Abstract
Nijmegen Breakage Syndrome (NBS) is a rare autosomal recessive genetic disorder caused by mutations within nibrin (NBN), a DNA damage repair protein. Hallmarks of NBS include chromosomal instability and clinical manifestations such as growth retardation, immunodeficiency, and progressive microcephaly. We employed induced pluripotent stem cell-derived cerebral organoids from two NBS patients to study the etiology of microcephaly. We show that NBS organoids carrying the homozygous 657del5 NBN mutation are significantly smaller with disrupted cyto-architecture. The organoids exhibit premature differentiation, and Neuronatin (NNAT) over-expression. Furthermore, pathways related to DNA damage response and cell cycle are differentially regulated compared to controls. After exposure to bleomycin, NBS organoids undergo delayed p53-mediated DNA damage response and aberrant trans-synaptic signaling, which ultimately leads to neuronal apoptosis. Our data provide insights into how mutations within NBN alters neurogenesis in NBS patients, thus providing a proof of concept that cerebral organoids are a valuable tool for studying DNA damage-related disorders.
Highlights
Development of the nervous system is a strictly regulated process whereby neural progenitor cells (NPCs) rapidly proliferate, differentiate, and undergo oxidative stress
Our results indicate that Nijmegen Breakage Syndrome (NBS) organoids display an impaired DNA damage response (DDR) pathway, with the accumulation of DNA damage and subsequent genome instability probably due to the lower levels of p53 suggesting that p53 plays a central role in orchestrating the fate of NPCs in NBS organoids
While microcephaly is the hallmark of NBS, the mechanisms that lead to reduced brain size in these patients are largely unknown, mostly due to the hurdles and limitations associated with studying NBS
Summary
Development of the nervous system is a strictly regulated process whereby neural progenitor cells (NPCs) rapidly proliferate, differentiate, and undergo oxidative stress. Several studies based on Nbn conditional knockouts and inducible Nbn-deletion mice have been generated These studies identified proliferation arrest and increased apoptosis in the neural progenitor cells due to over-activation of p53, which leads to microcephaly [14–18]. NBS organoids carrying the homozygous NBN 657del mutation are significantly smaller in size and have disrupted cyto-architecture Both patient-derived organoids exhibit premature differentiation, key pathways related to DNA damage response and cell cycle are differentially regulated compared to healthy controls. Our data highlights insights into how hypomorphic mutations within NBN alters neurogenesis in NBS patients, providing a proof of concept that iPSC-derived cerebral organoids are a valuable tool which enable research into DNA damage-related disorders such as Nijmegen Breakage Syndrome. The medium was changed every day and cells were passaged every 5–6 days using PBS without Calcium and Magnesium (Life Technologies, Waltham, MA, USA)
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