Dawn L. Brasaemle
Associate Professor

Biology of neutral lipid storage and release

The laboratory conducts pioneering research investigating the biochemistry and cell biology of lipid droplets. Lipid droplets are dynamic organelles that are found in nearly all mammalian cells, and serve a particularly vital function in adipocytes where they hold the body’s major energy reserves as triacylglycerols. Obesity is characterized by the excessive storage of triacylglycerols in adipocytes, and is a growing global health problem leading to increased prevalence of diabetes and cardiovascular disease in the human population. Despite a need for therapeutic options to control obesity, little is known about the intracellular mechanisms that regulate fat storage and release in adipocytes.

We are particularly interested in the role that structural lipid droplet-associated proteins within the PAT (perilipin, adipophilin, TIP47) family of proteins play in forming an organizing scaffold that regulates the access of lipid metabolic enzymes to stored neutral lipids. Perilipins are a family of polyphosphorylated proteins coating the surfaces of lipid droplets in adipocytes and steroidogenic cells of the adrenal gland, testes, and ovaries. In adipocytes, perilipins are required to maintain fat stores by controlling the rates of triacylglycerol turnover and release. Adipophilin (also called ADRP) and TIP47 are structurally related to perilipins, but are found on lipid droplets in many cell types throughout the body. A major project in the laboratory uses approaches of biochemistry and molecular and cellular biology to investigate the structural basis for perilipin function in controlling lipid droplet morphology and triacylglycerol storage and hydrolysis.

Figure 1. SDS-PAGE gel of lipid droplet-associated proteins from basal (left) and lipolytically stimulated (right) 3T3-L1 adipocytes.	Figure 2. CGI-58 associates with lipid droplets through an interaction with perilipin A in basal 3T3-L1 adipocytes.

Recent studies from our laboratory and others have shown that lipid droplets have a unique and dynamic protein composition (Figure 1). The identification of novel lipid droplet-associated proteins using proteomics technologies suggests that lipid droplets comprise a metabolically active pool of lipids that is used as a source of substrates for the production of energy, signaling molecules, and structural materials for membrane synthesis and repair.

Using proteomics, we have identified CGI-58 as a major component of adipocyte lipid droplets (Figure 2). Mutations in CGI-58 are respon­sible for a rare inherited neutral lipid storage disorder in humans, suggesting that CGI-58 plays a critical role in triacylglycerol metabolism. A second major project in the laboratory uses a variety of technologies including in vitro studies of recombinant proteins, RNAi approaches in cultured mammalian cells, and the characterization of transgenic mice to investigate the function of CGI-58 in triacylglycerol metabolism.

Finally, we are interested in further identification of novel lipid droplet-associated proteins and in studying the functions of these proteins.

Selected Publications

Brasaemle DL. (2007) Thematic review series: adipocyte biology. The perilipin family of structural lipid droplet proteins: stabilization of lipid droplets and control of lipolysis.
J Lipid Res. 48(12):2547-59. Review.

Brasaemle DL, Hansen JC. (2006) Developmental biology: holding pattern for histones.
Curr Biol. 16(21):R918-20.

Brasaemle DL, Wolins NE. (2006) Isolation of lipid droplets from cells by density gradient centrifugation. Curr Protoc Cell Biol. Chapter 3:Unit 3.15.

Wolins, N. E., Brasaemle, D. L., Bickel, P. E. (2006). A proposed model of fat packaging by exchangeable lipid droplet proteins. In press, FEBS Lett. 580:5484-5491.

Brasaemle, D. L. (2006). A metabolic push to proliferate. Science 313:1581-1582.

Marcinkiewicz, A., Gauthier, D., Garcia, A., and Brasaemle, D. L. (2006). Phosphorylation of serine 492 of perilipin A directs lipid droplet fragmentation and dispersion. J. Biol. Chem 281: 11901-11909.

Cohen, A. W., Schubert, W., Brasaemle, D. L., Scherer, P. E., and Lisanti, M. P. (2005). Caveolin-1 expression is essential for proper non-shivering thermogenesis in brown adipose tissue. Diabetes 54:679-686.

Garcia, A., Subramanian, V., Sekowski, A., Love, M., and Brasaemle, D. L. (2004). The amino and carboxyl termini of perilipin A facilitate the storage of triacylglycerol. J. Biol. Chem. 279: 8409-8416.

Cohen, A. W., Razani, B., Schubert, W., Williams, T. M., Wang, X. B., Iyengar, P., Brasaemle, D. L., Scherer, P. E., and Lisanti, M. P. (2004). Role of Caveolin-1 in the regulation of lipolysis and lipid droplet formation. Diabetes 53:1261-1270.

Subramanian, V., Rothenberg, A., Gomez, C., Cohen, A. W., Garcia, A., Bhattacharyya, S., Shapiro, L., Dolios, G., Wang, R., Lisanti, M. P., and Brasaemle, D. L. (2004). Perilipin A mediates the reversible binding of CGI-58 to lipid droplets in 3T3-L1 adipocytes. J. Biol. Chem. 279: 42062-42071.

Subramanian, V., Garcia, A., Sekowski, A., and Brasaemle, D. L. (2004). Hydrophobic sequences target and anchor perilipin A to lipid droplets. J. Lipid Res. 45:1983-1991.

Brasaemle, D. L., Dolios, G., Shapiro, L., and Wang, R. (2004). Proteomic analysis of proteins associated with lipid droplets in basal and lipolytically-stimulated 3T3-L1 adipocytes. J. Biol. Chem. 279:46835-46842.

Garcia, A., Sekowski, A., Subramanian, V., and Brasaemle, D. L. (2003). The central domain is required to target and anchor perilipin A to lipid droplets. J. Biol. Chem. 278:625-635.

Tansey, J. T., Huml, A. M., Vogt, R., Davis, K. E., Jones, J. M., Fraser, K. A., Brasaemle, D. L., Kimmel, A. R., and Londos, C. (2003). Functional studies on native and mutated forms of perilipins: A role in protein kinase A-activated lipolysis of triacylglcyerols in CHO cells. J. Biol. Chem. 278:8401-8406.

DiDonato, D., and Brasaemle, D. L. (2003). Fixation methods for the visualization of lipid droplets by immunofluorescence microscopy. J. Histochem. Cytochem. 51:773-780.

Cole, N. B., Murphy, D. D., Grider, T., Reuter, S., Brasaemle, D. L., and Nussbaum, R. L. (2002). Lipid droplet binding and oligomerization properties of the Parkinson’s disease protein a -synuclein. J. Biol. Chem. 277:6344-6352.

Wolins, N. E., Rubin, B., and Brasaemle, D. L. (2001). TIP47 associates with lipid droplets. J. Biol. Chem. 276:5101-5108.