Polyamine Analog Diethylnorspermidine Restricts Coxsackievirus B3 and Is Overcome by 2A Protease Mutation In Vitro

Hepatitis C Virus Dysregulates Polyamine and Proline Metabolism and Perturbs the Urea Cycle

Hepatitis C virus (HCV) is an oncogenic virus that causes chronic liver disease in more than 80% of patients. During the last decade, efficient direct-acting antivirals were introduced into clinical practice. However, clearance of the virus does not reduce the risk of end-stage liver diseases to the level observed in patients who have never been infected. So, investigation of HCV pathogenesis is still warranted. Virus-induced changes in cell metabolism contribute to the development of HCV-associated liver pathologies. Here, we studied the impact of the virus on the metabolism of polyamines and proline as well as on the urea cycle, which plays a crucial role in liver function. It was found that HCV strongly suppresses the expression of arginase, a key enzyme of the urea cycle, leading to the accumulation of arginine, and up-regulates proline oxidase with a concomitant decrease in proline concentrations. The addition of exogenous proline moderately suppressed viral replication. HCV up-regulated transcription but suppressed protein levels of polyamine-metabolizing enzymes. This resulted in a decrease in polyamine content in infected cells. Finally, compounds targeting polyamine metabolism demonstrated pronounced antiviral activity, pointing to spermine and spermidine as compounds affecting HCV replication. These data expand our understanding of HCV's imprint on cell metabolism.

Mechanistic insights into bone remodelling dysregulation by human viral pathogens

Bone-related diseases (osteopathologies) associated with human virus infections have increased around the globe. Recent findings have highlighted the intricate interplay between viral infection, the host immune system and the bone remodelling process. Viral infections can disrupt bone homeostasis, contributing to conditions such as arthritis and soft tissue calcifications. Osteopathologies can occur after arbovirus infections such as chikungunya virus, dengue virus and Zika virus, as well as respiratory viruses, such as severe acute respiratory syndrome coronavirus 2 and enteroviruses such as Coxsackievirus B. Here we explore how human viruses dysregulate bone homeostasis, detailing viral factors, molecular mechanisms, host immune response changes and bone remodelling that ultimately result in osteopathologies. We highlight model systems and technologies to advance mechanistic understanding of viral-mediated bone alterations. Finally, we propose potential prophylactic and therapeutic strategies, introduce 'osteovirology' as a research field highlighting the underestimated roles of viruses in bone-related diseases, and discuss research avenues for further investigation.

Persistent Coxsackievirus B3 Infection in Pancreatic Ductal Cells In Vitro Downregulates Cellular Polyamine Metabolism

Picornaviruses infect a wide variety of cell types in vitro, with rapid replication kinetics and pronounced cytopathic effect. Coxsackievirus B3 (CVB3) can also establish a persistent infection in vivo that can lead to pathology, including dilated cardiomyopathy and myocarditis. One model system to study persistent infection is the pancreatic ductal cell line PANC-1, which CVB3 infects and is maintained indefinitely. We have characterized this model for CVB3 infection to study persistent infection for over 6 months. We find that CVB3 rapidly replicates within PANC-1 cells without robust cytopathic effect, and after 1 month in culture, titers stabilize. We find that infection does not significantly affect cellular viability. Persistent virus reverts to lytic infection when transferred to Huh7 or Vero cells. We find that persistent CVB3 adapts to PANC-1 cells via mutation of its capsid proteins and, curiously, the viral polymerase (3Dpol) to generate a high-fidelity polymerase. Persistent infection is associated with reduced cleavage of eIF4G, reduced plaque size, and decreasing particle infectivity. We further find that polyamine metabolism is altered in persistently infected cells, with the rate-limiting enzyme ornithine decarboxylase (ODC1) reduced in translation. We further find that targeting polyamine synthesis reduces persistent infection without affecting the viability of the PANC-1 cells. Finally, we find that viral fidelity is essential to maintaining CVB3 infection, and targeting viral fidelity reduces persistent virus infection. Together, these data highlight a novel role for polyamines and fidelity in persistent CVB3 infection and suggest avenues for therapeutic development to target persistent infection. IMPORTANCE Enteroviruses are significant human pathogens that can cause severe disease, including cardiomyopathies. Viruses like coxsackievirus B3 (CVB3) can cause tissue damage by lytically infecting cells; however, CVB3 can also persistently infect, which has been associated with several pathologies. Studying persistent infection in vitro is challenging, as CVB3 lytically infects most cellular model systems. Here, we show that CVB3 establishes persistent infection in pancreatic ductal cells in vitro, similar to prior studies on other coxsackieviruses. We also show that this infection results in adaptation of the virus to these cells, as well as changes to cellular metabolism of polyamines.

