Glial cell response and microthrombosis in aneurysmal subarachnoid hemorrhage patients: An autopsy study

Abstract

Neuroinflammation and microthrombosis may be underlying mechanisms of brain injury after aneurysmal subarachnoid hemorrhage (aSAH), but they have not been studied in relation to each other. In postmortem brain tissue, we investigated neuroinflammation by studying the microglial and astrocyte response in the frontal cortex of 11 aSAH and 10 control patients. In a second study, we investigated the correlation between microthrombosis and microglia by studying the microglial surface area around vessels with and without microthrombosis in the frontal cortex and hippocampus of 8 other aSAH patients. In comparison with controls, we found increased numbers of microglia (mean ± SEM 50 ± 8 vs 20 ± 5 per 0.0026 mm³, p < 0.01), an increased surface area (%) of microglia (mean ± SEM 4.2 ± 0.6 vs 2.2 ± 0.4, p < 0.05), a higher intensity of the astrocytic intermediate filament protein glial fibrillary acidic protein (GFAP) (mean ± SEM 184 ± 28 vs 92 ± 23 arbitrary units, p < 0.05), and an increased GFAP surface area (%) (mean ± SEM 21.2 ± 2.6 vs 10.7 ± 2.1, p < 0.01) in aSAH tissue. Microglia surface area was approximately 40% larger around vessels with microthrombosis than those without microthrombosis (estimated marginal means [95% CI]; 6.1 [5.4-6.9] vs 4.3 [3.6-5.0], p < 0.001). Our results show that the microglial and astrocyte surface areas increased after aSAH and that microthrombosis and microglia are interrelated.

Keywords: Astrocytes; Autopsy; Brain aneurysm; Glia; Inflammation; Microglia; Microthrombosis; Subarachnoid hemorrhage.

Figure 1.

Microglial response in the frontal cortex of aSAH patients. (A, B) Representative images of Iba-1-positive cells in the frontal cortex of a control donor (A), and an aSAH patient (B). (C) Iba-1 area% is increased after human aSAH. (D) The number of Iba1-positive cells is increased after aSAH. Scale bars: 40 µm, points in graphs represent individuals; Student t-tests; *p ≤ 0.05; **p ≤ 0.01; Bars and error bars in mean ± SEM; aSAH: aneurysmal subarachnoid hemorrhage.

Figure 2.

Astrocyte response in the frontal cortex of aSAH patients. (A, B) Representative image of GFAP-positive cells in the frontal cortex of a control (A), and of an aSAH patient (B). (C) GFAP area% is increased after aSAH. (D) The intensity of GFAP is also increased after aSAH. Scale bars: 40 µm; points in graphs represent individuals; Student t-tests; *p ≤ 0.05; **p ≤ 0.01; Bars and error bars in mean ± SEM; aSAH: aneurysmal subarachnoid hemorrhage.

Figure 3.

Microthrombosis and microglial response in the hippocampal and frontal cortex of aSAH patients. (A) Representative images of fibrinogen, vimentin, and Iba-1 staining with the enlarged selections of a vessel without and with microthrombosis. The circles indicate the areas in which we quantified glial activation; (B) Estimated mean Iba-1 surface area percentage is higher around vessels with microthrombosis compared to vessels without microthrombosis in brain tissue from aSAH patients. Scale bars: 40 µm; Mixed model; **p ≤ 0.01; Bars and error bars in estimated mean ± SEM; aSAH: aneurysmal subarachnoid hemorrhage; Microthrombosis−: vessel without microthrombosis; Microthrombosis+: vessel with microthrombosis.