DO‐SRS imaging of diet regulated metabolic activities in Drosophila during aging processes

Abstract

Lipid metabolism plays crucial roles during aging processes, but how it is regulated by diets and how it interplays with aging still remain unclear. We proposed a new optical imaging platform by integrating heavy water (D 2 O) probing with stimulated Raman scattering (DO‐SRS) microscopy, for the first time, to directly visualize and quantify lipid metabolism regulated by different diets and insulin signaling pathway in Drosophila fat body during aging. We found that calorie restriction, low protein diet, and (moderately) high protein and high sucrose diets enhanced lipid turnover in flies at all ages, while (moderately) high fructose and glucose diets only promoted lipid turnover in aged flies. The measured lipid turnover enhancements under diverse diets were due to different mechanisms. High protein diet shortened the lifespan while all other diets extended the lifespan. Downregulating the insulin signaling pathway enhanced lipid turnover, which is likely related to lifespan increase, while upregulating insulin signaling pathway decreased lipid turnover that would shorten the lifespan. Our study offers the first approach to directly visualize spatiotemporal alterations of lipid turnover in aging Drosophila in situ, for a better understanding of the interconnections between lipid metabolism, diets, and aging.

Super-resolution stimulated Raman Scattering microscopy with A-PoD

“…Both groups showed a positive correlation between LD size and metabolic activity, suggesting that larger LDs have higher metabolic activity. This result is consistent with our studies on Drosophila fatbody metabolic activity (45-47). Importantly, quantitative analyses of CD/CH 2 ratio showed that the average lipid turnover rate in the high glucose group was about 10 times higher than that in the control group, suggesting more newly synthesized lipids were accumulated in flies on high glucose diet (Fig.…”

Optical Metabolic Imaging Uncovers Sex- and Diet-dependent Lipid Changes in Aging Drosophila Brain

“…The general lipid loss in old brains was likely due to the reduction of lipid synthesis or misallocation of lipids in LDs. Our results demonstrated that the regulation of lipid storage in the brain is a highly dynamic process as that in the adipose tissue 18 , which is balanced between lipid synthesis and mobilization at LDs. The metabolic homeostasis resolved at the aging of single LDs might further determine the brain aging.…”

“…We first visualized de novo lipogenesis using D 2 O probing with SRS (DO-SRS) imaging. After feeding flies at different ages (0, 10, 20, 30, 40 days posteclosion) with 20% D 2 O-containing standard diets for 5 days, we imaged LDs in the brains (Figure S4A) and quantified lipids turnover rate by the ratio of CD signal (newly-synthesized lipids) to CH signal (total lipids) collected at 2143 cm -1 and 2850 cm -1 , respectively 17,18 . As shown in Figures 2B and 2C, the lipids turnover rate (CD/CH ratio) displays a bell-shaped curve in aging female and male flies.…”

“…To analyze the lipolysis in brain LDs, we utilized the starvation assay that facilitates the mobilization of the stored lipids. We treated 0-day (young) and 30-day old (aged) flies with 20% D 2 O for 10 days to obtain saturated deuterium incorporation (∼2.7%) for DO-SRS imaging (Figure S4B) 18 , and then transferred the flies to 1% agar for starvation. The CD/CH ratios in brain LDs were examined at 24, 48, and 72 h, respectively, after the transfer (Figures 2D-F).…”

“…In this study, we used heavy water (D 2 O)-probed stimulated Raman scattering (DO-SRS) imaging 17,18 to investigate brain lipid metabolism in female and male Drosophila aging brain. We found heterogeneous volumetric distribution of newly synthesized lipids in brain.…”