Interferon-Stimulated Genes that Target Retrovirus Translation.

The innate immune system, particularly the interferon (IFN) system, constitutes the initial line of defense against viral infections. IFN signaling induces the expression of interferon-stimulated genes (ISGs), and their products frequently restrict viral infection. Retroviruses like the human immunodeficiency viruses and the human T-lymphotropic viruses cause severe human diseases and are targeted by ISG-encoded proteins. Here, we discuss ISGs that inhibit the translation of retroviral mRNAs and thereby retrovirus propagation. The Schlafen proteins degrade cellular tRNAs and rRNAs needed for translation. Zinc Finger Antiviral Protein and RNA-activated protein kinase inhibit translation initiation factors, and Shiftless suppresses translation recoding essential for the expression of retroviral enzymes. We outline common mechanisms that underlie the antiviral activity of multifunctional ISGs and discuss potential antiretroviral therapeutic approaches based on the mode of action of these ISGs.

Reduced vacuolar ATPase protects mice from Friend virus infection - an unintended but instructive effect in Hif-2afl mice.

During acute viral infections, innate immune cells invade inflamed tissues and face hypoxic areas. Hypoxia-inducible factors (HIFs) adapt cellular responses towards these conditions. We wanted to investigate the effects of a loss of HIF-2α in macrophages during acute Friend murine leukemia retrovirus (FV) infection in C57BL/6 mice using a Cre/loxP system. Remarkably, mice with floxed Hif-2a (Hif-2afl; Hif-2a is also known as Epas1) did not show any signs of FV infection independent of Cre activity. This prevented a detailed analysis of the role of macrophage HIF-2α for FV infection but allowed us to study a model of unexpected FV resistance. Hif-2afl mice showed a significant decrease in the expression of the Atp6v1e2 gene encoding for the E2 subunit of the vacuolar H+-ATPase, which resulted in a decreased acidification of lysosomes and limited virus entry into the cell. These findings highlight that the insertion of loxP sites is not always without functional consequences and has established a phenotype in the floxed Hif-2a mouse, which is not only unexpected, but unwanted and is of relevance for the use of this mouse strain in (at least virus) experiments.

In vitro analysis of Porcine Endogenous Retroviruses in different pig cell types.

The shortage of organs for human transplantation is a topic of extreme interest, and xenotransplantation with porcine organs has been recognized as a promising solution. However, the potential spillover linked to infectious agents present in pigs remains a concern. Among these, Pig Endogenous Retroviruses (PERVs), whose proviral DNAs are integrated in the genome of all pig breeds, represent an extremely important biological risk. This study aims to evaluate PERVs distribution in several swine cell lines and samples of domestic and feral pigs. Moreover, the capacity of PERVs to infect human and non-human primate cells and to integrate in the cellular genome was tested by Real-Time PCR and by Reverse Transcriptase assay. Results indicated a widespread diffusion of PERVs both in cell lines and samples analysed: the viral genome was found in all the established cell lines, in 40% of the primary cell lines and in 60% of the tissue samples tested. The assays indicated that the virus can be transmitted from porcine to human cells: in the specific case, infected NSK and NPTr cells allow passage to human 293 and MRC-5 cells with active production of the virus demonstrable via PCR and RT assay. In light of these aspects and also the lack of studies on PERVs, it appears clear that there are still many questions to be clarified, also by means of future studies, before xenotransplantation can be considered microbiologically safe.

Evaluation of leukocyte ratios as survival prognostic markers in feline retrovirus infections.

