NADPH oxidase-derived reactive oxygen species increases expression of monocyte chemotactic factor genes in cultured adipocytes.

Abstract

Excess glucose and free fatty acids delivered to adipose tissue causes local inflammation, which contributes to insulin resistance. Glucose and palmitate generate reactive oxygen species (ROS) in adipocytes, leading to monocyte chemotactic factor gene expression. Docosahexaenoate (DHA) has the opposite effect. In this study, we evaluated the potential sources of ROS in the presence of excess nutrients. Differentiated 3T3-L1 adipocytes were exposed to palmitate and DHA (250 μM) in either 5 or 25 mM glucose to evaluate the relative roles of mitochondrial electron transport and NADPH oxidases (NOX) as sources of ROS. Excess glucose and palmitate did not increase mitochondrial oxidative phosphorylation. However, glucose exposure increased glycolysis. Of the NOX family members, only NOX4 was expressed in adipocytes. Moreover, its activity was increased by excess glucose and palmitate and decreased by DHA. Silencing NOX4 inhibited palmitate- and glucose-stimulated ROS generation and monocyte chemotactic factor gene expression. NADPH, a substrate for NOX, and pentose phosphate pathway activity increased with glucose but not palmitate and decreased with DHA exposure. Inhibition of the pentose phosphate pathway by glucose-6-phosphate dehydrogenase inhibitors and siRNA suppressed ROS generation and monocyte chemotactic factor gene expression induced by both glucose and palmitate. Finally, both high glucose and palmitate induced NOX4 translocation into lipid rafts, effects that were blocked by DHA. Excess glucose and palmitate generate ROS via NOX4 rather than by mitochondrial oxidation in cultured adipocytes. NOX4 is regulated by both NADPH generated in the PPP and translocation of NOX4 into lipid rafts, leading to expression of monocyte chemotactic factors.

• Authors: Chang Yeop Han, Tomio Umemoto, Mohamed Omer, Laura J Den Hartigh, Tsuyoshi Chiba, Renee LeBoeuf, Carolyn L Buller, Ian R Sweet, Subramaniam Pennathur, E Dale Abel, Alan Chait
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 287 Issue 13 Pg. 10379-10393 (Mar 23 2012) ISSN: 1083-351X [Electronic] United States
• PMID: 22287546 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Enzyme Inhibitors
• Monocyte Chemoattractant Proteins
• Reactive Oxygen Species
• Sweetening Agents
• Docosahexaenoic Acids
• Palmitic Acid
• NADPH Oxidase 4
• NADPH Oxidases
• Nox4 protein, mouse
• Glucose

Topics

• 3T3-L1 Cells
• Adipocytes (cytology, metabolism)
• Animals
• Docosahexaenoic Acids (pharmacology)
• Enzyme Inhibitors (pharmacology)
• Glucose (metabolism, pharmacology)
• Membrane Microdomains (enzymology, genetics)
• Mice
• Mitochondria (enzymology, genetics)
• Monocyte Chemoattractant Proteins (biosynthesis, genetics)
• NADPH Oxidase 4
• NADPH Oxidases (genetics, metabolism)
• Palmitic Acid (pharmacology)
• Pentose Phosphate Pathway (drug effects, physiology)
• Protein Transport (drug effects, physiology)
• Reactive Oxygen Species (metabolism)
• Sweetening Agents (metabolism, pharmacology)