LIGHT/TNFSF14 Affects Adipose Tissue Phenotype

Abstract

LIGHT/TNFSF14 is linked to several signaling pathways as a crucial member of a larger immunoregulatory network. It is primarily expressed in inflammatory effector cells, and high levels of LIGHT have been reported in obesity. Thus, with the aim of deepening the knowledge of the role of LIGHT on adipose tissue phenotype, we studied wild-type (WT), Tnfsf14^-/-, Rag^-/- and Rag-/Tnfsf14- (DKO) mice fed a normal diet (ND) or high-fat diet (HFD). Our results show that, although there is no significant weight gain between the mice with different genotypes, it is significant within each of them. We also detected an increase in visceral White Adipose Tissue (vWAT) weight in all mice fed HFD, together with the lowest levels of vWAT weight in Tnfsf14^-/- and DKO mice fed ND with respect to the other strain. Inguinal WAT (iWAT) weight is significantly affected by genotype and HFD. The least amount of iWAT was detected in DKO mice fed ND. Histological analysis of vWAT showed that both the genotype and the diet significantly affect the adipocyte area, whereas the number is affected only by the genotype. In iWAT, the genotype and the diet significantly affect mean adipocyte area and number; interestingly, the area with the least adipocyte was detected in DKO mice fed ND, suggesting a potential browning effect due to the simultaneous lack of mature lymphocytes and LIGHT. Consistently, Uncoupling Protein 1 (UCP1) staining of iWAT demonstrated that few positive brown adipocytes appeared in DKO mice. Furthermore, LIGHT deficiency is associated with greater levels of UCP1, highlighting the lack of its expression in Rag^-/- mice. Liver examination showed that all mice fed HFD had a steatotic liver, but it was particularly evident for DKO mice. In conclusion, our study demonstrates that the adipose tissue phenotype is affected by LIGHT levels but also much more by mature lymphocytes.

Keywords: LIGHT/TNFSF14; adipose tissue; high fat diet.

Figure 1

Weight change in mice fed with normal diet (ND, (A)) and high-fat diet (HFD, (B)). Significance was evaluated using repeated measurement analysis of variance (ANOVA) (n = 6).

Figure 2

Average food intake of wild-type (WT), Tnfsf14^−/−, Rag^−/−, and Rag⁻/Tnfsf14⁻ (DKO) mice). Significance was evaluated using repeated measurement analysis of variance (ANOVA) (n = 6). All data were normalized to the total weight of the animals.

Figure 3

Blood glucose levels (mg/mL) of wild-type (WT), Tnfsf14^−/−, Rag^−/− and Rag⁻/Tnfsf14⁻ (DKO) mice fed ND or HFD (A). The results of two-way ANOVA were reported in table (B), (n = 6).

Figure 4

vWAT (A), iWAT (B), and BAT (C) weights of wild-type (WT), Tnfsf14^−/−, Rag^−/− and Rag⁻/Tnfsf14⁻ (DKO) mice fed ND or HFD. The results of two-way ANOVA are also reported in table (D), (n = 6). All vWAT, iWAT, and BAT weights were normalized to the total weight of the animals.

Figure 5

Microphotographs of vWAT of wild-type (WT), Tnfsf14^−/−, Rag^−/− and Rag⁻/Tnfsf14⁻ (DKO) mice fed ND or HFD (A), together with the measurement of Mean Adipocyte Area (B), Mean Adipocyte number (C) and two-way ANOVA results in table (D), n = 6. Magnification 60×.

Figure 6

Microphotographs of iWAT of wild-type (WT), Tnfsf14^−/−, Rag^−/− and Rag⁻/Tnfsf14⁻ (DKO) mice fed ND or HFD (A), magnification 40×, together with the measurement of Mean Adipocyte Area (B) and Mean Adipocyte number (C), as well as two-way ANOVA results in table (D), n = 6).

Figure 7

UCP1 immunohistochemical staining of iWAT sample from wild-type (WT), Tnfsf14^−/−, Rag^−/− and Rag⁻/Tnfsf14⁻ (DKO) mice fed ND or HFD (A), together with the measurement of the positive area of staining (B) with the results of two-way ANOVA in table (C), n = 6. Bars indicate 100 µm.

Figure 8

Microphotographs for the histological evaluation of liver of wild-type (WT), Tnfsf14^−/−, Rag^−/− and Rag⁻/Tnfsf14⁻ (DKO) mice fed ND or HFD (A), evaluation of steatosis by determining the area of lipid in the sections (B) and results of two-way ANOVA (C). Magnification 40×.