Growth factors exist as groups of proteins that play a role in stimulating the growth of particular tissues. These have a vital responsibility to promote the differentiation of cells and enhance cell division.

Growth factors are found in a wide array of organisms, such as insects, plants, humans, and amphibians. Growth factors were discovered when scientists started exploring the cellular effects of biological components and their impact on tissue cultures. It was found that a group of peptides exists which are diverse from the already identified hormones. Growth factors got their name as per their functions found through the investigations —active stimulation of cell and tissue growth.

 

 

 

Is Growth Factor A Hormone?

Most of the growth factors exist as polypeptides which bind to particular receptors on the surface of the cells. These are identified as hormone-like modulators that play a role in cell differentiation and proliferation. [1] Specific growth factors show similarity to hormones as they are secreted into the blood, in which they can be transported to the respective target tissues. The majority of these cell surface receptors show protein-tyrosine kinase activity present in the cytoplasm of the cells. [2]. The activity of the growth factors at a cellular and molecular level regulates cell proliferation [3]. However, unlike hormones, growth factors can also have additional biological activities besides enhancing cell proliferation [4]. In addition, hormone production is restricted to glandular tissue, while several types of tissue manufacture growth factors.

 

 

What Are Some Examples of Growth Factors?

There are several types of Growth factors, most of which were primarily obtained from animal tissues, such as cattle and mice. Examples of these are:

• Insulin-like growth factors called somatomedins that promote growth by facilitating growth hormone secretion from the pituitary gland.

• Epidermal growth factor — promotes epithelial cell growth.

 • Platelet-derived growth factor — promotes muscle and connective tissue cell growth. • Nerve growth factor — promotes neuronal cell growth.

• Lipoic acid is a uniformly distributed growth factor in animals, plants, animals, and microorganisms. It is used in carbohydrate and lipid metabolism and photosynthesis.

• Specific cytokines, which are small proteins released by a cell to regulate the activity of another cell, can serve as growth factors. Cytokines affect the pathways of signal transduction. However, only those cytokines which affect the cell growth and differentiation pathways are termed as growth factors. An example of a cytokine growth factor is the granulocyte-macrophage colony-stimulating factor (GM-CSF), which promotes white blood cell production by stem cells.

 

 

 

Do Growth Factors Really Work?

The growth of each cell in the human body in diverse organs and systems such as the skin and teeth is mediated by growth factors. The growth factors are the ones that regulate the specific stages of the cell cycle. The cell cycle phases are divided into two vital phases: the transition from the former to the latter.

• GO into GI phase • G 1 into S phase

For example, the GO to G1 transition is organized by growth factors:

• Nerve growth factor (NGF) for nerve cells

• Fibroblast growth factor (FGF) for mesenchymal cells or connective tissue

 • Epidermal growth factor (EGF) for skin cells

• Platelet-derived growth factor (PDGF) for blood vessel- lining thrombus-forming cells

 

Growth factor regulating G1 to S transition includes insulin-like growth factor (IGF-1). On the other hand, the growth-promoting effect of certain growth factors can be contrasted by antagonists, including the following.

• Transforming growth factor-beta (TGF-beta)

• Tumour necrosis factor (TNF).

 

 

 

 

Types of Growth Factors

There are four main categories of growth factors. These include the following:

1. Class I — Consists of growth factors that interact with certain cell surface receptors. This includes growth hormone (somatotropin), epidermal growth factor (EGF), and platelet-derived growth factor (PDGF).

2. Class II — are commonly tyrosine kinases which are cell-surface hormone receptors, in the cytoplasmic dominions of the receptor, as for EGF and PDGF.

3. Class III comprises a significant number of intracellular signal transducers or transmitters that belong to several families, for example, protein kinases and Ras proteins, including Src.

4. Class IV — exists as proteins that bond with particular segments of DNA called nuclear transcription factors, including promoters. These result in either stimulation of mRNA transcription or stoppage of transcription. The DNA transcription initiators include myc, fos, and N-myc. The cell division suppressors include proteins such as the retinoblastoma gene product and p53.

 

 

 

Why Are Growth Factors Essential in Humans?

Wound healing

The phases of wound healing include

1. The inflammatory phase

2. The proliferative phase

3. The remodeling phase

 

The platelets, which have a crucial role in the inflammatory phase, secrete TGF-beta and platelet-derived growth factors (PDGF) that attract neutrophils and macrophages. Macrophages secrete TGF-beta, EGF and vascular endothelial growth factor (VEGF). VEGF is also secreted by endothelial cells and plays a role in the formation of new blood vessels (angiogenesis).

 

Cancer

Growth factors, including epidermal growth factor (EGF) and insulin-like growth factor (IGF-1), play a crucial role in tumor progression. This is the reason why there has been considerable effort in the production of drugs that act on specific growth factors to restrict their activity for combatting tumor growth. Specific growth factors increase the proliferation of tumors by angiogenesis, and blocking their pathways can help kill tumor cells.

 

Role in the Organ System

VEGF has a vital role in the abnormal growth of new blood vessels in the retina of the eye. This occurs in age-related macular degeneration and diabetic retinopathy, the macula being a minute portion in the central part of the retina, playing a role in detailed vision. Drugs such as ranibizumab are monoclonal antibodies that inhibit the activity of VEGF. Thus, they can be helpful in effectively stopping the progression of some types of diabetic retinopathy and macular degeneration.

 

 

Conclusion

Growth factors are proteinaceous components in our body that play a vital role in the growth and differentiation of cells from head to toe. However, abnormal function of some growth factors at inappropriate times and places in the body can lead to diseases and even cancer. Researchers undertook several studies to investigate the precise role of each growth factor, and further studies are ongoing to improve their understanding. This will help in the development of new drugs to help treat diseases and cancers.

 

 

 

References

1. Stone WL, Leavitt L, Varacallo M. Physiology, Growth Factor. [Updated 2021 May 7]. In: StatPearls [batemet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from:  https://www.ncbi.nlm.nih.gov/books/NBK442024/

2. Gio.  The Complete Guide To Growth Factors: Do They Work & Are They Safe? BB.  https://www.beautifulwithbrains.com/guide-to-growth-factors-skincare/

3. Encyclopaedia Britannica Editors. Growth Factors.  https://www.britannica.com/science/growth-factor

4. Anonymous. What are Growth Factors? (Growth Factor Definition) https://www.sinobiological.com/resource/cytokines/what-are-growth-factors

 

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