Sertoli Cells: Their Function and Role in Male Fertility

Sertoli cells are the structural and metabolic backbone of sperm production. Found inside the seminiferous tubules of the testis, they physically cradle developing sperm cells from their earliest stem-cell stage through to release, feeding them, shielding them from the immune system, and coordinating signals that decide whether they multiply, mature, or die. Without functional Sertoli cells, spermatogenesis simply does not happen, and the total number of Sertoli cells a man has effectively caps how much sperm he can ever produce.

Where Sertoli Cells Come From

Sertoli cells are among the first cell types to differentiate in the developing testis. Their appearance is triggered by the SRY gene on the Y chromosome, the so-called testis-determining factor. SRY kicks off a cascade of gene activity that pushes undifferentiated gonadal cells toward a Sertoli cell fate, which in turn drives the entire gonad toward becoming a testis rather than an ovary.¹ A whole roster of genes has to switch on at the right time and place during this process, including WT1, GATA4, SOX9, and AMH. When any of these go awry, the result can range from ambiguous gonadal development to outright infertility later in life.²

Once established, embryonic Sertoli cells produce anti-Müllerian hormone (AMH), which causes the female reproductive ducts to regress. They also organize the other testicular cell types around them, essentially acting as architects of the fetal testis. By the time a boy is born, his Sertoli cells are already at work, though full maturation continues through childhood and into puberty.

Why Sertoli Cell Number Matters So Much

Each Sertoli cell can only support a limited number of developing germ cells at any given time. In humans, that ratio is strikingly low compared to other animals. A single human Sertoli cell supports roughly three spermatids, whereas in fish the same cell type can nurse over a hundred.³ Because of this constraint, the total number of Sertoli cells in a man’s testes sets the upper limit of his sperm output.⁴ Anything that shrinks the Sertoli cell population during development or puberty, whether illness, hormonal disruption, or environmental exposure, can permanently reduce fertility potential.

Sertoli cells proliferate mainly during fetal life and again around puberty. After puberty, they stop dividing and become terminally differentiated, meaning that the number you end up with is more or less fixed for life. This is why events during childhood, such as cryptorchidism (undescended testes) or certain hormonal conditions, can have lasting reproductive consequences even if corrected later.

The Blood-Testis Barrier

One of the most unusual things Sertoli cells do is build the blood-testis barrier, a physical wall of tight junctions between adjacent Sertoli cells that divides the seminiferous tubule into two compartments. The basal compartment sits near the outer edge of the tubule, where early-stage germ cells (spermatogonia) reside. The adluminal compartment is closer to the center, where germ cells undergo meiosis and transform into spermatids. The barrier keeps immune cells and antibodies out of that inner compartment, which is critical because developing sperm cells carry surface proteins the immune system has never seen and would otherwise attack.

Getting germ cells across this barrier without breaking it is an engineering feat. As preleptotene spermatocytes need to move inward, new tight junctions form behind them while old ones dissolve in front of them. The cell essentially travels through a series of transient sealed chambers, never leaving the barrier exposed.⁵ Specific tight-junction proteins orchestrate this process; for instance, claudin 3 is temporarily incorporated into new junctions and then swapped out for claudin 11 once transit is complete.

Feeding the Germ Cells

Developing sperm cells are metabolically unusual. They cannot efficiently use glucose on their own, at least not in the way most cells do. Instead, they depend on Sertoli cells to process glucose into lactate and shuttle it to them.⁶ This metabolic coupling is not optional. When researchers knocked out the gene for lactate dehydrogenase A (Ldha) in mouse Sertoli cells, lactate production dropped and spermatogenesis collapsed, specifically at the spermiogenesis stage where round spermatids are supposed to elongate into mature sperm.⁷

The downstream effects of lactate deprivation turned out to be surprisingly specific. In that same study, the earlier stages of germ cell development (spermatogonia and spermatocytes) were barely affected; it was the final maturation of sperm that broke down. Further analysis revealed that the real bottleneck was disrupted lipid metabolism, particularly a shortage of choline. Supplementing choline completely rescued sperm development even without restoring lactate, suggesting that lactate’s role in spermiogenesis works partly through lipid pathways rather than just energy supply.

Even in fetal life, this metabolic relationship matters. Sertoli cells in the developing testis accumulate glycogen and convert it to lactate during a critical window when both cell types are cut off from external carbon sources. Blocking lactate transport during that period reduces germ cell numbers, showing that the metabolic handshake between Sertoli cells and germ cells begins well before sperm production starts.⁸

Hormonal Signals and How Sertoli Cells Respond

Sertoli cells are the primary target of the two key reproductive hormones in males: follicle-stimulating hormone (FSH) from the pituitary gland and testosterone from neighboring Leydig cells. FSH drives Sertoli cell proliferation during development and stimulates many of the genes involved in supporting spermatogenesis. Testosterone, meanwhile, is essential for the later stages of sperm maturation.⁹

These two hormones do not just act independently; they reinforce each other. Research in primate Sertoli cells showed that prolonged testosterone exposure actually increases the number of FSH receptors on the cell surface and boosts the downstream signaling that FSH triggers. Testosterone also amplified FSH-driven expression of important factors like stem cell factor (SCF), GDNF, and transferrin.¹⁰ This synergy explains why men with either low FSH (due to pituitary problems) or low testosterone (due to Leydig cell dysfunction) can both end up infertile, and why treatments that address only one hormone sometimes fall short.

