But in fact, this search involving a large number of laboratories has been hotly debated for decades. Recently, more than 30 papers were rejected for falsifying data. The team of Hoobler Branch Institute plans to publish their findings in this week's Proceedings of the National Academy of Sciences (PNAS): There is no evidence that cardiac stem cells exist at all.
This conclusion confirms the long-standing suspicion of some people in this research field and goes straight to the core of a deeper problem, that is, what stem cells really mean.
As more complex technologies reveal the plasticity and heterogeneity of cell populations, some researchers have changed their views. They used to think that "stem cell" was the decisive feature of cell types.
Now they think this is a function that many types of cells can perform or play. In the 1950s and 1960s, researchers first discovered and described stem cells in bone marrow. Their original intention was to study the effects of radiation exposure after World War II and treat it.
These hematopoietic stem cells are rare, divide slowly, and have the ability of self-renewal and differentiation into other types of blood cells. They maintain the reserve of human blood cells and help the human body cope with injuries. When exposed to radiation, stem cells die and the body cannot replenish them-however, bone marrow transplantation (bone marrow contains stem cells) can regenerate the hematopoietic system.
Because stem cells are closely related to the healing and recovery of the body, researchers and doctors who are looking for various diseases and treatments for diseases are pursuing stem cells in other body tissues.
Then, the story becomes more complicated.
Researchers have found stem cells in other adult tissues all over the body, including skin, hair follicles and intestines, and just confirmed the existence of stem cells in bones a few months ago. These stem cells also have the ability of self-renewal and can differentiate into various types of functional cells in their tissues.
But other than that, they look very different from blood stem cells. They express different genes, display different protein and surface markers, and divide in different ways and at different speeds. In 1990s, scientists successfully isolated embryonic stem cells, which are more powerful than cells in adult tissues and have the ability to differentiate into all cell types in the body. Almost at the same time, scientists began to study the possible role of tumor stem cells in tumor growth. In 2006, researchers successfully transformed differentiated connective tissue cells into induced pluripotent stem cells (iPSC), which are as versatile as embryonic stem cells. The results showed that cell drying could be induced.
However, according to Hans Clevers, a molecular geneticist who recently published a paper on cardiac stem cells, what hangs over these findings is the hypothesis that,
That is, stem cells in all parts of the body, like hematopoietic stem cells in bone marrow, are "a precious, natural and magical entity." In fact, he said, the insights scientists initially gained from hematopoietic stem cells have influenced the way they think about stem cells in other tissues-sometimes, these ways of thinking are even greatly limited. "Any cell can be a stem cell" is often ignored. "Many organizations can repair themselves very skillfully," cleaves said. "There is no established strategy. In blood, small stem cell colonies are the only means of regeneration, but this is not always the case in those solid tissues.
Stem cells in solid tissues are different, for example, they tend to divide faster; And because they show unique molecular characteristics, researchers must use specific methods to identify them.
It is necessary to rely on tissue-specific markers for identification (not all stem cells have to do this), which is one of the reasons why there is so much debate about the existence of heart stem cells, and why researchers still have difficulty in identifying other types of stem cells. In addition, when stem cells in solid tissues are destroyed, the more specialized cells in those tissues can often return to a state similar to stem cells and take over the repair function on their own. Therefore, cells are more plastic than previously thought, and their identities are not immutable.
"There is increasing evidence that our bodies can respond to injuries independently even without the classic stem cell population we think," said Jonathan Hogg, a hematologist and stem cell researcher at Harvard Medical School (HMS) and Massachusetts General Hospital (MGH).
"We must be more open and accept the fact that any cell can become a stem cell in principle. 」
-Hans Clives, Hobler Institute.
This has been confirmed in a series of organs, including kidney, lung, stomach and intestine. Perhaps the most striking thing is that some tissues (not just the heart) seem to have no stem cell population. As a model of efficient organ regeneration, adult liver has no stem cells; On the contrary, differentiated cells in the liver can function like stem cells when needed. "Essentially, every cell in the liver has the potential as a stem cell," Clevers said. 」
Therefore, "it is more useful to find out how a specific tissue performs its stem cell function than to find a single stem cell," he said. The ways in which various cells contribute to maintaining tissues constitute dryness, which is not unique to any cell type or entity. If we blindly study what "real" stem cells should be, instead of thinking that they have a broader definition, it will undoubtedly hinder the progress of science.
In fact, researchers have found that even those so-called "real" stem cells have different functions and behaviors. "We know that there is actually more heterogeneity in the cell group that we thought was quite homogeneous before." Hogart said.
