The development of sophisticated strategies promotes the life cycle of viruses, which further causes evasion from antiviral immune systems, thus inducing diseases. The HCV-RNA consists of approximately 9,500 - 10,000 bp, including 5' and 3' non-coding regions (NCR) with 319 - 341 bp and 27 - 55 bp, respectively, containing several forward and reverse repeat sequences, which may be related to gene replication. An open reading frame (ORF) is located immediately downstream of the 5′ non-coding region, in which the genome sequence is 5′-C-E1-E2-p7-NS2-NS3-NS4-NS5-3′. It can encode a length of approximately 3,014 amino acids, and is a polyprotein precursor. The latter can be cleaved into 10 types of viral proteins by the host cell and the virus's own protease, including three structural proteins, namely nucleocapsid protein with a molecular weight of 19 KD (or core protein, Core) and two glycoproteins (E1 protein with a molecular weight of 33 KD and E2 protein with a molecular weight of 72 KD). Besides, p7 encodes a membrane-intrinsic protein, and its function may be an ion channel. Non-structural proteins include NS2, NS3, NS4A, NS5A, and NS5B. Non-structural proteins are very important to the life cycle of viruses. As known, NS2 and NS3 have protease activity and participate in the cleavage of viral polyprotein precursors. In addition, the NS3 protein has helicase activity and participates in unwinding HCV-RNA molecules to assist in RNA replication, and the function of NS4 is unclear. Besides, NS5A is a phosphoprotein that can interact with a variety of host cell proteins and plays an important role in virus replication. Also, NS5B has RNA-dependent RNA polymerase activity and participates in HCV genome replication (
31).
However, the pathogenesis of hepatitis C is still not very clear. When HCV replicates in hepatocytes, it causes changes in the structure and function of liver cells or interferes with protein synthesis in liver cells, then causing degeneration and necrosis of liver cells. It indicates that HCV directly damages the liver and plays a role in pathogenesis. However, most scholars believe that cellular immune pathological reactions might play an important role (
32).
As known, HCV is one of the major health concerns globally, and there is a lack of animal models for executing efficient HCV replicons and complete life cycle of HCV. The first discovery of hepatitis C was done by NIH researchers in the United States 40 years ago, and there are currently about 200 million people worldwide infected with or carrying HCV, including more than 40 million patients in my country. Hepatitis C can cause terrible consequences such as cirrhosis and liver cancer, and it also puts tremendous pressure on the health care systems of countries around the world. Because HCV is highly variable, it is easy to develop drug resistance. For a long time, many scientists have been exploring a suitable animal model for in-depth study of HCV. However, HCV only infects humans and chimpanzees, so developing an experimental mouse model encounters great difficulties in practice. The success of previous research provided the most advanced materials to reveal the pathogenic mechanism of hepatitis C, and it can fundamentally promote hepatitis C research on vaccines and drugs for prevention and treatment. The researchers expressed the two receptor molecules for HCV entry into liver cells, i.e., CD81 and OCLN, by transgenic technology on mouse liver cells. Hepatitis C virus can recognize and invade the liver cells of mice and replicate highly. At the same time, 80% of the infected mice subsequently showed typical acute HCV infection and chronic pathological progress, including fatty liver, liver fibrosis, and cirrhosis. Researchers in the laboratory have used this model to observe how HCV escapes the immune system and how antiviral drugs reduce viral titers (
7,
9,
33).
A network of mutual effects interacts between the hepatitis C virus and live human cell proteins. The results of the research will help to better understand the mechanism behind the hepatitis C virus causing inflammatory liver disease and open up new treatment avenues. Viruses use human cells to reproduce and spread. This process involves cell host factors and virus interactions. Hepatitis C virus forms a precursor protein, which is processed into 10 viral proteins. Now, scientists have discovered how these proteins interact with each other. The disclosure of this interaction network will help to better understand viral replication and pathogenesis, and pave the way for the design of new antiviral treatments. The results show how viral proteins interact with human cells, which provides a basis for finding new antiviral substances (
34-
36).
There is thus a great need for further study on the mechanism of HCV infection or its pathopoiesis. To better understand the host aspect for HCV infection, the transcriptome and miRNA sequencing analyses were conducted in Huh7.5.1 cell model infected with JFH-1 according to the technology of Illumina deep sequencing. Transcriptome analysis has been widely used in basic scientific research, as well as medical and drug research or development. Its technical advantages are mainly five points: (1) digitized signals, sequences obtained directly by sequencing, no background noise, no cross-hybridization, and ability to identify a base difference between sequences; (2) high throughput, tens of millions generated by one sequence, and sequencing detection of 100,000 to 300,000 sequence tags; (3) high repeatability, the correlation between two independent experiments in the same laboratory exceeds 99%, and the correlation between two independent experiments in different laboratories is as high as 98%; (4) a wide detection threshold, which spans six orders of magnitude, making it detect rare transcripts as low as two copies and accurately quantify hundreds of thousands of copies of high-expression transcripts; and (5) compatibility of analysis, the data format is the same as the chip, and compatible with chip analysis software (
37).
