Progress towards brain organoid models with representative neurovascular features

Abstract

Vascular dysfunction in the brain is a leading risk factor for dementia and neurodegeneration. However, brain vascular pathology is difficult to recapitulate in an animal model without influencing other aspects of disease. Thus, it remains challenging to understand how specific insults lead to brain vascular pathology and how the subsequent changes to vascular function mechanistically impact neurodegeneration. To complement animal models and help overcome these challenges, our lab develops engineered models of the vascularized human brain from combinations of human induced pluripotent stem cell (iPSC)-derived progenies and primary tissue. We specifically focus on developing models that have: (1) neural organization and architecture similar to human cortex; (2) representative neurovascular features. We previously fabricated a functionalized hydrogel (O'Grady et al, ACS Biomat Sci & Eng, 2020) that presents an extracellular peptide epitope from N-cadherin, an important cell-cell adhesion receptor that directs cortical development. This hydrogel forms the basis for our studies. (1) Brain organoids were differentiated from human induced pluripotent stem cells (iPSCs) using published methods, then embedded in the N-cadherin functionalized hydrogel and various controls. Microscopy techniques were used to assess cellular identity and organization. (2) Primary cortical tissue was isolated from euthanized mice or human autopsy and embedded in a variant of the N-cadherin functionalized hydrogel to induce vascular outgrowth. A custom microfluidic device was built to direct vascular organization using gradients of small molecules and growth factors. Microscopy and molecular biology techniques were used to assess vascular identity and function. (1) Organoids in the N-cadherin functionalized hydrogel have more representative features of the brain, including a single neuroepithelial core segregated from the outer progenitor zone and appropriate laminar patterning of cortical layers. (2) Arterioles and capillaries with biomimetic features, including proper size and multicellular organization, can be grown from primary tissue CONCLUSION: A unifying hydrogel can pattern iPSC-derived brain organoids and coax growth of blood vessels from primary brain tissue. Ongoing work is focused on integrating these platforms to generate a neurovascular organoid where the vessels can be perfused. Once completed, this model may provide an avenue for understanding how vascular dysfunction impacts neural function and subsequent degeneration.