Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, New Jersey, USA.
Obesity (Silver Spring). 2010 Sep;18(9):1701-9. doi: 10.1038/oby.2009.501. Epub 2010 Jan 21.
Although germ-line deletion of c-Jun NH(2)-terminal kinase (JNK) improves overall insulin sensitivity in mice, those studies could not reveal the underlying molecular mechanism and the tissue site(s) in which reduced JNK activity elicits the observed phenotype. Given its importance in nonesterified fatty acids (NEFA) and glucose utilization, we hypothesized that the insulin-sensitive phenotype associated with Jnk deletion originates from loss of JNK function in skeletal muscle. Short hairpin RNA (shRNA)-mediated gene silencing was used to identify the functions of JNK subtypes in regulating energy metabolism and metabolic responses to elevated concentrations of NEFA in C2C12 myotubes, a cellular model of skeletal muscle. We show for the first time that cellular JNK2- and JNK1/JNK2-deficiency divert glucose from oxidation to glycogenesis due to increased glycogen synthase (GS) activity and induction of Pdk4. We further show that JNK2- and JNK1/JNK2-deficiency profoundly increase cellular NEFA oxidation, and their conversion to phospholipids and triglyceride. The increased NEFA utilization was coupled to increased expressions of selective NEFA handling genes including Cd36, Acsl4, and Chka, and enhanced palmitic acid (PA)-dependent suppression of acetyl-CoA carboxylase (Acc). In JNK-intact cells, PA inhibited insulin signaling and glycogenesis. Although silencing Jnk1 and/or Jnk2 prevented PA-induced inhibition of insulin signaling, it did not completely block decreased insulin-mediated glycogenesis, thus indicating JNK-independent pathways in the suppression of glycogenesis by PA. Muscle-specific inhibition of JNK2 (or total JNK) improves the capacity of NEFA utilization and glycogenesis, and is a potential therapeutic target for improving systemic insulin sensitivity in type 2 diabetes (T2D).
虽然在老鼠中，细胞分裂系缺失 c-Jun NH(2)-末端激酶（JNK）可提高整体胰岛素敏感性，但这些研究无法揭示潜在的分子机制和降低 JNK 活性引起观察到的表型的组织部位。考虑到它在非酯化脂肪酸（NEFA）和葡萄糖利用中的重要性，我们假设与 Jnk 缺失相关的胰岛素敏感表型源于骨骼肌中 JNK 功能的丧失。短发夹 RNA（shRNA）介导的基因沉默用于鉴定 JNK 亚型在调节能量代谢和代谢对升高的 NEFA 浓度的反应中的功能，C2C12 肌管是骨骼肌的细胞模型。我们首次表明，由于糖原合酶（GS）活性增加和 Pdk4 的诱导，细胞 JNK2 和 JNK1/JNK2 缺陷会将葡萄糖从氧化转向糖生成，从而将葡萄糖从氧化转向糖生成。我们进一步表明，JNK2 和 JNK1/JNK2 缺陷会极大地增加细胞内 NEFA 的氧化，并将其转化为磷脂和甘油三酯。增加的 NEFA 利用率与选择性的 NEFA 处理基因的表达增加相关，包括 Cd36、Acsl4 和 Chka，并增强了棕榈酸（PA）依赖性的乙酰辅酶 A 羧化酶（Acc）的抑制。在 JNK 完整的细胞中，PA 抑制胰岛素信号和糖生成。虽然沉默 Jnk1 和/或 Jnk2 可以防止 PA 诱导的胰岛素信号抑制，但它并没有完全阻止胰岛素介导的糖生成减少，因此表明在 PA 抑制糖生成的过程中存在 JNK 非依赖性途径。肌肉特异性 JNK2（或总 JNK）抑制可提高 NEFA 利用和糖生成的能力，是改善 2 型糖尿病（T2D）患者全身胰岛素敏感性的潜在治疗靶点。
