Research in the Fitzgerald laboratory centers on describing the molecular mechanisms by which cells traffic and export lipids, a process termed lipid efflux. To efflux lipids, evolution has provided large polytopic membrane proteins that move hydrophobic lipids out of membrane bilayers by hydrolyzing ATP . Named ABC transporters, human genetics shows that these proteins are critical for normal physiology and survival in the terrestrial environment. The ABCA subgroup is particularly important. Mutation of ABCA1 and ABCA4 respectively cause Tangier disease and Stargardt macular degeneration, two non-fatal but devastating conditions. ABCA3 mutations cause fatal neonatal respiratory distress, and ABCA12 mutations cause harlequin ichthyosis, a fatal scaling condition of the skin due to loss of the lipid permeability barrier.

The Tangier phenotype and ABCA1 are of great interest regarding cardiovascular disease, since mutation of ABCA1 disrupts lipid efflux and ablates circulating levels of high-density lipoprotein (HDL). Since high HDL levels correlate with a low risk of cardiovascular disease, and because Tangier patients and mice lacking ABCA1 are prone to atherosclerosis, agents that stimulate ABCA1 efflux hold promise as therapies to prevent lipid-driven vascular disease.

We use mass spectrometry to conduct proteomic and lipid profiling screens to identify factors that modulate ABCA1 activity and integrate this activity into the larger signaling networks that control cellular membrane and lipid biogenesis. The functional importance of candidate ABCA1 interacting proteins identified in these screens are vetted using mutational analysis, shRNA knockdown and in vivo mouse models of reverse cholesterol transport (see the abcam gene card below for the role of ABCA1 and other ABC transporter in the process of whole body lipid trafficking).

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Research Support

Grant # RO1 HL074136-01A1 (PI Fitzgerald, Michael, L.) NIH/NHLBI: 8/1/05-7/31/10 “ABCA1 cholesterol efflux and protein-protein interactions”

This grant has developed a proteomic approach to analyze ABCA1 protein-protein interactions that control the efflux activity of the transporter. Mass spectrometry screens have identified candidate interacting proteins that bind the C-terminus of the transporter affecting its distribution and efflux activity. The mechanistic details of these interactions are being further characterized and follow up screens are being conducted.

Grant_in_Aid # 09GRNT2260352 (PI, Fitzgerald, Michael L.) American Heart Association 7/1/2009-6/30/2012 “Analysis of an ABCA1/SPTLC1 Protein Complex That Negatively Regulates Cholesterol Efflux”

This grant explores how SPTLC1 interacts with ABCA1 versus its binding of the SPTLC2 subunit of the serine palmitoyltransferase holoenzyme. Additionally, in vivo experiments will be conducted to test whether the ability of the SPT inhibitor myriocin to inhibit atherosclerosis in mice correlates with its ability to disrupt the ABCA1/SPTLC1 protein complex.

Grant #1R24RR020345 (PI Freeman, Mason, W) NIH/NCRR: 7/1/06-5/31/10 “Analysis of ABCA Transporter Function in Homologous Recombinant Mice”

This animal resource grant provides funds for the generation and initial phenotype analysis of mice lacking poorly characterized ABCA transporters whose mutation in humans are associated with significant genetic diseases. As part of this funding mechanism the animals and other research reagents: antibodies; cDNA clones are made readily available to the research community. Role: Co-investigator

Foundation for Ichthyosis Research Grant Award: 9/1/08-8/31/10 “Analysis of a Mouse Gene Deletion Model for the Lamellar/Harlequin Ichthyosis ABCA12 Transporter”

This award funds work to phenotype a Abca12 null mouse model we have developed that recapitulates the severe HI phenotype, which is associated with a disruption of the skin’s lipid permeability barrier Role: Co-investigator

National Research Service Award HL10398 (Fitzgerald, Michael, L.) NIH/NHLBI Dates 7/1/00-7/31/02

The overall goals of this project were to I. Determine whether PDZ-domain proteins bind ABCA1, and if so whether such binding is important for the apoA1-efflux of intracellular cholesterol-ester stores II. Determine the cellular localization of ABCA1 during apoA1 cholesterol-efflux with respect to phosphorylation status and interactions with PDZ-proteins. Role: Principal Investigator