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The loss of gut epithelium integrity leads to translocation of microbes and microbial products resulting in immune activation and drives systemic inflammation in acquired immunodeficiency syndrome (AIDS) patients. Although viral loads in HIV patients are significantly reduced in the post-cART era, inflammation and immune activation persist and can lead to morbidity. Here, we determined the interactive effects of the viral protein HIV-1 Tat and lipopolysaccharide (LPS) on enteric neurons and glia. Bacterial translocation was significantly enhanced in Tat-expressing (Tat+) mice. Exposure to HIV-1 Tat in combination with LPS enhanced the expression and release of the pro-inflammatory cytokines IL-6, IL-1β and TNF-α in the ilea of Tat+ mice and by enteric glia. This coincided with enhanced NF-κB activation in enteric glia that was abrogated in glia from TLR4 knockout mice and by knockdown (siRNA) of MyD88 siRNA in wild type glia. The synergistic effects of Tat and LPS resulted in a reduced rate of colonic propulsion in Tat+ mice treated with LPS. These results show that HIV-1 Tat interacts with the TLR4 receptor to enhance the pro-inflammatory effects of LPS leading to gastrointestinal dysmotility and enhanced immune activation.

Tat's transactivating activity is controlled by sirtuin 1 (SIRT1) that connects HIV transcription with the metabolic state of the cell. Nicotinamide phosphoribosyltransferase (NAMPT) is a key enzyme in the salvaging pathway for the synthesis of nicotinamide adenine dinucleotide (NAD(+)) that is involved in energy metabolism. Host encoded microRNAs (miRNAs) may influence viral replication. In this study, our goal was aimed to investigate the regulation of miR-182 in TZM-bl cells and explore the mechanisms by which miR-182 influenced Tat-induced HIV-1 transactivation through targeting at down-regulation of NAMPT expression. We showed that miR-182 was up-regulated when Tat was expressed in TZM-bl cells. MiR-182 significantly inhibited NAMPT protein expression by acting on the 3'-UTR of the NAMPT mRNA. MiR-182 was involved in Tat-induced NAD(+) depletion, down-regulation of SIRT1 protein expression and activity, increased acetylation of p65. Forced expression of "miR-182 mimics" increased Tat-induced LTR transactivation. Our results uncover previously unknown links between Tat and a specific host cell miRNA that targets NAMPT. Our results suggest that strategies to augment NAMPT protein expression by down-regulation of miR-182 may have therapeutic benefits to prevent HIV-1 replication., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The existence of multiple subtypes of HIV-1 worldwide has created new challenges to control HIV-1 infection and associated neuropathogenesis. Previous studies indicate a difference in neuropathogenic manifestations of HIV-1-associated neuroAIDS between clade B- and clade C-infected subjects with clade B being more neuropathogenic than clade C. However, the exact mechanism underlying the differences in the neuropathogenesis by both the subtypes remains elusive. Development of neuroAIDS is associated with a complex interplay between proinflammatory and antiinflammatory cytokines and chemokines. In the current study, we hypothesize that HIV-1 clade B and C Tat protein exert differential effects on human primary monocytes leading to differences in gene and protein expression of cytokines implicated in neuroAIDS. Primary human monocytes were treated with clade B and clade C Tat protein and quantitative real time PCR was performed to determine gene expression of proinflammatory cytokines (IL-6 and TNF-alpha) and antiinflammatory cytokines (IL-4 and IL-10). Further, cytokine secretion was measured in culture supernatants by ELISA, whereas intracellular cytokine expression was detected by flow cytometry. Results indicate that monocytes treated with Tat B showed significant upregulation of proinflammatory cytokines, IL-6 and TNF-alpha, as compared to Tat C-treated cultures. However, expression of antiinflammatory molecules and IL-4 and IL-10 was found to be higher in Tat C-treated compared to Tat B-treated cultures. Thus, our result shows for the first time that Tat B and Tat C differentially modulate expression of neuropathogenic molecules that may be correlated with the differences in neuroAIDS manifestation induced by clade-specific infections.