As for the action mechanism, Solinas et al. provided four distinct mechanisms to explain the involvement of JNK in T2D: (1) the phosphorylation of IRS1/2; (2) contribution to metabolic inflammation; (3) negative regulation of the TSH–thyroid hormone axis; and (4) inhibition of PPARa-FGF21 signaling [80]. This evidence concerns the gene MAPK8 and type 2 diabetes mellitus.