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. 2013 Mar 13;13(3):277-88.
doi: 10.1016/j.chom.201302005.

Leishmania donovani targets Dicer1 to downregulate miR-122, lower serum cholesterol, and facilitate murine liver infection

Affiliations

Leishmania donovani targets Dicer1 to downregulate miR-122, lower serum cholesterol, and facilitate murine liver infection

June Ghosh et al. Cell Host Microbe. .

Abstract

Leishmania donovani causes visceral leishmaniasis (VL) where the parasite infects and resides inside liver and spleen tissue macrophages. Given the abnormal lipid profile observed in VL patients, we examined the status of serum lipids in an experimental murine model of VL. The murine VL liver displayed altered expression of lipid metabolic genes, many of which are direct or indirect targets of the liver-specific microRNA-122. Concomitant reduction of miR-122 expression was observed in VL liver. High serum cholesterol caused resistance to L. donovani infection, while downregulation of miR-122 is coupled with low serum cholesterol in VL mice. Exosomes secreted by the infective parasites caused reduction in miR-122 activity in hepatic cells. Leishmania surface glycoprotein gp63, a Zn-metalloprotease, targets pre-miRNA processor Dicer1 to prevent miRNP formation in L. donovani-interacting hepatic cells. Conversely, restoration of miR-122 or Dicer1 levels in VL mouse liver increased serum cholesterol and reduced liver parasite burden.

