Neutrophil elastase promotes Leishmania donovani infection via interferon-β

Visceral leishmaniasis is a deadly illness caused by Leishmania donovani that provokes liver and spleen inflammation and tissue destruction. In cutaneous leishmaniasis, the protein of L. major named inhibitor of serine peptidases (ISP2) inactivates neutrophil elastase (NE) present at the macrophage surface, resulting in blockade of TLR4 activation, prevention of TNF and IFN production and parasite survival. We report poor intracellular growth of L. donovani in macrophages from knock-out mice for NE (ela-/-), TLR4 or TLR2. NE and TLR4 co-localized with the parasite in the parasitophorous vacuole. Parasite load in the liver and spleen of ela-/- mice were reduced and accompanied by increased nitric oxide and decreased TGF production. Expression of ISP2 was not detected in L. donovani and a transgenic line constitutively expressing ISP2, displayed poor intracellular growth in macrophages and decreased burden in mice. Infected ela-/- macrophages displayed significantly lower IFN mRNA than background mice macrophages and the intracellular growth of was fully restored by exogenous IFN. We propose that L. donovani utilizes the host NE-TLR machinery to induce IFN necessary for parasite survival/growth during early infection. Low or absent expression of parasite ISP2 in L. donovani is necessary to preserve the activation of the NE-TLR pathway

ACAT-related activity assay.

<p>The ability of <i>T</i>. <i>cruzi</i> epimastigotes to esterify cholesterol was tested using Sandoz 58-035-58-035 for 16–18 h (A) or Avasimibe for 24 h (B) in different concentrations, followed by addition of BSA-³H-palmitate (800,000 DPM; 1 mg/mL) for 24 h. Lipid analysis was performed by TLC; CHOE spots were scraped and the lipid eluted from silica. The lipid-associated radioactivity was measured by liquid scintillation counting. The results are expressed as the mean (±SD) per 1 mg of protein of two independent experiments in duplicate, and analysed by one-way ANOVA followed by the Bonferroni test (*<i>P</i><0.05).</p

<i>Trypanosoma cruzi</i> Epimastigotes Are Able to Manage Internal Cholesterol Levels under Nutritional Lipid Stress Conditions

<div><p><i>Trypanosoma cruzi</i> epimastigotes store high amounts of cholesterol and cholesteryl esters in reservosomes. These unique organelles are responsible for cellular digestion by providing substrates for homeostasis and parasite differentiation. Here we demonstrate that under nutritional lipid stress, epimastigotes preferentially mobilized reservosome lipid stocks, instead of lipid bodies, leading to the consumption of parasite cholesterol reservoirs and production of ergosterol. Starved epimastigotes acquired more LDL-NBD-cholesterol by endocytosis and distributed the exogenous cholesterol to their membranes faster than control parasites. Moreover, the parasites were able to manage internal cholesterol levels, alternating between consumption and accumulation. With normal lipid availability, parasites esterified cholesterol exhibiting an ACAT-like activity that was sensitive to Avasimibe in a dose-dependent manner. This result also implies that exogenous cholesterol has a role in lipid reservoirs in epimastigotes.</p></div

Free and total (after saponification) cholesterol and ergosterol contents in lipid starved <i>T</i>. <i>cruzi</i> epimastigotes, kept in LIT medium supplemented with 10% dFCS for 0, 24, 48 and 72h.

<p>All samples correspond to 5 μg/mL of protein.</p><p>Free and total (after saponification) cholesterol and ergosterol contents in lipid starved <i>T</i>. <i>cruzi</i> epimastigotes, kept in LIT medium supplemented with 10% dFCS for 0, 24, 48 and 72h.</p

Incorporation of ³H-cholesterol into cholesteryl esters in epimastigotes.

<p>Parasites were incubated in LIT medium with 10% FCS (control) or 10% dFCS (starved) in the presence of LDL-³H-cholesterol (1,000,000 DPM; 2 mg/mL) for 3 days at 28°C. Parasites were washed and their lipids were extracted and analysed by TLC. The cholesterol (CHO) and cholesteryl-ester (CHOE) spots were scraped and the lipid eluted from silica. The lipid-associated radioactivity was measured by liquid scintillation counting. The results are expressed as the mean (±SD) per 1 mg of protein of three independent experiments analysed by one-way ANOVA followed by the Bonferroni test (*<i>P</i><0.05).</p

ACAT-related activity assay.

<p>The ability of <i>T</i>. <i>cruzi</i> epimastigotes to esterify cholesterol was tested using Sandoz 58-035-58-035 for 16–18 h (A) or Avasimibe for 24 h (B) in different concentrations, followed by addition of BSA-³H-palmitate (800,000 DPM; 1 mg/mL) for 24 h. Lipid analysis was performed by TLC; CHOE spots were scraped and the lipid eluted from silica. The lipid-associated radioactivity was measured by liquid scintillation counting. The results are expressed as the mean (±SD) per 1 mg of protein of two independent experiments in duplicate, and analysed by one-way ANOVA followed by the Bonferroni test (*<i>P</i><0.05).</p

Quantification of NBD-cholesterol distribution in epimastigotes according to time.

<p>Starved parasites (A) uptake more LDL-NBD-cholesterol than controls (B), comparing fluorescence intensity in reservosomes/vesicles at time zero (immediately after washing off the tracer). The fluorescence intensity in reservosomes varies with time in starved parasites, but not significantly in control reservosomes, except after 2h. Starved parasites quickly redistribute the exogenous NBD-chol to their membranes (C) after 30 min, while in control cells (D) the NBD-chol rate increases only after 2 h of traffic. The results are expressed as the mean (±SD) and analysed with the one-way ANOVA test in comparison to time zero (*/**/*** significantly different, <i>P</i> < 0.05).</p

Morphometric analysis of the number and the area occupied by lipid bodies in the cytoplasm of epimastigotes cultivated in LIT medium supplemented with 10% dFCS.

<p>¹ n = 30 parasite profiles</p><p>*<i>P</i> > 0.05. The results are expressed as the mean ± S.E.M using one-way ANOVA.</p><p>Morphometric analysis of the number and the area occupied by lipid bodies in the cytoplasm of epimastigotes cultivated in LIT medium supplemented with 10% dFCS.</p

Morphometric analysis of the area of reservosomes and the area occupied by lipid inclusions inside them in epimastigotes cultivated in LIT medium supplemented with 10% dFCS.

<p>¹ n = 30 parasite profiles;</p><p>² n = 50 reservosomes</p><p>*<i>P</i> < 0.05 in relation to time zero. The results are expressed as the mean ± S.E.M using one-way ANOVA</p><p>Morphometric analysis of the area of reservosomes and the area occupied by lipid inclusions inside them in epimastigotes cultivated in LIT medium supplemented with 10% dFCS.</p

Transmission electron microscopy of epimastigotes cultivated in LIT medium supplemented with 10% dFCS.

<p>(A) 0 h—Reservosomes show many lipid inclusions in their lumen (asterisk). (B) After 6 h of lipid starvation, reservosomes filled with lipid inclusions could still be observed, but after 24 h (C), 48 h (D) and 72 h (E), an expressive decrease in reservosome lipids was registered. The insets show that there were reservosomes with typical lipid inclusions even after 24 to 72 h of starvation. The arrows point to lipid bodies throughout the cytoplasm. K- Kinetoplast, M—Mitochondrion, N—Nucleus, R- reservosomes. Bars correspond to 0.25 μm.</p