteoporosis. Our study is the first time to explore the role of the mitochondrial calcium uniporter (MCU) and its inhibitor ruthenium red (RR) in bone metabolism, clarifying the specific mechanism by which it inhibits osteoclast formation in vitro and plays a therapeutic role in osteoporosis in vivo. We verified the suppressive effects of RR on the receptor activator of nuclear factor-κB ligand (RANKL-)-induced differentiation and bone resorption function of osteoclasts in vitro. The reactive oxygen species (ROS) production stimulated by RANKL and the expression level of P38 MAPK/NFATc1 were also found to be inhibited by RR. Moreover, the promotion of RR on osteogenesis differentiation was investigated by alkaline phosphatase (ALP) and alizarin red S (ARS) staining and the detection of osteogenesis-specific gene expression levels by quantitative polymerase chain reaction (qPCR) and western blotting. Moreover, in ovariectomy (OVX-)-induced osteoporosis models, RR can downregulate the expression and function of the MCU, relieving bone loss and promoting osteogenesis to present a therapeutic effect on osteoporosis. This new finding will provide an important direction for the study of RR and MCU in the study of bone metabolism therapy targets.

Comprehensive analysis of differently expression mRNA and non-coding RNAs, and their regulatory mechanisms on relationship in thiram-induced tibial dyschondroplasia in chicken

Thiram pollution is one of the main causes of tibial dyschondroplasia (TD) induced by feed sources. Several studies have speculated that miRNA, circRNA and lncRNA may have significant impact on the development of TD, however, the specific mRNAs and noncoding RNAs and their respective regulatory mechanisms and functions in the development of TD have not been explored. Therefore, in this present study, we screened the differentially expressed mRNA, miRNA, circRNA and lncRNA by whole-transcriptome sequencing (RNA-seq) and differentially expressed genes (DEGs) enrichment, as well as constructed the interaction network among the mRNA-miRNA, mRNA-lncRNA and mRNA-miRNA-circRNA. The sequencing results were verified by fluorescence real-time quantitative PCR (RT-qPCR). The results obtained in this study, revealed that the cells were atrophied and disordered in the TD group, and the expression of BMP6, TGF-β and VEGF were significantly reduced. A total of 141 mRNAs, 10 miRNAs, 23 lncRNAs and 35 circRNAs of DEGs were obtained (p<0.05) Theses DEGs were enriched in the adhere junction and insulin signaling pathways. In addition, the mRNA-miRNA-circRNA network suggested that several pivotal ceRNA showed a regulatory relationship between the transcripts with miRNA, circRNA or lncRNA. Taken together, the results in the present study, represent an insight for further functional research on the ceRNA regulatory mechanism of TD in broilers.

Genome-Wide Identification and Characterization of Circular RNAs during Skeletal Muscle Development in Meat Rabbits

Simple Summary

Our knowledge of circRNAs regulating skeletal muscle development remains largely unknown in meat rabbits. Therefore, we collected the leg muscle tissues of ZIKA rabbits at three key growth stages. A combination of circRNA assembly from a circRNA-seq library and the whole-transcriptome sequencing data identified credible circRNAs in our samples. We found these circRNAs were more conserved between rabbits and humans than between rabbits and mice. A prediction of circRNA–microRNA–mRNAs networks revealed that circRNAs might be the regulators that mainly functioned in rabbits’ muscle neuron development and metabolic processes. Our work provides a catalog of circRNAs regulating skeletal muscle development at key growth stages in rabbits and might give a new insight into rabbit breeding.

