Lipopolysaccharide-enhanced transcellular transport of HIV-1 across the blood-brain barrier is mediated by the p38 mitogen-activated protein kinase pathway

Abstract

Chronic systemic inflammation in the late stage of human immunodeficiency virus type-1 (HIV-1) infection could increase neuroinvasion of infected monocytes and cell-free virus, causing an aggravation of neurological disorders in AIDS patients. We previously showed that the peripheral administration of lipopolysaccharide (LPS) enhanced the uptake across the blood-brain barrier (BBB) of the HIV-1 viral protein gp120. Brain microvessel endothelial cells are targets of LPS. Here, we investigated whether the direct interaction between LPS and the BBB also affected HIV-1 transport using primary mouse brain microvessel endothelial cells (BMECs). LPS produced a dose (1-100 microg/mL)- and time (0.5-4 h)-dependent increase in HIV-1 transport and a decrease in transendothelial electrical resistance (TEER). Whereas indomethacin (cyclooxygenase inhibitor) and L-NAME (NO synthase inhibitor) did not affect the LPS-induced changes in HIV-1 transport or TEER, pentoxifylline (TNF-alpha inhibitor) attenuated the decrease in TEER induced by LPS, but not the LPS-induced increase in HIV-1 transport. LPS also increased the phosphorylation of p44/42 MAPK and p38 MAPK but not that of JNK. U0126 (p44/42 MAPK inhibitor) and SP600125 (JNK inhibitor) did not inhibit the LPS-induced increase in HIV-1 transport although U0126 attenuated the reduction in TEER. SB203580 (p38 MAPK inhibitor) inhibited the LPS-induced increase in HIV-1 transport without affecting TEER. Thus, LPS-enhanced HIV-1 transport is independent of changes in TEER and so is attributed to increased transcellular trafficking of HIV-1 across the BBB. These results show that LPS increases HIV-1 transcellular transport across the BBB by a pathway that is mediated by p38 MAPK phosphorylation in BMECs.

Figure 1

Effect of LPS on the permeability of BMECs to ¹³¹I-HIV-1 (A and C) and TEER (B and D). In panels A and B, BMECs were treated with LPS for 4 hr. In panels C and D, BMECs were treated with 100 μg/mL LPS. In panels A and C, results are expressed as % of control. Control values were 5.24 ± 0.71 × 10⁻⁵ and 1.75 ± 0.07 × 10⁻⁵ cm/min (A and C, respectively). Values are means ± SEM (n = 4–9). *P < 0.05, **P < 0.01, ***P < 0.001, significant differences from control.

Figure 2

Effects of indomethacin, L-NAME, and pentoxifylline on the LPS-induced increase in permeability of ¹³¹I-HIV-1 to BMECs (A, C, and E) and the LPS-induced decrease in TEER (B, D, and F). BMECs were treated with LPS (100 μg/mL) for 4 hr in the presence or absence of indomethacin (1, 5 μM; A and B), L-NAME (1, 3 mM; C and D), or pentoxifylline (0.2, 2 mM; E and F). In panels A, C, and E, results are expressed as % of control. The control values of permeability coefficient for ¹³¹I-HIV-1 in panel A, C, and E were 2.90 ± 0.44 × 10⁻⁵, 2.83 ± 0.44 × 10⁻⁵, and 1.28 ± 0.09 × 10⁻⁵ cm/min, respectively. Values are means ± SEM (n = 6–21). *P < 0.05, **P < 0.01, ***P < 0.001, significant difference from control. ^#P < 0.05, significant difference from LPS (100 μg/mL).

Figure 3

Effects of various MAPK inhibitors on the LPS-induced increase in permeability of ¹³¹I-HIV-1 to BMECs (A, C, and E) and the LPS-induced decrease in TEER (B, D, and F). BMECs were treated with LPS (100 μg/mL) for 4 hr in the presence or absence of U0126 (5–20 μM; A and B), SB203580 (1–10 μM; C and D), or SP600125 (5–20 μM; E and F). In panels A, C, and E, results are expressed as % of control. The control values of permeability coefficient for ¹³¹I-HIV-1 in panel A, C, and E were 1.47 ± 0.19 × 10⁻⁵, 2.04 ± 0.35 × 10⁻⁵, and 1.24 ± 0.91 × 10⁻⁵ cm/min, respectively. Values are means ± SEM (n = 3–18). *P < 0.05, **P < 0.01, ***P < 0.001, significant difference from control. ^#P < 0.05, significant difference from LPS (100 μg/mL).

Figure 4

LPS increased phosphorylation of MAPKs in BMECs. BMECs were treated with LPS (1, 10 and 100 μg/mL) for 4 hr. Western blot analyses were performed to detect phosphorylated p44/42 MAPK, p38 MAPK and JNK as well as total p44/42 MAPK, p38 MAPK and JNK. Photographs are representative in three independent experiments.

Figure 5

Schematic diagram of the mechanisms by which LPS induced the activation of MAPKs followed by the increase in the BBB permeability through paracellular and transcelluar routes. LPS-increased HIV-1 transport is mainly dependent on transcellular route. Dashed lines indicate possible intermediate steps.