Microglia knockdown reduces inflammation and preserves cognition in diabetic animals after experimental stroke

Ladonya Jackson,Selin Dumanli,Susan C Fagan,Adviye Ergul,Maribeth H Johnson

doi:10.1186/s12974-020-01815-3

Abstract

IntroductionUnfortunately, over 40% of stroke victims have pre-existing diabetes which not only increases their risk of stroke up to 2–6 fold, but also worsens both functional recovery and the severity of cognitive impairment. Our lab has recently linked the chronic inflammation in diabetes to poor functional outcomes and exacerbated cognitive impairment, also known as post-stroke cognitive impairment (PSCI). Although we have shown that the development of PSCI in diabetes is associated with the upregulation and the activation of pro-inflammatory microglia, we have not established direct causation between the two. To this end, we evaluated the role of microglia in the development of PSCI.MethodsAt 13 weeks of age, diabetic animals received bilateral intracerebroventricular (ICV) injections of short hairpin RNA (shRNA) lentiviral particles targeting the colony stimulating factor 1 receptor (CSF1R). After 14 days, animals were subjected to 60 min middle cerebral artery occlusion (MCAO) or sham surgery. Adhesive removal task (ART), novel object recognition (NOR), and 2-trial Y-maze were utilized to evaluate sensorimotor and cognitive function. Tissue from freshly harvested brains was analyzed by flow cytometry and immunohistochemistry.ResultsCSF1R silencing resulted in a 94% knockdown of residential microglia to relieve inflammation and improve myelination of white matter in the brain. This prevented cognitive decline in diabetic animals.ConclusionMicroglial activation after stroke in diabetes may be causally related to the development of delayed neurodegeneration and PSCI.

Highlights

Over 40% of stroke victims have pre-existing diabetes which increases their risk of stroke up to 2–6 fold, and worsens both functional recovery and the severity of cognitive impairment
Bilateral injections of Colony-stimulating factor 1 receptor (CSF1R) ShRNA resulted in a significant reduction of both residential microglia and macrophages In order to identify the best short hairpin RNA (shRNA) construct to silence the CSF1R, 3 different shRNAs were injected into the lateral ventricles of normal Wistar rats
After identifying a shRNA of choice, we evaluated whether the silencing would produce similar results in diabetic animals, and whether that knockdown would be sustained over 5 weeks

Summary

Introduction

Over 40% of stroke victims have pre-existing diabetes which increases their risk of stroke up to 2–6 fold, and worsens both functional recovery and the severity of cognitive impairment. It is recognized that the balance of pro- and antiinflammatory mediators determines the detrimental or Jackson et al Journal of Neuroinflammation (2020) 17:137 beneficial effects of neuroinflammation on brain injury and repair after stroke [5, 6] This balance is altered in favor of pro-inflammatory cells and cytokines in comorbid diseases like diabetes [7, 8]. We showed that diabetes, as a chronic inflammatory disease, increases the number of activated ameboid microglia and worsens cognitive outcomes of stroke [12, 13] These studies suggest that the inflammatory status of microglia can be modulated by the microenvironment [14]. Given that 70% of stroke victims have pre-existing comorbidities such as diabetes and hypertension at the time of stroke, and diabetes worsens functional recovery and the severity of PSCI to an even greater extent, better understanding of the “primed” inflammatory microglia in the brain may allow us to modulate these cells to a beneficial phenotype to prevent progression of PSCI [8, 15]

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Conclusion