The utility of neutrophil-lymphocyte ratio (NLR), monocyte-lymphocyte ratio (MLR), and platelet-lymphocyte ratio (PLR) as prognostic markers in Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV) infections has not yet been investigated. The aim of this study was to investigate these leukocyte ratios in retrovirus-positive cats and to evaluate their prognostic value for survival. This retrospective case-control study included 142 cats, 75 FIV-Antibodies (Ab)-positive, 52 FeLV-Antigen (Ag)-positive, and 15 FIV-Ab+FeLV-Ag-positive, and a control population of 142 retrovirus-negative age-, sex-, and lifestyle-matched cats. Signalment, complete blood count at the time of serological testing, and outcome were recorded. Leukocyte ratios were compared within the same case-control population, among the three retrovirus-seropositive populations, and were related to survival time. No significant difference was found in NLR, MLR, or PLR between FIV-Ab-positive and FIV-Ab+FeLV-Ag-positive cats and their cross-matched controls. In the FeLV-Ag-positive population, MLR was significantly lower than in the control population (0.05 and 0.14, respectively, P=0.0008). No ratio discriminated among the three infectious states. No ratio was significantly different between survivors and non-survivors in the population of FIV-Ab-positive cats. MLR at diagnosis was significantly higher in FeLV-Ag-positive cats that died 1-3 years after diagnosis than in FeLV-Ag-positive cats still alive at 3 years (P=0.0284). None of the three ratios could predict retroviruses-positive cats that would survive to the end of the study. Overall the results indicate that NLR, MLR, and PLR are not significantly different among retrovirus statuses evaluated and had a very limited prognostic value for the survival time in retrovirus-positive cats.

Beyond pathogens: the intriguing genetic legacy of endogenous retroviruses in host physiology.

The notion that viruses played a crucial role in the evolution of life is not a new concept. However, more recent insights suggest that this perception might be even more expansive, highlighting the ongoing impact of viruses on host evolution. Endogenous retroviruses (ERVs) are considered genomic remnants of ancient viral infections acquired throughout vertebrate evolution. Their exogenous counterparts once infected the host's germline cells, eventually leading to the permanent endogenization of their respective proviruses. The success of ERV colonization is evident so that it constitutes 8% of the human genome. Emerging genomic studies indicate that endogenous retroviruses are not merely remnants of past infections but rather play a corollary role, despite not fully understood, in host genetic regulation. This review presents some evidence supporting the crucial role of endogenous retroviruses in regulating host genetics. We explore the involvement of human ERVs (HERVs) in key physiological processes, from their precise and orchestrated activities during cellular differentiation and pluripotency to their contributions to aging and cellular senescence. Additionally, we discuss the costs associated with hosting a substantial amount of preserved viral genetic material.

Identification and characterization of recent retrovirus in Rhinolophus ferrumequinum bats.

An investigation into retrovirus was conducted in six species of bats (Myotis aurascens, Myotis petax, Myotis macrodactylus, Miniopterus fuliginosus, Rhinolophus ferrumequinum, and Pipistrellus abramus) inhabiting South Korea. Exogenous retroviruses (XRVs) were detected in the tissue samples of R. ferrumequinum individuals by PCR assay. Proviruses were identified in all tissue samples through viral quantification using a digital PCR assay per organ (lung, intestine, heart, brain, wing, kidney, and liver), with viral loads varying greatly between each organ. In phylogenetic analysis based on the whole genome, the Korean bat retroviruses and the R. ferrumequinum retrovirus (RfRV) strain formed a new clade distinct from the Gammaretrovirus clade. The phylogenetic results determined these viruses to be RfRV-like viruses. In the Simplot comparison, Korean RfRV-like viruses exhibited relatively strong fluctuated patterns in the latter part of the envelope gene area compared to other gene areas. Several point mutations within this region (6,878-7,774 bp) of these viruses were observed compared to the RfRV sequence. One Korean RfRV-like virus (named Y4b strain) was successfully recovered in the Raw 264.7 cell line, and virus particles replicated in the cells were confirmed by transmission electron microscopy. RfRVs (or RfRV-like viruses) have been spreading since their first discovery in 2012, and the Korean RfRV-like viruses were assumed to be XRVs that evolved from RfRV.IMPORTANCER. ferrumequinum retrovirus (RfRV)-like viruses were identified in greater horseshoe bats in South Korea. These RfRV-like viruses were considered exogenous retroviruses (XRVs) that emerged from RfRV. Varying amounts of provirus detected in different organs suggest ongoing viral activity, replication, and de novo integration in certain organs. Additionally, the successful recovery of the virus in the Raw 264.7 cell line provides strong evidence supporting their status as XRVs. These viruses have now been identified in South Korea and, more recently, in Kenya since RfRV was discovered in China in 2012, indicating that RfRVs (or RfRV-like viruses) have spread worldwide.

A Variety of Mouse PYHIN Proteins Restrict Murine and Human Retroviruses.

