Adaptation of CD4 in gorillas and chimpanzees conveyed resistance to simian immunodeficiency viruses.

Simian immunodeficiency viruses (SIVs) comprise a large group of primate lentiviruses that endemically infect African monkeys. HIV-1 spilled over to humans from this viral reservoir, but the spillover did not occur directly from monkeys to humans. Instead, a key event was the introduction of SIVs into great apes, which then set the stage for infection of humans. Here, we investigate the role of the lentiviral entry receptor, CD4, in this key and fateful event in the history of SIV/HIV emergence. First, we reconstructed and tested ancient forms of CD4 at two important nodes in ape speciation, both prior to the infection of chimpanzees and gorillas with these viruses. These ancestral CD4s fully supported entry of diverse SIV isolates related to the viruses that made this initial jump to apes. In stark contrast, modern chimpanzee and gorilla CD4 orthologs are more resistant to these viruses. To investigate how this resistance in CD4 was gained, we acquired CD4 gene sequences from 32 gorilla individuals of two species, and identified alleles that encode 8 unique CD4 protein variants. Functional testing of these identified variant-specific differences in susceptibility to virus entry. By engineering single point mutations from resistant gorilla CD4 variants into the permissive human CD4 receptor, we demonstrate that acquired substitutions in gorilla CD4 did convey resistance to virus entry. We provide a population genetic analysis to support the theory that selection is acting in favor of more and more resistant CD4 alleles in ape species harboring SIV endemically (gorillas and chimpanzees), but not in other ape species that lack SIV infections (bonobos and orangutans). Taken together, our results show that SIV has placed intense selective pressure on ape CD4, acting to propagate SIV-resistant alleles in chimpanzee and gorilla populations.

The Impact of a Structured, Supervised Exercise Program on Daily Step Count in Sedentary Older Adults With and Without HIV.

BACKGROUND: People with HIV (PWH) may have lower daily activity levels compared with persons without HIV. We sought to determine the impact of initiating a supervised exercise program on the daily step count of sedentary PWH and uninfected controls. METHODS: PWH and controls, aged 50-75, were enrolled in a 24-week supervised exercise program. All individuals were given a pedometer and instructed in regular use. A linear mixed model taking into account random effects was used to model daily step count. RESULTS: Of 69 participants that began the study, 55 completed and 38 (21 PWH, 17 controls) had complete pedometer data. Baseline daily step count on nonsupervised exercise day was (estimated geometric mean, 95% confidence interval) 3543 (1306 to 9099) for PWH and 4182 (1632 to 10,187) for controls. Both groups increased daily steps on supervised [43% (20 to 69)%, P < 0.001] but not unsupervised exercise days [-12% (-24 to 1)%, P = 0.071]. Compared with controls, PWH had 26% [(-47 to 4)%, P = 0.08] fewer daily steps on days with supervised exercise and 35% [-53 to -10)%, P = 0.011] fewer daily steps on days without supervised exercise. Higher body mass index (per 1 unit) and smoking were associated with fewer daily steps [-5% (-9 to -1)%; -49% (-67 to -23)%; P ≤ 0.012]. Days with precipitation [-8% (-13 to -3)%, P = 0.002] or below freezing [-10% [-15 to -4)%, P < 0.001] were associated with fewer steps. CONCLUSION: Supervised exercise increased daily step counts in sedentary individuals, but at the expense of fewer steps on nonsupervised exercise days.

Two-stage ML Classifier for Identifying Host Protein Targets of the Dengue Protease.

Flaviviruses such as dengue encode a protease that is essential for viral replication. The protease functions by cleaving well-conserved positions in the viral polyprotein. In addition to the viral polyprotein, the dengue protease cleaves at least one host protein involved in immune response. This raises the question, what other host proteins are targeted and cleaved? Here we present a new computational method for identifying putative host protein targets of the dengue virus protease. Our method relies on biochemical and secondary structure features at the known cleavage sites in the viral polyprotein in a two-stage classification process to identify putative cleavage targets. The accuracy of our predictions scaled inversely with evolutionary distance when we applied it to the known cleavage sites of several other flaviviruses-a good indication of the validity of our predictions. Ultimately, our classifier identified 257 human protein sites possessing both a similar target motif and accessible local structure. These proteins are promising candidates for further investigation. As the number of viral sequences expands, our method could be adopted to predict host targets of other flaviviruses.

dsRNA-Seq: Identification of Viral Infection by Purifying and Sequencing dsRNA.

RNA viruses are a major source of emerging and re-emerging infectious diseases around the world. We developed a method to identify RNA viruses that is based on the fact that RNA viruses produce double-stranded RNA (dsRNA) while replicating. Purifying and sequencing dsRNA from the total RNA isolated from infected tissue allowed us to recover dsRNA virus sequences and replicated sequences from single-stranded RNA (ssRNA) viruses. We refer to this approach as dsRNA-Seq. By assembling dsRNA sequences into contigs we identified full length or partial RNA viral genomes of varying genome types infecting mammalian culture samples, identified a known viral disease agent in laboratory infected mice, and successfully detected naturally occurring RNA viral infections in reptiles. Here, we show that dsRNA-Seq is a preferable method for identifying viruses in organisms that don't have sequenced genomes and/or commercially available rRNA depletion reagents. In addition, a significant advantage of this method is the ability to identify replicated viral sequences of ssRNA viruses, which is useful for distinguishing infectious viral agents from potential noninfectious viral particles or contaminants.

A glycan shield on chimpanzee CD4 protects against infection by primate lentiviruses (HIV/SIV).

