3D in vitro modeling of the central nervous system

Abstract

There are currently more than 600 diseases characterized as affecting the central nervous system (CNS) which inflict neural damage. Unfortunately, few of these conditions have effective treatments available. Although significant efforts have been put into developing new therapeutics, drugs which were promising in the developmental phase have high attrition rates in late stage clinical trials. These failures could be circumvented if current 2D in vitro and in vivo models were improved. 3D, tissue-engineered in vitro systems can address this need and enhance clinical translation through two approaches: (1) bottom-up, and (2) top-down (developmental/regenerative) strategies to reproduce the structure and function of human tissues. Critical challenges remain including biomaterials capable of matching the mechanical properties and extracellular matrix (ECM) composition of neural tissues, compartmentalized scaffolds that support heterogeneous tissue architectures reflective of brain organization and structure, and robust functional assays for in vitro tissue validation. The unique design parameters defined by the complex physiology of the CNS for construction and validation of 3D in vitro neural systems are reviewed here.

Three-Dimensional Neural Spheroid Culture: AnIn VitroModel for Cortical Studies

“…23,32 The spheroid culture allows for high density, which can mimic in vivo intercellular distance and communication better than scaffold cultures. 1 Cell density in spheroids at 1 DIV (2 · 10 6 cells/ mm 3 ) was approximately one magnitude higher than in vivo density. Cell aggregation in the spheroid can be described as close packing of spheres, 33 thus the initial cell density within the spheroid is dependent on cell size rather than the number of cells per spheroid.…”

“…Thus, 3D cultures have typically been limited to extracellular field potential recordings of far lower resolution and generally do not identify neurotransmitter type. 1,16 Here, spheroids can be removed from the hydrogel mold and immobilized on coverslips, making this 3D culture compatible with patch-clamp recording. Wholecell recordings at 14 and 21 DIV showed that the neurons in the spheroids had matured and were able to fire spontaneous and evoked action potentials associated with mature neurons.…”

“…Neurons and glial cells in the brain form a complex three-dimensional (3D), intertwined system and, therefore, engineering the microenvironment for in vitro investigations presents many inherent challenges. 1 Microenvironmental cues, such as cellular, biochemical, mechanical, and topographical cues, can influence cell behaviors, including viability, proliferation, differentiation, migration, and protein and gene expressions. [2][3][4][5][6] Notably, many native microenvironmental cues are lost in traditional twodimensional (2D) cultures, in which cells spread on substrates that are often several orders of magnitudes stiffer than brain tissue and lack the brain's extracellular matrix (ECM) organization.…”

“…Three-dimensional in vitro neural models have exciting potential to bridge the gap between traditional 2D cultures and in vivo models. 1,8 For example, 3D culture of human induced pluripotent stem cells has enabled the study of microcephaly, 9 and the hallmarks of Alzheimer's disease, amyloid-b plaques, and neurofibrillary tangles, have been more effectively modeled in 3D cultures than in 2D. 10 Historically, 3D neural cultures were developed using scaffolds, 3,[11][12][13][14] and complex cell compartmentalization and organization have been achieved through scaffold design.…”

Brain infiltration by cancer cells: different roads to the same target?

“…The development and refinement of existing in vitro three-dimension models of BBB, traditionally employed in the screening of drugs or molecule designed to cross the BBB, could be used as a novel approach to investigate the genotype and phenotype of cancer cells that migrate through artifi cial BBBs. [114,115] Also, the previous mentioned breakthrough discovery of the presence of lymphatic vessels in the brain could open an avenue of cutting edge experimental approaches in the study of CTCs and BM.…”