Pathological study of tubular aggregates occurring spontaneously in the skeletal muscles of non-obese diabetic/Cg-Prkdc^scidIl2rgt^m1sug/ShiJic (NOG) mice

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To examine the biological and morphological features of tubular aggregates (TAs) in the skeletal muscles of non-obese diabetic/Cg-Prkdc^scidIl2rgt^m1Sug/ShiJic (NOG) mice, 73 male and 72 female specific-pathogen-free NOG mice were examined at 7, 18, 22, 26, and 52 weeks of age. TAs were observed as intracytoplasmic eosinophilic materials of the femoral muscles in males at 18, 22, 26, and 52 weeks of age and in females at 52 weeks of age; gender-related differences were noted in the onset time and lesion degree. Intracytoplasmic materials were positive for Gomori’s trichrome stain. Electron microscopy revealed that TAs were composed of an accumulation of dilated sarcoplasmic reticulum. In addition, TAs were observed in the femoral and gastrocnemius muscles, but not in the soleus and diaphragm muscles, suggesting that TAs are present in fast muscle fibers. The morphology of TAs and the type of myofibers involved, as well as the gender difference in NOG mice were essentially the same as those of TAs observed in C57BL/6J and MRL+/+ mice.