How intermittent hypoxia affects jaw cartilage growth

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Sleep Disorders | Sleep Review

Intermittent hypoxia is common in people with sleep disorders such as obstructive sleep apnea. While we know that intermittent hypoxia can cause neurodevelopmental problems, it is not clear how it affects cartilage. Researchers at Tokyo Medical and Dental University (TMDU) have now shown that IH can lead to underdeveloped jaw cartilage in rats.

In an article published in Scientific Reports, TMDU researchers revealed the inhibitory effects of intermittent hypoxia on the growth of cells in the mandibular condylar cartilage, the cartilage at the rounded end of the jawbone. Previous work had mainly focused on how intermittent hypoxia only affects bone growth.

Cartilage in different parts of the body often has different metabolic characteristics. Studies have shown that cartilage in the jaw has different growth patterns and gene expression profiles compared to cartilage in the limbs. Because of this, the TMDU group became interested in how intermittent hypoxia affects both mandibular and tibial cartilage. They compared both areas by examining the growth of cartilage cells called chondrocytes. The researchers also looked at the expression levels of specific genes in the cartilage cells that could help them recognize which stage of growth they were in.

[RELATED: During Hypoxia, High Blood Pressure Limits Protection to Vital Organs]

“It is very important to understand more about the effects of intermittent hypoxia as it can lead to significant developmental problems,” says lead author of the study Kochakorn Lekvijittada in a press release. “It can even precede Sudden Infant Death Syndrome (SIDS) – a terrible and tragic event that sadly affects many families around the world.”

To answer their questions, the researchers used newborn rats as a model system. They exposed one group of 1 week old rats to air with normal amounts of oxygen, while another group of rats was exposed to alternating air cycles with low oxygen levels. The researchers then examined the effects on the rats’ jaw and tibial cartilage growth.

Histological changes in mandibular condylar cartilage from IH rats. (a) Representative images of sagittal sections of the mandibular condyle stained with toluidine blue from the N and IH groups. Thickness of each cartilage layer of the anterior (b), middle (c) and posterior (d) parts of the mandibular condyle. The ratio of each cartilage layer to the total cartilage thickness is given in the fields (e.g.). F fiber layer, P proliferation layer, M maturation layer, H hypertrophic layer. Scale bar = 100 μm. Data are means ± SEM for each group. * P <0.05. CREDIT: DEPARTMENT OF ORTHODONTIC SCIENCE, TMDU

“We observed an inhibited growth of the cartilage in the rat jaw,” says Takashi Ono, lead author and professor, in a press release. “Interestingly, the tibial cartilage was not affected by the hypoxic air exposure.”

The authors also saw decreased expression levels of two genes known as TGF-? and SOX9 in the mandibular cartilage of rats exposed to intermittent hypoxia, while another gene called collagen X showed increased expression.

“The gene expression patterns that we observed in the mandibular cartilage of the rats exposed to hypoxia were consistent with the hypertrophy,” says Lekvijittada. “This indicates that the jaw cartilage was not growing properly. We did not see these patterns in the tibial cartilage. “

The results of this study provide new insights into how exposure to periods of low oxygen levels can affect the growth and development of jaw cartilage with potential uses in orthopedic medicine and the diagnosis of TMJ disease. This work also provides a better understanding of how cartilage differs throughout the body depending on its location.

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