AIM2 inflammasome dependent IL1β and IL-18 signaling is required for initiation of stress erythropoiesis in anemia of inflammation

Abstract Steady-state erythropoiesis continuously produces new erythrocytes, with an estimated rate of 2.5 × 10⁶ erythrocytes per second. However, infection or tissue damage induces pro-inflammatory cytokines that skew hematopoiesis toward myeloid effector cell production to combat pathogens and promote tissue repair. This shift comes at the expense of erythropoiesis, as pro-inflammatory signaling suppresses steady-state erythroid differentiation and may lead to Anemia of Inflammation (AI). To maintain erythropoietic homeostasis under these conditions, a compensatory pathway known as stress erythropoiesis is activated. In contrast to steady-state erythropoiesis, stress erythropoiesis is driven by inflammatory signals and supports the expansion of a self-renewing population of stress erythroid progenitors (SEPs). These progenitors, characterized by surface expression of c-Kit, Sca1, CD34, and CD133, arise from short-term hematopoietic stem cells (ST-HSCs) and are phenotypically and functionally distinct from steady-state erythroid precursors. To investigate the role of inflammasome signaling in the context of AI, we assessed the contribution of the innate immune effectors AIM2 and NLRP3 to SEP regulation. Loss of NLRP3 function had no detectable effect on SEP proliferation; however, loss of AIM2 function resulted in impaired proliferation of immature SEPs. AIM2 is activated by cytoplasmic double-stranded DNA and promotes a pro-inflammatory environment via Caspase-1–dependent cleavage and maturation of pro-inflammatory cytokines IL-1β and IL-18. In vitro, deletion of the IL-1β receptor (IL-1R) or AIM2, as well as neutralization of IL-18 in murine cultures, significantly reduced proliferation of immature SEPs (c-Kit⁺Sca1⁺CD34⁺CD133⁺ and c-Kit⁺Sca1⁺CD34⁻CD133⁺) and decreased BFU-E output. Conversely, exogenous IL-1β or IL-18 supplementation enhanced the proliferation of these early progenitors. These effects were distinct from our previous observations that pro-inflammatory signals -TNFα or nitric oxide(NO) signaling predominantly influence later-stage SEPs (CD34⁻CD133⁻c-Kit⁺Sca1⁺). In vivo, administration of heat-killed Brucella abortus (HKBA) to induce sterile inflammatory anemia in mice led to increased expression of AIM2, cleaved Caspase-1, IL-1β, and IL-18 during the early phase of erythroid recovery. AIM2-deficient mice exhibited a significant reduction in red blood cell output by day 10 post-injection, accompanied by a marked decrease in splenic immature SEP populations. Collectively, these findings identify the AIM2–Caspase-1–IL-1β/IL-18 signaling axis as a critical regulator of early SEP expansion during inflammation. As stress erythropoiesis is essential for maintaining red blood cell production when steady-state erythropoiesis is suppressed, disruption of this pathway impairs erythroid recovery in Anemia of Inflammation. Understanding this mechanism provides key insights into immune–erythroid crosstalk and its relevance to chronic inflammatory anemia.