# Cxcl12-Hedgehog signaling in cranial bone regeneration

> **NIH NIH R01** · HARVARD MEDICAL SCHOOL · 2024 · $584,827

## Abstract

Abstract:
How skeletal stem cells are activated to expand, migrate to the injury site, and become osteoblast cells to
restore damaged bone are central questions in skeletal regeneration, which is key for the maintenance of a
functional skeletal system. Craniofacial bones mainly form through intramembranous ossification with limited
bone marrow space and skeletal stem cells that reside in the suture, a special fibrous joint that connects
calvarial bones of the skull together, have been identified as a major cell population that are required for
craniofacial bone homeostasis and injury repair. Numerous studies in both human and mice have highlighted
the importance of stem cell niche, a microenvironment where stem cells reside and also regulate stem cell
behaviors. As the craniofacial skeleton encases the brain and protects it, calvarial bone defects in the skull, if
failed to heal with bony tissue and consequently fibrous non-unions occur, are associated with high morbidity
and mortality. Therefore, reconstruction and regeneration of calvarial defects, in particular critical-size defects,
continuously poses as an unmet therapeutic challenge. The G protein stimulatory α-subunit (Gas), encoded by
GNAS gene, transduces signals from G protein coupled receptors (GPCRs) and has emerged as a critical
regulator of osteoblast differentiation by inhibiting Hedgehog (Hh) signaling. Studies in both mouse models
and human genetic diseases supports the critical roles of both Gas and Hh signaling in regulating skeletal stem
cells in multiple contexts. Having showed that activation of Hh signaling by loss of Gas is a common pathway
that critically regulates intramembranous ossification in calvarial bone formation as in heterotopic ossification
(HO), we have also made novel findings in unpublished preliminary studies in an calvarial bone injury model
that directed suture stem cells (SuSCs) migration to the injury site correlates with upregulated expression of
chemokine (C-X-C motif) ligand 12 (Cxcl12) and Sonic Hedgehog (Shh), to a less extent Indian Hedgehog
(Ihh), in SuSC niche. Further, inhibition of the Cxcl12 cognate receptor Cxcr4, which is coupled to Gai that
counteracts Gas signaling, severely impaired calvarial bone regeneration. Loss of Gas enhanced Shh
expression, which induced osteoblast differentiation. We therefore hypothesize that Cxcl12 and Shh are critical
niche factors that are induced by calvarial injury and coordinately promote SuSC migration, expansion and
osteoblast differentiation, all of which are essential for calvarial bone injury repair. This hypothesis will be
tested in three specific aims: 1) To better define SuSCs and determine the roles of Cxcl12 and Gai/Gas
signaling in directing SuSC migration to the injury site during calvarial bone regeneration; 2) To determine the
roles of Gai/Gas and Shh signaling in SuSC expansion and osteoblast differentiation during calvarial bone
regeneration; 3) To determine the interaction of Cxcl12 and Sh...

## Key facts

- **NIH application ID:** 10883658
- **Project number:** 5R01DE025866-08
- **Recipient organization:** HARVARD MEDICAL SCHOOL
- **Principal Investigator:** Yingzi Yang
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $584,827
- **Award type:** 5
- **Project period:** 2016-07-05 → 2027-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10883658

## Citation

> US National Institutes of Health, RePORTER application 10883658, Cxcl12-Hedgehog signaling in cranial bone regeneration (5R01DE025866-08). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10883658. Licensed CC0.

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