The Role of Autophagy Dysregulation in Manganese-Induced Dopaminergic Neurodegeneration

Abstract

The etiological role of dysregulated autophagy in neurodegenerative diseases has been a subject of intense investigation. While manganese (Mn) is known to cause dopaminergic (DAergic) neurodegeneration, it has yet to be determined whether the dysregulation of autophagy plays a role in Mn-induced neuronal injury. In this study, we investigated the effect of Mn on autophagy in a rat model of manganism, a neurodegenerative disease associated with excessive exposure to Mn. After a single intrastriatal injection of Mn, the short- (4–12 h) and long-term (1–28 days) effect of Mn on DAergic neurons and autophagy were examined. Marked reduction in the number of TH-immunoreactive neurons in the substantia nigra pars compacta (SNpc) as well as TH protein expression, and a significant increase of apomorphine-induced rotations were observed in rats after Mn injection. Manganese also induced the down-regulation of dopamine levels and D1 dopamine receptor expression. In addition, autophagy was dysregulated and inhibited, as evidenced by increased number of abnormal lysosomes, decreased protein expression of Beclin1, and decreased ratio of microtubule-associated protein 1 light chain 3 (LC3) II over LC3 I, concomitant with activated mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase (p70s6k) signaling. In contrast, in the early phase of Mn exposure, the level of autophagy was not be suppressed but compensatorily activated. Although the morphology of the DAergic neuron was intact in the early phase, Mn caused a significant decrease in TH-immunoreactivity and a significant increase in apomorphine-induced rotations in the presence of wortmannin, an inhibitor of autophagy. Taken together, these results demonstrate, for the first time, that autophagy may play a protective role against Mn-induced neuronal damage, whilst dysregulation of autophagy at later phases may mediate DAergic neurodegeneration.

The role of NLRP3-CASP1 in inflammasome-mediated neuroinflammation and autophagy dysfunction in manganese-induced, hippocampal-dependent impairment of learning and memory ability

“…10,48 In our previous studies, we have found that Mn can result in impairment of motion ability through affecting the function of dopaminergic neurons via decreasing autophagy in substantia nigra and striatum. 27 In the present study, we found that activation of the NLRP3 inflammasome was involved in Mn-induced release of proinflammatory cytokines from microglia. 16 Next, we explored the possible relationships between autophagy and the formation of the NLRP3 inflammasome in response to Mn.…”

“…We have already reported that Mn exposure induces autophagy dysfunction in the substantia nigra. 27 We therefore studied the effect of Mn on autophagy in BV2 cells by determining LC3-II, ATG5, BECN1 (Beclin 1, autophagy related), SQSTM1 and CTSB protein expression 6 h after Mn exposure. LC3-II is an autophagosomal surface protein marker that is ultimately degraded inside the autolysosomes.…”

“…27 Briefly, hippocampal tissue and BV2 cells were fixed in 2% glutaraldehyde in 0.1 M PBS (pH 7.4) for 2 h at 4 C. Subsequently, they were postfixed in 1% osmium tetroxide in 0.1 M PBS (pH 7.4) for 2 h at 4 C. Next, the hippocampal tissue was dissected out (1 mm 3 ) and processed in 1% osmium tetroxide. The tissues and cells then were dehydrated in ascending ethanol solutions ranging from 20 to 100%, and embedded in Epon812 (Sigma, 45347-1L-F).…”

The autophagic- lysosomal pathway determines the fate of glial cells under manganese- induced oxidative stress conditions

“…A recent report described the effect on the autophagic pathway of a single intra-striatal injection of Mn [48]. Employing whole rat brain, the authors found that Mn induced autophagy activation in short term (4-12 h pi) but inhibited autophagy in long term (1-28 d pi).…”

Manganese and Oxidative Stress

“…59,60 In addition, it was shown that autophagy plays a pivotal role on Mn-induced DAergic neurodegeneration. 61 However, whether striatal levels of dopamine (DA) are altered in experimental manganism remains controversial. 62 This is likely associated with differential experimental conditions, the form of Mn (state of oxidation), route of administration, and time of exposure.…”