The effect of intracerebroventricular irisin application to the rats on the uncoupling protein family in brain

Irisin is a thermogenic protein that is secreted from muscle tissues. The most important physiological role of irisin is its promoting the conversion of white adipose tissue to brown adipose tissue. Irisin promotes this conversion by increasing the level of especially UCP1 and other proteins that stimulate browning in adipose tissue. UCPs reduce the rate of ATP production partially by decreasing the protein gradient in intermembrane space of a mitochondrion and generate heat. The probable relationship between irisin and UCP2-5 which are close relatives of UCP1 remains still a mystery although its relationship with UCP1 is known partially. With this study it was aimed to determine the probable effect of irisin on UCP2-5 proteins that are located in the inner membrane. 80 female Sprague Dawley rats which weighed in a range of 200 g to 250 g were used in the study. Experiment groups were formed by taking weights of the rats into account and irisin prepared at concentration of 1 µM (low dose), 3 µM (mid dose) and 10 µM (high dose) was applied via intracerebroventricular injection. After the application, the rats were decapitated by considering different waiting duration. In addition, preoperative and postoperative body temperatures of the rats in groups were measured. After decapitation, brain tissues (hypothalamus, hypophysis, hippocampus, cerebellum, striatum and cortex) were gathered and RT-PCR and UCP2-5 mRNA levels were detected. Student's t test was benefited from in determining differences between expression levels and p<0.05 value was accepted as meaningful. Applying high dose of irisin increased the UCP5 at a meaningful manner (p<0.05). On the other hand it reduced UCP4 in regions of brain except hypophysis. While UCP2 mRNA levels decreased in hypothalamus and hypophysis after irisin application, significant increases were observed especially in cerebellum in terms of doses and time (p<0.05). Moreover, after icv injection of irisin, body temperatures of the rats increased at a meaningful manner (p<0.05). All results considered, it is concluded that irisin can have effects not only on UCP1 and but also other UCPs directly or indirectly. Keywords: Irisin, UCP2, UCP3, UCP4, UCP5, Brain, Body temperature