# Molecular and Cellular Mechanisms of Mutant ASXL1-driven Clonal Hematopoiesis

> **NIH NIH R01** · UNIVERSITY OF WISCONSIN-MADISON · 2024 · $570,922

## Abstract

PROJECT SUMMARY/ABSTRACT
Clonal hematopoiesis of indeterminate potential (CHIP) broadly describes the clonal expansion of blood cells
derived from hematopoietic stem cells (HSCs) with somatic pre-leukemic mutation(s). CHIP is strongly linked to
aging and confers to an increased risk for blood cancers, non-hematological diseases, and all-cause mortality.
ASXL1 is one of the commonly mutated genes in CHIP. ASXL1 mutations are predominantly nonsense or
frameshift mutations. In particular, the hotspot frameshift mutation at codon 646 (corresponding to codon G643
in mice-Asxl1tm) represents a pathological CHIP mutation with high risk to drive myeloid diseases. We recently
discovered that Asxl1tm/+ bone marrow (BM) cells and HSCs underwent significant expansion in old/aged
recipients (20-24 months) but not in young recipients (2-4 months old). This expansion was associated with
alterations in epigenetic landscape. Further characterization of young vs old BM microenvironment (BMM) and
serum revealed local and systemic inflammation and expansion of mesenchymal stromal cells (MSCs) and
endothelial cells (ECs), two important regulatory components of BM niche. MSC expansion was likely due to
enhanced MSC survival, while both accumulation of senescent cells and increased survival attributed to EC
expansion. Consistent with our observation, treatment of ABT-263, a potent inhibitor of anti-apoptotic proteins
Bcl-2 and Bcl-xl, reduced the senescent MSCs in vitro. Moreover, ABT-263 effectively removed accumulated
MSCs, moderately reduced number of ECs, and partially mitigated the expansion of phenotypic HSCs in the old
mice. CITE-Seq analysis of RNA and ~120 immune cell surface proteins at single cell level identified aging-
associated cellular and molecular changes in old BM cells, including expansion of inflammatory neutrophil
subsets and overexpression of IL-1β. These alterations can be mitigated by dietary supplementation of
nicotinamide riboside (NR), a NAD+ precursor. In addition, human myeloid leukemia cells with ASXL1 mutations
were sensitive to GSK525762 (GSK), a pan-BET inhibitor. Based on our preliminary results, we hypothesize that
aged BMM promotes the expansion of Asxl1tm/+ HSCs. Targeting aged BMM and Asxl1tm/+ hematopoietic cells
through NR, ABT263, and/or GSK may prevent and/or inhibit Asxl1tm/+ HSC expansion. In this grant application,
we propose the following aims to test our hypothesis: 1) To investigate how aged BMM interacts with Asxl1tm/+
HSCs to promote their expansion; and 2) To determine whether targeting aged BMM and Asxl1tm/+ hematopoietic
cells alter Asxl1tm/+ HSC expansion in old recipients. Our proposal is in response to the SHINE Program from
NIA (PAS-22-096), aiming to provide new insights into the pathogenesis, prevention, and potential treatment of
nonmalignant hematologic diseases.

## Key facts

- **NIH application ID:** 10881106
- **Project number:** 1R01AG081469-01A1
- **Recipient organization:** UNIVERSITY OF WISCONSIN-MADISON
- **Principal Investigator:** Jing Zhang
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $570,922
- **Award type:** 1
- **Project period:** 2024-09-01 → 2029-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10881106

## Citation

> US National Institutes of Health, RePORTER application 10881106, Molecular and Cellular Mechanisms of Mutant ASXL1-driven Clonal Hematopoiesis (1R01AG081469-01A1). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10881106. Licensed CC0.

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