CircRNA AFF4 induced by KDM1A promotes osteogenic differentiation through FNDC5/Irisin pathway

Phytic acid promotes high glucose-mediated bone marrow mesenchymal stem cells osteogenesis via modulating circEIF4B that sponges miR-186-5p and complexes with IGF2BP3

Diabetes-related hyperglycemia inhibits bone marrow mesenchymal stem cell (BMSC) function, thereby disrupting osteoblast capacity and bone regeneration. Dietary supplementation with phytic acid (PA), a natural inositol phosphate, has shown promise in preventing osteoporosis and diabetes-related complications. Emerging evidence has suggested that circular (circ)RNAs implicate in the regulation of bone diseases, but their specific regulatory roles in BMSC osteogenesis in hyperglycemic environments remain elucidated. In this study, in virto experiments demonstrated that PA treatment effectively improved the osteogenic capability of high glucose-mediated BMSCs. Differentially expressed circRNAs in PA-induced BMSCs were identified using circRNA microarray analysis. Here, our findings highlight an upregulation of circEIF4B expression in BMSCs stimulated with PA under a high-glucose microenvironment. Further investigations demonstrated that circEIF4B overexpression promoted high glucose-mediated BMSC osteogenesis. In contrast, circEIF4B knockdown exerted the opposite effect. Mechanistically, circEIF4B sequestered microRNA miR-186-5p and triggered osteogenesis enhancement in BMSCs by targeting FOXO1 directly. Furthermore, circEIF4B inhibited the ubiquitin-mediated degradation of IGF2BP3, thereby stabilizing ITGA5 mRNA and promoting BMSC osteogenic differentiation. In vivo experiments, circEIF4B inhibition attenuated the effectiveness of PA treatment in diabetic rats with cranial defects. Collectively, our study identifies PA as a novel positive regulator of BMSC osteogenic differentiation through the circEIF4B/miR-186-5p/FOXO1 and circEIF4B/IGF2BP3/ITGA5 axes, which offers a new strategy for treating high glucose-mediatedBMSCosteogenic dysfunction and delayed bone regeneration in diabetes.

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.

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.

Epigenetics: Novel crucial approach for osteogenesis of mesenchymal stem cells

Bone has a robust regenerative potential, but its capacity to repair critical-sized bone defects is limited. In recent years, stem cells have attracted significant interest for their potential in tissue engineering. Applying mesenchymal stem cells (MSCs) for enhancing bone regeneration is a promising therapeutic strategy. However, maintaining optimal cell efficacy or viability of MSCs is limited by several factors. Epigenetic modification can cause changes in gene expression levels without changing its sequence, mainly including nucleic acids methylation, histone modification, and non-coding RNAs. This modification is believed to be one of the determinants of MSCs fate and differentiation. Understanding the epigenetic modification of MSCs can improve the activity and function of stem cells. This review summarizes recent advances in the epigenetic mechanisms of MSCs differentiation into osteoblast lineages. We expound that epigenetic modification of MSCs can be harnessed to treat bone defects and promote bone regeneration, providing potential therapeutic targets for bone-related diseases.

Epigenetic control of mesenchymal stem cells orchestrates bone regeneration

Recent studies have revealed the vital role of MSCs in bone regeneration. In both self-healing bone regeneration processes and biomaterial-induced healing of bone defects beyond the critical size, MSCs show several functions, including osteogenic differentiation and thus providing seed cells. However, adverse factors such as drug intake and body senescence can significantly affect the functions of MSCs in bone regeneration. Currently, several modalities have been developed to regulate MSCs' phenotype and promote the bone regeneration process. Epigenetic regulation has received much attention because of its heritable nature. Indeed, epigenetic regulation of MSCs is involved in the pathogenesis of a variety of disorders of bone metabolism. Moreover, studies using epigenetic regulation to treat diseases are also being reported. At the same time, the effects of epigenetic regulation on MSCs are yet to be fully understood. This review focuses on recent advances in the effects of epigenetic regulation on osteogenic differentiation, proliferation, and cellular senescence in MSCs. We intend to illustrate how epigenetic regulation of MSCs orchestrates the process of bone regeneration.