Living in a microbial world: The healthy oral microbiome contributes to
jaw bone health by influencing immune cell interactions with bone cells

Date:
February 16, 2022
Source:
Medical University of South Carolina
Summary:
Researchers have shown that commensal microbes in the mouth, in
contrast to commensal microbes colonizing other body surfaces, e.g.,
the gut or skin, modulate immune responses in the jaw bone that
promote bone- resorbing osteoclasts and bone loss. In a preclinical
model, depleting healthy commensal microbes in the mouth, using an
antiseptic oral rinse, was shown to protect against this bone loss.



FULL STORY ==========================================================================
It is becoming increasingly clear that the human microbiome -- the
collection of bacteria, viruses and fungi that live on and within us -- significantly contributes to our health. Indeed, several recent studies
have demonstrated the contribution of the microbiome to regulating immune
cells that influence bone health.


==========================================================================
To find out more, researchers at the Medical University of South Carolina (MUSC) who study osteoimmunology, the interface of the skeletal and
immune systems, have examined the impact of the oral microbiome on
alveolar bone. The alveolar bone, commonly known as the jaw bone, is a
unique bone tissue that houses and supports our teeth. Their results,
published online on Jan. 25 in the Journal of Clinical Investigation
Insight, showed that healthy microbes in the mouth activated a subset
of immune cells within the alveolar bone marrow, which in turn promoted osteoclastic cells that are responsible for breaking down bone. They
went on to show that depleting the healthy oral microbiome, using an
antiseptic mouthwash, protected against this bone loss in preclinical
models, demonstrating a direct link between microbes in the mouth and
naturally occuring alveolar bone loss.

"The alveolar bone is different from other bone tissues due to its
role in supporting the teeth," said Chad M. Novince, D.D.S., Ph.D.,
associate professor in the colleges of Medicine and Dental Medicine,
who studies the impact of the microbiome on osteoimmunology and skeletal metabolism. "What is most fascinating to me is that we were able to show
that the commensal oral microbiota modulates the communication between
immune cells and bone cells, separate from other microbiota communities,
that impact alveolar bone health." "I think this is really only the
start to understanding how the commensal oral microbiome can regulate
alveolar bone health and homeostasis," added Jessica D.

Hathaway-Schrader, Ph.D., a postdoctoral scholar in the College of Dental Medicine and first author on this study.

Previously, the Novince lab utilized mouse models with a defined
microbiota and showed that specific commensal microbes in the gut could influence normal skeletal development and homeostasis. In the current
study, they focused on the oral cavity -- a unique space in which the
microbes colonizing the mouth are in close proximity to the underlying
alveolar bone. Little was known about how interactions between microbes
and immune cells in the oral cavity, compared with other anatomic sites, influence alveolar bone health.

In order to understand the interplay between microbes and immune cells
within the oral cavity more fully, the Novince lab pioneered two new techniques. The first technique involved innovatively collecting bone
marrow from the mandible of mice, which enabled the researchers to
perform in-depth studies on immune cells within alveolar bone. The second technique involved developing a novel way to deplete microbes from the
oral cavity of mice. The team utilized a unique delivery sponge loaded
with chlorhexidine, an antiseptic used to treat gingivitis, to perform
oral rinses on the mice.

With these innovations in hand, the team used the chlorohexidine rinse
to deplete the commensal oral microbiota. Suppressing the commensal
microbial load in the oral cavity, while not altering the commensal
microbiota at other sites, dampened the immune response in the alveolar
bone marrow. This dampened immune response suppressed bone resorbing
osteoclast cells, which had an overall protective effect on alveolar
bone loss that naturally occurs due to the burden of commensal microbes.

Analysis of the bone marrow within the mandibles of mice revealed that a
subset of immune cells were activated by the presence of commensal oral microbes. One important class of activated immune cells were dendritic
cells. These cells act like sentinals of the immune system and alert
other immune cells that microbial invaders are present. The other
important immune cells that were activated by the presence of commensal
oral microbes were CD4+ helper T-cells. These cells help to coordinate
the immune response during an infection. Ultimately, these immune cells supported osteoclasts.

Together, these data suggest a tightly coordinated pathway in which
commensal oral microbes influence alveolar bone health. Furthermore,
reducing the burden of commensal microbes in the mouth through oral
antiseptic rinses prevented alveolar bone loss, which could have important clinical implications moving forward.

"We were able to show that the commensal oral microbiota influences
alveolar bone homeostasis through osteoimmune mechanisms that are
distinct from the systemic microbiome," said Novince. "If we are able
to suppress the healthy oral microbiome to lower levels, it could help
protect from alveolar bone loss, even in a state of health." This report
is the first investigation showing that chlorhexidine reduces naturally occurring alveolar bone loss and suggests that antiseptic oral rinses
could support alveolar bone health and homeostasis. To ensure that this potential treatment is safe and effective, future studies aimed at better describing the interaction between the microbiome, immune cells and bone
is warranted.

"Although we're broadly suppressing oral microorganisms with the
antiseptic rinse, it will be important to determine which specific
microbes are really driving this naturally occurring alveolar bone loss,"
said Hathaway-Schrader.

"The alveolar bone marrow is a unique environment, and this
is the first step in understanding interactions between oral
microbes and immune cells important for promoting bone health." ========================================================================== Story Source: Materials provided by
Medical_University_of_South_Carolina. Original written by Matthew
Greseth. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jessica D. Hathaway-Schrader, Johannes D. Aartun, Nicole
A. Poulides,
Megan B. Kuhn, Blakely E. McCormick, Michael E. Chew, Emily Huang,
Richard P. Darveau, Caroline Westwater, Chad M. Novince. Commensal
oral microbiota induces osteoimmunomodulatory effects separate
from systemic microbiome in mice. JCI Insight, 2022; DOI:
10.1172/jci.insight.140738 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220216121825.htm

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