Editing Insulin-like growth factor (section)

== IGF1/GH axis ==

The IGF "axis" is also commonly referred to as the Growth Hormone/IGF-1 Axis. [[Insulin-like growth factor 1]] (commonly referred to as IGF-1 or at times using [[Roman numerals]] as IGF-I) is mainly secreted by the liver as a result of stimulation by [[growth hormone]] (GH). IGF-1 is important for both the regulation of normal physiology, as well as a number of pathological states, including [[cancer]]. The IGF axis has been shown to play roles in the promotion of [[cell proliferation]] and the inhibition of [[cell death]] ([[apoptosis]]). 

[[Insulin-like growth factor 2]] (IGF-2, at times IGF-II) is thought to be a primary [[growth factor]] required for early development while [[IGF-1]] expression is required for achieving maximal growth. [[Gene knockout]] studies in mice have confirmed this, though other animals are likely to regulate the expression of these genes in distinct ways. While IGF-2 may be primarily [[fetus|fetal]] in action it is also essential for development and function of organs such as the [[brain]], [[liver]], and [[kidney]].<ref>{{cite journal|last1=Younis|first1=Shady|date=February 27, 2018|title=The ZBED6–IGF2 axis has a major effect on growth of skeletal muscle and internal organs in placental mammals|journal=PNAS|volume=9|issue=115|pages=E2048–E2057|doi=10.1073/pnas.1719278115|pmid=29440408|pmc=5834713|bibcode=2018PNAS..115E2048Y |doi-access=free}}</ref>

Factors that are thought to cause variation in the levels of GH and IGF-1 in the circulation include an individual's genetic make-up, the time of day, age, sex, exercise status, stress levels, nutrition level, [[body mass index]] (BMI), disease state, race, estrogen status, and [[xenobiotic]] intake.<ref>{{cite journal | vauthors = Takahashi Y, Kipnis DM, Daughaday WH | title = Growth hormone secretion during sleep | journal = The Journal of Clinical Investigation | volume = 47 | issue = 9 | pages = 2079–90 | date = September 1968 | pmid = 5675428 | pmc = 297368 | doi = 10.1172/JCI105893 }}</ref><ref>{{cite journal | vauthors = Giustina A, Mazziotti G, Canalis E | title = Growth hormone, insulin-like growth factors, and the skeleton | journal = Endocrine Reviews | volume = 29 | issue = 5 | pages = 535–59 | date = August 2008 | pmid = 18436706 | pmc = 2726838 | doi = 10.1210/er.2007-0036 }}</ref><ref>{{cite journal | vauthors = Sutton J, Lazarus L | title = Growth hormone in exercise: comparison of physiological and pharmacological stimuli | journal = Journal of Applied Physiology | volume = 41 | issue = 4 | pages = 523–7 | date = October 1976 | pmid = 985395 | doi = 10.1152/jappl.1976.41.4.523 }}</ref>

IGF-1 has an involvement in regulating [[neural development]] including [[neurogenesis]], [[myelination]], [[synaptogenesis]], and [[Dendrite|dendritic]] branching and [[neuroprotection]] after neuronal damage. Increased serum levels of IGF-I in children have been associated with higher [[IQ]].<ref>{{cite journal | vauthors = Gunnell D, Miller LL, Rogers I, Holly JM | title = Association of insulin-like growth factor I and insulin-like growth factor-binding protein-3 with intelligence quotient among 8- to 9-year-old children in the Avon Longitudinal Study of Parents and Children | journal = Pediatrics | volume = 116 | issue = 5 | pages = e681-6 | date = November 2005 | pmid = 16263982 | doi = 10.1542/peds.2004-2390 | doi-access =  }}</ref>

IGF-1 shapes the development of the [[cochlea]] through controlling [[apoptosis]]. Its deficit can cause [[hearing (sense)|hearing]] loss. Serum level of it also underlies a correlation between short [[human height|height]] and reduced hearing abilities particularly around 3–5 years of age, and at age 18 (late [[puberty]]).<ref>{{cite journal | vauthors = Welch D, Dawes PJ | title = Childhood hearing is associated with growth rates in infancy and adolescence | journal = Pediatric Research | volume = 62 | issue = 4 | pages = 495–8 | date = October 2007 | pmid = 17667854 | doi = 10.1203/PDR.0b013e3181425869 | doi-access = free }}</ref>