Combatting Fibrosis: Exosome-Based Therapies in the Regression of Liver Fibrosis

Immunomodulatory effect of curcumin on hepatic cirrhosis in experimental rats

Cirrhosis is a chronic liver disease. The present work aimed to evaluate the regulatory immune effect of curcumin in hepatic cirrhosis induced by carbon tetrachloride (CCl4) injections in experimental rats' model. Chronic liver fibrosis was induced in experiment animals by recurrent injections of CCl4 for more than 5 weeks. They were divided into five groups: first group was injected with normal saline, second group with CCl4, third, fourth, and fifth groups were injected with CCl4 (intraperitoneal injection) at dose 3 ml/kg, two times weekly for 6 weeks supplemented with the administration of curcumin with concentrations 250, 200, and 150 mg/kg. Immune response was analyzed to different treatments. Interleukin 10 (IL-10), pro-inflammatory cytokines TNF-α, TGF-1β, and liver histopathological examinations were conducted. The results showed that estimations of IL-10 concentrations were significantly increased in curcumin groups compared with CCl4 group, whereas TNF-α and TGF-1β levels were significantly decreased comparing with CCl4 group. The histopathological examinations for liver tissues showed that curcumin treated groups have almost retained the normal structure of liver tissues. In conclusion, curcumin inhibited hepatic fibrosis and liver fibrogenesis with regulation of the immune system mechanism against invader chemical toxicity. PRACTICAL APPLICATIONS: Curcumin is well documented for its medicinal properties, commonly used as a spice. Our work has thus demonstrated its effectiveness as an immunomodulatory agent. Practically, clinical studies have suggested that curcumin displays a diverse and powerful array of pharmacological effects in nearly all of the human body's major organ systems. These are: antidiabetes, anti-inflammatory, anticancer, antiaging, antioxidant, antibacterial infection, hepatoprotective, neurodegenerative, and cardiovascular effects.

The Roles and Mechanisms of lncRNAs in Liver Fibrosis

Many studies have revealed that circulating long noncoding RNAs (lncRNAs) regulate gene and protein expression in the process of hepatic fibrosis. Liver fibrosis is a reversible wound healing response followed by excessive extracellular matrix accumulation. In the development of liver fibrosis, some lncRNAs regulate diverse cellular processes by acting as competing endogenous RNAs (ceRNAs) and binding proteins. Previous investigations demonstrated that overexpression of lncRNAs such as H19, maternally expressed gene 3 (MEG3), growth arrest-specific transcript 5 (GAS5), Gm5091, NR_002155.1, and HIF 1alpha-antisense RNA 1 (HIF1A-AS1) can inhibit the progression of liver fibrosis. Furthermore, the upregulation of several lncRNAs [e.g., nuclear paraspeckle assembly transcript 1 (NEAT1), hox transcript antisense RNA (Hotair), and liver-enriched fibrosis-associated lncRNA1 (lnc-LFAR1)] has been reported to promote liver fibrosis. This review will focus on the functions and mechanisms of lncRNAs, the lncRNA transcriptome profile of liver fibrosis, and the main lncRNAs involved in the signalling pathways that regulate hepatic fibrosis. This review provides insight into the screening of therapeutic and diagnostic markers of liver fibrosis.

Exosomal miR-103-3p from LPS-activated THP-1 macrophage contributes to the activation of hepatic stellate cells

Hepatic fibrosis occurs during chronic hepatic injury and is involved in hepatic stellate cells (HSCs) activated by several types of immune cells. Among the immune cells, hepatic macrophages and their crosstalk with HSCs play a vital role in all stages of hepatic fibrosis. Exosomes, which are 30-150 nm lipid bilayer vehicles, can transfer specific lipid, nucleic acids, proteins, and other bioactive molecules. Exosomes can act as good communication between macrophages and HSCs. Herein, we investigated the role of exosomes between THP-1 macrophage and HSCs in the progression of liver fibrosis. Exosomes originating from lipopolysaccharide (LPS)-treated THP-1 macrophages promoted HSCs proliferation and induced the increased expression of fibrotic genes. LPS could alter the miRNA profile in exosomes secreted from THP-1 macrophages. The changed miR-103-3p in exosomes could promote HSCs proliferation and activation by targeting Krüppel-like factor 4 (KLF4) and it plays important roles in the crosstalk between THP-1 macrophages and HSCs during the progression of liver fibrosis. Moreover, miR-103-3p in serum exosomes from liver fibrosis patients could be a biomarker for liver fibrosis. Therefore, exosomes may have important roles in the crosstalk between macrophage and HSCs in the progression of chronic liver diseases.

