FIGURE 1.

Ceramide inhibition with fenretinide protects insulin signaling. A, murine C2C12 myotubes were treated with 0.75 mm BSA-conjugated PA for 16 h in the presence or absence of FEN (5 μm) followed by 10 min of insulin treatment (100 nm). pAkt, phosphorylated Akt; pGSK3β, phospho-glycogen synthase kinase 3β; GSK3β, glycogen synthase kinase 3β. B and C, the readdition of C2-ceramide (100 μm) bypassed the protection offered by FEN (B), an effect seen with as little as 20 μm ceramide (C). D, the improvement in insulin signaling with FEN does not require RBP4 as C2C12 cells appear to lack the protein. E and F, although PA induces ceramide and dihydroceramide accumulation, FEN prevents ceramide synthesis (E), whereas accumulating dihydroceramides (F). *, p < 0.05 for treatment versus BSA. +, p < 0.05 for PA+FEN versus PA (n = 3–6).