Insulin-like Growth Factor 1 (IGF-1) is a protein that plays a role in cellular growth, differentiation, and survival. It functions as a signaling molecule throughout the body. IGF-1 is similar in structure to insulin and contributes to various biological processes. Its signaling pathways influence numerous physiological processes and may have implications for various health conditions.
What is IGF-1
IGF-1, also known as somatomedin C, is a polypeptide hormone primarily produced in the liver. Its production is stimulated by Growth Hormone (GH) released from the pituitary gland. Other tissues, including cartilage, also produce it, where it can act locally.
IGF-1 is a small peptide composed of 70 amino acids. Its structure includes an A chain and a B chain connected by disulfide bonds, along with a C peptide region of 12 amino acids. This structural similarity to insulin allows IGF-1 to bind, albeit with lower affinity, to the insulin receptor. It circulates in the bloodstream, often bound to specific IGF binding proteins (IGFBPs), which help stabilize it and extend its presence in the blood.
How IGF-1 Functions
IGF-1 exerts its effects by binding to specific receptors on the surface of cells, primarily the IGF-1 receptor (IGF-1R). This receptor is a transmembrane tyrosine kinase protein. When IGF-1 binds to IGF-1R, it triggers a process called autophosphorylation, which activates the receptor.
Activated IGF-1R then initiates intracellular signaling pathways, notably the phosphoinositide-3 kinase (PI3K)/Akt pathway and the mitogen-activated protein kinase (MAPK) pathway. These pathways transmit signals to the cell nucleus, influencing processes such as cell proliferation, differentiation, and the inhibition of cell death.
The activity and availability of IGF-1 are regulated by IGF binding proteins (IGFBPs). These proteins bind to IGF-1 in the blood and extracellular fluids, modulating its access to cell surface receptors. IGFBPs can either inhibit or enhance IGF-1’s interaction with its receptor. They also prolong IGF-1’s half-life in circulation, enabling its transport throughout the body.
IGF-1’s Role in Body Processes
IGF-1 has widespread effects on various bodily functions, playing a role in growth, development, and tissue maintenance. During childhood, it is particularly involved in linear growth and bone development. It works in conjunction with Growth Hormone to promote the growth of many cell types, including those in muscle, cartilage, and bone.
In skeletal muscle, IGF-1 supports myoblast proliferation, differentiation, and fiber formation, contributing to muscle mass and strength. It also plays a part in muscle regeneration following injury and helps prevent muscle atrophy. For bone, IGF-1 stimulates the survival, proliferation, differentiation, and matrix production of osteoblast cells, which are responsible for bone formation.
Beyond growth, IGF-1 is involved in metabolic regulation. It influences glucose and fat metabolism, promoting protein synthesis and glucose uptake. IGF-1 also contributes to general tissue repair and cell survival throughout the body.
IGF-1 and Health Conditions
The relationship between IGF-1 levels and various health conditions is complex, with both elevated and reduced levels potentially contributing to disease. High levels of IGF-1 have been associated with an increased risk for certain cancers, including breast, prostate, and colon cancer. IGF-1 can promote the proliferation and survival of cancer cells, and it may also enhance their spread.
IGF-1 also plays a role in metabolic disorders. Altered IGF-1 signaling has been linked to conditions such as insulin resistance and type 2 diabetes. In obesity, the IGF-1 system can be dysregulated, potentially leading to increased levels of free IGF-1.
The hormone’s influence extends to the aging process. While IGF-1 is important for growth in youth, persistently high levels in adulthood may contribute to aging and age-related diseases. Conversely, reduced IGF-1 activity has been associated with extended longevity in some studies, suggesting a delicate balance for optimal health.
Influences on IGF-1 Levels
Growth Hormone (GH) is the primary regulator of IGF-1 production, stimulating the liver to synthesize and release IGF-1 into the bloodstream. The pulsatile secretion of GH, which is highest during puberty, directly influences IGF-1 levels.
Several other factors also affect IGF-1 concentrations. Nutrition, especially protein intake, can influence IGF-1 levels. Age is another determinant; IGF-1 levels increase throughout childhood, peak during puberty, and then decline with advancing age.
Body mass index (BMI), overall health status, and lifestyle factors like exercise and sleep can also impact IGF-1 levels. These diverse influences highlight the integrated nature of IGF-1 regulation within the body’s broader physiological systems.