Skeletal muscle
atrophy is common across a variety of pathologies. Underlying mechanisms of
atrophy differ between pathologies, and in many conditions, circulating factors are tied to
muscle atrophy. Therefore, we sought to identify alterations to the plasma
proteome across divergent forms of
muscle atrophy, disuse and
cancer cachexia, as potential mediators of
atrophy. C57BL6/J mice were assigned to
Lewis Lung Carcinoma (LLC)-induced
cachexia, disuse by hindlimb unloading (HU), or control (CON). Plasma samples were submitted for discovery proteomics and targets of interest confirmed by immunoblot. Considerably more
peptides were altered in plasma from LLC (91) than HU (9) as compared to CON. Five total
proteins were similarly modulated in HU and LLC compared to CON, none reached criteria for differential expression. Serum
Amyloid A1 (SAA) was 4 and 6 Log2 FC greater in LLC than CON or HU, respectively, confirmed by immunoblot. Recent reports suggest SAA is sufficient to induce
atrophy via TLR. Therefore, we assessed TLR2,4, and
IL-6 mRNAs in hindlimb muscles. TLR mRNAs were not altered, suggesting SAA effects on
atrophy during LLC are independent of TLR signaling. However, we noted > 6-fold induction of
IL-6 in soleus of HU mice, despite minimal shift in the plasma
proteome, indicating potential localized
inflammation in atrophying muscle. Furthermore,
paraoxonase 1 (PON1) was highly repressed in LLC mice and largely undetectable by immunoblot in this group. Our data suggest SAA and PON1 as potential novel atrokines for
cancer cachexia and indicate localized
inflammation in atrophying muscles independent of the plasma
proteome.