Increased Bone Mass in Female Mice Lacking Mast Cell Chymase

Area of Science:

• Bone Biology and Endocrinology
• Immunology and Cell Biology

Background:

• Chymase, a mast cell-restricted protease, has an under-explored role in bone remodeling.
• Mast cells are present in bone tissue and can influence skeletal homeostasis.

Purpose of the Study:

• To investigate the impact of the chymase Mcpt4 on mouse bone phenotype and homeostasis.
• To explore the relationship between chymase activity, mast cell degranulation, and bone formation.

Main Methods:

• Comparative analysis of bone phenotype in Mcpt4 knockout (Mcpt4-/-) mice and wild-type controls.
• Assessment of bone mineral density, cross-sectional area, and bone formation rates.
• Gene expression analysis and evaluation of osteoclast activity.
• Histological examination of mast cell distribution and degranulation in bone tissue.

Main Results:

• Mcpt4-/- female mice exhibited significantly larger diaphyseal bone area and increased periosteal bone formation.
• Absence of Mcpt4 led to age-dependent upregulation of bone formation genes but did not affect osteoclast activity.
• Mcpt4-/- bones showed increased cortical porosity and reduced endocortical mineralization, with enhanced mast cell degranulation observed.
• Chymase appears to regulate mast cell degranulation, influencing factors involved in bone remodeling.

Conclusions:

• Mast cell-derived chymase (Mcpt4) plays a regulatory role in normal mouse bone homeostasis.
• Chymase influences bone formation and mast cell degranulation, but not osteoporosis progression.
• Targeting chymase activity may represent a novel strategy for increasing bone volume.