The functional loss of ceramide metabolism enzymes ceramide synthase and acid sphingomyelinase on lipid metabolism and healthspan

Abstract

The increase in our aging population in combination with the growing incidence of late-life conditions presents a need for research on healthy aging. Here, we present work examining the roles of sphingolipid metabolism on aging. Sphingolipids play important roles in stress response, cell survival, cell signaling, and aging. Specifically, ceramide responds to oxidative stress and recruits apoptotic proteins to the cell membrane thereby causing cell cycle arrest. Furthermore, ceramide levels increase with age, making it an important lipid mediator of aging. The objective of this study is to examine the physiological role of ceramide metabolism on aging and lipid metabolism pathways in the roundworm, Caenorhabditis elegans. To assess these mechanisms, we utilized C. elegans’ mutants lacking acid sphingomyelinase (asm-3) and ceramide synthase (hyl-2) which we previously found to be long- and short-lived respectively. We performed a lipidomic analysis to explore longitudinal changes in lipid concentrations in wild type (N2), asm-3/acid sphingomyelinase, and hyl-2/ceramide synthase worms at 1, 5, and 10 days of age. Among our samples, we detected 700 different lipids that were abundant enough in concentration for analysis. Interestingly, 10 day old hyl-2 mutants, which have a reduced life-span, showed an increased concentration of eicosapentaenoic acid (EPA), an omega-3 fatty acid that has been shown to increase with longevity in worms. Conversely, asm-3 mutants, which are long-lived animals, have reduced levels of EPA. To expand upon our lipidomic data with enzymatic findings, we utilized RT-qPCR analysis to longitudinally analyze fatty acid desaturases (fat-1 and fat-4) involved in EPA metabolism in worms. We found that fat-4 expression is reduced in 1, 5, and 10 day hyl-2 animals, suggesting that ceramide metabolism may impact fatty acid genes involved in aging. Future work will examine the role of stress response genes including superoxide dismutase (sod-3) and fatty acid tail elongases (elo-5 and elo-6) in 1, 5, and 10 day old hyl-2 and asm-3 mutants. Finally, to expand upon the current knowledge of ceramide's role in lifespan, we present data on the RNAi mediated suppression of hyl-2 in long-lived mutants including mitochondrial respiration (clk-1/coenzyme Q), insulin-like signaling (daf-2/insulin-like receptor), and dietary starvation (eat-2/mAChR). Our goal is to identify whether ceramide metabolism works within these known pathways that mediate aging. With these assays, we hope to better understand the intrinsic biochemical lipid processes associated with ceramide metabolism in aging animals.