Novel insights into the role of 5-Methylcytosine RNA methylation in human abdominal aortic aneurysm

Background: It remains largely unclear about the function of 5-methylcytosine (m5C) RNA modification in the context of abdominal aortic aneurysm (AAA). In this regard, the present work focused on investigating m5C RNA methylation and related modulator expression levels in AAA. Materials and methods: To this end, we quantified the m5C methylation levels in AAA tissues (n = 32) and normal aortic tissues (n = 12) to examine the mRNA m5C status and m5C modulator expression at mRNA and protein levels. Meanwhile, modulator localization within AAA tissue samples was detected by immunohistochemistry (IHC). Moreover, RNA immunoprecipitation-sequencing (RIP-seq) was also used to analyze the lncRNAs and mRNA binding to Aly/REF, as an m5C reader. Results: m5C expression markedly elevated in AAA in comparison with normal aortic samples in the AAA cases. The major 5-methylcytosine modulators, including NSUN2, NSUN5, and Aly/REF, which represented the major parameters related to the abnormal m5C modification level, were observed up-regulating in AAA tissues at both protein and mRNA levels. In addition, NSUN2 mRNA level remarkably related to Aly/REF expression, and they were co-expressed in the same cells in AAA group. Regarding the cellular location, Aly/REF was associated with inflammatory (CD45+, CD3+) infiltrates. Simultaneously, after screening for reads in AAA tissue compare with anti-Aly/REF group relative to IgG as control, we obtained totally 477 differentially expressed Aly/REF-binding lncRNAs and 369 differentially expressed Aly/REF-binding mRNAs in AAA tissue. The functions of Aly/REF-interacting lncRNA were involved in immune system process and macrophages infiltration. Through regulatory network (lncRNA-mRNA) analysis, our findings predicted the potential mechanism of Aly/REF-induced lncBCL2L1 and Aly/REF-lncFHL1 axis in AAA and inspire the understanding of m5C and lncRNA in AAA. Conclusions: This study is the first to examine m5A modification within human AAA samples. Our results indicate that m5C modulators, namely, Aly/REF and NUSN2, play vital parts in the human AAA pathogenic mechanism, which shed new lights on the function of m5C modification within AAA. Taken together, findings in this work offer a possible RNA methylation modification mechanism within clinical AAA.