Long Non-Coding RNA MALAT1 Emerges as a Multifaceted Regulator of Bone Remodeling

Long non-coding RNAs were once dismissed as transcriptional noise, but one of them, metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), is now attracting attention far beyond its original identification as a prognostic marker for metastasis in lung cancer. A new narrative review published in Frontiers in Medicine by Yangkai Shi and Zikang Xie of Changzhou Hospital Affiliated to Nanjing University of Chinese Medicine pulls together the growing, and largely preclinical, evidence that MALAT1 acts as a regulatory component in bone homeostasis, influencing the differentiation and activity of both bone-forming osteoblasts and bone-resorbing osteoclasts. Crucially, the authors are explicit that the evidence base is almost entirely preclinical: MALAT1 has not yet been validated as a biomarker or therapeutic target in any clinical study.

MALAT1 is a roughly 8.7-kilobase transcript encoded on human chromosome 11q13, highly conserved among mammals and predominantly localized to nuclear speckles, subnuclear structures associated with pre-mRNA splicing factors. From that nuclear position it can influence alternative splicing, mRNA maturation and gene expression programs by interacting with RNA-binding proteins and chromatin modifiers. Its expression is itself regulated: specificity protein 1 and 3 (SP1 and SP3) bind the MALAT1 promoter and synergistically activate transcription, an effect demonstrated experimentally in hepatocellular carcinoma cells where the inhibitor mithramycin A reduced MALAT1 expression. Epigenetic mechanisms such as histone acetylation have also been implicated, although the specific marks remain to be clarified.

The review frames MALAT1’s skeletal role against the established machinery of bone remodeling. Bone is continuously renewed within the basic multicellular unit, where a phase of osteoclastic resorption is followed by osteoblastic formation, normally in balance. Osteocytes, the most abundant cells in bone, act as mechanosensors and regulate both arms, partly by secreting sclerostin to restrain Wnt signaling and by releasing RANKL. The central coupling module is the RANK-RANKL-OPG axis: osteoblast lineage cells present RANKL to receptors on osteoclast precursors, driving their differentiation, while osteoprotegerin (OPG) secreted by the same lineage acts as a decoy receptor that neutralizes RANKL. It is the ratio of RANKL to OPG, rather than the level of either molecule alone, that determines resorptive activity, and mechanical loading, parathyroid hormone, oestrogen and inflammatory cytokines all converge on this ratio.

Against that background, the review’s central mechanistic claim concerns the β-catenin-OPG/Jagged1 signaling axis. Studies in cultured cells and rodent models indicate that MALAT1 associates with β-catenin and favours its nuclear translocation and transcriptional activity, thereby promoting expression of downstream targets including OPG and Jagged1, a canonical Notch ligand. The authors are careful to note that a direct physical interaction between MALAT1 and the β-catenin protein has been inferred from co-precipitation and protein stabilization experiments rather than demonstrated structurally, so it is presented as a proposed rather than an established mechanism. The proposed route to β-catenin stabilization involves binding to the protein’s N-terminal domain to block its ubiquitin-mediated proteasomal degradation.

The strongest in vivo evidence comes from mouse genetics. Global Malat1 knockout mice on a C57BL/6 background, compared with wild-type littermates at 12 weeks of age in both sexes, showed reduced trabecular bone volume fraction, trabecular number, bone mineral density and connectivity density, with increased trabecular separation, while cortical bone was unaffected. Static histomorphometry revealed increased osteoclast surface per bone surface and osteoclast number per bone perimeter, and calcein double labelling showed a reduced mineral apposition rate and bone formation rate. Importantly, osteoblast-specific conditional knockout mice, generated by crossing Malat1-floxed animals with an osteocalcin promoter-driven Cre line, reproduced the low bone mass phenotype, indicating that the defect originates in the osteoblast lineage. In mice with increased Malat1 expression, higher serum OPG and lower serum CTX-1, a resorption marker, accompanied increased bone mineral density, though the authors stress that no corresponding serum data from human subjects with altered MALAT1 expression have been reported.

The direction of MALAT1’s influence is not uniform, and the review treats this as a central finding rather than a contradiction. In osteoblast and mesenchymal stem cell lineages, MALAT1 favours osteogenic differentiation: it rises during osteogenic induction of mesenchymal stem cells and supports expression of Runx2, Osterix, osteocalcin and osteopontin. In monocyte-macrophage lineage cells, by contrast, MALAT1 favours osteoclastogenesis. The best-supported ceRNA interaction in the osteoclast lineage is with miR-124: in bone marrow-derived macrophages and RAW264.7 cells, MALAT1 binds miR-124 and relieves its repression of NFATc1, the transcription factor that drives osteoclast differentiation, an interaction confirmed by dual-luciferase reporter assay and reciprocal knockdown and rescue experiments. MALAT1 expression is itself induced by RANKL stimulation in these precursor cells.