Good cop, bad cop: Polyamines play both sides in host immunity and viral replication

Viruses rely on host cells for energy and synthesis machinery required for genome replication and particle assembly. Due to the dependence of viruses on host cells, viruses have evolved multiple mechanisms by which they can induce metabolic changes in the host cell to suit their specific requirements. The host immune response also involves metabolic changes to be able to react to viral insult. Polyamines are small ubiquitously expressed polycations, and their metabolism is critical for viral replication and an adequate host immune response. This is due to the variety of functions that polyamines have, ranging from condensing DNA to enhancing the translation of polyproline-containing proteins through the hypusination of eIF5A. Here, we review the diverse mechanisms by which viruses exploit polyamines, as well as the mechanisms by which immune cells utilize polyamines for their functions. Furthermore, we highlight potential avenues for further study of the host-virus interface.

Combating coxsackievirus B infections

Coxsackieviruses B (CVB) are small, non-enveloped, single-stranded RNA viruses belonging to the Enterovirus genus of the Picornaviridae family. They are common worldwide and cause a wide variety of human diseases ranging from those having relatively mild symptoms to severe acute and chronic pathologies such as cardiomyopathy and type 1 diabetes. The development of safe and effective strategies to combat these viruses remains a challenge. The present review outlines current approaches to control CVB infections and associated diseases. Various drugs targeting viral or host proteins involved in viral replication as well as vaccines have been developed and shown potential to prevent or combat CVB infections in vitro and in vivo in animal models. Repurposed drugs and alternative strategies targeting miRNAs or based on plant extracts and probiotics and their derivatives have also shown antiviral effects against CVB. In addition, clinical trials with vaccines and drugs are underway and offer hope for the prevention or treatment of CVB-induced diseases.

Polyamine-Linked Cholesterol Incorporation in Rift Valley Fever Virus Particles Promotes Infectivity

Viruses rely on an array of cellular metabolites to replicate and form progeny virions. One set of these molecules, polyamines, are small aliphatic molecules, which are abundant in most cells, that support virus infection; however, the precise roles of polyamines in virus infection remain incompletely understood. Recent work demonstrated that polyamine metabolism supports cellular cholesterol synthesis through translation of the key transcription factor SREBP2. Here, we show that the bunyavirus Rift Valley fever virus (RVFV) relies on both cholesterol and polyamines for virus infection. Depletion of cellular cholesterol or interruption of cholesterol trafficking negatively impacts RVFV infection. Cholesterol is incorporated into RVFV virions and mediates their infectivity in a polyamine-dependent manner; we find that the virus derived from polyamine-depleted cells lacks cholesterol within the virion membrane. Conversely, we find that virion-associated cholesterol is linked to the incorporation of spermidine within the virion. Our prior work demonstrated that polyamines facilitate pH-mediated fusion and genome release, which may be a consequence of cholesterol depletion within virions. Thus, our work highlights the metabolic connection between polyamines and cholesterol synthesis to impact bunyavirus infection. These data demonstrate the connectedness between cellular metabolic pathways and reveal potential avenues of therapeutic intervention.

PEDV infection affects the expression of polyamine-related genes inhibiting viral proliferation

Porcine epidemic diarrhea virus (PEDV) is an alpha-coronavirus that causes epidemic diarrhea in swines. The mortality of PEDV infection in one-week-old piglets is extremely high, which causes a huge significant economic loss to the global pig husbandry and blocks its healthy development. There was a lack of adequate studies to elucidate pathogenic mechanism associated with PEDV infection. In the present study, we detected the expression profiles of polyamine metabolism associated genes in Vero cells infected with PEDV by RT-qPCR. It is shown that PAOX(acetylpolyamine oxidase), SMOX(spermine oxidase), SAT1(spermidine-spermine acetyltransferase 1), ODC1(ornithine decarboxylase 1), DHPS(deoxyhypusine synthase) and EIF5A( eukaryotic initiation factor 5A) were significantly upregulated. Through intervening SAT1 level in PEDV-infected Vero cells, it is identified that overexpression of SAT1 inhibited PEDV replication by reducing polyamine levels. Furthermore, polyamine depletion and upregulation were found to regulate the proliferation of PEDV. PEDV infection in Vero cells did not result in a significant change in the protein level of eIF5A, and in addition, the activated eIF5A did not affect the proliferation of PEDV. Our results provided new insights into the influence of polyamine metabolism on the proliferation of PEDV.