Molecular Raman signatures of fiber types in mouse soleus muscle

Muscle fiber types perform distinct functions within skeletal muscle tissue, enabling a wide range of physical and motor capabilities. Although specific fiber types are well characterized by their Myosin Heavy Chain isoform expression, it is highly informative to investigate these cells using further approaches. In this context, Raman spectroscopy represents a powerful tool for molecular discovery. Here, we characterized the Raman spectroscopic signatures of Type I, IIa, and IIx skeletal muscle fibers in the mouse soleus. Specific bands associated with amino acids such as tryptophan, phenylalanine, tyrosine, and the Amide I band are the main drivers of the observed variation. Interestingly, distinct spectral intensities and peak ratios particularly within the 1350 cm^-1 region and 1550-1750 cm^-1 range clearly differentiated Type I from Type IIa/IIx fibers. Principal Component Analysis further revealed that most of the observed variation is driven by changes near ∼1600 cm^-1. Overall, the detection of these spectral patterns provides valuable insights into the biochemical characteristics of muscle fibers and highlights the potential of Raman spectroscopy to identify fiber-type-specific signatures under various physiological and pathological conditions, including atrophy, hypertrophy, and sarcopenia.