CVB3 Nonstructural 2A Protein Modulates SREBP1a Signaling via the MEK/ERK Pathway

PEDV inhibits HNRNPA3 expression by miR-218-5p to enhance cellular lipid accumulation and promote viral replication

Porcine epidemic diarrhea virus (PEDV) requires complete dependence on the metabolic system of the host cell to complete its life cycle. There is a strong link between efficient viral replication and cellular lipid synthesis. However, the mechanism by which PEDV interacts with host cells to hijack cellular lipid metabolism to promote its replication remains unclear. In this study, PEDV infection significantly enhanced the expression of lipid synthesis-related genes and increased cellular lipid accumulation. Furthermore, using liquid chromatography-tandem mass spectrometry, we identified heterogeneous nuclear ribonucleoprotein A3 (HNRNPA3) as the interacting molecule of PEDV NSP9. We demonstrated that the expression of HNRNPA3 was downregulated by PEDV-induced miR-218-5p through targeting its 3' untranslated region. Interestingly, knocking down HNRNPA3 facilitated the PEDV replication by promoting cellular lipid synthesis. We next found that the knockdown of HNRNPA3 potentiated the transcriptional activity of sterol regulatory element-binding transcription factor 1 (SREBF1) through zinc finger protein 135 (ZNF135) as well as PI3K/AKT and JNK signaling pathways. In summary, we propose a model in which PEDV downregulates HNRNPA3 expression to promote the expression and activation of SREBF1 and increase cellular lipid accumulation, providing a novel mechanism by which PEDV interacts with the host to utilize cellular lipid metabolism to promote its replication.IMPORTANCEAs the major components and structural basis of the viral replication complexes of positive-stranded RNA viruses, lipids play an essential role in viral replication. However, how PEDV manipulates host cell lipid metabolism to promote viral replication by interacting with cell proteins remains poorly understood. Here, we found that SREBF1 promotes cellular lipid synthesis, which is essential for PEDV replication. Moreover, HNRNPA3 negatively regulates SREBF1 activation and specifically reduces lipid accumulation, ultimately inhibiting PEDV dsRNA synthesis. Our study provides new insight into the mechanisms by which PEDV hijacks cell lipid metabolism to benefit viral replication, which can offer a potential target for therapeutics against PEDV infection.

Cathelicidins Target HSP60 To Restrict CVB3 Transmission via Disrupting the Exosome and Reducing Cardiomyocyte Apoptosis

Cathelicidin antimicrobial peptides (mouse, CRAMP; human, LL-37) have broad-spectrum antiviral activities against enveloped viruses, but their mechanisms of action against nonenveloped viruses remain to be elucidated. Coxsackievirus B3 (CVB3), a member of nonenveloped virus belonging to the Enterovirus genus of Picornaviridae, is an important pathogen of viral myocarditis and dilated cardiomyopathy. Here, we observed that cardiac CRAMP expression was significantly upregulated in mice after CVB3 infection. The administration of CRAMP or LL-37 markedly suppressed CVB3 infection in mice, and CRAMP deficiency increased the susceptibility of mice to CVB3. CRAMP and LL-37 inhibited CVB3 replication in primary cardiomyocytes. However, they did not inactivate CVB3 particles and did not regulate the response of cardiomyocytes against CVB3 infection. Intriguingly, they inhibited CVB3 transmission through the exosome, but not virus receptor. In detail, CRAMP and LL-37 directly induced the lysis of exosomes by interfering with exosomal heat shock protein 60 (HSP60) and then blocked the diffusion of exosomes to recipient cells and inhibited the establishment of productive infection by exosomes. In addition, the interaction of CRAMP and LL-37 with HSP60 simultaneously inhibited HSP60-induced apoptosis in cardiomyocytes and reduced HSP60-enhanced CVB3 replication. Our findings reveal a novel mechanism of cathelicidins against viral infection and provide a new therapeutic strategy for CVB3-induced viral myocarditis. IMPORTANCE The relative mechanisms that cathelicidin antimicrobial peptides use to influence nonenveloped virus infection are unclear. We show here that cathelicidin antimicrobial peptides (CRAMP and LL-37) directly target exosomal HSP60 to destroy exosomes, which in turn block the diffusion of exosomes to recipient cardiomyocytes and reduced HSP60-induced apoptosis, thus restricting coxsackievirus B3 infection. Our results provide new insights into the mechanisms cathelicidin antimicrobial peptides use against viral infection.

