Cholesterol Flux Is Required for Endosomal Progression of African Swine Fever Virions during the Initial Establishment of Infection

Abstract

African swine fever virus (ASFV) is a major threat for porcine production that has been slowly spreading in Eastern Europe since its first appearance in the Caucasus in 2007. ASFV enters the cell by endocytosis and gains access to the cytosol to start replication from late endosomes and multivesicular bodies. Cholesterol associated with low-density lipoproteins entering the cell by endocytosis also follows a trafficking pathway similar to that of ASFV. Here we show that cholesterol plays an essential role in the establishment of infection as the virus traffics through the endocytic pathway. In contrast to the case for other DNA viruses, such as vaccinia virus or adenovirus 5, cholesterol efflux from endosomes is required for ASFV release/entry to the cytosol. Accumulation of cholesterol in endosomes impairs fusion, resulting in retention of virions inside endosomes. ASFV also remodels intracellular cholesterol by increasing its cellular uptake and redistributes free cholesterol to viral replication sites. Our analysis reveals that ASFV manipulates cholesterol dynamics to ensure an appropriate lipid flux to establish productive infection. IMPORTANCESince its appearance in the Caucasus in 2007, African swine fever (ASF) has been spreading westwards to neighboring European countries, threatening porcine production. Due to the lack of an effective vaccine, ASF control relies on early diagnosis and widespread culling of infected animals. We investigated early stages of ASFV infection to identify potential cellular targets for therapeutic intervention against ASF. The virus enters the cell by endocytosis, and soon thereafter, viral decapsidation occurs in the acid pH of late endosomes. We found that ASFV infection requires and reorganizes the cellular lipid cholesterol. ASFV requires cholesterol to exit the endosome to gain access to the cytoplasm to establish productive replication. Our results indicate that there is a differential requirement for cholesterol efflux for vaccinia virus or adenovirus 5 compared to ASFV.

Antiviral Role of IFITM Proteins in African Swine Fever Virus Infection

“…A collapse of endosomes to the perinuclear area is also a characteristic phenotype of an alteration of endosomal cholesterol efflux [ 26 ]. Also, recent publications from our laboratory demonstrated that accumulation of cholesterol in endosomes caused by a chemical inhibition of cholesterol flux, causes virion retention inside endosomes and inhibition of infection progression [ 37 ].…”

“…In the present study, we have described accumulation of cholesterol upon overexpression of IFITM2 and IFITM3. We have recently reported that inhibition of cholesterol exit from endosomes using chemical inhibitors causes retention of virions inside these vesicles, thus impairing progression of the infection [ 37 ]. Altogether these data could suggest that the antiviral action of IFITMs may affect to a higher extent to those viruses that require the endosomal pathway during the early stages of infection.…”

The ubiquitin-proteasome system is required for African swine fever replication

“…The acidic environment of late endosomes is necessary for the virus to loss its capsid and acidification inhibitors such as Bafilomycin inhibit decapsidation and further infectivity. Also, alterations of cholesterol transport inhibit virion fusion and progression along the endocytic pathway [ 27 ]. After fusion of viral internal membrane with the viral membrane, naked cores are released to the cytoplasm to start replication [ 24 ].…”

Identification of a Functional Small Noncoding RNA of African Swine Fever Virus

“…In macrophages, miR-10b is known to target ATP binding cassette transporter A1 ABCA1 ( 45 ), which is involved in the regulation of cholesterol efflux. During infection with ASFV, cholesterol remodeling is essential in the establishment of productive viral infection, and disruption of cellular cholesterol efflux leads to the impairment of virus entry and viral particles remained trapped in endosomes ( 46 ). This suggests a link between miR-10b, ABCA1, and cholesterol efflux during endocyte-mediated entry of ASFV in macrophages.…”