BACKGROUND: The prevailing treatment of Parkinson's disease (PD) is not yet satisfactory. The present investigate the neuroprotective effect of the GLP-1/GIP dual agonist tirzepatide and examine the potential mechanisms involved.
METHODS: Analysis of GLP1 receptor (GLP1R) and GIPR expression alterations in dopaminergic neurons from PD patients in the GSE238129 dataset. The MPTP-induced subacute PD mice was treated with tirzepatide, semaglutide and levodopa. Behavioral tests and brain histopathology of mice were evaluated. The transmission electron microscopy revealed the presence of ultrastructural alterations in the mitochondrial morphology. The ATP level was assessed in substantia nigra. Western blot and immunohistochemical staining were employed to quantify Drp1 and mitophagy proteins. Furthermore, Drp1 inhibitor and mitophagy activator were used to treat MPTP-induced subacute PD mice, and lysosome inhibitor chloroquine (CQ) and the autophagy inhibitor 3-methyladenine (3-MA) were used in SY5Y cells for validation.
RESULTS: The gene expression levels of both GLP1R and GIPR were significantly downregulated in dopaminergic neurons derived from PD patients. Tirzepatide could significantly ameliorate MPTP-induced the loss of tyrosine hydroxylase (TH) protein in the substantia nigra. There was no statistically difference observed between one-third doses of tirzepatide when compared with semaglutide and levodopa. In addition, tirzepatide not only improved mitochondrial ultrastructure, but also enhanced mitochondrial ATP content. Tirzepatide was found to reduce Drp1 expression and reverse the expressions of mitophagy-related proteins, including Pink1, Parkin, and p62. There was no statistically difference observed between one-third doses of tirzepatide compared with semaglutide in mitochondrial energy control. In addition, we observed that MPTP-induced subacute PD mice treated with a Drp1 inhibitor and mitophagy activator exhibited therapeutic effects. In SY5Y cells, lysosomal and autophagy inhibitors significantly reduced mitochondrial membrane potential, ATP levels, and the NAD+/NADH ratio.
CONCLUSION: This study demonstrates that the benefits of tirzepatide extend to mitochondrial networks, achieved by means of the inhibition of mitochondrial pathological fission, the promotion of mitophagy, in MPTP-induced subacute PD mice or cells model.