A T Cell Suppressive Circuitry Mediated by CD39 and Regulated by ShcC/Rai Is Induced in Astrocytes by Encephalitogenic T Cells

Abstract

Multiple sclerosis is an autoimmune disease caused by autoreactive immune cell infiltration into the central nervous system leading to inflammation, demyelination, and neuronal loss. While myelin-reactive Th1 and Th17 are centrally implicated in multiple sclerosis pathogenesis, the local CNS microenvironment, which is shaped by both infiltrated immune cells and central nervous system resident cells, has emerged a key player in disease onset and progression. We have recently demonstrated that ShcC/Rai is as a novel astrocytic adaptor whose loss in mice protects from experimental autoimmune encephalomyelitis. Here, we have explored the mechanisms that underlie the ability of Rai −/− astrocytes to antagonize T cell-dependent neuroinflammation. We show that Rai deficiency enhances the ability of astrocytes to upregulate the expression and activity of the ectonucleotidase CD39, which catalyzes the conversion of extracellular ATP to the immunosuppressive metabolite adenosine, through both contact-dependent and–independent mechanisms. As a result, Rai-deficient astrocytes acquire an enhanced ability to suppress T-cell proliferation, which involves suppression of T cell receptor signaling and upregulation of the inhibitory receptor CTLA-4. Additionally, Rai-deficient astrocytes preferentially polarize to the neuroprotective A2 phenotype. These results identify a new mechanism, to which Rai contributes to a major extent, by which astrocytes modulate the pathogenic potential of autoreactive T cells.

Differential Proteomic Analysis of Astrocytes and Astrocytes-Derived Extracellular Vesicles from Control and Rai Knockout Mice: Insights into the Mechanisms of Neuroprotection

“…To determine whether the Th17 signature cytokines, IL-17 and IFNγ are responsible for this effect, control and Rai −/− astrocytes were treated with these recombinant cytokines and the expression levels of transcripts known to be upregulated in neuroprotective astrocytes were measured by qRT-PCR. Rai −/− astrocytes showed a significant upregulation of the neuroprotective-specific transcripts Emp1 and S100a10 compared with control astrocytes ( Figure 1 A), consistent with the results obtained following treatment with conditioned media from MOG-specific T cells [ 17 ]. Analysis of the activation status of NF-kB, a key transcription factor in cytokine signaling and a known driver of the proinflammatory response of astrocytes [ 18 ], showed that it was completely inhibited in Rai −/− astrocytes both following stimulation with IL-17 and IFNγ, and in the presence of conditioned media from encephalitogenic T cells ( Figure 1 B) suggesting that Rai drives the astrocyte response to inflammatory soluble factors secreted by T cells through the activation of NF-kB.…”

“…We recently provided evidence that conditioned media from MOG-specific T cells induced the acquisition of a neuroprotective phenotype by astrocytes lacking the molecular adaptor Rai [ 17 ]. To determine whether the Th17 signature cytokines, IL-17 and IFNγ are responsible for this effect, control and Rai −/− astrocytes were treated with these recombinant cytokines and the expression levels of transcripts known to be upregulated in neuroprotective astrocytes were measured by qRT-PCR.…”

“…The reduced degree of demyelination was associated with a reduced activation of astrocytes, supporting the notion that Rai expression in astrocytes is an important determinant in MS immunopathology [ 16 ]. We recently demonstrated that the ability of astrocytes lacking Rai to control the pathogenic potential of autoreactive T cells involves the conversion of extracellular ATP to the immunosuppressive molecule adenosine through the enhancement of CD39 ectonucleotidase activity [ 17 ]. Moreover, we showed that astrocytes lacking Rai skew towards a neuroprotective phenotype in response to encephalitogenic T cells, both in vitro and in EAE mice [ 17 ].…”

“…We recently demonstrated that the ability of astrocytes lacking Rai to control the pathogenic potential of autoreactive T cells involves the conversion of extracellular ATP to the immunosuppressive molecule adenosine through the enhancement of CD39 ectonucleotidase activity [ 17 ]. Moreover, we showed that astrocytes lacking Rai skew towards a neuroprotective phenotype in response to encephalitogenic T cells, both in vitro and in EAE mice [ 17 ]. Together, these findings underscore the multifaceted role played by Rai in astrocyte reactivity during EAE, suggesting the possibility that targeting Rai expression in astrocytes may represent a strategy to impact on the course of disease.…”

MMP-9 Shedding Releases Truncated CD73 from Astrocytes

“…ATP is generally regarded as a pro-inflammatory factor, while adenosine is verified of having a strong anti-inflammatory function. In CNS inflammation, ATP was reported to promote immune response, while adenosine showed significant inhibitory effect [19][20][21][22][23][24].…”