PYHIN proteins are only found in mammals and play key roles in the defense against bacterial and viral pathogens. The corresponding gene locus shows variable deletion and expansion ranging from 0 genes in bats, over 1 in cows, and 4 in humans to a maximum of 13 in mice. While initially thought to act as cytosolic immune sensors that recognize foreign DNA, increasing evidence suggests that PYHIN proteins also inhibit viral pathogens by more direct mechanisms. Here, we examined the ability of all 13 murine PYHIN proteins to inhibit HIV-1 and murine leukemia virus (MLV). We show that overexpression of p203, p204, p205, p208, p209, p210, p211, and p212 strongly inhibits production of infectious HIV-1; p202, p207, and p213 had no significant effects, while p206 and p214 showed intermediate phenotypes. The inhibitory effects on infectious HIV-1 production correlated significantly with the suppression of reporter gene expression by a proviral Moloney MLV-eGFP construct and HIV-1 and Friend MLV LTR luciferase reporter constructs. Altogether, our data show that the antiretroviral activity of PYHIN proteins is conserved between men and mice and further support the key role of nuclear PYHIN proteins in innate antiviral immunity.

FeLIX is a restriction factor for mammalian retrovirus infection.

Endogenous retroviruses (ERVs) are remnants of ancestral viral infections. Feline leukemia virus (FeLV) is an exogenous and endogenous retrovirus in domestic cats. It is classified into several subgroups (A, B, C, D, E, and T) based on viral receptor interference properties or receptor usage. ERV-derived molecules benefit animals, conferring resistance to infectious diseases. However, the soluble protein encoded by the defective envelope (env) gene of endogenous FeLV (enFeLV) functions as a co-factor in FeLV subgroup T infections. Therefore, whether the gene emerged to facilitate viral infection is unclear. Based on the properties of ERV-derived molecules, we hypothesized that the defective env genes possess antiviral activity that would be advantageous to the host because FeLV subgroup B (FeLV-B), a recombinant virus derived from enFeLV env, is restricted to viral transmission among domestic cats. When soluble truncated Env proteins from enFeLV were tested for their inhibitory effects against enFeLV and FeLV-B, they inhibited viral infection. Notably, this antiviral machinery was extended to infection with the Gibbon ape leukemia virus, Koala retrovirus A, and Hervey pteropid gammaretrovirus. Although these viruses used feline phosphate transporter 1 (fePit1) and phosphate transporter 2 as receptors, the inhibitory mechanism involved competitive receptor binding in a fePit1-dependent manner. The shift in receptor usage might have occurred to avoid the inhibitory effect. Overall, these findings highlight the possible emergence of soluble truncated Env proteins from enFeLV as a restriction factor against retroviral infection and will help in developing host immunity and antiviral defense by controlling retroviral spread.IMPORTANCERetroviruses are unique in using reverse transcriptase to convert RNA genomes into DNA, infecting germ cells, and transmitting to offspring. Numerous ancient retroviral sequences are known as endogenous retroviruses (ERVs). The soluble Env protein derived from ERVs functions as a co-factor that assists in FeLV-T infection. However, herein, we show that the soluble Env protein exhibits antiviral activity and provides resistance to mammalian retrovirus infection through competitive receptor binding. In particular, this finding may explain why FeLV-B transmission is not observed among domestic cats. ERV-derived molecules can benefit animals in an evolutionary arms race, highlighting the double-edged-sword nature of ERVs.

Experimental infection of domestic turkeys with lymphoproliferative disease virus of North American origin.

