Delayed Administration of Angiotensin Receptor (AT2R) Agonist C21 Improves Survival and Preserves Sensorimotor Outcomes in Female Diabetic Rats Post-Stroke through Modulation of Microglial Activation

About 70% of stroke victims present with comorbid diseases such as diabetes and hypertension. The integration of comorbidities in pre-clinical experimental design is important in understanding the mechanisms involved in the development of stroke injury and recovery. We recently showed that administration of compound C21, an angiotensin II type 2 receptor agonist, at day 3 post-stroke improved sensorimotor outcomes by lowering neuroinflammation in diabetic male animals. In the current study, we hypothesized that a delayed administration of C21 would also lower chronic inflammation post-stroke in diabetic female animals. Young female diabetic rats were subjected to 1 h of middle cerebral artery occlusion (MCAO). Three days post-stroke, rats were administered C21 or vehicle in drinking water at a dose of 0.12 mg/kg/day for 4 weeks. The impact of C21 on microglial polarization was analyzed by flow cytometry in vivo and in vitro. Compound 21 treatment improved fine motor skills after MCAO through modulation of the microglia/macrophage inflammatory properties. In addition, C21 increased M2 polarization and reduced the M1:M2 ratio in vitro. In conclusion, delayed administration of C21 downregulates post-stroke inflammation in female diabetic animals. C21 may be a useful therapeutic option to lower neuro-inflammation and improve the post-stroke recovery in diabetes.

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

INTRODUCTION

Unfortunately, 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.

METHODS

At 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.

RESULTS

CSF1R 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.

CONCLUSION

Microglial activation after stroke in diabetes may be causally related to the development of delayed neurodegeneration and PSCI.

Abstract WP155: Delayed Administration of Angiotensin Receptor (AT2-R) Agonist C21 Downregulates Diabetes Induced Pro-Inflammatory Microglia Activation Post-Stroke in Female Rats: Therapeutic Indications for Vascular Cognitive Impairment & Dementia

Post-stroke cognitive impairment (PSCI) occurs in up to 48% of patients, for which there is no therapy. Although 70% of stroke victims present with comorbid diseases such as diabetes and hypertension, the inadequate integration of these comorbidities into experimental studies limited our understanding of the mechanisms involved in the development of PSCI. Based on our recent findings that 1) the increased prevalence of PSCI in male diabetic animals is linked to heightened chronic inflammation and 2) even delayed administration of compound 21 (C21), an angiotensin II Type 2 receptor agonist, effectively reduces PSCI by lowering inflammation in male animals, we hypothesized that a delayed administration of C21 would also lower chronic inflammation post-stroke in female animals.

Methods: Diabetes was induced by a high fat diet (HFD) and low dose streptozotocin (STZ) combination. Rats were subjected to 1 h middle cerebral artery occlusion (MCAO) or sham surgery. 3 days post-stroke, rats were administered C21 or vehicle in drinking water at a dose of 0.12 mg/kg/day for 4 weeks. The direct effect of C21 on microglia polarization was determined in mouse cells (C8B4) and the mature:pro BDNF ratio was evaluated through western blot. Samples from freshly harvested brains (B-D slice containing the prefrontal cortex through the hippocampus), and from cell culture were analyzed by flow cytometry.

Results: Delayed administration of C21 starting 3 days post-stroke improved inflammation through modulation of the M1/M2 ratio. Cell culture results indicated that along with decreasing the M1/M2 ratio, it also increased the mature/pro-BDNF ratio.

Conclusion: Delayed administration of C21 downregulates post-stroke inflammation in both male and female diabetic animals. This study emphasizes the importance of translational disease modeling and suggests that C21 may be a useful therapeutic option to lower inflammation and prevent PSCI in comorbid diseases.

Abstract WP478: Microglia Knockdown Reduces Inflammation and Improves Post-Stroke Cognitive Impairment in Diabetic Animals

Unfortunately, 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 that persists in diabetic animals to their 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 activation of pro-inflammatory microglia, we have not established a direct causation between the two. We tested the hypothesis that microglia depletion in the post-stroke recovery period prevents sustained inflammation and attenuates PSCI in diabetes.

Methods: Diabetes was induced by a high fat diet (HFD) and low dose streptozotocin (STZ) combination. At 13 weeks of age, diabetic animals received bilateral intracerebroventricular (ICV) injections of short hairpin RNA (shRNA) lentiviral particles targeted at the colony stimulating factor 1 receptor (CSF1R), a key factor for microglia survival. After 14 days, animals were subjected to 60 min middle cerebral artery occlusion (MCAO) or sham surgery. Novel object recognition (NOR), and 2-trial Y-maze were utilized to evaluate cognitive function. Brains were analyzed by flow cytometry (B-D slice containing the prefrontal cortex through the hippocampus) and immunohistochemistry (B slice) 3 weeks post-MCAO.

Results: CSF1R silencing resulted in a drastic 94% knockdown of residential microglia to relieve inflammation and decrease the macrophage infiltration by 74%. This also led to improved myelination of white matter in the brain and improved cognition in diabetic animals.

Conclusion: Neuroinflammation, through microglial and macrophage polarization, is largely responsible for the development of PSCI in diabetes.