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Lipopolysaccharide and phorbol 12-myristate 13-acetate both impair monocyte differentiation, relating cellular
S Basta1, S Knoetig, A Summerfield
1Institute of Virology and Immunoprophylaxis, Mittelhäusern, Switzerland.
Abstract:
Both lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA) impeded monocyte to macrophage differentiation with respect to typical phenotypic modulation and certain phagocyte-related processes. The down-regulation of the porcine monocyte marker SWC1, and up-regulation of the SWC9 macrophage marker were retarded, but not inhibited, as was the differentiation-associated down-regulation of p53 and myeloperoxidase. Despite this clear impairment of macrophage differentiation, not all cellular functions were equally susceptible. Both agents inhibited phagocytosis, but not low-density lipoprotein receptor-associated endocytosis. Only LPS inhibited tartrate-resistant acid phosphatase up-regulation. In contrast, increase of vacuolar acidification rates was more susceptible to PMA. The activity of certain endosomal/lysosomal enzymes - esterase, nucleotidase, peroxidase and cathepsins - was generally enhanced by both LPS and PMA. This contrasted with autophagosomal activity, detected through the induction of an antiviral state. Disruption of autophagosomes and lysosomes (methionine-O-methyl ester), but not lysosomes alone (glycyl-L-phenylalanine) reversed LPS-induced inhibition of virus replication, without influencing the PMA-induced antiviral effect. Thus, PMA is similar to LPS in inhibiting monocyte to macrophage differentiation, when primary blood monocytes are employed, but not all pathways are equally susceptible. The analyses demonstrate that the pathways modulated during monocyte differentiation function somewhat independently. Moreover, certain functions of monocytic cells are more important with respect to the outcome of virus infection, with autophagosomal activities in particular favouring cell survival.
Insights
Lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA) hinder monocyte to macrophage differentiation, affecting cellular functions differently. Autophagosomal activity particularly influences virus infection outcomes and cell survival.
Area of Science:
- Immunology
- Cell Biology
Background:
- Monocyte to macrophage differentiation is crucial for immune responses.
- Lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA) are known modulators of immune cell function.
Purpose of the Study:
- To investigate the differential effects of LPS and PMA on monocyte to macrophage differentiation.
- To determine the susceptibility of various cellular functions to LPS and PMA during differentiation.
- To elucidate the role of autophagosomal activity in viral infection outcomes.
Main Methods:
- Primary blood monocytes were treated with LPS or PMA to induce or inhibit differentiation.
- Phenotypic markers (SWC1, SWC9), enzyme activities (p53, myeloperoxidase, acid phosphatase), and endocytic/lysosomal/autophagosomal functions were assessed.
- Virus replication and antiviral state induction were monitored to evaluate autophagosomal activity.
Main Results:
- Both LPS and PMA impeded typical monocyte to macrophage differentiation markers and phagocyte functions.
- Cellular functions exhibited differential susceptibility; phagocytosis was inhibited, but not low-density lipoprotein receptor-associated endocytosis.
- LPS and PMA differentially affected specific enzyme upregulations and vacuolar acidification.
- Endosomal/lysosomal enzyme activity was generally enhanced, contrasting with autophagosomal activity.
- Autophagosomal activity, but not lysosomal activity alone, influenced LPS-induced inhibition of virus replication.
Conclusions:
- LPS and PMA similarly inhibit monocyte to macrophage differentiation but affect cellular pathways independently and to varying degrees.
- Autophagosomal activity plays a significant role in cell survival during viral infections.
- Understanding these independent pathways is key to comprehending monocytic cell function in disease.