# Hox-Regulated MSCs in Skeletal Development, Growth and Fracture Healing

> **NIH NIH R01** · UNIVERSITY OF WISCONSIN-MADISON · 2020 · $303,434

## Abstract

Mesenchymal multi-potent stromal/stem cells (MSCs) have historically been characterized as stromal
progenitors that can differentiate into a variety of cell types including bone, cartilage, muscle and fat. In
recent years, elegant genetic and molecular studies have allowed enrichment of MSCs with higher
progenitor potential. In mice, among the cell surface markers used for enrichment, co-expression of
PDGFR/ CD51 results in high enrichment of stem/progenitor activity. Likewise, LepR-Cre marks a
long-term, self-renewing cell population with the highest progenitor potential compared to other Cres.
During our studies of Hox11 function in the zeugopod skeleton (radius and ulna), we have made the
surprising discovery that Hox11 protein expression is excluded from all differentiated cell types of the
zeugopod, but is found uniquely in cells that co-express PDGFR/CD51 and with cells that retain the
LepR-Cre lineage trace. While not all PDGFR+/CD51+ or LepRCre+ cells are Hox11+, all Hox11+ cells
are PDGFR/+CD51+ and LepRCre+. When comparing the in vitro CFU-F progenitor potential of
PDGFR/+CD51+/Hoxa11eGFP+ cells to the population double-positive for PDGFR/+CD51+, we find
that the PDGFR/+CD51+/Hoxa11eGFP+ cells have three times higher progenitor potential than the
double-positive total population, consistent with enriching for higher progenitor potential. Further, triple-
positive cells can differentiate into cartilage, bone and adipocytes in vitro, further supporting their MSC
potential. Unlike the commonly used markers for MSCs, Hox11 genes also function in these cells. Loss
of Hox11 function eliminates the chondrogenic and osteogenic potential in this regionally restricted set of
MSCs in vitro. Postnatal defects arising in Hox11 compound mutants as well as impaired fracture repair
responses provide in vivo support for a continued role for Hox11 in MCSs throughout the life of the
animal. Importantly, defects are only observed in the zeugopod; other skeletal compartments of Hox11
mutants exhibit normal MSC tri-lineage differentiation in vitro and are able to heal normally after fracture.
In this application, we will use our Hox null mutants and Hoxa11eGFP reporter, in addition to a newly
generated a Hoxa11-CreERT2 and Hoxd11 conditional allele that will allow us to prove in vivo lineage
analyses, self-renewal potential and origin of this population, and dissection of continued function of this
MSC population through skeletal development, postnatal growth, maintenance and repair. We will also
explore preliminary data that shows that ALL endochondral bones maintain differential regional Hox
expression in the bone marrow MSCs and investigate global function for Hox genes in regionally
restricted MSC populations. Interrogation of these questions will directly impact our knowledge of skeletal
development and bone biology, but also have important implications for the isolation and use of MSCs in
tissue engineering and regenerative medicine approaches.

## Key facts

- **NIH application ID:** 9935037
- **Project number:** 5R01AR061402-09
- **Recipient organization:** UNIVERSITY OF WISCONSIN-MADISON
- **Principal Investigator:** Deneen M Wellik
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $303,434
- **Award type:** 5
- **Project period:** 2011-08-01 → 2022-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9935037

## Citation

> US National Institutes of Health, RePORTER application 9935037, Hox-Regulated MSCs in Skeletal Development, Growth and Fracture Healing (5R01AR061402-09). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9935037. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*