SIRT1 and its SUMOylation attenuate hyperoxia-induced lung injury by improving mitochondrial biogenesis and fusion.

OBJECTIVE: To investigate the role of silencing information regulator 2 related enzyme 1 (SIRT1) and its small ubiquitin-like modifier (SUMO) modification (SUMOylation) in hyperoxia lung injury in preterm infants.

METHODS: The roles of SIRT1 and its SUMOylation in hyperoxia-induced damage to HAECs were explored from the cellular level using CCK-8, MTT, scratch assay, reactive oxygen species (ROS), Mito SOX™, BeyoClick™ EdU-488, immunofluorescence and Western-blot, mitochondrial membrane potential, malondialdehyde and superoxide dismutase assays, MitoTracker® Red CMXRos, transmission electron microscopy, and SIRT1 activity assay. Type II alveolar epithelial cell-specific knockout SENP1 mice were constructed. The role of SUMOylation of SIRT1 in hyperoxia lung injury in mice was explored in vivo by HE staining, immunohistochemistry, immunofluorescence, Western-blot and transmission electron microscopy.

RESULTS: (1) Hyperoxia increased ROS in HAECs and decreased cell proliferation levels and survival, as well as reduced the expression of peroxisome-proliferator-γ coactivator-1α (PGC-1α), nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (TFAM), optic atrophy protein 1 (OPA1), mitofusins 1 (MFN1), and mitofusins 2 (MFN2) proteins. (2) N-Acetylcysteine inhibited SIRT1 nucleoplasmic shuttling and reversed the hyperoxia-induced decrease in SUMO1 and increase in SENP1. (3) SRT1720 reversed the hyperoxia-induced decrease of PGC-1α, NRF1, TFAM, MFN1, MFN2 and OPA1 proteins. (4) Overexpression of SUMO1 increased total SIRT1 and nuclear SIRT1 but decreased cytoplasmic SIRT1 protein expression levels, attenuated hyperoxia-induced mitochondrial injury. (5) On day 14 of hyperoxia exposure, type II alveolar epithelial cell-specific knockout SENP1 mice showed reduced lung injury, increased lung tissue total SIRT1 and nuclear SIRT1 but decreased cytoplasmic SIRT1 protein expression, and reduced mitochondrial injury.

CONCLUSION: Hyperoxia increases ROS levels to decrease SIRT1 and SUMO1 levels, thereby inhibiting mitochondrial biogenesis and fusion, and promotion of SIRT1 and its SUMOylation improves mitochondrial biogenesis and fusion, thereby attenuating hyperoxia lung injury.