The mesenchymal stem cells are precursor cells found in marrow
that make bone and cartilage.
The prospect of regenerating bone lost to cancer or trauma is a step
closer to the clinic as University of Wisconsin-Madison scientists have
identified two proteins found in bone marrow as key regulators of the
master cells responsible for making new bone.
‘Exposing mesenchymal stem cells to a combination of lipocalin-2 and prolactin in culture reduces and slows senescence, the natural process that robs cells of their power to divide and grow.’
In a study published online in the journal Stem Cell Reports
a team of UW-Madison scientists reports that the proteins govern the
activity of mesenchymal stem cells. The discovery opens the door to devising
implants seeded with cells that can replace bone tissue lost to disease
"These are pretty interesting molecules," explains Wan-Ju Li, a
UW-Madison professor of orthopedics and biomedical engineering, of the
bone marrow proteins lipocalin-2 and prolactin. "We found that they are
critical in regulating the fate of mesenchymal stem cells."
Li and Tsung-Lin Tsai, a UW-Madison postdoctoral researcher, scoured
donated human bone marrow using high-throughput protein arrays to
identify proteins of interest and then determined the activity of
mesenchymal stem cells exposed to the proteins in culture. A goal of the
study, says Li, is to better understand the bone marrow niche where
mesenchymal stem cells reside in the body so that researchers can
improve culture conditions for growing the cells in the lab and for
The Wisconsin researchers found that exposing mesenchymal stem cells
to a combination of lipocalin-2 and prolactin in culture reduces and
slows senescence, the natural process that robs cells of their power to
divide and grow. Li says keeping the cells happy and primed outside the
body, but reining in their power to grow and make bone tissue until
after they are implanted in a patient, is key.
The ability to precisely manipulate mesenchymal stem cells in the
laboratory dish and keep them poised to divide and form bone on cue
helps pave the way for using cell-bearing three-dimensional matrices to
reconstruct large swaths of bone lost to tumors or major trauma. Because
bone has some natural healing properties, things like breaks and
fractures can often mend themselves. But when large pieces of bone are
lost, clinical intervention is required.
"We're seeking better treatments for bone repair," says Li, who is affiliated with the UW School of Medicine and Public Health.
To engineer the growth of new bone in the body through regenerative
medicine first requires generating large amounts of good quality cells
in the lab, notes Li. In the body stem cells are rare. But if cell
growth, differentiation and quality can be controlled in the lab dish,
it may be possible to create stocks of cells for therapeutic
applications and prime them for bone regeneration once implanted in a
The Wisconsin team successfully tested human cells treated with
lipocalin-2 and prolactin to regrow bone by implanting them in mice with
a calvarial defect, where part of the skullcap has been surgically
removed to model critical-sized bone loss.
The human marrow used in the new Wisconsin study was donated by
patients undergoing hip replacement surgery. Thus, a caveat to the study
is that the protein factors identified by Li and his colleague came
from donors with osteoarthritis. However, Li expressed confidence that
the factors from the marrow used in the study would be similar or
identical to what occurs in a healthy patient.
The new study, says Li, demonstrates a key improvement to the lab
culture environment, which seeks to mimic the bone marrow niche where
mesenchymal stem cells are found in the body.