Lymphoproliferative disease virus (LPDV) was first documented in wild turkeys in North America in 2009. LPDV infection is often subclinical but can manifest as lymphoid proliferation or round cell neoplasia. Despite high prevalence across many sampled areas corresponding to declining populations of wild turkeys, knowledge regarding LPDV pathogenesis, risk factors for disease development, and associated impacts on population dynamics are unknown. To understand transmission, viral shedding, and tissue tropism, we inoculated 21 domestic turkeys via the oral cavity, crop, nasal cavity, subcutis, or coelomic cavity. For 12 weeks, oropharyngeal swabs, cloacal swabs, and whole blood were collected weekly. At 1 week postinoculation, 3 turkeys (3/21; 14%) had detectable LPDV proviral DNA in blood by polymerase chain reaction, and 10 developed DNAemia (50%; 10/20) by 12 weeks. LPDV proviral DNA was intermittently detected in oropharyngeal and cloacal swabs. Splenomegaly was the most consistent gross finding in DNAemic birds (8/11; 73%). Lymphoid hyperplasia in the spleen was the most significant microscopic finding (9/11; 82%). Three turkeys (3/11; 27%) developed round cell neoplasia characterized by sheets of pleomorphic, round to polygonal cells in the adrenal gland, bone marrow, skin, small intestine, and/or spleen. LPDV was detected in the spleen and bone marrow from all turkeys with DNAemia and all neoplasms. Our study establishes that infection and disease with North American LPDV from wild turkeys can be experimentally reproduced in domestic turkeys, laying the groundwork for future investigations into LPDV pathogenesis, development of diagnostic techniques, and understanding the impacts of LPDV on wild turkey populations.

Characterization of Megabat-Favored, CA-Dependent Susceptibility to Retrovirus Infection.

The isolation of the Koala retrovirus-like virus from Australian megabats and the identification of endogenous retroviruses in the bat genome have raised questions on bat susceptibility to retroviruses in general. To answer this, we studied the susceptibility of 12 cell lines from 11 bat species to four well-studied retroviruses (human and simian immunodeficiency viruses [HIV and SIV] and murine leukemia viruses [B- and N-MLV]). Systematic comparison of retroviral susceptibility among bats revealed that megabat cell lines were overall less susceptible to the four retroviruses than microbat cell lines, particularly to HIV-1 infection, whereas lineage-specific differences were observed for MLV susceptibility. Quantitative PCR of reverse transcription (RT) products, infection in heterokaryon cells, and point mutation analysis of the capsid (CA) revealed that (i) HIV-1 and MLV replication were blocked at the nuclear transport of the pre-integration complexes and before and/or during RT, respectively, and (ii) the observed lineage-specific restriction can be attributed to a dominant cellular factor constrained by specific positions in CA. Investigation of bat homologs of the three previously reported post-entry restriction factors constrained by the same residues in CA, tripartite motif-protein 5α (TRIM5α), myxovirus resistance 2/B (Mx2/MxB), and carboxy terminus-truncated cleavage and polyadenylation factor 6 (CPSF6-358), demonstrated poor anti-HIV-1 activity in megabat cells, whereas megabat TRIM5α restricted MLV infection, suggesting that the major known CA-dependent restriction factors were not dominant in the observed lineage-specific susceptibility to HIV-1 in bat cells. Therefore, HIV-1 susceptibility of megabat cells may be determined in a manner distinct from that of primate cells. IMPORTANCE Recent studies have demonstrated the circulation of gammaretroviruses among megabats in Australia and the bats' resistance to HIV-1 infection; however, the origins of these viruses in megabats and the contribution of bats to retrovirus spread to other mammalian species remains unclear. To determine the intrinsic susceptibility of bat cells to HIV-1 infection, we investigated 12 cell lines isolated from 11 bat species. We report that lineage-specific retrovirus restriction in the bat cell lines can be attributed to CA-dependent factors. However, in the megabat cell lines examined, factors known to bind capsid and block infection in primate cell culture, including homologs of TRIM5α, Mx2/MxB, and CPSF6, failed to exhibit significant anti-HIV-1 activities. These results suggested that the HIV-1 susceptibility of megabat cells occurs in a manner distinct from that of primate cells, where cellular factors, other than major known CA-dependent restriction factors, with lineage-specific functions could recognize retroviral proteins in megabats.

Isolation of Reticuloendotheliosis Virus from Chorio-allantoic Membrane of SPF Chicken Eggs inoculated with Fowl Pox Virus.

