Biology subjects

Mills, T. S.

Publications and source records attributed to Mills, T. S..

3 recordsLinked to original sources

bioRxiv2022

Hematopoietic stem cells are a long-term reservoir for trained immunity in a mouse model of chronic autoimmune disease

Trained immunity (TI) has been speculated to serve as a contributor to autoimmune disease (AD) pathogenesis via generation of hyper-inflammatory myeloid cells. Using a mouse model of systemic lupus erythematosus (SLE), we show that hematopoietic stem cells (HSC) constitute a transplantable, long-term reservoir for macrophages that exhibit features of TI, including increased Mycobacterium avium killing, inflammatory cytokine production, and augmented capacity to co-stimulate naive T cells. Strikingly, hematopoietic progenitor cells derived from these HSC exhibit unique molecular features characterized by reduced chromatin accessibility and transcription of metabolic genes, accompanied by reduced glycolysis and central carbon metabolism. Altogether, our data identify HSC as a functional unit of TI in chronic AD, establish increased T-cell costimulatory activity as a potentially pathogenic feature of TI in this setting, and show that macrophages inherit reduced metabolic activity from AD-exposed HSC, suggesting metabolic activation and TI can be decoupled. Our findings thus implicate HSC as a long-term reservoir for TI that could contribute to AD.

immunology↗

bioRxiv2021

PU.1 expression defines distinct functional activities in the phenotypic HSC compartment in a mouse model of inflammatory stress

The transcription factor PU.1 is a critical regulator of lineage fate in blood-forming hematopoietic stem cells (HSC). In response to inflammatory signals, PU.1 expression is increased in HSC, activating myeloid differentiation genes while repressing cell cycle and protein synthesis genes. To address potential functional heterogeneity arising in the phenotypic HSC compartment due to changes in PU.1 expression, here we fractionated phenotypic HSC using the SLAM code in conjunction with PU.1 expression levels using the PU.1-EYFP reporter mouse strain. While PU.1lo SLAM cells contain extensive long-term repopulating activity and a molecular signature corresponding to HSC activity at steady state, under inflammatory conditions the PU.1lo SLAM fraction is comprised almost entirely of HSC-like cells containing extensive short-term megakaryocytic potential. Our data demonstrate that the phenotypic HSC gate is heterogenous, and that similar PU.1 transcription factor levels can be tied to distinct functional activities under steady-state and inflammatory conditions.

cell biology↗

bioRxiv2020

Transcription factor PU.1 enforces quiescence and limits hematopoietic stem cell expansion during inflammatory stress

Loss of hematopoietic stem cell (HSC) quiescence and resulting clonal expansion are common initiating events in the development of hematological malignancy. Likewise, chronic inflammation related to aging, disease and/or tissue damage is associated with leukemia progression, though its role in oncogenesis is not clearly defined. Here, we show that PU.1-dependent repression of protein synthesis and cell cycle genes in HSC enforces homeostatic protein synthesis levels and HSC quiescence in response to IL-1 stimulation. These genes are constitutively de-repressed in PU.1-deficient HSC, leading to activation of protein synthesis, loss of quiescence and aberrant expansion of HSC. Taken together, our data identify a mechanism whereby HSC regulate their cell cycle activity and pool size in response to chronic inflammatory stress.

immunology↗