Trypanosoma brucei Lipid Droplets: An Unexpected Link with Cell Morphology and Glucose Metabolism

Lipid droplets (LDs) are dynamic organelles formed from the ER that are involved in lipid storage and metabolism and membrane homeostasis. LDs vary in size and number, both of which increase upon growth in media supplemented with serum, free fatty acids, or myriocin, an inhibitor of sphingolipid biosynthesis known to increase lipid droplet formation in yeast and mammalian cells. The T. brucei genome lacks homologs to other known lipid droplet structural proteins (e.g. Perilipins, Seipins, Caveolins, etc.), hampering our ability to define the role of these organelles in T. brucei survival and pathogenesis. To purify T. brucei lipid droplets for proteomic analysis, we undertook a heterologous tagging approach using an amphipathic helix in human Perilipin 1 (PLIN1) sufficient to target GFP to yeast LDs, and an endogenous approach using TbErg6, a cholesterol biosynthetic enzyme known to localize to LDs in other organisms. Surprisingly, we found that over-expression of both the exogenous and endogenous LD targeting constructs resulted in dramatic cellular elongation and growth arrest. Control transfections support the idea that it is over-expression of LD-targeting proteins that results in elongation and growth arrest. This effect on growth and morphology could be reversed by transferring the elongated cells into extremely low glucose media. The elongated forms superficially resembled epimastigotes, a later developmental stage in the tsetse fly. However DAPI staining showed no anterior re-positioning of the mitochondrial DNA (kDNA), a hallmark of epimastigote differentiation, suggesting this phenotypic response may represent an abortive attempt at differentiation. Taken together, these results suggest the possibility of a link between LD homeostasis, glucose metabolism, and cell morphology.

Dr. Kimberly Paul, PhD, Assoc. Professor, Dept. of Genetics & Biochemistry Eukaryotic Pathogens Innovation Center (EPIC) Clemson University, South Carolina, USA

Clemson University

http://paullab.org/