Fowl Pox Viruses (FPV) infect chickens and turkeys giving rise to pock lesions on various body parts like combs, wattles, legs, shanks, eyes, mouth etc. The birds, affected with FPV, also show anemia and ruffled appearance which are clinical symptoms of Reticuloendotheliosis. Interestingly, the field strains of FPV are integrated with the provirus of Reticuloendotheliosis Virus (REV). Due to this integration, the infected birds, upon replication of FPV, give rise to free REV virions, causing severe immunosuppression and anemia. Pox scabs, collected from the infected birds, not only show positive PCR results upon performing FPV-specific 4b core protein gene PCR but also show positive results for the PCR of REV-specific env gene and FPV-REV 5'LTR junction. Homogenized suspension of the pock lesions, upon inoculating to the Chorio-allantoic Membrane (CAM) of 10 days old specific pathogen-free embryonated chicken eggs, produces characteristic pock lesions in serial passages. But the lesions also harbor REV mRNA or free virion, which can be identified by performing REV-specific env gene PCR using REV RNA from FPV-infected CAMs. The study suggests successful replication and availability of REV mRNA and free virion alongside the FPV virus, although the CAM is an ill-suited medium for any retroviral (like REV) growth and replication.

Geographic patterns of koala retrovirus genetic diversity, endogenization, and subtype distributions.

Koala retrovirus (KoRV) subtype A (KoRV-A) is currently in transition from exogenous virus to endogenous viral element, providing an ideal system to elucidate retroviral-host coevolution. We characterized KoRV geography using fecal DNA from 192 samples across 20 populations throughout the koala's range. We reveal an abrupt change in KoRV genetics and incidence at the Victoria/New South Wales state border. In northern koalas, pol gene copies were ubiquitously present at above five per cell, consistent with endogenous KoRV. In southern koalas, pol copies were detected in only 25.8% of koalas and always at copy numbers below one, while the env gene was detected in all animals and in a majority at copy numbers above one per cell. These results suggest that southern koalas carry partial endogenous KoRV-like sequences. Deep sequencing of the env hypervariable region revealed three putatively endogenous KoRV-A sequences in northern koalas and a single, distinct sequence present in all southern koalas. Among northern populations, env sequence diversity decreased with distance from the equator, suggesting infectious KoRV-A invaded the koala genome in northern Australia and then spread south. The exogenous KoRV subtypes (B to K), two novel subtypes, and intermediate subtypes were detected in all northern koala populations but were strikingly absent from all southern animals tested. Apart from KoRV subtype D, these exogenous subtypes were generally locally prevalent but geographically restricted, producing KoRV genetic differentiation among northern populations. This suggests that sporadic evolution and local transmission of the exogenous subtypes have occurred within northern Australia, but this has not extended into animals within southern Australia.

Expansion of a retrovirus lineage in the koala genome.

Retroviruses have left their legacy in host genomes over millions of years as endogenous retroviruses (ERVs), and their structure, diversity, and prevalence provide insights into the historical dynamics of retrovirus-host interactions. In bioinformatic analyses of koala (Phascolarctos cinereus) whole-genome sequences, we identify a recently expanded ERV lineage (phaCin-ß) that is related to the New World squirrel monkey retrovirus. This ERV expansion shares many parallels with the ongoing koala retrovirus (KoRV) invasion of the koala genome, including highly similar and mostly intact sequences, and polymorphic ERV loci in the sampled koala population. The recent phaCin-ß ERV colonization of the koala genome appears to predate the current KoRV invasion, but polymorphic ERVs and divergence comparisons between these two lineages predict a currently uncharacterized, possibly still extant, phaCin-ß retrovirus. The genomics approach to ERV-guided discovery of novel retroviruses in host species provides a strong incentive to search for phaCin-ß retroviruses in the Australasian fauna.

Convergent evolution of antiviral machinery derived from endogenous retrovirus truncated envelope genes in multiple species.

Host genetic resistance to viral infection controls the pathogenicity and epidemic dynamics of infectious diseases. Refrex-1 is a restriction factor against feline leukemia virus subgroup D (FeLV-D) and an endogenous retrovirus (ERV) in domestic cats (ERV-DC). Refrex-1 is encoded by a subset of ERV-DC loci with truncated envelope genes and secreted from cells as a soluble protein. Here, we identified the copper transporter CTR1 as the entry receptor for FeLV-D and genotype I ERV-DCs. We also identified CTR1 as a receptor for primate ERVs from crab-eating macaques and rhesus macaques, which were found in a search of intact envelope genes capable of forming infectious viruses. Refrex-1 counteracted infection by FeLV-D and ERV-DCs via competition for the entry receptor CTR1; the antiviral effects extended to primate ERVs with CTR1-dependent entry. Furthermore, truncated ERV envelope genes found in chimpanzee, bonobo, gorilla, crab-eating macaque, and rhesus macaque genomes could also block infection by feline and primate retroviruses. Genetic analyses showed that these ERV envelope genes were acquired in a species- or genus-specific manner during host evolution. These results indicated that soluble envelope proteins could suppress retroviral infection across species boundaries, suggesting that they function to control retroviral spread. Our findings revealed that several mammalian species acquired antiviral machinery from various ancient retroviruses, leading to convergent evolution for host defense.

