Located on top of the kidneys like two tiny caps, the adrenal glands play a fundamental role in the endocrine system. We have previously described the human adrenal gland proteome and now it is time to shed light on proteins specific for the medullary compartment of the adrenal gland. These proteins are essential for the synthesis of two major stress coping hormones - adrenaline and noradrenaline.

The adrenal medulla represents the inner layer of the adrenal gland and is surrounded by the adrenal cortex. Unlike the cortex, the medulla originates from neural crest cells, resulting in a more neuronal-like way of functioning. While the cortex mainly signals through the Hypothalamic-pituitary-adrenal axis, the medulla responds through sympathetic innervations by releasing the catecholamines adrenaline and noradrenaline. These hormones increase the heart rate and respiration, and induces glucose synthesis in the liver - altogether known as the "fight-or-flight" response.

The chromaffin cells of the medulla are the major sources of adrenaline and noradrenaline. The starting material is the amino acid tyrosine, which is enzymatically converted through several reactions to either adrenaline, noradrenaline or dopamine. Many of the proteins involved in this pathway are specific to the medulla.

The image shows immunohistological staining of three medullary proteins involved in catecholamine synthesis. Most group enriched genes expressed in the adrenal medulla share an elevated expression with the brain. TH catalyzes the first rate-limiting step of the catecholamine synthesis by conversion of tyrosine to dopamine, and is also found in substantia nigra. Tissue enriched genes include DBH, which converts dopamine to noradrenaline, and PNMT, which catalyzes the last step in the formation of adrenaline from noradrenaline.

43 genes have been analyzed using full section tissue samples of the adrenal gland. Check them out here!

Charlotte Soläng