Human Spinal Cord-like Organoids to Model C9orf72 Amyotrophic Lateral Sclerosis and Test New Therapies In Vitro

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease. Underlying genetic pathomechanisms include the C9orf72 hexanucleotide GGGGCC repeat expansion, the most frequent genetic cause of ALS (C9-ALS) in Western countries.¹ Neurodegeneration in C9-ALS is supposedly associated with two mechanisms: a loss- and a gain-of-function mechanism.¹ They are not mutually exclusive and depend on the site of transcription start. The former refers to reduced transcription and translation of the C9orf72 protein. The latter involves the increased transcription and translation of hexanucleotide repeat expansion, leading to the generation of foci of transcribed RNA and the accumulation of translated toxic dipeptide repeat proteins.¹ Another pathological hallmark is represented by TDP-43, a ubiquitous intranuclear protein that can translocate and accumulate in a phosphorylated form into the cytoplasm of glial cells and neurons.² Despite recent progress in unravelling C9-ALS pathogenesis, reliable disease models and disease-modifying therapies are still lacking. Organoids refer to 3D cultures derived from induced pluripotent stem cells that present a complex cytoarchitecture with a layered structure, dynamically resembling some phases of early human development.³ Neural organoids consist of diverse cellular subpopulations, including proliferating, differentiating, migrating, and self-organising pools of neural progenitors, enabling the study of cell-to-cell communication, the patterning of peripheral and central nervous system regions, and the evaluation of neural connectivity.⁴ Their generation, coupled with genome editing, microfluidics, live imaging, and single-cell genomics, has allowed the modelling in vitro of different neurological disorders,5 including neurodegenerative diseases such as Huntington’s disease,⁶ Alzheimer’s disease,7 and Parkinson’s disease.⁸ To date, an organoid model of C9-ALS is still lacking. Here, the authors aim to model C9-ALS in vitro using 3D human spinal cord organoids (SCOs).