Inflammatory signals directly instruct PU.1 in HSCs via TNF

Abstract

The molecular mechanisms governing the transition from hematopoietic stem cells (HSCs) to lineage-committed progenitors remain poorly understood. Transcription factors (TFs) are powerful cell intrinsic regulators of differentiation and lineage commitment, while cytokine signaling has been shown to instruct the fate of progenitor cells. However, the direct regulation of differentiation-inducing hematopoietic TFs by cell extrinsic signals remains surprisingly difficult to establish. PU.1 is a master regulator of hematopoiesis and promotes myeloid differentiation. Here we report that tumor necrosis factor (TNF) can directly and rapidly upregulate PU.1 protein in HSCs in vitro and in vivo. We demonstrate that in vivo, niche-derived TNF is the principal PU.1 inducing signal in HSCs and is both sufficient and required to relay signals from inflammatory challenges to HSCs.

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

“…2C-D), reminiscent of our prior findings in cultured SLAM cells (Pietras et al, 2016). PU.1-EYFP levels were also rapidly and significantly increased in HSC LT cultured +IL-1 prior to the first cell division, also consistent with previous observations for IL-1 and TNF (Etzrodt et al, 2019) (Fig. 2E, Fig.…”

Erythropoietin directly remodels the clonal composition of murine hematopoietic multipotent progenitor cells

“…The direct effect of EPO on HSCs we described here could be one of the factors underlying the development of adverse side effects and comorbidities during long-term EPO use in the clinics. The effect of cytokines on HSCs has previously been suggested to consist of selective induction of proliferation in a preexisting lineage-biased HSC subset, and a de novo lineage instruction 45,46,47,48,16 . Our results highlight a more complex picture with changes in HSC differentiation apparent at the single cell level, while masked at the bulk level by compensation and feedback mechanisms.…”

“…It is now established that HSCs are heterogenous in the quantity (lineage-bias) and the type of cells (lineage-restriction) they produce, and myeloid-, lymphoid-, and platelet or platelet/erythroid-biased and restricted HSCs as well as lineage-balanced HSCs have been described 37,38,39,40,41,42,43,44 . Cytokines have been reported to act directly on the lineage production of the heterogenous pool of HSCs through the selective proliferation or survival of pre-existing lineage-biased HSCs 45,46 or through de novo lineage instruction of HSCs 47,48 . In addition indirect effects of cytokines on HSCs have been reported 36 .…”

Pitfalls and requirements in quantifying asymmetric mitotic segregation

“…Continuous quantitative long-term single-cell imaging is one way to address this issue and seems predestined to connect asymmetric inheritance with future daughter cell behaviors. 7,40 This technology has already contributed to answering other longstanding questions [41][42][43][44][45][46][47][48][49][50][51] and has been used to quantify fluorescence reporter expression continuously over time, [52][53][54][55][56][57][58] a prerequisite to demonstrate the functional relevance of asymmetrically inherited factors. Using the here-described protocols to reliably detect mitotic hematopoietic cells in fixed samples and live-cell imaging, we just published that the asymmetric inheritance of the cellular degradative machinery, including lysosomes, autophagosomes, mitophagosomes, and NUMB, can predict the fates of daughter cells.…”