CD4-Independent Entry and Replication of Simian Immunodeficiency Virus in Primary Rhesus Macaque Astrocytes Are Regulated by the Transmembrane Protein

Abstract

Previous studies have demonstrated that the genetic determinants of simian immunodeficiency virus (SIV) neurovirulence map to the env and nef genes. Recent studies from our laboratory demonstrated that SIV replication in primary rhesus macaque astrocyte cultures is dependent upon the nef gene. Here, we demonstrate that macrophage tropism is not sufficient for replication in astrocytes and that specific amino acids in the transmembrane (TM) portion of Env are also important for optimal SIV replication in astrocytes. Specifically, a Gly at amino acid position 751 and truncation of the cytoplasmic tail of TM are required for efficient replication in these cells. Studies using soluble CD4 demonstrated that these changes within the TM protein regulate CD4-independent, CCR5-dependent entry of virus into astrocytes. In addition, we observed that two distinct CD4-independent, neuroinvasive strains of SIV/DeltaB670 also replicated efficiently in astrocytes, further supporting the role of CD4 independence as an important determinant of SIV infection of astrocytes in vitro and in vivo.

Mechanisms of HIV-1 Neurotropism

“…Similar results were reported in a recent study by Gonzalez-Scarano and colleagues [83]. These observations together with the finding that BORI-15 and UK1-br induce multinucleated giant cells in MDM and UK1-br induces neuronal apoptosis in primary brain cultures [56,129] and the observation that neurovirulent CCR5-tropic SHIVs are CD4-independent [15,33,103] suggest that viruses with increased affinity for the CD4/CCR5 complex and/or reduced CCR5/CD4 dependence have increased neurotropism and pathogenicity in the CNS. Similarly, a pathogenic SHIV variant that is neurotropic and uses CXCR4 has reduced dependence on CD4/CXCR4 [130].…”

“…Other studies of HIV or SIV Envs also mapped determinants of reduced CD4 dependence or CD4 independence to the V1V2 regions [20,70,115,116,155]. However, additional determinants in the V3 and V4 regions and in gp41 can also contribute to reduced CD4 dependence or CD4 independence, with the specific determinants being strain-specific [15,20,32,73,102,103,115].…”

Canonical Type I IFN Signaling in Simian Immunodeficiency Virus-Infected Macrophages Is Disrupted by Astrocyte-Secreted CCL2

“…for mRNA analysis. As we and other groups have shown (39, 40), while virus infection in macrophages takes place during the course of days, infection in astrocytes takes longer because restrictive factors specific to this cell type severely slows down viral replication in vitro . (Figures 1A and 2A).…”

“…Primary rhesus macaque astrocytes (Cambrex, Walkersville MD) were cultured as previously described (39). Cells were infected with SIV/17E-Fr at an MOI of 0.05 for 6 hours and then washed 3 times with sterile PBS.…”

Laser Capture Microdissection Assessment of Virus Compartmentalization in the Central Nervous Systems of Macaques Infected with Neurovirulent Simian Immunodeficiency Virus

“…On the other hand, although we identified these gp41 truncations in only one of the two conventional progressors in this study, we previously reported the presence of similar truncations in isolates from the brain of the original SIVsmE543-infected animal (45). In addition, other studies using well-characterized neurovirulent SIV clones demonstrated that a similar truncation at the TM domain of gp41 is responsible for CD4 independence (46,47). These observations suggest that those gp41 truncations may play important roles in the pathogenesis of SIV in the CNS.…”