The relationship between depression and Parkinson's disease (PD) is complicated and still not fully understood. We investigated whether depression increased the susceptibility to PD and whether this resulted from neuroinflammation mediated by purinergic ligand-gated ion channel 7 receptor (P2X7R) of microglia in mice. Depression was induced by a 14-day chronic unpredictable mild stress (CUMS), and PD was induced by 1-day acute injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Before MPTP administration, some mice were given brilliant blue G (BBG), a P2X7R inhibitor. Changes in depression and motor function were assessed by sucrose preference, tail suspension, open field, and rotating rod tests. Differences in P2X7R, caspase-1, NLRP3 inflammasome, interleukin (IL)-1β, tyrosine hydroxylase (TH), and microglial activation among experimental groups were detected by immunofluorescence, immunohistochemistry, western blotting, and ELISA. CUMSinduced depression-like behavior, and MPTP induced PD in mice. CUMS mice had no motor dysfunction, but the dyskinesia and loss of TH-positive neurons in the substantia nigra after MPTP treatment were more serious than with MPTP treatment alone. With behavioral changes, neuroinflammatory markers, such as caspase-1, NLRP3 and IL-1β increased, and microglia were activated as well as expression of P2X7R increased. Additionally, BBG partly reversed the above abnormalities. Summarily, we suggest that CUMS aggravates dyskinesia and death of dopaminergic neurons in an MPTP-PD model via promoting activation of microglia and neuroinflammation, which may be mediated by P2X7R. Inhibition of P2X7R could be a new control strategy for PD associated with depression.

Inflammation is one of the pathogenic processes in Parkinson’s disease (PD). Dopamine receptor agonist pramipexole (PPX) is extensively used for PD treatment in clinics. A number of studies show that PPX exerts neuroprotection on dopaminergic (DA) neurons, but the molecular mechanisms underlying the protective effects of PPX on DA neurons are not fully elucidated. In the present study, we investigated whether PPX modulated PD-related neuroinflammation and underlying mechanisms. PD model was established in mice by bilateral striatum injection of lipopolyssaccharide (LPS). The mice were administered PPX (0.5 mg·kg−1·d−1, i.p.) 3 days before LPS injection, and for 3 or 21 days after surgery, respectively, for biochemical and histological analyses. We showed that PPX administration significantly alleviated the loss of DA neurons, and suppressed the astrocyte activation and levels of proinflammatory cytokine IL-1β in the substantia nigra of LPS-injected mice. Furthermore, PPX administration significantly decreased the expression of NLRP3 inflammasome-associated proteins, i.e., cleaved forms of caspase-1, IL-1β, and apoptosis-associated speck-like protein containing a caspase recruit domain (ASC) in the striatum. These results were validated in LPS+ATP-stimulated primary mouse astrocytes in vitro. Remarkably, we showed that PPX (100–400 μM) dose-dependently enhanced the autophagy activity in the astrocytes evidenced by the elevations in LC3-II and BECN1 protein expression, as well as the increase of GFP-LC3 puncta formation. The opposite effects of PPX on astrocytic NLRP3 inflammasome and autophagy were eliminated by Drd3 depletion. Moreover, we demonstrated that both pretreatment of astrocytes with autophagy inhibitor chloroquine (40 μM) in vitro and astrocyte-specific Atg5 knockdown in vivo blocked PPX-caused inhibition on NLRP3 inflammasome and protection against DA neuron damage. Altogether, this study demonstrates an anti-neuroinflammatory activity of PPX via a Drd3-dependent enhancement of autophagy activity in astrocytes, and reveals a new mechanism for the beneficial effect of PPX in PD therapy.

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Background: Neuroinflammation mediated by microglia plays a key role in the pathogenesis of Parkinson's disease (PD), and our previous studies showed this was significantly inhibited by enhanced autophagy. In the autophagy pathway, Bcl2-associated athanogene (BAG)3 is a prominent co-chaperone, and we have shown BAG3 can regulate autophagy to clear the PD pathogenic protein α-synuclein. However, the connection between BAG3 and microglia mediated neuroinflammation is not clear.Methods: In this study, we explored whether BAG3 regulated related neuroinflammation and its original mechanism in PD. An inflammatory model of PD was established by injecting adeno-associated virus (AAV)-BAG3 into the bilateral striatum of C57BL/6 male mice to induce overexpression of BAG3, followed by injection of lipopolysaccharide (LPS). The striatum was extracted at 3 days after injection of LPS for Western blotting and reverse transcription quantitative polymerase chain reaction (RT-qPCR), and immunohistochemical staining was performed at 21 days after injection. At the same time, LPS was used to induce activation of BV2 cells to verify the effect of BAG3 in vitro.Results: Overexpression of BAG3 reduced LPS-induced pyroptosis by reducing activation of caspase-1, the NOD-like receptor family, and the pyrin domain-containing 3 (NLRP3) inflammasome, and by release of interleukin (IL)-1β and tumor necrosis factor (TNF)-α. The LPS-induced inflammatory environment inhibits autophagy, and overexpression of BAG3 can restore autophagy, which may be the mechanism by which BAG3 reduces neuronal inflammation in PD.Conclusions: Our results demonstrate BAG3 promotes autophagy and suppresses NLRP3 inflammasome formation in PD.