Genetic deletion of the prostaglandin E₂ E prostanoid receptor subtype 3 improves anatomical and functional outcomes after intracerebral hemorrhage

Abstract

Intracerebral hemorrhage (ICH) is a stroke subtype associated with high mortality and morbidity. Following ICH, excitotoxicity and inflammation significantly contribute to secondary brain injury and poor outcomes. Prostaglandin E2 (PGE2) levels rise locally with insult to the nervous system, and PGE2 is known to modulate these processes mainly through its E prostanoid (EP) receptors, EP1–4. EP3 is the most abundant EP receptor in the brain and we have previously shown that signaling through the PGE2-EP3 axis exacerbates excitotoxicity and ischemic stroke outcomes. This study aimed to investigate the contribution of this pathway in modulating anatomical outcomes and functional recovery following ICH. Genetic deletion of the EP3 receptor resulted in 48.2 ± 7.3% less ICH-induced brain injury (p < 0.005) and improved functional recovery (p < 0.05), as identified by neurological deficit scoring. To start investigating the mechanisms involved in neuroprotection with impaired PGE2-EP3 signaling, histological staining was performed to evaluate blood and ferric iron accumulation, neuroinflammation, blood brain barrier dysfunction, and peripheral neutrophil infiltration. After ICH, EP3−/− mice demonstrated 49.5 ± 8.8% and 42.8 ± 13.1% less blood (p < 0.01) and ferric iron content (p < 0.05), respectively. Furthermore, EP3−/− mice had significantly reduced astrogliosis, microglial activation, blood brain barrier breakdown, and neutrophil infiltration. Collectively, these results suggest an injurious role for the PGE2-EP3 signaling axis in modulating brain injury, inflammation, and neurologic functional recovery after ICH. Modulation of the PGE2-EP3 signaling axis may represent a putative therapeutic avenue for the treatment of ICH.

Modulators of microglial activation and polarization after intracerebral haemorrhage

“…Although EP2 is expressed in neurons rather than in microglia, deletion of EP2 led to an increase in M1-like microglial activation, indicating a potential EP2-mediated interaction between neurons and microglia 148 . By contrast, EP3 receptors are expressed in microglia 108 , and EP3 deletion caused decreased micro-glial activation in mice with collagenase-induced ICH 151 . Similarly, treatment with an EP3 antagonist inhibited microglial activation in mice with thrombin-induced ICH 108 , although this treatment increased the number of M2 microglia (as shown by CD11b and Ym1 double immunostaining) 108 .…”

The absence of the CD163 receptor has distinct temporal influences on intracerebral hemorrhage outcomes

“…Functional outcomes were assessed by open field locomotor activity, rotarod, and neurological deficit scores (NDS) daily post-ICH. 16 Behavioral tests were performed in the same order and at the same time of day, with 1 h of rest between tests.…”

“…Histology and quantification were conducted as we have described. 16 Briefly, 10 sets of 16 sections equally distributed throughout the hematoma and anteroposterior brain regions were processed. Cresyl violet staining was used to assess lesion and hematoma volume, tissue injury, percent ipsilateral hemispheric enlargement, and hematoidin-pigment (bilirubin).…”

“…These algorithms were tuned for each stain such that the appropriate signal level was detected. 16 Hematoma volume: after running the algorithm, the number of blood-positive pixels was converted into an area using pixel size and a volume was calculated in an identical manner as for lesion volume. Tissue injury: hematoma volume was subtracted from total lesion volume.…”

Leukotriene D 4 and prostaglandin E 2 signals synergize and potentiate vascular inflammation in a mast cell–dependent manner through cysteinyl leukotriene receptor 1 and E-prostanoid receptor 3

“…31 High expression of EP 3 is observed in the brain, and recent findings suggest an injurious role for the PGE 2 -EP 3 signaling axis in modulating brain injury and inflammation after intracerebral hemorrhage. 38 Along similar lines, enhanced EP 3 expression and signaling were found in patients with diabetes and have been speculated as a new therapeutic target for β-cell dysfunction in patients with type 2 diabetes. 39 …”