It should be noted that this measurement is probably a gross underestimate of Tat’s local concentration; Tatin vivocan be sequestered by endogenous glycosaminoglycans and heparin sulfates effectively lowering the detectable amounts of Tat circulating unbound. for the neuropathogenesis of HIV-1 in the CNS. == Introduction == Infection of the central nervous system (CNS) with the human immunodeficiency virus type 1 (HIV) occurs rapidly after primary infection[1]. The phenotype of HIV associated dementia (HAD) after the introduction of highly active antiretroviral therapy (HAART) has changed considerably with a more indolent time course, frequently characterized by waxing and waning neurologic deficits, suggesting a change in nomenclature to HIV-1 associated neurologic deficits Rabbit polyclonal to ITLN2 (HAND)[2]. Alarmingly, more recent studies of incidence and prevalence of the neurologic component of HIV-1 infection demonstrate that neural injury continues in some patients regardless of the ability of HAART to achieve virologic suppression and normalization of immunologic parameters[3]. The CNS can act as a reservoir for HIV as agents that comprise HAART do not achieve a level of CNS penetration that can fully eradicate the virus[2],[4]. In patients with improved systemic health from HAART, it is HAART’s failure to control HIV-1’s effects on the signaling pathways that mediate normal communication between immune effecting glias and vulnerable neurons, that has substantially contributed to the rise in HAND prevalence since 2000[5]. Thus HAND continues to be a problem of pandemic proportions. Since HIV-1 only infects CNS cell types that express the chemokine receptors CD3, CCR5 and/or CXCR4 (i.e. microglia, Chlorogenic acid perivascular macrophages, and a restricted population of astrocytes)[6], structural damage with accompanying neurologic disease[7]occurs because of pathway activation that leads to release of inflammatory molecules such as nitric oxide (NO), tumor necrosis factor alpha (TNF-), and platelet activating factor (PAF); changes in ambient recycling of glutamate by astrocytes; and Chlorogenic acid the release of viral regulatory proteins, such as the trans activator of transcription protein (Tat)[8][11]and the envelope protein gp120[12]. At the light microscopic level, the neuropathology of HIV-1 infection is notable for Chlorogenic acid changes in the dendritic arbor with varicosities (beading13); accumulation of beta amyloid precursor protein (-APP) in axons[14]; neuronal apoptosis[15],[16]; and reactive astrocytosis, microgliosis, and multinucleated giant cells[17]. Surprisingly, ultrastructural analyses of brain tissue from patients with HIV-1 infection have focused on changes in endothelial architecture, including thinning and vacuolization of the basal lamina[18], but no study has focused on changes in intracellular organelles or synaptic architecture of neurons. Of the many HIV-induced neurotoxins, Tat is remarkable because it is actively released into the extracellular space by infected microglia, macrophages and astrocytes [10; 1921]. Unbound Tat has been detected in the sera of HIV+patients, reaching concentrations as high as 40 ng/mL[22]. It should be noted that this measurement is probably a gross underestimate of Tat’s local concentration; Tatin vivocan be sequestered by endogenous glycosaminoglycans and heparin sulfates effectively lowering the detectable amounts of Tat circulating unbound. This observation lends credence to the notion that infiltrating microglia/macrophage adjacent to a synapse would have greatly increased local concentrations of Tat. However, once released from a cell Tat can enter virtually all neural cell types via its arginine-rich basic domain, termed the protein transduction domain (PTD)[23][26]. Tat can modulate intracellular calcium concentrations through activation of endoplasmic reticulum (ER) pathways in vulnerable neurons[26][28]. Protein folding in the ER relies on foldases, chaperones, and lectins that require high concentrations of calcium and an oxidized environment in order to perform properly (Schroder 2005, Wetmore 1996). This in turn raises the question of whether Tat can overwhelm the protein folding capacity of the ER and induce the unfolded protein response (UPR) pathway[29]. Induction of the UPR pathway is designed to reduce net protein translation and results in the up-regulation of a specific set of genes that function to relieve this stress. Phosphorylation of the transmembrane protein kinaselike endoplasmic reticulum kinase (PERK) is one of the initial events in the UPR pathway and is Chlorogenic acid responsible for the downstream phosphorylation of eukaryotic initiation factor 2 (eIF2) that prevents 80S ribosome assembly, inhibiting protein translation[30]. Inositol requiring kinase 1 (IRE1) can dimerize in conjunction with PERK phosphorylation and cleave the mRNA of X-box binding protein 1 (XBP1) to.