Enamel Offers Clues to the Body’s Growth Cycles



Circadian rhythms guide the human body’s day-to-day development, but they don’t explain long-term maturation. New York University (NYU) College of Dentistry researchers, however, have found a different biological cycle that could explain our variations in age at maturity and other developmental milestones by looking at tooth enamel.

Through metabolomic analysis of blood plasma, the researchers have linked these variations to a timing mechanism operating on multi-day rhythms in growth and degradation. These findings build upon earlier observations of multi-day biological rhythms in tooth enamel and skeletal bone tissue.

“These rhythms, originating in the hypothalamus, a region of the brain that functions as the main control center for the autonomic nervous system, affect bone, body size, and many metabolic processes, including heart and respiration rates,” said Dr. Timothy Bromage, a professor of biomaterials and basic science and craniofacial biology at NYU.

“The rhythms affect an organism’s overall pace of life and its lifespan,” said Bromage, who is leading the research, “so a rat that grows teeth and bone in a fraction of the time of a human in fact also lives faster and dies at a much younger age.”

The researchers further characterized the rhythms through metabolome and genome analysis of blood plasma from the domestic pig. They found that blood plasma metabolites and RNA drawn from 33 pigs during a 2-week period oscillate on a 5-day rhythm. Microscopic analysis also revealed a corresponding 5-day rhythm in the pigs’ tooth enamel.

The researchers additionally found a pair of 5-day rhythms in tandem. One controls tissue growth, while the other begins 3 days later for degradation of growth-related molecular compounds back to their basic biological entities for use in the next growth round.

“These findings provide new insight into biological processes regulating growth and body size and controlling gestation length, weaning, age at maturity, and other developmental milestones,” said Bromage. “We believe this to be a key component to what regulates species’ life history evolution.”

Next, the researchers will use metabolic profiling to reveal the intricacies of a 4-day growth rhythm observed in the teeth of the rhesus macaque monkey. The final stage of research will examine human beings, who are expected to show 8- to 9-day rhythms, reflecting their larger body size and longer average lifespan.

The study, “The Swine Plasma Metabolome Chronicles ‘Many Days’ Biological Timing an Functions Linked to Growth,” was published by PLOS ONE.

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