MYOKINE IRISIN AND ITS METABOLIC ROLE ON TRICHINELLA SPIRALIS IN EXPERIMENTALLY INFECTED MURINE MODEL

Trichinella spiralis infects striated muscle cells and causes one of the most important parasitic
diseases. The rapidly growing intramuscular larvae depend on insulin signaling pathways to
supply their needs of glucose and glycogen. Irisin is a myokine secreted by skeletal muscles during
exercise to increase energy expenditure by stimulating glucose uptake and accumulation of
glycogen in muscle cells. This study investigated the potential role of irisin during experimental
trichinosis. Thirty albino mice were infected orally with T. spiralis (200larva/mouse) and five
healthy mice were assigned as normal control. On the 7th, 14th, 21st, 28th, 35th, &48th day postinfection,
mice were evaluated regarding the changes in body weight, blood glucose level, serum
insulin, histopathological changes, glycogen storage, and immunohistochemical expression of
irisin. The results revealed that during the early stage, from the 7th to 28th dpi there were gradual
insignificant decreases in mice body weight. Blood glucose levels showed significant decreases
and the lowest was on the 21st and 28th dpi (83.6±3.05 and 95.6±5.08, respectively). Also, during
this phase, there were significant increases in serum insulin and the highest was on the 21st dpi
(8.7±0.34). These changes correlated with the development and growth of nurse cells parallel
with increased glycogen accumulation and irisin expression in muscle bundles. During the late
stage, there were significant decreases in body weight, significant increases in blood glucose
levels, and significant decreases in serum insulin. The histopathological examination revealed
intense cellular inflammatory infiltrate associated with glycogen depletion. Strong irisin expressions
were observed in the inflammatory infiltrates, nerve bundles, and the adjacent adipose tissues
while in muscle bundles it decreased. In conclusion, the increased irisin expression in muscle
bundles is suggested to increase insulin secretion and responsiveness of T. spiralis-infected
muscles to facilitate glucose transport and glycogen accumulation during larval growth. Whereas,
during the late stage, irisin affects fat metabolism and might contribute to loss of body
weight. The increased irisin expression in the inflammatory infiltrates may have protective and
anti-inflammatory roles. However, further studies should be conducted to discover in-depth role
of irisin and host-endocrine interplay during T. spiralis infection.