FNDC5 and diabetes mellitus: Moreover, the data reveal a dualistic adipokine–mitochondria landscape in both sarcopenia and diabetes, whereby classical regulators EP, ITLN1, and RBP4 uniformly track positively with mitochondrial hub genes, indicating a preserved energy-support axis, whereas newer myokines/adipokines FNDC5, METRNL, RETN, and NAMPT are inversely correlated, hinting at a compensatory or counter-regulatory network.