Mavs mediates inflammatory memory in hematopoietic stem cells and promotes ineffective hematopoiesis Free

Chronic inflammatory stress is a key characteristic of bone marrow failure syndromes (BMFS) and myelodysplastic syndromes (MDS), but we do not fully understand how hematopoietic stem cells (HSCs) respond to and are affected by this ongoing stress. HSCs can show immunological memory after short-term exposure to inflammation. This leads to lasting changes in their transcription, metabolism, and function. However, the molecular basis of this memory and its role in MDS pathogenesis remain poorly defined. Here, we identify mitochondrial antiviral signaling protein (MAVS) as a critical mediator of dsRNA-induced HSC immune memory and inflammation-driven hematopoietic dysfunction.

Using repeated polyinosinic-polycytidylic acid (polyIC) exposure as a dsRNA mimetic, we show that HSCs undergo persistent transcriptional and epigenetic remodeling marked by increased expression and accessibility of immune and mitochondrial genes. ATAC-seq of polyIC-treated LSK cells revealed long-lasting chromatin changes with open region for CTCF, IRF1, and PU.1 binding motifs, closed regions for RUNX1, ERG, ETS binding motifs. RNA-seq identified sustained upregulation of innate immune effectors (CD74, S100a8/9) and mitochondrial regulators. We performed single-cell RNA-seq analysis of the LSK-SLAM pool. We identified 6 clusters, comprised of 3 clusters expressing HSC markers, one expressing multipotent progenitor markers, and 2 expressing cell cycle genes with megakaryocyte priming, consistent with LSK-SLAM heterogeneity. Interestingly, polyIC challenges expanded one HSC cluster marked by expression of immune genes (CD81, CD24a, Nr4a1, Cebpb), AP1 complex genes (Fos, Jun, Junb), as well as metabolic genes (OXPHOS, TCA, mTOR), at the expanse of other HSC-enriched clusters. This inflammatory signature is similar to what is found following LPS or mycobacterial challenges and consistent with immune memory. Immune memory involves metabolic reprograming. Mitochondria serve as platform of innate immune signaling, activating the inflammasome and the dsRNA sensing adaptor mitochondrial antiviral signaling protein (MAVS) to trigger immune responses. Confocal microscopy demonstrated persistent MAVS aggregation on mitochondria and elevated mitochondrial content in polyIC-challenged murine HSCs, months after transient polyIC challenge. Remarkably, MAVS-deficiency prevented expansion of HSC clones with immune memory in response to polyIC challenges. MAVS–/– mice resisted polyIC-induced HSC functional decline, and retained superior HSC engraftment capacity in serial competitive repopulation assay. Finally, MAVS-deficiency prevented the sustained activation of caspase-1 in HSCs that persisted in WT HSC months after polyIC challenge, linking MAVS to the inflammasome in polyIC-induced HSC dysfunction. Hence, HSC immune memory is mediated by MAVS.

To probe MAVS's pathogenic potential, we utilized an inducible model of active TGF-β1 overexpression (TgCre+) that phenocopies key features of high-risk MDS upon inflammatory stimulation. PolyIC-treated TgCre+;MAVS+/+ mice developed cytopenias, myeloid dysplasia, increased HSC frequencies, elevated mitochondrial membrane potential, and persistent MAVS aggregation with increased caspase-1 activity. MAVS deletion (TgCre+;MAVS–/–) reversed cytopenias, normalized stem/progenitor ratios, and prevented dysplastic features, establishing MAVS as a central node connecting inflammation, mitochondrial stress, and ineffective hematopoiesis. These observations were extended to human MDS. CD34+CD38- cells from high-risk MDS patients showed elevated phospho-SMAD2, mitochondrial aggregation, sustained MAVS clustering, and caspase-1 activation, similar to murine data.

Together, these findings indicate that repeated exposure to dsRNA elicits MAVS-dependent immune memory in HSCs, and causes HSC functional decline with expansion of a subset of inflammatory HSCs. MAVS-deficiency not only preserves HSC integrity following inflammatory stress but also reverses MDS-like features in vivo. Our findings establish MAVS as a critical molecular link between inflammation and hematopoietic failure and suggest mitochondrial associated immune signaling may be a promising therapeutic target in inflammation-driven MDS and related disorders.