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Bioluminescence Imaging of NADPH Oxidase Activity in Different Animal Models
Published on: October 22, 2012
Null mutation of gp91phox reduces muscle membrane lysis during muscle inflammation in mice
Hal X Nguyen1, James G Tidball
1Departments of Physiological Science.
Abstract:
Muscle inflammation is a common feature in muscle injury and disease. Recently, investigators have speculated that inflammatory cells may increase or decrease muscle damage following modified muscle use, although there are few experimental observations to confirm either possibility. In the present study, a null mutation of gp91phox in neutrophils prevented superoxide production in cytotoxicity assays in which muscle cells were targets, and prevented most neutrophil-mediated cytolysis of muscle cells in comparison to wild-type neutrophils in vitro. We further tested whether deficiency in superoxide production caused a decrease in muscle membrane damage in vivo during modified muscle use. Gp91phox null mutant mice and wild-type mice were subjected to 10 days of muscle hindlimb unloading followed by reloading through return to normal locomotion, which induced muscle membrane lesions and muscle inflammation. Membrane lesions were quantified by measuring the presence of extracellular marker dye in reloaded soleus muscle fibres. There was a 90 % reduction in the number of fibres showing extensive membrane injury in gp91phox null mice compared to controls. Mutation of gp91phox did not change the concentration of neutrophils or macrophages in the reloaded muscle. Furthermore, muscle fibre growth during the reloading period was unaffected by the reduction in membrane injury. Together, these findings show that neutrophils can induce muscle membrane lysis through superoxide-mediated events, and indicate that superoxide-mediated membrane damage in vivo is not required for myeloid cell chemotaxis or muscle growth during muscle reloading.
Insights
Neutrophils cause muscle membrane damage via superoxide production during muscle reloading. Reducing this superoxide production significantly decreases muscle injury without affecting immune cell presence or muscle growth.
Area of Science:
- Muscle physiology
- Immunology
- Cellular biology
Background:
- Muscle inflammation is common in injury and disease.
- The role of inflammatory cells in modulating muscle damage is not fully understood.
- Neutrophils are implicated in inflammatory responses and tissue damage.
Purpose of the Study:
- To investigate the role of neutrophil-derived superoxide in muscle membrane damage during reloading after unloading.
- To determine if superoxide production is necessary for neutrophil-mediated muscle cell lysis in vitro and in vivo.
- To assess the impact of reduced superoxide production on immune cell infiltration and muscle growth.
Main Methods:
- Utilized gp91phox null mutant mice, which lack superoxide production in neutrophils.
- Assessed neutrophil-mediated cytolysis of muscle cells in vitro.
- Subjected mice to a hindlimb unloading-reloading model to induce muscle membrane lesions and inflammation.
- Quantified muscle membrane injury using an extracellular marker dye in soleus muscle fibers.
- Measured neutrophil and macrophage concentrations in reloaded muscle.
- Assessed muscle fiber growth during reloading.
Main Results:
- Neutrophil-specific gp91phox deficiency prevented superoxide production and reduced in vitro muscle cell lysis.
- Gp91phox null mice exhibited a 90% reduction in muscle membrane injury during reloading compared to wild-type controls.
- Superoxide production deficiency did not alter neutrophil or macrophage concentrations in the reloaded muscle.
- Reduced membrane injury did not affect muscle fiber growth during the reloading period.
Conclusions:
- Neutrophils induce muscle membrane lysis through superoxide-mediated mechanisms.
- Superoxide-mediated membrane damage is a significant contributor to muscle injury during reloading.
- Superoxide production by neutrophils is not essential for myeloid cell chemotaxis or muscle growth following unloading-induced injury.
