Hemorrhagic Stroke Induces a Time-Dependent Upregulation of miR-150-5p and miR-181b-5p in the Bloodstream

To date, the only effective pharmacological treatment for ischemic stroke is limited to the clinical use of recombinant tissue plasminogen activator (rtPA), although endovascular therapy has also emerged as an effective treatment for acute ischemic stroke. Unfortunately, the benefit of this treatment is limited to a 4.5-h time window. Most importantly, the use of rtPA is contraindicated in the case of hemorrhagic stroke. Therefore, the identification of a reliable biomarker to distinguish hemorrhagic from ischemic stroke could provide several advantages, including an earlier diagnosis, a better treatment, and a faster decision on ruling out hemorrhage so that tPA may be administered earlier. microRNAs (miRNAs) are stable non-coding RNAs crucially involved in the downregulation of gene expression via mRNA cleavage or translational repression. In the present paper, taking advantage of three preclinical animal models of stroke, we compared the miRNA blood levels of animals subjected to permanent or transient middle cerebral artery occlusion (MCAO) or to collagenase-induced hemorrhagic stroke. Preliminarily, we examined the rat miRNome in the brain tissue of ischemic and sham-operated rats; then, we selected those miRNAs whose expression was significantly modulated after stroke to create a list of miRNAs potentially involved in stroke damage. These selected miRNAs were then evaluated at different time intervals in the blood of rats subjected to permanent or transient focal ischemia or to hemorrhagic stroke. We found that four miRNAs—miR-16-5p, miR-101a-3p, miR-218-5p, and miR-27b-3p—were significantly upregulated in the plasma of rats 3 h after permanent MCAO, whereas four other different miRNAs—miR-150-5p, let-7b-5p, let-7c-5p, and miR-181b-5p—were selectively upregulated by collagenase-induced hemorrhagic stroke. Collectively, our study identified some selective miRNAs expressed in the plasma of hemorrhagic rats and pointed out the importance of a precise time point measurement to render more reliable the use of miRNAs as stroke biomarkers.

The neuroprotective effect of meloxicam in a transient ischemia model involves an increase in axonal sprouting but a decrease in new neuron formation after 7 days of reperfusion

The inflammatory response plays an important role in neuroprotection and regeneration after ischemic insult. The use of non-steroidal anti-inflammatory drugs has been a matter of debate as to whether they have beneficial or detrimental effects. In this context, the effects of the anti-inflammatory agent meloxicam have been scarcely documented after stroke, but its ability to inhibit both cyclooxygenase isoforms (1 and 2) could be a promising strategy to modulate post-ischemic inflammation. This study analyzed the effect of the anti-inflammatory agent meloxicam in a transient focal ischemia model in rats, measuring its neuroprotective effect after 48 hours and 7 days of reperfusion and the effects of the treatment on the glial scar and regenerative events such as the generation of new progenitors in the subventricular zone and axonal sprouting at the edge of the damaged area. We show that meloxicam's neuroprotective effects remained after 7 days of reperfusion even if its administration was restricted to the two first days after ischemia. Moreover, meloxicam treatment modulated glial scar reactivity, which matched with an increase in axonal sprouting. However, this treatment decreased the formation of neuronal progenitor cells. This study discusses the dual role of anti-inflammatory treatments after stroke and encourages the careful analysis of both the neuroprotective and the regenerative effects in preclinical studies.

Abstract P835: Long Noncoding RNA FosDT is Developmentally Dispensable but Critical for Shaping the Therapeutic Post-Stroke Functional Outcome

Stroke induces the expression of several long noncoding RNAs (lncRNAs) in the brain. However, their functional significance in post-stroke outcome is poorly understood. We recently observed that a brain-specific lncRNA called Fos downstream transcript (FosDT) is induced rapidly in rodent brain following focal ischemia. We here show that FosDT expression is developmentally regulated with adults specifically display higher expression in the cerebral cortex than neonates. To understand its significance in ischemic brain damage, we developed FosDT knockout rats using CRISPR-Cas9 genome editing. We found that FosDT knockout rats did not show any anomalies in growth and development, fertility, brain cytoarchitecture and cerebral vasculature. However, when subjected to transient focal ischemia, FosDT knockout rats of both sexes showed enhanced sensorimotor recovery and reduced brain damage. To further understand the mechanistic implications of FosDT in the ischemic brain, we conducted RNA-seq analysis. The result showed that improved post-stroke functional outcome in FosDT knockout rats is partially associated with curtailed post-ischemic induction of inflammatory genes. When rats subjected to transient focal ischemia were treated with FosDT siRNA, there was significant neuroprotection and better functional outcome irrespective of sex and age. FosDT siRNA was efficacious when administered peripherally and also in a delayed manner. Thus, preventing FosDT activation is beneficial for the post-stroke outcome.

