Amyloid-Beta Peptides Trigger Premature Functional and Gene Expression Alterations in Human-Induced Neurons

Alzheimer's disease (AD) is the most prevalent cause of dementia in the elderly, characterized by the presence of amyloid-beta (A & beta;) plaques, neurofibrillary tangles, neuroinflammation, synapse loss and neurodegeneration in the brain. The amyloid cascade hypothesis postulates that deposition of A & beta; peptides is the causative agent of AD pathology, but we still lack comprehensive understanding of the molecular mechanisms connecting A & beta; peptides to neuronal dysfunctions in AD. In this work, we investigate the early effects of A & beta; peptide accumulation on the functional properties and gene expression profiles of human-induced neurons (hiNs). We show that hiNs acutely exposed to low concentrations of both cell-secreted A & beta; peptides or synthetic A & beta;1-42 exhibit alterations in the frequency of calcium transients suggestive of increased neuronal excitability. Using single-cell RNA sequencing, we also show that cell-secreted A & beta; up-regulates the expression of several synapse-related genes and down-regulates the expression of genes associated with metabolic stress mainly in glutamatergic neurons and, to a lesser degree, in GABAergic neurons and astrocytes. These neuronal alterations correlate with activation of the SEMA5, EPHA and NECTIN signaling pathways, which are important regulators of synaptic plasticity. Altogether, our findings indicate that slight elevations in A & beta; concentrations are sufficient to elicit transcriptional changes in human neurons, which can contribute to early alterations in neural network activity.