Very long-chain ceramides in skeletal muscle associate with systemic insulin resistance independent of obesity

Lipids are bioactive signaling molecules implicated in tissue-specific and whole-body insulin resistance, with ceramides and diacylglycerols (DAGs) as prominent species. Their precise roles remain unclear. Here, we leverage natural genetic variation in 399 male Diversity Outbred Australia (DOz) mice fed chow or a high-fat diet to examine the relationship between muscle lipids and insulin sensitivity. Fat mass was significantly associated with 55% of muscle lipid features and whole-body insulin sensitivity, with DAGs enriched in this association. To disentangle adiposity and muscle lipid contributions, we used: (1) linear models correcting lipid features for fat mass, and (2) insulin sensitivity quartiles within adiposity bins. Both approaches identified very long-chain ceramides, not DAGs, as linked to insulin resistance. RNA sequencing and proteomics from the same muscles associated these ceramides with cellular stress, mitochondrial dysfunction, and protein synthesis regulation. Meanwhile, DAGs correlated with leptin gene expression, suggesting an adipocyte, rather than myocyte, origin. These findings highlight very long-chain ceramides as key muscle lipids associated with insulin resistance, independent of adiposity. All samples are from quadriceps muscle from DOz mice fed chow diet ~18-20 weeks old.

脂质是一类具有生物活性的信号分子，与组织特异性及全身性胰岛素抵抗密切相关，其中神经酰胺（ceramides）与二酰基甘油（diacylglycerols, DAGs）是代表性的脂质种类。目前其确切作用尚未完全明确。本研究利用399只饲喂普通饲料或高脂饲料的澳大利亚远交群（Diversity Outbred Australia, DOz）雄性小鼠的自然遗传变异，探究肌肉脂质与胰岛素敏感性之间的关联。研究发现，脂肪量与55%的肌肉脂质特征及全身性胰岛素敏感性显著相关，且二酰基甘油（DAGs）在该关联中呈现富集特征。为厘清脂肪量与肌肉脂质各自的贡献，本研究采用两种分析策略：（1）构建校正脂肪量对脂质特征影响的线性模型；（2）按脂肪量分层后进行胰岛素敏感性四分位数分组。两种方法均鉴定出，与胰岛素抵抗相关的是超长链神经酰胺，而非二酰基甘油（DAGs）。对同一肌肉样本进行的RNA测序（RNA sequencing）与蛋白质组学（proteomics）分析显示，这类超长链神经酰胺与细胞应激、线粒体功能障碍及蛋白质合成调控存在关联。与此同时，二酰基甘油（DAGs）与瘦素基因表达呈正相关，提示其可能来源于脂肪细胞而非肌细胞。本研究结果表明，超长链神经酰胺是与胰岛素抵抗相关的关键肌肉脂质，且该关联不受脂肪量的影响。所有样本均取自饲喂普通饲料、月龄约18~20周的DOz小鼠的股四头肌。