Submitted on July 7, 2008
Revised on September 16, 2008
Accepted on October 6, 2008
ATTENUATION OF DEPRESSION OF MUSCLE PROTEIN SYNTHESIS INDUCED BY LIPOPOLYSACCHARIDE,TUMOUR NECROSIS FACTOR AND ANGIOTENSIN II BY 
-HYDROXY--METHYLBUTYRATE
Helen L Eley1, Steven T Russell1, and Michael J Tisdale2*
1 Aston University
2 Nutritional Biomedicine
* To whom correspondence should be addressed. E-mail: m.j.tisdale{at}aston.ac.uk.
-hydroxy--methylbutyrate (HMB) (50µM) has been shown to attenuate the depression in protein synthesis in murine myotubes in response to lipopolysaccharide (LPS) tumor necrosis factor-
(TNF-), with or without interferon-
(IFN-) and angiotensin II (Ang II). The mechanism for the depression of protein synthesis by all three agents was the same, and was attributed to activation of dsRNA-dependent protein kinase (PKR) with the subsequent phosphorylation of eukaryotic initiation factor 2 (eIF2) on the -subunit, as well as increased phosphorylation of the elongation factor (eEF2). Myotubes expressing a catalytically inactive PKR variant, PKR
6 showed no depression of protein synthesis in response to either LPS or TNF- confirming the importance of PKR in this process. There was no effect of any of the agents on phosphorylation of mammalian target of rapamycin (mTOR), or initiation factor 4E-binding protein (4E-BP1), and thus no change in the amount of eIF4E bound to 4E-BP1, or the concentration of the active eIF4E.eIF4G complex. HMB attenuated phosphorylation of eEF2, possibly by increasing phosphorylation of mTOR, and also attenuated phosphorylation of eIF2, by preventing activation of PKR. These results suggest that HMB may be effective in attenuating muscle atrophy in a range of catabolic conditions.
