Project description:Phagocytosis requires the activation of a plethora of mechanisms that include the activation of the actin cytoskeleton guided by the Arp2/3 complex. These are promoted by activators such as the Wiskott Aldrich Syndrome Protein (WASP) family members. In order to further understand the molecular mechanisms involved in the early events leading the phagocytosis of the pathogenic Mycobacterium tuberculosis, we set out to examine potential roles of miRNAs in phagocytosis using genome-wide expression profiling to identify miRNAs differentially regulated following mycobacterial infection. One of the miRNAs activated upon infection of mouse macrophages with the non-pathogenic Mycobacterium smegmatis, the widely conserved miR-142-3p, was predicted and confirmed to target the Neural-WASP (N-WASP). Upregulating of miR-142-3p in mouse macrophages inversely correlated with levels of N-WASP, upon infection with live pathogenic and non-pathogenic mycobacteria, suggesting an active role of Mycobacterium tuberculosis on the regulation of phagocytosis, at the post-transcriptional level, in host cells. The reduction of N-WASP correlated with a reduced internalization of bacteria per macrophage, independently of the phagocytosis index. Furthermore, the downregulation of WASP levels accompanied those of N-WASP, at early but not at late time points, suggesting a closely regulatory mechanism among both family members, dependent on the time frame of the phagocytosis. Additionally, upregulating of miR-142-3p promoted the change in the protein levels of another predicted and confirmed target, the Cofilin2 protein, in a phagocytosis-independent fashion. Downregulation experiments promoted aberrant morphologic phenotypes in macrophages, similar to observed by others in PBMCs of humans with Wiskott Aldrich Syndrome, suggesting the strong involvement of miR-142-3p on the regulation of the actin machinery in macrophages. Altogether these results show for the first time that miRNAs are involved in the regulation of actin-mediated phagocytosis of pathogenic bacteria and that these are direct targets of Mycobacterium tuberculosis. Expression analysis of mouse macrophage cell line J774A.1 in response to infection with Mycobacterium smegmatis mc2155 EGFP. Three biological replicates each for uninfected and infected samples.

Project description:Mouse macrophages J774A.1 were pre-treated with the anti-inflammatory lipid eicosapenaenoic acid (EPA) or the pro-inflammatory lipid ceramide (Cer) for 3h. Macrophages were then infected with Mycobacterium smegmatis for 1h, and total RNA was collected. In a parallel experiment, infected macrophages were infected for 1h, 4h and 24h. At these time points, macrophages were lysed, bacteria was collected and quantified by the Colony Forming Units (CFU) Assay. This provided the kinetics of the killing of Mycobacteria inside mouse macrophages. CFU experiments revealed that cells pre-treated with EPA showed an increased number of bacteria inside macrophages, in contrast to cells pre-treated with Cer. To dissect the molecular mechanisms involved in the survival and killing of mycobacteria infected macrophages, mediated by lipids, gene expression studies were performed. Cultures of Mycobacterium smegmatis mc2155 harbouring a p19-(long lived) EGFP plasmid were grown to exponential growth phase. Bacteria were pelleted, washed in PBS and resuspended in medium DMEM with a multiplicity of infection (MOI) of 10 (10 bacteria per macrophage). Clumps of bacteria were removed by ultrasonic treatment of bacterial suspensions in an ultrasonic water bath for 15 minutes, followed by a low speed centrifugation for 2 minutes. Mouse macrophages J774A.1 were pre-.treated with the anti-inflammatory lipid eicosapenaenoic acid (EPA) or the pro-inflammatory lipid ceramide (Cer), 3h before infection. Mouse macrophages J774A.1 were infected with Mycobacterium smegmatis mc2155 for 1h, at 37M-BM-:C and 5% CO2. After 1h of infection, cells were washed with PBS. After washing, 1 ml Trizol was added per well, to collect total RNA. The experimental condition were: samples 1.1, 1.2, 1.3: Untreated macrophages; samples 2.1, 2.2, 2.3: Mock treated macrophages (ethanol 1ul/ml); samples 3.1, 3.2, 3.3: EPA (15uM) treated macrophages (ethanol 1ul/ml); samples 4.1, 4.2, 4.3: Cer (5ug/ml) treated macrophages (ethanol 1ul/ml); samples 5.1, 5.2, 5.3: Untreated macrophages, infected with Mycobacterium smegmatis mc2155 for 1h; samples 6.1, 6.2, 6.3: Mock treated macrophages (ethanol 1ul/ml) infected with Mycobacterium smegmatis mc2155 for 1h; samples 7.1, 7.2, 7.3: EPA (15uM) treated macrophages (ethanol 1ul/ml) infected with Mycobacterium smegmatis mc2155 for 1h; samples 8.1, 8.2, 8.3: Cer (5ug/ml) treated macrophages (ethanol 1ul/ml) infected with Mycobacterium smegmatis mc2155 for 1h; In a parallel experiment, infected macrophages remained with the bacteria for 1h, 4h and 24h after infection. After these time points, the macrophages were lysed, the bacteria was collected and quantified by the Colony Forming Units (CFU) Assay. This provided the kinetics of the killing of non-pathogenic intracellular bacteria inside mouse macrophages. For the CFU assay, after 1h of infection, cells were washed with PBS and Gentamicin (10ug/ml) in DMEM to kill the extracellular bacteria. At discrete time points, cells were washed with PBS and lysed with sterilized water. Quantitative cultures of bacteria were performed in a 10-fold serial dilutions, inoculated on 7H10 agar plates. 5ul were plated in triplicate and the number of colonies were counted after 48h.

Project description:Phagocytosis requires the activation of a plethora of mechanisms that include the activation of the actin cytoskeleton guided by the Arp2/3 complex. These are promoted by activators such as the Wiskott Aldrich Syndrome Protein (WASP) family members. In order to further understand the molecular mechanisms involved in the early events leading the phagocytosis of the pathogenic Mycobacterium tuberculosis, we set out to examine potential roles of miRNAs in phagocytosis using genome-wide expression profiling to identify miRNAs differentially regulated following mycobacterial infection. One of the miRNAs activated upon infection of mouse macrophages with the non-pathogenic Mycobacterium smegmatis, the widely conserved miR-142-3p, was predicted and confirmed to target the Neural-WASP (N-WASP). Upregulating of miR-142-3p in mouse macrophages inversely correlated with levels of N-WASP, upon infection with live pathogenic and non-pathogenic mycobacteria, suggesting an active role of Mycobacterium tuberculosis on the regulation of phagocytosis, at the post-transcriptional level, in host cells. The reduction of N-WASP correlated with a reduced internalization of bacteria per macrophage, independently of the phagocytosis index. Furthermore, the downregulation of WASP levels accompanied those of N-WASP, at early but not at late time points, suggesting a closely regulatory mechanism among both family members, dependent on the time frame of the phagocytosis. Additionally, upregulating of miR-142-3p promoted the change in the protein levels of another predicted and confirmed target, the Cofilin2 protein, in a phagocytosis-independent fashion. Downregulation experiments promoted aberrant morphologic phenotypes in macrophages, similar to observed by others in PBMCs of humans with Wiskott Aldrich Syndrome, suggesting the strong involvement of miR-142-3p on the regulation of the actin machinery in macrophages. Altogether these results show for the first time that miRNAs are involved in the regulation of actin-mediated phagocytosis of pathogenic bacteria and that these are direct targets of Mycobacterium tuberculosis.

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Acidic Lysine Acylations in Mycobacteria

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