Inactivation of Hes1 in Skeletal Undifferentiated Cells Increases Bone Volume

Area of Science:

• Bone Biology
• Cell Biology
• Genetics

Background:

• Leptin receptor-positive (LepR+) cells are multipotent stromal cells crucial for bone formation and fat storage.
• Notch signaling inactivation in LepR+ cells boosts bone mass, but the specific gene target remained unknown.
• Hes1 is a predominant Notch target gene in LepR+ cells, making it a candidate for mediating these effects.

Purpose of the Study:

• To investigate the role of Hes1 deletion in LepR+ cells on bone mass and cellular differentiation.
• To determine if Hes1 inactivation influences osteogenesis and adipogenesis in bone marrow stromal cells.
• To identify the molecular mechanisms underlying Hes1's effect on bone metabolism.

Main Methods:

• Generated LepR-Cre;Hes1Δ/Δ mice to specifically delete Hes1 in LepR+ cells.
• Analyzed bone mass, structure, and cellularity using micro-CT and bone histomorphometry.
• Assessed osteogenesis and adipogenesis in bone marrow stromal cell cultures.
• Utilized single-cell RNA sequencing to analyze cellular composition and gene expression in femurs.

Main Results:

• LepR-Cre;Hes1Δ/Δ mice showed increased femoral bone volume due to higher trabecular number, with no changes in vertebral or cortical bone.
• Histomorphometry revealed decreased osteoclast number and eroded surface, and reduced osteoblast number in males, without affecting bone formation.
• Hes1 deletion did not alter osteogenesis or adipogenesis in vitro, but suppressed RANKL expression in osteogenic cultures.

Conclusions:

• Hes1 inactivation in LepR+ cells increases bone mass by reducing RANKL, osteoclast number, and bone resorption.
• Hes1 plays a limited role in osteogenesis and adipogenesis within bone marrow stromal cells.
• This study highlights Hes1 as a critical regulator of bone resorption in LepR+ cells.