Orsay Virus Infection of Caenorhabditis elegans Is Modulated by Zinc and Dependent on Lipids

Viruses utilize host lipids to promote the viral life cycle, but much remains unknown as to how this is regulated. Zinc is a critical element for life, and few studies have linked zinc to lipid homeostasis. We demonstrated that Caenorhabditis elegans infection by Orsay virus is dependent upon lipids and that mutation of the master regulator of lipid biosynthesis, sbp-1, reduced Orsay virus RNA levels by ~236-fold. Virus infection could be rescued by dietary supplementation with lipids downstream of fat-6/fat-7. Mutation of a zinc transporter encoded by sur-7, which suppresses the lipid defect of sbp-1, also rescued Orsay virus infection. Furthermore, reducing zinc levels by chemical chelation in the sbp-1 mutant also increased lipids and rescued Orsay virus RNA levels. Finally, increasing zinc levels by dietary supplementation led to an ~1,620-fold reduction in viral RNA. These findings provide insights into the critical interactions between zinc and host lipids necessary for virus infection. IMPORTANCE Orsay virus is the only known natural virus pathogen of Caenorhabditis elegans, which shares many evolutionarily conserved pathways with humans. We leveraged the powerful genetic tractability of C. elegans to characterize a novel interaction between zinc, lipids, and virus infection. Inhibition of the Orsay virus replication in the sbp-1 mutant animals, explained by the lipid depletion, can be rescued by a genetic and pharmacological approach that reduces the zinc accumulation and rescues the lipid levels in this mutant animal. Interestingly, the human ortholog of sbp-1, srebp-1, has been reported to play a role for virus infection, and zinc has been shown to inhibit the virus replication of multiple viruses. However, the mechanism through which zinc is acting is not well understood. These results suggest that the lipid regulation mediated by zinc may play a relevant role during mammalian virus infection.

MORG1—A Negative Modulator of Renal Lipid Metabolism in Murine Diabetes

Renal fatty acid (FA) metabolism is severely altered in type 1 and 2 diabetes mellitus (T1DM and T2DM). Increasing evidence suggests that altered lipid metabolism is linked to tubulointerstitial fibrosis (TIF). Our previous work has demonstrated that mice with reduced MORG1 expression, a scaffold protein in HIF and ERK signaling, are protected against TIF in the db/db mouse model. Renal TGF-ß1 expression and EMT-like changes were reduced in mice with single-allele deficiency of MORG1. Given the well-known role of HIF and ERK signaling in metabolic regulation, here we examined whether protection was also associated with a restoration of lipid metabolism. Despite similar features of TIF in T1DM and T2DM, diabetes-associated changes in renal lipid metabolism differ between both diseases. We found that de novo synthesis of FA/cholesterol and β-oxidation were more strongly disrupted in T1DM, whereas pathological fat uptake into tubular cells mediates lipotoxicity in T2DM. Thus, diminished MORG1 expression exerts renoprotection in the diabetic nephropathy by modulating important factors of TIF and lipid dysregulation to a variable extent in T1DM and T2DM. Prospectively, targeting MORG1 appears to be a promising strategy to reduce lipid metabolic alterations in diabetic nephropathy.

Endosomal Cholesterol in Viral Infections - A Common Denominator?

Cholesterol has gained tremendous attention as an essential lipid in the life cycle of virtually all viruses. These seem to have developed manifold strategies to modulate the cholesterol metabolism to the side of lipid uptake and de novo synthesis. In turn, affecting the cholesterol homeostasis has emerged as novel broad-spectrum antiviral strategy. On the other hand, the innate immune system is similarly regulated by the lipid and stimulated by its derivatives. This certainly requires attention in the design of antiviral strategies aiming to decrease cellular cholesterol, as evidence accumulates that withdrawal of cholesterol hampers innate immunity. Secondly, there are exceptions to the rule of the abovementioned virus-induced metabolic shift toward cholesterol anabolism. It therefore is of interest to dissect underlying regulatory mechanisms, which we aimed for in this minireview. We further collected evidence for intracellular cholesterol concentrations being less important in viral life cycles as compared to the spatial distribution of the lipid. Various routes of cholesterol trafficking were found to be hijacked in viral infections with respect to organelle-endosome contact sites mediating cholesterol shuttling. Thus, re-distribution of cellular cholesterol in the context of viral infections requires more attention in ongoing research. As a final aim, a pan-antiviral treatment could be found just within the transport and re-adjustment of local cholesterol concentrations. Thus, we aimed to emphasize the importance of the regulatory roles the endosomal system fulfils herein and hope to stimulate research in this field.

