Effects of the Myokine Irisin on Stromal Cells from Swine Adipose Tissue

Fibronectin type III domain-containing protein 5 (FNDC5)-like immunoreactivity and mRNA abundance in domestic animal tissues

Irisin is a 112-amino acid peptide hormone that is cleaved from fibronectin type III domain-containing protein 5 (FNDC5), a type I transmembrane protein abundantly found in muscle tissue. Irisin is a putative mediator of the benefits of exercise, neuroprotection, bone growth, and cardiac health. However, few studies have focused on irisin in domestic animals. Further, whether processed irisin is detectable in domestic animal tissues remains uncertain. To address this, we determined FNDC5 mRNA and protein concentration in anatine (duck) and porcine (pig) skeletal muscle, and in equine (horse), swine, and anatine serum samples. RT-PCR analysis identified FNDC5 mRNA in all pig and duck skeletal muscle samples. An approximately 25 kDa band representing FNDC5 was detected in both pig and duck skeletal muscle. Fluorescence immunohistochemistry using a rabbit monoclonal FNDC5/irisin primary antibody and a goat polyclonal anti-rabbit secondary antibody localized FNDC5/irisin-like immunoreactivity in both the glandular and muscular regions of pig stomach. FNDC5/irisin-like immunoreactivity was also identified in horse, pig, and duck serum using a multispecies irisin ELISA. The average values of irisin-like immunoreactivity were 13.7 (duck), 15.4 (horse), and 7.0 (pig) ng/mL in samples tested. Our results support the presence of irisin precursor in several domestic animals. Processed irisin, however, was not detectable. Further studies are required to validate reliable tools to detect and quantify processed irisin in domestic animals.

Irisin as an emerging target in the regulation of reproductive functions in health and disease

Germ cells are highly conserved in the gonads, nurtured to either develop into a gamete or self-renew into a stem cell reserve. Preserving the germ cell pool and protecting the reproductive organs is essential for maintaining an individual's fertility. Several factors, including a sedentary lifestyle, pollutants, hormonal disruption, drugs, and a disease condition, have been shown to impair normal reproductive function. Irisin has recently been identified as an adipomyokine involved in modulating physiological functions based on the body's metabolic status. It is being studied for its role in various functions, including fertility. Findings show the localization of irisin in various parts of the reproductive axis, with the highest levels observed during puberty and pregnancy. This raises questions about its role and function in reproduction. Studies support irisin's role in protecting against disease-induced reproductive abnormalities and infertility. Therefore, the current review focuses on how irisin influences spermatogenesis and ovarian follicular development and plays a significant role in indirectly preserving the germ cell pool by protecting the gonads against oxidative stress and inflammation.

Can irisin be developed as the molecular evolutionary clock based on the origin and functions?

Irisin, a myokine identified in 2012, has garnered research interest for its capacity to induce browning of adipocytes and improve metabolic parameters. As such, the potential therapeutic applications of this exercise-induced peptide continue to be explored. Though present across diverse animal species, sequence analysis has revealed subtle variation in the irisin protein. In this review, we consider the effects of irisin on disease states in light of its molecular evolution. We summarize current evidence for irisin's influence on pathologies and discuss how sequence changes may inform development of irisin-based therapies. Furthermore, we propose that the phylogenetic variations in irisin could potentially be leveraged as a molecular clock to elucidate evolutionary relationships.

Myokines: metabolic regulation in obesity and type 2 diabetes

Skeletal muscle plays a vital role in the regulation of systemic metabolism, partly through its secretion of endocrine factors which are collectively known as myokines. Altered myokine levels are associated with metabolic diseases, such as type 2 diabetes (T2D). The significance of interorgan crosstalk, particularly through myokines, has emerged as a fundamental aspect of nutrient and energy homeostasis. However, a comprehensive understanding of myokine biology in the setting of obesity and T2D remains a major challenge. In this review, we discuss the regulation and biological functions of key myokines that have been extensively studied during the past two decades, namely interleukin 6 (IL-6), irisin, myostatin (MSTN), growth differentiation factor 11 (GDF11), fibroblast growth factor 21 (FGF21), apelin, brain-derived neurotrophic factor (BDNF), meteorin-like (Metrnl), secreted protein acidic and rich in cysteine (SPARC), β-aminoisobutyric acid (BAIBA), Musclin, and Dickkopf 3 (Dkk3). Related to these, we detail the role of exercise in myokine expression and secretion together with their contributions to metabolic physiology and disease. Despite significant advancements in myokine research, many myokines remain challenging to measure accurately and investigate thoroughly. Hence, new research techniques and detection methods should be developed and rigorously tested. Therefore, developing a comprehensive perspective on myokine biology is crucial, as this will likely offer new insights into the pathophysiological mechanisms underlying obesity and T2D and may reveal novel targets for therapeutic interventions.

Irisin in domestic animals

Irisin is a 112 amino acid peptide hormone cleaved from the fibronectin type III domain-containing protein. Irisin is highly conserved across vertebrates, suggesting evolutionarily conserved common functions among domestic animals. These functions include the browning of white adipose tissue and increased energy expenditure. Irisin has been detected and studied primarily in plasma, serum, and skeletal muscle, but has also been found in adipose tissue, liver, kidney, lungs, cerebrospinal fluid, breast milk, and saliva. This wider tissue presence of irisin suggests additional functions beyond its role as a myokine in regulating energy use. We are beginning to understand irisin in domestic animals. The goal of this review is to provide an up-to-date commentary on irisin structure, tissue distribution, and functions across vertebrates, especially mammals of importance in veterinary medicine. Irisin could be explored as a potential candidate for developing therapeutic agents and biomarkers in domestic animal endocrinology.