# Role of Irisin in Endocrine and Metabolic Disorders--Possible New Therapeutic Agent?
## 10 Irisin: New Therapeutical Agent?  
Irisin supports the relationships between skeletal muscle, adipocytes, bones, and neurons. This specific crosstalk between fat, bone, muscle, and neurons indicates the significant role of this molecule in human metabolic processes [2]. Therefore, irisin can be seen as a possible treatment for diabetes, obesity, Alzheimer's, Parkinson's, and some other neurodegenerative diseases [49].  
Considering its metabolic and osteogenic potential, irisin might provide a therapeutic choice for treating diseases caused by sedentary lifestyles. The use of irisin as a new anabolic therapy in osteoporosis, sarcopenia, and tumor-associated cachexia has also shown promise [2].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Endocrine and Metabolic Disorders** & **Irisin Profile** & **References** \\ \hline \multirow{4}{*}{THYROID} & Variation according to the thyroid & \multirow{2}{*}{[PERSON] et al., 2016 [26]} \\  & function (hypothyroidism or & [PERSON] et al., 2012 [27] \\  & hyperthyroidism) & & \\  & Correlation with TSH and fT4 & & \\ \hline \multirow{4}{*}{SGA} & Decreased in SGA & \multirow{2}{*}{[PERSON] et al., 2016 [32]} \\  & Positive correlation with gestational age & & \\  & and birth weight & & \\ \hline \multirow{4}{*}{PRADER–WILLI SD.} & Increased in saliva & \multirow{2}{*}{[PERSON] et al., 2015 [40]} \\  & Compensatory role for the amelioration & & \\  & of lipid profile & & \\ \hline \multirow{4}{*}{OSTEOOROSIS} & Positive correlation with BMD and & \multirow{2}{*}{[PERSON] et al., 2017 [2]} \\  & bone strength & & \\  & & & \\  & Negative/positive (7) correlation & & \\  & with adiposity & & \\  & Positive correlation with BMI in children & & \\ \hline \multirow{4}{*}{PCOS} & Increased in serum & \multirow{2}{*}{[PERSON] et al., 2017 [42]} \\  & Irisin resistance (7) & & \\  & & & \\ \hline \multirow{4}{*}{DIABETES MELITUS} & Decreased in T2 DM & \multirow{2}{*}{[PERSON]. [PERSON] et al., 2016 [8]} \\  & Increased in obese T2 DM & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Irisin profiles with respect to various endocrine and metabolic disorders.  
The useful role of irisin in metabolic and osteogenic processes confirms that physical exercise is necessary for the development of the skeleton, the browning process in white adipose tissue, and normal functioning of neurons [2].  
However, new studies have started to question the initial expectations. Might the capacity of irisin to promote the \"browning\" of white adipocytes in mice be transposed to humans? The gene encoding irisin (FNDC5) is expressed robustly not only in muscle but also in various white adipose tissues cells in humans, raising the possibility for increased thermogenesis [3]. No effect of recombinant FNDC5 and irisin on the brightening of primary human adipocytes has been observed, and, thus, the authors concluded that the function of irisin proposed for mice is lost in humans [5; 49]. The thermogenic effect of irisin in humans remains controversial, and it is not yet clear whether exercise has an impact on irisin levels.  
In human subcutaneous adipocyte cell cultures, irisin had a beneficial effect on the expression of multiple genes related to the SARSCoV-2 viral infection, by causing a reduction in genes implicated in elevated viral infection and an increase in genes that block virus cell cleavage; these results raise hope for the beneficial effects of irisin in the treatment of SARSCoV-2 infection [50].