Feline immunodeficiency virus infection: a valuable model to study HIV-1 associated encephalitis

Insulin Treatment Prevents Neuroinflammation and Neuronal Injury with Restored Neurobehavioral Function in Models of HIV/AIDS Neurodegeneration

HIV-1 infection of the brain causes the neurodegenerative syndrome HIV-associated neurocognitive disorders (HAND), for which there is no specific treatment. Herein, we investigated the actions of insulin using ex vivo and in vivo models of HAND. Increased neuroinflammatory gene expression was observed in brains from patients with HIV/AIDS. The insulin receptor was detected on both neurons and glia, but its expression was unaffected by HIV-1 infection. Insulin treatment of HIV-infected primary human microglia suppressed supernatant HIV-1 p24 levels, reduced CXCL10 and IL-6 transcript levels, and induced peroxisome proliferator-activated receptor gamma (PPAR-γ) expression. Insulin treatment of primary human neurons prevented HIV-1 Vpr-mediated cell process retraction and death. In feline immunodeficiency virus (FIV) infected cats, daily intranasal insulin treatment (20.0 IU/200 μl for 6 weeks) reduced CXCL10, IL-6, and FIV RNA detection in brain, although PPAR-γ in glia was increased compared with PBS-treated FIV⁺ control animals. These molecular changes were accompanied by diminished glial activation in cerebral cortex and white matter of insulin-treated FIV⁺ animals, with associated preservation of cortical neurons. Neuronal counts in parietal cortex, striatum, and hippocampus were higher in the FIV⁺/insulin-treated group compared with the FIV⁺/PBS-treated group. Moreover, intranasal insulin treatment improved neurobehavioral performance, including both memory and motor functions, in FIV⁺ animals. Therefore, insulin exerted ex vivo and in vivo antiviral, anti-inflammatory, and neuroprotective effects in models of HAND, representing a new therapeutic option for patients with inflammatory or infectious neurodegenerative disorders including HAND.

SIGNIFICANCE STATEMENT

HIV-associated neurocognitive disorders (HAND) represent a spectrum disorder of neurocognitive dysfunctions resulting from HIV-1 infection. Although the exact mechanisms causing HAND are unknown, productive HIV-1 infection in the brain with associated neuroinflammation is a potential pathogenic mechanism resulting in neuronal damage and death. We report that, in HIV-infected microglia cultures, insulin treatment led to reduced viral replication and inflammatory gene expression. In addition, intranasal insulin treatment of experimentally feline immunodeficiency virus-infected animals resulted in improved motor and memory performances. We show that insulin restored expression of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR-γ), which is suppressed by HIV-1 replication. Our findings indicate a unique function for insulin in improving neurological outcomes in lentiviral infections, implicating insulin as a therapeutic intervention for HAND.

Differential type 1 interferon-regulated gene expression in the brain during AIDS: interactions with viral diversity and neurovirulence

The lentiviruses, human and feline immunodeficiency viruses (HIV-1 and FIV, respectively), infect the brain and cause neurovirulence, evident as neuronal injury, inflammation, and neurobehavioral abnormalities with diminished survival. Herein, different lentivirus infections in conjunction with neural cell viability were investigated, concentrating on type 1 interferon-regulated pathways. Transcriptomic network analyses showed a preponderance of genes involved in type 1 interferon signaling, which was verified by increased expression of the type 1 interferon-associated genes, Mx1 and CD317, in brains from HIV-infected persons (P<0.05). Leukocytes infected with different strains of FIV or HIV-1 showed differential Mx1 and CD317 expression (P<0.05). In vivo studies of animals infected with the FIV strains, FIV(ch) or FIV(ncsu), revealed that FIV(ch)-infected animals displayed deficits in memory and motor speed compared with the FIV(ncsu)- and mock-infected groups (P<0.05). TNF-α, IL-1β, and CD40 expression was increased in the brains of FIV(ch)-infected animals; conversely, Mx1 and CD317 transcript levels were increased in the brains of FIV(ncsu)-infected animals, principally in microglia (P<0.05). Gliosis and neuronal loss were evident among FIV(ch)-infected animals compared with mock- and FIV(ncsu)-infected animals (P<0.05). Lentiviral infections induce type 1 interferon-regulated gene expression in microglia in a viral diversity-dependent manner, representing a mechanism by which immune responses might be exploited to limit neurovirulence.

Domestic animal models for biomedical research

Experimental animals in biomedical research provide insights into disease mechanisms and models for determining the efficacy and safety of new therapies and for discovery of corresponding biomarkers. Although mouse and rat models are most widely used, observations in these species cannot always be faithfully extrapolated to human patients. Thus, a number of domestic species are additionally used in specific disease areas. This review summarizes the most important applications of domestic animal models and emphasizes the new possibilities genetic tailoring of disease models, specifically in pigs, provides.

