Influencia de la citoquina Interleuquina 6 (IL-6) adipocitaria y muscular en el control del metabolismo

Abstract

Interleukine 6 is a pleiotropic cytokine whose main function is regulating inflammation in the immune system. However, IL-6 also affects the central nervous system (CNS), and it participates in the exercise response and in metabolism (mainly insulin-related functions). Several studies show that IL-6 could have a role in the control of body weight in both the CNS and the periphery. It is unknown, and currently the matter of debate, whether CNS-acting IL-6 is produced in situ or elsewhere. It would then be possible that IL-6 produced by non-immunologic tissues had an important role in the control of body weight. In the last few decades, it has been shown that skeletal muscle produces and secretes myokines. IL-6 is the most abundant and it is produced during muscular contraction, possibly participating in some of the exercise-induced metabolic changes. Adipose tissue also produces and secretes this cytokine and it is the main source of IL-6 in non-inflammatory conditions. Skeletal muscle and adipose tissue play an important role in metabolism. These tissues are also the main source of IL-6 in non-inflammatory conditions. That is why we decided to investigate the metabolic role of IL-6 produced by these tissues and its actions in the control of body weight. We generated two different IL-6 conditional knock-outs: one in the skeletal muscle and the other in the adipose tissue. These animals were characterized in basal conditions and after being fed a high fat diet. Body weight and food intake were measured. Glucose and insulin response were studied. Several tissues were weighted. Some metabolites and hormones levels and metabolic and inflammatory gene expression were also analyzed. In both models IL-6 deficiency had a sex-dependent effect. Our data suggest that these mice had a normal growth. However, there were changes in body weight gain. Muscular IL-6 deficient mice gained less weight than controls, whereas in females the opposite occurred. These differences were exacerbated in mice fed a high fat diet. Regarding the adipose IL-6 deficiency model, adipose IL-6 deficiency only had an effect in body weight in mice fed a high fat diet. Thus, knockout females showed resistance to obesity, gaining less weight than controls. In males this effect was smaller and not significant. Food intake and hypothalamic neuropeptides controlling food intake and energy expenditure were analyzed, too. Our data suggest that body weight changes would be mainly caused by changes in energy expenditure rather than by changes in food intake. Thus, in basal conditions muscular IL-6 deficient males showed energy expenditure activation and in females the opposite occurred. In the case of adipose IL-6 deficiency, although body weight gain in basal conditions was unchanged, hypothalamic neuropeptide expression was altered. In conclusion, IL-6 has either central or peripheral effects on the control of energy homeostasis. Decreased levels of IL-6 have, depending on their origin, different local effects in the regulation of other factors that probably caused the observed changes.

Date of Award	24 May 2013
Original language	Spanish
Supervisor	Juan Hidalgo Pareja (Director)