A new HCV mouse model on the block

FAdV-4-induced ferroptosis affects fat metabolism in LMH cells

Ferroptosis is a form of controlled cell death that was first described relatively recently and that is dependent on the formation and accumulation of lipid free radicals through an iron-mediated mechanism. A growing body of evidence supports the close relationship between pathogenic infections and ferroptotic cell death, particularly for viral infections. Ferroptosis is also closely tied to the pathogenic development of hepatic steatosis and other forms of liver disease. Fowl adenovirus serotype 4 (FAdV-4) is a hepatotropic aviadenovirus causing hydropericardium syndrome (HPS) that is capable of impacting fat metabolism. However, it remains uncertain as to what role, if any, ferroptotic death plays in the context of FAdV-4 infection. Here, FAdV-4 was found to promote ferroptosis via the p53-SLC7A11-GPX4 axis, while ferrostain-1 was capable of inhibiting this FAdV-4-mediated ferroptotic death through marked reductions in lipid peroxidation. The incidence of FAdV-4-induced fatty liver was also found to be associated with the activation of ferroptotic activity. Together, these results offer novel insights regarding potential approaches to treating HPS.

Fowl Adenovirus Serotype 4 Induces Hepatic Steatosis via Activation of Liver X Receptor-α

Fowl adenovirus serotype 4 (FAdV-4) is a hepatotropic virus that causes severe hepatic damage characterized by basophilic intranuclear inclusion bodies, vacuolar degeneration, and multifocal necrosis in hepatocytes. Many aspects of FAdV-4 infection and pathogenesis, however, remain unknown. Here, we found that FAdV-4-induced hepatic injury is accompanied by the accumulation of oil droplets (triglycerides) in the cytoplasm of hepatocytes, a typical indicator of steatosis, in FAdV-4-infected chickens. Significant upregulation of adipose synthesis-related genes, such as liver X receptor-α (LXR-α), peroxisome proliferator-activated receptor gamma (PPAR-γ), and sterol regulatory element-binding protein-1c (SREBP-1c), and significant downregulation of low-density lipoprotein secretion-related genes and lipid oxidation- and lipid decomposition-related genes were observed in the infected chickens. FAdV-4 infection in cultured leghorn male hepatoma (LMH) cells caused similar signs of steatosis, with alterations in various lipogenesis-related genes. We eliminated the effect of LXR-α activation on FAdV-4-induced steatosis and found that treatment with an LXR-α antagonist (SR9243) and RNA interference (small interfering RNA targeting LXR-α [Si-LXR-α]) decreased the number of oil droplets and the accumulation of lipogenic genes, but treatment with an LXR-α agonist (T0901317) increased the number of oil droplets and the accumulation of lipogenic genes in the cells. Additionally, SR9243 treatment or Si-LXR-α transfection led to significant reductions in viral DNA level, protein expression, and virus production, whereas T0901317 treatment caused significant increases in viral DNA level, protein expression, and virus production. However, inhibition of SREBP-1c activity had no significant effect on virus production. Collectively, these results indicated that FAdV-4-induced steatosis involves activation of the LXR-α signaling pathway, which might be a molecular mechanism underlying the hepatic injury associated with FAdV-4 infection.IMPORTANCE Fowl adenovirus serotype 4 (FAdV-4) is an important hepatotropic adenovirus in chicken, but the underlying mechanism of FAdV-4-induced hepatic injury remains unclear. We report here that infection with FAdV-4 induced the accumulation of oil droplets (triglycerides) in the cytoplasm of hepatocytes, a typical indicator of steatosis, in the livers of chickens. FAdV-4-induced steatosis might be caused by a disrupted balance of fat metabolism, as evidenced by differential regulation of various lipase genes. The significant upregulation of liver X receptor-α (LXR-α) prompted us to investigate the interplay between LXR-α activation and FAdV-4-induced steatosis. Treatment with an agonist, an antagonist, or RNA interference targeting LXR-α in cultured leghorn male hepatoma (LMH) cells indicated that FAdV-4-induced steatosis was dependent upon LXR-α activation, which contributed to virus replication. These results provide important mechanistic insights, revealing that FAdV-4 induces hepatic steatosis by activating the LXR-α signaling pathway and highlighting the therapeutic potential of strategies targeting the LXR-α pathway for the treatment of FAdV-4 infection.

Identification of Interferon Receptor IFNAR2 As a Novel HCV Entry Factor by Using Chemical Probes

Upon sensing pathogen-associated patterns and secreting interferons (IFNs) into the environment, host cells perceive extracellular type I IFNs by the IFNα/β receptors IFNAR1 and IFNAR2 to stimulate downstream innate immune signaling cascades. Through the use of chemical probes, we demonstrated that IFNAR2 facilitates hepatitis C virus (HCV) entry. Silencing of IFNAR2 significantly attenuated HCV proliferation. IFNAR2 binds infectious HCV virions through a direct interaction of its D2 domain with the C-terminal end of apolipoprotein E (apoE) on the viral envelope and facilitates virus entry into host cells. The antibody against the IFNAR2 D2 domain attenuates IFNAR2-apoE interaction and impairs HCV infection. The recombinant IFNAR2 protein and the chemical probe potently inhibit major HCV genotypes in various human liver cells in vitro. Moreover, the impact of a chemical probe on HCV genotype 2a is also documented in immune-compromised humanized transgenic mice. Our results not only expand the understanding of the biology of HCV entry and the virus-host relationship but also reveal a new target for the development of anti-HCV entry inhibitors.

Cardiovascular inflammation: RNA takes the lead

Inflammation has recently gained tremendous attention as a key contributor in several chronic diseases. While physiological inflammation is essential to counter a wide variety of damaging stimuli and to improve wound healing, dysregulated inflammation such as in the myocardium and vasculature can promote cardiovascular diseases. Given the high severity, prevalence, and economic burden of these diseases, understanding the factors involved in the regulation of physiological inflammation is essential. Like other complex biological phenomena, RNA-based processes are emerging as major regulators of inflammatory responses. Among such processes are cis-regulatory elements in the mRNA of inflammatory genes, noncoding RNAs directing the production or localization of inflammatory cytokines/chemokines, or pathogenic RNA driving inflammatory responses. In this review, we describe several specific RNA-based molecular mechanisms by which physiological inflammation pertaining to cardiovascular diseases is regulated. These include the role of AU-rich element-containing mRNAs, long non-coding RNAs, microRNAs, and viral RNAs.