UCH-L1 in Alzheimer's Disease: A Crucial Player in Dementia-Associated Mechanisms.

Ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) is a critical deubiquitinating enzyme that is highly expressed in the central nervous system, where it participates in protein degradation and turnover as part of the ubiquitin-proteasome system (UPS). Convincing evidence supports the role of UCH-L1 dysfunction in several neurodegenerative disorders, given its unique position at the crossroad of several aetiopathogenic pathways, including those implicated in Alzheimer's disease (AD) onset. Indeed, UCH-L1 depletion correlates with decreased levels of triggering receptor expressed on myeloid cells 2 (TREM2), with consequent effects on neuroinflammation. Notably, UCH-L1 can affect the level of phosphorylated tau protein, thus contributing to the formation of neurofibrillary tangles (NFTs). In addition, UCH-L1 influences β-Secretase 1 (BACE1) expression, resulting in the abnormal accumulation of amyloid-β plaques in brain parenchyma. These findings underline UCH-L1's centrality in maintaining the homeostasis of protein folding and aggregation, which are significantly impaired in AD and AD-related dementias. Given these assumptions, UCH-L1 is recognized as a potential biomarker for AD, highlighting its relevance in governing the fate of crucial pathological mediators of cognitive impairment and neurodegeneration. Herein, we contextualize the involvement of UCH-L1 in different dementia-associated pathways and summarize the state of the art of UCH-L1 as a biomarker for AD diagnosis.