STAT3 inhibitor mitigates cerebral amyloid angiopathy and parenchymal amyloid plaques while improving cognitive functions and brain networks.

Previous reports indicate a potential role for signal transducer and activator of transcription 3 (STAT3) in amyloid-ß (Aß) processing and neuritic plaque pathogenesis. In the present study, the impact of STAT3 inhibition on cognition, cerebrovascular function, amyloid pathology, oxidative stress, and neuroinflammation was studied using in vitro and in vivo models of Alzheimer's disease (AD)-related pathology. For in vitro experiments, human brain vascular smooth muscle cells (HBVSMC) and human brain microvascular endothelial cells (HBMEC) were used, and these cultured cells were exposed to Aß peptides followed by measurement of activated forms of STAT3 expression and reactive oxygen species (ROS) generation. Further, 6 months old 5XFAD/APOE4 (5XE4) mice and age-matched negative littermates were used for in vivo experiments. These mice were treated with STAT3 specific inhibitor, LLL-12 for 2 months followed by neurobehavioral and histopathological assessment. In vitro experiments showed exposure of cerebrovascular cells to Aß peptides upregulated activated forms of STAT3 and produced STAT3-mediated vascular oxidative stress. 5XE4 mice treated with the STAT3-specific inhibitor (LLL-12) improved cognitive functions and functional connectivity and augmented cerebral blood flow. These functional improvements were associated with a reduction in neuritic plaques, cerebral amyloid angiopathy (CAA), oxidative stress, and neuroinflammation. Reduction in amyloid precursor protein (APP) processing and attenuation of oxidative modification of lipoprotein receptor related protein-1 (LRP-1) were identified as potential underlying mechanisms. These results demonstrate the broad impact of STAT3 on cognitive functions, parenchymal and vascular amyloid pathology and highlight the therapeutic potential of STAT3 specific inhibition for treatment of AD and CAA.

Sirtuin 1 Mediates Protection Against Delayed Cerebral Ischemia in Subarachnoid Hemorrhage in Response to Hypoxic Postconditioning.

Background Many therapies designed to prevent delayed cerebral ischemia (DCI) and improve neurological outcome in aneurysmal subarachnoid hemorrhage (SAH) have failed, likely because of targeting only one element of what has proven to be a multifactorial disease. We previously demonstrated that initiating hypoxic conditioning before SAH (hypoxic preconditioning) provides powerful protection against DCI. Here, we expanded upon these findings to determine whether hypoxic conditioning delivered at clinically relevant time points after SAH (hypoxic postconditioning) provides similarly robust DCI protection. Methods and Results In this study, we found that hypoxic postconditioning (8% O2 for 2 hours) initiated 3 hours after SAH provides strong protection against cerebral vasospasm, microvessel thrombi, and neurological deficits. By pharmacologic and genetic inhibition of SIRT1 (sirtuin 1) using EX527 and global Sirt1-/- mice, respectively, we demonstrated that this multifaceted DCI protection is SIRT1 mediated. Moreover, genetic overexpression of SIRT1 using Sirt1-Tg mice, mimicked the DCI protection afforded by hypoxic postconditioning. Finally, we found that post-SAH administration of resveratrol attenuated cerebral vasospasm, microvessel thrombi, and neurological deficits, and did so in a SIRT1-dependent fashion. Conclusions The present study indicates that hypoxic postconditioning provides powerful DCI protection when initiated at clinically relevant time points, and that pharmacologic augmentation of SIRT1 activity after SAH can mimic this beneficial effect. We conclude that conditioning-based therapies administered after SAH hold translational promise for patients with SAH and warrant further investigation.

SIRT1 mediates hypoxic preconditioning induced attenuation of neurovascular dysfunction following subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: Vasospasm and delayed cerebral ischemia (DCI) contribute significantly to the morbidity/mortality associated with aneurysmal subarachnoid hemorrhage (SAH). While considerable research effort has focused on preventing or reversing vasospasm, SAH-induced brain injury occurs in response to a multitude of concomitantly acting pathophysiologic mechanisms. In this regard, the pleiotropic epigenetic responses to conditioning-based therapeutics may provide an ideal SAH therapeutic strategy. We previously documented the ability of hypoxic preconditioning (PC) to attenuate vasospasm and neurological deficits after SAH, in a manner that depends on the activity of endothelial nitric oxide synthase. The present study was undertaken to elucidate whether the NAD-dependent protein deacetylase sirtuin isoform SIRT1 is an upstream mediator of hypoxic PC-induced protection, and to assess the efficacy of the SIRT1-activating polyphenol Resveratrol as a pharmacologic preconditioning therapy. METHODS: Wild-type C57BL/6J mice were utilized in the study and subjected to normoxia or hypoxic PC. Surgical procedures included induction of SAH via endovascular perforation or sham surgery. Multiple endpoints were assessed including cerebral vasospasm, neurobehavioral deficits, SIRT1 expression via quantitative real-time PCR for mRNA, and western blot for protein quantification. Pharmacological agents utilized in the study include EX-527 (SIRT1 inhibitor), and Resveratrol (SIRT1 activator). RESULTS: Hypoxic PC leads to rapid and sustained increase in cerebral SIRT1 mRNA and protein expression. SIRT1 inhibition blocks the protective effects of hypoxic PC on vasospasm and neurological deficits. Resveratrol pretreatment dose-dependently abrogates vasospasm and attenuates neurological deficits following SAH - beneficial effects that were similarly blocked by pharmacologic inhibition of SIRT1. CONCLUSION: SIRT1 mediates hypoxic preconditioning-induced protection against neurovascular dysfunction after SAH. Resveratrol mimics this neurovascular protection, at least in part, via SIRT1. Activation of SIRT1 is a promising, novel, pleiotropic therapeutic strategy to combat DCI after SAH.