Clonal hematopoiesis, a condition in which individual hematopoietic stem cell clones generate a disproportionate fraction of blood leukocytes, correlates with higher risk for cardiovascular disease. ...The mechanisms behind this association are incompletely understood. Here, we show that hematopoietic stem cell division rates are increased in mice and humans with atherosclerosis. Mathematical analysis demonstrates that increased stem cell proliferation expedites somatic evolution and expansion of clones with driver mutations. The experimentally determined division rate elevation in atherosclerosis patients is sufficient to produce a 3.5-fold increased risk of clonal hematopoiesis by age 70. We confirm the accuracy of our theoretical framework in mouse models of atherosclerosis and sleep fragmentation by showing that expansion of competitively transplanted Tet2−/− cells is accelerated under conditions of chronically elevated hematopoietic activity. Hence, increased hematopoietic stem cell proliferation is an important factor contributing to the association between cardiovascular disease and clonal hematopoiesis.
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•HSC proliferation is elevated in mice and humans with atherosclerosis•Increased proliferation accelerates somatic evolution and clonal hematopoiesis (CH)•Measured rates imply several-fold increased risk of CH in atherosclerosis patients•Mutant expansion is accelerated in mice with increased HSC proliferation
Heyde et al. propose that clonal hematopoiesis can be a symptom rather than a cause of atherosclerosis, since this disease increases hematopoietic stem cell division, which results in accelerated somatic evolution.
A sedentary lifestyle, chronic inflammation and leukocytosis increase atherosclerosis; however, it remains unclear whether regular physical activity influences leukocyte production. Here we show that ...voluntary running decreases hematopoietic activity in mice. Exercise protects mice and humans with atherosclerosis from chronic leukocytosis but does not compromise emergency hematopoiesis in mice. Mechanistically, exercise diminishes leptin production in adipose tissue, augmenting quiescence-promoting hematopoietic niche factors in leptin-receptor-positive stromal bone marrow cells. Induced deletion of the leptin receptor in Prrx1-creER
; Lepr
mice reveals that leptin's effect on bone marrow niche cells regulates hematopoietic stem and progenitor cell (HSPC) proliferation and leukocyte production, as well as cardiovascular inflammation and outcomes. Whereas running wheel withdrawal quickly reverses leptin levels, the impact of exercise on leukocyte production and on the HSPC epigenome and transcriptome persists for several weeks. Together, these data show that physical activity alters HSPCs via modulation of their niche, reducing hematopoietic output of inflammatory leukocytes.
Sleep is integral to life
. Although insufficient or disrupted sleep increases the risk of multiple pathological conditions, including cardiovascular disease
, we know little about the cellular and ...molecular mechanisms by which sleep maintains cardiovascular health. Here we report that sleep regulates haematopoiesis and protects against atherosclerosis in mice. We show that mice subjected to sleep fragmentation produce more Ly-6C
monocytes, develop larger atherosclerotic lesions and produce less hypocretin-a stimulatory and wake-promoting neuropeptide-in the lateral hypothalamus. Hypocretin controls myelopoiesis by restricting the production of CSF1 by hypocretin-receptor-expressing pre-neutrophils in the bone marrow. Whereas hypocretin-null and haematopoietic hypocretin-receptor-null mice develop monocytosis and accelerated atherosclerosis, sleep-fragmented mice with either haematopoietic CSF1 deficiency or hypocretin supplementation have reduced numbers of circulating monocytes and smaller atherosclerotic lesions. Together, these results identify a neuro-immune axis that links sleep to haematopoiesis and atherosclerosis.
Myeloid cell heterogeneity is known, but whether it is cell-intrinsic or environmentally-directed remains unclear. Here, an inducible/reversible system pausing myeloid differentiation allowed the ...definition of clone-specific functions that clustered monocytes into subsets with distinctive molecular features. These subsets were orthogonal to the classical/nonclassical categorization and had inherent, restricted characteristics that did not shift under homeostasis, after irradiation, or with infectious stress. Rather, their functional fate was constrained by chromatin accessibility established at or before the granulocyte-monocyte or monocyte-dendritic progenitor level. Subsets of primary monocytes had differential ability to control distinct infectious agents in vivo. Therefore, monocytes are a heterogeneous population of functionally restricted subtypes defined by the epigenome of their progenitors that are differentially selected by physiologic challenges with limited plasticity to transition from one subset to another.
Myeloid cells are the most evolutionarily ancient aspect of a specialized immune system and the cornerstone of innate immunity in vertebrates. Innate immunity serves at the front line of host defense ...playing essential roles in directly clearing infection while also activating adaptive immune cell populations. Even with the importance in its roles, the myeloid system has often been regarded as the ‘dumb brute’ side of cell-based immunity with limited specificity and variability of responses. Heterogeneity in innate immune cells is increasingly recognized but still modest compared to other cell types and constrained by limited investigative tools.
Monocytes have traditionally been categorized into two subsets: classical and non-classical. Classical monocytes are thought to readily convert to non-classical monocytes with exogenous cues. Studies on bulk monocyte populations have shown that monocytes acquire functional features dependent on physiological needs supporting a prevailing model that monocytes are highly plastic.
