Innate immunity provides the initial defence against infection and it is now clear that long non-coding RNAs (lncRNAs) are important regulators of this response. Following activation of the innate response, we commonly see rapid induction of these lncRNAs and this is often mediated via the pro-inflammatory transcription factor, nuclear factor-κB (NF-κB). Knockdown studies have shown that lncRNAs tend to act in trans to regulate the expression of multiple inflammatory mediators and other responses. Mechanistically, many lncRNAs have demonstrated acting through heterogeneous nuclear ribonucleoproteins, complexes that are implicated chromatin re-modelling, transcription process and translation. In addition, these lncRNAs have also been shown to interact with multiple other proteins involved in the regulation of chromatin re-modelling, as well as those proteins involved in intracellular immune signalling, which include NF-κB. In this review, we will describe the evidence that supports this emerging role of lncRNA in the innate immune response.

Objective To identify long noncoding RNAs (lncRNAs) associated with the inflammatory phenotype of synovial fibroblasts from obese patients with osteoarthritis (OA), and to explore the expression and function of these lncRNAs. Methods Synovium was collected from normal‐weight patients with hip fracture (non‐OA; n = 6) and from normal‐weight (n = 8) and obese (n = 8) patients with hip OA. Expression of RNA was determined by RNA‐sequencing and quantitative reverse transcription–polymerase chain reaction. Knockdown of lncRNA was performed using LNA‐based GapmeRs. Synovial fibroblast cytokine production was measured by enzyme‐linked immunosorbent assay. Results Synovial fibroblasts from obese patients with OA secreted greater levels of interleukin‐6 (IL‐6) (mean ± SEM 162 ± 21 pg/ml; P < 0.001) and CXCL8 (262 ± 67 pg/ml; P < 0.05) compared to fibroblasts from normal‐weight patients with OA (IL‐6, 51 ± 4 pg/ml; CXCL8, 78 ± 11 pg/ml) or non‐OA patients (IL‐6, 35 ± 3 pg/ml; CXCL8, 56 ± 6 pg/ml) (n = 6 patients per group). RNA‐sequencing revealed that fibroblasts from obese OA patients exhibited an inflammatory transcriptome, with increased expression of proinflammatory messenger RNAs (mRNAs) as compared to that in fibroblasts from normal‐weight OA or non‐OA patients (>2‐fold change, P < 0.05; n = 4 patients per group). A total of 19 lncRNAs were differentially expressed between normal‐weight OA and non‐OA patient fibroblasts, and a further 19 lncRNAs were differentially expressed in fibroblasts from obese OA patients compared to normal‐weight OA patients (>2‐fold change, P < 0.05 for each), which included the lncRNA for metastasis‐associated lung adenocarcinoma transcript 1 (MALAT1). MALAT1 was rapidly induced upon stimulation of OA synovial fibroblasts with proinflammatory cytokines, and was up‐regulated in the synovium from obese OA patients as compared to normal‐weight OA patients (1.6‐fold change, P < 0.001) or non‐OA patients (6‐fold change, P < 0.001). MALAT1 knockdown in OA synovial fibroblasts (n = 4 patients) decreased the levels of mRNA expression and protein secretion of CXCL8 (>1.5‐fold change, P < 0.01), whereas it increased expression of mRNAs for TRIM6 (>2‐fold change, P < 0.01), IL7R (<2‐fold change, P < 0.01), HIST1H1C (>1.5‐fold change, P < 0.001), and MAML3 (>1.5‐fold change, P < 0.001). In addition, MALAT1 knockdown inhibited the proliferation of synovial fibroblasts from obese patients with OA. Conclusion Synovial fibroblasts from obese patients with hip OA exhibit an inflammatory phenotype. MALAT1 lncRNA may mediate joint inflammation in obese OA patients.

There is accumulating evidence to indicate that long non-coding RNAs (lncRNAs) are important regulators of the inflammatory response. In this report, we have employed next generation sequencing to identify 14 lncRNAs that are differentially expressed in human lung fibroblasts following the induction of inflammation using interleukin-1β (IL-1β). Knockdown of the two most highly expressed lncRNAs, IL7AS, and MIR3142HG, showed that IL7AS negatively regulated IL-6 release whilst MIR3142HG was a positive regulator of IL-8 and CCL2 release. Parallel studies in fibroblasts derived from patients with idiopathic pulmonary fibrosis showed similar increases in IL7AS levels, that also negatively regulate IL-6 release. In contrast, IL-1β-induced MIR3142HG expression, and its metabolism to miR-146a, was reduced by 4- and 9-fold in IPF fibroblasts, respectively. This correlated with a reduced expression of inflammatory mediators whilst MIR3142HG knockdown showed no effect upon IL-8 and CCL2 release. Pharmacological studies showed that IL-1β-induced IL7AS and MIR3142HG production and release of IL-6, IL-8, and CCL2 in both control and IPF fibroblasts were mediated via an NF-κB-mediated pathway. In summary, we have cataloged those lncRNAs that are differentially expressed following IL-1β-activation of human lung fibroblasts, shown that IL7AS and MIR3142HG regulate the inflammatory response and demonstrated that the reduced inflammatory response in IPF fibroblast is correlated with attenuated expression of MIR3142HG/miR-146a.

Idiopathic pulmonary fibrosis (IPF) is a progressive chronic disease characterized by excessing scarring of the lungs leading to irreversible decline in lung function. The aetiology and pathogenesis of the disease are still unclear, although lung fibroblast and epithelial cell activation, as well as the secretion of fibrotic and inflammatory mediators, have been strongly associated with the development and progression of IPF. Significantly, long non-coding RNAs (lncRNAs) are emerging as modulators of multiple biological processes, although their function and mechanism of action in IPF is poorly understood. LncRNAs have been shown to be important regulators of several diseases and their aberrant expression has been linked to the pathophysiology of fibrosis including IPF. This review will provide an overview of this emerging role of lncRNAs in the development of IPF.

Phenotypic changes in lung fibroblasts are believed to contribute to the development of Idiopathic Pulmonary Fibrosis (IPF), a progressive and fatal lung disease. Long intergenic non-coding RNAs (lincRNAs) have been identified as novel regulators of gene expression and protein activity. In non-stimulated cells, we observed reduced proliferation and inflammation but no difference in the fibrotic response of IPF fibroblasts. These functional changes in non-stimulated cells were associated with changes in the expression of the histone marks, H3K4me1, H3K4me3 and H3K27ac indicating a possible involvement of epigenetics. Following activation with TGF-β1 and IL-1β, we demonstrated an increased fibrotic but reduced inflammatory response in IPF fibroblasts. There was no significant difference in proliferation following PDGF exposure. The lincRNAs, LINC00960 and LINC01140 were upregulated in IPF fibroblasts. Knockdown studies showed that LINC00960 and LINC01140 were positive regulators of proliferation in both control and IPF fibroblasts but had no effect upon the fibrotic response. Knockdown of LINC01140 but not LINC00960 increased the inflammatory response, which was greater in IPF compared to control fibroblasts. Overall, these studies demonstrate for the first time that lincRNAs are important regulators of proliferation and inflammation in human lung fibroblasts and that these might mediate the reduced inflammatory response observed in IPF-derived fibroblasts.