CCR5 knockout prevents neuronal injury and behavioral impairment induced in a transgenic mouse model by a CXCR4-using HIV-1 glycoprotein 120.

The innate immune system has been implicated in several neurodegenerative diseases, including HIV-1-associated dementia. In this study, we show that genetic ablation of CCR5 prevents microglial activation and neuronal damage in a transgenic model of HIV-associated brain injury induced by a CXCR4-using viral envelope gp120. The CCR5 knockout (KO) also rescues spatial learning and memory in gp120-transgenic mice. However, the CCR5KO does not abrogate astrocytosis, indicating it can occur independently from neuronal injury and behavioral impairment. To characterize further the neuroprotective effect of CCR5 deficiency we performed a genome-wide gene expression analysis of brains from HIVgp120tg mice expressing or lacking CCR5 and nontransgenic controls. A comparison with a human brain microarray study reveals that brains of HIVgp120tg mice and HIV patients with neurocognitive impairment share numerous differentially regulated genes. Furthermore, brains of CCR5 wild-type and CCR5KO gp120tg mice express markers of an innate immune response. One of the most significantly upregulated factors is the acute phase protein lipocalin-2 (LCN2). Using cerebrocortical cell cultures, we find that LCN2 is neurotoxic in a CCR5-dependent fashion, whereas inhibition of CCR5 alone is not sufficient to abrogate neurotoxicity of a CXCR4-using gp120. However, the combination of pharmacologic CCR5 blockade and LCN2 protects neurons from toxicity of a CXCR4-using gp120, thus recapitulating the finding in CCR5-deficient gp120tg mouse brain. Our study provides evidence for an indirect pathologic role of CCR5 and a novel protective effect of LCN2 in combination with inhibition of CCR5 in HIV-associated brain injury.

Activation of p38 MAPK is required in monocytic and neuronal cells for HIV glycoprotein 120-induced neurotoxicity.

HIV-1 envelope protein gp120 has been implicated in neurotoxin production by monocytic cells (i.e., macrophages and microglia), as well as in the pathogenesis of HIV-1-associated neurocognitive disorders. We previously showed in cerebrocortical cell cultures from rodents containing microglia, astrocytes, and neurons that overall inhibition of p38 MAPK signaling abrogated the neurotoxic effect of HIV-1 gp120. However, the time course of p38 MAPK activation and the contribution of this kinase in the various cell types remained unknown. In this study, we found that active p38 MAPK is required in monocytic lineage cells (i.e., macrophages and microglia) and neuronal cells for HIV gp120-induced neurotoxicity to occur. In cerebrocortical cell cultures, HIV-1 gp120 stimulated a time-dependent overall increase in active p38 MAPK, and the activated kinase was primarily detected in microglia and neurons. Interestingly, increased activation of p38 MAPK and neuronal death in response to gp120 were prevented by prior depletion of microglia or the presence of CCR5 ligand CCL4 or p38 MAPK inhibitors. In human monocytic THP-1 cells and primary monocyte-derived macrophages, HIV gp120-stimulated production of neurotoxins was abrogated by prior introduction into the cells of a dominant-negative p38 MAPK mutant or p38 MAPK small interfering RNA. In addition, the neurotoxic effects of cell-free supernatants from gp120-stimulated monocytic THP-1 cells were prevented in microglia-depleted cerebrocortical cells pretreated with a pharmacological inhibitor of p38 MAPK. Thus, p38 MAPK signaling was critical, upon exposure to HIV gp120, for the neurotoxic phenotype of monocytic cells and subsequent toxin-initiated neuronal apoptosis.

An Alzheimer's disease-relevant presenilin-1 mutation augments amyloid-beta-induced oligodendrocyte dysfunction.

White matter pathology has been documented in the brains of familial Alzheimer's disease (FAD)-afflicted individuals during presymptomatic and preclinical stages of AD. How these defects in myelination integrity arise and what roles they may play in AD pathophysiology have yet to be fully elucidated. We previously demonstrated that triple-transgenic AD (3xTg-AD) mice, which harbor the human amyloid precursor Swedish mutation, presenilin-1 M146V (PS1(M146V) ) knock-in mutation, and tau(P301L) mutation, exhibit myelin abnormalities analogous to FAD patients and that Aß(1-42) contributes to these white matter deficits. Herein, we demonstrate that the PS1(M146V) mutation predisposes mouse oligodendrocyte precursor (mOP) cells to Aß(1-42) -induced alterations in cell differentiation in vitro. Furthermore, PS1(M146V) expression compromised mOP cell function and MBP protein distribution, a process that is further aggravated with exposure to Aß(1-42) . We found that the myelination defect and MBP subcellular mislocalization triggered by PS1(M146V) and Aß(1-42) can be effectively prevented by treatment with the GSK-3ß inhibitor, TWS119, thereby implicating GSK-3ß kinase activity in this pathogenic cascade. Overall, this work provides further mechanistic insights into PS1(M146V) and Aß(1-42) -driven oligodendrocyte dysfunction andmyelin damage during early presymptomatic stages of AD, and provides a new target in oligodendrocytes for developing therapies designed to avert AD-related white matter pathology.

