Expression, purification and biological characterisation of recombinant human irisin (12.5 kDa).

Fibronectin type III domain containing 5 (FNDC5) is a transmembrane protein. Upon cleavage, it yields a peptide called irisin that is supposedly bind to an unknown receptor and facilitates browning of white adipose tissue (WAT). Increased levels of irisin are associated with increased levels of energy expenditure markers PGC-1α, UCP-1, besides abundance of beige adipocytes in WAT. Though varied sizes of irisin were reported in humans and rodents it is not yet clear about the actual size of the irisin produced physiologically. Hence, we cloned and expressed human irisin (32-143 aa of FNDC5) in Escherichia coli based on the proposed cleavage site that yields 12.5 kDa peptide to study its antigenicity and other biological functions in vitro . We purified recombinant human irisin (rh-irisin) to 95% homogeneity with simple purification method with a yield of 25 mg/g wet cell pellet. rh-irisin has been detected by commercially available antibodies from different sources with similar antigenicity. Biological activity of the rh-irisin was confirmed by using 3T3-L1 pre-adipocyte differentiation by Oil red O staining. Further, rh-irisin treatment on pre-adipocytes showed increased expression of markers associated with energy expenditure. As it is involved in energy expenditure process, it could be considered as potential therapeutic option for various metabolic diseases.