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Lipoarabinomannan induced cytotoxic effects in human mononuclear cells
Abstract:
Mycobacteria produce large quantities of lipoarabinomannan, a cell wall associated glycolipid, which confers virulence in many of the disease causing members of the genus. We studied the lipoarabinomannan induced altered signaling mechanism in human peripheral mononuclear cells. Lipoarabinomannan isolated from Mycobacterium smegmatis (a non-pathogenic species) at concentrations of 2, 5 and 10 microg ml(-1) was used for the study. It was found that protein kinase C activity of human mononuclear cells was significantly inhibited by lipoarabinomannan at these concentrations in a dose dependent manner. Calcium, phosphatidyl serine and diglyceride dependent phosphorylation of endogenous proteins (mainly 90-, 80-, 66-, 38-, 36- and 34-kDa proteins) were also inhibited. Potentially cytotoxic superoxide anions generated by peripheral blood mononuclear cells were scavenged by lipoarabinomannan. It was also observed that incubation of peripheral blood mononuclear cells with lipoarabinomannan at concentrations of 5 and 10 microg ml(-1) for 6 h directed the cells towards apoptotic cell death, confirmed by DNA degradation analysis, microscopic observation of Wright-Giemsa as well as DAPI stained nuclei. These results clearly demonstrate that lipoarabinomannan from M. smegmatis may exert its cytotoxic activity via inhibition of protein kinase C, a key signaling molecule inside the mononuclear cells, which ultimately affects the phosphorylation of various proteins imperative for cellular defence and survival.
Insights
Lipoarabinomannan from Mycobacterium smegmatis inhibits protein kinase C activity in human mononuclear cells, leading to reduced cellular defense and potential apoptosis. This glycolipid impacts key signaling pathways essential for cell survival.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Mycobacteria synthesize lipoarabinomannan (LAM), a crucial cell wall glycolipid.
- LAM contributes to the virulence of pathogenic mycobacteria.
- Understanding LAM's interaction with host cells is vital for disease control.
Purpose of the Study:
- To investigate the effects of lipoarabinomannan (LAM) on signaling pathways in human peripheral mononuclear cells (PBMCs).
- To determine the mechanism by which LAM influences cellular functions and viability.
Main Methods:
- Human PBMCs were treated with purified LAM from Mycobacterium smegmatis at varying concentrations (2, 5, 10 μg/mL).
- Protein kinase C (PKC) activity and protein phosphorylation were assessed.
- Superoxide anion generation and apoptotic cell death (DNA degradation, microscopy) were analyzed.
Main Results:
- LAM significantly inhibited PKC activity in PBMCs in a dose-dependent manner.
- Phosphorylation of key endogenous proteins (90, 80, 66, 38, 36, 34 kDa) was reduced.
- LAM scavenged cytotoxic superoxide anions and induced apoptotic cell death at higher concentrations.
Conclusions:
- Mycobacterium smegmatis LAM exerts cytotoxic effects by inhibiting PKC, a critical signaling molecule.
- Inhibition of PKC disrupts essential protein phosphorylation, impairing cellular defense and survival mechanisms.
- LAM's impact on host cell signaling pathways highlights its role in mycobacterial pathogenesis.