Alterations in Autophagy and Mammalian Target of Rapamycin (mTOR) Pathways Mediate Sarcopenia in Patients with Cirrhosis

Abstract

The pathophysiology of sarcopenia in cirrhosis is poorly understood. We aimed to evaluate the histological alterations in the muscle tissue of patients with cirrhosis and sarcopenia, and identify the regulators of muscle homeostasis. Computed tomography images at third lumbar vertebral level were used to assess skeletal muscle index (SMI) in 180 patients. Sarcopenia was diagnosed based on the SMI cut-offs from a population of similar ethnicity. Muscle biopsy was obtained from the vastus lateralis in 10 sarcopenic patients with cirrhosis, and the external oblique in five controls (voluntary kidney donors during nephrectomy). Histological changes were assessed by hematoxylin and eosin staining and immunohistochemistry for phospho-FOXO3, phospho-AKT, phospho-mTOR, and apoptosis markers (annexin V and caspase 3). The messenger ribonucleic acid (mRNA) expressions for MSTN, FoxO3, markers of ubiquitin-proteasome pathway (FBXO32, TRIM63), and markers of autophagy (Beclin-1 and LC3) were also quantified. The prevalence of sarcopenia was 14.4%. Muscle histology in sarcopenics showed atrophic angulated fibers (P= 0.002) compared to controls. Immunohistochemistry showed a significant loss of expression of phospho-mTOR (P= 0.026) and an unaltered phospho-AKT (P= 0.089) in sarcopenic patients. There were no differences in the immunostaining for annexin-V, caspase-3, and phospho-FoxO3 between the two groups. The mRNA expressions of MSTN and Beclin-1 were higher in sarcopenics (P= 0.04 and P= 0.04, respectively). The two groups did not differ in the mRNA levels for TRIM63, FBXO32, and LC3. Significant muscle atrophy, increase in autophagy, MSTN gene expression, and an impaired mTOR signaling were seen in patients with sarcopenia and cirrhosis.