Nuclear stress bodies (nSBs) are nuclear membraneless organelles formed around stress‐inducible HSATIII architectural long noncoding RNAs (lncRNAs). nSBs repress splicing of hundreds of introns during thermal stress recovery, which are partly regulated by CLK1 kinase phosphorylation of temperature‐dependent Ser/Arg‐rich splicing factors (SRSFs). Here, we report a distinct mechanism for this splicing repression through protein sequestration by nSBs. Comprehensive identification of RNA‐binding proteins revealed HSATIII association with proteins related to N6‐methyladenosine (m6A) RNA modification. 11% of the first adenosine in the repetitive HSATIII sequence were m6A‐modified. nSBs sequester the m6A writer complex to methylate HSATIII, leading to subsequent sequestration of the nuclear m6A reader, YTHDC1. Sequestration of these factors from the nucleoplasm represses m6A modification of pre‐mRNAs, leading to repression of m6A‐dependent splicing during stress recovery phase. Thus, nSBs serve as a common platform for regulation of temperature‐dependent splicing through dual mechanisms employing two distinct ribonucleoprotein modules with partially m6A‐modified architectural lncRNAs.

Nuclear stress bodies (nSBs) are thermal stress-inducible membrane-less nuclear bodies that are formed on highly repetitive satellite III architectural noncoding RNAs (HSATIII arcRNAs). Upon thermal stress exposure, HSATIII expression is induced to sequestrate specific sets of RNA-binding proteins and form nSBs. The major population of nSBs contain SAFB as a marker, whereas the minor population are SAFB-negative. Here, we found that HNRNPM, which was previously reported to localize in nuclear foci adjacent to SAFB-positive foci upon thermal stress, localizes in a minor population of HSATIII-dependent nSBs. Hence, we used the terms nSB-S and nSB-M to distinguish the SAFB foci and HNRNPM foci, respectively. Analysis of the components of the nSBs revealed that each set contains distinct RNA-binding proteins, including SLTM and NCO5A in nSB-Ss and HNRNPA1 and HNRNPH1 in nSB-Ms. Overall, our findings indicate that two sets of nSBs containing HSATIII arcRNAs and distinct sets of RNA-binding proteins are formed upon thermal stress exposure.

Tian et al. XCL1/Lymphotactin in Periprosthetic Osteolysis inflammatory and osteoclastogenic factors, including IL-6, IL-8, and RANKL in human differentiated osteoblasts. Together, these results suggested the potential role of XCL1 in the pathogenesis of periprosthetic osteolysis and aseptic loosening. Our data broaden knowledge of the pathogenesis of aseptic prosthesis loosening and highlight a novel molecular target for therapeutic intervention.

Summary Synovial macrophages that are activated by cartilage fragments initiate synovitis, a condition that promotes hypertrophic changes in chondrocytes leading to cartilage degeneration in OA. In this study, we analyzed the molecular response of chondrocytes under condition of this type of stimulation to identify a molecular therapeutic target. Stimulated macrophages promoted hypertrophic changes in chondrocytes resulting in production of matrix-degrading enzymes of cartilage. Among the top-upregulated genes, FliI was found to be released from activated chondrocytes and exerted autocrine/paracrine effects on chondrocytes leading to an increase in expression of catabolic and hypertrophic factors. Silencing FliI in stimulated cells significantly reduced expression of catabolic and hypertrophic factors in cocultured chondrocytes. Our further results demonstrated that the FliI-TLR4-ERK1/2 axis is involved in the hypertrophic signaling of chondrocytes and catabolism of cartilage. Our findings provide a new insight into the pathogenesis of OA and identify a potentially new molecular target for diagnostics and therapeutics.

The introduction of vitamin E-blended ultra-high molecular weight polyethylene (VE-UHMWPE) for use in prosthetic components of hip implants has resulted in the production of implants that have excellent mechanical properties and substantially less adverse cellular responses. Given the importance of a biological response to wear in the survival of a prosthesis, we generated wear debris from UHMWPE that had been prepared with different concentrations of vitamin E of 0.1, 0.3, 0.5, and 1% and evaluated their biological reaction in vitro and in vivo. All types of VE-UHMWPE debris promoted a significantly lower expression of Tnf-α in murine peritoneal macrophages than that induced by conventional UHMWPE debris. However, levels of Tnfα were not significantly different among the macrophages that were stimulated with VE-UHMWPE wear at the concentrations tested. The ability of wear debris to induce inflammatory osteolysis was assessed in a mouse calvarial osteolysis model. The expressions of Tnf-α, Il-6, and Rankl in granulomatous tissue formed around the wear debris were significantly reduced in mice that had been implanted with 0.3%VE-UHMWPE debris as compared to the corresponding values for mice that had been implanted with UHMWPE debris. Consistent with this finding, 0.3%VE-UHMWPE debris showed the lowest osteolytic activity, as evidenced by the reduced bone resorption area, the degree of infiltration of inflammatory cells and the TRAP staining area. Our results suggested that a 0.3% vitamin E concentration is the most appropriate concentration for use in prosthetic components with a reduced adverse cellular response for prolonging the life-span of the implant.

Growth arrest‐specific 5 ( GAS5 ) is a nonprotein‐coding small nucleolar ribonucleic acid (snoRNA) host gene. Ten box C/D snoRNAs are encoded within the 11 introns of the human GAS5 gene, whereas the spliced exons have little protein‐coding potential. GAS5 has been classified as a member of the 5′ oligopyrimidine tract (5′ TOP) gene family. Growth‐dependent translation mediated by the 5′ TOP sequence determines the level of the GAS5 spliced transcript ( GAS5 long noncoding RNA (lncRNA)) by a mechanism of translation‐linked RNA degradation. GAS5 lncRNA plays a critical role in arresting cell growth and inducing apoptosis. The decreased expression of GAS5 in multiple cancers suggests that GAS5 acts as a tumour suppressor. GAS5 lncRNA controls the gene expression of critical cell cycle and apoptosis regulators. GAS5 lncRNA suppresses steroid‐responsive transcription by direct association with several steroid receptors and acts as a molecular decoy. GAS5 lncRNA also sequestrates a specific functional microRNA. Key Concepts GAS5 is a nonprotein‐coding small nucleolar RNA host gene. A translation‐linked mRNA decay pathway controls growth arrest‐specific accumulation of GAS5 by way of its 5′‐terminal oligopyrimidine tract (5′ TOP). GAS5 functions to arrest cell growth and induce apoptosis. GAS5 controls expression of genes for critical regulators of the cell cycle and apoptosis. GAS5 binds to steroid hormone receptors through its 3′‐terminal stem‐loop structure to suppress steroid‐responsive transcription. GAS5 sequestrates a specific functional microRNA.