<i>VGF</i> AS BIOMARKER OF PRE-SYMPTOMATIC PHASE OF PARKINSON’S DISEASE

Parkinson’s disease (PD) is a progressive neurodegenerative disorder whose early detection remains a major challenge. The Vgf gene, encoding the VGF neuroprotein, has been implicated in PD, with previous studies reporting reduced GF C-terminal peptide levels in the plasma of drug-naïve PD patients and in the substantia nigra (SN) of advanced PD models. However, similar studies, are lacking in progressive mouse models of PD. In this study, we developed a progressive and early PD mouse model using intranasal rotenone administration, based on the hypothesis that PD pathology begins in the olfactory bulb (OB) and progresses to the midbrain over time (Braak’s hypothesis). This study aimed to validate VGF C-terminal peptide levels as presymptomatic biomarkers of PD. Male BALB/c mice were divided into three cohorts based on the time of rotenone treatment, i.e., at 2, 3, and 6 months. Behavioral tests included the butyric acid avoidance to assess olfactory dysfunction and inverted grid and pole tests to assess motor impairment. At each time point, the mice were sacrificed, and brain and plasma were collected for q-PCR, immunohistochemistry (IHC) and ELISA. The total RNA was extracted from the isolated OB to perform q-PCR for the following genes: Vgf, Th (tyrosine hydroxylase), and Snca (synuclein alpha) while IHC was performed in OB and SN for TH, alpha-synuclein, and VGF C-terminal peptides. VGF C-terminal levels were measured using ELISA in plasma and OB extracted samples. Behavioral study showed significant olfactory deficits starting from 3-month time point and was persistent throughout the study, whereas motor impairments appeared only after 6 months of rotenone treatment. At 3 months, concurrent with olfactory deficits, using the OB samples, the VGF C-terminus levels were significantly reduced along with the increased immunoreactivity for alpha-synuclein, and decrease of TH. Same results for alpha-synuclein, TH and VGF were observed in the SN along with a decrease for VGF C-terminus levels in plasma. All these changes persisted even after 6 months, at which point gene alterations were observed for the first time. Indeed, the q-PCR results at 6 months showed increased Snca and decreased Th expression in the rotenone treated mice OB while Vgf mRNA levels remained unchanged in all brain regions suggesting a post-translational VGF changes. In conclusion, a role of VGF C-terminal peptides as a potential biomarker of pre-symptomatic PD is suggested.