Visualization of Retroviral Gag-Genomic RNA Cellular Interactions Leading to Genome Encapsidation and Viral Assembly: An Overview.

Retroviruses must selectively recognize their unspliced RNA genome (gRNA) among abundant cellular and spliced viral RNAs to assemble into newly formed viral particles. Retroviral gRNA packaging is governed by Gag precursors that also orchestrate all the aspects of viral assembly. Retroviral life cycles, and especially the HIV-1 one, have been previously extensively analyzed by several methods, most of them based on molecular biology and biochemistry approaches. Despite these efforts, the spatio-temporal mechanisms leading to gRNA packaging and viral assembly are only partially understood. Nevertheless, in these last decades, progress in novel bioimaging microscopic approaches (as FFS, FRAP, TIRF, and wide-field microscopy) have allowed for the tracking of retroviral Gag and gRNA in living cells, thus providing important insights at high spatial and temporal resolution of the events regulating the late phases of the retroviral life cycle. Here, the implementation of these recent bioimaging tools based on highly performing strategies to label fluorescent macromolecules is described. This report also summarizes recent gains in the current understanding of the mechanisms employed by retroviral Gag polyproteins to regulate molecular mechanisms enabling gRNA packaging and the formation of retroviral particles, highlighting variations and similarities among the different retroviruses.

Human reproduction is regulated by retrotransposons derived from ancient Hominidae-specific viral infections.

Germ cells are essential to pass DNA from one generation to the next. In human reproduction, germ cell development begins with the specification of primordial germ cells (PGCs) and a failure to specify PGCs leads to human infertility. Recent studies have revealed that the transcription factor network required for PGC specification has diverged in mammals, and this has a significant impact on our understanding of human reproduction. Here, we reveal that the Hominidae-specific Transposable Elements (TEs) LTR5Hs, may serve as TEENhancers (TE Embedded eNhancers) to facilitate PGC specification. LTR5Hs TEENhancers become transcriptionally active during PGC specification both in vivo and in vitro with epigenetic reprogramming leading to increased chromatin accessibility, localized DNA demethylation, enrichment of H3K27ac, and occupation of key hPGC transcription factors. Inactivation of LTR5Hs TEENhancers with KRAB mediated CRISPRi has a significant impact on germ cell specification. In summary, our data reveals the essential role of Hominidae-specific LTR5Hs TEENhancers in human germ cell development.

LFA1 and ICAM1 are critical for fusion and spread of murine leukemia virus in vivo.

Murine leukemia virus (MLV)-presenting cells form stable intercellular contacts with target cells during infection of lymphoid tissue, indicating a role of cell-cell contacts in retrovirus dissemination. Whether host cell adhesion proteins are required for retrovirus spread in vivo remains unknown. Here, we demonstrate that the lymphocyte-function-associated-antigen-1 (LFA1) and its ligand intercellular-adhesion-molecule-1 (ICAM1) are important for cell-contact-dependent transmission of MLV between leukocytes. Infection experiments in LFA1- and ICAM1-deficient mice demonstrate a defect in MLV spread within lymph nodes. Co-culture of primary leukocytes reveals a specific requirement for ICAM1 on donor cells and LFA1 on target cells for cell-contact-dependent spread through trans- and cis-infection. Importantly, adoptive transfer experiments combined with a newly established MLV-fusion assay confirm that the directed LFA1-ICAM1 interaction is important for retrovirus fusion and transmission in vivo. Taken together, our data provide insights on how retroviruses exploit host proteins and the biology of cell-cell interactions for dissemination.

SAMHD1 Promotes the Antiretroviral Adaptive Immune Response in Mice Exposed to Lipopolysaccharide.

