Daily rhythm and heat shock protein expression in obese ob/ob mice

Abstract

Objectives

This study examined heat shock protein (HSP) 70 expression and rhythms of drinking behavior and locomotor activity in obesity, in order to clarify the involvement of HSPs in obesity-induced disturbance of circadian rhythms.

Methods

C57BL/6J ob/ob mice were used as a murine model of severe obesity. Drinking behavior and locomotor activity of male C57BL/6J (control) mice and ob/ob mice were recorded with the behavioral analyzing system. HSP70 concentration in the homogenized supernatant of each tissue, including the brain, liver, and kidney, was measured by an enzyme-linked immunosorbent assay.

Results

We observed an attenuated locomotor activity rhythm in the ob/ob mice compared with the control mice at 13 weeks of age and especially at 27 weeks of age. The drinking rhythm was little affected by obesity. HSP70 protein expression was reduced in the brain and kidney of the ob/ob mice compared with the control mice. However, HSP70 expression in the liver was not altered.

Discussion

This study suggests that the obesity-induced reduction of HSP70 expression in the brain and kidney can be directly or indirectly associated with disturbance of rhythms of the master clock and peripheral clocks. The study provides a link between circadian rhythm and HSP expression in obesity; the disturbance of these factors may lead to the progression of metabolic disorders.

Keywords:

• Drinking
• HSP
• Locomotor activity
• Obesity
• Rhythm

Acknowledgements

This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology in Japan.