Macrophage-sensory neuronal interaction in HIV-1 gp120-induced neurotoxicity‡

Abstract

Background: Human immunodeficiency virus (HIV)-associated sensory neuropathy (SN) is the most frequent neurological complication of HIV disease. Among the probable mechanisms underlying HIV-SN are neurotoxicity induced by the HIV glycoprotein gp120 and antiretroviral therapies (ART). Since HIV-SN prevalence remains high in patients who have not been exposed to toxic ART drugs, here we focused on gp120-mediated mechanisms underlying HIV-SN.

Methods: We hypothesized that a direct gp120-sensory neurone interaction is not the cause of neurite degeneration; rather, an indirect interaction of gp120 with sensory neurones involving macrophages underlies axonal degeneration. Rat dorsal root ganglion (DRG) cultures were used to assess gp120 neurotoxicity. Rat bone marrow-derived macrophage (BMDM) cultures and qPCR array were used to assess gp120-associated gene expression changes.

Results: gp120 induced significant, but latent onset, neurite degeneration until 24 h after application. gp120-neurone interaction occurred within 1 h of application in <10% of DRG neurones, despite neurite degeneration having a global effect. Application of culture media from gp120-exposed BMDMs induced a significant reduction in DRG neurite outgrowth. Furthermore, gp120 significantly increased the expression of 25 cytokine-related genes in primary BMDMs, some of which have been implicated in other painful polyneuropathies. The C-C chemokine receptor type 5 (CCR5) antagonist, maraviroc, concentration-dependently inhibited gp120-induced tumour necrosis factor-α gene expression, indicating that these effects occurred via gp120 activation of CCR5.

Conclusions: Our findings highlight macrophages in the pathogenesis of HIV-SN and upstream modulation of macrophage response as a promising therapeutic strategy.

Keywords: cytokines; HIV envelope protein; macrophages; maraviroc; peripheral nervous system diseases; peripheral neuropathies.

Fig 1

Temporal course of gp120-associated neurite degeneration and accumulation of biotinylated-gp120_MN in the neuronal cell body. Untreated cultures were fixed at the time of application (t=0 h) to assess baseline neurite outgrowth. Remaining cultures were treated with vehicle or 2 nM gp120_MN or, in a separate experiment, 2 nM biotinylated-gp120_MN (B-gp120_MN) in C-DMEM. (a–i) Representative images of untreated DRG cultures at t=0 h (a and f) and treated DRG cultures after 24 h (b and c) or 48 h (d and e) exposure to vehicle (b and d) or 2 nM gp120_MN (c and e), or those treated with B-gp120_MN after 3.5 (g), 10 (h), or 24 h (i). Treated cultures were fixed at set time-points after application, and immunostained for βIII-tubulin (red) to complete neurite analysis. (j) Quantification of the temporal course of neurite outgrowth, and (k) its association with the temporal localization of B-gp120_MN with neuronal cell bodies. White arrowheads indicate neuronal cell bodies positive for B-gp120_MN immunolabelling (green). Inset shows ×5.2 magnification of indicated white box. Data presented as mean and (sd). *P<0.05 and **P<0.01 vs 0 h baseline, and ^#P<0.05 vs the respective baselines using two-factor ANOVA; n=6. Percentage (%) of baseline was used to normalize across the two biological replicates. Scale bars: (a–e) 50 µm and (f–i) 100 µm.

Fig 2

Neurite analysis after exposure to conditioned BMDM media. (a–c) Representative images of primary DRG cultures immunolabelled for βIII-tubulin (green) and nuclei counterstained with Hoechst 32258 (blue). One-day-old DRG cultures were treated for 24 h with DMEM/F-12 supplemented 1:1 with culture media from BMDMs stimulated for 4 h prior with (a) vehicle, (b) 2 nM denatured-gp120_Bal, or (c) 2 nM gp120_Bal. Scale bars=50 µm. DRG cultures treated with culture media from gp120_Bal-treated BMDMs showed a significant reduction in the mean NOPN, as a percentage of vehicle-treated cultures (d). Conditioned media from denatured-gp120_Bal-treated BMDMs induced no change in neurite outgrowth relative to vehicle control. Data presented as mean (sd). *P<0.05 vs vehicle-treated cultures, using one-way anova and Tukey's post hoc analysis (n=5–6; five to six technical replicates across two biological studies).

Fig 3

TNF-α expression changes in BMDMs after gp120 exposure and inhibition with the CCR5 antagonist maraviroc. (a) gp120_Bal induced a concentration-dependent increase in TNF-α expression after 4 h stimulation of BMDMs with vehicle, 2 nM denatured-gp120_Bal or 2, 200 pM, 1 or 2 nM gp120_Bal, in IMDM. Data presented as mean 2^−ΔΔCt-fold change (sd), n=4. *P<0.05 vs vehicle- and den.gp120-treated control levels using one-way anova and Tukey's post hoc analysis. (b) Primary BMDM cells were pretreated for 1 h with either vehicle control or 10 nM maraviroc and then exposed for 4 h to either vehicle, 1 nM denatured-gp120_Bal ,or 1 nM gp120_Bal diluted in IMDM or presence of 1, 10, or 100 nM maraviroc. Changes in TNF-α mRNA gene expression were assessed relative to vehicle control. Data presented as mean 2^−ΔΔCt-fold change (sd), n=4. *P<0.05 vs 1 nM gp120-treated baseline values using two-way anova and Tukey's post hoc analysis.

Fig 4

Effect of TNF-α on neurite outgrowth in primary adult DRG cultures. Representative images of adult primary DRG cultures treated for 24 h with vehicle (a) or 0.25 nM (b), 0.5 nM (c), 1 nM (d), and 2 nM (e) TNF-α in C-DMEM. Addition of TNF-α induced reduced neurite outgrowth that was significant at 2 nM (f). Data presented as mean neurite outgrowth/neurone (sd), after 24 h treatment, normalized to (percentage of) the mean neurite outgrowth/neurone of vehicle-treated cultures (n=3–9). *P<0.05 using one-way anova and Tukey's post hoc analysis. Scale bars=50 µm.