Liver transplantation arrests and reverses muscle wasting.

Muscle wasting, sarcopenia, is common in advanced cirrhosis and predicts adverse outcomes while awaiting and following liver transplantation. Frequent post-transplant worsening of sarcopenia has attracted recent interest. It is unknown whether this serious problem is an expected metabolic consequence of transplantation or results from confounding conditions such as recurrent allograft liver disease or avoidable post-transplant complications. To clarify this question, we studied pre- and post-transplant muscle mass in a retrospective cohort of 40 patients transplanted for three diseases - alcoholic cirrhosis, non-alcoholic steatohepatitis cirrhosis, and primary sclerosing cholangitis cirrhosis - in whom allograft disease recurrence was monitored and excluded, and who lacked common post-transplant muscle wasting complications such as sepsis, renal failure, ischemia, and cholestasis. We measured skeletal muscle index (SMI) using computed tomography before and 12-48 months after transplant. SMI as a categorical variable significantly improved, from 18 patients above the normal cutoff pre-transplant to 28 post-transplant (p = 0.008). SMI increases were greatest in patients with the lowest pre-transplant SMI (p < 0.01). As a continuous variable, mean SMI remained stable, with a non-significant trend toward improvement. We conclude that after liver transplantation sarcopenia does not progress but is arrested and frequently improves in the absence of confounding conditions.

Neutral endopeptidase is a myristoylated protein.

Neutral endopeptidase (NEP) is a cell-surface peptidase normally expressed by prostate epithelial cells and lost in ~50% of primary prostate cancers. NEP directly associates with multiple proteins at the cell surface including Ezrin/Radixin/Moesin (ERM) proteins and the PTEN tumor suppressor protein. Analysis of the N-terminal sequence of the NEP cytosolic domain (N-terminal MGKSESQMDI TDINTPKPKK KQRWTR) identified a myristoylation consensus site. Mutation of Gly-2 to Arg significantly decreased (3)H-myristoylation activity, and correlated with translocation of NEP from the plasma membrane to a perinuclear domain as demonstrated by immunofluorescence staining and Western blotting with an NEP-specific antibody. Removal of this myristoylation residue did not affect NEP enzymatic specific activity. Myristoylated NEP recruited more PTEN protein to the cell membrane fraction than unmyristoylated NEP. These data demonstrate that NEP is myristoylated at Gly-2 and that this modification is an intrinsic signal for membrane targeting.