The adrenal gland-specific proteome

The main function of the adrenal gland is to supply the body with two different sets of hormones, steroid hormones from the adrenal cortex and catecholamines from the adrenal medulla. The cortical steroid hormones are involved in metabolic function, electrolyte balance and have androgenic effects. Catecholamines are released in response to stress and their effect is mainly described as the flight-and-fight response. Transcriptome analysis shows that 68% (n=13755) of all human proteins (n=20162) are expressed in the adrenal gland and 226 of these genes show an elevated expression in the adrenal gland compared to other tissue types.

226 elevated genes
25 enriched genes
49 group enriched genes
Adrenal gland has most group enriched gene expression in common with brain

The adrenal gland transcriptome

Transcriptome analysis of the adrenal gland can be visualized with regard to the specificity and distribution of transcribed mRNA molecules (Figure 1). Specificity illustrates the number of genes with elevated or non-elevated expression in the adrenal gland compared to other tissues. Elevated expression includes three subcategory types of elevated expression:

Tissue enriched: At least four-fold higher mRNA level in adrenal gland compared to any other tissues.
Group enriched: At least four-fold higher average mRNA level in a group of 2-5 tissues compared to any other tissue.
Tissue enhanced: At least four-fold higher mRNA level in adrenal gland compared to the average level in all other tissues.

Distribution, on the other hand, visualizes how many genes have, or do not have, detectable levels (nTPM≥1) of transcribed mRNA molecules in the adrenal gland compared to other tissues. As evident in Table 1, all genes elevated in adrenal gland are categorized as:

Detected in single: Detected in a single tissue
Detected in some: Detected in more than one but less than one-third of tissues
Detected in many: Detected in at least a third but not all tissues
Detected in all: Detected in all tissues

A. Specificity

B. Distribution

Figure 1. (A) The distribution of all genes across the five categories based on transcript specificity in adrenal gland as well as in all other tissues. (B) The distribution of all genes across the six categories, based on transcript detection (nTPM≥1) in adrenal gland as well as in all other tissues.

As shown in Figure 1, 226 genes show some level of elevated expression in the adrenal gland compared to other tissues. The three categories of genes with elevated expression in adrenal gland compared to other organs are shown in Table 1. In Table 2, the 25 enriched genes are defined.

Table 1. The number of genes in the subdivided categories of elevated expression in adrenal gland.

		Distribution in the 36 tissues
		Detected in single	Detected in some	Detected in many	Detected in all	Total
Specificity	Tissue enriched	3	7	10	5	25
	Group enriched	0	28	19	2	49
	Tissue enhanced	3	38	72	39	152
	Total	6	73	101	46	226

Table 2. The 12 genes with the highest level of enriched expression in adrenal gland. "Tissue distribution" describes the transcript detection (nTPM≥1) in adrenal gland as well as in all other tissues. "mRNA (tissue)" shows the transcript level in adrenal gland as nTPM values. "Tissue specificity score (TS)" corresponds to the fold-change between the expression level in adrenal gland and the tissue with the second-highest expression level.

Gene	Description	Tissue distribution	mRNA (tissue)	Tissue specificity score
CYP11B2	cytochrome P450 family 11 subfamily B member 2	Detected in single	173.3	941
CYP11B1	cytochrome P450 family 11 subfamily B member 1	Detected in some	3571.8	834
CYP17A1	cytochrome P450 family 17 subfamily A member 1	Detected in many	7970.9	83
HSD3B2	hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 2	Detected in some	2106.0	56
GML	glycosylphosphatidylinositol anchored molecule like	Detected in some	187.3	56
CYP21A2	cytochrome P450 family 21 subfamily A member 2	Detected in many	1977.6	45
CCN3	cellular communication network factor 3	Detected in many	1072.3	44
MC2R	melanocortin 2 receptor	Detected in some	56.1	32
CYP11A1	cytochrome P450 family 11 subfamily A member 1	Detected in many	978.1	26
ADGRV1	adhesion G protein-coupled receptor V1	Detected in many	516.2	12
STAR	steroidogenic acute regulatory protein	Detected in many	4914.3	10
AKR1B1	aldo-keto reductase family 1 member B	Detected in all	2944.0	8

Protein expression of genes elevated in adrenal gland

In-depth analysis of the elevated genes in the adrenal gland using antibody-based protein profiling allowed us to visualize where these proteins are expressed with regards to localization in the adrenal cortex and adrenal medulla.

