Impact of Four Common Hydrogels on Amyloid-β (Aβ) Aggregation and Cytotoxicity: Implications for 3D Models of Alzheimer’s Disease

Abstract

The physiochemical properties of hydrogels utilized in 3D culture can be used to modulate cell phenotype and morphology with a striking resemblance to cellular processes that occur in vivo . Indeed, research areas including regenerative medicine, tissue engineering, in vitro cancer models, and stem cell differentiation have readily utilized 3D biomaterials to investigate cell biological questions. However, cells are only one component of this biomimetic milieu. In many models of disease such as Alzheimer’s disease (AD) that could benefit from the in vivo -like cell morphology associated with 3D culture, other aspects of the disease such as protein aggregation have yet to be methodically considered in this 3D context. A hallmark of AD is the accumulation of the peptide amyloid-β (Aβ), whose aggregation is associated with neurotoxicity. We have previously demonstrated the attenuation of Aβ cytotoxicity when cells were cultured within type I collagen hydrogels versus on 2D substrates. In this work, we investigated the extent to which this phenomenon is conserved when Aβ is confined within hydrogels of varying physiochemical properties, notably mesh size and bioactivity. We investigated the Aβ structure and aggregation kinetics in solution and hydrogels composed of type I collagen, agarose, hyaluronic acid, and polyethylene glycol using fluorescence correlation spectroscopy and thioflavin T assays. Our results reveal that all hydrogels tested were associated with enhanced Aβ aggregation and Aβ cytotoxicity attenuation. We suggest that confinement itself imparts a profound effect, possibly by stabilizing Aβ structures and shifting the aggregate equilibrium toward larger species. If this phenomenon of altered protein aggregation in 3D hydrogels can be generalized to other contexts including the in vivo environment, it may be necessary to reevaluate aspects of protein aggregation disease models used for drug discovery.

Colonization versus encapsulation in cell-laden materials design: porosity and process biocompatibility determine cellularization pathways

“…(b) Non-cancerous disease models and regenerative medicine Preclinical models for a large spectrum of pathological conditions also take advantage of the elaboration of cellularized materials. Indicatively, corneal stromal disease models can be obtained using collagen bioinks [266], hydrogels can serve as Alzheimer's disease models [267], and liver toxicity can be assessed through core-shell hydrogel fibres [268]. In addition, the field of regenerative medicine exploits macroporous scaffolds to repair or replace defective tissues unable to self-regenerate.…”

Polysaccharide-Based Hydrogels for Microencapsulation of Stem Cells in Regenerative Medicine

“…In vitro modeling of the more prevalent, sporadic version of such diseases are often more challenging as the replication of disease phenotypes are highly dependent on the physical, chemical and mechanical cues in the microenvironment. A recent study had demonstrated that the amyloid-β plaques formed in an Alzheimer’s disease model may exhibit varying cytotoxicity depending on whether they were confined in 2D or 3D space ( Simpson et al, 2020 ). Agarose, collagen, hyaluronic acid and polyethylene glycol hydrogel cultures were shown to enhance the amyloid-β aggregation towards the larger species which confer lower cytotoxicity as compared to when amyloid-β plaques were found in monolayer cultures.…”

Alzheimer’s Disease: Current Perspectives and Advances in Physiological Modeling

“…In any scaffold-based model, thought must be given to the way in which the properties of the chosen scaffold affect Aβ aggregation and Aβ-mediated cytotoxicity. Simpson et al [ 105 ] recently investigated the effect of hydrogel mesh size on Aβ-mediated cytotoxicity and Aβ aggregate size and structure. They found that 3D scaffolds alleviate some Aβ-related cytotoxicity compared to 2D cultures, a phenomenon that is not related to mesh size or bioactivity, but instead likely results from the rapid stabilization of larger, less toxic Aβ aggregates that is common to 3D hydrogels.…”