Particle Hydrogels Decrease Cerebral Atrophy and Attenuate Astrocyte and Microglia/Macrophage Reactivity after Stroke

Abstract

Increasing numbers of individuals live with stroke related disabilities. Following stroke, highly reactive astrocytes and pro-inflammatory microglia can release cytokines and lead to a cytotoxic environment that causes further brain damage and prevents endogenous repair. Paradoxically, these same cells also activate pro-repair mechanisms that contribute to endogenous repair and brain plasticity. Here, it is shown that the direct injection of a hyaluronic acid-based microporous annealed particle (MAP) hydrogel into the stroke core in mice reduces the percent of highly reactive astrocytes, increases the percent of alternatively activated microglia, decreases cerebral atrophy, and preserves NF200 axonal bundles. Further, MAP hydrogel is shown to promote reparative astrocyte infiltration into the lesion, which directly coincides with axonal penetration into the lesion. This work shows that the injection of a porous scaffold into the stroke core can lead to clinically relevant decrease in cerebral atrophy and modulates astrocytes and microglia toward a pro-repair phenotype.

Reactive astrocyte derived extracellular vesicles promote functional repair post stroke

“…MAPS scaffolds are infiltrated by stroke and peri-infarct resident cells through its void space, space between microgel particles, and not through direct microgel infiltration. 18 Thus, the void space within the implanted MAPS is filled by residing and infiltrating cells (Fig. 1d and Extended Data Fig.…”

“…Thus, we moved to combine the EVs with a defined matrix that can be injected into the stroke core to deliver therapeutic cargo 16,17 and that was previously found to reduce the inflammatory phenotype of astrocytes and microglia. 18…”

“…We first investigated injection of Rep-EV (1.8 × 10 6 particles/mL) directly into the stroke cavity following our prior therapeutic approach 16,17 to assess their therapeutic potential. In our therapeutic strategy, therapeutic agents are injected into the infarct at Day 5 post-stroke, a timepoint at which a cavity has formed and pro-repair pathways remain active.…”

“…18 Though, repeated injections, higher dose, or a different timepoint, could improve outcomes by direct EV delivery, we moved to combine the EVs with a defined matrix that can be injected into the stroke core to deliver therapeutic cargo 19,20 and that was previously found to reduce the inflammatory phenotype of astrocytes and microglia. 17 Our defined matrix is a hydrogel composed of hyaluronic acid microgel building blocks, which undergoes gelation in situ through a bio-orthogonal strain-promoted azide-alkyne click reaction to form a porous hydrogel that allows for diffusion of soluble factors and cell infiltration. These hydrogels are termed microporous annealed particle scaffolds (MAPS).…”

Mechanical Evaluation of Hydrogel-Elastomer Interfaces Generated Through Thiol-Ene Coupling

“…Hydrogels generated through thiol-ene coupling, the reaction of thiol residues with alkenes, are increasingly used for the encapsulation of cells within 3D hydrogels and the design of soft materials for drug release [1][2][3] . This enables to achieve a broad control of physico-chemical properties that, in turn, can regulate cell phenotype [4][5][6][7] , the delivery of therapeutics 8,9 and repair of soft tissues [10][11][12][13] . Indeed, the excellent control of crosslinking through Michael addition and radical mechanisms, even in the presence of air and in physiological conditions, allows the control of mechanical properties of resulting hydrogels whilst enabling the incorporation of a broad range of eukaryotic cells with excellent viabilities 4,[14][15][16][17] .…”