The goal of this study is to identify the key mechanisms through which branched chain amino acids (BCAAs; leucine, isoleucine and valine) modulate hepatic insulin sensitivity and mitochondrial function. Previous studies indicate a strong association between BCAAs and insulin resistance. Recent evidence points to crosstalk between BCAAs and hepatic mitochondrial function, which is disrupted during non-alcoholic fatty liver disease. Moreover, elevated levels of BCAAs during hepatic insulin resistance may be a good predictor of Type-2 Diabetes Mellitus (T2DM) onset. Based on these observations, we hypothesize that elevated
levels of BCAAs can disrupt insulin signaling in the liver and will alter hepatic mitochondrial metabolism and function. To test this hypothesis, mice were fed either a control diet (10% fat calories) or a high fat diet (60% fat calories) for 16 weeks. A jugular vein catheter was then implanted. After four days of recovery, a subset of mice from each group received either a saline or BCAA infusion for 8 hours. After the 8-hour infusion, blood and liver tissue were collected and frozen at -80C for metabolic analysis. Insulin signaling pathway was investigated by
examining serine/threonine-specific protein kinases total Akt and phosphorylated-Akt (p-Akt; S473) using western blotting. Expression of total Akt remained constant among all groups. In control-fed mice, BCAA infusion increased p-Akt expression, indicating that BCAAs impacted insulin signaling. High fat-fed mice infused with saline also showed elevated p-Akt compared to matched controls. In contrast, BCAAs in high fat-fed mice had no effect on Akt phosphorylation, demonstrating persistent stimulation to insulin signaling. Though elevated levels of BCAAs in the presence of a lipid-rich environment have been found to be linked to NAFLD and hepatic insulin resistance, their specific roles in these diseases are unclear. We analyzed the effects of BCAAs on diet-induced obese mice by comparing insulin signaling protein expression and modification. We discovered that BCAAs promoted insulin signaling in obese, insulin-resistant mice. Although BCAAs have an important role in regulating the tricarboxylic acid (TCA) cycle,
an overabundance of BCAAs in the presence of insulin resistance could weaken the normal response of the hepatic TCA cycle; a major factor in causing dysfunction in mitochondrial metabolism.