Strain-specific viral distribution and neuropathology of feline immunodeficiency virus

Feline immunodeficiency virus (FIV) is a naturally occurring lentivirus of domestic cats, and is the causative agent of feline AIDS. Similar to human immunodeficiency virus (HIV), the pathogenesis of FIV involves infection of lymphocytes and macrophages, and results in chronic progressive immune system collapse and death. Neuropathologic correlates of FIV infection have not yet been elucidated, and may be relevant to understanding HIV-associated neurologic disease (neuroAIDS). As in HIV, FIV strains have been shown to express differential tendencies towards development of clinical neuroAIDS. To interrogate viral genetic determinants that might contribute to neuropathogenicity, cats were exposed to two well-characterized FIV strains with divergent clinical phenotypes and a chimeric strain as follows: FIV(PPR) (PPR, relatively apathogenic but associated with neurologic manifestations), FIV(C36) (C36, immunopathogenic but without associated neurologic disease), and Pcenv (a chimeric virus consisting of a PPR backbone with substituted C36 env region). A sham inoculum control group was also included. Peripheral nerve conduction velocity, CNS imaging studies, viral loads and hematologic analysis were performed over a 12 month period. At termination of the study (350 days post-inoculation), brain sections were obtained from four anatomic locations known to be involved in human and primate lentiviral neuroAIDS. Histological and immunohistochemical evaluation with seven markers of inflammation revealed that Pcenv infection resulted in mild inflammation of the CNS, microglial activation, neuronal degeneration and apoptosis, while C36 and PPR strains induced minimal neuropathologic changes. Conduction velocity aberrations were noted peripherally in all three groups at 63 weeks post-infection. Pcenv viral load in this study was intermediate to the parental strains (C36 demonstrating the highest viral load and PPR the lowest). These results collectively suggest that (i) 3' C36 genomic elements contribute to viral replication characteristics, and (ii) 5' PPR genomic elements contribute to CNS manifestations. This study illustrates the potential for FIV to provide valuable information about neuroAIDS pathogenesis related to genotype and viral kinetics, as well as to identify strains useful to evaluation of therapeutic intervention.

The neuropathogenesis of feline immunodeficiency virus infection: barriers to overcome

Feline immunodeficiency virus (FIV), like human immunodeficiency virus (HIV)-1, is a neurotropic lentivirus, and both natural and experimental infections are associated with neuropathology. FIV enters the brain early following experimental infection, most likely via the blood-brain and blood-cerebrospinal fluid barriers. The exact mechanism of entry, and the factors that influence this entry, are not fully understood. As FIV is a recognised model of HIV-1 infection, understanding such mechanisms is important, particularly as HIV enters the brain early in infection. Furthermore, the development of strategies to combat this central nervous system (CNS) infection requires an understanding of the interactions between the virus and the CNS. In this review the results of both in vitro and in vivo FIV studies are assessed in an attempt to elucidate the mechanisms of viral entry into the brain.

Neurobehavioral performance in feline immunodeficiency virus infection: integrated analysis of viral burden, neuroinflammation, and neuronal injury in cortex

Human immunodeficiency virus (HIV) infection causes motor and neurocognitive abnormalities affecting >50% of children and 20% of adults with HIV/AIDS (acquired immunodeficiency syndrome). The closely related lentivirus, feline immunodeficiency virus (FIV), also causes neurobehavioral deficits. Herein, we investigated the extent to which FIV infection affected specific motor and cognitive tasks in conjunction with viral burden and immune responses within the brain. Neonatal animals were infected with a neurovirulent FIV strain (FIV-Ch) and assessed in terms of systemic immune parameters, viral burden, neurobehavioral performance, and neuropathological features. FIV-infected animals displayed less weight gain and lower blood CD4(+) T-cell levels than mock-infected animals (p < 0.05). Gait analyses disclosed greater gait width with increased variation in FIV-infected animals (p < 0.05). Maze performance showed that FIV-infected animals were slower and made more navigational errors than mock-infected animals (p < 0.05). In the object memory test, the FIV-infected group exhibited fewer successful steps with more trajectory errors compared with the mock-infected group (p < 0.05). Performance on the gait, maze, and object memory tests was inversely correlated with F4/80 and CD3 epsilon expression (p < 0.05) and with viral burden in parietal cortex (p < 0.05). Amino acid analysis in cortex showed that D-serine levels were reduced in FIV-infected animals, which was accompanied by diminished kainate and AMPA receptor subunit expression (p < 0.05). The neurobehavioral findings in FIV-infected animals were associated with increased gliosis and reduced cortical neuronal counts (p < 0.05). The present studies indicated that specific motor and neurocognitive abilities were impaired in FIV infection and that these effects were closely coupled with viral burden, neuroinflammation, and neuronal loss.