Pandemic HIV-1 (group M) emerged following the cross-species transmission of a simian immunodeficiency virus from chimpanzees (SIVcpz) to humans. Primate lentiviruses (HIV/SIV) require the T cell receptor CD4 to enter into target cells. By surveying the sequence and function of CD4 in 50 chimpanzee individuals, we find that all chimpanzee CD4 alleles encode a fixed, chimpanzee-specific substitution (34T) that creates a glycosylation site on the virus binding surface of the CD4 receptor. Additionally, a single nucleotide polymorphism (SNP) has arisen in chimpanzee CD4 (68T) that creates a second glycosylation site on the same virus-binding interface. This substitution is not yet fixed, but instead alleles containing this SNP are still circulating within chimpanzee populations. Thus, all allelic versions of chimpanzee CD4 are singly glycosylated at the virus binding surface, and some allelic versions are doubly glycosylated. Doubly glycosylated forms of chimpanzee CD4 reduce HIV-1 and SIVcpz infection by as much as two orders of magnitude. Full restoration of virus infection in cells bearing chimpanzee CD4 requires reversion of both threonines at sites 34 and 68, destroying both of the glycosylation sites, suggesting that the effects of the glycans are additive. Differentially glycosylated CD4 receptors were biochemically purified and used in neutralization assays and microscale thermophoresis to show that the glycans on chimpanzee CD4 reduce binding affinity with the lentiviral surface glycoprotein, Env. These glycans create a shield that protects CD4 from being engaged by viruses, demonstrating a powerful form of host resistance against deadly primate lentiviruses.

Species-Specific Deamidation of cGAS by Herpes Simplex Virus UL37 Protein Facilitates Viral Replication.

Herpes simplex virus 1 (HSV-1) establishes infections in humans and mice, but some non-human primates exhibit resistance via unknown mechanisms. Innate immune recognition pathways are highly conserved but are pivotal in determining susceptibility to DNA virus infections. We report that variation of a single amino acid residue in the innate immune sensor cGAS determines species-specific inactivation by HSV-1. The HSV-1 UL37 tegument protein deamidates human and mouse cGAS. Deamidation impairs the ability of cGAS to catalyze cGAMP synthesis, which activates innate immunity. HSV-1 with deamidase-deficient UL37 promotes robust antiviral responses and is attenuated in mice in a cGAS- and STING-dependent manner. Mutational analyses identified a single asparagine in human and mouse cGAS that is not conserved in many non-human primates. This residue underpins UL37-mediated cGAS deamidation and species permissiveness of HSV-1. Thus, HSV-1 mediates cGAS deamidation for immune evasion and exploits species sequence variation to disarm host defenses.

Dengue viruses cleave STING in humans but not in nonhuman primates, their presumed natural reservoir.

Human dengue viruses emerged from primate reservoirs, yet paradoxically dengue does not reach high titers in primate models. This presents a unique opportunity to examine the genetics of spillover versus reservoir hosts. The dengue virus 2 (DENV2) - encoded protease cleaves human STING, reducing type I interferon production and boosting viral titers in humans. We find that both human and sylvatic (reservoir) dengue viruses universally cleave human STING, but not the STING of primates implicated as reservoir species. The special ability of dengue to cleave STING is thus specific to humans and a few closely related ape species. Conversion of residues 78/79 to the human-encoded 'RG' renders all primate (and mouse) STINGs sensitive to viral cleavage. Dengue viruses may have evolved to increase viral titers in the dense and vast human population, while maintaining decreased titers and pathogenicity in the more rare animals that serve as their sustaining reservoir in nature.

Non-human Primate Schlafen11 Inhibits Production of Both Host and Viral Proteins.

Schlafen11 (encoded by the SLFN11 gene) has been shown to inhibit the accumulation of HIV-1 proteins. We show that the SLFN11 gene is under positive selection in simian primates and is species-specific in its activity against HIV-1. The activity of human Schlafen11 is relatively weak compared to that of some other primate versions of this protein, with the versions encoded by chimpanzee, orangutan, gibbon, and marmoset being particularly potent inhibitors of HIV-1 protein production. Interestingly, we find that Schlafen11 is functional in the absence of infection and reduces protein production from certain non-viral (GFP) and even host (Vinculin and GAPDH) transcripts. This suggests that Schlafen11 may just generally block protein production from non-codon optimized transcripts. Because Schlafen11 is an interferon-stimulated gene with a broad ability to inhibit protein production from many host and viral transcripts, its role may be to create a general antiviral state in the cell. Interestingly, the strong inhibitors such as marmoset Schlafen11 consistently block protein production better than weak primate Schlafen11 proteins, regardless of the virus or host target being analyzed. Further, we show that the residues to which species-specific differences in Schlafen11 potency map are distinct from residues that have been targeted by positive selection. We speculate that the positive selection of SLFN11 could have been driven by a number of different factors, including interaction with one or more viral antagonists that have yet to be identified.

D316 is critical for the enzymatic activity and HIV-1 restriction potential of human and rhesus APOBEC3B.

APOBEC3B is one of seven human APOBEC3 DNA cytosine deaminases that function to inhibit the replication and persistence of retroelements and retroviruses. Human APOBEC3B restricts the replication of HIV-1 in HEK293 cells, while our laboratory clone of rhesus macaque APOBEC3B did not. We mapped the restriction determinant to a single amino acid difference that alters enzymatic activity. Human APOBEC3B D316 is catalytically active and capable of restricting HIV-1 while rhesus APOBEC3B N316 is not; swapping these residues alters the activity and restriction phenotypes respectively. Genotyping of primate center rhesus macaques revealed uniform homozygosity for aspartate at position 316. Considering the C-to-T nature of the underlying mutation, we suspect that our rhesus APOBEC3B cDNA was inactivated by its own gene product during subcloning in Escherichia coli. This region has been previously characterized for its role in substrate specificity, but these data indicate it also has a fundamental role in deaminase activity.