Growth factor
A growth factor is a naturally occurring substance in the body that plays a crucial role in regulating cell division, growth, and survival. These proteins bind to cell surfaces, initiating various cellular actions, including reproduction and differentiation. While some growth factors are universal, others are specific to certain cell types. They are vital for overall health and have implications in the development and treatment of diseases, particularly cancer. Historically, the discovery of growth factors stemmed from research on embryonic development and cellular interactions, leading to the identification of various types, including cytokines, neurotrophins, and epidermal growth factors.
Synthetic growth factors can also be produced in laboratories, allowing for medical advancements in treating conditions like blood disorders, neuro-muscular diseases, and cancer. Additionally, growth factors have found applications in sports, where they are sometimes used to enhance athletic performance, although this practice is generally prohibited in professional sports. In cosmetic medicine, growth factors are utilized to promote skin regeneration and combat the effects of aging. Overall, growth factors represent a significant area of research with promising therapeutic potential across a range of health issues.
On this Page
Subject Terms
Growth factor
A growth factor is a substance made by the body that helps to control how cells divide, grow, and survive. Synthetic growth factor can also be made in a laboratory. Growth factors are proteins that attach to the surface of a cell and trigger a variety of actions; for instance, they can tell cells to reproduce, make changes in how the cell is formed, or slow down or stop reproduction. Some growth factors work on many types of cells, while others are specific to a certain kind of cell. They are important to everyday health and to the causes and treatments of some diseases such as cancer. Because of these functions, growth factors are sometimes used in treatments intended to enhance athletic performance or slow the aging process.
Background
The existence of something that could alter how cells develop was theorized long before researchers identified the first growth factor. German biologist Viktor Hamburger conducted experiments on developing chick embryos that showed that when cells for a limb were removed, nearby nerve cells did not develop in the same way as they did when the limb remained intact. Experiments during the 1940s that grafted an extra limb in place caused more nerve cells to grow. Hamburger theorized the missing nerve cells contained something that helped the nearby cells organize and form.
Italian neurobiologist Rita Levi-Montalcini developed a different theory about what affected the cells toward the end of the 1940s. She believed there was something in the limb cells that provided nourishment to support the cells as they formed. Levi-Montalcini's theory, for which she won the Nobel Prize in 1986, was that the cells did develop but could not grow and thrive without a substance—a growth factor—released by the cells in the missing limb. Additional experiments isolated nerve growth factors from snake venom in 1959 and from the salivary glands of a mouse in 1962.
The first class of growth factor to be identified and named was a type of factor known as a cytokine. The name comes from the Greek words cyto, meaning "cell," and kinisi, meaning "movement." Researchers had observed the function of these substances before the first cytokine—interferon—was discovered in the 1950s by British virologist Alick Isaacs and Swiss virologist Jean Lindenmann. In 1957, the pair injected chick embryos with the influenza virus and noted that this started a reaction that created a substance that killed the virus and helped the cells fight off other infections as well. They named the newly discovered protein interferon in recognition of how it interfered with the function of the invading cells.
Additional research by scientists around the world soon uncovered more information about interferon, which would become an important tool in the fight against some cancers, hepatitis, herpes, multiple sclerosis, and HIV. Building on the work done by Isaacs and Lindenmann, researchers also began finding more growth factors and gaining a better understanding about how they work. They learned that while some growth factors will work across various species, others will only work on viruses found in the species where the factor originated. In the 1980s, researchers found ways to manufacture interferon in a laboratory, making interferon more cost-effective and widely available to treat illnesses and advance the study of growth factors.
Overview
Since the identification of interferon, researchers have found many other types of growth factors. These include other cytokines and their subfamilies, such as chemokines, adipocytokines, and interleukins; neurotrophins; epidermal growth factor (EGF); platelet-derived growth factor (PDGF); fibroblast growth factor (FGF); transforming growth factors (TGF); erythropoietin (EPO); insulin-like growth factors 1 and 2 (IGF-1, IGF-2); and tumor necrosis factor superfamily (TNFSF). These various types of growth factors are differentiated by where they are found and what types of cells they affect.
For instance, cytokines affect how cells communicate and develop, including during the embryo stage. They also play a role in the effectiveness of the immune system. They can be formed in the same locations that produce blood cells and some other locations as well. Growth factors in the cytokine group function in a way similar to hormones in addition to stimulating growth of affected cell types. Neurotrophins affect nerve cells. EGF is formed in certain glands in the salivary and digestive systems, and assists with the reproduction of glial cells that protect nerves and epithelial cells that line the inner membranes of the body. PDGF is formed in the placenta that supports a developing fetus and in platelets, and helps in the development of connective tissue, glial cells, and muscle cells. FGF is found in a wide range of locations and helps with a variety of different cell functions, including both promoting and deterring them from growing. TGF plays an important role in the growth of cells needed to heal wounds and support the female reproductive system, and aids in embryonic development. EPO is formed in the kidneys and helps in the development of red blood cells. IGF-1 is made in the liver and helps in the formation of many types of cells. IGF-2 is made in a variety of cells and specializes in helping in the development of various fetal cells. TNFSF is responsible for a number of functions, mostly related to the immune system.
As scientists have identified the types of growth factors, they have also found ways either to stimulate more of them or to produce them artificially. This allows scientists to manipulate the function of the cells affected by the growth factors to help treat many serious health conditions. The outcomes for people with cancer, blood disorders, neuro-muscular disorders, and other diseases have greatly improved because of growth factors. Growth factors can be used in children who are not reaching typical heights, and to help people overcome the side effects of treatments for other conditions; for instance, EPO can be used to help boost the production of blood cells for people undergoing cancer chemotherapy treatments that deplete blood cells.
Growth factors are also used to enhance athletic performance. This is usually done with factors that enhance the development of blood and muscle cells, and is generally not permitted in organized sports. Some cosmetic treatments also employ growth factors to help stimulate the regeneration of skin cells and other cells that are affected by the aging process.
Bibliography
"The Body's Wonderful Growth Factors." HGH-Pro, www.hgh-pro.com/growthfactors.html. Accessed 25 Sept. 2017.
Burke, Derek. "Interferon: The Early Days." Microbiology Today, Nov. 2007, molbiol.ru/forums/index.php?act=Attach&type=post&id=49759. Accessed 25 Sept. 2017.
"Growth Factors." ProSpec, www.prospecbio.com/Growth‗Factors. Accessed 25 Sept. 2017.
Holloway, Marguerite. "Finding the Good in the Bad: A Profile of Rita Levi-Montalcini." Scientific American, 30 Dec. 2012, www.scientificamerican.com/article/finding-the-good-rita-levi-montalcini/. Accessed 25 Sept. 2017.
"Introduction." Medical Biochemistry Page, themedicalbiochemistrypage.org/growth-factors.php#intro. Accessed 25 Sept. 2017.
"Jean Lindenmann, Scientist—Obituary." Telegraph, 27 Jan. 2015, www.telegraph.co.uk/news/obituaries/11372608/Jean-Lindenmann-scientist-obituary.html. Accessed 25 Sept. 2017.
Ranaweera, Anoma. "Role of Growth Factors in Skin Creams." DermNet New Zealand, www.dermnetnz.org/topics/role-of-growth-factors-in-skin-creams. Accessed 25 Sept. 2017.
"What Are Growth Factors?" Sino Biological, www.sinobiological.com/What-are-Growth-Factors-a-6339.html. Accessed 25 Sept. 2017.