Sertoli cells are highly specialized cells within the male testes. Often referred to as “nurse cells,” they provide the necessary physical and nutritional support for developing sperm cells. Their functions include structural support, immunological protection, and hormonal signaling, all required for the production of viable sperm. Proper function of these cells is directly linked to male fertility and reproductive health.
Defining the Sertoli Cell and Location
Sertoli cells reside exclusively within the seminiferous tubules, the microscopic structures inside the testes where sperm production (spermatogenesis) occurs. They are somatic cells, meaning they are not the germ cells that become sperm, but they interact intimately with every stage of germ cell development. The Sertoli cell is large and columnar, extending from the tubule’s basement membrane to its central lumen.
These cells possess a complex shape, with their cytoplasm forming deep pockets that surround the developing germ cells. This extensive cellular contact allows them to provide essential nutrients, growth factors, and structural guidance to the sperm precursors. Sertoli cells are identified by their position attached to the basal lamina. The number of Sertoli cells established during development determines the maximum sperm-producing capacity of the adult testes.
The Role of the Blood-Testis Barrier
A primary structural function of the Sertoli cell is the formation of the Blood-Testis Barrier (BTB). This barrier is created by continuous tight junctions linking neighboring Sertoli cells near the base of the seminiferous tubule. This complex divides the tubule’s interior into two distinct environments: the basal compartment (closer to the blood supply) and the adluminal compartment, where later stages of sperm development occur.
The BTB serves an immunological purpose by isolating developing sperm cells from the body’s immune system. As germ cells undergo meiosis, they acquire unique surface proteins that the immune system would recognize as foreign. By sequestering these post-meiotic cells, the barrier prevents a harmful autoimmune response. The barrier also creates a specialized chemical microenvironment by controlling the passage of substances, ensuring the optimal concentration of ions, hormones, and nutrients required for spermatogenesis.
Hormonal Regulation and Signaling
Sertoli cells respond to external hormonal signals and produce internal signals that regulate sperm production. They express receptors for Follicle-Stimulating Hormone (FSH), which stimulates their supportive functions in adulthood. These cells also respond to high local concentrations of Testosterone, produced by adjacent Leydig cells, which acts synergistically with FSH to drive spermatogenesis.
Sertoli cells secrete Androgen-Binding Protein (ABP), which binds to testosterone and maintains the high intratesticular concentration required for sperm maturation. They also produce Anti-Müllerian Hormone (AMH) and Inhibin B. During fetal development, AMH is responsible for the regression of the Müllerian ducts, preventing the formation of female reproductive organs.
In adult males, Inhibin B provides a negative feedback loop to the pituitary gland. When sperm production is progressing well, Sertoli cells release Inhibin B, suppressing the release of FSH and modulating the rate of spermatogenesis. AMH remains a useful clinical marker for Sertoli cell function across the lifespan, though its production is suppressed by testosterone after puberty.
Clinical Implications of Dysfunction
Impairment of Sertoli cell function is a common cause of male infertility and can lead to specific pathological conditions. A severe form of reproductive failure is Sertoli Cell Only Syndrome (SCOS). This condition is defined by the complete absence of germ cells within the seminiferous tubules, leaving only the Sertoli cells lining the walls.
SCOS results in azoospermia, the complete lack of sperm in the semen, and is a significant cause of nonobstructive infertility. Potential causes include genetic deletions on the Y-chromosome, exposure to radiation, or certain environmental toxins. The failure of Sertoli cells to support or protect the germ cells can also contribute to the development of testicular tumors.
The Blood-Testis Barrier can be compromised by exposure to environmental factors, such as chemicals or drugs, which affect Sertoli cell tight junctions. This breach can expose developing sperm to harmful circulating substances or trigger an autoimmune response, leading to impaired fertility.