I thought I should write something about a book and an academic paper I read recently on the benefits and evolutionary history of exercise – especially as boosting the immune system has become critical in this new era of the COVID-19 pandemic (NB: I would highly recommend Prof. Lieberman’s book, which is provided in the references section).
Paleoanthropologist* Daniel Lieberman famously wrote that humans were not evolved to exercise – that is, going out running or weightlifting for the sake of ‘keeping healthy’ rather than chasing your prey. We may not be hard-wired to get running but weight-loss and/or maintenance is nevertheless important. Furthermore, a recent study sheds light into the potential additional benefits of exercise.
Scientists at the University of Texas identified a new set of bone marrow cells that are activated during exercise. They carried out a series of experiments and ultimately showed that exercise triggers a cascade of previously unknown biological pathways in these cells which ultimately led to bone formation but also a boosted immune response.
These specialised bone-cell progenitors, cells that differentiate to become bone cells, are different from nearby cells in that they express the proteins leptin receptor and osteolectin. Movements, such as exercise, can activate a protein called Piezo1 in these set of cells which leads to the expression of a signalling molecule called stem cell factor (SCF). This is the mechanism which links exercise to the immune system as SCF also helps to maintain nearby common lymphoid progenitors (CLPs) – cells which can differentiate into cells of the immune system called lymphocytes (more commonly known as white blood cells) that can fight bacterial infections. Increased expression of SCF makes sure that there are more CLPs ready to become white blood cells when needed, ultimately boosting the immune system.
The study was published last week by Bo Shen and colleagues in the prominent science journal Nature. The research findings have attracted a lot of interest in the science world too. The study’s senior author and Director of Children’s Research Institute at University of Texas Southwestern Prof. Sean Morrison wrote on Twitter: “Mechanical loading was thought to promote bone formation by acting on the bone itself – that bone marrow was insulated from movement-induced forces. Bo shows mechanical forces are transmitted deep into the marrow along arterioles, where they promote proliferation by bone-forming cells.”. This thread received a lot of attention in academic social media circles, with many stating that the findings could be “transformative”.
However, one must note that these studies were carried out in mice – which are usually good models for humans due to their high genetic similarity (85% on average) and physiology. However, not all findings in mice apply to humans and therefore it is unclear whether this finding will generalise to humans and/or to other types of exercise other than running (e.g. weightlifting).
If relevant to humans, this finding is likely to have direct clinical applications. For example, increasing the numbers of these newly characterised cells and/or CLPs in the bone marrow would help to provide protection against other disease-causing agents such as bacteria and viruses. It is also possible that the same mechanism can boost vaccination responses.
We currently do not know the answers to these questions. However, it is still a good idea to put on your running shoes and not only strengthen your bones but most likely also boost your immune system in the process – especially if you are an adult as white blood cell production at the bone marrow declines with age.
Footnotes:
* Paleoanthropologists try to understand the early development of anatomically modern humans
References:
- Exercised. Why something we never evolved to do is healthy and rewarding. Daniel Lieberman. 5 January 2021
- Shen et al. A mechanosensitive peri-arteriolar niche for osteogenesis and lymphopoiesis. Nature. 24 February 2021
- Twitter: @SJMorrison_ (URL: https://twitter.com/SJMorrison_/status/1364614665662160898; date accessed: 04/03/21)
- Mehmet Saçma & Hartmut Geige. Exercise generates immune cells in bone. Nature. 24 February 2021
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