# Epigenetic Regulation of Osteoclastogenic Gene Expression: Factors, Targets, and Mechanisms

> **NIH NIH R01** · UNIVERSITY OF SOUTHERN CALIFORNIA · 2024 · $352,110

## Abstract

PROJECT SUMMARY
Osteoclasts are multinucleated bone-resorbing cells and formed by the fusion of mononuclear precursor cells
of the monocyte-macrophage lineage. Osteoclasts play a crucial role in the maintenance of bone remodeling
and regeneration. A group of genes regulating osteoclast differentiation have been identified, and the
deregulated expression of these genes has been documented to cause various skeletal diseases. Given the
fact that all genes encoding osteoclastogenic factors are expressed in the context of chromatin, a fundamental
mechanism underlying osteoclast differentiation should involve chromatin regulatory pathways. Studies of
transcription regulation mechanisms by chromatin reorganization may thus aid in the understanding and
treatment of bone disorders caused by abnormal gene expression. MMP-9 is a member of MMP family that
has been studied mainly with respect to its role in extracellular matrix remodeling. Unexpectedly, our recent
studies have revealed that MMP-9 moves into the nucleus and mediates histone H3 N-terminal tail (NT)
proteolysis at osteoclastogenic genes in RANKL-induced osteoclast precursor (OCP) cells. Furthermore, we
found that p300/CBP-mediated H3K18 acetylation stimulates MMP-9 enzymatic activity toward H3NT in OCP-
induced cells. More recent work from our laboratory also demonstrated that MMP-9 binds target nucleosomes
in a manner dependent upon G9a-mediated H3K27me1 and that this binding is critical for MMP-9 recruitment
and H3NT proteolysis at osteoclastogenic genes. In light of these findings, we have generated cell-permeable
H3NTK27me1 mimics as a cellular tool to define H3NT residues important for MMP-9 recruitment and function.
The long-term goal of the proposed research is to understand the biological processes that are controlled by
H3NT proteolysis and the molecular basis of its action as an essential mediator of osteoclastogenesis. The
overall objectives are to investigate MMP-9-dependent H3NT proteolysis as an osteoclastogenic signal, and to
determine the molecular mechanisms whereby H3NT proteolysis activates the genes encoding master
regulators of osteoclastogenesis. Our hypothesis is that MMP-9 establishes and maintains the active state of
osteoclastogenic genes by a two-step mechanism wherein it gets to target genes by sensing local H3K27me1
states and cleaving H3NT in a K18ac-dependent manner. In Aim 1, we will employ the CRISPR-Cas9 system
in which we can manipulate H3NT proteolysis at specific loci, and identify the genes that are directly activated
by MMP-9-dependent H3NT proteolysis and necessary for proficient osteoclast differentiation. In Aim 2, we will
use combined functional and structural approaches, and investigate the role of G9a-mediated H3K27me1 in
the recruitment and osteoclastogenic function of MMP-9 at target genes. In Aim 3, we will examine a possible
involvement of MMP-9-dependent H3NT proteolysis in disrupting nucleosome/chromatin structure, and
generate a mechanistic pic...

## Key facts

- **NIH application ID:** 10754262
- **Project number:** 5R01AR073233-05
- **Recipient organization:** UNIVERSITY OF SOUTHERN CALIFORNIA
- **Principal Investigator:** WOOJIN AN
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $352,110
- **Award type:** 5
- **Project period:** 2019-08-01 → 2025-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10754262

## Citation

> US National Institutes of Health, RePORTER application 10754262, Epigenetic Regulation of Osteoclastogenic Gene Expression: Factors, Targets, and Mechanisms (5R01AR073233-05). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10754262. Licensed CC0.

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