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 singleDetected in someDetected in manyDetected in all Total
Specificity
Tissue enriched 37105 25
Group enriched 028192 49
Tissue enhanced 3387239 152
Total 67310146 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.
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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.