Engagement of T cells with antigenpresenting cells requires T-cell receptor (TCR) stimulation at the immune synapse.We previously reported that TCR stimulation induces the release of cellular adenosine-5-triphosphate (ATP) that regulates T-cell activation. Here we tested the roles of pannexin-1 hemichannels, which have been implicated in ATP release, and of various P2X receptors, which serve as ATP-gated Ca 2؉ channels, in events that control T-cell activation. TCR stimulation results in the translocation of P2X1 and P2X4 receptors and pannexin-1 hemichannels to the immune synapse, while P2X7 receptors remain uniformly distributed on the cell surface. Removal of extracellular ATP or inhibition, mutation, or silencing of P2X1 and P2X4 receptors inhibits Ca 2؉ entry, nuclear factors of activated T cells (NFAT) activation, and induction of interleukin-2 synthesis. Inhibition of pannexin-1 hemichannels suppresses TCR-induced ATP release, Ca 2؉ entry, and T-cell activation. We conclude that pannexin-1 hemichannels and P2X1 and P2X4 receptors facilitate ATP release and autocrine feedback mechanisms that control Ca 2؉ entry and T-cell activation at the immune synapse. (Blood. 2010; 116(18):3475-3484) IntroductionT-cell activation requires a sustained elevation of intracellular Ca 2ϩ levels, which is accomplished by Ca 2ϩ entry through calcium release-activated calcium (CRAC) channels that are composed of stromal interaction molecule 1 (STIM1) and Orai1 proteins. [1][2][3] Both proteins translocate to the immune synapse upon T-cell activation, where they mediate localized influx of extracellular Ca 2ϩ . 4 Ca 2ϩ entry contributes to the activation of nuclear factors of activated T cells (NFATs) that induce interleukin-2 (IL-2) gene expression and subsequent signaling events that lead to T-cell proliferation. [5][6][7] Recent studies have shown that extracellular adenosine-5Ј-triphosphate (ATP) regulates T-cell activation. [8][9][10] T cells release ATP in a controlled manner, as do other leukocytes, thereby facilitating intercellular communication and autocrine feedback regulation of cell function. [8][9][10][11][12][13] Stimulation of T cells by T-cell receptor (TCR) ligation, mechanical stimulation, membrane deformation, or osmotic stress induces the release of cellular ATP. 9,10,[13][14][15][16] T cells express the gap junction hemichannels pannexin-1, which can mediate ATP release and T-cell activation. 8,10 T-cell activation has been shown to involve P2X receptor subtypes. 8,10 The 7 mammalian P2X receptor family members (P2X1-7) are ATPgated ion channels. 17,18 All these receptors, with the exception of P2X5, can facilitate entry of Ca 2ϩ in response to stimulation by extracellular ATP, [18][19][20] thus suggesting that P2X receptors regulate T-cell activation by mediating Ca 2ϩ entry.T-cell activation during antigen recognition requires the formation of an immune synapse between T cells and antigen-presenting cells. The immune synapse is a complex structure with a limited number of TCRs, implying that TCR stimu...

Efficient activation of neutrophils is a key requirement for effective immune responses. We found that neutrophils released cellular adenosine triphosphate (ATP) in response to exogenous stimuli such as formylated bacterial peptides and inflammatory mediators that activated receptors for Fcγ, interleukin-8, C5a complement, and leukotriene B4. The release of ATP in response to stimulation of the formyl peptide receptor (FPR) occurred through pannexin-1 hemichannels that colocalized with FPR and P2Y2 nucleotide receptors on the cell surface to form a purinergic signaling system that facilitated the activation of neutrophils. Disruption of this purinergic signaling system by inhibiting or silencing pannexin-1 hemichannels or P2Y2 receptors blocked the activation of neutrophils and impaired innate host responses to bacterial infection. Thus, purinergic signaling is a fundamental mechanism that is required for neutrophil activation and immune defense.

Wiskott–Aldrich syndrome protein (WASP) is in a complex with WASP-interacting protein (WIP). WASP levels, but not mRNA levels, were severely diminished in T cells from WIP −/− mice and were increased by introduction of WIP in these cells. The WASP binding domain of WIP was shown to protect WASP from degradation by calpain in vitro . Treatment with the proteasome inhibitors MG132 and bortezomib increased WASP levels in T cells from WIP −/− mice and in T and B lymphocytes from two WAS patients with missense mutations (R86H and T45M) that disrupt WIP binding. The calpain inhibitor calpeptin increased WASP levels in activated T and B cells from the WASP patients, but not in primary T cells from the patients or from WIP −/− mice. Despite its ability to increase WASP levels proteasome inhibition did not correct the impaired IL-2 gene expression and low F-actin content in T cells from the R86H WAS patient. These results demonstrate that WIP stabilizes WASP and suggest that it may also be important for its function.

