Analysis of the role of the integrin signaling pathway in hepatocytes during rat liver regeneration

HCMV-miR-US33-5p promotes apoptosis of aortic vascular smooth muscle cells by targeting EPAS1/SLC3A2 pathway

Background

In patients with acute aortic dissection (AAD), increased vascular smooth muscle cell (VSMC) apoptosis has been found. Human cytomegalovirus (HCMV)-miR-US33-5p was significantly increased in the plasma of patients with AAD. However, the roles of miR-US33-5p in human aortic VSMC (HA-VSMC) apoptosis remain to be elucidated.

Methods

In the current study, cell apoptosis was analyzed by flow cytometry, cell proliferation by CCK-8 assay, and differentially expressed genes by RNA sequencing. Luciferase reporter assay was used for binding analysis between miR-US33-5p and endothelial PAS domain protein 1 (EPAS1), and EPAS1 and amino acid transporter heavy chain, member 2 (SLC3A2). The enrichment degree of SLC3A2 promoter DNA was analyzed by chromatin immunoprecipitation assay. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and immunoblotting were performed for measuring messenger RNA (mRNA) and protein levels, respectively.

Results

It was found that HCMV infection inhibited proliferation but promoted HA-VSMC apoptosis by upregulating HCMV-miR-US33-5p. Transfection of HCMV-miR-US33-5p mimics the significant effect on several signaling pathways including integrin signaling as shown in the RNA sequencing data. Western blotting analysis confirmed that HCMV-miR-US33-5p mimics suppression of the activity of key factors of the integrin signal pathway including FAK, AKT, CAS, and Rac. Mechanistic study showed that HCMV-miR-US33-5p bound to the 3′-untranslated region of EPAS1 to suppress its expression, leading to suppression of SLC3A2 expression, which ultimately promoted cell apoptosis and inhibited cell proliferation. This was confirmed by the findings that silencing EPAS1 significantly reduced the SLC3A2 expression and inhibited proliferation and key factors of integrin signal pathway.

Conclusions

HCMV-miR-US33-5p suppressed proliferation, key factors of integrin signal pathway, and EPAS1/SLC3A2 expression, but promoted HA-VSMC apoptosis. These findings highlighted the importance of HCMV-miR-US33-5p/EPAS1/SCL3A2 signaling and may provide new insights into therapeutic strategies for AAD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00340-w.

Phosphoproteomic Profiling Identifies Aberrant Activation of Integrin Signaling in Aggressive Non-Type Bladder Carcinoma

Bladder carcinoma is highly heterogeneous and its complex molecular landscape; thus, poses a significant challenge for resolving an effective treatment in metastatic tumors. We computed the epithelial-mesenchymal transition (EMT) scores of three bladder carcinoma subtypes—luminal, basal, and non-type. The EMT score of the non-type indicated a “mesenchymal-like” phenotype, which correlates with a relatively more aggressive form of carcinoma, typified by an increased migration and invasion. To identify the altered signaling pathways potentially regulating this EMT phenotype in bladder cancer cell lines, we utilized liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based phosphoproteomic approach. Bioinformatics analyses were carried out to determine the activated pathways, networks, and functions in bladder carcinoma cell lines. A total of 3125 proteins were identified, with 289 signature proteins noted to be differentially phosphorylated (p ≤ 0.05) in the non-type cell lines. The integrin pathway was significantly enriched and five major proteins (TLN1, CTTN, CRKL, ZYX and BCAR3) regulating cell motility and invasion were hyperphosphorylated. Our study reveals GSK3A/B and CDK1 as promising druggable targets for the non-type molecular subtype, which could improve the treatment outcomes for aggressive bladder carcinoma.

A three-dimensional collagen-sponge-based culture system coated with simplified recombinant fibronectin improves the function of a hepatocyte cell line

Hepatocytes are widely used in pharmaceutical drug discovery tests, but their hepatic functions decrease rapidly during in vitro culture. Many culture systems have been devised to address this problem. We here report that a three-dimensional (3D) collagen-based scaffold coated with simplified recombinant fibronectin (FN) enhanced the function of a hepatocyte cell line. The developed culture system uses a honeycomb collagen sponge coated with collagen-binding domain (CBD)-cell attachment site (CAS), a chimeric protein comprising the CBD and CAS of FN. The function of HepG2 cells grown on honeycomb collagen sponge coated with CBD-CAS was investigated by determining the messenger RNA (mRNA) expression levels of several genes. The mRNA expression level of albumin increased 3.25 times in cells grown on CBD-CAS-coated honeycomb collagen sponge for 3 days; the expression level of CCAAT/enhancer binding protein (C/EBPα) increased 40-fold after 1 d and up to 150-fold after 3 d. These results suggested that CBD-CAS-coated honeycomb collagen sponge could improve the functions of hepatocytes by inducing C/EBPα expression. The activation of cytochrome P450 (CYP) enzymes in HepG2 cells grown on CBD-CAS-coated honeycomb collagen sponge was measured at the mRNA level and was found to increase between two and six times compared to cells grown without the CBD-CAS coating, showing that this culture system induced CYP gene expression and thus may be useful in drug metabolism assays.