We adapted a system for inducible clonal expansion of mouse granulocyte-monocyte progenitor (GMP) capable of differentiating into mature myeloid cells to address at a clonal level the issues of monocyte heterogeneity, plasticity, and whether changes in monocyte functional groups are due to induction or selection, Using inducible HoxB8-ER, large numbers of primary self-renewing GMP can undergo progressive maturation to fully functional granulocytes or monocytes upon removal of estrogen. The resulting GMP clones could then be characterized molecularly and immunophenotypically in correlation with the specialized functions of their descendent monocytes (Figure 1A). Four GMP differentiation trajectories that yield functionally distinct monocytes were defined (Figures 1B and 1C). Notably the functional monocyte groups were evident at the GMP level based on unsupervised clustering of chromatin configuration data (Figure 1D). GMP bore epigenetic scripting of the potential of their descendent monocytes and this fate had little flexibility once differentiation had begun. Testing cells under in vitro and in vivo homeostasis and stress conditions revealed that the cells maintain their differentiation path and do not transition from one state to another (Figures 1E and 1F). These data imply a model whereby monocyte stimulus-specific selection may occur and may contribute to an innate immune memory that resembles adaptive immune memory.
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Sykes: Keros Therapeutics: Consultancy; SAFI Biosolutions: Consultancy, Current equity holder in publicly-traded company; Clear Creek Bio: Current equity holder in publicly-traded company. Scadden: Magenta Therapeutics: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Clear Creek Bio: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; LifeVaultBio: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Editas Medicines: Membership on an entity's Board of Directors or advisory committees; Fate Therapeutics: Current holder of individual stocks in a privately-held company; Clear Creek Bio: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Dainippon Sumitomo Pharma: Other: Sponsored research; FOG Pharma:: Consultancy; Garuda Therapeutics: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; VCanBio: Consultancy; Inzen Therapeutics: Membership on an entity's Board of Directors or advisory committees.
The myeloid system has often been regarded as the ‘dumb brute’ side of cell-based immunity with limited specificity and variability of responses. Heterogeneity in innate immune cells is ...increasingly-recognized but still modest compared to other cell types and constrained by limited investigative tools. Here, we show that myeloid cells have inherent, restricted capabilities that can be defined and potentially exploited for the development of myeloid cell-based therapies.
To study myeloid heterogeneity in vitro, we adapted a system for inducible clonal expansion of primary mouse granulocyte-monocyte progenitors (GMP) capable of differentiating into mature myeloid cells (Sykes et al., Cell, 2016). This system allows for the generation of large numbers of primary self-renewing GMP that can undergo progressive maturation to fully functional granulocytes or monocytes upon removal of an inducing agent (Fig. 1A).
By isolating individual self-renewing GMP, clone-specific behaviors and genetic characterization can be tested and repeatedly evaluated. We isolated individual GMP that were capable of maturing into monocytes in vitro and tested whether their functional features were distinctive and reproducible on a clonal level. Functional capabilities that were quantitated include: 1. phagocytosis, 2. bacterial killing, 3. reactive oxygen species generation, 4. TNF-alpha production, 5. proliferation, and 6. cell surface marker production.
Unsupervised clustering of clone-specific monocytic cells defined four different functional groups with distinctive gene expression programs (Fig. 1B). Surprisingly, this clustering is evident in chromatin accessibility at the GMP level without apparent transcriptomic alterations (Figs. 1C, D). Subgroups of monocytes injected into recipient mice, differentially trafficked to and resided in tissues such as bone marrow, spleen, and peritoneum. Furthermore, clones competent in phagocytizing E.coli (gram-negative) versus S.aureus (gram-positive) in vitro demonstrated differential functional ability to reduce peritoneal bacteria burden when adoptively transferred into animals with induced peritonitis.
Molecular characterization of the functional subgroups defined novel subset-specific cell surface protein expression signatures. Antibody combinations reflecting each of these subgroups were applied to primary blood monocytes and enabled prospective isolation of endogenous cells representing each subset. Upon isolation, the mouse primary subset had specialized functional capabilities in vitro and in vivo comparable to the characteristics defined from the in vitro GMP system. Further, human monocyte populations in the blood could be isolated based on the parameters derived from our model and confirmed to have distinctive functional attributes.
These data strongly suggest that diversity among monocytic subsets exists at baseline rather than monocytes transitioning between cellular states in response to particular stimuli. The subset-specific features appear to be established and epigenetically constrained by the time cells have achieved the level of GMP. By defining monocytic subsets with distinctive roles in disease settings, targeting or adoptively transferring them may be of therapeutic benefit.
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Sykes:Clear Creek Bio: Equity Ownership, Other: Co-Founder. Scadden:Clear Creek Bio: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Fog Pharma: Consultancy; Red Oak Medicines: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; LifeVaultBio: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Bone Therapeutics: Consultancy; Novartis: Other: Sponsored research; Editas Medicine: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Fate Therapeutics: Consultancy, Equity Ownership; Agios Pharmaceuticals: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Magenta Therapeutics: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.
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