Association of RDM1 with osteosarcoma progression via cell cycle and MEK/ERK signalling pathway regulation

RAD52 motif‐containing 1 (RDM1), a key regulator of DNA double‐strand break repair and recombination, has been reported to play an important role in the development of various human cancers, such as papillary thyroid carcinoma, neuroblastoma and lung cancer. However, the effect of RDM1 on osteosarcoma (OS) progression remains unclear. Here, this study mainly explored the connection between RDM1 and OS progression, as well as the underlying mechanism. It was found that RDM1 was highly expressed in OS cells compared with human osteoblast cells. Knockdown of RDM1 caused OS cell proliferation inhibition, cell apoptosis promotion and cell cycle arrest at G1 stage, whereas RDM1 overexpression resulted in the opposite phenotypes. Furthermore, RDM1 silencing leads to a significant decrease in tumour growth in xenograft mouse model. RDM1 also increased the protein levels of MEK 1/2 and ERK 1/2. All these findings suggest that RDM1 plays an oncogenic role in OS via stimulating cell cycle transition from G1 to S stage, and regulating MEK/ERK signalling pathway, providing a promising therapeutic factor for the treatment of OS.

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.

Fulminant myocarditis: a comprehensive review from etiology to treatments and outcomes

Fulminant myocarditis (FM) is characterized by a rapid progressive decline in cardiac function and a high mortality rate. Since the first report of FM patients in the 1980s, several clinical trials and research studies have been published increasing our knowledge regarding FM. Currently, the diagnosis of FM depends on various techniques including electrocardiography, echocardiography, endomyocardial biopsy, and cardiac magnetic resonance. The development of mechanical circulation support (MCS) devices and progress in our understanding of the pathophysiological mechanisms underlying FM, treatment regimens have evolved from simple symptomatic treatment to a life support-based comprehensive treatment approach. The core mechanism underlying the development of FM is the occurrence of an inflammatory cytokine storm. This review provides a comprehensive account of the current understanding of FM pathophysiology and knowledge regarding its etiology, pathophysiology, treatments, and outcomes.

Lipid raft-associated PI3K/Akt/SREBP1 signaling regulates coxsackievirus A16 (CA16) replication

Coxsackievirus A16 (CA16) is one of predominant Enterovirus that possesses high pathogenicity. Lipid rafts, as cholesterol - and sphingolipid - enriched membrane nanodomains, are involved into many aspects of the virus life cycle. Our previous study found that lipid rafts integrity was essential for CA16 replication, but how lipid rafts regulate CA16 replication through activating downstream signaling remains largely unknown. Thus, in this study, we revealed that lipid rafts were required for activation of PI3K/Akt signaling at early stage of CA16 infection. Treatment with wortmannin significantly reduced the expression of virus protein, indicating PI3K/Akt signaling was beneficial for early stage of virus infection. In addition, lipid rafts integrity was also indispensable for PI3K/Akt activation during the late stage of CA16 infection, which played critical functions in mediating sterol regulatory element-binding proteins 1 (SREBP1) maturation. Whereas, over-expression of SREBP1 exhibited inhibition on virus replication, suggesting that PI3K/Akt signaling and SREBP1 might positively and negatively influence virus replication in two different stages of infection, respectively. Taken together, our study demonstrates an important role of the lipid raft-associated PI3K/Akt/SREBP1 signaling in modulating CA16 replication, which will deepen our understanding mechanism of CA16 infection.

Virus Impact on Lipids and Membranes

Viruses manipulate cellular lipids and membranes at each stage of their life cycle. This includes lipid-receptor interactions, the fusion of viral envelopes with cellular membranes during endocytosis, the reorganization of cellular membranes to form replication compartments, and the envelopment and egress of virions. In addition to the physical interactions with cellular membranes, viruses have evolved to manipulate lipid signaling and metabolism to benefit their replication. This review summarizes the strategies that viruses use to manipulate lipids and membranes at each stage in the viral life cycle.