Both insulin deprivation and treatment leads to accumulation of acyl-carnitines and suggests incomplete fatty acid β-oxidation in skeletal muscle of T1D mice. Expression of FA intracellular transport and β-oxidation proteins is affected in insulin-deprived mice and not fully corrected by insulin replacement, as revealed by high-throughput proteomic analysis (A) and Western blot (E). Insulin deprivation increases skeletal muscle short-chain acyl-carnitine content (B and C) and elevates CPT1 and SCAD inhibition indexes (D). Insulin treatment corrects expression of proteins of intracellular FA uptake and short-chain FA β-oxidation (A) and reverses short-chain acyl-carnitine (SC-AC) accumulation and CPT1 and SCAD inhibition indexes (B and C) but leads to accumulation of medium-chain (MC-AC), long-chain (LC-AC), and 3-hydroxy (total OH) acyl-carnitine species (B and C) and increases the LCAD inhibition index (D). SC-AC, C2–C5 acyl-carnitines; MC-AC, C6–C12 acyl-carnitines; LC-AC, C14–C20 acyl-carnitines. Data are means ± SEM (n = 6 per group). AU, arbitrary unit; M/SCHAD, medium-/short-chain 3-hydroxyacyl-coenzyme A dehydrogenase. *P < 0.05 vs. ND; #P < 0.05 vs. STZ–I group.