Hepatic Sympathetic Denervation Reduces Non‐alcoholic Fatty Liver Disease in Diet‐Induced Obese Mice

Non‐alcoholic fatty liver disease (NAFLD), characterized by elevated liver triglycerides (i.e. hepatic steatosis), is directly associated with obesity and a significant contributor to chronic liver, metabolic, and cardiovascular diseases. We have recently demonstrated that hepatic sympathetic nerve activity is significantly elevated in mice that were fed a high fat diet (HFD), relative to normal chow controls (NC) (0.24±0.02 vs. 0.36±0.03 v*s/min, NC vs. HFD; p<0.05). These findings indicate a state of hepatic sympathetic overactivity during diet‐induced NAFLD; however, the role of the hepatic sympathetic nervous system in NAFLD pathology remains unknown. Therefore, we tested the hypothesis that selective removal of hepatic sympathetic nerve activity would rescue obesity‐induced NAFLD. Male C57B1/6 mice were fed a high fat diet (60% fat) or normal chow (5% fat) for 10 weeks. Liver sympathetic denervation was performed by applying 10% phenol in ethanol to the hepatic nerve bundle, whereas saline was used as a sham control. Metabolic indices were monitored using indirect calorimetry for 7 days after surgery and mice were then sacrificed. Hepatic denervation did not influence body mass (28±1 vs. 27±1 vs. 37±2 vs. 35±2 g, NC Sham vs. NC Denervation vs. HFD Sham vs. HFD Denervation; p<0.05 between NC and HFD, p>0.05 between Sham vs. Denervation), caloric intake, water consumption, metabolic rate, and ambulatory activity in NC or HFD mice. Similarly, inguinal, abdominal, gonadal, and subscapular brown adipose tissue masses were not influenced by removal of the hepatic sympathetic nerves. As expected, HFD feeding resulted in significant elevations in hepatic triglyceride levels, when compared to NC (2.4±0.5 vs. 6.4±0.6 nmol/mg of liver tissue, NC Sham vs. HFD Sham; p<0.05). Following liver denervation, hepatic steatosis was partially reduced in HFD fed mice back towards normal chow levels (2.4±0.4 vs. 4.5±0.7 nmol/mg of liver tissue, NC Sham vs. HFD Denervation; p>0.05). In line with this, histological examination (H&E staining) revealed widespread and severe lipid accumulation in the liver of HFD sham animals, which was reduced following liver denervation ( Figure). Interestingly, real time PCR analysis revealed that liver denervation in obese mice was associated with a reduction in markers of hepatic free fatty acid uptake (e.g. FAT/CD36 , 8.2±1.6 vs. 2.8±0.6 fold NC sham group; HFD Sham vs. HFD Denervation; p<0.05) and gluconeogenesis (e.g. G6Pase , 23.1±5.3 vs. 9.2±2.7 fold NC sham group; HFD Sham vs. HFD Denervation; p=0.15). Examination of tissue norepinephrine levels, as an indicator of sympathetic nerve activity, confirmed an ~70% reduction in the liver (1.0±0.25 vs. 0.3±0.13 relative to sham; HFD Sham vs. HFD Denervation; p<0.05), but not in organs that are also innervated by the mesenteric and celiac ganglia including the pancreas, spleen, and kidney (p>0.05 for all). Collectively, these findings demonstrate that selective ablation of hepatic sympathetic nerve activity partially ameliorates hepatic steatosis in diet‐induced obesity, independent of changes in body weight, food intake and adiposity. Moreover, these data suggest that targeting hepatic sympathetic overactivity may provide a novel therapeutic strategy to treat NAFLD. Support or Funding Information NIH HL116776Liver hematoxylin and eosin (H&E) staining following liver denervation or sham surgery in NC and HFD mice. Scale bar = 100 μm.