Because existing therapies can have limitations and side effects, researchers are looking for new biological targets that could lead to more effective ways of preserving or rebuilding bone. Scientists at Leipzig University have now identified one such target in GPR133, a receptor that appears to play an important role in keeping bones strong.

A Little-Known Receptor With a Major Role in Bone Health

GPR133 belongs to a group known as adhesion G protein-coupled receptors. These receptors sit on the surface of cells and help them respond to signals from their surroundings. Although this family of receptors is still not fully understood, the new findings suggest GPR133 is closely involved in the processes that build and maintain healthy bone.

“If this receptor is impaired by genetic changes, mice show signs of loss of bone density at an early age – similar to osteoporosis in humans. Using the substance AP503, which was only recently identified via a computer-assisted screen as a stimulator of GPR133, we were able to significantly increase bone strength in both healthy and osteoporotic mice,” explains Professor Ines Liebscher, lead investigator of the study from the Rudolf Schönheimer Institute of Biochemistry at the Faculty of Medicine.

The results point to GPR133 as a potentially valuable target for future osteoporosis treatments. The researchers found that stimulating the receptor with AP503 increased bone strength not only in healthy mice, but also in mice with osteoporosis-like bone loss.

How GPR133 Helps Build Stronger Bones

Inside bone tissue, GPR133 responds to physical forces and interactions between nearby bone cells. When the receptor is activated, it sets off signaling that changes the balance between the cells that build bone and those that break it down.

Bone-forming cells (osteoblasts) are responsible for producing new bone tissue. Bone-resorbing cells (osteoclasts), by contrast, remove old bone as part of the skeleton’s normal cycle of renewal. Healthy bones depend on maintaining the right balance between these two processes.

Activation of GPR133 encourages the activity of osteoblasts while reducing the activity of osteoclasts. This shifts the balance toward stronger and more durable bone.

AP503 appears to imitate the natural process that activates GPR133. That raises the possibility that the compound could eventually be used to increase bone strength or help restore bone that has already been weakened. One potential application would be osteoporosis associated with menopause, when declining hormone levels can accelerate bone loss in women.

Potential Benefits for Both Bone and Muscle

The findings could have broader implications because AP503 may affect more than the skeleton.

In an earlier study, researchers at Leipzig University had already found that activation with AP503 also strengthens skeletal muscle.

“The newly demonstrated parallel strengthening of bone once again highlights the great potential this receptor holds for medical applications in an aging population,” says Dr. Juliane Lehmann, lead author of the study and a researcher at the Rudolf Schönheimer Institute of Biochemistry.

A treatment capable of improving both bone and muscle strength could be especially relevant for older adults, who often experience declines in both tissues at the same time. Maintaining stronger muscles can also support mobility and stability, while stronger bones can reduce vulnerability to fractures.

The Leipzig team is now pursuing several follow-up projects aimed at understanding GPR133 more fully. Researchers are also investigating whether AP503 could have applications in other diseases and are continuing to examine the receptor’s wider functions throughout the body.

Leipzig’s Longstanding Research Into GPR Receptors

For more than a decade, Leipzig University has made adhesion G protein-coupled receptors a major research priority through Collaborative Research Center 1423, Structural Dynamics of GPCR Activation and Signaling.

The program focuses on understanding how these receptors change shape, become activated, and transmit signals inside cells. Leipzig University is internationally recognized as a leading center for research in this area.

Such moments capture the imagination. But they also raise an important question: what do the majority of scientists actually think?

Surprisingly, we usually don’t know. When a scientific controversy or breakthrough dominates headlines, press officers and journalists often quote a handful of experts. These views may be insightful, but they rarely tell us what the wider scientific community thinks. And yet public discussions frequently rely on phrases such as “the science says” or “scientists believe”, as if there were a clear and measurable answer.

In reality, systematic evidence about scientific opinion is often missing. My colleagues and I recently tried to change that in the domain of astrobiology. Shortly after the two major announcements of possible extraterrestrial life in 2025, we surveyed astrobiologists to understand how expert judgment was distributed across the field.

The first case concerned the exoplanet K2-18b. In April 2025, researchers reported possible traces of molecules called dimethyl sulfide and/or dimethyl disulfide. On Earth, these are associated with biological activity. Media coverage was extensive, with many reports framing the finding as an extraordinary advance in the search for alien life.

The second case came in September, when NASA announced that Cheyava Falls appeared to preserve a potential biosignature – so-called “leopard spots” which are mineral rings that on Earth are often formed by microbial activity. Again, headlines, and NASA officials themselves, suggested something momentous.

What scientists actually thought

We surveyed hundreds of astrobiologists from across the global research community, within days of each announcement. We asked a simple question: did scientists think extraterrestrial life had probably been found?

The results revealed a rather cautious picture. For K2-18b, only 6.6% of surveyed astrobiologists agreed that scientists had probably found extraterrestrial life. Nearly two-thirds disagreed, while 28.0% remained neutral. For the Mars case, confidence was higher but still cautious: 15.1% agreed, disagreement fell to 44.6% and neutrality rose to 40.3%.

Looking only at agreement and disagreement, however, misses an important part of the story. The proportion of astrobiologists who strongly disagreed fell dramatically, from 35.1% in the K2-18b case to just 11.1% for Mars. Much of the movement was therefore not from rejection to endorsement, but from strong rejection towards more tentative positions.

