Matrix Gla protein maintains normal and malignant hematopoietic progenitor cells by interacting with bone...

Area of Science:

• Hematology
• Stem Cell Biology
• Molecular Biology

Background:

• Matrix Gla protein (MGP) is known to inhibit arterial calcification in a carboxylation-dependent manner.
• The role of MGP, particularly when highly expressed in bone marrow (BM) mesenchymal stem/stromal cells, remains largely unknown.
• Understanding MGP's function in the hematopoietic stem cell niche is crucial for comprehending myelopoiesis.

Purpose of the Study:

• To investigate the role of MGP expressed in bone marrow stromal cells as a niche factor for both normal and malignant myelopoiesis.
• To elucidate the mechanism by which MGP influences hematopoietic progenitor cell growth and maintenance.
• To determine if MGP's biological effects are dependent on its Glu γ-carboxylation status.

Main Methods:

• Coculture of mouse BM hematopoietic cells with mitomycin C-treated BM stromal cells.
• Inhibition of MGP using anti-MGP antibody and BMP signaling using LDN-193189.
• Assessment of cell growth, long-term culture-initiating cells (LTC-ICs), and cobblestone formation.
• Analysis of MGP and bone morphogenetic protein (BMP)-2/4 expression patterns.
• GST-pulldown and luciferase reporter assays to study MGP-BMP interactions.
• Inhibition of vitamin K-dependent Glu γ-carboxylation using warfarin.

Main Results:

• Antibody-mediated MGP blockage significantly reduced hematopoietic cell growth and LTC-IC maintenance.
• MGP blockage also inhibited the growth and cobblestone formation of MB-1 myeloblastoma cells.
• MGP was expressed in mesenchymal cells and aberrantly high in MB-1 cells, but undetectable in normal hematopoietic cells.
• MGP and BMP-4 were co-induced in stromal cells cocultured with hematopoietic or myeloblastoma cells.
• Uncarboxylated MGP interacted with BMP-4, and BMP signaling inhibition affected MB-1 cell growth.
• Warfarin did not affect MB-1 cell growth, indicating MGP's biological effect is independent of carboxylation.

Conclusions:

• MGP functions as a niche factor that supports normal and malignant hematopoietic progenitor cells.
• MGP likely modulates hematopoietic progenitor cell behavior through BMP signaling, independent of its Glu γ-carboxylation.
• Aberrant MGP expression by leukemic cells and selective BMP-4 induction may contribute to a malignant hematopoietic niche.