Growth Factors

Key Biological Properties: GH is a 191-amino acid, single-chain polypeptide . It stimulates protein synthesis, increases fat breakdown, and opposes the action of insulin . GH also stimulates the production of insulin-like growth factor 1 (IGF-1), which mediates many of its growth-promoting effects .

Expression Patterns and Tissue Distribution: GH is synthesized and secreted by somatotropic cells in the anterior pituitary gland . It is released in a pulsatile manner, with surges occurring after the onset of deep sleep . GH receptors are widely distributed in various tissues, including the liver, muscle, and bone .

Primary Biological Functions: GH stimulates the growth of essentially all tissues of the body, including bone . It plays a vital role in normal physical growth in children, with levels peaking during puberty . GH also promotes lipolysis, increases muscle mass, and enhances protein synthesis .

Role in Immune Responses and Pathogen Recognition: GH has been shown to stimulate immune function, although the exact mechanisms are not fully understood . It is believed to enhance the activity of immune cells and promote the production of cytokines .

Mechanisms with Other Molecules and Cells: GH exerts its effects by binding to the growth hormone receptor (GHR) on target cells . This binding activates the JAK-STAT signaling pathway, leading to the transcription of GH-responsive genes . GH also stimulates the production of IGF-1, which acts in an autocrine and paracrine manner to promote growth .

Binding Partners and Downstream Signaling Cascades: GH binds to GHR, which then associates with Janus kinase 2 (JAK2), leading to the phosphorylation of both GHR and JAK2 . This activation triggers downstream signaling cascades, including the MAPK and PI3K/AKT pathways .

Regulatory Mechanisms Controlling Expression and Activity: GH secretion is regulated by the hypothalamic hormones growth hormone-releasing hormone (GHRH) and somatostatin . GHRH stimulates GH release, while somatostatin inhibits it . Additionally, GH secretion is influenced by metabolic factors, such as glucose and lipid levels, and peripheral hormones like insulin .

Transcriptional Regulation and Post-Translational Modifications: GH gene expression is regulated by transcription factors, including Pit-1 . Post-translational modifications, such as phosphorylation, also play a role in modulating GH activity .

Biomedical Research: GH is used in research to study growth disorders and metabolic diseases . It is also employed in experiments to understand its role in cell growth and differentiation .

Diagnostic Tools: GH levels are measured to diagnose growth hormone deficiency (GHD) and acromegaly . GH stimulation tests and IGF-1 measurements are commonly used diagnostic tools .

Therapeutic Strategies: Recombinant human growth hormone (rhGH) is used to treat children with growth disorders and adults with GH deficiency . GH therapy has also been explored for its potential to enhance fertility and improve outcomes in assisted reproductive technologies .

Development: GH is essential for normal growth and development in children . It promotes the growth of bones and tissues, leading to increased height and muscle mass .

Aging and Disease: GH levels decline with age, which is associated with decreased muscle mass and increased fat accumulation . GH therapy has been investigated for its potential to counteract some of the effects of aging . Additionally, GH dysregulation is implicated in various diseases, including acromegaly and growth hormone deficiency .