# Mechanisms of granulocyte homeostasis

> **NIH NIH R01** · CINCINNATI CHILDRENS HOSP MED CTR · 2020 · $592,095

## Abstract

SUMMARY
Understanding the cellular and molecular processes underlying granulocyte homeostasis is crucial because
producing too few granulocytes results in increased risk for infection (neutropenia), while producing too many
granulocytes can result in severe tissue damage and death (myeloproliferative disorders). To delineate the
molecular mechanisms underlying homeostatic neutrophil production, we previously delineated hierarchical
genomic and regulatory states culminating in neutrophil or macrophage specification. Myeloid cells undergoing
lineage specification traverse successive states of mixed-lineage gene expression dictated by antagonistic
transcriptional programs (HSCP vs. myeloid progenitor, then Irf8 vs. Gfi1) that culminate in generation of
neutrophil or monocyte precursors. Using neutropenia-patient-derived mutations in the GFI1 transcription
factor, we generated mouse models of congenital neutropenia. To delineate the molecular mechanisms
underlying homeostatic neutropenia and innate immune dysfunction in these mice, we first captured normal
cell states encompassing neutrophil specification and commitment, then built a computational approach to
assign neutropenia-model cells to normal cell states and assess cell-state specific variation in gene
expression. Surprisingly, the majority of differentially expressed GFI1-target genes are sequentially altered as
cells traverse successive states. Underscoring these cell state-specific insights, genetic rescue impacts
specification but not innate immunity programmed during commitment. Here, we propose to provide regulatory
insight explaining this finding; defining altered Gfi1-mutant binding and stage-specific open chromatin. Next, we
will determine how neutrophil defense functions are programmed during commitment, and how that fails in
humans and mice with neutropenia. Finally, we will revisit the gene regulatory network underlying homeostatic
neutrophil versus macrophage specification in the context of establishing neutrophil homeostasis through
waves of neonatal gut microbiome colonization. We propose that mouse modeling of mutations identified in
neutropenic patients can be exploited to reveal the essential pathobiology of neutropenia, and to dissect
mechanisms underlying normal innate immune function and the establishment of granulocyte homeostasis.
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## Key facts

- **NIH application ID:** 9973861
- **Project number:** 2R01HL122661-05
- **Recipient organization:** CINCINNATI CHILDRENS HOSP MED CTR
- **Principal Investigator:** H. LEIGHTON GRIMES
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $592,095
- **Award type:** 2
- **Project period:** 2015-07-01 → 2024-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9973861

## Citation

> US National Institutes of Health, RePORTER application 9973861, Mechanisms of granulocyte homeostasis (2R01HL122661-05). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9973861. Licensed CC0.

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