title: Differential effects of angiopoietin-like 4 in brain and muscle on regulation of lipoprotein lipase activity.
abstract: OBJECTIVE
  Lipoprotein lipase (LPL) is a key regulator of circulating triglyceride rich lipoprotein hydrolysis. In brain LPL regulates appetite and energy expenditure. Angiopoietin-like 4 (Angptl4) is a secreted protein that inhibits LPL activity and, thereby, triglyceride metabolism, but the impact of Angptl4 on central lipid metabolism is unknown.
  
  
  METHODS
  We induced type 1 diabetes by streptozotocin (STZ) in whole-body Angptl4 knockout mice (Angptl4(-/-) ) and their wildtype littermates to study the role of Angptl4 in central lipid metabolism.
  
  
  RESULTS
  In type 1 (streptozotocin, STZ) and type 2 (ob/ob) diabetic mice, there is a ~2-fold increase of Angptl4 in the hypothalamus and skeletal muscle. Intracerebroventricular insulin injection into STZ mice at levels which have no effect on plasma glucose restores Angptl4 expression in hypothalamus. Isolation of cells from the brain reveals that Angptl4 is produced in glia, whereas LPL is present in both glia and neurons. Consistent with the in vivo experiment, in vitro insulin treatment of glial cells causes a 50% reduction of Angptl4 and significantly increases LPL activity with no change in LPL expression. In Angptl4(-/-) mice, LPL activity in skeletal muscle is increased 3-fold, and this is further increased by STZ-induced diabetes. By contrast, Angptl4(-/-) mice show no significant difference in LPL activity in hypothalamus or brain independent of diabetic and nutritional status.
  
  
  CONCLUSIONS
  Thus, Angptl4 in brain is produced in glia and regulated by insulin. However, in contrast to the periphery, central Angptl4 does not regulate LPL activity, but appears to participate in the metabolic crosstalk between glia and neurons.
authors: Joslin Diabetes Center and Harvard Medical School, Boston, MA, USA.
authors: Sara Gry
authors: SG
authors: Vienberg
authors: Joslin Diabetes Center and Harvard Medical School, Boston, MA, USA.
authors: André
authors: A
authors: Kleinridders
authors: Joslin Diabetes Center and Harvard Medical School, Boston, MA, USA.
authors: Ryo
authors: R
authors: Suzuki
authors: Joslin Diabetes Center and Harvard Medical School, Boston, MA, USA.
authors: C Ronald
authors: CR
authors: Kahn
keywords: ARC, arcuate nucleus; AgRP, agouti-related protein; Angptl4; Angptl4, angiopoietin-like 4; CART, cocaine-and-amphetamine-regulated transcript; CNS, central nervous system; FFA, free fatty acid; LPL, lipoprotein lipase; Lipid metabolism; Lipoprotein lipase; NPY, neuropeptide-Y; POMC, pro-opiomelanocortin; STZ, streptozotocin; TG, triglyceride