Alpha‐synuclein aggregation and cell death triggered by energy deprivation and dopamine overload are counteracted by D₂/D₃ receptor activation

Abstract

Progressive degeneration and intraneuronal Lewy bodies made of filamentous a-synuclein (a-syn) in dopaminergic cells of the nigrostriatal system are characteristics of Parkinson's disease (PD). Glucose uptake is reduced in some of the brain regions affected by PD neurodegenerative changes. Defects in mitochondrial activity in the substantia nigra have been observed in the brain of patients affected by PD and substantia nigra lesions can induce the onset of a secondary parkinsonism. Thus, energy starvation and consequently metabolic impairment to dopaminergic neurons may be related to the onset of PD. On this line, we evaluated the effect of nutrient starvation, reproduced 'in vitro' by glucose deprivation (GD), in primary mesecephalic neuronal cultures and dopaminergic-differentiated SH-SY5Y cells, to evaluate if decreased glucose support to dopaminergic cells can lead to mitochondrial damage, neurodegeneration and a-syn misfolding. Furthermore, we investigated the effect of dopamine (DA) treatment in the presence of a DA-uptake inhibitor or of the D 2 /D 3 receptor (D 2 R/D 3 R) agonist quinpirole on GDtreated cells, to evaluate the efficacy of these therapeutic compounds. We found that GD induced the formation of fibrillary aggregated a-syn inclusions containing the DA transporter in dopaminergic cells. These alterations were accompanied by dopaminergic cell death and were exacerbated by DA overload. Conversely, the block of DA uptake and D 2 R/D 3 R agonist treatment exerted neuroprotective effects. These data indicate that glucose starvation is likely involved in the induction of PD-related pathological changes in dopaminergic neurons. These changes may be counteracted by the block of DA uptake and by dopaminergic agonist treatment.

α-synuclein and synapsin III cooperatively regulate synaptic function in dopamine neurons

“…We have previously shown that glucose deprivation, which mimics decreasing energy supply in the ageing brain, induces the formation of α-syn insoluble aggregates, decreases dopamine cell viability and alters their function (Bellucci et al, 2008(Bellucci et al, , 2011a. In addition, we have shown that glucose deprivation is also able to induce α-syn aggregation within the endoplasmic reticulum (ER).…”

“…S1E-G; Bellucci et al, 2008Bellucci et al, , 2011a. Indeed, urea-soluble α-syn aggregates (Bellucci et al, 2008) and thioflavin-S-positive α-syn inclusions (supplementary material Fig.…”

“…4F,I). To exclude the possibility that the variations in the synapsin-III levels observed in primary neurons were due to non-dopaminergic neurons or glial cells present in the primary cell cultures, we evaluated the expression of synapsin III in a more uniform dopaminergic cell population -dopaminergic differentiated SH-SY5Y neuroblastoma cells (Bellucci et al, 2008) To confirm whether α-syn affected DAT and synapsin III distribution, besides their expression, we used a differentiated neuronal SK-N-SH cell line that stably expressed a green fluorescent protein (GFP)-conjugated form of DAT to overexpress the SYN120 mutant protein (Bellucci et al, 2011a). This form of α-syn can be found in LBs (Prasad et al, 2012), and promotes α-syn aggregation (Crowther et al, 1998), DAT redistribution (Bellucci et al, 2011a) and the induction of axonal and synaptic damage (Games et al, 2013;GarciaReitbock et al, 2010).…”

“…Given the fact that we found that synapsin-Ia/b levels in the striatum of α-syn-null mice were not changed with respect to controls, our studies of behavior suggest that cocaine could stimulate the locomotor activity of these animals by inducing the release of synapsin-III-regulated vesicle pools of dopamine. Interestingly, high doses of cocaine have been found to alter α-syn distribution (Brenz Verca et al, 2003) and to block the formation of intracellular α-syn inclusions (Bellucci et al, 2008). Cocaine abuse elevates α-syn levels in the human striatum (Qin et al, 2005), whereas overexpression of α-syn in the nucleus accumbens influences the behavior of rats in response to cocaine (Boyer and Dreyer, 2007).…”

“…Primary embryonic mouse ventral mesencephalic cells were isolated and cultured as previously described (Bellucci et al, 2008) with minor modifications. Briefly, ventral mesencephalic tissues were dissected from C57BL/6J and C57BL/6JOlaHsd mice at embryonic day 13.5.…”