Pathogenesis of HIV encephalitis

Contribution of a single host genetic locus to mouse adenovirus type 1 infection and encephalitis

Susceptibility to mouse adenovirus type 1 (MAV-1) is mouse strain dependent; susceptible mice die from hemorrhagic encephalomyelitis. The MAV-1 susceptibility quantitative trait locus Msq1 accounts for ~40% of the phenotypic (brain viral load) variance that occurs between resistant BALB/c and susceptible SJL mice after MAV-1 infection. Using an interval-specific congenic mouse strain (C.SJL-Msq1^SJL), in which the SJL-derived allele Msq1^SJL is present in a BALB/c background, we demonstrate that Msq1^SJL controls the development of high brain viral titers in response to MAV-1 infection, yet does not account for the total extent of brain pathology or mortality in SJL mice. C.SJL-Msq1^SJL mice had disruption of the blood-brain barrier and increased brain water content after MAV-1 infection, but these effects occurred later and were not as severe, respectively, as those noted in infected SJL mice. As expected, BALB/c mice showed minimal pathology in these assays. Infection of SJL- and C.SJL-Msq1^SJL-derived primary mouse brain endothelial cells resulted in loss of barrier properties, whereas BALB/c-derived cells retained their barrier properties despite being equally capable of supporting MAV-1 infection. Finally, we provide evidence that organ pathology and inflammatory cell recruitment to the brain following MAV-1 infection were both influenced by Msq1. These results validate Msq1 as an important host factor in MAV-1 infection and refine the major role of the locus in development of MAV-1 encephalitis. They further suggest that additional host factors or gene interactions are involved in the mechanism of pathogenesis in MAV-1-infected SJL mice.

A successful viral infection requires both host and viral factors; identification of host components involved in viral replication and pathogenesis is important for development of therapeutic interventions. A genetic locus (Msq1) controlling mouse adenovirus type 1 (MAV-1) brain infection was previously identified. Genes in Msq1 belong to the same family of genes associated with susceptibility to other encephalitic viruses, HIV-1 and West Nile virus. We constructed an interval-specific congenic mouse strain to examine the contribution of Msq1 to MAV-1 susceptibility and brain morbidity. We compared infected resistant, susceptible, and congenic mice regarding known MAV-1 disease manifestations in the brain (survival, viral loads, blood-brain barrier disruption, edema, mouse brain endothelial cell barrier properties, pathology, and inflammatory cell recruitment) to determine the extent to which Msq1 influences MAV-1 infection outcome. Our results showed that Msq1 is a critical host genetic factor that controls many aspects of MAV-1 infection.

Blood-brain barrier and retroviral infections

Homeostasis in the central nervous system (CNS) is maintained by active interfaces between the bloodstream and the brain parenchyma. The blood-brain barrier (BBB) constitutes a selective filter for exchange of water, solutes, nutrients, and controls toxic compounds or pathogens entry. Some parasites, bacteria, and viruses have however developed various CNS invasion strategies, and can bypass the brain barriers. Concerning viruses, these strategies include transport along neural pathways, transcytosis, infection of the brain endothelial cells, breaching of the BBB, and passage of infected-leukocytes. Moreover, neurotropic viruses can alter BBB functions, thus compromising CNS homeostasis. Retroviruses have been associated to human neurological diseases: HIV (human immunodeficiency virus 1) can induce HIV-associated dementia, and HTLV-1 (human T lymphotropic virus 1) is the etiological factor of tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). The present review focuses on how the different retroviruses interact with this structure, bypass it and alter its functions.

Neuronal injury in simian immunodeficiency virus and other animal models of neuroAIDS

The success of antiretroviral therapy has reduced the incidence of severe neurological complication resulting from human immunodeficiency virus (HIV) infection. However, increased patient survival has been associated with an increased prevalence of protracted forms of HIV encephalitis leading to moderate cognitive impairment. NeuroAIDS remains a great challenge to patients, their families, and our society. Thus development of preclinical models that will be suitable for testing promising new compounds with neurotrophic and neuroprotective capabilities is of critical importance. The simian immunodeficiency virus (SIV)-infected macaque is the premiere model to study HIV neuropathogenesis. This model was central to the seminal work of Dr. Opendra "Bill" Narayan. Similar to patients with HIV encephalitis, in the SIV model there is injury to the synaptodendritic structure of excitatory pyramidal neurons and inhibitory calbindin-immunoreactive interneurons. This article, which is part of a special issue of the Journal of NeuroVirology in honor of Dr. Bill Narayan, discusses the most important neurodegenerative features in preclinical models of neuroAIDS and their potential for treatment development.

Molecular mechanisms of HIV-1 associated neurodegeneration

Since identification of the human immunodeficiency virus-1 (HIV-1), numerous studies suggest a link between neurological impairments, in particular dementia, with acquired immunodeficiency syndrome (AIDS) with alarming occurrence worldwide. Approximately, 60% of HIV-infected people show some form of neurological impairment, and neuropathological changes are found in 90% of autopsied cases. Approximately 30% of untreated HIV-infected persons may develop dementia. The mechanisms behind these pathological changes are still not understood. Mounting data obtained by in vivo and in vitro experiments suggest that neuronal apoptosis is a major feature of HIV associated dementia (HAD), which can occur in the absence of direct infection of neurons. The major pathway of neuronal apoptosis occurs indirectly through release of neurotoxins by activated cells in the central nervous system (CNS) involving the induction of excitotoxicity and oxidative stress. In addition a direct mechanism induced by viral proteins in the pathogenesis of HAD may also play a role. This review focuses on the molecular mechanisms of HIV-associated dementia and possible therapeutic strategies.

Neuroprotective activities of sodium valproate in a murine model of human immunodeficiency virus-1 encephalitis

Human immunodeficiency virus-1 (HIV-1) infection of the nervous system can result in neuroinflammatory events leading first to neuronal dysfunction then to cognitive and behavioral impairments in infected people. The multifaceted nature of the disease process, commonly called HIV-1-associated dementia (HAD), provides a number of adjunctive therapeutic opportunities. One proposed adjunctive therapy is sodium valproate (VPA), an anticonvulsant known to promote neurite outgrowth and increase beta-catenin through inhibiting glycogen synthase kinase 3beta activity and tau phosphorylation. We now show that VPA treatment of rat cortical neurons exposed to HIV-1 gp120 prevents resultant neurotoxic activities. This includes the induction of significant neurite outgrowth and microtubule-associated protein 2 (MAP-2) and neuron-specific nuclear protein (NeuN) antigens in affected neuronal cell bodies and processes. Similarly, VPA protects severe combined immunodeficient (SCID) mice against the neurodegeneration of HIV-1ADA infected monocyte-derived macrophages (MDMs). In SCID mice with HIV-1 MDM-induced encephalitis, VPA treatment significantly reduced neuronal phosphorylatedbeta-catenin and tau without affecting HIV-1 replication or glial activation. We conclude that VPA protects neurons against HIV-1 infected MDM neurotoxicity, possibly through its effects on the phosphorylation of tau and beta-catenin. The use of VPA as an adjuvant in treatment of human HAD is being pursued.