Circadian clock protein Bmal1 protects against transient focal cerebral ischemia in mice by regulating master signals controlling cell survival and metabolism

Abstract

The circadian rhythm, regulated by the suprachiasmatic nucleus through a transcription-translation feedback loop, plays a crucial role in maintaining homeostasis and optimizing physiological processes based on time of day. Recent studies have highlighted its role in cell survival under pathophysiological conditions. In this study, we explored the impact of the transcription factor Bmal1, a key clock protein, on ischemic brain injury by manipulating its expression through lentiviral vectors and Bmal1 knockout in mice exposed to 30 min of middle cerebral artery occlusion followed by 72 h or 42 days survival. Ischemic injury was evaluated alongside proteome analyses and Western blots in the acute stroke phase at 72 h post-ischemia/reperfusion. In the long-term phase, we examined neurogenesis, gliogenesis, angiogenesis, and brain atrophy at 42 days post-ischemia/reperfusion. Our results demonstrate that Bmal1 overexpression enhances neuronal survival and reduces cell injury in the ischemic brain, whereas Bmal1 knockdown or knockout has opposite effects. At the molecular level, Bmal1 was found to control key signaling pathways, including the master regulator mTOR in ischemic brain tissue. Proteome analyses by LC-MS/MS showed that Bmal1 potently regulated pathways involved in oxidative phosphorylation, cell metabolism, neurodegeneration, and oxidative stress. In the long-term phase, Bmal1 overexpression was shown to promote neurogenesis and angiogenesis, while reducing gliogenesis and glial scar formation, thereby facilitating brain recovery. These findings suggest that Bmal1 plays a pivotal role in ischemic stroke recovery, positioning it as a potential target for stroke treatment.