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PIEZO1 is a cation channel that is activated by mechanical forces such as fluid shear stress or membrane stretch. PIEZO1 loss-of-function mutations in patients are associated with congenital lymphedema with pleural effusion. However, the mechanistic link between PIEZO1 function and the development or function of the lymphatic system is currently unknown. Here, we analyzed two mouse lines lacking PIEZO1 in endothelial cells (via Tie2Cre or Lyve1Cre) and found that they exhibited pleural effusion and died postnatally. Strikingly, the number of lymphatic valves was dramatically reduced in these mice. Lymphatic valves are essential for ensuring proper circulation of lymph. Mechanical forces have been implicated in the development of lymphatic vasculature and valve formation, but the identity of mechanosensors involved is unknown. Expression of FOXC2 and NFATc1, transcription factors known to be required for lymphatic valve development, appeared normal in Tie2Cre;Piezo1cKO mice. However, the process of protrusion in the valve leaflets, which is associated with collective cell migration, actin polymerization, and remodeling of cell–cell junctions, was impaired in Tie2Cre;Piezo1cKO mice. Consistent with these genetic findings, activation of PIEZO1 by Yoda1 in cultured lymphatic endothelial cells induced active remodeling of actomyosin and VE-cadherin⁺ cell–cell adhesion sites. Our analysis provides evidence that mechanically activated ion channel PIEZO1 is a key regulator of lymphatic valve formation.

In Alzheimer’s disease, amyloid deposits along the brain vasculature lead to a condition known as cerebral amyloid angiopathy (CAA), which impairs blood–brain barrier (BBB) function and accelerates cognitive degeneration. Apolipoprotein ( APO E4 ) is the strongest risk factor for CAA, yet the mechanisms underlying this genetic susceptibility are unknown. Here we developed an induced pluripotent stem cell-based three-dimensional model that recapitulates anatomical and physiological properties of the human BBB in vitro. Similarly to CAA, our in vitro BBB displayed significantly more amyloid accumulation in APOE4 compared to APOE3. Combinatorial experiments revealed that dysregulation of calcineurin–nuclear factor of activated T cells (NFAT) signaling and APOE in pericyte-like mural cells induces APOE4-associated CAA pathology. In the human brain, APOE and NFAT are selectively dysregulated in pericytes of APOE4 carriers, and inhibition of calcineurin–NFAT signaling reduces APOE4-associated CAA pathology in vitro and in vivo. Our study reveals the role of pericytes in APOE4-mediated CAA and highlights calcineurin–NFAT signaling as a therapeutic target in CAA and Alzheimer’s disease. An iPSC-based three-dimensional model of the human blood–brain barrier reveals that NFAT and APOE dysregulation in pericyte-like mural cells contributes to cerebral amyloid angiopathy and can potentially be targeted to treat Alzheimer’s disease.

The transcription factors nuclear factor of activated T cells (NFAT) and activator protein 1 (AP-1; Fos–Jun) cooperate to promote the effector functions of T cells, but NFAT in the absence of AP-1 imposes a negative feedback program of T cell hyporesponsiveness (exhaustion). Here, we show that basic leucine zipper ATF-like transcription factor (BATF) and interferon regulatory factor 4 (IRF4) cooperate to counter T cell exhaustion in mouse tumor models. Overexpression of BATF in CD8 + T cells expressing a chimeric antigen receptor (CAR) promoted the survival and expansion of tumor-infiltrating CAR T cells, increased the production of effector cytokines, decreased the expression of inhibitory receptors and the exhaustion-associated transcription factor TOX and supported the generation of long-lived memory T cells that controlled tumor recurrence. These responses were dependent on BATF–IRF interaction, since cells expressing a BATF variant unable to interact with IRF4 did not survive in tumors and did not effectively delay tumor growth. BATF may improve the antitumor responses of CAR T cells by skewing their phenotypes and transcriptional profiles away from exhaustion and towards increased effector function. Chronic antigen stimulation leads to CD8 + T cell exhaustion, which is mediated by persistent activation of the transcription factor NFAT in the absence of AP-1. Seo, González-Avalos and colleagues show that overexpressed BATF cooperates with IRF4 to counteract NFAT-induced exhaustion and promote better tumor control by CAR T cells in mouse models.

