Longitudinal modeling of human neuronal aging reveals the contribution of the RCAN1-TFEB pathway to Huntington's disease neurodegeneration
Aging is a common risk factor in neurodegenerative disorders and the ability to investigate aging of neurons in an isogenic background would facilitate discovering the interplay between neuronal aging and onset of neurodegeneration. Here, we perform direct neuronal reprogramming of longitudinally collected human fibroblasts to reveal genetic pathways altered at different ages. Comparative transcriptome analysis of longitudinally aged striatal medium spiny neurons (MSNs), a primary neuronal subtype affected in Huntington's disease (HD), identified pathways associated with RCAN1, a negative regulator of calcineurin. Notably, RCAN1 undergoes age-dependent increase at the protein level detected in reprogrammed MSNs as well as in human postmortem striatum. In patient-derived MSNs of adult-onset HD (HD-MSNs), counteracting RCAN1 by gene knockdown (KD) rescued HD-MSNs from degeneration. The protective effect of RCAN1 KD was associated with enhanced chromatin accessibility of genes involved in longevity and autophagy, mediated through enhanced calcineurin activity, which in turn dephosphorylates and promotes nuclear localization of TFEB transcription factor. Furthermore, we reveal that G2-115 compound, an analog of glibenclamide with autophagy-enhancing activities, reduces the RCAN1-Calcineurin interaction, phenocopying the effect of RCAN1 KD. Our results demonstrate that RCAN1 is a potential genetic or pharmacological target whose reduction-of-function increases neuronal resilience to neurodegeneration in HD through chromatin reconfiguration. Overall design: To investigate age-related differences in reprogrammed MSNs from longitudinally collected fibroblasts from three independent healthy individuals, we carried out comparative transcriptome analysis between the age groups. We designate fibroblasts initially collected during middle age as “young” and samples subsequently collected approximately 20 years later from three independent individuals as “old” groups (Coriell NINDS and NIGMS Repositories: AG10049 (48 years), AG16030 (68 years); AG10047 (53 years), AG14048 (71 84 years); AG04456 (49 years), AG14251 (68 years). RNA-seq analysis in both longitudinally collected fibroblasts and corresponding reprogrammed MSNs revealed differentially expressed genes (DEGs) between young and old samples.