# Regulation and function of hematopoietic stem cell niches

> **NIH NIH R01** · ALBERT EINSTEIN COLLEGE OF MEDICINE · 2020 · $513,214

## Abstract

PROJECT SUMMARY:
The hematopoietic stem cell (HSC) niche is a complex structure thought to play an important role
in regulating HSC function and numbers. Among the niche constituents, MSCs express the
highest levels of the major niche factors. Yet, their ability to maintain HSCs ex vivo has been
limited thus far. MSCs indeed rapidly loose expression of major niche factors in culture. We have
tested the hypothesis that MSCs’ transcriptional machinery was altered in culture conditions and
that reinstating the expression of key transcription regulators would revitalize niche activity. We
have carried out a genetic screen using 28 transcription regulators that were expressed at high
levels in Nestin-GFP+ niche cells in vivo but downregulated in culture, and identified a combination
of 5 genes (Ostf1, Xbp1, Irf3, Irf7 and Klf7) that can revitalize MSCs. Revitalized MSCs (rMSCs)
exhibit higher niche factor expression and capacity to expand either murine or human HSCs
compared to control MSCs. Using RNA-seq and ATAC-seq analyses, we have identified Mef2c
as downstream effector of the revitalization process. This continuation proposal will evaluate the
hypothesis that HSCs are finely regulated by a niche programmed to maintain their numbers. In
Specific Aim 1, we will assess the function of human orthologues of the 5 factors in revitalization
of human MSCs. We will use stable isotope labeling with amino acids in cell culture (SILAC) and
labeling by azidohomoalanine (AHA) to identify by mass spectrometry novel soluble factors
derived from rMSCs. We will test the function of rMSCs in the maturation of embryonic stem (ES)
cell-derived HSCs to promote their engraftment in immunodeficient mice. In Specific Aim 2, we
will evaluate the role of key transcription regulators in HSC niche activity, focusing our studies on
Snai2, Ostf1 and Mef2c using conditional deletions using floxed mouse lines. In Specific Aim 3,
we will assess whether HSC numbers are regulated by local niche availability or systemic sensing
using transplantation, local irradiation, and mathematical modeling. The proposed studies will
shed new light on mechanisms by which HSC numbers are regulated and provide new methods
toward their ex vivo expansion.

## Key facts

- **NIH application ID:** 9869190
- **Project number:** 2R01DK056638-21
- **Recipient organization:** ALBERT EINSTEIN COLLEGE OF MEDICINE
- **Principal Investigator:** Paul S Frenette
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $513,214
- **Award type:** 2
- **Project period:** 2000-03-01 → 2023-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9869190

## Citation

> US National Institutes of Health, RePORTER application 9869190, Regulation and function of hematopoietic stem cell niches (2R01DK056638-21). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9869190. Licensed CC0.

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