CircFam190a: a critical positive regulator of osteoclast differentiation via enhancement of the AKT1/HSP90β complex

The bone microenvironment: new insights into the role of stem cells and cell communication in bone regeneration

Mesenchymal stem cells (MSCs) play a crucial role in bone formation and remodeling. Intrinsic genetic factors and extrinsic environmental cues regulate their differentiation into osteoblasts. Within the bone microenvironment, a complex network of biochemical and biomechanical signals orchestrates bone homeostasis and regeneration. In addition, the crosstalk among MSCs, immune cells, and neighboring cells-mediated by extracellular vesicles and non-coding RNAs (such as circular RNAs and micro RNAs) -profoundly influences osteogenic differentiation and bone remodeling. Recent studies have explored specific signaling pathways that contribute to effective bone regeneration, highlighting the potential of manipulating the bone microenvironment to enhance MSC functionality. The integration of advanced biomaterials, gene editing techniques, and controlled delivery systems is paving the way for more targeted and efficient regenerative therapies. Furthermore, artificial intelligence could improve bone tissue engineering, optimize biomaterial design, and enable personalized treatment strategies. This review explores the latest advancements in bone regeneration, emphasizing the intricate interplay among stem cells, immune cells, and signaling molecules. By providing a comprehensive overview of these mechanisms and their clinical implications, we aim to shed light on future research directions in this rapidly evolving field.

CircFak promotes mechanical force-induced osteogenesis via FAK/AKT phosphorylation

OBJECTIVES

Orthodontic treatment is widely applied for addressing orofacial skeletal deformities, with the remodeling of the alveolar bone under mechanical force being the key factor. FAK is essential for cellular response to mechanical force. However, the function of circFak has never been reported. In this study, the microarrays showed that circFak may affect osteogenesis under mechanical force. We aimed to verify the effect of circFak in force-related bone remodeling and investigate the underlying mechanisms.

METHODS

Arraystar microarrays were used to identify differentially expressed circRNAs and microRNAs in response to mechanical stress. The subcellular distribution of circFak was analyzed via RT‒qPCR and FISH. ALP and ARS staining assays were performed to investigate the effects of circFak on osteogenesis. RNA sequencing, bioinformatics analysis, dual-luciferase reporter assays, and RNA immunoprecipitation were accomplished to discover the molecular mechanisms of circFak. AAV-sh-circFak mouse models with tooth movements were established. The role of circFak under mechanical force in vivo was assessed via immunofluorescence and micro-CT analyses.

RESULTS

CircFak expression was significantly upregulated under mechanical force. Osteogenic capacity of osteoblasts was positively correlated with the level of circFak. CircFak promoted mechanical force-induced osteogenesis through miR-425-5p/Ccn3 pathway, and further stimulated the phosphorylation of its parental sourced protein FAK. Our murine models showed that AAV-mediated circFak silencing suppressed osteogenesis.

CONCLUSION

CircFak could obviously promote osteogenesis under mechanical force and may possess ability to become a novel biomarker for prognosis of orthodontic treatments.

Research progress of circRNAs in bone-related diseases

Circular RNAs (circRNAs) are non-coding RNAs that exist naturally in various eukaryotic organisms. The majority of circRNAs are produced through the splicing of exons, although there are a limited number that are generated through the circularization of introns. Studies have shown that circRNAs play an irreplaceable role in the pathogenesis, disease progression, diagnosis, and targeted therapy of motor system tumors (osteosarcoma), metabolic diseases (osteoporosis), and degenerative diseases (osteonecrosis of the femoral head, osteoarthritis, intervertebral disc degeneration). This review summarizes the advancements in circRNA detection techniques and the research progress of circRNAs in orthopedic diseases.

Noncoding RNA as a crucial epigenetic modulator in the degeneration of the ligamentum flavum

Ligamentum flavum degeneration, including hypertrophy and ossification of the ligamentum flavum, leads to degenerative spinal stenosis in older adults. However, the underlying mechanisms of ligamentum flavum degeneration remain unclear, and therapeutic strategies are limited. Noncoding RNAs include microRNAs, circular RNAs, and long noncoding RNAs. As important epigenetic modifications, noncoding RNAs are involved in the progression of several age-related diseases, including ligamentum flavum degeneration. Previous studies have shown that noncoding RNAs can regulate the osteogenic differentiation and fibrosis of ligamentum flavum cells by regulating the expression of related genes. In this review, we discuss noncoding RNAs and their role in ligamentum flavum degeneration.

