Injection of Microporous Annealing Particle (MAP) Hydrogels in the Stroke Cavity Reduces Gliosis and Inflammation and Promotes NPC Migration to the Lesion

Abstract

With the number of deaths due to stroke decreasing, more individuals are forced to live with crippling disability resulting from the stroke. To date, no therapeutics exist after the first 4.5 h after the stroke onset, aside from rest and physical therapy. Following stroke, a large influx of astrocytes and microglia releasing proinflammatory cytokines leads to dramatic inflammation and glial scar formation, affecting brain tissue's ability to repair itself. Pathological conditions, such as a stroke, trigger neural progenitor cells (NPCs) proliferation and migration toward the damaged site. However, these progenitors are often found far from the cavity or the peri-infarct tissue. Poststroke tissue remodeling results in a compartmentalized cavity that can directly accept a therapeutic material injection. Here, this paper shows that the injection of a porous hyaluronic acid hydrogel into the stroke cavity significantly reduces the inflammatory response following stroke while increasing peri-infarct vascularization compared to nonporous hydrogel controls and stroke only controls. In addition, it is shown that the injection of this material impacts NPCs proliferation and migration at the subventricular zone niche and results, for the first time, in NPC migration into the stroke site.

Keywords: inflammation; neural progenitor cells; particle hydrogels; porous hydrogels; stroke.

Figure 1

A. Schematic illustration of a coronal mouse brain section showing the location of the cortical stroke cavity. The magnified schematics illustrate the no gel, the nano-porous and the MAP hydrogel injection conditions. B. Fluorescent images of GFAP staining showing post-stroke astrocytic response in the different conditions (scale 100 μm). C. Iba-1 staining showing post-stroke microglial response in the different conditions (scale 100 μm). D. Analysis of the GFAP positive response in terms of scar thickness, astrocytic infiltration in the infarct area and the positive area for GFAP signal in both infarct and peri-infarct regions. E. Analysis of the Iba-1 positive response in terms of positive area for GFAP signal in both infarct and peri-infarct regions. *, ** and **** indicate P < 0.05, P < 0.01 and P < 0.0001, respectively (Anova 1 way, Tukey's opst-hoc test).

Figure 2

A. Full section fluorescent image and magnification showing DCX positively labeled NPCs (green) migrating from the ipsilateral ventricle to the stroke area (scale 0.5mm). B. Co-staining of Ki67 (green) and DCX positive NPCs (white) (scale 100μm). C. Analysis of KI67 / DCX total cell number and migrating distance. *, *** and **** indicate P < 0.05, P < 0.001 and P < 0.0001, respectively (Anova 1 way, Tukey's opst-hoc test).

Figure 3

A. Fluorescent images and B. magnification of the stroke area in both the nanoporous and the MAP gel condition showing DCX positive cells (green) in the lesion site of the MAP–treated animals only (scale 100 μm). C. Analysis of the positive area for DCX signal in the stroke site in the different conditions. **** indicates P < 0.0001 (Anova 1 way, Tukey's opst-hoc test).

Scheme 1

A. Schematic illustration of flow focusing microfluidic device to produce μgels that can be annealed to each other using enzyme factor XIII to form a scaffold. B. Important flow rates and device parameters to produce the μgels. C. Distribution of μgels diameters produced using the microfluidic device. D. Young's Modulus in compression calculated using Instron mechanical tests showing scaffold stiffness similar to brain cortex