SINGLE MUSCLE FIBER PROTEOMICS REVEALS UNEXPECTED MITOCHONDRIAL SPECIALIZATION

To perform their diverse tasks, skeletal muscles employ four different fiber types, one type 1/slow and three different type 2/fast fibers. These multinucleated cellular units are characterized by different contractile and metabolic properties and can be combined in muscles in a dynamic way resulting in muscle plasticity. To dissect the composite and plastic metabolic properties of skeletal muscle we have developed a high sensitivity workflow based on liquid chromatography/mass spectrometry-based shotgun proteomics optimized for low abundant and high dynamic range samples. Using this procedure in mouse soleus and EDL muscles, we have obtained not only the quantification of single fiber proteomes but even of different segments of the same fiber. Our data indicate that the four fiber types significantly differ in the expression of structural and regulatory proteins which are likely to contribute to their specific physiology. In particular, specialization of mitochondria within the oxidative subset of muscle fibers emerged as one of the prominent insights revealed by this analysis, highlighting fiber type-specific patterns in the utilization of metabolic intermediates. As the single cell proteomics analysis performed here is rapid and robust, it can be applied to a wide variety of physiological and pathological conditions.