Lipopolysaccharide-enhanced transcellular transport of HIV-1 across the blood-brain barrier is mediated by luminal microvessel IL-6 and GM-CSF

Elevated levels of cytokines/chemokines contribute to increased neuroinvasion of human immunodeficiency virus type 1 (HIV-1). Previous work showed that lipopolysaccharide (LPS), which is present in the plasma of patients with HIV-1, enhanced transcellular transport of HIV-1 across the blood-brain barrier (BBB) through the activation of p38 mitogen-activated protein kinase (MAPK) signaling in brain microvascular endothelial cells (BMECs). Here, we found that LPS (100 μg/mL, 4 hr) selectively increased interleukin (IL)-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) release from BMECs. The enhancement of HIV-1 transport induced by luminal LPS was neutralized by treatment with luminal, but not with abluminal, antibodies to IL-6 and GM-CSF without affecting paracellular permeability as measured by transendothelial electrical resistance (TEER). Luminal, but not abluminal, IL-6 or GM-CSF also increased HIV-1 transport. U0126 (MAPK kinase (MEK)1/2 inhibitor) and SB203580 (p38 MAPK inhibitor) decreased the LPS-enhanced release of IL-6 and GM-CSF. These results show that p44/42 and p38 MAPK signaling pathways mediate the LPS-enhanced release of IL-6 and GM-CSF. These cytokines, in turn, act at the luminal surface of the BMEC to enhance the transcellular transport of HIV-1 independently of actions on paracellular permeability

Nitric Oxide Isoenzymes Regulate Lipopolysaccharide-Enhanced Insulin Transport across the Blood-Brain Barrier

Insulin transported across the blood-brain barrier (BBB) has many effects within the central nervous system. Insulin transport is not static but altered by obesity and inflammation. Lipopolysaccharide (LPS), derived from the cell walls of Gram-negative bacteria, enhances insulin transport across the BBB but also releases nitric oxide (NO), which opposes LPS-enhanced insulin transport. Here we determined the role of NO synthase (NOS) in mediating the effects of LPS on insulin BBB transport. The activity of all three NOS isoenzymes was stimulated in vivo by LPS. Endothelial NOS and inducible NOS together mediated the LPS-enhanced transport of insulin, whereas neuronal NOS (nNOS) opposed LPS-enhanced insulin transport. This dual pattern of NOS action was found in most brain regions with the exception of the striatum, which did not respond to LPS, and the parietal cortex, hippocampus, and pons medulla, which did not respond to nNOS inhibition. In vitro studies of a brain endothelial cell (BEC) monolayer BBB model showed that LPS did not directly affect insulin transport, whereas NO inhibited insulin transport. This suggests that the stimulatory effect of LPS and NOS on insulin transport is mediated through cells of the neurovascular unit other than BECs. Protein and mRNA levels of the isoenzymes indicated that the effects of LPS are mainly posttranslational. In conclusion, LPS affects insulin transport across the BBB by modulating NOS isoenzyme activity. NO released by endothelial NOS and inducible NOS acts indirectly to stimulate insulin transport, whereas NO released by nNOS acts directly on BECs to inhibit insulin transport