The TyrRS cascade: circadian gating of neuronal DNA repair and its collapse in aging.

Age-related neurodegenerative diseases are characterized by progressive DNA damage in post-mitotic neurons against a backdrop of deteriorating circadian rhythms, yet the molecular link between these conjoined features of brain aging remains unclear. We propose the TyrRS cascade as that link: a signaling architecture in which the noncanonical nuclear functions of tyrosyl-tRNA synthetase (TyrRS/YARS1) schedule neuronal genome maintenance across the day through three coregulated streams, PARP1-mediated damage sensing, TRIM28/NuRD heterochromatin maintenance, and LIN9/DREAM control of a 67-gene repair archive. The model's central commitment is that the operative variable is oscillation amplitude rather than mean activity. We argue that as serum tyrosine rises with age and circadian amplitude flattens, these insults compound into a double-hit collapse that traps the cascade in a frozen-intermediate state, which bulk-tissue assays misread as elevated mean activity when the oscillation has merely lost its excursion. Placed in dialogue with oscillatory-clearance models of sleep, the cascade and the glymphatic system emerge as complementary, compartment-separated arms of a single sleep-dependent maintenance program that fail together through amplitude collapse, yielding a signature of preserved phase architecture with reduced dynamic range. Reframing neurodegeneration as a scheduling failure rather than a capacity failure carries three translational consequences: Pulsatile, phase-aligned dosing should outperform sustained-release pharmacology, which is predicted to flatten the rhythm it aims to restore; demonstrating target engagement will require phase-resolved rather than single-timepoint measurement; and because both arms fail together, combined restoration of intracellular repair and extracellular clearance should outperform single-arm intervention.