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Changes in energy metabolism, structure and function in alveolar macrophages under anaerobic conditions
Abstract:
To determine whether the change in energy metabolism of guinea-pig alveolar macrophages (AM) would alter their function to resemble peritoneal macrophages (PM), AM were exposed to strict anaerobic environments for 96 h. Exposure of cultivated AM to hypoxic conditions resulted in a decreased activity of cytochrome oxidase, a key enzyme in oxidative phosphorylation, whereas pyruvate kinase activity, a key enzyme in glycolysis, increased to levels observed in PM. Under hypoxic conditions the total mitochondrial structure available for respiratory activity also decreased in the glycolytic energy-dependent AM. Accompanying the shift in energy metabolism, adaptive changes in the functional responses of lectin-receptor activity occurred in the AM exposed to hypoxic conditions. Culture of AM in an anaerobic environment led to a loss in their ability to mobilize their lectin receptors in response to cytochalasin B, whereas AM maintained in an aerobic environment could mobilize their receptors in response to either cytochalasin B and D. Alterations in O2 tension affect AM metabolism, morphology and function and indicate that the AM is able to change its energy metabolism according to environmental circumstances.
Insights
Guinea-pig alveolar macrophages (AM) shifted their energy metabolism from oxidative phosphorylation to glycolysis under anaerobic conditions. This metabolic change altered AM function, impacting lectin-receptor activity and resembling peritoneal macrophages (PM).
Area of Science:
- Cellular Biology
- Immunology
- Metabolic Biochemistry
Background:
- Alveolar macrophages (AM) typically rely on oxidative phosphorylation for energy.
- Peritoneal macrophages (PM) exhibit a more glycolytic energy metabolism.
- The functional and metabolic differences between AM and PM are not fully understood.
Purpose of the Study:
- To investigate if altering AM energy metabolism to a glycolytic state changes their function.
- To determine if AM can adapt their metabolic pathways in response to environmental cues.
- To compare the functional responses of AM under hypoxic versus aerobic conditions.
Main Methods:
- Cultured guinea-pig AM were exposed to strict anaerobic (hypoxic) environments for 96 hours.
- Enzyme activities of cytochrome oxidase (oxidative phosphorylation) and pyruvate kinase (glycolysis) were measured.
- Mitochondrial structure was assessed under varying oxygen tensions.
- Lectin-receptor mobilization in response to cytochalasin B and D was analyzed.
Main Results:
- Hypoxic exposure decreased cytochrome oxidase activity and increased pyruvate kinase activity in AM, mimicking PM metabolism.
- Mitochondrial structure decreased in AM under hypoxic conditions.
- AM in anaerobic environments lost the ability to mobilize lectin receptors in response to cytochalasin B, unlike aerobically maintained AM.
Conclusions:
- Oxygen tension significantly affects AM metabolism, morphology, and function.
- AM can adapt their energy metabolism from oxidative phosphorylation to glycolysis when exposed to anaerobic environments.
- This metabolic adaptation leads to functional changes in AM, including altered lectin-receptor activity.