ZAKα/P38 kinase signaling pathway regulates hematopoiesis by activating the NLRP1 inflammasome.

Chronic inflammatory diseases are associated with hematopoietic lineage bias, including neutrophilia and anemia. We have recently identified that the canonical inflammasome mediates the cleavage of the master erythroid transcription factor GATA1 in hematopoietic stem and progenitor cells (HSPCs). We report here that genetic inhibition of Nlrp1 resulted in reduced number of neutrophils and increased erythrocyte counts in zebrafish larvae. We also found that the NLRP1 inflammasome in human cells was inhibited by LRRFIP1 and FLII, independently of DPP9, and both inhibitors regulated hematopoiesis. Mechanistically, erythroid differentiation resulted in ribosomal stress-induced activation of the ZAKα/P38 kinase axis which, in turn, phosphorylated and promoted the assembly of NLRP1 in both zebrafish and human. Finally, inhibition of Zaka with the FDA/EMA-approved drug Nilotinib alleviated neutrophilia in a zebrafish model of neutrophilic inflammation and promoted erythroid differentiation and GATA1 accumulation in K562 cells. In conclusion, our results reveal that the NLRP1 inflammasome regulates hematopoiesis and pave the way to develop novel therapeutic strategies for the treatment of hematopoietic alterations associated with chronic inflammatory and rare diseases.

Impact of Comorbidities of Patients with Psoriasis on Phototherapy Responses.

A retrospective study of 200 psoriasis patients and 100 healthy donors in a Spanish cohort was carried out to study the comorbidities associated with psoriasis and their association with the response to phototherapy. The results showed a higher incidence of psychiatric disease, liver disease, kidney disease, hypertension, heart disease, vascular disease, diabetes, gastrointestinal disease, autoimmune and infectious diseases, dyslipidemia, and psoriatic arthritis in patients with psoriasis than in the control group. The incidence of comorbidities was higher in psoriasis patients over 40 years old than in the control individuals of the same age, which could be indicative of premature aging. Phototherapy was seen to be an effective treatment in cases of moderate-severe psoriasis, total whitening being achieved in more than 30% of patients, with women showing a better response than men. Narrow-band ultraviolet B was found to be the most effective type of phototherapy, although achievement of PASI100 was lower in patients with liver disease, hypertension, heart disease, vascular disease, or diabetes. Strikingly, liver disease and anemia comorbidities favored therapeutic failure. Finally, zebrafish and human 3D organotypic models of psoriasis point to the therapeutic benefit of inhibiting the glucose transporter GLUT1 and the major regulator of blood glucose dipeptidyl peptidase 4. Our study reveals that specific comorbidities of psoriasis patients are associated to failure of phototherapy and, therefore, need to be considered when planning treatment for these patients.

Gasdermin E mediates pyroptotic cell death of neutrophils and macrophages in a zebrafish model of chronic skin inflammation.

Chronic diseases and hematopoietic disorders are associated with dysregulation of the inflammasome. Our group has recently reported the relevance of the inflammasome in the differentiation of hematopoietic stem and progenitor cells. However, the impact of the inflammasome of myeloid cells in the regulation of hematopoiesis is largely unknown. In this study, we used the unique advantages of the zebrafish model to demonstrate that genetic inhibition of macrophage inflammasome resulted in increased number of macrophages in larvae with skin inflammation without affecting erythrocyte and neutrophil counts. Similarly, the inhibition of the neutrophil inflammasome by the same strategy resulted in increased number of neutrophils in larvae with skin inflammation but did not affect erythrocytes and macrophages. Consistently, hyperactivation of the inflammasome in neutrophils in this model promoted neutrophil death, which was recovered by pharmacological inhibition of Gasdermin E. We conclude that the myeloid inflammasome autonomously regulates pyroptotic cell death in chronic inflammation through a Gasdermin E-dependent pathway in zebrafish.

Zebrafish Models to Study Inflammasome-Mediated Regulation of Hematopoiesis.

Hematopoiesis is a complex process through which immature bone marrow precursor cells mature into all types of blood cells. Although the association of hematopoietic lineage bias (including anemia and neutrophilia) with chronic inflammatory diseases has long been appreciated, the causes involved are obscure. Recently, cytosolic multiprotein inflammasome complexes were shown to activate inflammatory and immune responses, and directly regulate hematopoiesis in zebrafish models; this was deemed to occur via cleavage and inactivation of the master erythroid transcription factor GATA1. Herein summarized are the zebrafish models that are currently available to study this unappreciated role of inflammasome-mediated regulation of hematopoiesis. Novel putative therapeutic strategies, for the treatment of hematopoietic alterations associated with chronic inflammatory diseases in humans, are also proposed.

RAC1-Dependent ORAI1 Translocation to the Leading Edge Supports Lamellipodia Formation and Directional Persistence.

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 Ca2+ 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 Ca2+ channel on lamellipodia formation, lamellipodial persistence, and cell directness, which are required for tumor cell invasiveness in vivo.

Inflammasome Regulates Hematopoiesis through Cleavage of the Master Erythroid Transcription Factor GATA1.

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.