Human adipose stem cell-derived extracellular nanovesicles for treatment of chronic liver fibrosis

Liver fibrosis is an excessive wound healing process that occurs in response to liver damage depending on underlying aetiologies. Currently, there are no effective therapies and FDA-approved therapeutics for the treatment of liver fibrosis except liver transplantation. Multipotent adipose-derived stem cells (ADSCs) have received significant attention as regenerative medicine for liver fibrosis owing to their advantages over stem cells with other origins. However, intrinsic limitations of stem cell therapies, such as cellular rejection and tumor formation, have impeded clinical applications of the ADSC-based liver therapeutics. To overcome these problems, the extracellular nanovesicles (ENVs) responsible for the therapeutic effect of ADSCs (A-ENVs) have shown considerable promise as cell-free therapeutics for liver diseases. However, A-ENVs have not been used for the treatment of intractable chronic liver diseases including liver fibrosis and cirrhosis. Therefore, in this study, we investigated the in vitro and in vivo antifibrotic efficacy of A-ENVs in thioacetamide-induced liver fibrosis models. A-ENVs significantly downregulated the expression of fibrogenic markers, such as matrix metalloproteinase-2, collagen-1, and alpha-smooth muscle actin. The systemic administration of A-ENVs led to high accumulation in fibrotic liver tissue and the restoration of liver functionality in liver fibrosis models through a marked reduction in α-SMA and collagen deposition. These results demonstrate the significant potential of A-ENVs for use as extracellular nanovesicles-based therapeutics in the treatment of liver fibrosis and possibly other intractable chronic liver diseases.

Crosstalk network among multiple inflammatory mediators in liver fibrosis

Liver fibrosis is the common pathological basis of all chronic liver diseases, and is the necessary stage for the progression of chronic liver disease to cirrhosis. As one of pathogenic factors, inflammation plays a predominant role in liver fibrosis via communication and interaction between inflammatory cells, cytokines, and the related signaling pathways. Damaged hepatocytes induce an increase in pro-inflammatory factors, thereby inducing the development of inflammation. In addition, it has been reported that inflammatory response related signaling pathway is the main signal transduction pathway for the development of liver fibrosis. The crosstalk regulatory network leads to hepatic stellate cell activation and proinflammatory cytokine production, which in turn initiate the fibrotic response. Compared with the past, the research on the pathogenesis of liver fibrosis has been greatly developed. However, the liver fibrosis mechanism is complex and many pathways involved need to be further studied. This review mainly focuses on the crosstalk regulatory network among inflammatory cells, cytokines, and the related signaling pathways in the pathogenesis of chronic inflammatory liver diseases. Moreover, we also summarize the recent studies on the mechanisms underlying liver fibrosis and clinical efforts on the targeted therapies against the fibrotic response.

Fibrocytes and fibroblasts-Where are we now

Fibroblasts are considered major contributors to the process of fibrogenesis and the progression of matrix deposition and tissue distortion in fibrotic diseases such as Pulmonary Fibrosis. Recent discovery of the fibrocyte, a circulating possible precursor cell to the tissue fibroblast in fibrosis, has raised issues regarding the characterization of fibrocytes with respect to their morphology, growth characteristics in vitro, their biological role in vivo and their potential utility as a biomarker and/ or treatment target in various human diseases. Characterization studies of the fibrocyte continue as does emerging conflicting data concerning the relationship to or with the lung fibroblast. The source of signals that direct the traffic of these cells, as well as their response to therapeutic intervention with newly available drugs, bring new insights to the understanding of this cell type. The identification of exosomes from fibrocytes that can affect resident fibroblast activities suggest mechanisms of their influence on pathogenesis. Moreover, interesting comparisons with other pathologies are emerging involving the influence of circulating mesenchymal precursor cells on tissue responses.

Endoglin Trafficking/Exosomal Targeting in Liver Cells Depends on N-Glycosylation

Injury of the liver involves a wound healing partial reaction governed by hepatic stellate cells and portal fibroblasts. Individual members of the transforming growth factor-β (TGF-β) superfamily including TGF-β itself and bone morphogenetic proteins (BMP) exert diverse and partially opposing effects on pro-fibrogenic responses. Signaling by these ligands is mediated through binding to membrane integral receptors type I/type II. Binding and the outcome of signaling is critically modulated by Endoglin (Eng), a type III co-receptor. In order to learn more about trafficking of Eng in liver cells, we investigated the membranal subdomain localization of full-length (FL)-Eng. We could show that FL-Eng is enriched in Caveolin-1-containing sucrose gradient fractions. Since lipid rafts contribute to the pool of exosomes, we could consequently demonstrate for the first time that exosomes isolated from cultured primary hepatic stellate cells and its derivatives contain Eng. Moreover, via adenoviral overexpression, we demonstrate that all liver cells have the capacity to direct Eng to exosomes, irrespectively whether they express endogenous Eng or not. Finally, we demonstrate that block of N-glycosylation does not interfere with dimerization of the receptor, but abrogates the secretion of soluble Eng (sol-Eng) and prevents exosomal targeting of FL-Eng.

