Effect of α-Synuclein Overexpression on NAPP-129 and TLQP-62 in Rat Brain and Plasma

Background: In Parkinson's disease (PD), changes in the brain begin before clinical symptoms. We have previously shown that VGF precursor levels were reduced in a presymptomatic PD animal model. Objectives: In the present study, we investigated whether two VGF precursor-derived products, namely NAPP-129 protein and TLQP-62 peptide, also exhibit alterations using the same PD animal model. Methods: Specifically, rats were unilaterally injected in the substantia nigra with a viral vector overexpressing green fluorescent protein (N = 12) or α-synuclein (N = 13), the latter resulting in mild dopaminergic alterations without overt motor deficits. Results: NAPP-129 and TLQP-62 were investigated in the substantia nigra, striatum, and plasma by Western blotting or immunoassays using specific antibodies against NAPP and TLQP sequences, alongside other NERP-1- and AQEE-related products. Plasma samples of a Huntington's disease mouse model were also analyzed. We found reductions in NAPP-129 and TLQP-62 levels in the substantia nigra along with a decrease in NAPP- and TLQP-like plasma immunoreactivity in α-synuclein-overexpressed rats, while the striatum was not affected. NERP-1- and AQEE-related products were not altered. No changes were found in the Huntington's disease model. Conclusions: These findings indicate that NAPP-129 and TLQP-62 may enhance the sensitivity and specificity of biomarker-based strategies for PD.