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Figures

None
Graphical abstract
Figure 1
Figure 1
Reduction in Serum Lipids with Progress of L. donovani Infection in Mouse Liver (A) Level of total serum cholesterol in L. donovani-infected BALB/c mice. Serum cholesterol levels in mice infected for 8, 15, 30, or 60 days were measured and plotted individually. (B–D) Levels of HDL (B), LDL (C), and triglyceride (D) in the blood serum of 8, 15, 30, or 60 days of infected or age-matched normal animals. (E) Liver parasite load in individual animals from different experimental groups estimated and plotted as LDU against infection time. (F) Level of serum glucose in L. donovani-infected (1 or 2 months) and normal animals. Data represent mean ± SEM. For each experiment n = 8. Significance levels: ns (not significant), p > 0.05, ∗p < 0.05, ∗∗p < 0.001, ∗∗∗p < 0.0001. See also Table S1 and Figure S1.
Figure 2
Figure 2
Altered Expression of Lipid Metabolizing Genes in the Livers of L. donovani-Infected Animals (A–C) Whole-genome microarray analysis revealed differentially expressed genes in L.donovani-infected liver. A pie chart representation of number of genes that showed altered expression in mouse livers after 60 days p.i. is shown. RNA was isolated from normal (n = 3) or infected (n = 2) livers, and whole genome microarray analysis was done (A). Heatmap of lipid metabolic genes (B). Fold changes obtained from both real-time quantification and microarray analysis were plotted for the key lipid metabolizing genes that showed either an increased or decreased expression in infected livers (C). (D) Decreased expression of cholesterol anabolic proteins HMGCR or ACAT2 in infected mouse liver. Liver tissue extracts were western blotted for HMGCR or ACAT2 detection. β-actin was used as loading control. n = 4 for noninfected control and 60 days p.i. (E) Changes in expression of important lipid metabolic genes in infected animal livers with progress of infection. Respective fold changes in expression were quantified by real-time PCR. For all real-time estimations, n ≥ 3. SD was from three independent measurements. Data represented as ±SEM. See also Table S2.
Figure 3
Figure 3
miR-122 Acts as a Modulator of Parasitic Infection in L. donovani-Infected Mouse Liver (A and B) Downregulation of miR-122 in L. donovani-infected mouse liver. Liver miR-122 levels in L. donovani-infected BALB/c mice were quantified by real-time quantification. U6 small nuclear RNA (snRNA) was used for normalization. miR-122 content in age-matched noninfected animals were used as reference value (A). Northern blot to detect miR-122 changes in infected mouse livers (B). Ethidium bromide (EtBr)-stained gel was used for loading control. For real-time quantification n = 8 for each time point. (C) Levels of AGO2 and RCK/p54 protein in L. donovani-infected mice. Western blot analysis for AGO2 and RCK/p54 proteins in liver extracts from normal and infected animals. β-actin was used as loading control. (D) Changes in expression of miR-122 and the serum cholesterol level in mice after introduction of miR-122 expression plasmid pmir122 through tail vein injection. Animals were sacrificed after indicated time; liver miR-122 and serum cholesterol levels were measured. (E) A schematic representation of the time course of exogenous miR-122 expression in infected mouse liver. Infection time is marked by a white arrow, and the black arrow defines the time of sacrifice 30 days p.i. The black arrowheads mark the injection time of miR-122 expression plasmids. (F–H) Effect of upregulation of miR-122 on infection level in mouse livers. Infected animals were treated as per the schedule described in (E) and were sacrificed after a month. Relative miR-122 expression (F), serum cholesterol level (G), and hepatic parasite load (H) were compared in pmiR-122-treated versus sham-treated groups. Data represent mean ± SEM. For all experiments, n = 8. ∗∗∗p < 0.0001, ∗∗p < 0.001. L.d, L.donovani. See also Table S3 and Figure S2.
Figure 4
Figure 4
Inhibition of miR-122 in Huh7 Cells by L. donovani (A) Schematic picture of the miR-122 reporter used to measure the miR-122 activity in Huh7 cells. For relative fold repression, the calculation level of repression for controls was always settled to 1. (B–E) Modulation of miR-122 activity in Huh7 cells by L.donovani. Huh7 expressing either the RL-con or RL-3 ×ばつ bulge-miR-122 Renilla luciferase reporter along with firefly luciferase encoding control mRNA were grown and treated differently (as described below) before the luciferase activities were measured and relative fold repression values calculated. (B) Huh7 cultured with Leishmania-infected human PBMC supernatant. (C) Huh7 cocultured with human PBMC and with increasing numbers of L. donovani parasite. Huh7 cultured with L. donovani promastigotes (1:1, 1:10, 1:100) (D) or amastigotes (1:1, 1:10, 1:100) (E). (F–J) Exosomes released by L.donovani affects miR-122 activity in Huh7 cells. As described above, Huh7 cells expressing miR-122 reporter or control mRNAs were treated with L.donovani culture supernatant (grown at either 22°C or 37°C) or control medium used for parasite growth (M199), and fold repression values were calculated (F). Exosomes isolated from the L. donovani promastigote-grown (G) or amastigote-grown (H) medium or control medium were also used to test its effect on miR-122-mediated repression. In similar experiments, L.donovani exosomes either pretreated with the Zn-chelator o-Phenantholine (I) or anti-gp63 antibody (J) were used to score their effect on exosome-dependent inhibition of miRNA-mediated repression. Normal IgG was used as a control. Data represent mean ± SEM. Significance level, ∗p < 0.05, ∗∗p < 0.001, ∗∗∗p < 0.0001). Ld, Leishmania donovani. See also Figure S3 and Movie S1.
Figure 5
Figure 5