Tissue Remodelling following Resection of Porcine Liver

AIM

To study genes regulating the extracellular matrix (ECM) and investigate the tissue remodelling following liver resection in porcine.

METHODS

Four pigs with 60% partial hepatectomy- (PHx-) induced liver regeneration were studied over six weeks. Four pigs underwent sham surgery and another four pigs were used as controls of the normal liver growth. Liver biopsies were taken upon laparotomy, after three and six weeks. Gene expression profiles were obtained using porcine-specific oligonucleotide microarrays. Immunohistochemical staining was performed and a proliferative index was assessed.

RESULTS

More differentially expressed genes were associated with the regulation of ECM in the resection group compared to the sham and control groups. Secreted protein acidic and rich in cysteine (SPARC) and collagen 1, alpha 2 (COL1A2) were both upregulated in the early phase of liver regeneration, validated by immunopositive cells during the remodelling phase of liver regeneration. A broadened connective tissue was demonstrated by Masson's Trichrome staining, and an immunohistochemical staining against pan-Cytokeratin (pan-CK) demonstrated a distinct pattern of migrating cells, followed by proliferating cell nuclear antigen (PCNA) positive nuclei.

CONCLUSIONS

The present study demonstrates both a distinct pattern of PCNA positive nuclei and a deposition of ECM proteins in the remodelling phase of liver regeneration.

Expression profiles uncover the relationship between erythropoietin and cell proliferation in rat hepatocytes after a partial hepatectomy

Erythropoietin (EPO) has a beneficial effect on hepatic cell proliferation during liver regeneration. However, the underlying mechanism has not yet been elucidated. To uncover the proliferation response of EPO in rat liver regeneration after partial hepatectomy (PH) at the cellular level, hepatocytes (HCs) were isolated using Percoll density gradient centrifugation. The genes of the EPO-mediated signaling pathway and the target genes of the transcription factor (TF) in the pathway were identified in a pathway and TF database search. Their expression profiles were then detected using Rat Genome 230 2.0 Microarray. The results indicated that the EPO-mediated signaling pathway is involved in 19 paths and that 124 genes participate, of which 32 showed significant changes and could be identified as liver regeneration-related genes. In addition, 443 targets regulated by the TFs of the pathway and 60 genes associated with cell proliferation were contained in the array. Subsequently, the synergetic effect of these genes in liver regeneration was analyzed using the E(t) mathematical model based on their expression profiles. The results demonstrated that the E(t) values of paths 3, 8, 12 and 14-17 were significantly strengthened in the progressing phase of liver regeneration through the RAS/MEK/ERK or PI3K/AκT pathways. The synergetic effect of the target genes, in parallel with target-related cell proliferation, was also enhanced 12-72 h after PH, suggesting a potential positive effect of EPO on HC proliferation during rat liver regeneration. These data imply that the EPO receptor may allow EPO to promote HC proliferation through paths 3, 8, 12 and 14-17, mediating the RAS/MEK/ERK and PI3K/AκT pathways in rat liver regeneration after PH.

Study on the activity of the signaling pathways regulating hepatocytes from G0 phase into G1 phase during rat liver regeneration

Under normal physiological conditions, the majority of hepatocytes are in the functional state (G0 phase). After injury or liver partial hepatectomy (PH), hepatocytes are rapidly activated to divide. To understand the mechanism underlying hepatocyte G0/G1 transition during rat liver regeneration, we used the Rat Genome 230 2.0 Array to determine the expression changes of genes, then searched the GO and NCBI databases for genes associated with the G0/G1 transition, and QIAGEN and KEGG databases for the G0/G1 transition signaling pathways. We used expression profile function (E t ) to calculate the activity level of the known G0/G1 transition signal pathways, and Ingenuity Pathway Analysis 9.0 (IPA) to determine the interactions among these signaling pathways. The results of our study show that the activity of the signaling pathways of HGF, IL-10 mediated by p38MAPK, IL-6 mediated by STAT3, and JAK/STAT mediated by Ras/ERK and STAT3 are significantly increased during the priming phase (2-6 h after PH) of rat liver regeneration. This leads us to conclude that during rat liver regeneration, the HGF, IL-10, IL-6 and JAK/STAT signaling pathways play a major role in promoting hepatocyte G0/G1 transition in the regenerating liver.

