Abstract
Elevated concentrations of sphingomyelinase (SMase) have been detected in a variety of diseases. SMase has been shown to increase muscle derived oxidants and decrease skeletal muscle force; however, the sub-cellular site of oxidant production has not been elucidated. Using redox sensitive biosensors targeted to the mitochondria and NADPH oxidase (Nox2), we demonstrate that SMase increased Nox2-dependent ROS and had no effect on mitochondrial ROS in isolated FDB fibers. Pharmacological inhibition and genetic knockdown of Nox2 activity prevented SMase induced ROS production and provided protection against decreased force production in the diaphragm. In contrast, genetic overexpression of superoxide dismutase within the mitochondria did not prevent increased ROS production and offered no protection against decreased diaphragm function in response to SMase. Our study shows that SMase induced ROS production occurs in specific sub-cellular regions of skeletal muscle; however, the increased ROS does not completely account for the decrease in muscle function.
Highlights
A variety of chronic diseases such as chronic heart failure (Doehner et al, 2007; Empinado et al, 2014), inflammatory disease (Wong et al, 2000), and sepsis (Okazaki et al, 2014) have been correlated with muscle weakness
Previous research has shown that SMase can induce either mitochondrial or Nox2 Reactive oxygen species (ROS) in non-muscle cells (Sawada et al, 2004; Reinehr et al, 2005) while recent indirect evidence suggests SMase induced ROS in skeletal muscle was generated by the mitochondria (Ferreira et al, 2012)
Using the general ROS probe, DCFH, and a Nox2-specific peptide inhibitor, we show that Nox2 plays a significant role in SMase induced ROS production
Summary
A variety of chronic diseases such as chronic heart failure (Doehner et al, 2007; Empinado et al, 2014), inflammatory disease (Wong et al, 2000), and sepsis (Okazaki et al, 2014) have been correlated with muscle weakness. SMase induced sphingolipid metabolism results in an increase in ceramide production which has been shown to decrease force production and increase fatigue and muscle atrophy (Ferreira et al, 2010, 2012; De et al, 2012; Empinado et al, 2014). Reactive oxygen species (ROS) have been shown to play a key role in modulating muscle function (Reid et al, 1993). In non-muscle cells, SMase has been shown to increase both mitochondrial and Nox2-dependent ROS (Sawada et al, 2004; Reinehr et al, 2005); while in skeletal muscle the mitochondria appear to be the primary source (Ferreira et al, 2012)
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