α‐Synuclein activates innate immunity but suppresses interferon‐γ expression in murine astrocytes

Abstract

Glial activation and neuroinflammation contribute to pathogenesis of neurodegenerative diseases, linked to neuron loss and dysfunction. α-Synuclein (α-syn), as a metabolite of neuron, can induce microglia activation to trigger innate immune response. However, whether α-syn, as well as its mutants (A53T, A30P, and E46K), induces astrocyte activation and inflammatory response is not fully elucidated. In this study, we used A53T mutant and wild-type α-syns to stimulate primary astrocytes in dose- and time-dependent manners (0.5, 2, 8, and 20 μg/ml for 24 hr or 3, 12, 24, and 48 hr at 2 μg/ml), and evaluated activation of several canonical inflammatory pathway components. The results showed that A53T mutant or wild-type α-syn significantly upregulated mRNA expression of toll-like receptor (TLR)2, TLR3, nuclear factor-κB and interleukin (IL)-1β, displaying a pattern of positive dose-effect correlation or negative time-effect correlation. Such upregulation was confirmed at protein levels of TLR2 (at 20 μg/ml), TLR3 (at most doses), and IL-1β (at 3 hr) by western blotting. Blockage of TLR2 other than TLR4 inhibited TLR3 and IL-1β mRNA expressions. By contrast, interferon (IFN)-γ was significantly downregulated at mRNA, protein, and protein release levels, especially at high concentrations of α-syns or early time-points. These findings indicate that α-syn was a TLRs-mediated immunogenic agent (A53T mutant stronger than wild-type α-syn). The stimulation patterns suggest that persistent release and accumulation of α-syn is required for the maintenance of innate immunity activation, and IFN-γ expression inhibition by α-syn suggests a novel immune molecule interaction mechanism underlying pathogenesis of neurodegenerative diseases.

The link between neuroinflammation and the neurovascular unit in synucleinopathies

“…However, because the disease progresses with constant stimulation from α-synuclein inclusions and the microenvironment, astrocytes may become overactive and respond accordingly. The release of neuroinflammatory factors, including NF-κB, TNF-α, and IL-1β, by astrocytes can be amplified by IFN-γ ( 116 ). In addition, after CX3CR1 deletion, the A53T mutant of α-synuclein exacerbated neuroinflammatory markers and microgliosis, which were accompanied by neurodegeneration, indicating the modulatory effect of CX3CR1 on pathological proteins ( 117 ).…”

Relationship among α‑synuclein, aging and inflammation in Parkinson's disease (Review)

“…In astrocytes, the uptake of extracellular α-Syn relies on TLR2 rather than TLR4 ( Fig. 2 ) ( 18 ), while intracellular α-Syn relies on TLR2, TLR3 and TLR4 to induce inflammatory responses in astrocytes ( 18 , 80 ). Notably, α-Syn entry into microglia is dependent on TLR2 and TLR4( 78 ).…”

The Specific Role of Reactive Astrocytes in Stroke

“…After the stroke, astrocytes express multiple Toll-like receptors (TLR), including TLR4, TLR2, and TLR3, which respond to distress-associated molecular patterns (DAMPs) released by injured cells (Sofroniew, 2014;Wang et al, 2019). Besides, neurotransmitters released by damaged neurons and proinflammatory factors secreted by adjacent cells act together on astrocytes, leading to significant changes in astrocyte morphology, molecular expression, and other levels (Johnston, 2005;Lan et al, 2017).…”

“…After the stroke, SBI involves vascular endothelial cells, neurons, glial cells, and other cell types, which interact to jointly determine the damage response's occurrence, development, and outcome. Astrocytes are the most abundant subtype among these cells, highly expressing the interleukin-1 receptor (IL-1R), tumor necrosis factor receptor (TNFR), interferon-γ receptor (IFN-γR), and other inflammatory signal receptors (Lovatt et al, 2007;Wang et al, 2019), so they are one of the cells targeted for inflammatory factors. Moreover, astrocytes can also secrete CXCL12, CCl2, C1q, and other inflammatory factors to aggravate SBI (Yamada et al, 1992).…”