MicroRNAs are an important class of epigenetic regulators, researching their relationship with fibrotic liver would be of great significance to elucidating the mechanism of the condition2. In this study, 34 miRNAs were differentially expressed by ≥ 2 fold (P < 0.005) in the liver tissue of patients with CHB-associated fibrotic liver compared with that in patients with liver fibrosis grade ≥ S2. Of these 34 miRNAs, 18 were upregulated and 16 were downregulated. Some of the miRNAs were verified by qPCR. Following further screening based on the criteria of a differential expression multiple of ≥ 2 times, P < 0.005, and the original signal RI value being larger, 9 miRNAs were selected, of which 4 were upregulated (viz., hsa-miR-125b-2-3p, hsa-miR-4639-3p, hsa-miR-4764-3p, and hsa-miR-3133) and 5 were downregulated (viz., hsa-miR-519d-3p, hsa-miR-1297, hsa-miR-3183, hsa-miR-154-5p, and hsa-miR-663a). qPCR verified that these 9 miRNAs were consistent with the chip results and that the data were credible. Other miRNA chip results are pending further validation.
The miRNA hsa-miR-3133 screened in this study has been confirmed to be involved in the formation of fibrotic liver. Peng found that miR-3133 could downregulate TGF-β (and its receptor TGFBR1) that promotes liver fibrosis in vivo14. MiR-3133 downregulated might be an independent prognostic biomarker in ccRCC patients and plays inhibitory roles in aggressive progression of ccRCC15. At the same time, studies have shown that miR-3133 can increase the expression of the recombinant adeno-associated virus by downregulating the ErbB signaling pathway that involves its target gene CBL, thereby improving the expression efficiency of this gene therapy vector for hepatic fibrosis.
Some of the differentially expressed miRNAs found in this present study, such as hsa-miR-125b-2-3p, hsa-miR-4639-3p, hsa-miR-4764-3p, hsa-miR-1297, hsa-miR-3183, hsa-miR-154-5p, hsa-miR-663a, and hsa-miR-519d-3p, have not been reported to be related to fibrotic liver, but they have been reported in other diseases. For example, hsa-miR-125b-2-3p was found to regulate prostaglandin F2α receptor inhibitors by regulating its target gene PTGFRN, which is closely related to the metastatic status of osteosarcoma. Studies have also shown that miR-125b-2-3p may be involved in the inflammatory response following cerebral ischemic injury and is closely related to the pathophysiology of the condition16. miR-4639-3p is currently reported to be associated with the development of early-onset familial Alzheimer’s disease, and its high expression in the plasma of patients with chronic gout may be associated with gout formation17. Recent studies have shown that hsa-miR-154-5p may play a role in smoking-induced lung cancer through the regulation of its target genes (ACTB, ATP2A2, BDNF, and CUL2) and the HIF-1, MAPK, Notch, and autophagic molecular signaling pathways and autophagic molecules18. Some scholars have suggested that hsa-miR-154-5p could contribute to the antitumor activity of vitamin D in prostatic hyperplasia through direct or indirect targeting of the stromal-epithelial crosstalk gene during the progression of prostate cancer19. miR-663a is associated with the progression of endometrial carcinoma20. miR-519d-3p and miR-1297 can be used as tumor suppressor genes in cervical cancer21. In addition, some of the miRNAs found in this study that are not related to the formation of fibrotic liver, such as hsa-miR-4764-3p, hsa-miR-3941, hsa-miR-4694-5p, hsa-miR-138-5p, hsa-miR-5571-5p, and hsa-miR-4421, are worth further study.
The GO analysis found that the differentially expressed miRNAs could regulate cell development, proliferation, and apoptosis, and may also regulate molecular metabolic processes, nitrogen complex metabolic processes, protein modification processes, and the positive regulation of cellular processes. The pathway analysis suggested that the differentially expressed miRNAs were mainly involved in proliferation- and apoptosis-related signaling pathways, as well as pathways related to microcirculation in fibrotic liver. The finding of these two types of signaling pathways is consistent with that of current literature reports. For example, proliferation- and apoptosis-related signaling pathways, such as the Wnt signaling pathway and TGF-β signaling pathway, have been reported to be closely related to the formation of hepatic fibrosis23–25. In addition, our analysis also found a relationship between fibrotic liver and some other signaling pathways, such as the intracellular tropism pathway, axon guidance pathway, TNF signaling pathway, insulin signaling pathway, and the ABC transporter, which has not been reported before. Therefore, our study suggests that these miRNAs may regulate the progression of fibrotic liver through these pathways, although further experimental studies are needed to confirm this.
Using the graph theory method to evaluate the regulatory status of the miRNAs and genes in the network, it was found that the most significant gene in the network map may play the most significant role in the signaling pathway. The key targets of miRNA regulation were the genes NM_021843 (regulated by 7 microRNAs) and NM_ 012671 (regulated by 6 microRNAs). NM_053679 (DNA fragmentation factor subunit alpha (DFFA)) and NM_012775 (TGF-β1), the key target genes regulated by 5 downregulated miRNAs, were located at the center of the gene regulatory network. TGF-β1 is a member of the cytokine TGF-β superfamily, which is named for its ability to promote the transformation and growth of fibroblasts. The miRNA may target DFFA and TGF-β1 to regulate the signaling pathways involved in fibrotic liver.