The review explains the apparent discrepancy through three variables. First, the cell source matters: pro-osteoclastogenic effects are seen when MALAT1 is manipulated within the precursor itself, whereas anti-resorptive effects appear when it is manipulated in osteoblast lineage or mesenchymal cells and osteoclast behaviour is read out indirectly through the RANKL-to-OPG ratio those cells present. Second, stimulation conditions differ: pro-osteoclastogenic effects emerge under sustained RANKL or exosome challenge in culture, where the opposing OPG arm is largely absent, while in vivo OPG produced by osteoblasts buffers the signal. Third, disease context matters, as in multiple myeloma, where NSUN2-dependent methylation stabilizes MALAT1 in tumour cells and the modified transcript is exported in exosomes to osteoclast precursors, inducing RANKL expression and activating AKT and MAPK signaling, a route specific to the tumour setting rather than normal remodeling.

Beyond the β-catenin axis, MALAT1 operates through competing endogenous RNA (ceRNA) mechanisms, sponging microRNAs that repress osteogenic transcription factors. Reporter or immunoprecipitation assays with functional readouts in skeletal or dental cells support interactions with miR-30 (derepressing Runx2 in adipose-derived stem cells), miR-96 (derepressing Osterix in human bone marrow-derived mesenchymal stem cells), miR-93-5p (relieving repression of SMAD5 in periodontal ligament stem cells) and miR-129-5p in aged bone marrow stem cells. Two further axes are narrower: the miR-214 axis, whose effector is ATF4 and whose setting is steroid-induced avascular necrosis of the femoral head, and the miR-204 axis, demonstrated in human aortic valve interstitial cells rather than skeletal cells. The authors also flag a general limitation of ceRNA biology: competition for a microRNA is only meaningful at comparable transcript concentrations, most reported sponge effects rest on overexpression or knockdown plus dual-luciferase reporters, and independent appraisals show such effects are frequently not reproduced once target abundance is measured rather than inferred.

MALAT1’s reach extends to the bone microenvironment more broadly. Its expression responds to mechanical stimuli such as cyclic stretching and fluid shear stress, with YAP/TAZ mechanotransduction implicated; inflammatory cytokines such as TNF-α suppress MALAT1 via NF-κB activation, a pattern seen in inflammatory bone disease and steroid-induced osteonecrosis; and hypoxia has been associated with MALAT1 induction, though a direct interaction between hypoxia-inducible factors and the MALAT1 locus remains proposed rather than demonstrated in bone cells. MALAT1 is also shuttled between cells in exosomes, where osteoblast- or mesenchymal stem cell-derived vesicles carrying the transcript have been reported to promote osteoblast activity through the miR-34c/SATB2 axis in osteoporotic rodent models. In immune compartments, MALAT1 shapes macrophage polarization and T cell cytokine output, although the review notes that key T cell steps, such as a route from MALAT1 through NFAT to RANKL, remain proposed rather than demonstrated, and macrophage findings come largely from non-skeletal or periodontal models.

On the translational side, the review is candid about the obstacles. In disease contexts, MALAT1 is lower in peripheral blood from elderly patients with osteoporosis than in healthy volunteers, an observational association only, and elevated in osteosarcoma, where high levels predict poorer overall survival. Antisense oligonucleotides and siRNAs have modulated MALAT1 in cancer and multiple myeloma models, and nanoparticle and exosome delivery platforms are under consideration, but no CRISPR-mediated modulation of MALAT1 has been reported in any skeletal model. Systemic suppression is complicated by MALAT1’s widespread expression in lung, liver, vasculature and immune compartments, by known liabilities of phosphorothioate antisense chemistry such as liver and kidney accumulation, thrombocytopenia and complement activation, and by the fact that a non-cell-selective agent could worsen the very formation-resorption imbalance it aims to correct, given the transcript’s opposing effects in osteoblast and osteoclast lineages. The authors propose single-cell RNA sequencing and spatial transcriptomics as the tools positioned to resolve whether MALAT1 is enriched in particular bone cell populations, whether the opposing effects reflect distinct cell states, and whether the ceRNA interactions occur at stoichiometrically plausible transcript ratios. Until such work and clinical validation are done, the integrated network model they present should be read as a hypothesis for testing rather than an established description of skeletal regulation.

Subject of Research: The role of the long non-coding RNA MALAT1 in regulating bone homeostasis and remodeling

Article Title: Emerging regulatory role of lncRNA MALAT1 in bone homeostasis: from the β–catenin–OPG/Jagged1 signalling axis to a broader regulatory network

Article References: Shi, Y., & Xie, Z. (2026). Emerging regulatory role of lncRNA MALAT1 in bone homeostasis: from the β–catenin–OPG/Jagged1 signalling axis to a broader regulatory network. Frontiers in Medicine, 13, Article 1980028. https://doi.org/10.3389/fmed.2026.1980028

Image Credits: AI Generated

DOI: 10.3389/fmed.2026.1980028

Keywords: MALAT1, long non-coding RNA, bone homeostasis, bone remodeling, osteoblasts, osteoclasts, osteoporosis, β-catenin, OPG, Jagged1, mesenchymal stem cells, ceRNA