Endothelin-1 (ET-1) is a neuroactive peptide produced by neurons, reactive astrocytes, and endothelial cells in the brain. Elevated levels of ET-1 have been detected in the post-mortem brains of individuals with Alzheimer's disease (AD). We have previously demonstrated that overexpression of astrocytic ET-1 exacerbates memory deficits in aged mice or in APPK670/M671 mutant mice. However, the effects of ET-1 on neuronal dysfunction remain elusive. ET-1 has been reported to mediate superoxide formation in the vascular system via NADPH oxidase (NOX) and to regulate the actin cytoskeleton of cancer cell lines via the cofilin pathway. Interestingly, oxidative stress and cofilin activation were both reported to mediate one of the AD histopathologies, cofilin rod formation in neurons. This raises the possibility that ET-1 mediates neurodegeneration via oxidative stress- or cofilin activation-driven cofilin rod formation. Here, we demonstrate that exposure to 100 nm ET-1 or to a selective ET type B receptor (ETB) agonist (IRL1620) induces cofilin rod formation in dendrites of primary hippocampal neurons, accompanied by a loss of distal dendrites and a reduction in dendritic length. The 100 nm IRL1620 exposure induced superoxide formation and cofilin activation, which were abolished by pretreatment with a NOX inhibitor (5 μm VAS2870). Moreover, IRL1620-induced cofilin rod formation was partially abolished by pretreatment with a calcineurin inhibitor (100 nm FK506), which suppressed cofilin activation. In conclusion, our findings suggest a role for ETB in neurodegeneration by promoting cofilin rod formation and dendritic loss via NOX-driven superoxide formation and cofilin activation.
The post-transcriptional modification of tRNAs plays a crucial role in tRNA structure and function. Pathogenic variants in tRNA-modification enzymes have been implicated in a wide range of human neurodevelopmental and neurological disorders. However, the molecular basis for many of these disorders remains unknown. Here, we describe a comprehensive cohort of 43 individuals from 31 unrelated families with bi-allelic variants in tRNA methyltransferase 1 (TRMT1). These individuals present with a neurodevelopmental disorder universally characterized by developmental delay and intellectual disability, accompanied by variable behavioral abnormalities, epilepsy, and facial dysmorphism. The identified variants include ultra-rare TRMT1 variants, comprising missense and predicted loss-of-function variants, which segregate with the observed clinical pathology. Our findings reveal that several variants lead to mis-splicing and a consequent loss of TRMT1 protein accumulation. Moreover, cells derived from individuals harboring TRMT1 variants exhibit a deficiency in tRNA modifications catalyzed by TRMT1. Molecular analysis reveals distinct regions of TRMT1 required for tRNA-modification activity and binding. Notably, depletion of Trmt1 protein in zebrafish is sufficient to induce developmental and behavioral phenotypes along with gene-expression changes associated with disrupted cell cycle, immune response, and neurodegenerative disorders. Altogether, these findings demonstrate that loss of TRMT1-catalyzed tRNA modifications leads to intellectual disability and provides insight into the molecular underpinnings of tRNA-modification deficiency caused by pathogenic TRMT1 variants.