Somatic gene mutations expose cytoplasmic DNA to co-opt the cGAS/STING/NLRP3 axis in myelodysplastic syndromes

Abstract

NLRP3 inflammasome and IFN-stimulated gene (ISG) induction are key biological drivers of ineffective hematopoiesis and inflammation in myelodysplastic syndromes (MDSs). Gene mutations involving mRNA splicing and epigenetic regulatory pathways induce inflammasome activation and myeloid lineage skewing in MDSs through undefined mechanisms. Using immortalized murine hematopoietic stem and progenitor cells harboring these somatic gene mutations and primary MDS BM specimens, we showed accumulation of unresolved R-loops and micronuclei with concurrent activation of the cytosolic sensor cyclic GMP-AMP synthase. Cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) signaling caused ISG induction, NLRP3 inflammasome activation, and maturation of the effector protease caspase-1. Deregulation of RNA polymerase III drove cytosolic R-loop generation, which upon inhibition, extinguished ISG and inflammasome response. Mechanistically, caspase-1 degraded the master erythroid transcription factor, GATA binding protein 1, provoking anemia and myeloid lineage bias that was reversed by cGAS inhibition in vitro and in Tet2 –/– hematopoietic stem and progenitor cell–transplanted mice. Together, these data identified a mechanism by which functionally distinct mutations converged upon the cGAS/STING/NLRP3 axis in MDS, directing ISG induction, pyroptosis, and myeloid lineage skewing.

Biological drivers of clinical phenotype in myelofibrosis

“…Increased calprotectin production in cytopenic MF arises in part from the traditional non-driver, somatic gene mutations common to this disease subset. Although unrestrained JAK2/STAT activation induces S100A8/S100A9 in clonal hematopoietic progenitors and the surrounding stroma, both epigenetic regulatory and mRNA spicing gene mutations induce S100A8 and S100A9 overexpression to compound ineffective blood production in cytopenic MF [ 64 , 106 , 107 ]. Importantly, overexpression of S100A9 in a transgenic mouse model is alone sufficient to cause pancytopenia as a result of ineffective hematopoiesis that was ameliorated by NLRP3 inflammasome inhibition [ 108 ].…”

NLRP3-induced systemic inflammation controls the development of JAK2V617F mutant myeloproliferative neoplasms

“…Caspase-1 inhibition upregulates GATA1 protein in mouse HSPCs thereby promoting erythrocytosis. Degradation of GATA1 downstream of NLRP3 inflammasome activation has been proposed as a mechanism leading to anemia in MDS 32 .…”

Pathogen and human NDPK-proteins promote AML cell survival via monocyte NLRP3-inflammasome activation

“…Although a novel concept in these diseases, the association between microbiota and solid cancers is becoming accepted (40)(41)(42)(43)(44) and the association of inflammation with cancer is well established (43,45). In addition, the association of sterile NLRP3 inflammasome activation with AML and MDS is also well accepted (10)(11)(12)(13)(14)(15)(16). To date, the role of NLRP3 inflammasomes in myeloid malignancies has focused on classical pyroptotic pathways, where cells dying by pyroptosis release DAMPS that further activate inflammation via TLRs including TLR4 (13,15,17,(46)(47)(48).…”

“…Several studies have implicated the NLRP3inflammasome in AML progression (10)(11)(12). Equally, the importance of NLRP3 activation in the pathogenesis of myelodysplastic syndromes (MDS) is well established (13)(14)(15)(16). The NLRP3 inflammasome (comprised of the NOD-, leucine-rich repeat (LRR)-and pyrin domain (PYD)-containing protein 3 (NLRP3), the adapter apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and the effector protease caspase-1) orchestrates Toll-like receptor 4 (TLR4) responses to both sterile and infection-related inflammation.…”