Here we address whether FATP2 is 1) a peroxisomal enzyme, 2) a plasma membrane-associated long-chain fatty acid (LCFA) transporter, or 3) a multifunctional protein. We found that, in mouse livers, only a minor fraction of FATP2 localizes to peroxisomes, where it contributes to approximately half of the peroxisomal VLACS activity. However, total hepatic (V)LACS activity was not significantly affected by loss of FATP2, while LCFA uptake was reduced by 40%, indicating a more prominent role in hepatic LCFA uptake. This suggests FATP2 as a potential target for a therapeutic intervention of hepatosteatosis. Adeno-associated virus 8-based short hairpin RNA expression vectors were used to achieve liver-specific FATP2 knockdown, which significantly reduced hepatosteatosis in the face of continued high-fat feeding, concomitant with improvements in liver physiology, fasting glucose, and insulin levels. Based on our findings, we propose a model in which FATP2 is a multifunctional protein that shows subcellular localization-dependent activity and is a major contributor to peroxisomal

Non-alcoholic fatty liver disease is a serious health problem linked to obesity and type 2 diabetes. To investigate the biological outcome and therapeutic potential of hepatic fatty acid uptake inhibition, we utilized an adeno-associated virus-mediated RNA interference technique to knock down the expression of hepatic fatty acid transport protein 5 in vivo prior to or after establishing non-alcoholic fatty liver disease in mice. Using this approach, we demonstrate here the ability to achieve specific, non-toxic, and persistent knockdown of fatty acid transport protein 5 in mouse livers from a single adeno-associated virus injection, resulting in a marked reduction of hepatic dietary fatty acid uptake, reduced caloric uptake, and concomitant protection from diet-induced non-alcoholic fatty liver disease. Importantly, knockdown of fatty acid transport protein 5 was also able to reverse already established non-alcoholic fatty liver disease, resulting in significantly improved whole-body glucose homeostasis. Thus, continued activity of hepatic fatty acid transport protein 5 is required to sustain caloric uptake and fatty acid flux into the liver during high fat feeding and may present a novel avenue for the treatment of non-alcoholic fatty liver disease.The worldwide prevalence of non-alcoholic fatty liver disease (NAFLD) 2 is presently estimated at 30% of the general population and affects a majority of patients with obesity and type 2 diabetes (1, 2). In obese individuals, chronically elevated serum free fatty acids (FFAs) and high insulin levels lead to both increased FFA uptake by the liver and increased synthesis of lipids, resulting in hepatic triglycerides (TG) accumulation, typically accompanied by hepatic insulin desensitization (1, 3) involving protein kinase C ⑀ (3). Current pharmacological treatment strategies for NAFLD focus principally on increasing hepatic fatty acid oxidation (4) and improving extrahepatic insulin sensitivity (5). However, none of these treatment methods reduce hepatic uptake of dietary fats, and novel therapeutics that specifically aim at reversing NAFLD in the context of obesity would be highly desirable.Based on the premises that obesity-associated NAFLD is primarily driven by the continuous protein-mediated uptake of fatty acids by the liver and that NAFLD is a contributing factor to whole-body insulin desensitization, we argued that blocking proteins responsible for hepatic fatty acid uptake should prevent or reverse hepatic steatosis, thus improving insulin sensitivity and glucose homeostasis. Two members of the fatty acid transport protein (FATP) family, FATP2 and FATP5, are robustly expressed in liver (6) and are thought to be involved in the early steps of long-chain fatty acid uptake/activation (7,8). We recently demonstrated the importance of FATP5 in hepatic lipid metabolism by showing that deletion of FATP5 partially protected mice from developing high fat diet-induced obesity and improved insulin-sensitivity (9, 10).To explore the consequences of hepatic FATP5 ablation ...

