Abstract
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.