Irish scientists have discovered why and how the movement of a baby in the womb is critical to developing strong bones and joints.
A team at Trinity College, working with researchers in India, have shown there are key "molecular interactions" stimulated by movement, which guide cells and tissues of the embryo to build a functionally robust yet flexible skeleton.
"If an embryo doesn't move, a vital signal may be lost or an inappropriate one delivered in error, which can lead to the development of brittle bones or abnormal joints," explained embryologist Prof Paula Murphy, who co-led the research published on Monday.
Cells in the early embryo receive biological signals that direct them to contribute to different types of tissue, and in different places.
Bones need to be made of strong and resilient material to protect and support our bodies, whereas our articulating joints (such as knees and elbows) need to be able to move smoothly.
“As a result, at [the location of] joints, bones need to be covered in smooth, lubricated cartilage. Cells in the early embryo are thus directed to make a decision to either form bone or cartilage, depending on where they are,” Prof Murphy added.
The TCD team has identified how the cells receive the signal that says “make bone” and when they should receive the signal that says “make cartilage” – and both responses are determined by movement. It the culmination of 10 years work on the topic.
Scientists understand many of the signals that direct the cells to build bone, but know a lot less about how the cartilage at the joint is directed, Prof Murphy said.
Joint degeneration
Yet “clinical treatment for joint degeneration is joint replacement, which improves the quality of life for many people but involves invasive surgery and is not a permanent solution”.
“If we understood better how the embryo forms articular cartilage [covering the ends of bones] at the joint, we would be in a better position to come up with ways of regenerating cartilage from stem cells to provide improved treatments for joint injuries and diseases.”
Lack of understanding around how cartilage was directed presented an unfortunate knowledge gap because “there are many painful, debilitating diseases that affect joints – like osteoarthritis – and because we also often injure our joints, which leads to them losing this protective cartilage cover”.
“Our new findings show that in the absence of embryonic movement the cells that should form articular cartilage receive incorrect molecular signals, where one type of signal is lost while another inappropriate signal is activated in its place.”
Prior to this discovery, using chick and mouse embryos where movement could be altered, the scientists had previously shown that when movement is reduced the articular cells at the joint do not form properly, and that in extreme cases the bones can fuse at the joint, but they didn’t know why. They also knew stimulation was good for bone repair.
Now, they have isolated the mechanism underlying healthy development, which has provided new insights into what type of embryo movement is important and the specific signals that are needed to make a healthy joint.
It does not mean that more vigorous movement such as in the form of baby kicking leads to stronger bones and cartilage, Prof Murphy told The Irish Times.
Normal movement
She wanted to reassure mothers and mothers-to-be that a normal amount of movement is all that is needed. The number of skeletal conditions, which arise in a minority of cases, involve “extremely low movement”.
The next steps will see them attempt to activate the correct signals to make stable cartilage that is capable of contributing to a healthy joint. This will involve exposing cells to different combinations of the all-important biological and biophysical signals to find the perfect combination, she said.
Their continued work will also build knowledge around what exact movements are needed, which may help diagnose problems earlier and suggest how clinicians may compensate for natural movements if required. “It could, for example, inform physiotherapeutic regimes that would alleviate resulting problems,” Prof Murphy said.
Their latest findings, details of which are published in the journal Development, is the result of collaboration between her research group at TCD School of Natural Sciences and researchers at the Indian Institute of Technology.