Maintaining the Stem Cell Pool

Sperm production has to continue for decades, which means the testis needs a self-renewing reservoir of spermatogonial stem cells (SSCs). Sertoli cells are the key architects of the niche that keeps these stem cells alive and in balance. They produce glial cell line-derived neurotrophic factor (GDNF), which binds to receptors on undifferentiated spermatogonia and drives them to self-renew rather than differentiate.¹¹ Too much GDNF and the stem cells keep dividing without ever maturing; too little and the pool depletes. Other Sertoli-cell-expressed genes like Cyp26b1, which degrades retinoic acid, help fine-tune whether stem cells stay quiescent or commit to differentiation.¹²

The physical niche itself involves more than just Sertoli cells. The basement membrane on which the seminiferous tubule sits, the peritubular myoid cells that wrap the outside of the tubule, and the vascular network between tubules all contribute signals.¹³ But Sertoli cells are the central coordinator, integrating hormonal cues from FSH and testosterone with local growth factor signals to control how many stem cells renew versus differentiate at any given time.

Cleanup Duty and Sperm Release

Spermatogenesis is a surprisingly wasteful process. A large fraction of developing germ cells undergo programmed cell death before ever becoming sperm. On top of that, the germ cells that do complete maturation shed most of their cytoplasm as leftover residual bodies during the final shaping step. All of this debris has to be cleared, and Sertoli cells handle the job through phagocytosis. They recognize dying germ cells by a phospholipid signal (phosphatidylserine) that appears on the cell surface and engulf them using a set of receptors that includes TAM family tyrosine kinases and their ligand Gas6.¹⁴ If this cleanup stalls, the buildup of dead cells and residual bodies disrupts the tubule environment and impairs ongoing sperm production.

At the opposite end of the cycle, Sertoli cells are also responsible for releasing mature spermatids into the tubule lumen in a process called spermiation. They do this through a structure called the apical ectoplasmic specialization (apical ES), a testis-specific adhesion junction that grips the head of the elongated spermatid. When the time comes, this junction disassembles in a tightly regulated sequence, freeing the spermatid. The integrity of the apical ES depends on both the actin filament network and tubulin-based structures, and a kinase called MARK4 appears critical for holding it together until the right moment.¹⁵ When MARK4 expression drops prematurely, spermatids detach too early and sperm release fails.

Sertoli Cell-Only Syndrome

The most dramatic clinical illustration of Sertoli cell importance is Sertoli cell-only syndrome (SCOS), a condition where the seminiferous tubules contain Sertoli cells but no germ cells at all. Men with SCOS are azoospermic, meaning no sperm appear in their ejaculate, and it represents the most severe histological form of male infertility.¹⁶

Known genetic causes include Klinefelter syndrome (an extra X chromosome) and microdeletions on the Y chromosome, which together account for over a fifth of cases in unselected patient groups.¹⁷ The majority of SCOS cases, however, remain unexplained by known genetic mutations, which has pushed researchers toward whole-exome sequencing and epigenetic analyses to find new culprits. For affected men, the options are limited. Some undergo testicular sperm extraction (micro-TESE), a surgical procedure that searches for small pockets of surviving spermatogenesis, but success rates vary widely depending on the underlying cause.

Diagnosing Sertoli Cell Problems Without Surgery

Because Sertoli cells are so active during childhood, when testosterone and sperm production are essentially dormant, blood markers of Sertoli cell function can reveal gonadal problems years before puberty would make them obvious. AMH is high from fetal life through mid-puberty and responds to FSH stimulation, while inhibin B is elevated in the first few years of life, dips somewhat during mid-childhood, and rises again at puberty.¹⁸

Both markers become undetectable in boys who have no functioning testicular tissue (anorchia). In primary or central hypogonadism that affects the whole gonad from early in life, AMH and inhibin B are both low. But if the problem is confined to Leydig cells (the testosterone producers), AMH and inhibin B stay normal, which helps clinicians distinguish between different causes of hypogonadism without resorting to stimulation tests. This is particularly useful in pediatric patients, where hormonal stimulation tests can be invasive and stressful.