SAMHD1 is a potent HIV-1 restriction factor that blocks reverse transcription in monocytes, dendritic cells and resting CD4+ T cells by decreasing intracellular dNTP pools. However, SAMHD1 may diminish innate immune sensing and Ag presentation, resulting in a weaker adaptive immune response. To date, the role of SAMHD1 on antiretroviral immunity remains unclear, as mouse SAMHD1 had no impact on murine retrovirus replication in prior in vivo studies. Here, we show that SAMHD1 significantly inhibits acute Friend retrovirus infection in mice. Pretreatment with LPS, a significant driver of inflammation during HIV-1 infection, further unmasked a role for SAMHD1 in influencing immune responses. LPS treatment in vivo doubled the intracellular dNTP levels in immune compartments of SAMHD1 knockout but not wild-type mice. SAMHD1 knockout mice exhibited higher plasma infectious viremia and proviral DNA loads than wild-type mice at 7 d postinfection (dpi), and proviral loads inversely correlated with a stronger CD8+ T cell response. SAMHD1 deficiency was also associated with weaker NK, CD4+ T and CD8+ T cell responses by 14 dpi and weaker neutralizing Ab responses by 28 dpi. Intriguingly, SAMHD1 influenced these cell-mediated immune (14 dpi) and neutralizing Ab (28 dpi) responses in male but not female mice. Our findings formally demonstrate SAMHD1 as an antiretroviral factor in vivo that could promote adaptive immune responses in a sex-dependent manner. The requirement for LPS to unravel the SAMHD1 immunological phenotype suggests that comorbidities associated with a "leaky" gut barrier may influence the antiviral function of SAMHD1 in vivo.

Porcine Endogenous Retroviruses and Xenotransplantation, 2021.

Porcine endogenous retroviruses (PERVs) are integrated in the genome of all pigs, and some of them are able to infect human cells. Therefore, PERVs pose a risk for xenotransplantation, the transplantation of pig cells, tissues, or organ to humans in order to alleviate the shortage of human donor organs. Up to 2021, a huge body of knowledge about PERVs has been accumulated regarding their biology, including replication, recombination, origin, host range, and immunosuppressive properties. Until now, no PERV transmission has been observed in clinical trials transplanting pig islet cells into diabetic humans, in preclinical trials transplanting pig cells and organs into nonhuman primates with remarkable long survival times of the transplant, and in infection experiments with several animal species. Nevertheless, in order to prevent virus transmission to the recipient, numerous strategies have been developed, including selection of PERV-C-free animals, RNA interference, antiviral drugs, vaccination, and genome editing. Furthermore, at present there are no more experimental approaches to evaluate the full risk until we move to the clinic.

The expression profile of miR-222b-5p/MAPK10 in spleens of SPF chickens infected with REV-SNV at 28-42 dpi.

Reticuloendotheliosis virus (REV) is an avian oncogenic retrovirus that causes atrophy of immune organs, such as the spleen, thymus, and bursa of Fabricius, leading to severe immunosuppression. However, there is limited information describing the genes or microRNAs (miRNAs) that play a role in replicating REV-spleen necrosis virus (SNV). Our previous miRNA and RNA sequencing data showed that the expression of gga-miR-222b-5p was significantly upregulated in REV-SNV-infected chicken spleens of 7, 14, and 21 dpi compared to non-infected chicken spleens, but mitogen-activated protein kinase 10 (MAPK10), which is related to innate immunity, had the opposite expression pattern. To understand chicken cellular miRNA function in the virus-host interactions during REV infection, we used quantitative reverse transcription PCR (qRT-PCR) to determine whether the expression of gga-miR-222b-5p and MAPK10 in the spleen of specific-pathogen-free chickens at 28, 35, and 42 dpi was consistent with the first 3 time points, and dual-luciferase reporter assay was used to determine the targeting relationship between gga-miR-222b-5p and MAPK10. Results show that MAPK10 was downregulated at all 3 time points; however, significant difference (p⟨0.01) was noted only at 35 dpi. Moreover, the expression of gga-miR-222b-5p was upregulated; however, significant difference (p⟨0.01) was observed only at 28 and 35 dpi. A dual-luciferase reporter assay showed that MAPK10 is a direct target of gga-miR-222b-5p. This study suggests that gga-miR-222b-5p may target MAPK10 to promote the REV-SNV-induced tumorigenesis via the RLRs signaling pathway.