Long Non-coding RNAs and MicroRNAs Interplay in Osteogenic Differentiation of Mesenchymal Stem Cells

Abstract

Long non-coding RNAs (lncRNAs) have gained great attention as epigenetic regulators of gene expression in many tissues. Increasing evidence indicates that lncRNAs, together with microRNAs (miRNAs), play a pivotal role in osteogenesis. While miRNA action mechanism relies mainly on miRNA-mRNA interaction, resulting in suppressed expression, lncRNAs affect mRNA functionality through different activities, including interaction with miRNAs. Recent advances in RNA sequencing technology have improved knowledge into the molecular pathways regulated by the interaction of lncRNAs and miRNAs. This review reports on the recent knowledge of lncRNAs and miRNAs roles as key regulators of osteogenic differentiation. Specifically, we described herein the recent discoveries on lncRNA-miRNA crosstalk during the osteogenic differentiation of mesenchymal stem cells (MSCs) derived from bone marrow (BM), as well as from different other anatomical regions. The deep understanding of the connection between miRNAs and lncRNAs during the osteogenic differentiation will strongly improve knowledge into the molecular mechanisms of bone growth and development, ultimately leading to discover innovative diagnostic and therapeutic tools for osteogenic disorders and bone diseases.

Keywords: crosstalk; interplay; lncRNA; long non-coding RNA; mesenchymal stem cell; miRNA; microRNA; osteogenic differentiation.

FIGURE 1

Long non-coding RNAs (lncRNAs) classification on the basis of localization. lncRNAs transcription mainly occurs in intronic regions. Enhancer and promoter regions can also undergo lncRNAs transcription. Based on the genomic position, lncRNAs can be divided into five categories, such as sense, antisense, bidirectional, intronic, and intergenic lncRNAs. Following biosynthesis, lncRNAs form a complex which includes a number interacting proteins to eventually sponge miRNA targets.

FIGURE 2

Biogenesis of long non-coding RNAs (lncRNAs) and microRNAs (miRNAs). lncRNAs and miRNAs are both transcribed by RNA polymerases II (Pol II). Transcribed lncRNAs directly bind mRNAs and/or miRNAs targets. Differently from lncRNAs, miRNAs undergo a series of processes to become mature. The primary miRNA precursor, i.e., pri-microRNA, is processed in pre-microRNA through the cutting activity of Drosha and DGCR8 enzymes. Then, pre-microRNA is transported into the cytoplasm by Exportin-5 where it is processed by Dicer and TRBP enzymes, forming microRNA duplex. The single strand of microRNA duplex is then complexed with RISC to act as formed mature microRNA by targeting mRNAs.

FIGURE 3

The crosstalk between long non-coding RNAs (lncRNAs) and microRNAs (miRNAs). lncRNAs and miRNAs are both transcribed from a non-coding region of the genome, meanwhile mRNAs are transcribed. lncRNAs compete with mRNAs to bind miRNA targets, by acting as sponge of miRNAs and thus abolishing the miRNA’s inhibitory action. miRNA–mRNA binding inhibits protein expression, whereas lncRNA–miRNA binding allows protein translation.

FIGURE 4

Long non-coding RNA (lncRNAs) and microRNAs (miRNAs) involved in osteogenic pathways in Bone Marrow Mesenchymal Stem Cells (BMSCs). Transforming growth factor-beta (TGF-β), bone morphogenic protein (BMP), and the Wingless/Int-1(Wnt)/β-catenin cascades are the pivotal pathways leading to BMSCs osteogenic differentiation. The binding between TGF-β and BMP with respective receptors activate SMAD-dependent and SMAD-dependent cascades. In TGF-β SMAD-dependent signaling, SMAD2/3 (R-SMAD) is phosphorylated upon ligan-receptor binding. Phosphorylated R-SMAD interacts with SMAD4 and translocate into the nucleus where, together with CBP and P300 co-activators, induce RUNX2 expression. In the cell nucleus R-SMAD without SMAD4 interacts with HDAC4/5 blocking RUNX2 expression. Unphosphorylated R-SMAD are degraded by ubiquitination. TGF-β SMAD-dependent pathways is positively regulated by lncH19-miR-675 and lncH19-miR-675, whereas it is negatively regulated by lncHOTAIR-miR-17-5p. In BMP SMAD-dependent cascade R-SMAD comprise SMAD1/5/8. SMAD6/7 and Smurf1/2 are negative regulators of this pathway. LncKCNQ1OT1-miR-214, lncKCNQ1OT1-miR-320a, lncLOC103691336-miR138-5p, lncNEAT1-miR-29b-3p trigger BMSCs differentiation. SMAD-independent signaling pathway induces DLX5, RUNX2 and OSX phosphorylation, which is favored by lncH19-miR-188, lncHULC-miR-195, lncMALAT1-miR-143, lncMALAT1-miR-34c axes. Wnt/β-catenin induces BMSCs osteogenic differentiation by β-catenin translocation into the nucleus and following expression of target genes. lncH19-miR-141, lncLINC00707-miR-370-3p, lncLINC00707-miR-145, lncHULC-miR-195, lncFAM83H-AS1-miR-541-3p, lncLINC-ROR- miR-138 and miR-145 positively regulate Wnt/β-catenin signaling pathway. lncXIXT-miRNA-30a-5p, lncDGCR5-miR-30d-5p directly positively regulate RUNX2, whereas lncMEG3-miR-133a-3p hamper RUNX2 expression.