Induction of the peroxisomal glycerolipid-synthesizing enzymes during differentiation of 3T3-L1 adipocytes - Role in triacylglycerol synthesis

The glycerophosphate backbone for triglyceride synthesis is commonly believ ed to be created through the conversion of dihydroxyacetone phosphate (DHAP ) by glycerophosphate dehydrogenase (GPD) to sn-glycerol 3-phosphate (GP), which is then converted by glycerophosphate acyltransferase (GPAT) to 1-acy l-GP. Consistent with this, GPD and GPAT are highly induced during differen tiation of mouse 3T3-L1 preadipocytes. While the acyl dihydroxyacetone phos phate (acyl-DHAP) pathway for glycerolipid synthesis is commonly believed t o be involved only in glycerol ether lipid synthesis, we report here that d uring conversion of 3T3 L1 preadipocytes to adipocytes, the specific activi ty of peroxisomal DHAP acyltransferase (DHAPAT) is increased by 9-fold in 6 days, while acyl-DHAP:NADPH reductase is induced by 5-fold. A parallel inc rease in the catalase (the peroxisomal marker enzyme) activity is also seen . In contrast, the specific activity of alkyl-DHAP synthase, the enzyme cat alyzing the synthesis of the ether bond, is decreased by 60% during the sam e period. Unlike microsomal GPAT, the induced DHAPAT is found to have high activity at pH 5.5 and is resistant to inhibition by sulfhydryl agents, hea t, and proteolysis, On subcellular fractionation, DHAPAT is found to be ass ociated with microperoxisomes whereas GPAT activity is mainly present in mi crosomes, Northern blot analyses reveal that induction of DHAPAT can be lar gely explained through increases in DHAPAT mRNA A comparison of microsomal and peroxisomal glycerolipid synthetic pathways, using D-[3-H-3, U-C-14]glu cose as the precursor of the lipid glycerol backbone shows that about 40 -5 0% of triglyceride is synthesized via the acyl-DHAP pathway. These results indicate that the acyl-DHAP pathway is important not only for the synthesis of ether lipids, but also for the synthesis of triacylglycerol and other n on-ether glycerolipids.