On July 23, 2009, an experimental study by Chinese scientists Qi Zhou and others was published online in Nature, the world’s top scientific journal, causing a global sensation. The study was named as one of the top ten basic research results in China in 2009, and was also selected as one of the top ten medical advances in 2009 by Time magazine, an international authoritative media. What research is so compelling? It starts with stem cell research, which is now flourishing all over the world.
What are stem cells? Stem cells are translated from the English word ‘Stem cells’. Stem’ means ‘trunk’ and ‘origin’, just like a tree trunk Just like a tree trunk can grow branches, leaves, flowers and fruits, stem cells also have a strong potential for long-term self-renewal and multiple differentiation. Stem cells can divide symmetrically into two new daughter stem cells or two functional cells, or asymmetrically into one daughter stem cell and one functional cell. Under certain conditions, stem cells can differentiate into different types of mature cells, thus maintaining a dynamic balance of growth and decline in tissues and organs, so stem cells are the ‘ancestors’ of all 220 kinds of cells that make up the human body. Stem cells are a kind of “potential talents”, just like a newborn baby, which does not have specialized talents, but through learning and cultivation, they will grow up to be “specialized talents” with one skill and can differentiate into many kinds of human cells. Once differentiation is completed, the “occupation” of these cells is determined. Therefore, the “future” of stem cells has unlimited possibilities compared to the ordinary body cells.
Stem cells can produce all the tissues and organs in the body, so where do these amazing stem cells come from? Research has shown that stem cells can come from embryonic and fetal tissues, known as embryonic stem cells, or from postnatal organs and adult individual tissues, known as adult stem cells.
Embryonic stem cells can differentiate into fetal or human cells of various tissues under suitable conditions and are known as pluripotent stem cells. Research has shown that human embryonic stem cells can repair injured organs, and in 2007 scientists demonstrated that transplanting heart muscle cells derived from human embryonic stem cells into rats with heart disease helped to repair the heart muscle and improve the function of the entire heart. This was the first strong evidence that embryonic stem cells could be used to treat hearts damaged by myocardial infarction or heart disease. Because of the “all-purpose” nature of embryonic stem cells, it is technically optimal to use embryonic stem cells to culture human tissues and organs for the treatment of diseases. However, since human embryonic stem cells are derived from embryos, some people believe that ‘destroying an embryo is destroying life’, and therefore using human embryos for embryonic stem cell research is unethical and strongly opposed by religious communities, so many governments have not approved human embryonic stem cell research. So scientists have been struggling to find alternatives.
In 2007, scientists at Kyoto University in Japan and the University of Wisconsin in the United States successfully transformed ordinary skin fibroblasts into stem cells called induced pluripotent stem cells, or iPS cells for short. Induced pluripotent stem cells have embryonic stem cell-like properties, and at the same time the source is convenient, only somatic cells from epidermis and other tissues are needed, avoiding the ethical issues that embryonic stem cell research has been facing, and quickly became a hot spot for stem cell research. Scientists are further exploring whether iPS, like embryonic stem cells, also have the omnipotence of differentiation and development. In 2009, Qi Zhou et al. reported that iPS induced by skin cells from experimental mice could be grown into healthy mice and successfully produced second- and third-generation healthy mice. Our scientists have taken an important place in iPS research with experiments that indisputably demonstrate the totipotency of iPS.
In addition to embryonic stem cells, there is another type of adult stem cells in the tissues and organs of adult individuals. These stem cells can also renew themselves over time and generate adult cells with certain morphology and specific functions. The main function of adult stem cells is to maintain a certain degree of dynamic cellular homeostasis and to replace cells that have died due to injury or disease. For example, a proportion of white blood cells, red blood cells and platelets die of senescence every day in the body, but our routine blood values are always maintained at normal levels, and this stability is maintained by the hematopoietic stem cells in the bone marrow (about less than 1% of the bone marrow mononuclear cells). There are also bone marrow mesenchymal stem cells, which make up about 0.01% to 0.001% of bone marrow single nucleated cells, and they are regulated so that they are directed to differentiate into bone, cartilage, adipocytes, etc.