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科普: The Amazing Stem Cells
来源：Stem Cell Home
2020-09-04
Humanity’s long journey began with a single cell—yet the human body is composed of a dazzling array of diverse cells. An adult typically has around 200 different cell types, with the total number of cells ranging from 40 to 60 trillion. Cells are the fundamental building blocks of both structure and function in the human body. Similar-shaped cells that share specific functions come together to form tissues, which then assemble into organs and, ultimately, systems. Each system plays a unique role, working in harmony to sustain life and enable the body’s daily activities.
The human body develops step by step, starting with the fusion of a sperm cell from the father and an egg cell from the mother, which forms a fertilized egg—or zygote. This zygote is the very first cell that gives rise to the entire human organism, capable of growing into a fully developed individual. The zygote divides repeatedly: one becomes two, two become four, and so on. By the time it has split into 16 to 32 cells, it’s called a morula; once it reaches more than 32 cells, it’s known as a blastocyst. At the blastocyst stage, the inner cell mass contains what are referred to as embryonic stem cells—highly undifferentiated cells with the remarkable potential to develop into any of the body’s over 200 different cell types.
Some tissues within the human body also contain undifferentiated cells—cells with the remarkable ability to self-renew and differentiate into multiple cell types. These are known as adult stem cells, and they can be found in tissues such as skin, fat, bone marrow, umbilical cord, and the placenta, where they retain their stem-cell-like characteristics. Compared to embryonic stem cells, adult stem cells have a more limited differentiation potential—they typically can only give rise to specific tissues or organs. For instance, adult stem cells present in the skin can both generate new skin stem cells and, when the skin tissue is damaged due to injury, aging, or disease, differentiate into entirely new skin cells, helping maintain the body’s delicate balance and repair processes.
Now, scientists can also use genetic engineering techniques outside the body to introduce genes into fully differentiated, mature cells—such as skin cells—altering their genetic traits and reprogramming them into cells that closely resemble embryonic stem cells, with high proliferative activity and the ability to differentiate in multiple directions. These cells are known as induced pluripotent stem cells, or iPS cells.
Theoretically, iPS cells can also develop into all cell types found in the human body. By studying stem cells and uncovering the mechanisms behind their differentiation into other cell types, scientists can harness these cells to repair or regenerate damaged cells, tissues, or organs caused by injuries, aging, diseases, or other conditions.
So, what are the mechanisms behind stem cell therapy for treating diseases?
First, stem cells can replace and repair dead or damaged cells. Stem cells possess "chemotaxis," meaning they migrate purposefully to the site of injury or cellular damage, where they replace and restore dead or injured cells—directly helping to heal damaged tissues.
Secondly, stem cells possess a powerful "paracrine" effect. They can secrete various neurotrophic factors, anti-apoptotic factors, and other molecules essential for the body, playing a key role in processes such as angiogenesis, bone repair, hematopoietic regulation, and neuroprotection—thereby enhancing the function of multiple systems throughout the organism.
Third, exogenous stem cells can activate dormant and suppressed stem cells within our body, increasing the overall number of stem cells and restoring their original quality, enabling them to resume their normal functions.
Fourth, stem cells can promote the restoration of electrical communication and conductivity between cells. For instance, among adult stem cells, there is a type we call mesenchymal stem cells, which secrete connexins that help strengthen cell-to-cell connections and facilitate the opening of ion channels—processes that have already shown promising applications in treating various diseases.
Additionally, stem cells can participate in shaping and regulating the local immune microenvironment through their immunomodulatory mechanisms, playing a critical role in immune-mediated disorders.
Stem cell technology, also known as regenerative medicine, involves isolating stem cells, culturing them in vitro, directing their differentiation, and even performing genetic modifications to generate entirely new, healthy, or even rejuvenated cells, tissues, or organs. Given the immense potential of stem cells, advancements in this field hold promise for addressing many complex medical challenges in the near future.
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