Mechanical forces are fundamental regulators of cell behaviors. However, molecular regulation of mechanotransduction remain poorly understood. Here, we identified the mechanosensitive channels Piezo1 and Piezo2 as key force sensors required for bone development and osteoblast differentiation. Loss of Piezo1, or more severely Piezo1/2, in mesenchymal or osteoblast progenitor cells, led to multiple spontaneous bone fractures in newborn mice due to inhibition of osteoblast differentiation and increased bone resorption. In addition, loss of Piezo1/2 rendered resistant to further bone loss caused by unloading in both bone development and homeostasis. Mechanistically, Piezo1/2 relayed fluid shear stress and extracellular matrix stiffness signals to activate Ca2+ influx to stimulate Calcineurin, which promotes concerted activation of NFATc1, YAP1 and ß-catenin transcription factors by inducing their dephosphorylation as well as NFAT/YAP1/ß-catenin complex formation. Yap1 and ß-catenin activities were reduced in the Piezo1 and Piezo1/2 mutant bones and such defects were partially rescued by enhanced ß-catenin activities.

RANKL, the essential cue for osteoclast differentiation, is the membrane-bound factor expressed by osteoclastogenesis-supporting cells such as osteoblasts and osteocytes. In vivo evidence indicates that RANKL functions as the indispensable and irreplaceable in the program of osteoclast differentiation. The reason why RANKL plays a critical role in osteoclastogenesis is discussed from the viewpoint of the distinct signaling pathways mediated by co-stimulatory receptors and the key transcription factor NFATc1.

The role of mitochondria in haematopoietic stem-cell maintenance has not been examined in detail; here mitofusin 2, which modulates mitochondrial fusion and tethering of endoplasmic reticulum to the mitochondria, is shown to be necessary for the maintenance of haematopoietic stem cells with extensive lymphoid potential. Maintenance of HSC lymphoid potential The role of mitochondria in maintaining haematopoietic lineages has not been examined in detail. Hans-Willem Snoeck and colleagues have found that the haematopoietic stem cell (HSC) regulator Prdm16 induces the expression of mitofusin 2 (Mfn2), which modulates mitochondrial fusion and tethering of endoplasmic reticulum to the mitochondria. By adjusting the levels of Mfn2 in HSCs, they demonstrate that Mfn2 is necessary for the maintenance of HSCs with lymphoid potential. Mechanistically, Mfn2 modulates calcium signalling to negatively regulate the transcription factor Nfat and sustains lymphoid lineages. Haematopoietic stem cells (HSCs), which sustain production of all blood cell lineages 1 , rely on glycolysis for ATP production 2 , 3 , yet little attention has been paid to the role of mitochondria. Here we show in mice that the short isoform of a critical regulator of HSCs, Prdm16 (refs 4 , 5 ), induces mitofusin 2 (Mfn2), a protein involved in mitochondrial fusion and in tethering of mitochondria to the endoplasmic reticulum. Overexpression and deletion studies, including single-cell transplantation assays, revealed that Mfn2 is specifically required for the maintenance of HSCs with extensive lymphoid potential, but not, or less so, for the maintenance of myeloid-dominant HSCs. Mfn2 increased buffering of intracellular Ca 2+ , an effect mediated through its endoplasmic reticulum–mitochondria tethering activity 6 , 7 , thereby negatively regulating nuclear translocation and transcriptional activity of nuclear factor of activated T cells (Nfat). Nfat inhibition rescued the effects of Mfn2 deletion in HSCs, demonstrating that negative regulation of Nfat is the prime downstream mechanism of Mfn2 in the maintenance of HSCs with extensive lymphoid potential. Mitochondria therefore have an important role in HSCs. These findings provide a mechanism underlying clonal heterogeneity among HSCs 8 , 9 , 10 , 11 and may lead to the design of approaches to bias HSC differentiation into desired lineages after transplantation.

Exhausted CD8 + T (T ex ) cells in chronic infections and cancer have limited effector function, high co-expression of inhibitory receptors and extensive transcriptional changes compared with effector (T eff ) or memory (T mem ) CD8 + T cells. T ex cells are important clinical targets of checkpoint blockade and other immunotherapies. Epigenetically, T ex cells are a distinct immune subset, with a unique chromatin landscape compared with T eff and T mem cells. However, the mechanisms that govern the transcriptional and epigenetic development of T ex cells remain unknown. Here we identify the HMG-box transcription factor TOX as a central regulator of T ex cells in mice. TOX is largely dispensable for the formation of T eff and T mem cells, but it is critical for exhaustion: in the absence of TOX, T ex cells do not form. TOX is induced by calcineurin and NFAT2, and operates in a feed-forward loop in which it becomes calcineurin-independent and sustained in T ex cells. Robust expression of TOX therefore results in commitment to T ex cells by translating persistent stimulation into a distinct T ex cell transcriptional and epigenetic developmental program. The transcription factor TOX is a central regulator of the transcriptional and epigenetic development of exhausted T cells.

