HIV-1 phylogenetic analysis shows HIV-1 transits through the meninges to brain and peripheral tissues

Abstract

Brain infection by the human immunodeficiency virus type 1 (HIV-1) has been investigated in many reports with a variety of conclusions concerning the time of entry and degree of viral compartmentalization. To address these diverse findings, we sequenced HIV-1 gp120 clones from a wide range of brain, peripheral and meningeal tissues from five patients who died from several HIV-1 associated disease pathologies. High-resolution phylogenetic analysis confirmed previous studies that showed a significant degree of compartmentalization in brain and peripheral tissue subpopulations. Some intermixing between the HIV-1 subpopulations was evident, especially in patients that died from pathologies other than HIV-associated dementia. Interestingly, the major tissue harboring virus from both the brain and peripheral tissues was the meninges. These results show that (1) HIV-1 is clearly capable of migrating out of the brain, (2) the meninges are the most likely primary transport tissues, and (3) infected brain macrophages comprise an important HIV reservoir during highly active antiretroviral therapy.

Introduction

One of the primary HIV-associated diseases caused by infection with the human immunodeficiency virus type 1 (HIV-1) is HIV-associated dementia (HAD). Since the institution of HAART therapy, the incidence of HAD has decreased, but the prevalence of HAD and neurocognitive dysfunction now exceeds 20% and may be increasing (McArthur, 2004). While some patients develop a slower, progressive form of HAD, others only develop neurological complications at advanced stages of AIDS and near the time of death. In the latter case, neurological complications are often secondary to other AIDS-associated diseases. In the brain, HIV infects macrophages that release cytokines that present a toxic environment for neurons. In the presence of HIV, astrocytes also synthesize complimentary factors that contribute to neuronal degeneration (Speth et al., 2002). Infected macrophages may also release sphingolipids (Campbell et al., 2002), which alter the functional plasticity of neurons in patients with Alzheimer's disease (Haughey et al., 2010), a disease with similarities to post-HAART HIV-associated neurocognitive dysfunction.

Despite what is known about the effect of HIV in the brain, some debate exists concerning the timing of HIV entry into the central nervous system. Phylogenetic analysis has shown that viral variants in the brain are more compartmentalized than in peripheral tissues (Haggerty and Stevenson, 1991, Salemi et al., 2007, van’t Wout et al., 1998, Wong et al., 1997). Other phylogenetic studies have identified a subset of brain viruses within the periphery (Liu et al., 2000, Wang et al., 2001). Early biological studies suggested that HIV enters the brain via monocyte trafficking in the early stages of infection (Kim et al., 2003) and begins to evolve independently from the virus in the periphery (i.e. compartmentalization) with subsequent viral entry into the brain inhibited by the establishment of an immune barrier (Williams and Hickey, 2002). Later studies suggested HIV enters the brain much later in infection due to general immune failure during the onset of AIDS (Fischer-Smith et al., 2008). A phylogenetic analysis of patients viruses with different disease pathologies showed that both models are possible (Lamers et al., 2010). An additional study by Zhao et al. (2009) showed that 46% of 13 patients were qPCR-negative for HIV within the brain at the time of death, indicating that many patients never develop an active infection in the brain. The biological mechanism(s) responsible for the wide spectrum of potential outcomes remains unclear. However, a recent study by Sacktor et al. (2009) showed that specific HIV-1 subtypes are associated with a higher incidence of HAD than infection with other subtypes in the same geographic region. This finding suggests that particular genetic variants have increased neuropathogenesis. A better understanding of brain and periphery viral transport is fundamental to the identification of the tissue or tissues involved in viral gene flow between the two compartments. In this study, we examined brain and peripheral tissues from five patients who died due to varied disease pathologies to determine the degree of compartmentalization within the brain and to follow up on our earlier finding that showed evidence of the meninges acting as a transit route between brain compartments in one patient (Salemi et al., 2005).