Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide. Up to one third of individuals with NAFLD will develop nonalcoholic steatohepatitis (NASH), which is associated with progression to cirrhosis and is rapidly becoming the leading indication for liver transplantation. Sarcopenia is defined as a progressive and generalized loss of skeletal muscle mass, strength, and function. It is observed in up to 60% of patients with end-stage liver disease and portends a poor prognosis. Recent studies have shown that sarcopenia is a novel risk factor for developing NAFLD. Pathophysiological mechanisms relating sarcopenia and NASH may include insulin resistance (IR) and increased inflammation. IR leads to accumulation of triglycerides in both muscle tissue and the liver. It also exacerbates proteolysis and leads to muscle depletion. Chronic inflammation leads to liver injury and progression of fibrosis. The inflammatory milieu also stimulates protein catabolism. Viewing skeletal muscle as an endocrine organ that secretes various salutary myokines may help us understand its role in the development of steatosis. A better understanding of the pathophysiology will aid in developing physical and pharmacological therapeutic interventions. In this review, we will explore the complex inter-relationships between sarcopenia and NASH. We will discuss the impact of sarcopenia in patients with NASH and therapeutic options for the management of sarcopenia. (Hepatology 2017;66:2055-2065).

Auditory sensory hair cells depend on stereocilia with precisely regulated lengths to detect sound. Since stereocilia are primarily composed of cross-linked, parallel actin filaments, regulated actin dynamics are essential for controlling stereocilia length. Here, we assessed stereocilia actin turnover by monitoring incorporation of inducibly expressed β-actin-GFP in adult mouse hair cells in vivo and by directly measuring β-actin-GFP turnover in explants. Stereocilia actin incorporation is remarkably slow and restricted to filament barbed ends in a small tip compartment, with minimal accumulation in the rest of the actin core. Shorter rows of stereocilia, which have mechanically-gated ion channels, show more variable actin turnover than the tallest stereocilia, which lack channels. Finally, the proteins ADF and AIP1, which both mediate actin filament severing, contribute to stereocilia length maintenance. Together, the data support a model whereby stereocilia actin cores are largely static, with dynamic regulation at the tips to maintain a critical length.

Sarcopenia and frailty are commonly encountered in patients with end‐stage liver disease and are associated with adverse clinical outcomes, including decompensation and wait‐list mortality. The impact of these entities in patients with differing disease etiologies has not been elucidated. We aim to ascertain the change in their prevalence over time on the wait list and determine their impact on hospitalization, delisting, and wait‐list survival, specifically for patients with nonalcoholic steatohepatitis (NASH) and alcoholic liver disease (ALD). Adult patients who were evaluated for their first liver transplant from 2014 to 2016 with a primary diagnosis of NASH (n = 136) or ALD (n = 129) were included. Computed tomography scans were used to determine the presence of sarcopenia and myosteatosis. Frailty was diagnosed using the Rockwood frailty index. Patients with NASH had a significantly lower prevalence of sarcopenia (22% versus 47%; P < 0.001) but a significantly higher prevalence of frailty (49% versus 34%; P = 0.03) when compared with patients with ALD at the time of listing. In patients with NASH, sarcopenia was not associated with adverse events, but a higher frailty score was associated with an increased length of hospitalization (P = 0.05) and an increased risk of delisting (P = 0.02). In patients with ALD, univariate analysis showed the presence of sarcopenia was associated with an increased risk of delisting (P = 0.01). In conclusion, sarcopenia and frailty occur with differing prevalence with variable impact on outcomes in wait‐listed patients with NASH and ALD.

Allograft steatosis is common, but not associated with survival or cardiovascular events in this study. Larger prospective studies are needed to better define the natural history of allograft steatosis.

Stereocilia are actin-based protrusions on auditory sensory hair cells that are deflected by sound waves to initiate the conversion of mechanical energy to neuronal signals. Stereocilia maintenance is essential because auditory hair cells are not renewed in mammals. This process requires both β-actin and γ-actin as knockout mice lacking either isoform develop distinct stereocilia pathology during aging. In addition, stereocilia integrity may hinge on immobilizing actin, which outside of a small region at stereocilia tips turns over with a very slow, months-long half-life. Here, we establish that β-actin and the actin crosslinking protein fascin-2 cooperate to maintain stereocilia length and auditory function. We observed that mice expressing mutant fascin-2 (p.R109H) or mice lacking β-actin share a common phenotype including progressive, high-frequency hearing loss together with shortening of a defined subset of stereocilia in the hair cell bundle. Fascin-2 binds β-actin and γ-actin filaments with similar affinity in vitro and fascin-2 does not depend on β-actin for localization in vivo. Nevertheless, double mutant mice lacking β-actin and expressing fascin-2 p.R109H have a more severe phenotype suggesting that each protein has a different function in a common stereocilia maintenance pathway. Since the fascin-2 p.R109H mutant binds but fails to efficiently crosslink actin filaments, we propose that fascin-2 crosslinks function to slow actin depolymerization at stereocilia tips to maintain stereocilia length.