Proteins specifically expressed in the adrenal cortex

The hormones released from the adrenal cortex are vital to life. Glucocorticoids regulate the body's metabolic processes and stress response. Mineralocorticoids are involved in the control of electrolyte balance and blood pressure. Small amounts of sex hormones are also released from the adrenal gland but mainly produced in other organs (testis and ovaries).

One example is CYP11A1 which converts cholesterol to pregnenolone. CYP11A1 is also expressed in other steroid hormone-producing organs. HSD3B2 and STAR are also essential for all steroid hormone synthesis and therefore expressed in other steroid hormone-producing organs as well. However, these genes are expressed at much higher levels in the adrenal gland than in any other tissue, signifying in the adrenal cortex which is highly specialized in steroid hormone synthesis. Another example of a protein expressed in the adrenal gland is FDX1 which encodes an iron-sulfur protein involved in electron transfer.

Figure 2. Full section of an adrenal gland with immunohistochemical staining of the cortex using an antibody towards CYP11A1.

CYP11A1
HSD3B2

STAR
FDX1

Proteins specifically expressed in the adrenal medulla

The adrenal medulla is stimulated by preganglionic sympathetic neurons to release adrenalin and noradrenalin and has a rapid response to external and internal stress. The release of adrenalin and noradrenalin leads to increased heart rate increased blood pressure and increased blood flow to the muscles.

Proteins specific to the adrenal medulla are predominantly related to noradrenaline and adrenaline synthesis. Examples of these proteins are DBH and PNMT, both expressed in the medulla of the adrenal gland.

Figure 3. A full section of an adrenal gland with immunohistochemical staining of the medulla using an antibody towards DBH.

DBH
PNMT

Gene expression shared between adrenal gland and other tissues

There are 49 group enriched genes expressed in adrenal gland. Group enriched genes are defined as genes showing a 4-fold higher average level of mRNA expression in a group of 2-5 tissues, including adrenal gland, compared to all other tissues.

To illustrate the relation of adrenal gland tissue to other tissue types, a network plot was generated, displaying the number of genes with a shared expression between different tissue types.

Figure 2. An interactive network plot of the adrenal gland enriched and group enriched genes connected to their respective enriched tissues (grey circles). Red nodes represent the number of adrenal gland enriched genes and orange nodes represent the number of genes that are group enriched. The sizes of the red and orange nodes are related to the number of genes displayed within the node. Each node is clickable and results in a list of all enriched genes connected to the highlighted edges. The network is limited to group enriched genes in combinations of up to 3 tissues, but the resulting lists show the complete set of group enriched genes in the particular tissue.

The adrenal gland mainly shares group enriched gene expression with brain (n=9). Two examples of such genes are proenkephalin (PENK) and secretogranin II (SCG2). PENK is a hormone that plays a role in a number of functions including pain perception and responses to stress. SCG2 is involved in the biogenesis of secretory vesicle by the suggested mechanism of packaging or sorting peptide hormones and neuropeptides into secretory vesicles.

PENK - adrenal gland
PENK - caudate

SCG2 - adrenal gland
SCG2 - cerebral cortex

Proteins analyzed in extended samples of adrenal gland

The standard setup in the Tissue Atlas is based on Tissue Microarray technique (TMA), thus saving valuable tissue material as well as reagents and providing a wide tissue representation for protein profiling. However, due to the complex nature of the adrenal gland, with different layers, a larger tissue sample is required to fully understand protein localization. The full list of genes used for protein profiling on extended samples of the adrenal gland is defined in Table 3.