Stem cell VS regenerative therapy As it becomes more and more difficult to distinguish stem cells from cells that have begun to differentiate and perform specific functions, it may be necessary for us to re-examine the early research.
Pamela Robey, a biologist specializing in bone system research at the National Institutes of Health (NIH), believes that the newly discovered backbone cells may actually be progenitor cells-they are descendants formed after stem cells are slightly differentiated. Robbie suggested that real backbone cells are even rarer, and we still need to identify them. "We can easily believe that we have found a real stem cell," she said, "but this may not be the case. 」
This sometimes leads to controversy, especially when it comes to so-called mesenchymal stem cells, which are pluripotent cell groups with multi-directional differentiation potential, originally extracted from bone marrow, although they do not make blood cells. At present, most researchers think that they are not stem cells at all (many people no longer call them stem cells), but there has been a chaotic history about what they are and what they do. Robbie said that this situation "prepares for abuse." Unauthorized stem cell clinics use their controversial status to treat thousands of patients with ineffective, unproven and potentially dangerous therapies. In fact, the US Food and Drug Administration (FDA) only allows a few confirmed stem cells to be used for stem cell therapy, and these treatments all involve some form of bone marrow or blood cell transplantation.
However, for law-abiding scientists, a broader definition of stem cells may be good news for medical research: it means that regenerative therapy does not need to target only stem cell groups that do not necessarily exist. Instead, scientists can use differentiated cells with some characteristics of stem cells. Some people suggest that dryness should no longer be regarded as a factor when creating new drugs involving living cells. "It makes things easier," Clives said.
Looking ahead, he added, "We must be more open and accept the fact that any cell can become a stem cell in principle. 」
Why are there no fish?
Review: Lily
Editor: Man Qian
Source: Quanta Magazine
"We must be more open and accept the fact that any cell can become a stem cell in principle. 」
-Hans Clives, Hobler Institute.
This has been confirmed in a series of organs, including kidney, lung, stomach and intestine. Perhaps the most striking thing is that some tissues (not just the heart) seem to have no stem cell population. As a model of efficient organ regeneration, adult liver has no stem cells; On the contrary, differentiated cells in the liver can function like stem cells when needed. "Essentially, every cell in the liver has the potential as a stem cell," Clevers said. 」
Therefore, "it is more useful to find out how a specific tissue performs its stem cell function than to find a single stem cell," he said. The ways in which various cells contribute to maintaining tissues constitute dryness, which is not unique to any cell type or entity. If we blindly study what "real" stem cells should be, instead of thinking that they have a broader definition, it will undoubtedly hinder the progress of science.
In fact, researchers have found that even those so-called "real" stem cells have different functions and behaviors. "We know that there is actually more heterogeneity in the cell group that we thought was quite homogeneous before." Hogart said.
Stem cell VS regenerative therapy As it becomes more and more difficult to distinguish stem cells from cells that have begun to differentiate and perform specific functions, it may be necessary for us to re-examine the early research.
Pamela Robey, a biologist specializing in bone system research at the National Institutes of Health (NIH), believes that the newly discovered backbone cells may actually be progenitor cells-they are descendants formed after stem cells are slightly differentiated. Robbie suggested that real backbone cells are even rarer, and we still need to identify them. "We can easily believe that we have found a real stem cell," she said, "but this may not be the case. 」
This sometimes leads to controversy, especially when it comes to so-called mesenchymal stem cells, which are pluripotent cell groups with multi-directional differentiation potential, originally extracted from bone marrow, although they do not make blood cells. At present, most researchers think that they are not stem cells at all (many people no longer call them stem cells), but there has been a chaotic history about what they are and what they do. Robbie said that this situation "prepares for abuse." Unauthorized stem cell clinics use their controversial status to treat thousands of patients with ineffective, unproven and potentially dangerous therapies. In fact, the US Food and Drug Administration (FDA) only allows a few confirmed stem cells to be used for stem cell therapy, and these treatments all involve some form of bone marrow or blood cell transplantation.
However, for law-abiding scientists, a broader definition of stem cells may be good news for medical research: it means that regenerative therapy does not need to target only stem cell groups that do not necessarily exist. Instead, scientists can use differentiated cells with some characteristics of stem cells. Some people suggest that dryness should no longer be regarded as a factor when creating new drugs involving living cells. "It makes things easier," Clives said.
Looking ahead, he added, "We must be more open and accept the fact that any cell can become a stem cell in principle. 」
Why are there no fish?
Review: Lily
Editor: Man Qian
Source: Quanta Magazine