Raphael A. Zoeller, Ph.D.
Associate Professor of Physiology and Biophysics
B.S. University of Maine
Ph.D. Texas A&M University
Phone:(617) 638-4010 • Fax: (617) 638-4041
Cell and Membrane Biology
Lipids are not only structural units of membranes. They also participate in important cellular functions, serving as second messengers, hormones, pheromones and membrane anchors for proteins. Although several “active” lipid species have been identified, there are many others that remain undiscovered. To identify functional roles for lipids, we develop mutant animal cell lines that are deficient in the biosynthesis of specific lipid species. Using these mutants, we can determine what cellular processes are affected by the loss of the lipid, establishing a role for the lipid in that process. The mutants can also serve as tools for the isolation of the genes involved in the biosynthesis of the lipid. Most importantly, the study of these mutants leads to new biochemistry, not achievable through conventional approaches.
Plasmalogens: endogenous antioxidants. This “subclass” of phospholipids makes up approximately 18% of the phospholipids in humans and they are enriched in certain cell types or tissues including macrophages, neutrophils, brain and heart. Although their presence in mammalian tissue is well characterized, their role in cell function remained unclear. We developed a selection protocol to isolate mutant strains with defects in plasmalogen biosynthesis. Using these mutant strains, we have identified two phenotypes that are tied to the loss of plasmalogens. First, the plasmalogen-deficient cells are hypersensitive to reactive oxygen species (ROS) and this is reversed with the restoration of plasmalogens. This has lead to the suggestion that plasmalogens function as endogenous antioxidants. This may help to explain the rapid development of cataracts in the plasmalogen-deficient patients. The second phenotype associated with plasmalogen loss is a decrease in cholesterol transport.
Based on our findings using the mutants, we examined the possibility that plasmalogen levels could be increased in normal cells and if this would protect them under conditions in which ROS are formed. We found that supplementation of human endothelial cells with a plasmalogen biosynthetic precursor, hexadecylglycerol (HG) elevated plasmalogen levels 2-fold and protected them from damage due to oxidants. Importantly, this also protected these cells during chronic hypoxia, a physiologically relevant condition (Figure 1). This opens up the possibility of treatment of patients under conditions of chronic hypoxia such as pulmonary dysfunction. We are now attempting to determine the exact mechanism by which HG rescues these cells.
Mutants in global glycerolipid synthesis
The control of glycerolipid biosynthesis, including triacylglycerols is an area of intense interest, particularly with concerns about obesity and diabetes. Glycolysis is coordinated with and controls lipogenesis through mechanisms that are still poorly understood. We have developed a procedure for selecting mutants that are deficient in general glycerolipid biosynthesis in an effort to identify factors that are important for lipogenesis in animal cells. We have recently identified one mutant, named GroD1, that is defective in the synthesis of phosphatidylethanolamine (PE), phosphatidylcholine (PC) (Figure 2). These cells are also defective in the synthesis of triacylglycerols. This phenotype is due to a severe reduction in the activity of phosphatidate phosphohydrolase 1 (PAP1). Expression cloning of the gene responsible for this lesion has revealed a relationship between glycolysis and lipogenesis that was previously unknown. We are currently attempting to explain the mechanics of this relationship using the GroD1 cells. We are also screening for additional, novel mutants with additional lesions in glycerolipid biosynthesis to identify additional factors regulating this process.
Nakahara K, Ohkuni A, Kitamura T, Abe K, Naganuma T, Ohno Y, Zoeller RA and Kihara A (2012) The Sjögren-Larsson Syndrome Gene Encodes a Hexadecenal Dehydrogenase of the Sphingosine 1-Phosphate Degradation Pathway. Molecular Cell 46:461-71.
Krawczyk SA, Haller JF, Ferrante T, Zoeller RA, Corkey BE. (2012) Reactive Oxygen Species Facilitate Translocation of Hormone Sensitive Lipase to the Lipid Droplet During Lipolysis in Human Differentiated Adipocytes. PLoS ONE, 7: e349042012.
Haller JF, Krawczyk SA, Gostilovitch L, Corkey BE and Zoeller RA (2011) Glucose-6-phosphate isomerase deficiency results in mTOR activation, failed translocation of lipin 1α to the nucleus and hypersensitivity to glucose: Implications for the inherited glycolytic disease. Biochim Biophys Acta. 1812:1393-402.
Anbukumar, D.S., Shornick, L.P., Albert, C.J., Steward, M.M., Zoeller, R.A., Neumann, W.L., and Ford, D.A. (2010) Chlorinated lipid species in activated human neutrophils: Lipid metabolites of 2-chlorohexadecanal. J Lipid Res. 51:1085-1092.
Haller, J.F., Smith, C., Liu, D., Zheng, H., Tornheim, K., Han, G., Carman, G.M. and Zoeller, R.A. (2010) Isolation of novel animal cell lines defective in glycerolipid biosynthesis reveals mutations in glucose-6-phosphate isomerase. J. Biol. Chem. 285:866-877.
Gaposchkin, D. P., Farber, H. W. and Zoeller, R.A. (2008) On the importance of plasmalogen status in stimulated arachidonic acid release in the macrophage cell line RAW 264.7. Biochim Biophys Acta. 1781:213-219.
Zheng H, Duclos RI Jr, Smith CC, Farber HW, Zoeller RA. 2006. Synthesis and biological properties of the fluorescent ether lipid precursor 1-O-[9'-(1''-pyrenyl)]nonyl-sn-glycerol. J Lipid Res. 47: 633-642.
Liu D, Nagan N, Just WW, Rodemer C, Thai TP, Zoeller RA. 2005. Role of dihydroxyacetonephosphate acyltransferase in the biosynthesis of plasmalogens and nonether glycerolipids. J Lipid Res. 46:727-735
Zoeller RA, Grazia TJ, LaCamera P, Park J, Gaposchkin DP, Farber HW. 2002. Increasing plasmalogen levels protects human endothelial cells during hypoxia. Am J Physiol Heart Circ Physiol. 283: H671-679.
Zoeller RA, Lake AC, Nagan N, Gaposchkin DP, Legner MA, Lieberthal W. 1999. Plasmalogens as endogenous antioxidants: somatic cell mutants reveal the importance of the vinyl ether. Biochem J. 338: 769-776.
Department of Physiology and Biophysics
Boston University School of Medicine
700 Albany Street
Boston MA 02118-2526
Fax: (617) 638-4041