Insights into lipid accumulation in skeletal muscle in dysferlin-deficient mice

Loss of dysferlin (DYSF) protein in humans results in limb-girdle muscular dystrophy 2B, characterized by progressive loss of muscles in the distal limbs with impaired locomotion. The DYSF-null (Bla/J) mouse develops severe steatotic muscles upon aging. Here, we report a marked increase in adipocytes, especially in the psoas and gluteus muscles but not in the soleus and tibialis anterior muscles in aged Bla/J mice compared with WT mice. There was a robust upregulation in the mRNA expression of enzymes involved in lipogenesis and triacylglycerol (TAG) synthesis pathways in the steatotic skeletal muscles. Lipidomic analysis of the steatotic skeletal muscles revealed an increase in several molecular species of TAG, although it is unclear whether it was at the expense of phosphatidylcholine and phosphatidylserine. The adipocytes in steatotic muscles were extramyocellular, as determined by the increased expression of caveolin 1 (a cellular marker for adipocytes) and lipid-droplet protein, perilipin 1. This increase in adipocytes occured as a consequence of the loss of myocytes.