Dopamine neuron loss by selective deletion of autophagy-related gene 5 is not exacerbated by MPTP toxicity in midbrain.

Parkinson's disease (PD) is a progressive neurological disease, one of the pathological characteristics is a gradual loss of midbrain dopaminergic (mDA) neurons in the substantia nigra pars compacta (SNpc). In animals, PD-like symptoms can be induced by genetic mutations or by neurotoxins such as 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). It has been reported that deletion of autophagy-related gene 5 (Atg5) in the brain can disrupt neural function and is accompanied by the accumulation of cytoplasmic inclusions. However, the exact role of autophagy in PD etiology has not fully been asserted. In this study, we used tyrosine hydroxylase (TH)-Cre mice to generate conditional knockouts (CKO) with the specific deletion of Atg5 in mDA neurons, and found that adult Atg5 CKO mice contained ubiquitin- and p62-positive inclusions and fewer TH-positive mDA neurons compared with wild-type controls. Interestingly, MPTP-induced loss of mDA neurons was not observed in Atg5 CKO mice. Thus, Atg5-associated autophagy is required for the survival of mDA neurons, and may be involved in MPTP-induced neuronal degeneration.

Deletion of autophagy-related gene 7 in dopaminergic neurons prevents their loss induced by MPTP.

Parkinson's disease (PD) is a neurodegenerative disease caused by a gradual loss of midbrain dopaminergic (mDA) neurons in the substantia nigra pars compacta (SNpc) during aging. 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) is one of the neurotoxins used widely to induce PD-like symptoms in PD animal models, including rodents and non-human primates. It has been reported that deletion of autophagy-related gene 7 (Atg7) in the brain results in a reduction of mDA neurons in adulthood. In this study, we used tyrosine hydroxylase (TH)-Cre mice to generate conditional knockout (CKO) mice with the specific deletion of Atg7 in mDA neurons. Consistent with previous reports, adult Atg7 CKO mice contained fewer TH-positive mDA neurons compared with wild-type (WT) controls. TH-expressing neurons containing puncta-like structures with p62 and ubiquitin immunoreactivity were observed in the midbrain of Atg7 CKO mice but were not detected in control mice. However, MPTP-induced loss of mDA neurons was not observed in Atg7 CKO mice. Our results indicate that Atg7-involved autophagy is required not only for the survival of mDA neurons in the mouse brain, but also for MPTP-induced mDA neuron degeneration.