FGF21 and type 2 diabetes mellitus: According to the literature records, FGF-21 can regulate glucose and lipid metabolism, maintain energy balance, and play a role in regulating blood lipid and resisting oxidation (104), protect the blood-brain barrier from traumatic brain injury and prevent the blood-brain barrier leakage in type 2 diabetes mellitus (105, 106), and promote remyelination and functional recovery of injured peripheral nerves.