Early oligodendrocyte/myelin pathology in Alzheimer's disease mice constitutes a novel therapeutic target.

The detection of myelin disruptions in Alzheimer's disease (AD)-affected brain raises the possibility that oligodendrocytes undergo pathophysiological assault over the protracted course of this neurodegenerative disease. Oligodendrocyte compromise arising from direct toxic effects imparted by pathological amyloid-beta peptides and/or through signals derived from degenerating neurons could play an important role in the disease process. We previously demonstrated that 3xTg-AD mice, which harbor the human amyloid precursor protein Swedish mutant transgene, presenilin knock-in mutation, and tau P301L mutant transgene, exhibit significant alterations in overall myelination patterns and oligodendrocyte status at time points preceding the appearance of amyloid and tau pathology. Herein, we demonstrate that Abeta(1-42) leads to increased caspase-3 expression and apoptotic cell death of both nondifferentiated and differentiated mouse oligodendrocyte precursor (mOP) cells in vitro. Through use of a recombinant adeno-associated virus serotype-2 (rAAV2) vector expressing an Abeta(1-42)-specific intracellular antibody (intrabody), oligodendrocyte and myelin marker expression, as well as myelin integrity, were restored in the vector-infused brain regions of 3xTg-AD mice. Overall, this work provides further insights into the impact of Abeta(1-42)-mediated toxicity on the temporal and spatial progression of subtle myelin disruption during the early presymptomatic stages of AD and may help to validate new therapeutic options designed to avert these early impairments.

Triple-transgenic Alzheimer's disease mice exhibit region-specific abnormalities in brain myelination patterns prior to appearance of amyloid and tau pathology.

Alzheimer's disease (AD) is a progressively debilitating brain disorder pathologically defined by extracellular amyloid plaques, intraneuronal neurofibrillary tangles, and synaptic disintegrity. AD has not been widely considered a disease of white matter, but more recent evidence suggests the existence of abnormalities in myelination patterns and myelin attrition in AD-afflicted human brains. Herein, we demonstrate that triple-transgenic AD (3xTg-AD) mice, which harbor the human amyloid precursor protein Swedish mutant transgene, presenilin knock-in mutation, and tau P301L mutant transgene, exhibit significant region-specific alterations in myelination patterns and in oligodendrocyte marker expression profiles at time points preceding the appearance of amyloid and tau pathology. These immunohistochemical signatures are coincident with age-related alterations in axonal and myelin sheath ultrastructure as visualized by comparative electron microscopic examination of 3xTg-AD and nontransgenic mouse brain tissue. Overall, these findings indicate that 3xTg-AD mice represent a viable model in which to examine mechanisms underlying AD-related myelination and neural transmission defects that occur early during presymptomatic stages of the disease process.

Genetic knockouts suggest a critical role for HIV co-receptors in models of HIV gp120-induced brain injury.

Infection with HIV-1 frequently affects the brain and causes NeuroAIDS prior to the development of overt AIDS. The HIV-1 envelope protein gp120 interacts with host CD4 and chemokine co-receptors to initiate infection of macrophages and lymphocytes. In addition, the virus or fragments of it, such as gp120, cause macrophages to produce neurotoxins and trigger neuronal injury and apoptosis. Moreover, the two major HIV co-receptors, the chemokine receptors CCR5 and CXCR4, serve numerous physiological functions and are widely expressed beyond immune cells, including cells in the brain. Therefore, HIV co-receptors are poised to play a direct and indirect part in the development of NeuroAIDS. Although rodents are not permissive to infection with wild type HIV-1, viral co-receptors - more than CD4 - are highly conserved between species, suggesting the animals can be suitable models for mechanistic studies addressing effects of receptor-ligand interaction other than infection. Of note, transgenic mice expressing HIV gp120 in the brain share several pathological hallmarks with NeuroAIDS brains. Against this background, we will discuss recently completed or initiated, ongoing studies that utilize HIV co-receptor knockout and viral gp120-transgenic mice as models for in vitro and in vivo experimentation in order to address the potential roles of HIV gp120 and its co-receptors in the development of NeuroAIDS.