JNK1 ablation in mice confers long-term metabolic protection from diet-induced obesity at the cost of moderate skin oxidative damage

Abstract

Obesity and insulin resistance are associated with oxidative stress, which may be implicated in the progression of obesity-related diseases. The kinase JNK1 has emerged as a promising drug target for the treatment of obesity and type 2 diabetes. JNK1 is also a key mediator of the oxidative stress response, which can promote cell death or survival, depending on the magnitude and context of its activation. In this article, we describe a study in which the long-term effects of JNK1 inactivation on glucose homeostasis and oxidative stress in obese mice were investigated for the first time. Mice lacking JNK1 (JNK1(-/-)) were fed an obesogenic high-fat diet (HFD) for a long period. JNK1(-/-) mice fed an HFD for the long term had reduced expression of antioxidant genes in their skin, more skin oxidative damage, and increased epidermal thickness and inflammation compared with the effects in control wild-type mice. However, we also observed that the protection from obesity, adipose tissue inflammation, steatosis, and insulin resistance, conferred by JNK1 ablation, was sustained over a long period and was paralleled by decreased oxidative damage in fat and liver. We conclude that compounds targeting JNK1 activity in brain and adipose tissue, which do not accumulate in the skin, may be safer and most effective.-Becattini, B., Zani, F., Breasson, L., Sardi, C., D'Agostino, V. G., Choo, M.-K., Provenzani, A., Park, J. M., Solinas, G. JNK1 ablation in mice confers long-term metabolic protection from diet-induced obesity at the cost of moderate skin oxidative damage.

Keywords: antioxidants; insulin resistance; metabolic inflammation; oxidative stress tolerance; type-2 diabetes.

Figure 1.

JNK1^−/− mice display sustained metabolic protection from an HFD, but also display signs of exacerbated skin aging. A) Survival curve of 15 WT mice and 15 JNK1^−/− mice that were kept on an HFD from weaning to death. B) Growth curve of the mice. C) ITT of 48-wk-old WT mice and JNK1^−/− mice on an HFD. D) Incidence of alopecia, overt alopecia, and hair depigmentation in 80-wk-old WT mice and JNK1^−/− mice kept on an HFD.

Figure 2.

JNK1^−/− mice display sustained protection against HFD-induced adipose tissue inflammation and insulin resistance. Body weight (A) and ITT results (B) of 23-wk-old WT mice and JNK1^−/− mice kept on an HFD. Body weight (C) and GTT results (D) of 24-wk-old WT mice and JNK1^−/− mice kept on an HFD. Body weight (E) and ITT results (F) of the same mice at the age of 42 wk. Body weight (G) and GTT results (H) of the same mice at the age of 43 wk. I) Mac2 staining of CLSs of adipose tissue sections from the mice at the age of 44 wk. J) Quantification of the number of CLSs from (I). K) Real-time qPCR analysis of the expression of proinflammatory genes in adipose tissue of the mice in (I). L) Significant terms from a gene ontology analysis of DNA microarray data, for genes that were down-regulated in adipose tissue of the JNK1^−/− mice vs. their controls.

Figure 3.

JNK1^−/− mice display sustained protection against HFD-induced steatosis, but not against liver inflammation. A) Hematoxylin and eosin staining of representative liver sections of 44-wk-old WT mice and JNK1^−/− mice kept on an HFD. B) F4/80 immunostaining of liver sections from the same mice. C) Quantification of the number of F4/80⁺ cells from the liver sections in (B). D) Real-time qPCR analysis of the expression of proinflammatory genes in mouse liver.

Figure 4.

JNK1^−/− mice fed an HFD for a prolonged period are predisposed to skin damage and inflammation. A) Representative photographs of 44-wk-old WT and JNK1^−/− mice kept on an HFD. B) Incidence of hair depigmentation, alopecia (any sign), and mild-to-overt alopecia in the same mice. C) Hematoxylin and eosin staining of representative skin sections of the mice. D) Average epidermal thickness of 44-wk-old WT and JNK1^−/− mice kept on an HFD. E) Real-time qPCR analysis of the expression of M1 cytokines (top) and M2 genes (bottom) in skin samples of WT and JNK1^−/− mice. F) Significant terms from a gene ontology analysis of DNA microarray data for genes with expression induced in the skin of JNK1^−/− mice compared to WT controls.

Figure 5.

Loss of JNK1 in mice fed an HFD for a prolonged period protects liver and adipose tissue, but predisposes skin to oxidative damage. A) MDA levels in different tissues from 44-wk-old WT and JNK1^−/− kept on an HFD. B) Real-time qPCR analysis of the expression of HO-1 in the tissues. C) qPCR analysis of the expression of genes implicated in oxidative stress tolerance in the skin of the same mice. D) Immunoblot analysis of catalase, SOD2, HO-1, and Sesn-2 protein levels in the skin samples in (C). E) Quantification of the immunoblots panel D. WAT, white adipose tissue.