The ESCRT-III Protein Chmp1 Regulates Lipid Storage in the Drosophila Fat Body

Abstract

Defects in how excess nutrients are stored as triglycerides can result in several diseases including obesity, heart disease, and diabetes. Understanding the genes responsible for normal lipid homeostasis will help understand the pathogenesis of these diseases. RNAi screens performed in Drosophila cells identified genes involved in vesicle formation and protein sorting as important for the formation of lipid droplets; however, all of the vesicular trafficking proteins that regulate lipid storage are unknown. Here, we characterize the function of the Drosophila Charged multivesicular protein 1 (Chmp1) gene in regulating fat storage. Chmp1 is a member of the ESCRT-III complex that targets membrane localized signaling receptors to intralumenal vesicles in the multivesicular body of the endosome and then ultimately to the lysosome for degradation. When Chmp1 levels are decreased specifically in the fly fat body, triglyceride accumulates while fat-body-specific Chmp1 overexpression decreases triglycerides. Chmp1 controls triglyceride storage by regulating the number and size of fat body cells produced and not by altering food consumption or lipid metabolic enzyme gene expression. Together, these data uncover a novel function for Chmp1 in controlling lipid storage in Drosophila and supports the role of the endomembrane system in regulating metabolic homeostasis.

Keywords: Chmp1; Drosophila; fat body; triglyceride.

Figure 1

Decreasing Chmp1 expression in the Drosophila fat body results in triglyceride accumulation. (A) Fat body Chmp1 expression, (B) μg triglyceride/μg protein levels and (C) food consumption over 24 h were measured in 1-week-old yolk-Gal4>Chmp1-RNAi females and compared to yolk-Gal4/+ controls. Bars indicate mean ± standard error. *, p < 0.05, **, p < 0.01 by Student’s t test.

Figure 2

Overexpressing Chmp1 in the Drosophila fat body blunts triglyceride storage. (A) μg triglyceride/μg protein levels and (B) food consumption over 24 h were measured in 1-week-old yolk-Gal4>Chmp1 females and compared to yolk-Gal4>GFP controls. Bars indicate mean ± standard error. ** p < 0.01 by Student’s t test.

Figure 3

Fat body Chmp1 regulates triglyceride storage but not by altering lipid metabolic enzyme gene expression. μg triglyceride/μg protein levels were measured in cuticles with fat bodies attached dissected from abdomens of 1-week-old female (A) yolk-Gal4>Chmp1-RNAi or (C) yolk-Gal4>Chmp1 flies and compared to those dissected from (A) yolk-Gal4/+ or (C) yolk-Gal4>GFP controls. qPCR was performed for FASN1, ATPCL, bmm, and whd in cuticles with fat bodies attached dissected from abdomens of 1-week-old female (B) yolk-Gal4>Chmp1-RNAi or (D) yolk-Gal4>Chmp1 flies and compared to those dissected from (B) yolk-Gal4/+ or (D) yolk-Gal4>GFP controls. Expression of all genes was normalized to rp49. Bars indicate mean ± standard error. **, p < 0.01 by Student’s t test.

Figure 4

Fat body Chmp1 regulates fat cell number. Fat body DNA content was measured in 1-week-old female (A) yolk-Gal4>Chmp1-RNAi flies and yolk-Gal4/+ controls and (B) yolk-Gal4>Chmp1 flies and yolk-Gal4>GFP controls. Bars indicate mean ± standard error. *, p < 0.05, **, p < 0.01 by Student’s t test.

Figure 5

Fat body Chmp1 regulates fat cell size. Total fat body protein normalized to DNA content was measured in 1-week-old female (A) yolk-Gal4>Chmp1-RNAi or (C) yolk-Gal4>Chmp1 flies and compared to (A) yolk-Gal4/+ or (C) yolk-Gal4>GFP controls. Fat body triglycerides normalized by total DNA were measured in 1-week-old female (B) yolk-Gal4>Chmp1-RNAi or (D) yolk-Gal4>Chmp1 flies and compared to (B) yolk-Gal4/+ or (D) yolk-Gal4>GFP controls. Bars indicate mean ± standard error. **, p < 0.01 by Student’s t test.