Background: Epitranscriptomics is an emerging field in rheumatic diseases and refers to the post-transcriptional regulation of gene expression through RNA modifications affecting RNA metabolism, stability, splicing, localization, and translation. Among these modifications, N6-methyladenosine (m6A) is the most abundant and best-characterized and exhibits tissue-specific regulatory functions. m6A is dynamically regulated by the interplay of three classes of proteins: RNA methyltransferases “writers” (e.g. METTL3), RNA demethylases “erasers” (e.g. FTO), and RNA binding proteins “readers” (e.g. YTHDF2) [1]. To date, data on m6A modification and alterations of its regulatory enzymes in rheumatoid arthritis (RA) are limited and inconsistent, while no data are available for psoriatic arthritis (PsA). Moreover, the potential impact of biologic and targeted-synthetic modifying antirheumatic drugs (b/tsDMARDs) on m6A regulation has not yet been explored.

Objectives: To investigate m6A epitranscriptomic alterations by assessing global m6A RNA methylation levels and the expression of the regulatory genes METTL3 , FTO , YTHDF2 in RA and PsA patients treated with b/tsDMARDs at baseline (T0) and after 12 months of therapy (T12), compared with healthy controls (CTRLs).

Methods: Patients were enrolled at initiation of b/tsDMARDs therapy (T0) and followed for 12 months (T12). Treatment response was assessed using the Disease Activity Index for PsA score (DAPsA) for PsA and 28-joint disease activity score (DAS28) for RA. For each patient, peripheral blood mononuclear cells (PBMCs) were isolated at T0 and T12.

Global m6A RNA methylation levels were measured using the EpiQuik™ m6A RNA Methylation Quantification Kit on total RNA extracted from PBMCs. Gene expression analyses were performed by real-time quantitative polymerase chain reaction assay. Unpaired t-test or Mann-Whitney test was used for baseline comparisons, while paired t-tests were applied for T0–T12 comparisons.

Results: A total of 60 rheumatic patients were included: 30 PsA patients (mean age 48.87±13.33 years; disease duration 6.29±5.60 years) and 30 RA patients (mean age 53.46±17.56 years; disease duration 11.20±10.15 years). Among them, 17 patients were treated with TNFα- inhibitors and 13 with JAK-inhibitors. Additionally, 22 age- and sex-matched controls were collected.

At baseline, global m6A RNA methylation was significantly higher in PsA patients compared to CTRLs (P= 0.03) and positively correlated with age (P= 0.02); this difference remained significant after adjustment for age (P=0.01). Consistently with the increased global m6A levels, the methyltransferase METTL3 gene expression was significantly higher in PsA patients compared to CTRLs (P= 0.012) and positively correlated with disease duration (P= 0.025). No significant alterations were observed for FTO and YTHDF2 expression levels. After 12-month of therapy, neither the global percentage of m6A RNA methylation nor the expression levels of the regulatory genes differed between T0 and T12 PsA patients.

In contrast, RA patients showed no significant differences in global m6A levels compared with CTRLs at baseline, nor after 12-month follow-up. Similarly, the expression levels of the regulatory genes remain unchanged at all time point.

Conclusions: Our results provide the first evidence of altered m6A epitranscriptomic regulation in PBMCs from patients with PsA, characterized by increased global m6A RNA methylation and upregulation of the m6A methyltransferase METTL3, supporting a role for m6A-dependent post-transcriptional regulation in disease pathogenesis.

The positive correlation between METTL3 expression and disease duration suggests that m6A dysregulation contributes to inflammatory persistence and chronicity. Accordingly, the lack of normalization of global m6A levels and regulatory gene expression after 12 months of b/tsDMARD treatment indicates that these epitranscriptomic alterations may be relatively stable or reflect a persistent inflammatory memory. In contrast, no significant changes in global m6A levels and regulatory gene expression were observed in RA patients at baseline and during follow-up, suggesting reliance on alternative regulatory mechanisms. This is consistent with known differences in PsA and RA immunopathogenesis, particularly the stronger involvement of innate immunity and IL-17–mediated pathways in PsA, biological contexts in which m6A is relevant.

Overall, these findings identify m6A RNA methylation and METTL3 as distinctive molecular features of PsA and support further validation in larger cohorts and across different tissue compartments.

REFERENCES: [1] Liu Z, Gao L, Cheng L. et al. The roles of N6-methyladenosine and its target regulatory noncoding RNAs in tumors: classification, mechanisms, and potential therapeutic implications. Exp Mol Med 2023; 55: 487–501.

Acknowledgments: NIL.

Disclosure of Interests: None declared.