Dynamic intracellular remodelling of lipoprotein-derived ceramide as a novel regulator of insulin signalling in skeletal muscles – LIPIDE

Insulin resistance (IR) plays a major role in the pathophysiology of type 2 diabetes (T2D) and is mediated by a phenomenon called lipotoxicity. With overweight, excess fatty acids (FA) accumulate in peripheral tissues like muscle, and are metabolized into sphingolipid derivatives such as ceramides (Cer). Cer are mainly synthesized de novo from a saturated FA (palmitate) to give different Cer species, depending on the length of the FA linked to the sphingosine by Cer synthases. C16:0 and C18:0-Cer are among the most active ceramide species to alter insulin sensitivity in skeletal muscles. While the role of de novo produced Cer is well established, extracellular Cer could act as cell-non-autonomous signals to alter muscle functions. C24Cer species, who do not have IR properties, when transported by low density lipoproteins (LDL) can exert a remote action on insulin signaling in myotubes by an unknown mechanism. The objective of this study will be to study the remote role and the mechanisms of action of these circulating LDL-C24Cer in the development of IR in myotubes. On the basis of our preliminary results, it seems that the C24Cer species transported in LDL act negatively on the muscle insulin response after their intracellular recycling into different ceramide species with insulin resistant functions. This project will combine biochemical and molecular approaches using lipidomic, deuterated precursors to follow Cer metabolism and adenovirus shRNA and CRISPR technology to analyse the signalling pathways involved in the metabolism and action of LDL-C24Cer. It will allow us to characterize the mechanisms by which circulating Cer accumulate in myotubes and to determine the role of Cer recycling in the effect of circulating Cer on the insulin response in muscle cells. This project could open up new perspectives to counteract the development of IR by better understanding the mechanisms involved in chronic exposure of cells to circulating Cer.