Neuroimmunology: PIK3R1 Ile571TyrfsTer31 plays an important role in neuronal function and survival

Abstract

Neurological complications are important causes of morbidity and mortality in patients with inborn errors of immunity (IEIs). However, the role of immune gene defects in the nervous system has not been well studied.A 42 yo M presented with recurrent infections and hypogammaglobulinemia in childhood and was found to have Ile571TyrfsTer31 in the PIK3R1. He developed spastic paraparesis at age 30 but extensive neuroinfectious and neuroinflammatory work up was unrevealing. Significant weakness in all limbs and bulbar symptoms progressed despite treatment with IVIg, cyclophosphamide and rituximab to target potential neuroinflammation. Further neurological evaluation showed both upper and lower motor neuron disease clinically consistent with ALS. We used our newly developed pipeline to evaluate the potential contribution of his PIK3R1 mutation to CNS disease.The patient’s CSF cells showed active antigen presentation and T cell activation in the CNS compartment, suggesting the possibility of immune activation due to neuronal destruction. We generated an iPSC line from patient CD34+ cells and repaired the mutation with CRISPR-Cas9 technology to investigate the role of PIK3R1 in neurons. We then differentiated patient-derived and gene-edited cells into Motor Neurons (MNs), as well as iPSC from a healthy donor. Morphologically, cells from all three lines differentiated normally to neuroepithelial cells, motor neuron precursors and terminally differentiated MNs. Electrophysiology showed significantly lower activity in patient-derived neurons compared to healthy or edited MNs, indicating that PI3KR1 plays an important role in neuronal function. NMDA treatment increased firing in MNs in healthy and edited lines but not in patient-derived neurons, indicating an abnormal response to stimulation. We also found higher levels of phosphorylated AKT in patient MNs compared to edited and healthy cells, indicating upregulation of the PI3K pathway in patient-derived cells. Patient-derived neurons were also more prone to apoptosis as shown by higher expression of Caspase 3 compared to healthy control.These findings strongly suggest that PIK3R1 plays an essential role in neuronal function and survival. iPSC-derived neuronal cells provide powerful new platforms to better investigate manifestations of IEIs in the CNS.