Association of hepatitis c with insulin resistance and related disorders Muhammad ilyas 09-Arid-1307 Ph. D scholar (Biochemistry)

Contents Introduction Primary role of insulin HCV genome Role of HCV core protein in IR HCV NS5 A and IR HCV NS3 and IR Major disorders associated with HCV-induced insulin Resistance Hepatic fibrosis Hepatic steatosis Hepatocarcinogenesis Antiviral-drug resistance Conclusion

Introduction Hepatitis C virus (HCV) infection is a serious health problem affecting over 130 million people worldwide Approximately 85% of the HCV-infected population develops severe complications, such as chronic HCV (CHCV), cirrhosis, diabetes, and hepatocellular carcinomas It is recognized as a metabolic disease mainly because of its major role in the development of insulin resistance (IR) and type 2 diabetes melllitis (T2DM)

Continue… Several HCV-induced pathways lead to fibrosis, inflammation, hepatocellular carcinoma, and insulin resistance To understand these pathways we need to study the basic mechanism of insulin …..

Insulin Insulin, which is synthesized by the pancreatic β cells, is the most effective anabolic hormone. It is important for cell growth, cell differentiation, protein synthesis, and maintenance of glucose levels in the body. It regulates blood glucose levels by inhibiting the production of liver glucose and by promoting the absorption of glucose in muscle and adipose tissue

Insulin signal transduction Insulin binds to extracellular α subunit of insulin receptor substrate (IRS), Further intracellular tyrosine-kinase domain of the β subunit phosphorylate phosphatidylinositol 3-kinase (PI3K) which phosphorylate phosphatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol triphosphate (PIP3). Phosphosinositide -dependent kinase 1 (PDK1), in turn, activates protein kinase B (Akt/PKB)

Continue… Protein kinase B decreases the blood glucose levels mainly through 2 pathways. Firstly, by stimulating the phosphorylation of glycogen synthase, which converts surplus glucose into glycogen. Secondly, by suppressing glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, which are involved in gluconeogenesis. Moreover, AKT is important for the localization of GLUT4 in the cell membrane and thus stimulates glucose uptake into skeletal muscle and adipose tissue

Insulin signal transduction Transcription factor α subunit of insulin receptor β subunit of the insulin receptor localization of GLUT4 in the cell membrane

Insulin resistance Insulin resistance arises from the impairment of the above- stated insulin-signaling pathway at multiple steps. One of the most important steps is the phosphorylation of key serine residues including Ser307, Ser318, Ser636, and Ser639 and not phosphorylation of the tyrosine residues for the inhibition of IRS

HCV genome The genome HCV encodes Structural proteins designated as core (C), envelope 1 (E1), envelope 2 (E2), and P7 (unknown function), providing for virion architecture, Nonstructural proteins, mainly enzymes essential to the virion's life cycle, designated as NS2, NS3, NS4A, NS4B, NS5A, and NS5B.

Role of HCV core protein in insulin resistance 1. HCV core protein has been reported to induce overexpression of tumor necrosis factor-α (TNF-α) in the liver of transgenic mice and human hepatoma cell lines Which results in the inhibition of PI3K-mediated activation of insulin receptor substrate 1 (IRS-1) This leads to the impairment of glucose uptake in skeletal muscles

Continue… 2. Expression of core protein in hepatocytes causes an increase in the phospholrylation of IRS-1 at Ser312, impairs the activation of AKT at the Thr308 phosphorylation site and also impairs insulin-stimulated glucose uptake 3. Increased production of TNF-α and suppression of cytokine signaling-3 (SOCS-3) in HCV infection promotes IR mainly through the inhibition of the insulin receptor and tyrosine phosphorylation of IRS-1.

1. TNF inhibit PI3K 2.increase in the phosphorylation of IRS-1 at Ser312 impairs the activation of AKT

Role of HCV NS5A in insulin resistance The NS5A of HCV plays a significant role in virus-driven IR. HCV NS5A contributes to overexpression of protein phosphatase 2A (PP2A).PP2A modulates insulin-signaling pathway by dephosphorylation of AKT, leading to IR NS5A promotes fatty acid synthesis by the upregulation of lipogenic gene sterol regulatory element binding protein 1c. (SCREBP-1c). which promotes the transcriptional activation of other lipogenic genes like acetyl CoA carboxylase, ATP citrate lyase, hydroxyl methyl glutaryl CoA reductase the expression of gluconeogenic genes in turns, enhances insulin resistance

Role of HCV NS3 in insulin resistance NS3 has been shown to induce oxidative stress by the way of reactive oxygen species (ROS). During viral replication, NS-3 induces the up regulation of NADPH oxidase 2 (NOX2) which, in turns, accelerates the production of ROS eventually leading to the modulation in downstream signaling pathways like hepatic fibrosis. It has been found that NS-3 cans down regulate T cells and natural killer cells thereby promoting its proteolytic activity.

