Paraoxonase 2 (PON2) attenuates macrophage triglyceride accumulation via inhibition of diacylglycerol acyltransferase 1 (DGAT1), the rate limiting enzyme in triglycerides biosynthesis

Mira Rosenblat, Raymond Coleman, Srinivasa T. Reddy, and Michael Aviram

Lipid Research Laboratory, Rambam Medical Center, Haifa 31096

Corresponding Author: aviram{at}tx.technion.ac.il

The present study questioned the role of paraoxonase2 (PON2) in attenuation of macrophage lipids accumulation. Mouse peritoneal macrophages (MPM) harvested from PON2-deficient mice vs. control C57BL/6 mice, were larger in size and filled with lipid droplets. Triglyceride (but not cholesterol) content in PON2-deficient vs. control MPM was significantly increased, by 4.6 fold. The extent of macrophage triglyceride biosynthesis was substantially increased, by 3.6 fold, in PON2-deficient vs. control MPM, whereas cellular triglyceride degradation rate was almost similar in both groups. Microsomal acyl CoA: diacylglycerol acyltransferase 1 (DGAT1), activity was significantly higher, by 4.4 fold, in PON2-deficient vs. control MPM, while DGAT1 mRNA and protein levels were similar in both groups. Microsomal DGAT1 activity and cellular triglyceride content were both significantly decreased, by 53% - 55%, in human PON2-transfected cells, as compared to control cells (transfected with the empty plasmid). Furthermore, incubation of PON2-deficient MPM with increasing concentrations of recombinant PON2, also significantly decreased DGAT1 activity, in a PON2 dose-dependent manner. DGAT1 has indeed a major role in triglyceride accumulation in PON2-deficient MPM, since the DGAT1 inhibitor oleanolic acid (50µM) significantly inhibited both DGAT1 activity and the extent of triglyceride biosynthesis in these cells (by 70%). In all the above experimental systems, PON2 decreased macrophage oxidative stress, as measured by lipid peroxides content. Finally, incubation of PON2-deficient MPM with the free radicals generator 2, 2'-amidinopropane hydrochloride (AAPH), increased cellular oxidative stress, and in parallel, increased DGAT1 activity (by 2.2 fold and 3.4 fold, respectively). Furthermore, incubation of microsomes from PON2-deficient MPM with superoxide dismutase (SOD) decreased DGAT1 activity by 40%. We thus conclude that PON2 attenuates triglyceride accumulation in macrophages via inhibition of microsomal DGAT1 activity, which appears to be sensitive to oxidative state.

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