LncRNA AWPPH is downregulated in osteoporosis and regulates type I collagen α1 and α2 ratio

LINC01234 Sponging of the miR-513a-5p/AOX1 Axis is Upregulated in Osteoporosis and Regulates Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells

Non-coding RNAs, including long-chain non-coding RNA (lncRNA) and micro-RNA (miRNA), have been implicated in osteoporosis (OP) progression by regulating osteoblast-dependent bone metabolism. Herein, we investigated whether LINC01234, miR-513a-5p, and AOX1 regulate osteogenic differentiation and proliferation of human bone marrow mesenchymal stem cells (hMSCs). The expression of LINC01234, miR-513a-5p, and AOX1 was monitored using RT-qPCR or western blotting. Cell proliferation was assessed using a CCK8 assay. Alkaline phosphatase activity (ALP) and alizarin red dye staining were performed to determine osteogenic differentiation. Furthermore, the expression of osteoblast differentiation markers, such as ALP, BMP1 (bone morphogenetic protein 1), osteocalcin (OCN), and osteopontin (OPN), was determined by RT-qPCR. Luciferase reporter and RNA immunoprecipitation (RIP) assays were performed to verify the interplay between miR-513a-5p and LINC01234 or AOX1. Compared with the plasma of healthy controls, LINC01234 and AOX1 were highly expressed in the plasma of patients with OP, whereas miR-513a-5p showed low expression. In contrast, LINC01234 and AOX1 expression displayed a gradual decrease in induced differentiated hMSCs, while miR-513a-5p expression was upregulated with induction time. The predicted binding sites between miR-513a-5p and LINC01234 or AOX1 were verified by luciferase reporter and RIP assays. LINC01234 silencing induced osteogenic differentiation and proliferation in vitro, and miR-513a-5p silencing blunted osteogenic differentiation and proliferation modulated by LINC01234. AOX1 silencing caused by miR-513a-5p enhances osteogenic proliferation and differentiation. LINC01234 sponging of the miR-513a-5p/AOX1 axis impeded the osteogenic differentiation of hMSCs, favoring OP progression.

Long non-coding RNA MIR4435-2HG: a key molecule in progression of cancer and non-cancerous disorders

MIR4435-2HG (LINC00978) is a long non-coding RNA (lncRNA) that acts as an oncogene in almost all cancers. This lncRNA participates in the molecular cascades involved in other disorders such as coronary artery diseases, osteonecrosis, osteoarthritis, osteoporosis, and periodontitis. MIR4435-2HG exerts its functions via the spectrum of different mechanisms, including inhibition of apoptosis, sponging microRNAs (miRNAs), promoting cell proliferation, increasing cell invasion and migration, and enhancing epithelial to mesenchymal transition (EMT). MIR4435-2HG can regulate several signaling pathways, including Wnt, TGF-β/SMAD, Nrf2/HO-1, PI3K/AKT, MAPK/ERK, and FAK/AKT/β‑catenin signaling pathways; therefore, it can lead to tumor progression. In the present review, we aimed to discuss the potential roles of lncRNA MIR4435-2HG in developing cancerous and non-cancerous conditions. Due to its pivotal role in different disorders, this lncRNA can serve as a potential biomarker in future investigations. Moreover, it may serve as a potential therapeutic target for the treatment of various diseases.

LncMIR181A1HG is a novel chromatin-bound epigenetic suppressor of early stage osteogenic lineage commitment

Bone formation requires osteogenic differentiation of multipotent mesenchymal stromal cells (MSCs) and lineage progression of committed osteoblast precursors. Osteogenic phenotype commitment is epigenetically controlled by genomic (chromatin) and non-genomic (non-coding RNA) mechanisms. Control of osteogenesis by long non-coding RNAs remains a largely unexplored molecular frontier. Here, we performed comprehensive transcriptome analysis at early stages of osteogenic cell fate determination in human MSCs, focusing on expression of lncRNAs. We identified a chromatin-bound lncRNA (MIR181A1HG) that is highly expressed in self-renewing MSCs. MIR181A1HG is down-regulated when MSCs become osteogenic lineage committed and is retained during adipogenic differentiation, suggesting lineage-related molecular functions. Consistent with a key role in human MSC proliferation and survival, we demonstrate that knockdown of MIR181A1HG in the absence of osteogenic stimuli impedes cell cycle progression. Loss of MIR181A1HG enhances differentiation into osteo-chondroprogenitors that produce multiple extracellular matrix proteins. RNA-seq analysis shows that loss of chromatin-bound MIR181A1HG alters expression and BMP2 responsiveness of skeletal gene networks (e.g., SOX5 and DLX5). We propose that MIR181A1HG is a novel epigenetic regulator of early stages of mesenchymal lineage commitment towards osteo-chondroprogenitors. This discovery permits consideration of MIR181A1HG and its associated regulatory pathways as targets for promoting new bone formation in skeletal disorders.

SMAD4 contributes to chondrocyte and osteocyte development

Different cellular and molecular mechanisms contribute to chondrocyte and osteocyte development. Although vital roles of the mothers against decapentaplegic homolog 4 (also called 'SMAD4') have been discussed in different cancers and stem cell-related studies, there are a few reviews summarizing the roles of this protein in the skeletal development and bone homeostasis. In order to fill this gap, we discuss the critical roles of SMAD4 in the skeletal development. To this end, we review the different signalling pathways and also how SMAD4 defines stem cell features. We also elaborate how the epigenetic factors-ie DNA methylation, histone modifications and noncoding RNAs-make a contribution to the chondrocyte and osteocyte development. To better grasp the important roles of SMAD4 in the cartilage and bone development, we also review the genotype-phenotype correlation in animal models. This review helps us to understand the importance of the SMAD4 in the chondrocyte and bone development and the potential applications for therapeutic goals.