Table 3. Following 59 genes have been analyzed in extended samples of adrenal gland.

Gene	Gene description	Staining pattern
AGRP	Agouti related neuropeptide	Cytoplasmic staining in adrenal medulla.
AKR1B1	Aldo-keto reductase family 1 member B	Adrenal cortex showed strong nuclear and cytoplasmic positivity. Cells in adrenal medulla were negative.
ARHGAP36	Rho GTPase activating protein 36	Strong in a subset of cells in medulla.
AS3MT	Arsenite methyltransferase	Strong cytoplasmic and nuclear positivity was observed in cells in adrenal cortex. Medullary cells were negative.
CALY	Calcyon neuron specific vesicular protein	Strong granular positivity was observed in ganlion cells in adrenal gland. Cortical and medullary cells were negative.
CARTPT	CART prepropeptide	Strong cytoplasmic positivity was displayed in adrenal medulla. Cells in adrenal cortex were negative.
CCN3	Cellular communication network factor 3	Strong cytoplasmic positivity was displayed in cells in zona glomerulosa and fractions of cells in zona fasciculata. Cells in zona reticularis and medullary cells were negative.
CHGB	Chromogranin B	Strong cytoplasmic poitivity was observed in adrenal medulla. Cortical cells were negative.
CPLX1	Complexin 1	Strong cytoplasmic and nucelar staining in adrenal medulla
CPLX2	Complexin 2	Strong cytoplasmic and nucelar staining in adrenal medulla
CYP11A1	Cytochrome P450 family 11 subfamily A member 1	Strong cytoplasmic positivity was displayed in adrenal cortex.
CYP11B1	Cytochrome P450 family 11 subfamily B member 1	Strong cytoplasmic positivity was displayed in adrenal cortex.
CYP11B2	Cytochrome P450 family 11 subfamily B member 2	Strong cytoplasmic positivity was displayed in adrenal cortex.
CYP17A1	Cytochrome P450 family 17 subfamily A member 1	Strong cytoplasmic positvity was observed in adrenal cortex. Adrenal medulla was negative.
CYP21A2	Cytochrome P450 family 21 subfamily A member 2	Strong cytoplasmic positivity was observed in adrenal cortex. Adrenal medulla was negative.
DBH	Dopamine beta-hydroxylase	Strong cytoplasmic positivity was observed in adrenal medulla.
DLK1	Delta like non-canonical Notch ligand 1	Cytoplasmic and membranous staining in most adrenal zones, not zona reticularis.
DPYSL2	Dihydropyrimidinase like 2	Strong to moderate cytoplasmic staining in adrenal cortex.
ELAVL4	ELAV like RNA binding protein 4	Strong nuclear positivity was observed in adrenal medulla. Adrenal cortex was negative.
ELOVL5	ELOVL fatty acid elongase 5	Strong granular cytoplasmic positivity was observed in adrenal cortex. Adrenal medulla showed moderate nuclear staining.
ESR2	Estrogen receptor 2	Cytoplasmic and/or nuclear staining in adrenal gland.
FDX1	Ferredoxin 1	Strong cytoplasmic positivity was displayed in adrenal cortical cells. Medullary cells were negative.
FDXR	Ferredoxin reductase	Strong cytoplasmic staining with a granular pattern was displayed in cells in adrenal cortex. Medullary cells were negative.
FGF11	Fibroblast growth factor 11	Strong cytoplasmic staining was observed in cells in zona reticularis. Cells in zona fasciculata and glomerulosa were weakly stained. Medullary cells were negative.
HCN4	Hyperpolarization activated cyclic nucleotide gated potassium channel 4	Moderate in adrenal medulla.
HSD3B1	Hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1	Strong cytoplasmic positivity was observed in zona glomerulosa and fasciculata. Cells in zona reticularis and medullary cells were negative.
HSD3B2	Hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 2	Strong cytoplasmic positivity was observed in zona glomerulosa and fasciculata. Cells in zona reticularis and medullary cells were negative.
HTR4	5-hydroxytryptamine receptor 4	Strong cytoplasmic positivity in adrenal medulla.
MC2R	Melanocortin 2 receptor	Strong cytoplasmic positivity in subset of cells in adrenal medulla.