Major disorders associated with HCV-induced IR

Hepatic Fibrosis IR plays a pivotal role in accelerating the severity of hepatic fibrosis in HCV-infected patients, IR stimulates the production of free fatty acids and increases lipid deposition in the liver, which, results in the development of liver fibrosis Moreover, IR is also involved in the proliferation of hepatic stellate cells, which are the main site of deposition of abnormal extracellular matrix in hepatic fibrosis

Hepatic steatosis (Fatty liver) The rate of incidence of hepatic steatosis in HCV-infected patients is approximately twice than the prevalence rate of steatosis in people with other common liver disorders such as hepatitis B One of the major factors responsible for the development of steatosis in HCV-infected patients is the production of triglycerides

Continue… The core protein of HCV induces aggregation of triglycerides through many mechanisms like activation of fatty acid synthase and up regulation of sterol regulatory element-binding protein -1c. (SCREBP- 1c). SREBP-1c is transcriptionally regulated by liver X receptor (LXR) and retinoid X receptor (RXR), which belong to a family of nuclear hormone receptors, Accumulation of cellular fatty acids by HCV core protein is modulated by the SCREBP-1c pathway because RXR is activated by HCV core protein HCV core protein is also responsible for the production of reactive oxygen species, which, in turn, trigger lipid peroxidation, thus resulting in severe damage to the liver and ultimately to the development of steatosis

Continue… Proteosome activator PA28 gamma forms a homoheptamer in the nucleus, and it enhances trypsin-like peptidase activity of 20S proteasome. PA28 gamma binds to steroid receptor coactivator-3 (SRC-3) and enhances the degradation of SRC-3 in a ubiquitin- and ATP independent manner. The results from a PA28 gamma Knockout HCV Core Gene Transgenic Mice was compared to a wild type which clearly indicated that PA28 gamma is responsible for hepatic steatosis.

PA28-Knockout HCV Core Gene Transgenic Mice and wild type B

Hepatocarcinogenesis IR is another key factor that plays a crucial role in the progression of liver cancer in HCV-infected patients However, the precise nature of the association is unknown. IR is responsible for the excessive production of free fatty acids, which causes increased liver adiposity, thus resulting in a reduction in the adiponectin levels and consequently the development of HCC, In addition, fatty acid deposition in hepatocytes causes oxidative stress, which is another risk factor responsible for hepato carcinogenesis

Antiviral-Drug Resistance Resistance to antiviral treatment is another serious problem associated with HCV-induced IR. Although, the exact relationship between IR and poor response to antiviral treatment is not clearly understood, IR is known to cause an accumulation of hepatic lipids important for HCV replication. These droplets activate viral replication and eventually lead to resistance to antiviral treatment.

Continue… Moreover, SOCS-3 production is upregulated by the HCV core protein, which is involved in reducing interferon activity

Conclusion HCV-associated IR is responsible for many HCV-related conditions such as hepatic fibrosis, antiviral-drug resistance, steatosis, and hepato carcinogenesis. IR arises from the impairment of the insulin-signaling pathway at multiple steps. Core protein of HCV induces IR mainly by modulating the insulin-signaling pathway at the level of IRS.

Continue.. HCV NS5A lead to overexpression of PP2A, which leads to the impairment of interferon signaling, and is thus responsible for poor response to interferon therapy for treating IR in HCV- infected patients. NS3 has been shown to induce oxidative stress by the way of reactive oxygen species (ROS).

References Rachel J. Perry, V. T. Samuel, K. F. Petersen & Gerald I. Shulman The role of hepatic lipids in hepatic insulin resistance and type 2 diabetes. Nature 510, 84–91. Kohji Moriishi, R. Mochizuki, K. Moriya, H. Miyamoto, Y. Mori, T. Abe, S. Murata, K. Tanaka, T. Miyamura, T. Suzuki, K. Koike and Y. Matsuura Critical role of PA28 in hepatitis C virus- associated steatogenesis and Hepatocarcinogenesis. Science,