Human immunodeficiency virus 1 and its envelope protein gp120 reduce synaptodendritic complexity. However, the mechanisms contributing to this pathological feature are still not understood. The proneurotrophin brain-derived neurotrophic factor promotes synaptic simplification through the activation of the p75 neurotrophin receptor (p75NTR). Here, we have used gp120 transgenic (gp120tg) mice to investigate whether p75NTR has a role in gp120-mediated neurotoxicity. Old (~10 months) gp120tg mice exhibited an increase in proneurotrophin brain-derived neurotrophic factor levels in the hippocampus as well as a decrease in the number of dendritic spines when compared to age-matched wild type. These effects were not observed in 3- or 6-month-old mice. To test if the reduction in spine density and morphology is caused by the activation of p75NTR, we crossed gp120tg mice with p75NTR null mice. We found that deletion of only 1 copy of the p75NTR gene in gp120tg mice is sufficient to normalize the number of hippocampal spines, strongly suggesting that the neurotoxic effect of gp120 is mediated by p75NTR. These data indicate that p75NTR antagonists could provide an adjunct therapy against synaptic simplification caused by human immunodeficiency virus 1.

Human plasminogen is a β-globulin (2 % carbohydrate, molecular weight 90 KD), which in its native form has NH₂-terminal glutamic acid (Glu-plasminogen) whose primary structure is known (31, 37, 38). From human plasma plasminogen can easily be isolated by affinity chromatography techniques (10, 25, and Table 1). Plasminogen is synthesized in many organs. The production site of the zymogen may be the liver (21), the eosinophiles (3) or the kindney (15). The plasma-plasminogen level is low in newborns (22) and even lower in the premature infant (2). In healthy adults it is found in plasma or serum in a concentration of 200 mg/l (= 2 μM, 22, 39). The half-life of the native (Glu-) plasminogen is 2.24 ± 0.29 days (6). Two types of Glu-plasminogen occur in human plasma, which differ in their carbohydrate composition as well as in their content of sialic acid. Genetic variants (see Mayr, 3.1.); of plasminogen have been reported (16) after isoelectric focusing of human plasma in polyacrylamide gels. Three patterns were found, two completely different and the third most likely a mixture of the other two. Characteristical functional properties of plasminogen are related to its molecular structure, e.g. its in vivo specificity for fibrin in contrast to the fairly unspecific in vitro activity of plasmin. Glu-plasminogen is easily converted by limited plasmic digestion to modified forms with NH₂-terminal lysine, valine or methionine (35, 36), which are commonly designated Lys-plasminogen” (26) displaying a plasma half-life time of 0,8 days (6). Lys-plasminogen forms are easily converted to plasmin which results in the formation of two-chain molecule (Lys-plasmin) from the single-chain monomer (zymogen).

The Angiotensin II Receptor Blocker (ARB) Telmisartan reduces inflammation through Angiotensin II AT1 receptor blockade and peroxisome proliferator-activated receptor gamma (PPARγ) activation. However, in a mouse microglia-like BV2 cell line, imitating primary microglia responses with high fidelity and devoid of AT1 receptor gene expression or PPARγ activation, Telmisartan reduced gene expression of pro-injury factors, enhanced that of anti-inflammatory genes, and prevented LPS-induced increase in inflammatory markers. Using global gene expression profiling and pathways analysis, we revealed that Telmisartan normalized the expression of hundreds of genes upregulated by LPS and linked with inflammation, apoptosis and neurodegenerative disorders, while downregulating the expression of genes associated with oncological, neurodegenerative and viral diseases. The PPARγ full agonist Pioglitazone had no neuroprotective effects. Surprisingly, the PPARγ antagonists GW9662 and T0070907 were neuroprotective and enhanced Telmisartan effects. GW9226 alone significantly reduced LPS toxic effects and enhanced Telmisartan neuroprotection, including downregulation of pro-inflammatory TLR2 gene expression. Telmisartan and GW9662 effects on LPS injury negatively correlated with pro-inflammatory factors and upstream regulators, including TLR2, and positively with known neuroprotective factors and upstream regulators. Gene Set Enrichment Analysis (GSEA) of the Telmisartan and GW9662 data revealed negative correlations with sets of genes associated with neurodegenerative and metabolic disorders and toxic treatments in cultured systems, while demonstrating positive correlations with gene sets associated with neuroprotection and kinase inhibition. Our results strongly suggest that novel neuroprotective effects of Telmisartan and GW9662, beyond AT1 receptor blockade or PPARγ activation, include downregulation of the TLR2 signaling pathway, findings that may have translational relevance.

