Fig. 4: Thiorphan increases growth of monkey and human cortical neurons and induces pro-regenerative state.

a, Thiorphan significantly increased total neurite outgrowth from primary cultures of adult cynomolgus macaque motor cortex labelled for Tuj (***P < 0.001, two-tailed t-test). Control cultures received DMSO. Each point represents the total neurite length of individual neurons. Samples were run as technical duplicates, with neurons cultured for 5 days. b, Thiorphan treatment also significantly increased the maximum neurite length per cell by 1.8-fold (****P < 0.0001, two-tailed t-test). c, Representative images of cultures of adult primate motor cortex treated with diluent or thiorphan. d, Thiorphan significantly increased total neurite outgrowth from primary cultures of normal 56-year-old human cortex neurons labelled for Tuj (****P < 0.0001, two-tailed t-test). Neurons cultured for 5 days. Each point represents the total neurite length of one neuron. e, Thiorphan treatment of human cortical neurons also significantly increased the maximum neurite length per cell (**P < 0.01, two-tailed t-test). f, Representative images of 56-year-old human cortical neurons in culture labelled for Tuj1. g, RNA sequencing was performed on cultures of adult primary motor cortex from rhesus monkeys treated for 5 days with thiorphan or vehicle (DMSO). A total of 177 genes changed ±1.5-fold on a log₂ scale. h, Gene ontology of these 177 genes demonstrates clear enrichment for developmental processes (Gene Ontology database²⁴, https://doi.org/10.5281/zenodo.10536401). i, To identify in vivo mechanisms recruited by thiorphan treatment, rat brains were removed after 2 weeks of thiorphan infusion and compared with diluent-infused controls. Thiorphan treatment increased immunolabelling for both BDNF and phospho-AKT in the infused motor cortex, reflecting a shift to a state that is developmental and pro-regenerative. Scale bars, 20 μm (c,f). Scale bars, 25 μm, inset scale bars, 10 μm.