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 72% (n=14181) of all human proteins (n=19670) are expressed in the adrenal gland and 228 of these genes show an elevated expression in adrenal gland compared to other tissue types.

  • 228 elevated genes
  • 9 enriched genes
  • 84 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 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 that have, or do not have, detectable levels (NX≥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 (NX≥1) in adrenal gland as well as in all other tissues.


As shown in Figure 1, 228 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 9 enriched genes are defined.

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

Distribution in the 37 tissues
Detected in singleDetected in someDetected in manyDetected in all Total
Specificity
Tissue enriched 2421 9
Group enriched 039441 84
Tissue enhanced 2416131 135
Total 48410733 228

Table 2. The 9 genes with enriched expression in adrenal gland. "Tissue distribution" describes the transcript detection (NX≥1) in adrenal gland as well as in all other tissues. "mRNA (tissue)" shows the transcript level in adrenal gland as NX values. "Tissue specificity score (TS)" corresponds to the fold-change between the expression level in adrenal gland and the tissue with second highest expression level.

Gene Description Tissue distribution mRNA (tissue) Tissue specificity score
CYP11B1 cytochrome P450 family 11 subfamily B member 1 Detected in single 224.9 781
CYP11B2 cytochrome P450 family 11 subfamily B member 2 Detected in single 51.3 259
CYP21A2 cytochrome P450 family 21 subfamily A member 2 Detected in some 170.9 23
GML glycosylphosphatidylinositol anchored molecule like Detected in some 68.3 10
NOV nephroblastoma overexpressed Detected in many 236.7 8
KCNK2 potassium two pore domain channel subfamily K member 2 Detected in many 49.1 6
CYP17A1 cytochrome P450 family 17 subfamily A member 1 Detected in some 425.4 5
HSD3B2 hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 2 Detected in some 223.2 5
BABAM2 BRISC and BRCA1 A complex member 2 Detected in all 172.1 4


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 response to stress. Mineralocorticoids are involved in 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 adrenal gland.


Figure 3. 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 84 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.

In order to illustrate the relation of adrenal gland tissue to other tissue types, a network plot was generated, displaying the number of genes with 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 4 tissues, but the resulting lists show the complete set of group enriched genes in the particular tissue.


Adrenal gland mainly shares group enriched gene expression with brain (n= 19). Two examples of such genes are Proenkephalin (PENK) and CART prepropeptide (CARTPT). PENK is a hormone which plays a role in a number of functions including pain perception and responses to stress. CARTPT is a anorectic peptide that plays a role in appetite, by inhibiting both normal and starvation-induced feeding. Also, PENK regulates the energy balance, maintenance of body weight, addiction, and the stress response and is closely associated with the actions of leptin and neuropeptide Y.


PENK - adrenal gland

PENK - caudate


CARTPT - adrenal gland

CARTPT - hypothalamus


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 provides a wide tissue representation for protein profiling. However, due to the complex nature of 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 adrenal gland is defined in Table 3.

Table 3. Following 56 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.
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.
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.
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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 androgenic effect, two examples are dehydroepiandrosterone (DHEA) and androstenedione.


Adrenal gland histology

The adrenal glands are small endocrine glands with triangular to semilunar shape. 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 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 three transcriptomics datasets (HPA, GTEx and FANTOM5, corresponding to a total of 483 samples from 37 different human normal tissue types. The final consensus normalized expression (NX) value for each tissue type was used for 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, 2015. Tissue-based map of the human proteome. Science
PubMed: 25613900 DOI: 10.1126/science.1260419

Yu NY et al, 2015. Complementing tissue characterization by integrating transcriptome profiling from the Human Protein Atlas and from the FANTOM5 consortium. Nucleic Acids Res.
PubMed: 26117540 DOI: 10.1093/nar/gkv608

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

Bergman J et al, 2016. The human adrenal gland proteome defined by transcriptomics and antibody-based profiling. Endocrinology.
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.