Chronic corticosterone exposure induces liver inflammation and fibrosis in association with m6A-linked post-transcriptional suppression of heat shock proteins in chicken.

Our previous study had shown that chronic corticosterone (CORT) exposure causes excessive fat deposition in chicken liver, yet it remains unknown whether it is associated with inflammation and fibrosis. In general, heat shock proteins (HSPs) are activated in response to acute stress to play a cytoprotective role, and this activation is associated with m⁶A-mediated post-transcriptional regulation. However, changes of HSPs and the m⁶A methylation on their mRNAs in response to chronic CORT treatment in chicken liver have not been reported. In this study, chronic CORT exposure induced inflammation and fibrosis in chicken liver, associated with significantly modulated expression of HSPs that was significantly upregulated at mRNA level yet downregulated at protein level. Concurrently, m⁶A methyltransferases METTL3 content was upregulated together with the level of m⁶A methylation on HSPs transcripts. The m⁶A-seq analysis revealed 2-6 significantly (P < 0.05) hypermethylated m⁶A peaks in the mRNA of 4 different species of HSPs in CORT-treated chicken liver. HSP90B1 transcript had 6 differentially methylated m⁶A peaks among which peaks on exon 16 and exon 17 showed 3.14- and 4.72-fold of increase, respectively. Mutation of the 8 predicted m⁶A sites on exon 16 and exon 17 resulted in a significant (P < 0.05) increase in eGFP-fused content of HSP90B1 exon 16 and exon 17 fragment in 293 T cells, indicating a possible role of m⁶A in post-transcriptional regulation of HSPs. In conclusion, chronic CORT exposure induces inflammation and fibrosis in chicken liver along with an increase in the levels and m6A methylation of several HSPs mRNAs; HSPs levels were however reduced under the indicated conditions. Results presented suggest that the reduction in HSPs levels may be associated with m6A methylation in CORT-exposed chickens.