Inhibition of astrocytic DRD2 suppresses CNS inflammation in an animal model of multiple sclerosis.

Astrocyte activation is associated with progressive inflammatory demyelination in multiple sclerosis (MS). The molecular mechanisms underlying astrocyte activation remain incompletely understood. Recent studies have suggested that classical neurotransmitter receptors are implicated in the modulation of brain innate immunity. We investigated the role of dopamine signaling in the process of astrocyte activation. Here, we show the upregulation of dopamine D2 receptor (DRD2) in reactive astrocytes in MS brain and noncanonical role of astrocytic DRD2 in MS pathogenesis. Mice deficient in astrocytic Drd2 exhibit a remarkable suppression of reactive astrocytes and amelioration of experimental autoimmune encephalomyelitis (EAE). Mechanistically, DRD2 regulates the expression of 6-pyruvoyl-tetrahydropterin synthase, which modulates NF-κB activity through protein kinase C-δ. Pharmacological blockade of astrocytic DRD2 with a DRD2 antagonist dehydrocorybulbine remarkably inhibits the inflammatory response in mice lacking neuronal Drd2. Together, our findings reveal previously an uncharted role for DRD2 in astrocyte activation during EAE-associated CNS inflammation. Its therapeutic inhibition may provide a potent lever to alleviate autoimmune diseases.

Suppression of astrocytic autophagy by αB-crystallin contributes to α-synuclein inclusion formation.

BACKGROUND: Parkinson's disease (PD) is characterized by a chronic loss of dopaminergic neurons and the presence of proteinaceous inclusions (Lewy bodies) within some remaining neurons in the substantia nigra. Recently, astroglial inclusion body has also been found in some neurodegenerative diseases including PD. However, the underlying molecular mechanisms of how astroglial protein aggregation forms remain largely unknown. Here, we investigated the contribution of αB-crystallin (CRYAB), a small heat shock protein, in α-synuclein inclusion formation in astrocytes. METHODS: Small interfering RNA (siRNA)-mediated CRYAB (siCRYAB) knockdown or CRYAB overexpression was performed to investigate the impact of CRYAB on the autophagy in human glioblastoma cell line U251 cells. Co-immunoprecipitation (co-IP) and immunoblotting were used to dissect the interaction among multiple proteins. The clearance of α-synuclein in vitro was evaluated by immunocytochemistry. CRYAB transgenic mice and transgenic mice overexpressing A30P mutant form of human α-synuclein were used to examine the influence of CRYAB to α-synuclein accumulation in vivo. RESULTS: We found that knockdown of CRYAB in U251 cells or primary cultured astrocytes resulted in a marked augmentation of autophagy activity. In contrast, exogenous CRYAB disrupted the assembly of the BAG3-HSPB8-HSC70 complex via binding with BAG3, thereby suppressing the autophagy activity. Furthermore, CRYAB-regulated autophagy has relevance to PD pathogenesis. Knockdown of CRYAB remarkably promoted cytoplasmic clearance of α-synuclein preformed fibrils (PFFs). Conversely, selective overexpression of CRYAB in astrocytes markedly suppressed autophagy leading to the accumulation of α-synuclein aggregates in the brain of transgenic mice expressing human α-synuclein A30P mutant. CONCLUSIONS: This study reveals a novel function for CRYAB as a natural inhibitor of astrocytic autophagy and shows that knockdown of CYRAB may provide a therapeutic target against proteinopathies such as synucleinopathies.

Extracellular αB-crystallin modulates the inflammatory responses.

Neuroinflammation is considered a challenging clinical problem. Chronic inflammatory responses play important roles in the onset and progression of various neurodegenerative diseases, including multiple sclerosis (MS). Previous studies have shown that astrocytes express small heat shock protein αB-crystallin (CRYAB) which is capable of inhibiting inflammatory responses in astrocytes per se. However, the underlying mechanisms of CRYAB-induced modulation of neuroinflammation are still not fully understood. In the present study, we investigated the role of extracellular CRYAB in the interaction between microglia and astrocytes in the context of MS-associated neuroinflammation. We found that the expression of CRYAB was profoundly increased in EAE mice. CRYAB was preferentially expressed in astrocytes and could be secreted via exosomes. Levels of exosomal CRYAB secreted from astrocytes were markedly increased under stress conditions. Furthermore, incubation of immortalized astrocytes or microglia cell lines with CRYAB remarkably suppressed astrocytes and microglia-mediated inflammatory responses in both autocrine and paracrine manners. Our results reveal a novel function for extracellular CRYAB in the regulation of neuroinflammation. Targeting extracellular CRYAB-modulated neuroinflammation is a potential therapeutic intervention for MS.