Here's from mullet soldier on atrogin 1
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Great question!
I unfortunately do not have access to this full journal, so my commentary will be mostly speculative at this time. This being said, I will address the comments as best as possible.
As we see from the abstract, it appears that berberine extract-induced decreased muscle protein synthesis and increased muscle protein degradation is dependent on an increased expression of both atrogin-1, a key proteolytic gene present in a variety of catabolic states, and eIF3-f, a key component of the mTOR activation pathway. At first blush, this obviously appears to be indefensibly negative, as the atrogin-1 induction was not dependent upon the Atk/PI3K transcription pathway, and is thus entirely the result of berberine.
With that being said, we need to remember an important fact: these were diabetic mice. Insulin resistance is often associated with an increased in the activity of the ubiquitin-proteasome proteolytic pathway, and in particular, the expression of atrogin-1 to promote muscle atrophy. The mechanisms here are complex, but for a reference, the expression of both atrogin-1 and atrogin-1 transcription promoters have been shown to be increased by 15 fold in insulin resistant states."