m⁶A RNA methylation controls salivary gland epithelial cell function and has a protective role in Sjögren's disease.

Abstract

The RNA epitranscriptomic modification known as <i>N6</i>-methyladenosine (m⁶A) represents a novel mechanism of gene regulation that is poorly understood in human autoimmune diseases. Our research explores the role of this RNA m⁶A modification in salivary gland epithelial cells (SGEC) and its impact on the pathogenesis of Sjögren's disease (SjD). SGECs from SjD patients and controls were analysed for m⁶A writers METTL3 and METTL14 expression using RNA-seq, quantitative PCR and immunohistochemistry. Functional assays assessed the impact of <i>METTL3</i> knockdown or pharmacological inhibition on proinflammatory gene expression and immune cell interactions (using transwell and coculture systems). Mechanistic studies examined METTL3-mediated m⁶A modifications in double-stranded RNA (dsRNA) formation through immunofluorescence. Unsupervised clustering identified patterns of interferon activation in salivary glands and their correlation with m⁶A writers. METTL3 and METTL14 were elevated in SGEC from SjD patients in comparison to controls. Paradoxically, inhibiting METTL3 increased proinflammatory gene expression, enhancing SGEC's ability to attract immune cells and activate B cells. Conversely, inhibiting the eraser FTO had the opposite effect. METTL3-mediated m⁶A modifications prevented dsRNA formation and IFN signalling activation. SGEC from SjD showed insufficient <i>METTL3</i> upregulation compared with controls in response to inflammatory triggers, indicating a limited capacity to regulate the inflammatory response. SjD patients with elevated disease activity and higher interferon signature exhibit reduced <i>METTL3</i> expression. Impairment of m⁶A modifications in SGEC in response to inflammatory triggers favour the formation of dsRNA, potentially amplifying the interferon loop and contributing to SjD pathogenesis.