SUMMARY Chronic inflammatory diseases are associated with altered hematopoiesis that could result in neutrophilia and anemia. Here we report that genetic or chemical manipulation of different inflammasome components altered the differentiation of hematopoietic stem and progenitor cells (HSPC) in zebrafish. Although the inflammasome was dispensable for the emergence of HSPC, it was intrinsically required for their myeloid differentiation. In addition, Gata1 transcript and protein amounts increased in inflammasome-deficient larvae, enforcing erythropoiesis and inhibiting myelopoiesis. This mechanism is evolutionarily conserved, since pharmacological inhibition of the inflammasome altered erythroid differentiation of human erythroleukemic K562 cells. In addition, caspase-1 inhibition rapidly upregulated GATA1 protein in mouse HSPC promoting their erythroid differentiation. Importantly, pharmacological inhibition of the inflammasome rescued zebrafish disease models of neutrophilic inflammation and anemia. These results indicate that the inflammasome plays a major role in the pathogenesis of neutrophilia and anemia of chronic diseases and reveal druggable targets for therapeutic interventions.

TREIMM 1740 No. of Pages 12 flammation in response to various stimuli, including infection, tissue damage, or metabolic dys-55 regulation. They are multiprotein complexes formed by a receptor, the adaptor protein 56 apoptosis-associated speck-like protein containing a CARD (ASC), and an effector that 57 interacts through homotypic interactions [18]. Recently, the guanylate-binding protein (GBP) 58 family was found to also form a part of these multiprotein complexes in humans, mice, and 59 zebrafish [19-22]. Inflammasomes act by activating inflammatory caspases, namely caspase 60 1 (CASP1) (canonical inflammasomes), and CASP4, CASP5 (human), and Casp11 (mouse) 61 (noncanonical inflammasomes) [18]. 62 Inflammasome sensors are grouped, depending on their structure, into nucleotide-binding do-63 main (NOD)-like receptors (NLRs), absent in melanoma 2 (AIM2)-like receptors (ALRs), 64 or pyrin [18]. When a specific stimulus is detected, the sensor interacts with and promotes the b0:2 Box 1. Anemia-Associated with FMF and CAPS b1:3 Familiar Mediterranean Fever (FMF) and cryopyrin-associated periodic syndrome (CAPS) are two inflammatory diseases b1:4 driven by germ-line mutations in genes encoding inflammasome components. FMF is the most common monogenic b1:5 autoinflammatory disease worldwide, affecting an estimated 150 000 patients [88]. More than 60% of FMF patients b1:6 develop anemia that is associated with iron status rather than inflammation, assayed as plasma IL-6 concentrations b1:7 [89]. Similarly, iron-resistant hypochromic anemia has also been associated with CAPS [90]. It is tempting to speculate that b1:8 overactivation of the inflammasome in HSPCs could directly promote anemia by enforcing erythropoiesis, explaining the b1:9 usual iron-refractory nature Q3 of these diseases, but this remains to be robustly investigated. Furthermore, released Asc b1:10 specks are able to propagate inflammation in mouse models of CAPS and are found in the serum of patients with CAPS, b1:11 but not with FMF [60,61]. Therefore, macrophage-derived ASC specks may be taken up by HSPCs, activating b1:12 their inflammasome and further enhancing myelopoiesis at the expense of erythropoiesis, which might explain the iron-b1:13 resistance anemia-associated with CAPS (see Clinician's Corner and Outstanding Questions) (Figure 2).

Tumor invasion requires efficient cell migration, which is achieved by the generation of persistent and polarized lamellipodia. The generation of lamellipodia is supported by actin dynamics at the leading edge where a complex of proteins known as the WAVE regulatory complex (WRC) promotes the required assembly of actin filaments to push the front of the cell ahead. By using an U2OS osteosarcoma cell line with high metastatic potential, proven by a xenotransplant in zebrafish larvae, we have studied the role of the plasma membrane Ca 2+ channel ORAI1 in this process. We have found that epidermal growth factor (EGF) triggered an enrichment of ORAI1 at the leading edge, where colocalized with cortactin (CTTN) and other members of the WRC, such as CYFIP1 and ARP2/3. ORAI1-CTTN co-precipitation was sensitive to the inhibition of the small GTPase RAC1, an upstream activator of the WRC. RAC1 potentiated ORAI1 translocation to the leading edge, increasing the availability of surface ORAI1 and increasing the plasma membrane ruffling. The role of ORAI1 at the leading edge was studied in genetically engineered U2OS cells lacking ORAI1 expression that helped us to prove the key role of this Ca 2+ channel on lamellipodia formation, lamellipodial persistence, and cell directness, which are required for tumor cell invasiveness in vivo.