MGARP	Mitochondria localized glutamic acid rich protein	Strong cytoplasmic positivity with a granular pattern was observed in adrenal cotex. Adrenal medulla was negative.
NPTX2	Neuronal pentraxin 2	Strong cytoplasmic positivity in a subset of medullary cells. Cortical cells were negative.
NRIP3	Nuclear receptor interacting protein 3	Cytoplasmic staining in adrenal cortex.
PCSK1N	Proprotein convertase subtilisin/kexin type 1 inhibitor	Cytoplasmic staining of varying intensity was observed in cells in adrenal medulla. Cortical cells were negative.
PCSK2	Proprotein convertase subtilisin/kexin type 2	Strong cytoplasmic positivity was displayed in adrenal medulla. Adrenal cortex was negative.
PENK	Proenkephalin	A majority of cells in adrenal medulla showed moderate to strong cytoplasmic staining. Adrenal cortex was negative.
PHOX2A	Paired like homeobox 2A	Strong nuclear positivity was observed in cells in adrenal medulla. Cortical cells were negative.
PHOX2B	Paired like homeobox 2B	Nuclear staining in adrenal medulla.
PNMT	Phenylethanolamine N-methyltransferase	Strong cytoplasmic positivity was observed in adrenal medulla. Adrenal cortex was negative.
PRPH	Peripherin	Strong cytoplasmic staining in ganglion in adrenal medulla and nervendings.
PTPRN	Protein tyrosine phosphatase receptor type N	Strong cytoplasmic positivity was displayed in cells in adrenal medulla. Cortical cells were negative.
PTPRN2	Protein tyrosine phosphatase receptor type N2	Strong cytoplasmic staining in adrenal medulla.
QPCT	Glutaminyl-peptide cyclotransferase	Moderate cytoplasmic positivity was observed in adrenal medulla. Adrenal cortex was negative.
REEP6	Receptor accessory protein 6	Cytoplasmic staining in adrenal gland.
RGN	Regucalcin	Strong cytoplasmic, nuclear and membranous positivity was observed in adrenal cortex.
RIMS2	Regulating synaptic membrane exocytosis 2	Strong granulated cytoplasmic positivity was observed in adrenal cortex. Adrenal medulla was negative.
SCARB1	Scavenger receptor class B member 1	Strong membranous positivity was observed in cells in adrenal cortex. Medullary cells were negative.
SCG2	Secretogranin II	Strong cytoplasmic positivity was displayed in cells in adrenal medulla. Cortical cells were negative.
SLC18A1	Solute carrier family 18 member A1	Moderate cytoplasmic positivity was observed in adrenal medulla. Adrenal cortex was negative.
SLC18A2	Solute carrier family 18 member A2	Strong cytoplasmic positivity was observed in adrenal medulla. Cells in adrenal cortex were negative.
SLC35G2	Solute carrier family 35 member G2	Morderate cytoplasmic staining in certain cells in zona reticularis.
SLC6A2	Solute carrier family 6 member 2	Ganglion cells showed granular cytoplasmic positivity in adrenal medulla. Cortical and medullary cells were negative.
SOAT1	Sterol O-acyltransferase 1	Strong cytoplasmic positivity was displayed in cells in adrenal cortex. Adrenal medulla was negative.
SPTBN4	Spectrin beta, non-erythrocytic 4	Moderate cytoplasmic positivity was observed in cells in adrenal medulla. Cells in adrenal cortex were negative.
SST	Somatostatin	Strong cytoplasmic positivity was observed in a subset of cells in adrenal medulla. Cortical cells were negative.
STAR	Steroidogenic acute regulatory protein	Strong cytoplasmic positivity was observed in cells in adrenal cortex. Medullary cells are negative.
TH	Tyrosine hydroxylase	Strong cytoplasmic positivity was displyed in adrenal medulla. Cells in adrenal cortex were negative.
VAT1L	Vesicle amine transport 1 like	Staining in zona glomerulosa and medulla.
VGF	VGF nerve growth factor inducible	Strong cytoplasmic positivity was observed in adrenal medulla. A subset of cells in zona reticularis showed moderate positivity. Remaining cortical cells were mainly negative.
ZBTB8B	Zinc finger and BTB domain containing 8B	Moderate cytoplasmic positivity was displayed in cells in adrenal medulla. Adrenal cortex was negative.
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Adrenal gland function

