Tyrosine and Phenylalanine Activate Neuronal DNA Repair but Exhibit Opposing Effects on Global Transcription and Adult Female Mice Are Resilient to TyrRS/YARS1 Depletion.

Serum tyrosine and phenylalanine levels increase during aging and age-associated disorders. We previously showed that tyrosyl-tRNA synthetase (TyrRS/YARS1) is reduced in Alzheimer's Disease (AD) brains, and tyrosine and phenylalanine decrease TyrRS in neurons. Here, we found that tau is a negative regulator, whereas estrogen and leucine act as positive regulators of TyrRS. Young female mice exhibit increased TyrRS in the cortex compared to male mice. Notably, young Tau knockout male, but not female mice showed increased cortical TyrRS. Tau accumulation in middle-aged female mice did not decrease cortical TyrRS compared to males, suggesting that middle-aged females are resilient to tau-mediated TyrRS depletion. Tyrosine and phenylalanine treatment decreased tubulin tyrosination, activated DNA repair pathways, and protected against etoposide (ETO) and camptothecin (CPT)-induced toxicity, respectively, in neurons. While tyrosine facilitated topoisomerase 1 (TOP1) recruitment to chromatin and inhibited global transcription, in contrast, phenylalanine recruited topoisomerase 2 beta (TOP2β) to chromatin and stimulated global transcription. Furthermore, tyrosine decreased the presence of DNA fragments in a comet assay whereas phenylalanine increased them. Addition of cis-resveratrol (cis-RSV) protected against tyrosine-induced transcription inhibition by facilitating the recruitment of both TOP1 and TOP2β to chromatin and increasing tubulin tyrosination. Moreover, cis-RSV decreased both total and phosphorylated tau and protected neurons against amyloid beta (Aβ)-induced neurite degeneration and DNA damage. Gene expression profiling using human embryonic stem cell (hESC)-derived neurons demonstrated that cis-RSV is a broad-spectrum neuroprotective and anti-viral agent. In contrast, trans-RSV mimics phenylalanine-induced gene expression, including downregulation of long genes and induction of an AD-like gene expression signature. This work suggests that age and disease-associated increases in serum tyrosine and phenylalanine levels would activate neuronal DNA repair while inhibiting transcription and tubulin tyrosination. cis-RSV protects against their toxicity by restoring tubulin tyrosination, TOP1 and TOP2β-mediated transcription, and decreasing tau in primary neurons.