Background: Long non-coding RNAs (lncRNAs) have little or no coding capacity, but studies show they influence many biological and immune responses by regulating gene expression. It has been established that noncoding RNAs can influence inflammatory processes in rheumatic conditions such as rheumatoid arthritis (RA) (1). Since macrophages play an important role in the onset of inflammation and the subsequent return to homeostasis, lnc184M is a potential marker of disease state, responsiveness to treatment and a valid target for novel siRNA therapeutic agents. The expression and role of lnc184M in myeloid anti-inflammatory state are unknown.

Objectives: We aimed to study the expression and biological effect of lnc184M in human monocyte derived macrophages.

Methods: Enriched human CD14+ monocytes were isolated from peripheral blood of healthy controls (HC) and RA patients and differentiated into pro and anti-inflammatory phenotypes of macrophages using GM-CSF and M-CSF cytokines respectively. Expression of lnc184M was assessed with and without Dexamethasone (Dex) treatment. Secondly, to better understand the biologic role of lnc184M, differentiated cells from HC were transfected at day 5 with siRNA184M or its control equivalent for 48 hours. On day 7, 100nM of Dex was added to the culture for 4 hours. Cells and supernatants were harvested thereafter for quantitative gene expression and functional protein assays.

Results: lncRNA RP11-184M15.1 (lnc184M) is upregulated in human monocyte M-CSF derived macrophages (anti-inflammatory) with approximately ten-fold greater expression compared to GM-CSF derived (pro-inflammatory) macrophages. In addition, we have shown that lnc184M is upregulated upon Dexamethasone treatment of myeloid cells in vitro in HC and RA. Successful siRNA transfection specifically targeted and silenced lnc184M compared to control for both macrophage types, switching the phenotype of the anti-inflammatory M-CSF derived macrophage cells into a more pro-inflammatory phenotype. This was particularly highlighted by an increase of TNF and IL-6 at the gene level in M-CSF derived macrophages after silencing of nc184M while this effect was not observed in GM-CSF derived macrophages. The addition of Dexamethasone reverses this effect.

Conclusion: This work has identified a novel lncRNA that contributes to the resolution of inflammation in the myeloid compartment. Lnc184M is upregulated by glucocorticoids as well as in M-CSF derived macrophages in both healthy controls and RA patients. Silencing endogenous lnc184M in M-CSF derived macrophages contribute to a switching of phenotypic profile to a more pro-inflammatory cell and this effect can be partially reversed using Dexamethasone. These data suggest an anti-inflammatory role of lnc184M, upregulated upon treatment with glucocorticoids.

REFERENCES: [1] Najm A, Blanchard F, Le Goff B. Micro-RNAs in inflammatory arthritis: From physiopathology to diagnosis, prognosis and therapeutic opportunities. Biochem Pharmacol. 2019 Jul;165:134-144. doi: 10.1016/j.bcp.2019.02.031. Epub 2019 Feb 27. PMID: 30825433.

Acknowledgements: NIL.

Disclosure of Interests: None declared.