Growth factors and why they play an important role in modern medicine

Background

Growth factors can be described as complex molecules which play an important role during many different processes such as cell growth, proliferation, and differentiation. For majority of cases, they function as signalling proteins that are usually secreted by various types of cells. The first step for many growth factors involves binding to specific receptors, these receptors can be found on the surface of specific target cells. This protein binding action often leads to the activation a complex cascade of intracellular signalling pathways. The eventual outcome of this process is a change in cell behaviour or change in gene expression.

There are many different types of growth factors that have been identified, for example: epidermal growth factor (EGF), fibroblast growth factor (FGF), insulin-like growth factor (IGF), nerve growth factor (NGF), and platelet-derived growth factor (PDGF). Each of these growth factors are known to target specific cell types and have a unique function.

Types of growth factors

There are various GFs that have been identified. We will list some of the most common types below.

1. EGF: This is a protein that is involved in stimulating cell growth and division. Predominately present in epidermis cells. Some of the functions it carries out include regulating the cell proliferation and differentiation. Also providing aid to the process of tissue repair and wound healing. There is evidence to indicate that EGF can lead to developing certain types of cancer cells.
2. FGF: These are a family of proteins that stimulate the growth and division of fibroblasts. Are largely involved in a many of biological processes, for example wound healing, angiogenesis, and the development of the nervous system.
3. IGF: The structure and the effect it has on cells for IGFs is similar to that of the insulin molecule. Bone, muscle and cartilage cells are found to stimulated using this growth factor. Its main role involves regulating cell proliferation, differentiation and the maintenance of tissues.
4. PDGF: Predominately found in connective tissues and blood vessels. The main functions of PDGF are to regulate cell proliferation, differentiation, tissue repair and wound healing.
5. VEGF: Responsible for stimulating cell growth and division in the blood vessels. This can either be maintaining existing blood vessels or angiogenesis (the developing new blood vessels). Other functions of VEGF are to help in the growth and survival of cells within various tissues. This can be found in the eye, brain and heart.
6. TGF-beta: This protein regulates cell growth, proliferation and differentiation. It is involved in inflammation, various immune responses and plays a key role in the development and maintenance of many tissues. TGF-beta is known to have both a stimulatory and an inhibitory effect on cell growth. This is determined by the cell types and context.
7. NGF: Plays an important function during the growth and differentiation of neurons. It can also help in repairing and regenerating damaged nerves.
8. GM-CSF: Is produced by white blood cells (such as macrophages and monocytes). These cells are vital during the inflammation process and one of the main roles of GM-CSF is to elevate the production of cells such as basophils, neutrophils, mast cells and eosinophils.
9. IFNs: Are proteins that numerous cells secrete in response to a viral infection. IFNs can induce an immune reaction and have antiviral activity.

Functions of growth factors

Growth factors are regarded as proteins that are important in regulating cell growth and proliferation. They can be categorized into two main groups. Firstly, those that are signalling molecules and second those that are hormones.

Below is a list of various roles performed by many growth factors:

• Development: Playing key roles during the development and differentiation process of various cells, tissues, and organs. This has been shown to be both during the fetal development stage and during many stages throughout the lifetime.
• Tissue repair: Involved in the repair and regeneration of many different types of damaged tissues. This can be the form of damaged tissues following an injury or from post-surgery.
• Immune response: Important for the efficient functioning of immune system. They are found to be involved in the activation and proliferation of immune cells during an immune response.
• Cell survival: involved in promoting the survival of many different types of cells. This is especially during times of extreme stress or injury.
• Cancer: Can help to stimulate the process of proliferation and cell survival for many cancer cells. In many cases where they have been over expressed, this contributes to the development and further progression of specific cancer. However, they are evidence to indicate that they can provide a tool during the cancer treatment procedure. In many cases they have been used to stimulate the immune system to attack cancer cells or to inhibit the proliferation of cancer cells.
• Degenerative diseases: Have been studied as potential therapy treatment for many degenerative diseases. Examples of this is found during the treatment of Alzheimer’s disease and Parkinson’s disease.
• Tissue engineering: They can be used to stimulate the growth and repair of tissues. Examples of this include the development of artificial organs or in the treatment of wounds.

An important tool in modern medicine

There are many publications that have described the use of growth factors for various therapeutic treatments. This is further supported by the ability of GFs to be able to stimulate the growth and repair of vast amounts of tissues and organs. Some of the common treatments include cancer therapy, wound healing and the repair of damaged tissues.

One major example is the use of PRP (which is short for platelet-rich plasma) therapy. This process that involves injecting a patient with a concentrated solution of their own platelets. These platelets will contain many growth factors such as PDGF. The use of PRP therapy has been extremely effective in promoting the healing of injuries (for example tendon, surgical wounds and sports injuries).

GFs have been used to study and learn more about various conditions and diseases. For example, FGF has been used to treat patients with coronary artery disease, this is due to its ability to promote the growth of new blood vessels within the heart. Similarly, EGF has been used to treat burns and other skin injuries, this again is due to its ability to stimulate the growth of new cells within the skin.

Growth factors have also been explored as a potential treatment for various neurodegenerative diseases. Examples include Parkinson’s disease and Alzheimer’s disease. NGF is of particular interest since it can promote the survival and growth of neurons within the brain.

Final thoughts

Growth factors play a key role during the development of novel therapeutic drugs. They have also been extensively used in regenerative medicine. A better understanding of growth factor activity in relation to normal and abnormal processes can lead to the discovery of new therapeutic treatments.

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