Abstract 109: Depletion of Microglia Does Not Improve Functional Outcomes in Aged Mice After Transient Focal Ischemia

Introduction: With aging, microglia acquire a dysfunctional phenotype characterized by dystrophic morphology, impaired phagocytosis, reduced motility, and an exaggerated response to injury. Microglia become pathologically activated with aging and play a detrimental role in age-associated cognitive decline and neurodegenerative diseases. Older mice exhibit a differential response to stroke and have worse outcomes despite smaller infarcts compared to young mice. Microglia from aged mice produce higher levels of reactive oxidative species and have an exaggerated inflammatory response after ischemic stroke. Hypothesis: We hypothesized that ablation of microglia would reduce the exaggerated neuroinflammatory responses in aged mice and loss of microglia would improve early recovery after ischemic stroke. Aged (18-19 months) male mice were fed a control chow diet (CD) or PLX5622 chow diet (PLXD) for 21 days. On day 22, 60-minute middle cerebral artery occlusion (MCAo) or sham surgery was performed. Twenty-four hours after MCAo, neurological deficit scores (NDS) and immunohistochemistry assessments, as well as flow cytometry, were performed. Results: There was a significant reduction in Iba1 + cells in striatum and cortex of the aged mice with PLX treatment: day 7 (p<0.05), day 14 (p<0.001), and day 21 (p<0.001) vs day 0. Twenty-four hours after MCAo, the NDS were not different between CD (3.0±0.18) and PLXD (2.92±0.21). However, an increase in infarct size was seen in the aged PLXD group compared to the aged CD group (p<0.05). After MCAo, there was an increase in infiltrating monocytes and neutrophils in both diet groups compared to their respective shams (p<0.05). However, an increase in infiltrating monocytes was observed in the PLXD MCAo vs. CD MCAo (p<0.0001) reflecting a differential monocyte response in animals without microglia. Additionally, a decrease in NeuN immunoreactivity was seen in the PLXD MCAo group compared to PLXD sham (p<0.01). GFAP + cells increased in PLXD sham group as compared to CD sham (p<0.05). Conclusions: Our results suggest that microglia are essential immune cells that surprisingly limit immune cell infiltration, decrease neuronal degeneration, and reduce neuroinflammation after ischemic stroke in aged mice.

Abstract 111: Myeloid Specific Deletion of CD36 Increases Microglia-Like CD45 Low Subset and Exacerbates Stroke-Induced Brain Injury

Objective: CD36 regulates biological and pathological processes including inflammation, resolution, phagocytosis, and angiogenesis. Highly expressed in monocytes/macrophages (MM), MM CD36 has been implicated in both detrimental and beneficial effects in acute stroke outcome and recovery. Using myeloid specific deficiency of CD36 (CD36KO MM ) mice, the present study addresses the role of MM CD36 on subset composition of MM in the acute and recovery phases of stroke. Methods: WT (CD36 fl/fl ) and CD36KO MM (M/F, 12w old) mice were subjected to transient focal ischemia. Brain immune cells were collected at 3d, 7d and 2m (n=8-12/timepoint). Infarct volume and hemispheric swelling were measured at 3d (n=13/genotype). In the isolated brain immune cells, CD11b+ cells were further distinguished by CD45 Hi and CD45 Low subsets. The extent of MM trafficking was determined by an intravenous infusion of control GFP+ splenocytes into the stroked WT and CD36KO MM mice 1d prior to sacrifice and MM subset analyses. Results: Compared to WT mice, CD36KO MM mice showed no difference in CD45 Low subset at 3d, 7d and 2m after stroke. However, CD36KO MM mice displayed a significant reduction of CD45 Hi subset, presumably infiltrating cells, at these time points (n=4-8 /group, P<0.01). Adoptive transfer of control GFP+ splenocytes to stroked CD36KO MM mice resulted in an increase of GFP+ cells in CD45 Low but a profound reduction in CD45 Hi subset. Despite the near absence of CD45 Hi and increased CD45 Low population in the post-ischemic brain, CD36KO MM mice displayed exacerbation of brain injury (15.1±13.7 vs 25.8±17.5 mm 3 , p<0.05) and brain swelling (12.1±10.3 vs 18.4±12.7 %, p=0.1). Conclusion: The observed reduction of CD45 Hi subset and exacerbation of brain injury in CD36KO MM mice suggests a beneficial role of infiltrated CD45 Hi MMs in limiting stroke injury. The sustained trafficking at 2m indicates potential involvement of MM CD36 in the recovery process. Further studies to assess long-term outcomes of CD36KO MM mice will provide critical insights on the role of macrophage CD36 in stroke recovery.