The Lymphatic Headmaster of the Mast Cell-Related Splanchnic Inflammation in Portal Hypertension

Portal hypertension is a common complication of liver disease, either acute or chronic. Consequently, in chronic liver disease, such as the hypertensive mesenteric venous pathology, the coexisting inflammatory response is classically characterized by the splanchnic blood circulation. However, a vascular lymphatic pathology is produced simultaneously with the splanchnic arterio-venous impairments. The pathological increase of the mesenteric venous pressure, by mechanotransduction of the venous endothelium hyperpressure, causes an inflammatory response involving the subendothelial mast cells and the lymphatic endothelium of the intestinal villi lacteal. In portal hypertension, the intestinal lymphatic inflammatory response through the development of mesenteric-systemic lymphatic collateral vessels favors the systemic diffusion of substances with a molecular pattern associated with damage and pathogens of intestinal origin. When the chronic hepatic insufficiency worsens the portal hypertensive inflammatory response, the splanchnic lymphatic system transports the hyperplasied intestinal mast cells to the mesenteric lymphatic complex. Then, an acquired immune response regulating a new hepato-intestinal metabolic scenario is activated. Therefore, reduction of the hepatic metabolism would reduce its key centralized functions, such as the metabolic, detoxifying and antioxidant functions which would try to be substituted by their peroxisome activity, among other functions of the mast cells.

Effect of NLRC5 on activation and reversion of hepatic stellate cells by regulating the nuclear factor-κB signaling pathway

BACKGROUND

The formation of liver fibrosis is mainly caused by the activation of hepatic stellate cells (HSCs) and the imbalance of extracellular matrix (ECM) production and degradation. The treatment of liver fibrosis mainly includes removing the cause, inhibiting the activation of HSCs, and inhibiting inflammation. NOD-like receptor (NLR) family, caspase activation and recruitment domain (CARD) domain containing 5/NOD27/CLR16.1 (NLRC5) is a highly conserved member of the NLR family and is involved in inflammation and immune responses by regulating various signaling pathways such as nuclear factor-κB (NF-κB) signaling. It has been found that NLRC5 plays an important role in liver fibrosis, but its specific effect and possible mechanism remain to be fully elucidated.

AIM

To investigate the role of NLRC5 in the activation and reversion of HSCs induced with transforming growth factor-β (TGF-β) and MDI, and to explore its relationship with liver fibrosis.

METHODS

A total of 24 male C57BL/6 mice were randomly divided into three groups, including normal, fibrosis, and recovery groups. Twenty-four hours after a liver fibrosis and spontaneous reversion model was established, the mice were sacrificed and pathological examination of liver tissue was performed to observe the degree of liver fibrosis in each group. LX-2 cells were cultured in vitro and treated with TGF-β1 and MDI. Real-time quantitative PCR (qPCR) and Western blot were used to analyze the expression levels of NLRC5, α-smooth muscle actin (α-SMA), and collagen type I alpha1 (Col1a1) in each group. The activity of NF-κB in each group of cells transfected with NLRC5-siRNA was detected.

RESULTS

Compared with the normal mice, the expression level of NLRC5 increased significantly (P < 0.01) in the fibrosis group, but decreased significantly in the recovery group (P < 0.01). In in vitro experiments, the content of NLRC5 was enhanced after TGF-β1 stimulation and decreased to a lower level when treated with MDI (P < 0.01). The expression of α-SMA and Col1a1 proteins and mRNAs in TGF-β1-mediated cells was suppressed by transfection with NLRC5-siRNA (P < 0.01). Western blot analysis showed that the expression of NF-κB p65 protein and phosphorylated IκBα (p-IκBα) was increased in the liver of mice in the fibrosis group but decreased in the recovery group (P < 0.01), and the protein level of nuclear p65 and p-IκBα was significantly increased after treatment with NLRC5-siRNA (P < 0.01).

CONCLUSION

NLRC5 may play a key role in the development and reversal of hepatic fibrosis through the NF-κB signaling pathway, and it is expected to be one of the clinical therapeutic targets.