The cerebral cortex is essential for integration and processing of information that is required for most behaviors. The exquisitely precise laminar organization of the cerebral cortex arises during embryonic development when neurons migrate successively from ventricular zones to coalesce into specific cortical layers. While radial glia act as guide rails for projection neuron migration, pre-formed vascular networks provide support and guidance cues for GABAergic interneuron migration. This study provides novel conceptual and mechanistic insights into this paradigm of vascular-neuronal interactions, revealing new mechanisms of GABA and its receptor-mediated signaling via embryonic forebrain endothelial cells. With the use of two new endothelial cell specific conditional mouse models of the GABA pathway (Gabrb3ΔTie2-Cre and VgatΔTie2-Cre), we show that partial or complete loss of GABA release from endothelial cells during embryogenesis results in vascular defects and impairs long-distance migration and positioning of cortical interneurons. The downstream effects of perturbed endothelial cell-derived GABA signaling are critical, leading to lasting changes to cortical circuits and persistent behavioral deficits. Furthermore, we illustrate new mechanisms of activation of GABA signaling in forebrain endothelial cells that promotes their migration, angiogenesis and acquisition of blood-brain barrier properties. Our findings uncover and elucidate a novel endothelial GABA signaling pathway in the CNS that is distinct from the classical neuronal GABA signaling pathway and shed new light on the etiology and pathophysiology of neuropsychiatric diseases, such as autism spectrum disorders, epilepsy, anxiety, depression and schizophrenia.

CD4+ T cells are involved in the development of autoimmunity, including multiple sclerosis (MS). Here we show that nicotinamide adenine dinucleotide (NAD+) blocks experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, by inducing immune homeostasis through CD4+IFNγ+IL-10+ T cells and reverses disease progression by restoring tissue integrity via remyelination and neuroregeneration. We show that NAD+ regulates CD4+ T-cell differentiation through tryptophan hydroxylase-1 (Tph1), independently of well-established transcription factors. In the presence of NAD+, the frequency of T-bet−/− CD4+IFNγ+ T cells was twofold higher than wild-type CD4+ T cells cultured in conventional T helper 1 polarizing conditions. Our findings unravel a new pathway orchestrating CD4+ T-cell differentiation and demonstrate that NAD+ may serve as a powerful therapeutic agent for the treatment of autoimmune and other diseases.

Older organs represent an untapped potential to close the gap between demand and supply in organ transplantation but are associated with age-specific responses to injury and increased immunogenicity, thereby aggravating transplant outcomes. Here we show that cellfree mitochondrial DNA (cf-mt-DNA) released by senescent cells accumulates with aging and augments immunogenicity. Ischemia reperfusion injury induces a systemic increase of cfmt-DNA that promotes dendritic cell-mediated, age-specific inflammatory responses. Comparable events are observed clinically, with the levels of cf-mt-DNA elevated in older deceased organ donors, and with the isolated cf-mt-DNA capable of activating human dendritic cells. In experimental models, treatment of old donor animals with senolytics clear senescent cells and diminish cf-mt-DNA release, thereby dampening age-specific immune responses and prolonging the survival of old cardiac allografts comparable to young donor organs. Collectively, we identify accumulating cf-mt-DNA as a key factor in inflamm-aging and present senolytics as a potential approach to improve transplant outcomes and availability.

GABA neurons, born in remote germinative zones in the ventral forebrain (telencephalon), migrate tangentially in two spatially distinct streams to adopt their specific positions in the developing cortex. The cell types and molecular cues that regulate this divided migratory route remains to be elucidated. Here we show that embryonic vascular networks are strategically positioned to fulfill the task of providing support as well as critical guidance cues that regulate the divided migratory routes of GABA neurons in the telencephalon. Interestingly, endothelial cells of the telencephalon are not homogeneous in their gene expression profiles. Endothelial cells of the periventricular vascular network have molecular identities distinct from those of the pial network. Our data suggest that periventricular endothelial cells have intrinsic programs that can significantly mold neuronal development and uncovers new insights into concepts and mechanisms of CNS angiogenesis from both developmental and disease perspectives.

MicroRNAs (miRNA) regulate fundamental biological processes, including neuronal plasticity, stress response, and survival. Here, we describe a neuroprotective function of miR-132, the miRNA most significantly downregulated in neurons in Alzheimer’s disease. We demonstrate that miR-132 protects primary mouse and human wild-type neurons and more vulnerable Tau-mutant neurons against amyloid β-peptide (Aβ) and glutamate excitotoxicity. It lowers the levels of total, phosphorylated, acetylated, and cleaved forms of Tau implicated in tauopathies, promotes neurite elongation and branching, and reduces neuronal death. Similarly, miR-132 attenuates PHF-Tau pathology and neurodegeneration, and enhances long-term potentiation in the P301S Tau transgenic mice. The neuroprotective effects are mediated by direct regulation of the Tau modifiers acetyltransferase EP300, kinase GSK3β, RNA-binding protein Rbfox1, and proteases Calpain 2 and Caspases 3/7. These data suggest miR-132 as a master regulator of neuronal health and indicate that miR-132 supplementation could be of therapeutic benefit for the treatment of Tau-associated neurodegenerative disorders.Electronic supplementary materialThe online version of this article (10.1007/s00401-018-1880-5) contains supplementary material, which is available to authorized users.