Abstract The ability of hematopoietic stem cells (HSCs) to return to quiescence after inflammatory activation is critical for long-term stem cell maintenance. While the regulation of HSC quiescence in steady-state conditions is well studied, much less is known about the signals that govern resolution of inflammatory activation. IL-10 is a key anti-inflammatory cytokine that limits excessive immune activation following Toll-like receptor (TLR) signaling. In monocytes, IL-10 acts through a negative feedback loop to suppress pro-inflammatory cytokine production. We asked whether IL-10 signaling plays a similar role in regulating inflammatory responses in HSCs. We exposed mice to acute or chronic TLR4 stimulation with lipopolysaccharide (LPS), with or without IL-10 receptor (IL-10R) blockade, and evaluated HSC proliferation (BrdU, H2B-GFP), transcriptional changes (RNA-seq), polarity (image flow cytometry), and regenerative function (competitive transplantation). After a single dose of LPS, HSCs returned to quiescence by 48 hours. In contrast, IL-10R blockade prolonged HSC cycling, with a significant fraction continuing to proliferate 72 hours post-exposure. RNA-seq of HSCs from mice treated with LPS plus IL-10R blockade showed sustained activation of inflammatory and metabolic pathways (e.g., E2F, mTOR, type I IFN) and downregulation of genes involved in stem cell maintenance. In models of chronic inflammation, H2B-GFP label dilution revealed greater proliferative history in HSCs from mice treated with LPS + IL-10R blockade compared to LPS alone. Combination treated HSCs also exhibited reduced polarity, a feature associated with functional decline. In transplantation assays, bone marrow from LPS + IL-10R-treated mice showed impaired competitive transplantation ability. Given that resistance to inflammatory stress is a hallmark of mutant clones in clonal hematopoiesis and myeloid malignancies, we asked whether IL-10R blockade might create selective pressure favoring inflammation-resistant HSCs. While common mutations such as TET2 and DNMT3A are selected under common inflammatory conditions encountered during aging, we hypothesized that more specific inflammatory contexts, such as defective IL-10R signaling, might favor clones like JAK2V617F. We previously observed defective IL-10R signaling in monocytes from JAK2V617F-positive MPN patients, and notably, this defect was also present in an unaffected identical twin, suggesting a possible inherited predisposition. In Ba/F3 cells, Jak2V617F enhanced IL-10R signaling, supporting cell growth under limiting concentrations of IL-10 and resulted in cytokine independence with long latency after withdrawal of cytokines. In vivo, Jak2V617F knock-in HSCs exhibited elevated baseline proliferation but were resistant to the prolonged cycling triggered by IL-10R blockade. Unlike wild-type cells, Jak2V617F HSCs retained features of quiescence despite inflammatory challenge. In competitive repopulation, IL-10R blockade drove preferential expansion of Jak2V617F-mutant cells, which over time gave rise to a more aggressive MPN phenotype, including accentuated thrombocytosis, splenomegaly, and megakaryocytic hyperplasia. These findings identify IL-10R signaling as a critical regulator of inflammatory resolution in HSCs. Disruption of this pathway prolongs inflammatory activation, accelerates HSC exhaustion, and creates a selective environment that promotes expansion of inflammation-resistant clones such as JAK2V617F. This work suggests that defects in anti-inflammatory signaling pathways may contribute to clonal evolution in early MPN and raises the possibility that enhancing IL-10R signaling could help preserve stem cell function in the setting of chronic inflammation.
Wadley et al. (Mon,) studied this question.