The human immunodeficiency virus (HIV) envelope protein gp120 promotes axonal damage and neurite pruning, similar to that observed in HIV-positive subjects with neurocognitive disorders. Thus, gp120 has been used to examine molecular and cellular pathways underlying HIV-mediated neuronal dysfunction. Gp120 binds to tubulin beta III, a component of neuronal microtubules. Microtubule function, which modulates the homeostasis of neurons, is regulated by polymerization and post-translational modifications. Based on these considerations, we tested the hypothesis that gp120 induces dynamic instability of neuronal microtubules. We first observed that gp120 prevents the normal polymerization of tubulin in vitro. We then tested whether gp120 alters the post-translational modifications in tubulin by examining the ability of gp120 to change the levels of acetylated tubulin in primary rat neuronal cultures. Gp120 elicited a time-dependent decrease in tubulin acetylation that was reversed by Helix-A peptide, a compound that competitively displaces the binding of gp120 to neuronal microtubules. To determine whether post-translational modifications in tubulin also occur in vivo, we measured acetylated tubulin in the cerebral cortex of HIV transgenic rats (HIV-tg). We observed a decrease in tubulin acetylation in 5- and 9-month-old HIV-tg rats when compared to age-matched wild type. Neither changes in microglia morphology nor alterations in mRNA levels for interleukin-1β and tumor necrosis factor α were detected in 5-month-old animals. Our findings propose neuronal microtubule instability as a novel mechanism of HIV neurotoxicity, without evidence of enhanced inflammation.

Despite successful antiretroviral drug therapy, a subset of human immunodeficiency virus-1 (HIV)-positive individuals still display synaptodendritic simplifications and functional cognitive impairments referred to as HIV-associated neurocognitive disorders (HANDs). The neurological damage observed in HAND subjects can be experimentally reproduced by the HIV envelope protein gp120. However, the complete mechanism of gp120-mediated neurotoxicity is not entirely understood. Gp120 binds to neuronal microtubules and decreases the level of tubulin acetylation, suggesting that it may impair axonal transport. In this study, we utilized molecular and pharmacological approaches, in addition to microscopy, to examine the relationship between gp120-mediated tubulin deacetylation, axonal transport, and neuronal loss. Using primary rat cortical neurons, we show that gp120 decreases acetylation of tubulin and increases histone deacetylase 6 (HDAC6), a cytoplasmic enzyme that regulates tubulin deacetylation. We also demonstrate that the selective HDAC6 inhibitors tubacin and ACY-1215, which prevented gp120-mediated deacetylation of tubulin, inhibited the ability of gp120 to promote neurite shortening and cell death. We further observed by co-immunoprecipitation and confirmed with mass spectroscopy that exposure of neurons to gp120 decreases the association between tubulin and motor proteins, a well-established consequence of tubulin deacetylation. To assess the physiological consequences of this effect, we examined the axonal transport of brain-derived neurotrophic factor (BDNF). We report that gp120 decreases the velocity of BDNF transport, which was restored to baseline levels when neurons were exposed to HDAC6 inhibitors. Overall, our data suggest that gp120-mediated tubulin deacetylation causes impairment of axonal transport through alterations to the microtubule cytoskeleton.