Abstract
Irisin is a myokine primarily secreted by skeletal muscles and is known as an exercise-induced hormone. The purpose of this study was to determine whether the PGC-1α -FNDC5 /Irisin-UCP1 expression which is an irisin-related signaling pathway, is activated by an acute swimming exercise. Fourteen to sixteen weeks old male C57BL/6J mice (n = 20) were divided into control (CON, n = 10) and swimming exercise groups (SEG, n = 10). The SEG mice performed 90 min of acute swimming exercise, while control (non-exercised) mice were exposed to shallow water (2 cm of depth) for 90 min. The mRNA and protein expression of PGC-1α, FNDC5 and browning markers including UCP1 were evaluated by quantitative real-time PCR and western blotting. Serum irisin concentration was measured by enzyme-linked immunosorbent assay. An acute swimming exercise did not lead to alterations in the mRNA and protein expression of PGC-1α in both soleus and gastrocnemius muscles, the mRNA and protein expression of UCP1 in brown adipose tissue, mRNA browning markers in visceral adipose tissue and circulating irisin when compared with the control group. On the other hand, an acute swimming exercise led to increases in the mRNA and protein expressions of FNDC5 in the soleus muscle, the protein expression of FNDC5 in the gastrocnemius muscles and the protein expression of UCP1 in subcutaneous adipose tissue.
Highlights
Irisin is a myokine secreted primarily by skeletal muscles and is known as an exerciseinduced hormone [1]
In order to verify whether a 90 min acute swimming exercise activates proliferatoractivated receptor-gamma coactivator-1α (PGC-1α) in skeletal muscles, we evaluated mRNA and protein expression in gastrocnemius and soleus muscles which were mixed muscle fiber and slow-twitch muscle fiber, respectively, between control (CON) and swimming exercise group (SEG)
There was a tendency toward an increase in the mRNA and protein expressions of PGC-1α in soleus muscle but it did not reach to the statistical difference (p = 0.1448, p = 0.1473, respectively, Figure 1b,d)
Summary
Irisin is a myokine secreted primarily by skeletal muscles and is known as an exerciseinduced hormone [1]. PGC-1α and FNDC5 expression and increment in circulating level of irisin are known to enhance energy consumption and stimulate the browning of white adipose tissue (WAT), thereby ameliorating insulin resistance [3]. Recent studies have reported that irisin had a protective effect on the dysfunction of pancreatic β cell [4,5] and vascular dysfunction [6] In this regard, irisin is attracting attention as a signaling mechanism that can be used to treat metabolic diseases such as obesity, insulin resistance, and metabolic syndrome because it increases the expression of uncoupling protein 1 (UCP1) present in the inner membrane of mitochondria, thereby inducing the browning of WAT
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