Upregulation of NOX2 and NOX4 Mediated by TGF-β Signaling Pathway Exacerbates Cerebral Ischemia/Reperfusion Oxidative Stress Injury

Background/Aims: Ischemic stroke is still one of the leading debilitating diseases with high morbidity and mortality. NADPH oxidase (NOX)-derived reactive oxygen species (ROS) play an important role in cerebral ischemia/reperfusion (I/R) injury. However, the mechanism underlying the regulation of ROS generation is still not fully elucidated. This study aims to explore the role of transforming growth beta (TGF-β) signals in ROS generation. Methods: Sprague–Dawley rats were subjected to I/R injury, and PC-12 cells were challenged by hypoxia/reoxygenation (H/R) and/or treated with activin receptor-like kinase (ALK5) inhibitor Sb505124 or siRNA against ALK5. Brain damage was evaluated using neurological scoring, triphenyl tetrazolium chloride staining, hematoxylin and eosin staining, infarct volume measurement, TUNEL staining, and caspase-3 activity measurement. Expression of TGF-β and oxidative stress-related genes was analyzed by real-time polymerase chain reaction and Western blot; NOX activity and ROS level were measured using spectrophotometry and fluorescence microscopy, respectively. Results: I/R contributed to severe brain damage (impaired neurological function, brain infarction, tissue edema, apoptosis), TGF-β signaling activation (upregulation of ALK5, phosphorylation of SMAD2/3) and oxidative stress (upregulation of NOX2/4, rapid release of ROS [oxidative burst]). However, Sb505124 significantly reversed these alterations and protected rats against I/R injury. As in the animal results, H/R also contributed to TGF-β signaling activation and oxidative stress. Likewise, the inhibition of ALK5 or ALK5 knockdown significantly reversed these alterations in PC-12 cells. Other than ALK5 knockdown, ALK5 inhibition had no effect on the expression of ALK5 in PC-12 cells. Conclusions: Our studies demonstrated that TGF-β signaling activation is involved in the regulation of NOX2/NOX4 expression and exacerbates cerebral I/R injury.