L. donovani Downregulates DICER1 and Prevents miRNP Formation in Huh7 Cells (A) L. donovani increases pre-miR-122 levels in livers of L donovani-infected animals. RNA isolated from the livers of BALB/c mice after 15, 30, or 60 days infected were subjected to real-time analysis, and β-actin mRNA levels were used for normalization. n = 6 for each group. (B) pre-miR-122 levels in Huh7 cells before and after treatment with L. donovani promastigotes for 24 hr. Real-time quantification for pre-miR-122 was performed. SDs were from three independent measurements. (C) Association of miR-122 with AGO2 in Huh7 cells interacted with L. donovani. RNA was isolated from immunoprecipitated (IP) materials from normal and infected cell lysates, and miR-122 levels were quantified by real-time quantification and normalized against immunoprecipitated AGO2. Quantification data are the mean values obtained from three IP reactions. Western blot was used to detect AGO2 in immunoprecipitated materials. (D) Dicer1 levels in Leishmania-infected animal livers. Protein extracts were prepared from normal and infected mouse livers (15 or 60 days p.i.) and western blotted for Dicer1. Huh7 cells treated with L. donovani also showed reduction in DICER1 levels. (E) Exogenous expression of DICER1 inhibits L. donovani-mediated inhibition of miR-122 activity in Huh7 cells. Cells expressing RL reporters were transfected with plasmids encoding FLAG-DICER1, FLAG-HA-AGO2, or GFP, and the effects of L. donovani on miR-122 activity was scored. DICER1 overexpression was confirmed by western blot. (F) Unlike pmiR-122 overexpressed cells, cells transfected with miR-122 mimics can escape L. donovani-mediated repression of miR-122 activity. miR-122 repressive activity was measured in normal and L.donovani-interacting Huh7 cells expressing pre-miR-122 or miR-122 mimic. (G) DICER1 can be specifically cleaved by the Zn-metalloprotease present in the SLAs. Huh7 extracts were incubated with SLA in the presence and absence of Zn-chelator for 30 or 60 min at 37°C and were western blotted for HA-DICER1, AGO2, and DGCR8. β-actin was used as loading control. (H) L. donovani surface protease gp63 cleaves DICER1 and generates two fragments in vitro. Lysates of HEK293T cells expressing NHA-DICER1 were incubated with an increasing concentration of purified gp63 in the absence and presence of Zn-chelator, and cleaved product was visualized by western blot using an HA-specific antibody. It detected a shortened DICER1 band that was ∼180 KDa after cleavage of full-length protein by gp63. Digestion of FLAG-DICER1 also generated a 180 KDa fragment (marked by ∗). The N-terminal and short C-terminal half (marked by an arrowhead) of DICER1 were both detected with a DICER1-specific antibody. (I) Treatment with specific polyclonal and/or monoclonal antibody modify gp63 activity in vitro. Blocking of gp63 with a polyclonal antibody raised against the recombinant protein reduces DICER1 cleavage activity. Anti-GRP78 antibody was used as control (upper panel). Pretreatment of gp63 against a monoclonal antibody augments its activity in DICER1 cleavage assay (lower panel). Anti-GFP antibody was used as control. The arrowhead denotes a secondary cleaved product increased in the presence of anti-gp63 monoclonal antibody. (J) The cleavage of AGO2-associated NHA-DICER1 by gp63 and its effect on pre-miRNA processing. Extracts of HEK293 stably expressing FLAG-HA-AGO2 and transfected with NHA-DICER1 were digested with purified gp63 and subsequently FLAG-HA-AGO2 was immunoprecipitated. FLAG-HA-AGO2-associated DICER1 was detected by western blot, and pre-miR-122 processing activities associated with immunoprecipitated materials were quantified. ∗∗ denotes the pre-miR-122 substrate; # denotes the mature miR-122 formed; WB, western blot. Data represent mean ± SEM. See also Figure S4.
Figure 6
Figure 6
Restoration of Dicer1 Expression Rescues Serum Cholesterol Levels and Lowers Hepatic Parasite Load in L.donovani-Infected Mouse Livers (A) Dicer1 expression in L. donovani-infected mouse liver. Expression of NHA-DICER1 in the livers of control or infected (30 days p.i.) L. donovani BALB/c mice three days postinjection of NHA-DICER1 expression plasmid through tail vein. (B) Increase of gp63 in infected mouse liver extracts western blotted for gp63. (C) Effects of liposomal delivery of gp63 on miR-122 activity in Huh7 cells. Liposomal formulations with or without purified gp63 were delivered to cells expressing miR-122 reporter, and fold repression was calculated. (D) Treatment with gp63-containing liposomes delivers the protein to animal liver. Western blot detection of gp63 was done in liver lysates from control and liposome-treated animals using an anti-gp63 antisera. (E) Effect of gp63-containing liposomes on liver DICER1. Adult BALB/c mice were injected first with NHA-DICER1-expressing plasmids and then with liposomes (100 μl liposome suspension with or without 100 μg of purified gp63). Liver lysates were prepared after 24 hr of liposome injection and western blotted for NHA-DICER1. (F) Effect of L. donovani exosome treatment on the mouse liver DICER1 level. Adult BALB/c mice expressing NHA-DICER1 protein were injected through the intracardiac path with L. donovani exosomes secreted by 5 ×ばつ 107 parasites. After 24 hr of exosome treatment, liver lysates were prepared and western blotted for the NHA-DICER1. (G) Expression of NHA-DICER1 increases cellular Dicer levels in mouse livers. Schematic representation of protocol of NHA-DICER1 expression in BALB/c mice livers (upper panel). Endogeneous Dicer1 levels in both normal and NHA-DICER1 expression-plasmid-injected mouse livers after 3 days of plasmid injection (Lower panel). (H–J) NHA-DICER1 can prevent infection progression in mice. L. donovani-infected animals were injected with NHA-DICER1 expression plasmids and sacrificed as per the schedule in (G). Relative miR-122 expression (H), serum cholesterol level (I), and hepatic parasite load (J) were compared between NHA-DICER1 plasmids injected and control groups. For all experiments, n was either 4 or 6, and representative western blots were shown. For all western blot experiments β-actin was used as loading control. Data represent mean ± SEM. ∗∗∗p < 0.0001, ∗∗p < 0.001, ∗p < 0.01. See also Figure S5.

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