Skeletal muscle-derived exosomes prevent osteoporosis by promoting osteogenesis

Skeletal muscle and bone are the major organs for physical activity, in which there is a parallel correlation between muscle mass and bone density throughout a lifetime. Osteoporosis is a systemic bone metabolic disorder caused by reduced bone formation and increased bone resorption. Based on the metabolic symbiosis relationship between skeletal muscle and bone, we hypothesis that skeletal muscle secretory factors could play constructive roles in osteoporosis. Exosomes have been verified to transfer bioactive factors among cells. However, the role of skeletal muscle derived-exosomes (SM-Exos) in osteoporosis is still unclear. In this study, we performed neuromuscular electrical stimulation (NMES) intervention on denervated skeletal muscles and subsequently extracted exosomes (DN + ES-Exo) from the skeletal muscles, and then injected these DN + ES-Exo into sarco-osteoporotic rats through tail vein. In vitro studies, we cocultured SM-Exos from different states with differentiated MC3T3-E1 osteoblasts. In brief, our research findings demonstrate that SM-Exos could partially promote osteogenesis both in vivo and in vitro. Further, our findings indicate that skeletal muscle contraction induced by NMES can reverse the incidence of sarco-osteoporosis to a certain degree, and DN + ES-Exo contributes to the improvement in osteoporosis by facilitating osteoblast differentiation. Then, we revealed that NMES might regulate several miRNAs in skeletal muscle, the miRNAs that are encapsulated by SM-Exos might be involved in osteogenic differentiation in a network manner. All in all, this study confirmed the effect of NMES on sarco-osteoporosis and explored the role of SM-Exos in the improvement of osteoporosis, which provide an effective theoretical support for the physical therapy of clinical sarco-osteoporosis.

Attenuating bone loss in osteoporosis: the potential of corylin (CL) as a therapeutic agent

The global prevalence of osteoporosis is being exacerbated by the increasing number of aging societies and longer life expectancies. In response, numerous drugs have been developed in recent years to mitigate bone resorption and enhance bone density. Nonetheless, the efficacy and safety of these pharmaceutical interventions remain constrained. Corylin (CL), a naturally occurring compound derived from the anti-osteoporosis plant Psoralea corylifolia L., has exhibited promising potential in impeding osteoclast differentiation. This study aims to evaluate the effect and molecular mechanisms of CL regulating osteoclast differentiation in vitro and its potential as a therapeutic agent for osteoporosis treatment in vivo. Our investigation revealed that CL effectively inhibits osteoclast formation and their bone resorption capacity by downregulating the transcription factors NFATc1 and c-fos, consequently resulting in the downregulation of genes associated with bone resorption. Furthermore, it has been observed that CL can effectively mitigate the migration and fusion of pre-osteoclast, while also attenuating the activation of mitochondrial mass and function. The results obtained from an in vivo study have demonstrated that CL is capable of attenuating the bone loss induced by ovariectomy (OVX). Based on these significant findings, it is proposed that CL exhibits considerable potential as a novel drug strategy for inhibiting osteoclast differentiation, thereby offering a promising approach for the treatment 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.

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.

Silencing hsa_circ_0032449 inhibits the pancreatic differentiation of human embryonic stem cells via the hsa_miR-195-5p/CCND1/PI3K/AKT signaling pathway

Stem cell-derived β cells (SC-β cells) differentiated from stem cell-derived pancreatic progenitor (PP) cells are promising tools for enabling normal glucose control of islet transplants and have therapeutic potential for type 1 diabetes treatment. Pancreatic specification is essential for SC-β cell induction in vitro and low-quality PP cells may convert into derivatives of non-pancreatic lineages both in vivo and in vitro, impeding PP-derived β cell safety and differentiation efficiency. Circular RNA (circRNA) commonly determines the fate of stem cells by acting as competing endogenous RNA (ceRNA). Currently, the relationships between endogenous circRNA and pancreatic specification remain elusive. Herein, we used whole transcriptome sequencing analysis and functional experiments to reveal that deficiency of hsa_circ_0032449 resulted in posterior foregut-derived PP cells with a weakened the progenitor state with decreased expression of PDX1, NKX6.1 and CCND1. As differentiation processed into maturation, silencing of hsa_circ_0032449 suppressed PP cell development into functionally mature and glucose-responsive SC-β cells. These SC-β cells exhibited lower serum C-peptide levels compared with those of control groups in nude mice and had difficulties in reversing hyperglycemia in STZ-induced diabetic nude mice. Mechanistically, loss of hsa_circ_0032449 participated in PI3K-AKT signaling transduction by acting as a ceRNA to sponge miR-195-5p and by influencing the expression of the downstream target CCND1 at transcription and translation levels. Overall, our findings identified hsa_circ_0032449 as an essential PP cell-fate specification regulator, indicating a promising potential in clinical applications and basic research.