UC San Diego

The individual unit of computation in the human brain is the neuron. To advance our understanding of the human brain, we need to generate relevant cellular models of human neurons in vitro. Direct conversion of human somatic fibroblasts into induced neurons (iNs) allows for the generation of functional neurons while bypassing any stem cell intermediary stages. Although iN technology has an enormous potential for modeling age-related diseases, as well as therapeutic approaches, the technology faces limitations due to variable conversion efficiencies and a lack of thorough understanding of the signaling pathways directing iN conversion. Here, I introduce a new all-in-one inducible lentiviral system that simplifies fibroblast transgenesis for the two pioneer transcription factors, Ngn2 and Ascl1, and a small molecule cocktail that markedly improves iN yields and sheds new insight into the mechanisms influencing direct iN conversion. Next, I will apply the iN protocol on a cohort of Alzheimer’s disease (AD) and healthy age matched control donor samples to model age-related molecular phenotypes in AD neurons. I previously found that AD brains have significantly higher proportions of neurons that express senescence markers, and their distribution indicates bystander effects. AD patient-derived iNs exhibit strong transcriptomic, epigenetic, and molecular biomarker signatures that illuminate a specific human neuronal senescence-like state. AD iN single-cell transcriptomics revealed that senescent neurons face oncogenic challenges, and metabolic dysfunction, and they display a proinflammatory signature. Integrative profiling of the inflammatory secretome of AD iNs and patient cerebral spinal fluid revealed a neuronal senescence-associated-secretory-phenotype, that can trigger astrogliosis in human astrocytes. Finally, I show that targeting senescence-like neurons with senotherapeutics could be a novel strategy for preventing or treating AD.