In other words, expert opinion moved in structured ways. The shift from K2-18b to Mars was not a simple movement from “no” to “yes”. Instead, the community became more open to the possibility without embracing it outright.

One possible reason is that the two cases involved different kinds of evidence. The K2-18b claim relied on possible atmospheric signatures detected from across interstellar distances, whereas the Martian case concerned a rock that could be studied directly and in much greater detail. At the same time, astrobiologists have long been aware that apparently lifelike features can sometimes arise through non-biological processes. Often, the challenge is not imagining how life could produce a signal, but understanding all the ways nature might produce something similar without life.

Scientific opinion is rarely binary. Public discussion often treats science as though communities either agree or disagree. But the distribution of opinion matters too. Strong agreement, agreement, neutrality, disagreement and strong disagreement can each tell us something different about how a scientific community is responding to a claim.

A large neutral response can indicate several things. Scientists may judge the evidence genuinely inconclusive. They may hold an intermediate level of confidence. Or they may regard a claim as too speculative to endorse or reject decisively. Likewise, movement from strong disagreement towards ordinary disagreement may signal a softening of attitudes even when overall disagreement remains high. Treating scientific opinion as simply “for” or “against” risks flattening these important distinctions.

Beyond extraterrestrial life

The broader lesson extends well beyond extraterrestrial life. In areas such as climate science, pandemics, artificial intelligence or medical research, public conversations frequently invoke scientific consensus.

Sometimes strong agreement genuinely exists. Sometimes it does not. But we often lack systematic ways of measuring what scientists actually think, especially where evidence is emerging or uncertainty remains substantial. Instead, discussions rely heavily on selective quotation, vocal individuals or assumptions about community views.

Efforts to do this more systematically are beginning to emerge. At Durham University, our research group, C-Scope (the Centre for Scientific Community Opinion Polling and Evaluation), studies how expert opinion is distributed and how it changes over time. We are not trying to replace evidence with polling, nor to treat majority opinion as truth. Our aim is to better understand how scientific communities respond to uncertainty.

Scientific knowledge advances through uncertainty, disagreement and gradual revision. If public discussion, and perhaps political will, increasingly turns on claims about what scientists think, we should make more effort to find out.

“Observing 3I/ATLAS is like taking a fingerprint from another solar system,” shares Nathan Roth, lead author on this research, and a professor with American University, “The details reveal what it’s made of, and it’s bursting with methanol in a way we just don’t usually see in comets in our own solar system.”

A Chemical Fingerprint From Another Solar System

The research team used ALMA’s Atacama Compact Array in Chile to observe 3I/ATLAS on several dates in late 2025 as it moved closer to the Sun. As sunlight heated the comet’s icy surface, gas and dust escaped and created a bright cloud (or coma) around its core.

By studying the molecules in this coma, astronomers could identify the chemical makeup of material carried by the comet. Because 3I/ATLAS originated outside our solar system, those measurements provide a rare opportunity to investigate how small icy bodies may form in another planetary system without traveling beyond our own.

The scientists concentrated on the faint submillimeter signatures of two molecules: methanol (CH₃OH), a type of alcohol, and hydrogen cyanide (HCN), a nitrogen-bearing organic molecule commonly seen in comets.

ALMA revealed that 3I/ATLAS contains an unusually high amount of methanol relative to hydrogen cyanide. On two observation dates, researchers measured methanol-to-HCN ratios of roughly 70 and 120. Those values place 3I/ATLAS among the most methanol-rich solar system comets ever studied.

Unusual Chemistry Points to Different Origins

The measurements suggest that the ice inside 3I/ATLAS formed under, or was later exposed to, conditions very different from those experienced by most comets in our solar system.

Earlier observations with the James Webb Space Telescope found that 3I/ATLAS had a coma dominated by carbon dioxide while it was still far from the Sun. The new ALMA measurements now add abundant methanol to the growing list of unusual features in the comet’s chemical makeup.

ALMA’s high resolution for imaging also allowed astronomers to track how different molecules are released and travel away from the comet. The observations revealed a striking contrast between methanol and hydrogen cyanide.

Hydrogen cyanide appears to originate mostly from the comet’s central body, or nucleus. That behavior is common among comets in our solar system. Methanol, however, appears to come from both the nucleus AND from ice particles floating within the coma.

Tiny Ice Grains Act Like Mini-Comets

These small icy grains effectively behave like miniature comets. As 3I/ATLAS approaches the Sun and temperatures rise, ice within the grains turns into gas and releases additional methanol into the surrounding coma.

Astronomers have seen similar behavior in some comets from our own solar system. However, this is the first time researchers have traced the detailed physics of this type of outgassing in an object that originated in interstellar space.

Comet 3I/ATLAS is only the third confirmed object ever observed entering our solar system from interstellar space, following 1I/’Oumuamua and 2I/Borisov. Studies of those earlier visitors also uncovered unusual characteristics.

As astronomers find and examine more interstellar objects, each one offers another opportunity to compare our solar system with planetary systems elsewhere in the galaxy. The unusual chemistry of 3I/ATLAS is adding another intriguing piece to the broader picture of how planets, comets, and other small bodies form around distant stars.