Melatonin Alleviates Cerebral Ischemia/Reperfusion Injury by Mitigating AIM2-Mediated PANoptosis in Ischemic Penumbra

Cerebral ischemia/reperfusion injury (CIRI) commonly occurs during the treatment of ischemic stroke and leads to severe consequences, including neuronal death and permanent loss of motor function. Accurate differentiation between the ischemic penumbra (IP) and the ischemic core area is crucial for timely intervention. Multimodal MRI plays a crucial role in the early diagnosis and treatment evaluation of acute ischemic stroke. PANoptosis is a recently discovered form of programmed cell death including apoptosis, necroptosis, and pyroptosis. It has been implicated in neuronal loss during CIRI, especially through absent in melanoma 2 (AIM2). Melatonin (Mel) exerts neuroprotective effects; however, whether PANoptosis is the main cause of neuronal death in CIRI and whether Mel exerts anti-PANoptotic effects to rescue CIRI remain unclear. This study aimed to examine the effects of Mel on PANoptosis in the IP of rats with CIRI and to systematically investigate the underlying mechanisms using multimodal MRI combined with histopathologic techniques. A rat CIRI model comprising 42 healthy male Sprague-Dawley rats, weighing 240-270 g, was established using the modified Zea-Longa wire bolus method. Multimodal MRI, including T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI)-MRI, and chemical exchange saturation transfer (CEST), was performed to evaluate the ischemic lesions and identify IP. T2WI, DWI-MRI, and tissue staining demonstrated that Mel significantly reduced infarct volume, improved neuron morphology, and decreased the proportion of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells. The IP was identified as the mismatch region between CEST and DWI-MRI, which was expanded by Mel treatment. In addition, Mel inhibited the expression of PANoptotic key proteins, as well as AIM2 expression, in IP neurons. In summary, multimodal MRI enables dynamic monitoring of IP after CIRI in vivo and effectively evaluates the neuroprotective effects of Mel on IP. Mel broadens the time window for CIRI rescue and exerts a neuroprotective effect by downregulating AIM2 expression in neurons, thereby suppressing PANoptotic neuronal death in the IP areas and alleviating brain injury in rats with CIRI.