Abstract

Skeletal muscle development plays a vital role in muscle quality and yield in meat rabbits. Circular RNAs (circRNAs) are a new type of single-stranded endogenous non-coding RNAs involved in different biological processes. However, our knowledge of circRNAs regulating skeletal muscle development remains largely unknown in meat rabbits. In this study, we collected the leg muscle tissues of ZIKA rabbits at three key growth stages. By performing whole-transcriptome sequencing, we found the sequential expression of day 0- (D0-), D35-, and D70-selective mRNAs mainly functioned in muscle development, nervous development, and immune response during skeletal muscle development, respectively. Then, a combination of circRNA assembly from a circRNA-seq library and the whole-transcriptome sequencing data identified 6845 credible circRNAs in our samples. Most circRNAs were transcribed from exons of known genes, contained few exons, and showed short length, and these circRNAs were more conserved between rabbits and humans than between rabbits and mice. The upregulated circRNAs, which were synchronously changed with host genes, primarily played roles in MAPK signaling pathways and fatty acid biosynthesis. The prediction of circRNA–microRNA–mRNAs networks revealed that circRNAs might be the regulators that mainly functioned in rabbits’ muscle neuron development and metabolic processes. Our work provides a catalog of circRNAs regulating skeletal muscle development at key growth stages in rabbits and might give a new insight into rabbit breeding.

Circ_0114428 promotes proliferation, fibrosis and EMT process of high glucose-induced glomerular mesangial cells through regulating the miR-185-5p/SMAD3 axis

Circular RNA (circRNA) has been confirmed to be the key regulators of diabetic nephropathy (DN) progression. However, the role of circ_0114428 in the DN progression remains unclear. Glomerular mesangial cells (GMCs) were treated with high glucose (HG) to mimic DN cell models in vitro. The expression levels of circ_0114428, microRNA (miR)-185-5p, and SMAD3 mRNA were examined by quantitative real-time PCR. Cell proliferation ability was detected by MTT assay, EdU staining and flow cytometry. The protein levels of proliferation marker, fibrosis markers, epithelial-mesenchymal transition (EMT) markers and SMAD3 were measured by western blot assay. The interaction between miR-185-5p and circ_0114428 or SMAD3 was confirmed via dual-luciferase reporter assay, RIP assay and RNA pull-down assay. Our data showed that circ_0114428 was upregulated in HG-induced GMCs. Circ_0114428 overexpression could aggravate the promotion effect of HG on the proliferation, fibrosis and EMT process of GMCs, while its knockdown had an opposite effect. In the terms of mechanisms, circ_0114428 could sponge miR-185-5p to regulate SMAD3. MiR-185-5p inhibitor could reverse the suppressive effect of circ_0114428 knockdown on the proliferation, fibrosis and EMT process in HG-induced GMCs. Also, SMAD3 overexpression abolished the inhibition of miR-185-5p on the proliferation, fibrosis and EMT process in HG-induced GMCs. Taken together, our data suggested that circ_0114428 might promote DN progression by regulating the miR-185-5p/SMAD3 axis.

Exosome mediated biological functions within skeletal microenvironment

Exosomes are membranous lipid vesicles fused with intracellular multicellular bodies that are released into the extracellular environment. They contain bioactive substances, including proteins, RNAs, lipids, and cytokine receptors. Exosomes in the skeletal microenvironment are derived from a variety of cells such as bone marrow mesenchymal stem cells (BMSCs), osteoblasts, osteoclasts, and osteocytes. Their biological function is key in paracrine or endocrine signaling. Exosomes play a role in bone remodeling by regulating cell proliferation and differentiation. Genetic engineering technology combined with exosome-based drug delivery can therapy bone metabolic diseases. In this review, we summarized the pathways of exosomes derived from different skeletal cells (i.e., BMSCs, osteoblasts, osteocytes, and osteoclasts) regulate the skeletal microenvironment through proteins, mRNAs, and non-coding RNAs. By exploring the role of exosomes in the skeletal microenvironment, we provide a theoretical basis for the clinical treatment of bone-related metabolic diseases, which may lay the foundation to improve bone tumor microenvironments, alleviate drug resistance in patients.

lncRNA SNHG15 as a ceRNA modulates Osteoclast Differentiation, Proliferation, and Metastasis by Sponging miR-381-3p/NEK2 Axis

Background

A growing number of studies have shown that long noncoding RNAs play an important role in osteoclast differentiation. However, there are few studies on the roles of lncRNA small nucleolar RNA host gene 15 (SNHG15) in osteoclast differentiation.