Knockdown and knockout of β1-integrin in hepatocytes impairs liver regeneration through inhibition of growth factor signalling

The liver has a unique regenerative capability, which involves extensive remodelling of cell-cell and cell-matrix contacts. Here we study the role of integrins in mouse liver regeneration using Cre/loxP-mediated gene deletion or intravenous delivery of β1-integrin siRNA formulated into nanoparticles that predominantly target hepatocytes. We show that although short-term loss of β1-integrin has no obvious consequences for normal livers, partial hepatectomy leads to severe liver necrosis and reduced hepatocyte proliferation. Mechanistically, loss of β1-integrin in hepatocytes impairs ligand-induced phosphorylation of the epidermal growth factor and hepatocyte growth factor receptors, thereby attenuating downstream receptor signalling in vitro and in vivo. These results identify a crucial role and novel mechanism of action of β1-integrins in liver regeneration and demonstrate that protein depletion by nanoparticle-based delivery of specific siRNA is a powerful strategy to study gene function in the regenerating liver.

Principles of liver regeneration and growth homeostasis

Liver regeneration is perhaps the most studied example of compensatory growth aimed to replace loss of tissue in an organ. Hepatocytes, the main functional cells of the liver, manage to proliferate to restore mass and to simultaneously deliver all functions hepatic functions necessary to maintain body homeostasis. They are the first cells to respond to regenerative stimuli triggered by mitogenic growth factor receptors MET (the hepatocyte growth factor receptor] and epidermal growth factor receptor and complemented by auxiliary mitogenic signals induced by other cytokines. Termination of liver regeneration is a complex process affected by integrin mediated signaling and it restores the organ to its original mass as determined by the needs of the body (hepatostat function). When hepatocytes cannot proliferate, progenitor cells derived from the biliary epithelium transdifferentiate to restore the hepatocyte compartment. In a reverse situation, hepatocytes can also transdifferentiate to restore the biliary compartment. Several hormones and xenobiotics alter the hepatostat directly and induce an increase in liver to body weight ratio (augmentative hepatomegaly). The complex challenges of the liver toward body homeostasis are thus always preserved by complex but unfailing responses involving orchestrated signaling and affecting growth and differentiation of all hepatic cell types.

Induction of albumin expression in HepG2 cells using immobilized simplified recombinant fibronectin protein

Optimization of the extracellular environment is very important for hepatocyte function in vitro. We expressed new chimeric proteins of the collagen-binding domain (CBD) with cell attachment site (CAS) of fibronectin to enhance hepatocyte function, and the CBD-CAS proteins were immobilized on collagen-coated plates. We hypothesized that the high density of CAS would increase activity of the integrin-dependent intracellular signaling pathway, thus inducing hepatocyte function. Expression of albumin in the human hepatocyte cell line HepG2 was assessed on CBD-CAS-immobilized dishes. The results indicated that the CBD-CAS-immobilized plates induced albumin expression. Immobilized CBD-CAS induced activation of focal adhesion kinase and integrin-ligand clustering on the cell membrane. These results suggest that immobilized CBD-CAS improves the function of HepG2 cells. This system could therefore be applied to drug metabolism assay in the development of new drugs.

Signals and cells involved in regulating liver regeneration

Liver regeneration is a complex phenomenon aimed at maintaining a constant liver mass in the event of injury resulting in loss of hepatic parenchyma. Partial hepatectomy is followed by a series of events involving multiple signaling pathways controlled by mitogenic growth factors (HGF, EGF) and their receptors (MET and EGFR). In addition multiple cytokines and other signaling molecules contribute to the orchestration of a signal which drives hepatocytes into DNA synthesis. The other cell types of the liver receive and transmit to hepatocytes complex signals so that, in the end of the regenerative process, complete hepatic tissue is assembled and regeneration is terminated at the proper time and at the right liver size. If hepatocytes fail to participate in this process, the biliary compartment is mobilized to generate populations of progenitor cells which transdifferentiate into hepatocytes and restore liver size.