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Nitric oxide inhibits expression of cytochrome B in endotoxin-stimulated murine macrophages
1Department of Surgery, Duke University Medical Center, Durham, North Carolina 27710, USA.
Abstract:
In LPS-mediated states of sepsis, inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production inhibit cellular respiration and mitochondrial electron transport. NO has been demonstrated to inhibit mitochondrial respiration by nitrosylation of the iron-sulfur centers of aconitase, complex I (NADH-ubiquinone oxidoreductase), complex II (succinate-ubiquinone oxidoreductase), and complex IV (cytochrome c oxidase). However, little is known of the effect of NO on expression of critical proteins in the electron transport chain. In ANA-1 murine macrophages, LPS-mediated NO synthesis decreases Cyt b protein expression and steady-state mRNA levels. Mitochondrial run-on analysis demonstrates unaltered Cyt b mitochondrial gene transcription. In this study utilizing LPS-stimulated ANA-1 murine macrophages, we demonstrate that expression of the mitochondrial protein, Cyt b, is significantly decreased as the result of a unique and previously unknown, NO-dependent posttranscriptional regulatory mechanism. (c)2001 Elsevier Science.
Insights
Sepsis-induced nitric oxide (NO) reduces mitochondrial protein Cyt b expression via a novel posttranscriptional mechanism. This impacts cellular respiration and electron transport chain function in macrophages.
Area of Science:
- Cellular Biology
- Biochemistry
- Immunology
Background:
- Sepsis involves inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production.
- NO inhibits mitochondrial respiration by nitrosylating key enzymes in electron transport chain complexes.
- The effect of NO on electron transport chain protein expression remains largely unknown.
Purpose of the Study:
- To investigate the impact of NO on the expression of mitochondrial proteins in LPS-stimulated macrophages.
- To elucidate the regulatory mechanism behind NO-mediated changes in mitochondrial protein expression.
Main Methods:
- Utilized ANA-1 murine macrophages stimulated with lipopolysaccharide (LPS).
- Assessed protein and mRNA levels of cytochrome b (Cyt b).
- Performed mitochondrial run-on assays to evaluate gene transcription.
Main Results:
- LPS-induced NO synthesis significantly decreased Cyt b protein expression in ANA-1 macrophages.
- Steady-state mRNA levels of Cyt b were also reduced.
- Mitochondrial run-on analysis indicated that Cyt b mitochondrial gene transcription remained unaltered.
Conclusions:
- NO-dependent posttranscriptional regulation significantly decreases mitochondrial Cyt b expression.
- A novel regulatory mechanism, independent of transcription, underlies NO's effect on Cyt b.
- This finding sheds light on NO's complex role in modulating mitochondrial function during sepsis.
