Transthyretin at the crossroads of neurodegeneration: a silent guardian in Parkinson's disease.

Parkinson's disease (PD) is a progressive neurodegenerative disease characterised by disruption of brain homeostasis and degeneration of dopaminergic neurons in the substantia nigra. PD is characterised by motor symptoms, like tremor, rigidity, bradykinesia, and postural instability, as well as non-motor symptoms like cognitive impairment, mood disorders, sleep disturbances, and autonomic abnormalities that significantly affect quality of life. The molecular pathogenesis of PD involves Oxidative stress, neuroinflammation, mitochondrial dysfunction, α-synuclein (α-syn) misfolding and aggregation, insufficient autophagy-lysosomal clearance, and synaptic degeneration, leading to progressive neuronal loss. Transthyretin (TTR), a tetrameric transport protein that is primarily produced in the liver and choroid plexus, is well-known for carrying thyroxine and retinol-binding protein. Experimental studies have shown that TTR can protect neurons by binding misfolded proteins, such as α-syn, decreasing toxic aggregation, regulating oxidative stress responses, and affecting selective autophagic degradation. PD-related changes in TTR expression in brain tissue and cerebrospinal fluid provide strong evidence of TTR's significance as a molecular biomarker and a physiological regulator in the pathogenesis of the disease. This review highlights TTR involvement in neuroinflammation, oxidative stress, and α-syn aggregation, and discusses emerging evidence supporting TTR stabilizers as potential biomarkers and therapeutic targets for modulating disease progression in PD.