Early Dopaminergic Dysfunction Induces PRO-VGF Changes in Blood and Brain of Rats with Alpha-Synuclein Overexpression

Previous research revealed a reduction in the VGF immunoreactivity within the substantia nigra (SN) of rats with a 60-90% dopaminergic neuron loss and in the plasma of newly diagnosed Parkinson's disease (PD) patients. Hence, our aim was to explore whether central and peripheral proVGF changes occur during early dopaminergic dysfunction. To investigate this, we employed a rat model mimicking early-stage PD by injecting the SN unilaterally with an adeno-associated virus (AAV) carrying either the human α-synuclein (α-syn; n = 19) or green fluorescent protein (GFP; n = 18) gene. After conducting motor assessments and sacrificing the animals, brain and blood samples were collected. Tyrosine hydroxylase (TH)-, glutamic acid decarboxylase (GAD)-, and phosphorylated (p)-α-syn antibodies were used for immunohistochemistry (IHC), while an antibody targeting the C-terminus of proVGF was employed for IHC, western blot (WB), and enzyme linked immunosorbent asssay (ELISA). The α-syn overexpression caused a modest (~ 30%) reduction in TH immunoreactivity within the SN-without affecting the striatum-and did so without producing overt motor symptoms, effectively modeling a pre-symptomatic PD stage. This early dopaminergic dysfunction was accompanied by decreased immunostaining for both proVGF C-trerminus and GAD in the SN, but not the striatum. Reduction in plasma proVGF levels were also observed, indicating systemic changes during initial dopaminergic impairment. Analysis using WB confirmed a decrease in a 70 kDa band consistent with proVGF in both SN and plasma. These findings suggest proVGF as a promising early biomarker for PD, opening new avenues for intervention before the onset of clinical symptoms.