A groundbreaking discovery from the University of Hong Kong (HKUMed) is offering recent hope for individuals at risk of osteoporosis and bone loss, particularly those unable to engage in weight-bearing exercise. Researchers have identified a key protein, Piezo1, that acts as a biological “exercise sensor” within bone marrow, opening the door to potential treatments that mimic the benefits of physical activity. This research, published in the journal Signal Transduction and Targeted Therapy, could revolutionize how we approach bone health for vulnerable populations, including the elderly, those recovering from injury, and individuals with chronic illnesses.
The team’s findings center on understanding how movement strengthens bones at a molecular level. For years, the importance of exercise in maintaining bone density has been well-established, but the precise mechanisms remained elusive. Now, scientists have pinpointed Piezo1 as a crucial component in this process. “We have essentially decoded how the body converts movement into stronger bones,” explained Professor Xu Aimin, Director of the State Key Laboratory of Pharmaceutical Biotechnology and Chair Professor in the Department of Medicine at HKUMed, who led the study. “We have identified the molecular exercise sensor, Piezo1, and the signalling pathways it controls. This gives us a clear target for intervention.”
The Cycle of Bone Loss and the Role of Stem Cells
Osteoporosis, a condition characterized by weakened bones, affects millions worldwide. According to the World Health Organization, approximately one in three women and one in five men over the age of 50 will experience a fracture due to weakened bones. In Hong Kong, the problem is particularly acute, with 45% of women and 13% of men aged 65 and above affected by osteoporosis. These fractures can lead to chronic pain, reduced mobility, and a diminished quality of life, placing a significant burden on healthcare systems.
A key factor in age-related bone loss is the shift in the behavior of mesenchymal stem cells within the bone marrow. These cells have the potential to develop into either bone tissue or fat cells. Healthy bones rely on a balance where stem cells primarily differentiate into bone-building cells. Yet, as we age, this balance shifts, and more stem cells become fat cells. This accumulation of fat crowds out healthy bone tissue, weakening the skeletal structure and creating a cycle of deterioration that is tough to reverse with current treatments.
Piezo1: The Body’s Internal Exercise Detector
Through experiments using both mouse models and human stem cells, the HKUMed team discovered that the Piezo1 protein, located on the surface of mesenchymal stem cells, functions as a mechanical sensor. This protein detects physical forces generated during movement, and exercise. When activated by physical activity, Piezo1 limits the buildup of fat in the bone marrow and promotes the formation of new bone. Conversely, when Piezo1 is absent, stem cells are more likely to become fat cells, accelerating bone loss.
The researchers as well found that the absence of Piezo1 triggers the release of inflammatory signals – specifically Ccl2 and lipocalin-2 – which further encourage stem cells to become fat cells and hinder bone growth. Importantly, blocking these inflammatory signals was shown to facilitate restore healthier bone conditions, suggesting a potential therapeutic avenue.
“Exercise Mimetics” and Future Treatments
The implications of this discovery are far-reaching. Dr. Wang Baile, Research Assistant Professor in the Department of Medicine at HKUMed and co-leader of the study, emphasized the potential for developing “exercise mimetics” – drugs that could chemically activate the Piezo1 pathway, effectively mimicking the benefits of physical activity even in the absence of movement. “This discovery is especially meaningful for older individuals and patients who cannot exercise due to frailty, injury or chronic illness,” Dr. Wang said. “Our findings open the door to developing ‘exercise mimetics’ — drugs that chemically activate the Piezo1 pathway to help maintain bone mass and support independence.”
Professor Eric Honoré, Team Leader at the Institute of Molecular and Cellular Pharmacology, French National Centre for Scientific Research, and a co-leader of the research, added that this approach offers a promising strategy beyond traditional physical therapy. “In the future, we could potentially provide the biological benefits of exercise through targeted treatments, thereby slowing bone loss in vulnerable groups such as the bedridden patients or those with limited mobility, and substantially reducing their risk of fractures.”
The research team is now focused on translating these findings into clinical applications, with the ultimate goal of developing new therapies that preserve bone strength and improve the quality of life for aging individuals and those confined to bed. The collaborative study involved researchers from HKUMed and the French National Centre for Scientific Research (CNRS).
This research was supported by multiple funding sources, including the Areas of Excellence Scheme and the General Research Fund of the Research Grants Council, as well as grants from the Health and Medical Research Fund and the National Key R&. D Program of China.
This discovery represents a significant step forward in our understanding of bone biology and offers a promising new direction for the treatment of osteoporosis and related conditions. The next phase of research will focus on developing and testing potential drug candidates that can activate the Piezo1 pathway, bringing the possibility of “exercise in a pill” closer to reality.
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