Mesenchymal progenitor cells in red and yellow bone marrow

Area of Science:

• Hematology
• Stem Cell Biology
• Developmental Biology

Background:

• Red bone marrow (BM) contains hematopoietic and stromal cells supporting hematopoiesis.
• Yellow BM, characterized by lipid-rich mesenchymal cells, replaces red BM in mammals, leading to hematopoietic tissue loss.
• The dynamic interplay between red and yellow BM and their progenitor cells is crucial for maintaining hematopoietic function.

Purpose of the Study:

• To investigate the potential of mesenchymal cell progenitors from red and yellow bone marrow (BM) to regenerate bone and hematopoietic microenvironments.
• To analyze the in vivo behavior of these progenitors after transplantation into normal and hematopoietically deficient recipients.
• To understand the mechanisms underlying the age-related transition from red to yellow BM and its impact on hematopoiesis.

Main Methods:

• Transplantation of mesenchymal cell progenitors from red and yellow BM into normal, irradiated, and aged recipient mice.
• Analysis of the recipients' bone and hematopoietic microenvironment post-transplantation.
• Characterization of mesenchymal stem cells (MSCs) and their differentiation potential in different BM compartments.

Main Results:

• Normal red to yellow BM conversion is linked to a progressive loss of bone and hematopoietic microenvironment-generating MSCs.
• Mesenchymal cells in yellow BM retain the capacity to generate functional hematopoietic microenvironments, particularly under conditions of hematopoietic insufficiency.
• Hematopoietic microenvironment renewal relies on precursor cells, as it cannot self-maintain.
• Evidence suggests the existence of bi-potential stromal precursors capable of forming either bone or both bone and hematopoietic microenvironment.

Conclusions:

• The decline of MSCs contributes to the shift from red to yellow bone marrow and reduced hematopoietic capacity.
• Mesenchymal cells in yellow bone marrow offer a potential source for regenerating hematopoietic tissue in compromised individuals.
• Targeting these mesenchymal progenitors could enable the expansion of hematopoietic territories and improve hematopoiesis in conditions like cytotoxic treatment, irradiation, or aging.