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Previous studies have shown that hematopoietic stresses—such as myelofibrosis, anemia, and myeloablation—can induce extramedullary hematopoiesis (EMH), in which hematopoietic stem cells (HSCs) are mobilized to sites outside the bone marrow.
The splenic red pulp is known to be a prominent site of EMH in both mice and humans, but not much is known about the EMH niche.
Now, investigators say they have characterized this niche.
They detailed their findings in Nature.
The team used mouse models to examine the expression patterns of 2 known niche cell factors, SCF and CXCL12.
They discovered that the hematopoietic microenvironment in the spleen is found near sinusoidal blood vessels and is created by endothelial cells and perivascular stromal cells, just like the microenvironment in the bone marrow.
“Under emergency conditions, the endothelial cells and perivascular stromal cells that reside in the spleen are induced to proliferate so they can sustain all the new blood-forming stem cells that migrate into the spleen,” explained study author Sean Morrison, PhD, of the University of Texas Southwestern Medical Center, Dallas.
“We determined that this process in the spleen is physiologically important for responding to hematopoietic stress. Without it, the mice we studied could not maintain normal blood cell counts during pregnancy or quickly regenerate blood cell counts after bleeding or chemotherapy.”
The investigators believe these findings could aid the development of therapeutic interventions to enhance blood formation following chemotherapy or HSC transplant and thus accelerate the recovery of blood cell counts. 
Image by John Perry
Previous studies have shown that hematopoietic stresses—such as myelofibrosis, anemia, and myeloablation—can induce extramedullary hematopoiesis (EMH), in which hematopoietic stem cells (HSCs) are mobilized to sites outside the bone marrow.
The splenic red pulp is known to be a prominent site of EMH in both mice and humans, but not much is known about the EMH niche.
Now, investigators say they have characterized this niche.
They detailed their findings in Nature.
The team used mouse models to examine the expression patterns of 2 known niche cell factors, SCF and CXCL12.
They discovered that the hematopoietic microenvironment in the spleen is found near sinusoidal blood vessels and is created by endothelial cells and perivascular stromal cells, just like the microenvironment in the bone marrow.
“Under emergency conditions, the endothelial cells and perivascular stromal cells that reside in the spleen are induced to proliferate so they can sustain all the new blood-forming stem cells that migrate into the spleen,” explained study author Sean Morrison, PhD, of the University of Texas Southwestern Medical Center, Dallas.
“We determined that this process in the spleen is physiologically important for responding to hematopoietic stress. Without it, the mice we studied could not maintain normal blood cell counts during pregnancy or quickly regenerate blood cell counts after bleeding or chemotherapy.”
The investigators believe these findings could aid the development of therapeutic interventions to enhance blood formation following chemotherapy or HSC transplant and thus accelerate the recovery of blood cell counts.
Image by John Perry
Previous studies have shown that hematopoietic stresses—such as myelofibrosis, anemia, and myeloablation—can induce extramedullary hematopoiesis (EMH), in which hematopoietic stem cells (HSCs) are mobilized to sites outside the bone marrow.
The splenic red pulp is known to be a prominent site of EMH in both mice and humans, but not much is known about the EMH niche.
Now, investigators say they have characterized this niche.
They detailed their findings in Nature.
The team used mouse models to examine the expression patterns of 2 known niche cell factors, SCF and CXCL12.
They discovered that the hematopoietic microenvironment in the spleen is found near sinusoidal blood vessels and is created by endothelial cells and perivascular stromal cells, just like the microenvironment in the bone marrow.
“Under emergency conditions, the endothelial cells and perivascular stromal cells that reside in the spleen are induced to proliferate so they can sustain all the new blood-forming stem cells that migrate into the spleen,” explained study author Sean Morrison, PhD, of the University of Texas Southwestern Medical Center, Dallas.
“We determined that this process in the spleen is physiologically important for responding to hematopoietic stress. Without it, the mice we studied could not maintain normal blood cell counts during pregnancy or quickly regenerate blood cell counts after bleeding or chemotherapy.”
The investigators believe these findings could aid the development of therapeutic interventions to enhance blood formation following chemotherapy or HSC transplant and thus accelerate the recovery of blood cell counts.