Methods

The expressions of SNHG15, miR-381-3p, and never in mitosis-related kinase 2 (NEK2) mRNA were detected by real-time quantitative polymerase chain reaction (RT-qPCR); Western blot detected NEK2 and osteoclast markers (Cathepsin K, CTSK), matrix metalloproteinase 9 (MMP9), nuclear factor of activated T cell 2 (NFAT2), and tartrate-resistant acid phosphatase (TRAP) protein levels; cell proliferation was detected by Cell Counting Kit-8 (CCK-8), and the formation of osteoclasts was observed by TRAP staining; the F-actin skeleton was stained with tetramethylrhodamine isothiocyanate (TRITC) phalloidin; cell migration rate was detected by Transwell; dual-luciferase reporter gene assay and RNA-binding protein immunoprecipitation (RIP) assay verified the targeting relationship between miR-381-3p, SNHG15, and NEK2.

Results

The expression of SNHG15 was increased in THP-1 cells stimulated by macrophage colony-stimulating factor (M-CSF)/receptor activator of nuclear factor-kappa B ligand (RANKL). Overexpression of SNHG15 significantly promoted the proliferation, migration, osteoclast differentiation, and expression of osteoclast markers CTSK, MMP9, NFAT2, and TRAP of THP-1 cells induced by M-CSF/RANKL. Knockdown of SNHG15 reversed this effect. Overexpression of SNHG15 downregulated the inhibitory effect of overexpression of miR-381-3p on the proliferation, migration, and differentiation of THP-1 cells induced by M-CSF/RANKL. Knockdown of miR-381-3p reversed the inhibitory effect of knockdown of NEK2 on the proliferation, migration, and differentiation of THP-1 cells induced by M-CSF/RANKL.

Conclusion

SNHG15 acted as a ceRNA promoted the proliferation, migration, and differentiation of THP-1 cells induced by M-CSF/RANKL through sponging miR-381-3p to promote the expression of NEK2.

Novel insights into the interaction between N6-methyladenosine methylation and noncoding RNAs in musculoskeletal disorders

BACKGROUND

Musculoskeletal disorder (MSD) are a class of inflammatory and degener-ative diseases, but the precise molecular mechanisms are still poorly understood. Noncoding RNA (ncRNA) N6-methyladenosine (m6A) modification plays an essential role in the pathophysiological process of MSD. This review summarized the interaction be-tween m6A RNA methylation and ncRNAs in the molecular regulatory mechanism of MSD. It provides a new perspective for the pathophysiological mechanism and ncRNA m6A targeted therapy of MSD.

METHODS

A comprehensive search of databases was conducted with musculoskeletal disorders, noncoding RNA, N6-methyladenosine, intervertebral disc degeneration, oste-oporosis, osteosarcoma, osteoarthritis, skeletal muscle, bone, and cartilage as the key-words. Then, summarized all the relevant articles.

RESULTS

Intervertebral disc degeneration (IDD), osteoporosis (OP), osteosarcoma (OS), and osteoarthritis (OA) are common MSDs that affect muscle, bone, cartilage, and joint, leading to limited movement, pain, and disability. However, the precise pathogenesis remains unclear, and no effective treatment and drug is available at present. Numerous studies confirmed that the mutual regulation between m6A and ncRNAs (i.e., microRNAs, long ncRNAs, and circular RNAs) was found in MSD, m6A modification can regulate ncRNAs, and ncRNAs can also target m6A regulators. ncRNA m6A modification plays an essential role in the pathophysiological process of MSDs by regulating the homeostasis of skeletal muscle, bone, and cartilage.

CONCLUSION

m6A interacts with ncRNAs to regulate multiple biological processes and plays important roles in IDD, OP, OS, and OA. These studies provide new insights into the pathophysiological mechanism of MSD and targeting m6A-modified ncRNAs may be a promising therapy approach.