TGF-β2-induced alterations of m6A methylation in hTERT RPE-1 cells

N6-methyladenosine (m6A) is a major type of RNA modification implicated in various pathophysiological processes. Transforming growth factor β2 (TGF-β2) induces epithelial-mesenchymal transition (EMT) in retinal pigmental epithelial (RPE) cells and promotes the progression of proliferative vitreoretinopathy (PVR). However, the role of m6A methylation in the EMT of human telomerase reverse transcriptase (hTERT) retinal pigmental epithelium (RPE)-1 cells has not been clarified. Here, we extracted RNA from RPE cells subjected to 0 or 20 ng/mL TGF-β2 for 72 h and identified differentially methylated genes (DMGs) by m6A-Seq and differentially expressed genes (DEGs) by RNA-Seq. We selected the genes related to EMT by conjoint m6A-Seq/RNA-Seq analysis and verified them by qRT-PCR. We then confirmed the function of m6A methylation in the EMT of RPE cells by knocking down the methyltransferase METTL3 and the m6A reading protein YTHDF1. Sequencing yielded 5814 DMGs and 1607 DEGs. Conjoint analysis selected 467 genes altered at the m6A and RNA levels that are closely associated with the EMT-related TGF-β, AGE-RAGE, PI3K-Akt, P53, and Wnt signaling pathways. We also identified ten core EMT genes ACTG2, BMP6, CDH2, LOXL2, SNAIL1, SPARC, BMP4, EMP3, FOXM1, and MYC. Their RNA levels were evaluated by qRT-PCR and were consistent with the sequencing results. We observed that METTL3 knockdown enhanced RPE cell migration and significantly upregulated the EMT markers N-cadherin (encoded by CDH2), fibronectin (FN), Snail family transcription repressor (SLUG), and vimentin. However, YTHDF1 knockdown had the opposite effects and decreased both cell migration and the N-cadherin, FN, and SLUG expression levels. The present study clarified TGF-β2-induced m6A- and RNA-level differences in RPE cells, indicated that m6A methylation might regulate EMT marker expression, and showed that m6A could regulate TGF-β2-induced EMT.

Microcystin-LR induces lactate production disruption via altering the m6A modification in Sertoli cells

We have previously reported the toxicity of microcystin-LR (MC-LR) to the male reproductive system, which results in functional changes in mouse testes. In this study, mice were orally exposed to MC-LR at 1, 7.5, 15, or 30 μg/L daily for 180 days. We found an increase in germ cell apoptosis in the seminiferous tubules and low-quality sperm in the epididymis. A decrease in lactate dehydrogenase A (Ldha) expression in testes through high-throughput sequencing was observed. We validated that MC-LR disrupted lactate production in Sertoli cells by suppressing the expression of Ldha. Further studies identified that methyltransferase 3 (Mettl3) catalysed N6-methyladenosine (m6A) methylation of Ldha mRNA. Mettl3 was downregulated in Sertoli cells following exposure to MC-LR, decreasing m6A levels of Ldha. The stability of Ldha mRNA decreased when m6A levels of Ldha were inhibited. In conclusion, these results showed that MC-LR inhibits the expression of Ldha in an m6A-dependent manner, which might result in the apoptosis of spermatogenic cells and a decline in sperm quality. Our work provides a new perspective to understanding MC-LR-induced male infertility.