HKU Study: ‘Exercise Sensor’ Protein Piezo1 Holds Key to New Osteoporosis Treatments

The body possesses a remarkable, built-in mechanism for maintaining bone strength – one that doesn’t necessarily require strenuous physical activity. Researchers at the University of Hong Kong (HKUMed) have identified a protein, Piezo1, that acts as an “exercise sensor” within bone marrow, triggering processes that promote bone growth even in the absence of movement. This discovery, published in the journal Signal Transduction and Targeted Therapy, offers a potential pathway to new treatments for osteoporosis and bone loss, particularly for those unable to engage in weight-bearing exercise.

The Challenge of Bone Loss and Current Limitations

Osteoporosis, characterized by weakened bones and increased fracture risk, affects millions globally. 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 fragile bones. The problem is particularly acute in aging populations, like that of Hong Kong, where osteoporosis affects 45% of women and 13% of men aged 65 and above. These fractures often lead to chronic pain, reduced mobility, and a diminished quality of life, placing a significant burden on healthcare systems.

Current treatments often emphasize physical activity, but this isn’t always feasible for elderly individuals, those recovering from injury, or patients with chronic illnesses. Professor Xu Aimin, Director of the State Key Laboratory of Pharmaceutical Biotechnology at HKUMed, explains, “Current treatments rely heavily on physical activity, which many patients simply cannot perform. We need to understand how our bones get stronger when we move or exercise before we can find a way to replicate the benefits of exercise at the molecular level.”

How Bones Respond to Movement: The Role of Mesenchymal Stem Cells

As we age, bone density naturally declines, and bones become more porous. Within the bone marrow reside mesenchymal stem cells (MSCs), which have the potential to develop into either bone tissue or fat cells. These cells are highly responsive to physical forces – movement and pressure stimulate them to build bone. Yet, with age, this balance shifts. MSCs increasingly differentiate into fat cells, contributing to bone loss and a cycle of deterioration.

The accumulation of fat within the bone marrow crowds out healthy bone tissue, further weakening the skeletal structure. Existing therapies struggle to reverse this process effectively.

Piezo1: The Molecular Exercise Sensor

The HKUMed research team, through experiments using both mouse models and human stem cells, pinpointed Piezo1 as the key protein responsible for sensing mechanical forces. Located on the surface of MSCs in the bone marrow, Piezo1 acts as a mechanical sensor, detecting physical activity. When activated by movement, Piezo1 limits fat buildup and promotes the formation of new bone tissue. Conversely, when Piezo1 is absent, MSCs are more likely to become fat cells, accelerating bone loss.

The study likewise revealed that the absence of Piezo1 triggers the release of inflammatory signals – specifically Ccl2 and lipocalin-2 – which further encourage MSCs to become fat cells and hinder bone growth. Blocking these inflammatory signals demonstrated a potential to restore healthier bone conditions.

Mimicking Exercise: A New Therapeutic Avenue

“We have essentially decoded how the body converts movement into stronger bones,” states Professor Xu Aimin. “We have identified the molecular exercise sensor, Piezo1, and the signalling pathways it controls. This gives us a clear target for intervention.” The researchers believe that by activating the Piezo1 pathway, it may be possible to mimic the benefits of exercise, even in individuals who are unable to be physically active.

Dr. Wang Baile, co-leader of the study, emphasizes the potential impact on vulnerable populations. “This discovery is especially meaningful for older individuals and patients who cannot exercise due to frailty, injury or chronic illness. Our findings open the door to developing ‘exercise mimetics’ – drugs that chemically activate the Piezo1 pathway to aid maintain bone mass and support independence.”

Beyond Physical Therapy: A Broader Impact

Professor Eric Honoré, from the French National Centre for Scientific Research, highlights the potential to move beyond traditional physical therapy. “This 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.”

Translating Research into Clinical Applications

The HKUMed research team is now focused on translating these findings into practical clinical applications. Their immediate goal is to develop new therapies that can 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, highlighting an international effort to address this global health challenge.

The 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 various health and medical research funds from Hong Kong and China.

Next Steps: From Laboratory to Patient

The team’s work represents a significant step forward in understanding the complex interplay between physical activity and bone health. While the research is promising, further investigation is needed to determine the safety and efficacy of potential “exercise mimetic” drugs in human clinical trials. The researchers are actively pursuing these avenues, with the hope of bringing new treatment options to those who need them most.