Nonshivering thermogenesis in brown adipose tissue (BAT) generates heat through the uncoupling of mitochondrial ␤-oxidation from ATP production. The principal energy source for this process is fatty acids that are either synthesized de novo in BAT or are imported from circulation. How uptake of fatty acids is mediated and regulated has remained unclear. Here, we show that fatty acid transport protein (FATP)1 is expressed on the plasma membrane of BAT and is upregulated in response to cold stimuli, concomitant with an increase in the rate of fatty acid uptake. In FATP1-null animals, basal fatty acid uptake is reduced and remains unchanged following cold exposure. As a consequence, FATP1 knockout (KO) animals display smaller lipid droplets in BAT and fail to defend their core body temperature at 4°C, despite elevated serum free fatty acid levels. Similarly, FATP1 is expressed by the BATderived cell line HIB-1B upon differentiation, and both fatty acid uptake and FATP1 protein levels are rapidly elevated following isoproterenol stimulation. Stimulation of fatty uptake by isoproterenol required both protein kinase A and mitogen-activated kinase signaling and is completely dependent on FATP1 expression, as small-hairpin RNA-mediated knock down of FATP1 abrogated the effect. Diabetes 55:3229 -3237, 2006

Gallstone disease is a widespread disorder costing billions for annual treatment in the United States. The primary mechanisms underlying gallstone formation are biliary cholesterol supersaturation and gallbladder hypomotility. The relative contribution of these two processes has been difficult to dissect, as experimental lithogenic diets cause both bile supersaturation and alterations in gallbladder motility. Importantly, there is no mechanistic explanation for obesity as a major risk factor for cholelithiasis. We discovered that lithogenic diets induce ectopic triacylglycerol (TAG) accumulation, a major feature of obesity and a known muscle contraction impairing condition. We hypothesized that prevention of TAG accumulation in gallbladder walls may prevent gallbladder contractile dysfunction without impacting biliary cholesterol saturation. We utilized adeno-associated virus-mediated knock down of the long-chain fatty acid transporter 2 (FATP2; Slc27A2), which is highly expressed by gallbladder epithelial cells, to downregulate lithogenic diet-associated TAG accumulation. FATP2-knockdown significantly reduced gallbladder TAG, but did not affect key bile composition parameters. Importantly, measurements with force displacement transducers showed that contractile strength in FATP2-knockdown gallbladders was significantly greater than in control gallbladders following lithogenic diet administration, and the magnitude of this effect was sufficient to prevent the formation of gallstones. FATP2-driven fatty acid uptake and the subsequent TAG accumulation in gallbladder tissue plays a pivotal role in cholelithiasis, and prevention of this process can protect from gallstone formation, even in the context of supersaturated bile cholesterol levels, thus pointing to new treatment approaches and targets.

Aim The hormonally controlled mobilization and release of fatty acids from adipocytes into the circulation is an important physiological process required for energy homeostasis. While uptake of fatty acids by adipocytes has been suggested to be predominantly protein-mediated, it is unclear whether the efflux of fatty acids also requires membrane proteins. Methods We used fluorescent fatty acid efflux assays and colorimetric assays for free fatty acids and glycerol to identify inhibitors with effects on fatty acid efflux, but not lipolysis, in 3T3-L1 adipocytes. We assessed the effect of these inhibitors on a fibroblast-based cell line expressing fatty acid transport protein 1, hormone-sensitive lipase, and perilipin, that presumably lacks adipocyte-speicific proteins for fatty acid efflux. Results We identified DIDS as an inhibitor of fatty acid efflux that did not impair lipolysis or the cellular exit of glycerol, but lead to an accumulation of intracellular fatty acids. In contrast, fatty acid efflux by the reconstituted cellular model for fatty acid efflux was responsive to lipolytic stimuli, but insensitive to DIDS inhibition. Conclusion We propose that adipocytes specifically express an as yet unidentified DIDS sensitive protein that enhances the efflux of fatty acids and therefore may lead to novel treatment approaches for obesity-related disorders characterized by abnormal lipid fluxes and ectopic triglyceride accumulation.