Harnessing 3D and 4D in vitro models to deconstruct human neurodisorders

Mechanisms controlling human brain development, despite their relevance, remain poorly understood, given the challenges of studying human embryos and the developmental divergence from animal models. Human (h)iPSC-based in vitro models can be used to understand mechanisms of human brain development and its possible alterations, thereby bypassing substantial interspecies differences. Indeed, human brain complexity suggests tightly regulated and detailed developmental steps, which can be undermined by several insults leading to severe pathologies.Conventional 2D-cell cultures do not recapitulate the complex 3D structure of the developing human brain. To bridge this gap, hiPSC-based 3D models have been explored to mirror spatial and structural complexity of the developing human brain environment in healthy and pathological contexts. 3D can be further improved with the addition of a fourth dimension to closely resemble the in vivo organ formation. 4D printing is a bio-fabrication approach that adds the fourth dimension - “time” - to the three spatial dimensions. A 4D object is characterized by changes in shape after a stimulus mimicking physiological movements, possibly promoting cell growth and differentiation. We applied this approach to model early neurodevelopmental processes during neural tube formation. Then, by taking advantage of patient and isogenic control iPSC-derived 3D and 4D neuroderivatives (i.e., cerebrocortical organoids and 4D scaffolds), we investigated the cellular and molecular aspects of autosomal recessive primary microcephaly, a rare neurodevelopmental pathology linked to WDR62 mutations. Thus, by applying these innovative 3D and 4D neural models, we established relevant in vitro platforms to unravel human neural development and its alterations.