What is the blood-testis barrier?

The blood-testis barrier is a highly selective permeability barrier formed by Sertoli cells located between the capillaries and the seminiferous tubules of the testes. It is also known as Sertoli cell barrier or SCB for short. Sertoli cell barrier. It is present in male individuals of the human species and other mammals.

Sertoli cells

Sertoli cells, or Sertoli pilasters, are specialized endothelial cells found in the seminiferous tubules. They establish intercellular junctions between them to form the blood-testis barrier, a barrier that isolates the germ cells that are in the lumen of the seminiferous tubules and allows control of the microenvironment in which they mature to form sperm, providing structural and metabolic support to spermatogenesis.

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Scheme of Sertoli cells Histological section of the testicular parenchyma of a wild boar

Sertoli cells are stimulated by follicle stimulating hormone (FSH) and also secrete substances that regulate spermatogenesis and reproductive development at some stages of life:

Anti-Mullerian Hormone (AMH): Secreted during the early stages of development of a male fetus. inhibits the development of the Müllerian ducts until it disappears. In female fetuses, Müller’s ducts will give rise to the uterus, cervix, fallopian tubes, and upper vagina. inhibin and activin: activin increases the synthesis and secretion of FSH; inhibin decreases it. Activin is also involved in cell proliferation and differentiation, promoting the proliferation and differentiation of germ cells in sperm. Both substances are secreted by other tissues and also in women. Androgen binding protein (ABP, androgen binding protein): binds to testosterone to increase its concentration in the seminiferous tubules and stimulate spermiogenesis (maturation of spermatids in spermatozoa). Estradiol: Stimulates and maintains spermatogenesis. glial cell-derived neurotrophic factor (GDNF, Neurotrophic factor derived from glial cell lineage): Transcription factor MRE Transferrin
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blood-testis barrier

The hamatotesticular barrier formed by intercellular junctions between Sertoli cells. Intercellular junctions can be classified into three types, and all three commonly occur in this and other types of blood barriers, such as the blood-brain barrier or the blood-intestinal barrier. The three types of joints are:

junction occlusion: these junctions, also called zonula occludens, are formed by a protein structure, especially claudin and occludin-like proteins, which bring the lipid membranes of adjacent cells together and prevent the free flow of substances between the basolateral part and the apical part of the endothelium cells. Adherent joints: also called adherent zonules or banded desmosomes, they are unions between cells that appear mainly in the basolateral part and that are formed by cadherins and caterins. The union between the two cells occurs through the union of the ends of the transmembrane cadherin. At the intracytoplasmic end, cadherins bind to catherins and the latter to F-actin, which is abundant in the cytoplasm of the adherent zonule. opening joints: They are also called nexus or gap junctions and are intercellular connections that occur in many types of cells, for example, in neurons they appear at so-called electrical synapses. They are formed by channels of connexin proteins that communicate the cytoplasm of two adjacent cells and allow the passage of some molecules, ions and electrical impulses.

Through these junctions between Sertoli cells, a barrier is formed that separates the interstitial space of blood capillaries and the lumen of the seminiferous tubules where spermatogenesis occurs.

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Schematic of intercellular tight junctions Schematic of intercellular adherent junctions Diagram of intercellular gap junctions
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Occupation

The presence of the blood-testis barrier allows Sertoli cells to influence the chemical composition of the lumen of the seminiferous tubules and to control the environment in which spermatogenesis occurs. The fluid in the lumen of the seminiferous tubules is rich in androgens, estrogens, inositol, glutamic acid, and aspartic acid and, unlike plasma, is low in protein and glucose.

The blood-testis barrier also prevents the passage of cytotoxic substances transported in the blood so that they do not interfere with the formation of sperm. At the same time, the barrier prevents germ cell antigens from entering the circulation and triggering an autoimmune response.

medical implications

When the continuity of the blood-testis barrier is broken in some way, sperm and germ cell antigens can trigger an autoimmune response. This situation can occur for a variety of reasons, including trauma, and is the cause of male infertility. Antibodies produced by the immune system can bind to sperm and decrease its mobility or ability to fertilize.

Some substances can cross the blood-testis barrier, e.g. steroid substances, and can also be affected by endocrine disruptors, such as lead or cadmium, and by some diseases, e.g. liver cirrhosis,

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