Re-activation of neurogenic niches in aging brain

Recent studies proposing induced glia-to-neuron conversion raised the potential for generating new neurons to replace those lost due to injury, aging or neurodegenerative diseases. Here, single-cell spatial transcriptomics [Multiplexed Error Robust Fluorescence In Situ Hybridization (MERFISH)] is used to construct a spatial cell atlas of the subventricular and dentate gyrus neurogenic niches of young and aged adult murine brain. RNAs that encode the RNA binding protein Polypyrimidine Tract-Binding Protein (PTBP1) in the aged murine brain are determined to be highest in glia that line previously active neurogenic niches. A glial cell population with ependymal character within an initially quiescent subventricular neurogenic niche in the aged murine brain is identified that upon transient suppression of PTBP1 reenters the cell cycle, replicates DNA, and converts into neurons through a canonical adult neurogenesis pathway. Glia-derived neurons migrate from this niche, with some neurons transiting to the striatum and acquiring a transcriptome characteristic of GABAergic inhibitory neurons. Similar PTBP1 expressing quiescent glia are identified in the corresponding neurogenic niche of aged human brain. Thus, transient reduction of PTBP1 holds potential for inducing the generation of new neurons in quiescent neurogenic niches of the aged nervous system, thereby offering promising therapeutic applications. Bullet point summary1) Single-cell spatial transcriptomics is used to validate active neurogenesis in the two neurogenic niches of the young adult murine brain, determine that those niches are quiescent in the aging adult brain of mice, and demonstrate the absence of neurogenesis in the aging human brain. 2) The RNA binding protein PTBP1 is determined to be most highly expressed within glia that line the aged murine and human neurogenic niches, with its transient reduction sufficient in mice to activate/re-activate expression of genes characteristic of immature neurons. 3) Suppression of PTBP1 using a single intra-cerebral-ventricular injection of PTBP1-targeting antisense oligonucleotide (ASO) induces generation of new immature neurons in the neurogenic niches of the aged mouse brain via a canonical adult neurogenesis pathway. 4) Single-cell RNA signature tracing is used to identify a) a subclass of ependymal cells in a previously quiescent neurogenic niche of the aged mouse brain that convert into GABAergic inhibitory neurons following transient suppression of PTBP1, and b) the molecular steps in the conversion process including cell cycle re-entry, DNA replication, and transcriptome changes that mimic canonical neurogenesis. 5) A similar class of PTBP1-expressing ependymal cells lining the ventricle of the aging non-human primate and human brains is identified, suggesting the promise of re-activation of neurogenesis as a therapeutic approach in humans.