Arkansas Children's Nutrition Center, Little Rock, Arkansas.
Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas.
Am J Physiol Endocrinol Metab. 2020 Aug 1;319(2):E265-E275. doi: 10.1152/ajpendo.00515.2019. Epub 2020 May 27.
Saturated fatty acids (SFAs) are implicated in muscle inflammation/cell stress and insulin resistance, but the catalog of factors involved is incomplete. SFA derivatives that accumulate with mismatched FA availability and FA oxidation (FAO) are likely involved, and evidence has emerged that select acylcarnitines should be considered. To understand if excessive long-chain acylcarnitine accumulation and limited FAO associate with lipotoxicity, carnitine palmitoyltransferase 2 knockout C2C12 cells were generated (CPT2 KO). CPT2 KO was confirmed by Western blot, increased palmitoylcarnitine accumulation, and loss of FAO capacity. There was no effect of CPT2 KO on palmitic acid (PA) concentration-dependent increases in media IL-6 or adenylate kinase. PA at 200 and 500 µM did not trigger cell stress responses (phospho-Erk, -JNK, or -p38) above that of vehicle in WT or CPT2 KO cells. In contrast, loss of CPT2 exacerbated PA-induced insulin resistance (acute phospho-Akt; 10 or 100 nM insulin) by as much as ~50-96% compared with WT. Growing cells in carnitine-free media abolished differences between WT and CPT2 KO, but this did not fully rescue PA-induced insulin resistance. The results suggest that PA-induced insulin resistance stems in part from palmitoylcarnitine accumulation, further supporting the hypothesis that select acylcarnitines participate in cell signaling and, when in excess, can compromise cell function. Since carnitine-free conditions could not fully rescue insulin signaling, and CPT2 KO did not alter cell stress responses, the majority of PA-induced "lipotoxicity" in C2C12 myotubes cannot be attributed to palmitoylcarnitine alone.
饱和脂肪酸（SFAs）与肌肉炎症/细胞应激和胰岛素抵抗有关，但涉及的因素目录并不完整。与不匹配的 FA 可用性和 FA 氧化（FAO）相关的 SFA 衍生物可能涉及其中，并且有证据表明，应该考虑选择酰基辅酶 A。为了了解是否存在过量的长链酰基辅酶 A 积累和有限的 FAO 与脂肪毒性相关，生成了肉毒碱棕榈酰转移酶 2 敲除 C2C12 细胞（CPT2 KO）。CPT2 KO 通过 Western blot 得到证实，棕榈酰肉毒碱积累增加，FAO 能力丧失。CPT2 KO 对棕榈酸（PA）浓度依赖性增加培养基中 IL-6 或腺苷酸激酶没有影响。PA 在 200 和 500 µM 时，在 WT 或 CPT2 KO 细胞中，不会引发高于载体的细胞应激反应（磷酸化-Erk、-JNK 或 -p38）。相比之下，与 WT 相比，CPT2 的缺失使 PA 诱导的胰岛素抵抗（急性磷酸化-Akt；10 或 100 nM 胰岛素）恶化了约 50-96%。在无肉碱的培养基中培养细胞消除了 WT 和 CPT2 KO 之间的差异，但这并没有完全挽救 PA 诱导的胰岛素抵抗。结果表明，PA 诱导的胰岛素抵抗部分源于棕榈酰肉毒碱的积累，进一步支持了这样的假设，即选择的酰基辅酶 A 参与细胞信号转导，并且当过量时，会损害细胞功能。由于无肉碱条件不能完全挽救胰岛素信号转导，并且 CPT2 KO 没有改变细胞应激反应，因此 C2C12 肌管中大部分由 PA 诱导的“脂肪毒性”不能仅归因于棕榈酰肉毒碱。