MicroRNA sequencing refers to the collection of all transcribed microRNA products in a certain species or specific cell under a certain physiological function state, including the limitation of time and space. The microRNA transcription regulation level is the most current investigation, and it is also the most important regulation method of organisms. High-throughput technology for transcriptome sequencing is a fast and reliable method to obtain transcriptome information. MicroRNA transcript expression analysis and its accurate counting method can also carry out precise quantitative analysis of genes.
In this work, an HCV-infected cell model was used to conduct the combination of transcriptome and microRNA sequencing analyses. We found 21, 827,299, and 42, 588,251 Illumina read pairs from cDNA libraries of JFH-1-infected (HCV) and non-infected (blank) Huh7.5.1 cells, respectively. Moreover, 678 and 1,041 mRNAs with a length of 101 bp from cDNA libraries of HCV and blank Huh7.5.1 cells were generated, respectively. Comparative transcriptome analysis confirmed 460 differentially expressed mRNAs in the HCV-infected cell model, including 152 upregulated and 308 downregulated unigenes in HCV vs. blank, respectively. The results of GO analysis revealed that the differentially expressed genes were involved in MAPK, p53, and PI3K/Akt signaling pathways, oocyte meiosis, and pathways in cancer. Our work acquired transcriptome data came from a cell model of HCV infection with JFH-1 by next-generation sequencing (NGS) techniques. Therefore, valuable information associated with gene expression and regulation or signaling pathways was obtained in the mechanism and pathopoiesis of HCV infection.
Besides, the key pathways involved in HCV infection or the interaction between HCV and host liver cells were confirmed. Therefore, we thought that they were associated with the key signaling pathways affecting actin filament growth, bundling, branching, crosslinking, and severing. Moreover, the results from analysis confirmed that focal adhesion kinase (FAK), HTLV-1-infected, JNK, and p38 MAPK, P53-mediated, proteoglycans, PI3K-Akt and Ras-ERK cell signal transduction pathways might all play an important role in the process of HCV infection. The inhibitors of integrin-linked kinase (ILK) or FAK restored the IFN-stimulated response element (ISRE) luciferase activity and the expression of IFN-stimulated Genes (ISG) proteins. It suggested that β1-integrin-mediated signals affected the IFN signaling and promoted HCV replication. Therefore, the accumulation of extracellular matrix (ECM) in liver fibrosis may impair IFN signaling through β1-integrin-mediated signaling involving ILK and FAK (
38). In addition, the facilitation of HCV replication by Tax protein may partially account for more severe clinical consequences of HCV-related disease in HCV/HTLV co-infected individuals (
39). Furthermore, cellular responses to oxidative stress in HCV subgenomic replicon-expressing and Ad-NS5A-transduced cells are regulated by two distinct signaling pathways involving p38 MAPK and JNK via AP-1 that are linked to increased oxidative stress and therefore to an increased antioxidant MnSOD response (
40). Besides, the Pro variant of P53 rs1042522 may be used as a genetic predictor for non-responsiveness, while the A/A variant of CD95 rs1800682 may be used as a sensitive biomarker for responsiveness to antiviral therapy of HCV genotype-4a infection (
41). Additionally, infection with HCV leads to the activation of nuclear factor-κB, resulting in increased expression of SMAD6 and SMAD7. The upregulation of SMAD6 and SMAD7 induces the expression of heparan sulfate proteoglycans (HSPGs), such as syndecan 1 (SDC1), as well as LDLR, very LDLR, and the scavenger receptor class B member 1, which promote HCV entry and propagation, as well as cellular uptake of cholesterol and lipoprotein (
42). Besides, the PI3K-Akt signaling pathway positively regulates HCV translation through SREBPs (
43). The effects of GBV-B and HCV NS5A on the PI3K and Ras-Erk pathways were confirmed in cells harboring subgenomic replicons derived from the two viruses (
44). Furthermore, deep research will carry out the interaction roles among HCV infection and mRNA regulation medicated by miRNAs involved in the pathways of host cells.
4.1. Conclusions
Our work confirmed the transcriptome and microRNA data profiling from the cell model of HCV infection with JFH-1 using Next-generation Sequencing (NGS). Furthermore, the gene expression and regulation information or signaling pathways associated with the pathopoiesis mechanism of HCV infection were initially identified.