Design and synthesis of membrane fusion inhibitors against the feline immunodeficiency virus

Feline immunodeficiency virus (FIV) is a pathogenic virus that causes an AIDS-like syndrome in the domestic cats. For viral entry and infection, fusion between the virus and the cell membrane is the critical process and this process is mediated by an envelope glycoprotein gp40. We have identified fusion inhibitory peptides from the heptad repeat-2 (HR2) of gp40. Remodeling of the original sequences using alpha-helix-inducible motifs revealed the interactive residues of gp40. Comparative analysis of HR2 peptides derived from four FIV strains demonstrated that the interactive surface of the Shizuoka strain-derived HR2 peptides provides the highest affinity of all the FIV strains examined.

CXCR3 activation by lentivirus infection suppresses neuronal autophagy: neuroprotective effects of antiretroviral therapy

Previous studies have implicated CXCL12 in the neuropathogenesis of HIV infection. Proteolysis of CXCL12 generates a neurotoxic molecule, CXCL12(5-67), which engages and activates CXCR3, in addition to exhibiting increased expression in the brains of patients with HIV-associated dementia (HAD). Herein, we investigated CXCR3-mediated neuronal injury, particularly, its contribution to autophagy suppression and the concomitant effects of antiretroviral therapy using human brain samples and models of HIV neuropathogenesis. Neurons in the brains of HAD patients and feline immunodeficiency virus (FIV)-infected animals, as well as cultured human neurons, expressed CXCR3, which was modulated in a ligand-specific manner. Exposure of human neurons to CXCL12(5-67) caused a reduction in the autophagy-associated molecule LC3 (P<0.05) and neuronal survival (P<0.05), which recapitulated findings in FIV- and HIV-infected brains (P<0.05). Oral didanosine (ddI) treatment of FIV-infected animals reduced neurobehavioral abnormalities in conjunction with diminished plasma viral load (P<0.05). F4/80 transcript abundance and CXCL12(5-67) immunoreactivity were reduced with restored neuronal LC3 expression in the brains of FIV-infected animals after ddI treatment (P<0.05). ddI treatment also prevented microglial activation and depletion of synaptic proteins in the cortex of FIV-infected animals (P<0.05). These findings indicate that the beneficial effects of ddI might be a consequence of a reduced systemic viral burden and concurrent leukocyte activation, leading to diminished neuroinflammation with preservation of neuronal autophagy by regulating CXCR3 activation.

Alteration of blood-brain barrier integrity by retroviral infection

The blood–brain barrier (BBB), which forms the interface between the blood and the cerebral parenchyma, has been shown to be disrupted during retroviral-associated neuromyelopathies. Human T Lymphotropic Virus (HTLV-1) Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) is a slowly progressive neurodegenerative disease associated with BBB breakdown. The BBB is composed of three cell types: endothelial cells, pericytes and astrocytes. Although astrocytes have been shown to be infected by HTLV-1, until now, little was known about the susceptibility of BBB endothelial cells to HTLV-1 infection and the impact of such an infection on BBB function. We first demonstrated that human cerebral endothelial cells express the receptors for HTLV-1 (GLUT-1, Neuropilin-1 and heparan sulfate proteoglycans), both in vitro, in a human cerebral endothelial cell line, and ex vivo, on spinal cord autopsy sections from HAM/TSP and non-infected control cases. In situ hybridization revealed HTLV-1 transcripts associated with the vasculature in HAM/TSP. We were able to confirm that the endothelial cells could be productively infected in vitro by HTLV-1 and that blocking of either HSPGs, Neuropilin 1 or Glut1 inhibits this process. The expression of the tight-junction proteins within the HTLV-1 infected endothelial cells was altered. These cells were no longer able to form a functional barrier, since BBB permeability and lymphocyte passage through the monolayer of endothelial cells were increased. This work constitutes the first report of susceptibility of human cerebral endothelial cells to HTLV-1 infection, with implications for HTLV-1 passage through the BBB and subsequent deregulation of the central nervous system homeostasis. We propose that the susceptibility of cerebral endothelial cells to retroviral infection and subsequent BBB dysfunction is an important aspect of HAM/TSP pathogenesis and should be considered in the design of future therapeutics strategies.

The blood–brain barrier (BBB) forms the interface between the blood and the central nervous system (CNS). BBB disruption is considered to be a key event in the pathogenesis of retroviral-associated neurological diseases. The present paper deals with the susceptibility of the endothelial cells (i.e., one of the main cellular components of BBB) to retroviral infection, and with the impact of infection in BBB function. This study focuses on the Human T-Lymphotropic Virus (HTLV-1), which infects 20 million people worldwide, and is the etiological agent of a neurodegenerative disease called HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). We first demonstrated that the cerebral endothelial cells express the receptors for the retrovirus in vitro, and on spinal cord autopsy sections from non-infected and HAM/TSP patients. We found on these latter that vascular-like structures were infected and confirmed in vitro that the endothelial cells could be productively infected by HTLV-1. We demonstrated that such an infection impairs BBB properties in vitro, as well as tight junctions, that are cell adhesion structures. This study is the first to demonstrate the impact of HTLV-1 infection on human BBB integrity; such a susceptibility has to be considered in the design of future therapeutics strategies.