Baylor College of Dentistry
New findings
could revolutionize dogma
on bone formation in the
temporomandibular joint
By Jennifer Eure Fuentes
Findings from researchers at Texas A&M University Baylor College
of Dentistry could prove to upend previous dogma on bone formation in the temporomandibular joint.
The current school of thought on bone formation in the mandibular
condyle, the rounded knob where the mandible and upper jaw
meet, is that cartilage cells — called chondrocytes — must form and
then experience cell death before bone cells can form. Preliminary
findings from the lab of Dr. Jerry Feng, professor in the department
of biomedical sciences, show this may not be the case. Bone marrow cells may not be the only ones that build bone.
“The chondrocytes do not die. They transform into bone,” says
Feng. “This is the most exciting part. That’s a big switch. People in
this field never thought about such a mechanism.”
Feng’s team submitted a proposal to the National Institutes of
Health – National Institute of Dental and Craniofacial Research to
secure more than $1.8 million in grant funding to further evaluate
how this transformation of cartilage into bone takes place.
Cell lineage tracing on a transgenic mouse model lies at the crux of
their hypothesis. In confocal microscopic images, cells tagged with
reporter genes reveal the merging of bone and cartilage proteins
seen in representative shades of red and green, one for each type
of protein. Several published articles, including one in the Journal
of Dental Research in fall 2014, bolster the proposal.
“The idea is that the cell lineage tracing enables you to follow cartilage cells and see where they end up during growth,” says
Dr. Robert Hinton, Regents professor emeritus. “You would expect
the condylar cartilage cells under the normal theory to end up dying
off, but it appears that a number of them are turning into bone cells
or potentially forming the walls of blood vessels.”
If the five-year grant is funded, TAMBCD researchers will further
study the role of a gene known as BMPR1A in mediating Osterix, a
gene vital to bone mineralization. They will do this by separately
removing, or “knocking out” BMPR1A in one control group of models and Osterix in another to gauge the impact on cartilage and
bone formation.
Hinton has worked with Feng on this research and says the potential for transmitting this cutting-edge research to students is tantalizing, as it creates unique research opportunities for students.
“This is stuff that is not in textbooks right now that can be brought
into discussions about how bone is formed from cartilage during
growth,” says Hinton.
Feng works on research with orthodontic residents and biomedical
doctoral students, to whom he also teaches bone biology.
Physiology course instruction for predoctoral students is also a part
of his role at the college.
The research stands to impact the knowledge base regarding how
the temporomandibular joint grows and develops. In turn, this new
information could change approaches to treating malocclusions
and even have an impact on new therapies for injuries to cartilage,
which, unlike bone, cannot repair itself.
“You can’t solve this problem overnight,” says Feng, “but step by step.”
Founded in 1905, Texas A&M University Baylor College of Dentistry in Dallas is
a college of the Texas A&M Health Science Center. TAMBCD is a nationally recognized center for oral health sciences education, research, specialized patient
care and continuing dental education.
Jennifer Eure Fuentes is a communications specialist at Texas A&M Health
Science Center Baylor College of Dentistry. A 2006 graduate of Texas Christian
University, she has worked in the communications and editorial field for five years.
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