Characterization of Neutral Sphingomyelinase Isoforms in Skeletal Muscle Mitochondria
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Skeletal muscle is composed of fiber types that differ in mitochondrial content, antioxidant capacity, and susceptibility to apoptosis. Ceramides have been linked to apoptosis by increasing mitochondrial permeability, a common hallmark of apoptotic signalling. The enzyme neutral sphingomyelinase (nSMase) generates ceramides by hydrolysing sphingomyelin. Despite the role of ceramides in mediating apoptosis, there is a gap in the literature regarding nSMase in skeletal muscle mitochondria. This study aimed to characterize activity and content of nSMase isoforms in isolated subsarcolemmal (SS) mitochondria from soleus, diaphragm, plantaris, and extensor digitorum longus (EDL). Total nSMase activity did not differ between isolated SS mitochondria. nSMase2 content was higher in SS mitochondria from EDL compared to soleus or diaphragm, and positively correlated to total nSMase activity in soleus. nSMase3 was undetectable in all samples, suggesting it is not associated with SS mitochondria, and likely does not contribute to total nSMase activity in SS mitochondria.