Multimodal imaging reveals structural and functional heterogeneity in different bone marrow compartments: functional...

Area of Science:

• Hematology
• Stem Cell Biology
• Microscopy

Background:

• Intravital microscopy of the calvarium offers noninvasive high-resolution imaging of bone marrow (BM) and hematopoietic stem cell (HSC) niches.
• The representativeness of the calvarium for all BM compartments remains uncertain.

Purpose of the Study:

• To compare HSCs and their niches across calvaria, epiphyses, and diaphyses using advanced imaging techniques.
• To investigate the heterogeneity of BM compartments regarding bone remodeling, blood volume, and hypoxia.

Main Methods:

• Utilized whole-body optical imaging, intravital microscopy, and in vivo fluorescence trapping.
• Analyzed hematopoietic stem cells (HSCs) and their niches in different bone marrow compartments.
• Assessed bone remodeling activity (BRA), blood volume fraction (BVF), and hypoxia.

Main Results:

• Demonstrated significant heterogeneity in BRA and BVF across BM compartments.
• Observed preferential seeding and engraftment of HSCs in compartments with high BVF and BRA post-transplantation.
• Found homogeneous HSC distribution at steady state, independent of BVF and BRA, suggesting distinct niche types.

Conclusions:

• The calvarium contains both homeostatic and reconstituting HSC niches, indicating endochondral ossification is not essential for adult niche formation.
• Identified distinct 'reconstituting niches' separate from 'homeostatic niches' based on HSC distribution patterns.
• Highlighted the heterogeneity of bone marrow niches and its implications for HSC transplantation and biology.