PD	Parkinson’s disease
IR	Insulin resistance
IGF-1	Insulin-like growth factor-1
AD	Alzheimer’s disease
LB	Lewy Bodies
NGS	Next Generation Sequencing
ROS	Reactive oxygen species
ENS	Enteric nervous system
IGF-1r	Insulin-like growth factor-1 receptor
IDE	Insulin-degrading enzyme
GSK3β	Glycogen synthase kinase β
GLP-1	Glucagon-like receptor
PLK2	Polo-like kinase-2
UPS	Ubiquitin proteasome system
PGC-1 α	Peroxisome proliferator-activated receptor gamma coactivator 1 alpha
mTOR	Mammalian target of rapamycin
PED/PEA-15	Phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes-15
L-DOPA	Levodopa
STZ	Streptozotocin
Aβ	Amyloid β
CI	Cognitive impairment
BBB	Blood–brain barrier
IRS-1/2	Insulin receptor substrate-1 and 2
PI3k	Phosphatidylinositol 3-kinase
PIP3	3, 4, 5-triphosphate
PDK	Phosphoinositide-dependent protein kinase
Akt	Protein kinase B
MPTP	1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine
T2DM	Type 2 diabetes mellitus
ULK1	Unc-51-like autophagy activating kinase 1
FDA	Food and Drug Administration
DPP4i	Dipeptidyl peptidase-4 inhibitors