Dietary polyunsaturated fatty acids (PUFA) are generally regarded as beneficial to human health. Obese humans with diabetes (NIDDM), metabolic syndrome (MetS) or non-alcoholic fatty liver disease (NAFLD), however, have low a low ratio of 20:4w6 relative to 18:2w6 in plasma and liver when compared to healthy individuals. This outcome implicates a problem with PUFA metabolism. While the linkage between PUFA metabolism and diabetic complications in humans is unclear, recent studies with diet-induced obese-diabetic mice have established a link between PUFA synthesis and diabetic complications. We reported that the activity of hepatic fatty acid elongase-5 (Elovl5), a key enzyme involved in PUFA synthesis, was suppressed in livers of diet-induced obese-diabetic C57BL/6J mice. Restoration of hepatic Elovl5 activity abrogated high fat diet-induced hyperglycemia, insulin resistance, and fatty liver in 4 days without changing body weight or appetite. The mechanism for the control of blood glucose was linked to the suppression of hepatic nuclear content of forkhead box O1 (FoxO1), a major transcription factor controlling gluconeogenesis (GNG). Elevated Elovl5 activity increased the phosphorylation and acetylation status of FoxO1 and attenuated the expression of genes involved in GNG, e.g., phosphoenolpyruvate carboxykinase and glucose-6 phosphatase. Preliminary studies show that Elovl5 controls FoxO1 phosphorylation through the mTorc2 (rictor)-Akt2 pathway. Moreover, elevated Elovl5 activity induced adipocyte triglyceride lipase (ATGL), comparative gene identification-58 (CGI58, ATGL co-activator) and short &long chain acylcarnitines in livers of obese mice. This outcome suggests Elovl5 activity controls hepatic triglyceride (TAG) by regulating TAG hydrolysis and fatty acid oxidation (FAO). Finally, elevated hepatic Elovl5 activity attenuated stress pathways ([ER-stress, XBP1 and ATF6];NFkB, Jnk &p38) and induced the anti-oxidant enzyme, i.e., hemeoxygenase-1 (HMOX1). Both ER- and oxidant stress control FoxO1 and GNG. This grant proposal will provide additional mechanistic insight to explain how hepatic PUFA synthesis controls FoxO1, GNG, TAG metabolism and stress pathways. Using cultured hepatocytes and obese-diabetic mice, Aim 1 will define how endogenously generated and exogenously supplied PUFA control hepatic FoxO1, GNG, TAG and stress pathways.
Aim 2 will establish the requirement for ATGL and CGI58 in the Elovl5 control of hepatic TAG &FoxO1, GNG and anti-oxidant-response pathways (HMOX1).
Aim 3 will establish the requirement for HMOX1 and other anti-oxidant enzymes in the Elovl5 control of FoxO1, GNG, ATGL, CGI58 and TAG. Defining the mechanistic linkage between PUFA synthesis, TAG hydrolysis, FoxO1, GNG &stress pathways will identify novel methods to manage diabetic complications, like hyperglycemia &fatty liver.

Public Health Relevance

Dietary polyunsaturated fatty acids (PUFA) are generally regarded as beneficial to human health and well being. Obese humans with diabetes, metabolic syndrome or non-alcoholic fatty liver disease have impaired PUFA metabolism. We have linked hepatic PUFA synthesis to the control of hepatic triglycerides and stress pathways that impact fasting blood glucose. Further study of this novel mechanism will lead to better methods to control hepatic metabolism and diabetic complications.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK094600-02
Application #
8434823
Study Section
Integrative Nutrition and Metabolic Processes Study Section (INMP)
Program Officer
Maruvada, Padma
Project Start
2012-04-01
Project End
2016-03-31
Budget Start
2013-04-01
Budget End
2014-03-31
Support Year
2
Fiscal Year
2013
Total Cost
$300,961
Indirect Cost
$91,073
Name
Oregon State University
Department
Nutrition
Type
Other Domestic Higher Education
DUNS #
053599908
City
Corvallis
State
OR
Country
United States
Zip Code
97339