SUMMARY Genetic conservation allows ancient features of fat storage endocrine pathways to be explored in C. elegans. Multiple studies have used Nile red or BODIPY-labeled fatty acids to identify regulators of fat mass. When mixed with their food, E. coli bacteria, Nile red, and BODIPY-labeled fatty acids stain multiple spherical cellular structures in the C. elegans major fat storage organ, the intestine. However, here we demonstrate that, in the conditions previously reported, the lysosome-related organelles stained by Nile red and BODIPY-labeled fatty acids are not the C. elegans major fat storage compartment. We show that the major fat stores are contained in a distinct cellular compartment that is not stained by Nile red. Using biochemical assays, we validate oil red O staining as a method to assess major fat stores in C. elegans, allowing for efficient and accurate genetic and functional genomic screens for genes that control fat accumulation at the organismal level.

SummaryFat metabolism, reproduction, and aging are intertwined regulatory axes; however, the mechanism by which they are coupled remains poorly understood. We found that germline stem cells (GSCs) actively modulate lipid hydrolysis in Caenorhabditis elegans, which in turn regulates longevity. GSC arrest promotes systemic lipolysis via induction of a specific fat lipase. Subsequently, fat mobilization is promoted and life span is prolonged. Constitutive expression of this lipase in fat storage tissue generates lean and long-lived animals. This lipase is a key factor in the lipid hydrolysis and increased longevity that are induced by decreased insulin signaling. These results suggest a link between C. elegans fat metabolism and longevity.Abalance of fat storage and mobilization is a universal feature of animal physiology (1). Reproduction is an energy-intensive process, which is modulated by the availability of nutrients and in turn influences lipid metabolism (2). Reproductive ability declines with age, and many organisms undergo reproductive senescence (3). Obesity increases with age and is also associated with the transition to menopause in women (4). Genetic studies have suggested endocrine roles of adipose tissue and the reproductive system in regulation of life span (5-8). Thus, understanding the mechanisms by which fat metabolism is coupled to reproductive cues may reveal systemic regulation of fat metabolism and provide insights into the control of aging.In C. elegans, the energetic demands of progeny production are profound. The gonad undergoes many more mitoses than does somatic tissue, and the biomass of the oocytes produced is approximately equal to the biomass increase from egg to adult. Thus, in the absence of reproduction, a surfeit of available energy could lead to an increase in fat storage. To test this idea, we ablated the precursor cells of the germ line in C. elegans with the use of a laser microbeam. The vital dye Nile Red was used to visualize fat storage droplets in living animals (9). Opposite to the expected increase in fat storage, germ line-ablated animals stored 50% as much fat as untreated animals (Fig. 1, A to C). This finding suggested a regulatory mechanism coupling reproduction and fat metabolism.Fat storage is also aberrant in the sterile mutants glp-1(e2141ts) and glp-4(bn2ts), which are defective in germline proliferation (10,11). The glp mutants showed a 50% decrease in fat storage at the nonpermissive temperature relative to the wild type (N2) (Fig. 1, D to G). A similar decrease was observed by staining with a BODIPY-labeled fatty acid analog ( fig. S1)

Adaptation to nutrient scarcity depends on the activation of metabolic programs to efficiently use internal reserves of energy. Activation of these programs in abundant food regimens can extend life span. However, the common molecular and metabolic changes that promote adaptation to nutritional stress and extend life span are mostly unknown. Here we present a response to fasting, enrichment of ω-6 polyunsaturated fatty acids (PUFAs), which promotes starvation resistance and extends Caenorhabditis elegans life span. Upon fasting, C. elegans induces the expression of a lipase, which in turn leads to an enrichment of ω-6 PUFAs. Supplementing C. elegans culture media with these ω-6 PUFAs increases their resistance to starvation and extends their life span in conditions of food abundance. Supplementation of C. elegans or human epithelial cells with these ω-6 PUFAs activates autophagy, a cell recycling mechanism that promotes starvation survival and slows aging. Inactivation of C. elegans autophagy components reverses the increase in life span conferred by supplementing the C. elegans diet with these fasting-enriched ω-6 PUFAs. We propose that the salubrious effects of dietary supplementation with ω-3/6 PUFAs (fish oils) that have emerged from epidemiological studies in humans may be due to a similar activation of autophagic programs.