Identification and antioxidative mechanism of novel mitochondria-targeted MFG-E8 polypeptides in virtual screening and in vitro study

Milk fat globule-EGF factor VIII (MFG-E8) has been identified as an important source of bioactive peptides, which may exert a pivotal role in regulating biologic redox equilibrium. However, the composition of MFG-E8 polypeptides and their mechanisms on mitigating sarcopenia remain unknown. The aim of this study was to identify the composition of MFG-E8 polypeptides and its effects against oxidative stress in dexamethasone-induced L6 cell injury. Simulated digestion in vitro and liquid chromatography-tandem mass spectrometry were used in this investigation. A total of 95 peptides were identified during complete simulated digestion; among them, the contents of 21 peptides were analyzed, having been determined to exceed 1%. Molecular docking assay found that IDLG, KDPG, YYR, and YYK exhibited high binding affinity with keap1. MTT, dichlorodihydrofluorescein diacetate, mito- and lyso-tracker, and transmission electron microscope assay demonstrated that IDLG and KDPG can alleviate oxidative stress-injured L6 cell vitality, mitochondria activity, vacuolation, and function decrease, and increased autophagy, thereby improving mitochondrial homeostasis. From a molecular perspective, IDLG and KDPG can decrease the expression of keap1 and increase the expression of Nrf2, HO-1, and PGC-1α. Therefore, MFG-E8-derived IDLG and KDPG could be potential polypeptides countering oxidative stress in the treatment of sarcopenia, via the keap1/Nrf2/HO-1 signaling pathway.