LAT1-mediated delivery of engineered R13A-MOTS-c attenuates radiation-induced lung injury via Nrf2 activation and...

MOTS-c exhibits substantial antioxidant and anti-inflammatory properties, yet its therapeutic potential is constrained by poor membrane permeability due to its high polarity. To overcome this limitation, we engineered R13A-MOTS-c by substituting the polar arginine at position 13 with alanine in the wild-type peptide (Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg). This modification increased the peptide's hydrophobicity index from -0.938 to -0.544, measurably improving its cellular uptake. Functional uptake assays, including competition with canonical LAT1 substrates (leucine, BCH) and LAT1 knockdown experiments, further confirmed that R13A-MOTS-c enters cells via LAT1-mediated transport. In vitro experiments revealed that R13A-MOTS-c suppressed inflammatory responses, oxidative damage, and mitochondrial impairment in MLE-12 cells. In vivo studies demonstrated that daily intraperitoneal administration of R13A-MOTS-c (5 mg/kg for 2 weeks) effectively mitigated radiation-induced pulmonary inflammation, oxidative stress, and mitochondrial dysfunction in C57BL/6 mice exposed to 20 Gy thoracic irradiation. Mechanistically, R13A-MOTS-c activated the Nrf2 signaling pathway, as evidenced by increased nuclear translocation of Nrf2 and upregulation of its downstream targets gene. These effects were abolished upon LAT1 inhibition, Nrf2 inhibition, or in Nrf2-knockout conditions. Collectively, these findings indicate that LAT1-mediated uptake of R13A-MOTS-c alleviates radiation-induced lung injury through Nrf2 pathway activation and mitochondrial function restoration, offering a promising therapeutic strategy for clinical applications.