# PTH actions on early cells of the osteoblast lineage

> **NIH NIH P01** · MASSACHUSETTS GENERAL HOSPITAL · 2021 · $408,539

## Abstract

Parathyroid hormone (PTH), whether administered intermittently to treat osteoporosis, or administered 
continuously in rodent experiments, increases bone formation rate. While osteoblasts, osteocytes, and bone 
lining cells contribute to the PTH response, the role of osteoblast precursors in the PTH response is poorly 
understood. We have used expression of Sox9, a gene expressed in many stem cell types, to mark early cells 
in the osteoblast lineage and to understand how PTH affects these cells. In Aim 1, we will determine the 
signaling pathways inside osteoblast precursors that are activated downstream from the PTH receptor in order 
to increase the number of these precursors. Because Gs, the heterotrimeric G protein, is an important 
signaling relay downstream of the PTH receptor in mature osteoblasts and osteocytes, we will knockout Gsa in 
Sox9-expressing osteoblast precursors and their descendants. Because mice with a mutant PTH receptor (so- 
called DSEL receptor) that cannot activate Gq/11 have abnormal bone, we will determine whether PTH 
increases the number of osteoblast precursors in DSEL receptor mice in the same way that PTH does in wild 
type mice. Because salt-induced kinases (SIKs) are prominent regulatory targets of PTH signaling in 
osteocytes, we will determine whether inhibition of SIKs is an important strategy downstream of activation of 
Gsa in the PTH-induced increase in the number of osteoblast precursors. In Aim 2, we will address the 
heterogeneity of the early cells of the osteoblast lineage. Osteoblast precursors can be found in the growth 
plate, bone marrow, and periosteum. We will use lineage tracing in Aim 2A to determine whether growth plate 
osteoblast precursors (marked with PTHrPcreERt) become Sox9-expressing cells in the marrow and whether 
Sox9 marked cells become CXCL12-abundant reticular (CAR) cells in the marrow. Further, we have found 
that Sox9-marked cells in the metaphysis, the endosteum and periosteum have strikingly different paths to 
osteogenesis. To determine these paths, and also to compare Sox9-marked paths with those marked by 
growth plate stem cells and marrow CAR cells, we will use single cell RNA sequencing in collaboration with Dr. 
Alexandra-Chloé Villani, a leader in this field in Aim 2B. The characterization of the genetic makeup of 
individual cells will allow us to define the variety of distinct fates of skeletal stem cells and the signaling 
molecules/transcription factors that regulate these cells. In Aim 3, we will use these same methods to 
determine how PTH increases the numbers of cells descended from skeletal precursors and how the cellular 
pathways change when Gs signaling is blocked in these cells. Single cell RNA sequencing will be used to 
determine the mechanisms downstream of the pathways established in Aim 1 that PTH uses to increase the 
numbers of osteoblast precursors. Thus, we will clarify the relationships between the varieties of skeletal stem 
cells and how PTH...

## Key facts

- **NIH application ID:** 10207597
- **Project number:** 5P01DK011794-53
- **Recipient organization:** MASSACHUSETTS GENERAL HOSPITAL
- **Principal Investigator:** HENRY M. KRONENBERG
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $408,539
- **Award type:** 5
- **Project period:** 2020-07-01 → 2024-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10207597

## Citation

> US National Institutes of Health, RePORTER application 10207597, PTH actions on early cells of the osteoblast lineage (5P01DK011794-53). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10207597. Licensed CC0.

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