The paired endocrine adrenal glands are located on top of the kidneys. Each gland is divided into two distinct parts, a centrally located adrenal medulla and an outer adrenal cortex. These two different parts are derived from different embryological layers, the medulla from the ectoderm and the cortex from the mesoderm.

The adrenal cortex secretes three groups of corticosteroid hormones: mineralocorticoids, glucocorticoids, and sex hormones. The principal mineralocorticoid is aldosterone, which is involved in controlling normal electrolyte balance and blood pressure. The principal glucocorticoid is cortisol, a hormone that is essential for normal metabolic function. The adrenal sex hormones have primarily an androgenic effect, two examples are dehydroepiandrosterone (DHEA) and androstenedione.

Adrenal gland histology

The adrenal glands are small endocrine glands with triangular to semilunar shapes. They are located right on top of the kidneys and are enveloped by a fibrous capsule surrounded by adipose tissue. Each gland has two parts, the adrenal cortex and the adrenal medulla. The adrenal gland has a rich blood supply and nervous innervation, for the rapid release of hormones into the bloodstream.

The outermost adrenal cortex secretes corticosteroids and sex hormones and consists of three layers, namely zona glomerulosa, zona fasciculata and zona reticularis. Microscopically the three layers can be easily distinguished from each other, looking at the cell's shapes and orientation. The outermost zona glomerulosa produces mineralocorticoids, the middle zona fasciculata produces glucocorticoids, and the inner zona reticularis produce sex hormones and some glucocorticoids.

The histology of human adrenal gland including detailed images and information can be viewed in the Protein Atlas Histology Dictionary.

Background

Here, the protein-coding genes expressed in adrenal gland are described and characterized, together with examples of immunohistochemically stained tissue sections that visualize corresponding protein expression patterns of genes with elevated expression in adrenal gland.

Transcript profiling was based on a combination of two transcriptomics datasets (HPA and GTEx), corresponding to a total of 14590 samples from 50 different human normal tissue types. The final consensus normalized expression (nTPM) value for each tissue type was used for the classification of all genes according to the tissue-specific expression into two different categories, based on specificity or distribution.

Relevant links and publications

Uhlén M et al., Tissue-based map of the human proteome. Science (2015)
PubMed: 25613900 DOI: 10.1126/science.1260419

Fagerberg L et al., Analysis of the human tissue-specific expression by genome-wide integration of transcriptomics and antibody-based proteomics. Mol Cell Proteomics. (2014)
PubMed: 24309898 DOI: 10.1074/mcp.M113.035600

Bergman J et al., The human adrenal gland proteome defined by transcriptomics and antibody-based profiling. Endocrinology. (2016)
PubMed: 27901589 DOI: 10.1210/en.2016-1758

Histology dictionary - the adrenal gland

Symptoms and causes of endocrine disorders and how they can be treated.