Heterozygous germline mutations in the zinc finger transcription factor GATA2 have recently been shown to underlie a range of clinical phenotypes, including Emberger syndrome, a disorder characterized by lymphedema and predisposition to myelodysplastic syndrome/acute myeloid leukemia (MDS/AML). Despite well-defined roles in hematopoiesis, the functions of GATA2 in the lymphatic vasculature and the mechanisms by which GATA2 mutations result in lymphedema have not been characterized. Here, we have provided a molecular explanation for lymphedema predisposition in a subset of patients with germline GATA2 mutations. Specifically, we demonstrated that Emberger-associated GATA2 missense mutations result in complete loss of GATA2 function, with respect to the capacity to regulate the transcription of genes that are important for lymphatic vessel valve development. We identified a putative enhancer element upstream of the key lymphatic transcriptional regulator PROX1 that is bound by GATA2, and the transcription factors FOXC2 and NFATC1. Emberger GATA2 missense mutants had a profoundly reduced capacity to bind this element. Conditional Gata2 deletion in mice revealed that GATA2 is required for both development and maintenance of lymphovenous and lymphatic vessel valves. Together, our data unveil essential roles for GATA2 in the lymphatic vasculature and explain why a select catalogue of human GATA2 mutations results in lymphedema.

The oncometabolite ( R )-2-hydroxyglutarate (R-2-HG) produced by isocitrate dehydrogenase ( IDH ) mutations promotes gliomagenesis via DNA and histone methylation. Here, we identify an additional activity of R-2-HG: tumor cell–derived R-2-HG is taken up by T cells where it induces a perturbation of nuclear factor of activated T cells transcriptional activity and polyamine biosynthesis, resulting in suppression of T cell activity. IDH1 -mutant gliomas display reduced T cell abundance and altered calcium signaling. Antitumor immunity to experimental syngeneic IDH1 -mutant tumors induced by IDH1-specific vaccine or checkpoint inhibition is improved by inhibition of the neomorphic enzymatic function of mutant IDH1 . These data attribute a novel, non-tumor cell-autonomous role to an oncometabolite in shaping the tumor immune microenvironment. An oncometabolite produced by tumor cells acts as a paracrine immunosuppressant dampening antitumor T cell responses in glioma.

Group 2 innate lymphoid cells express the neuromedin U receptor 1 (NMUR1) and respond to neuromedin U (NMU) released by adjacent enteric neurons, and this interaction results in an enhanced immediate early response to the nematode Nippostrongylus brasiliensis . Neuron regulation of immune cells Group 2 innate lymphoid cells (ILC2s) are innate regulators of inflammation and tissue repair. Henrique Veiga-Fernandes and colleagues provide evidence that ILC2s express the neuromedin U receptor 1 ( Nmur1 ) and respond to neuromedin expressed by adjacent enteric neurons. In mice, the interaction results in an enhanced and immediate response of ILC2s to infection by the parasite Nippostrongylus brasiliensis . Elsewhere in this issue, David Artis and colleagues also report that ILC2s express NMUR1, making them responsive to neuronal neuromedin. This promoted a tissue-protective type 2 response and accelerated expulsion of the gastrointestinal nematode N. brasiliensis in mice. Group 2 innate lymphoid cells (ILC2s) regulate inflammation, tissue repair and metabolic homeostasis 1 , and are activated by host-derived cytokines and alarmins 1 . Discrete subsets of immune cells integrate nervous system cues 2 , 3 , 4 , but it remains unclear whether neuron-derived signals control ILC2s. Here we show that neuromedin U (NMU) in mice is a fast and potent regulator of type 2 innate immunity in the context of a functional neuron–ILC2 unit. We found that ILC2s selectively express neuromedin U receptor 1 ( Nmur1 ), and mucosal neurons express NMU. Cell-autonomous activation of ILC2s with NMU resulted in immediate and strong NMUR1-dependent production of innate inflammatory and tissue repair cytokines. NMU controls ILC2s downstream of extracellular signal-regulated kinase and calcium-influx-dependent activation of both calcineurin and nuclear factor of activated T cells (NFAT). NMU treatment in vivo resulted in immediate protective type 2 responses. Accordingly, ILC2-autonomous ablation of Nmur1 led to impaired type 2 responses and poor control of worm infection. Notably, mucosal neurons were found adjacent to ILC2s, and these neurons directly sensed worm products and alarmins to induce NMU and to control innate type 2 cytokines. Our work reveals that neuron–ILC2 cell units confer immediate tissue protection through coordinated neuroimmune sensory responses.