FGF2 Boost for Driving Forebrain Organoid Maturation Under Static Conditions

Abstract

Forebrain organoids (FOs) closely replicate key features of human brain, but often develop necrotic cores due to oxygen diffusion limits, resulting in disassembly. While dynamic culture devices can mitigate this, they add variability and diverge from adult cerebral static environment. Inspired by allometric scaling principles of brain growth, we developed a uniform, static culture protocol applying a 1-day transient high-dose Fibroblast Growth Factor 2 (100 ng/ml) treatment before neural induction. This acted as a proliferative stimulus, promoting long-term viability and structural integrity. Using human embryonic stem cells, early-FOs with diameters of 500–1000 µm achieved an 83.33% survival rate at 20 days in vitro (DIV). Area and volume increased significantly during 60 DIV culture period, but between 30 and 60 DIV they plateaued, indicating a transition from neural development to maturation. Weight increased until 30 DIV, but it significantly dropped between 30 and 60 DIV, possibly reflecting the formation of lumen-like structures. At 60 DIV, immunofluorescence revealed organized PAX6+ ventricle-like structures, where SOX2 marked neural progenitors, TUJ1 and MAP2 indicated mature neurons, GFAP identified astrocytes, and SYN1 highlighted emerging synaptic networks. This scalable protocol supports robust FOs generation, providing optimization and practical improvement within established frameworks to advance precision medicine.