Immune Privilege and Viral Reservoirs

The blood-testis barrier does not just protect developing sperm. It creates an immune-privileged environment that can, unfortunately, shelter pathogens. Zika virus drew attention to this when it became clear that the virus could persist in semen for months after clearing from the bloodstream. Research showed that human Sertoli cells support high levels of Zika virus replication and may function as a major viral reservoir in the testis.¹⁹ Infection of Sertoli cells also disrupted the barrier itself, potentially giving the virus access to the deeper compartment where sperm develop. The finding identified Sertoli cells as a possible therapeutic target for clearing testicular infections, though no such treatment exists yet.

The immune-privileged properties of Sertoli cells have also attracted interest in transplantation medicine. When Sertoli cells are grafted into sites outside the testis, they can survive and protect co-transplanted cells from immune rejection.²⁰ In one striking experiment, co-aggregates of Sertoli cells and insulin-producing islet cells were transplanted into the livers of diabetic mice via the portal vein, and the grafts survived long-term without any immunosuppression.²¹ This line of research is still experimental, but it highlights how Sertoli cells’ natural immune-suppressive toolkit could be harnessed for conditions well beyond infertility.

Heat, Toxins, and Aging

Sertoli cells are vulnerable to heat, which is part of why the testes sit outside the body cavity. Acute heat exposure triggers apoptosis in Sertoli cells, and the degree of damage depends partly on whether protective heat-shock proteins ramp up in time. In mouse experiments, upregulating heat shock protein 32 (hsp32) reduced heat-induced Sertoli cell death by suppressing caspase-3, a key executioner enzyme in the apoptosis pathway.²² This finding resonates with real-world concerns about occupational heat exposure, laptop use, and tight clothing, all of which raise scrotal temperature and could theoretically stress Sertoli cells over time.

Aging also takes a toll. As men get older, chronic low-grade inflammation and oxidative damage progressively impair testicular cell populations, including Sertoli cells.²³ Because adult Sertoli cells do not divide, lost cells are not replaced. The blood-testis barrier may weaken, metabolic support for germ cells declines, and hormone responsiveness drops. This contributes to the gradual decline in semen quality and fertility that begins around a man’s forties and continues with advancing age.

Sertoli Cell Tumors

Sertoli cell tumors are rare, accounting for a small fraction of all testicular neoplasms. Most are benign, but a subset can metastasize. One well-characterized variant, the large cell calcifying Sertoli cell tumor (LCCSCT), may arise sporadically or in the setting of genetic syndromes like Carney complex and Peutz-Jeghers syndrome.²⁴ Carney complex is typically caused by mutations in PRKAR1A, a gene encoding a regulatory subunit of protein kinase A. Molecular analysis of LCCSCTs found that nearly all harbored PRKAR1A mutations, but the tumors that metastasized carried additional hits in genes like BRCA2 and CDKN2A/B, while non-metastasizing tumors did not.²⁵ This suggests a multi-hit model where PRKAR1A loss gets the tumor started, but progression to malignancy requires accumulating further mutations.

Building Sertoli Cells and Testes in the Lab

One of the more exciting frontiers in reproductive biology is the push to create functional testicular tissue outside the body. Several research groups have derived Sertoli-like cells from human induced pluripotent stem cells (hiPSCs) and combined them with other testicular cell types to build miniature testicular organoids. These lab-grown structures self-assemble into organized tissues that, in some cases, contain tubular formations reminiscent of seminiferous tubules. In one approach, hiPSC-derived Sertoli cells expressing mature markers like SOX9 and GATA1 organized alongside Leydig cells, endothelial cells, and peritubular myoid cells into organoids with distinct spatial architecture.²⁶

A more recent study used hiPSC-derived testicular organoids to test the reproductive effects of semaglutide, demonstrating the practical utility of these models as platforms for drug safety screening.²⁷ Earlier organoid attempts using actual testicular tissue, rather than stem cells, managed to maintain undifferentiated germ cells for up to four weeks and produced testosterone and inhibin B, though they did not achieve in-vitro spermatogenesis.²⁸ Full sperm production in a dish remains out of reach, but these models are already valuable for toxicology testing and for understanding how disruptions to the Sertoli cell niche play out without relying on animal experiments.

Sertoli Cells Across the Animal Kingdom

Comparing Sertoli cells across species reveals how much variation evolution has produced. Fish Sertoli cells can each support well over a hundred developing germ cells, making their spermatogenesis extraordinarily efficient. As you move up to amphibians, reptiles, birds, and mammals, that support capacity steadily drops.³ Human spermatogenesis is among the least efficient in the animal kingdom, which partly explains why human sperm counts are relatively modest and why even small perturbations to Sertoli cell function can tip a man into subfertility.

The differences go beyond capacity. In many fish species, Sertoli cells remain able to divide throughout life, meaning the population can expand in response to breeding demands. Mammalian Sertoli cells lose that ability after puberty. These contrasts have made lower vertebrates attractive models for studying Sertoli cell biology, since their higher support capacity and continued proliferation may offer clues about regulatory mechanisms that mammals have lost or suppressed.²⁹