Scaffold Protein AKAP12 Shields Sperm Production From BPAF Damage, Mouse Study Shows

A new study has identified a molecular guardian that stands between an everyday plastic chemical and the delicate machinery of sperm production. Researchers report that a scaffold protein called AKAP12, operating inside the nurse cells that support developing sperm, protects the blood-testis barrier from damage caused by bisphenol AF, a widely used replacement for the controversial chemical bisphenol A. When the gene encoding AKAP12 was deleted specifically from Sertoli cells in male mice, exposure to BPAF caused a dramatic collapse in fertility, revealing for the first time how an endogenous defense system within the testis can determine whether an environmental toxin leaves a lasting mark on male reproduction.

The work, published as an open-access original article in Cellular and Molecular Life Sciences, addresses a question that has lingered in reproductive toxicology: most research on bisphenol compounds has catalogued their direct toxic effects on reproductive tissue, but far less is known about the protective mechanisms that testicular cells deploy to resist such insults. The team, led by investigators at Naval Medical University, Fudan University and Shanghai Jiao Tong University School of Medicine, with co-corresponding authors Feng Zhang, Hongyang Wang, Chunyu Liu and Lei Chen, set out to fill that gap by focusing on the blood-testis barrier, a specialized structure whose integrity is central to male fertility.

The blood-testis barrier is built by Sertoli cells, the somatic cells that line the seminiferous tubules of the testis and physically cradle germ cells as they mature into sperm. Tight junctions between adjacent Sertoli cells seal the tubule, creating an immune-privileged microenvironment that shields developing sperm from the immune system and restricts the passage of toxins and other blood-borne molecules. Because spermatogenesis depends absolutely on this protected compartment, any breach in the barrier can ripple outward into impaired sperm production and reduced fertility. Yet the molecular scaffolds that keep these junctions stable under chemical assault have remained poorly defined.

AKAP12, or A-kinase anchor protein 12, is a scaffold protein that orchestrates the localization and activity of multiple signaling kinases, and it has previously been implicated in the maintenance of other biological barriers in the body. What it did inside the testis, however, was unknown. To find out, the researchers generated mice in which Akap12 was deleted specifically in Sertoli cells, leaving the rest of the animal genetically intact. They then exposed the animals to BPAF by oral gavage over a period of 28 days, a regimen designed to mimic repeated dietary exposure to the chemical, and assessed fertility, sperm motility and the structural integrity of the blood-testis barrier.

The results were striking. Sertoli cell-specific Akap12-deficient male mice showed markedly reduced fertility after BPAF exposure compared with animals that retained the protein. To probe what was happening at the barrier itself, the team used a biotin tracer assay, in which a small labeled molecule is injected into the circulation and its penetration into the seminiferous tubules is tracked; leakage of the tracer past the barrier signals a loss of tight junction sealing. They complemented this functional readout with transmission electron microscopy, which visualizes the ultrastructure of the junctional complexes between Sertoli cells. Together, the two techniques revealed that loss of AKAP12 left the barrier vulnerable to BPAF-induced destabilization.

The mechanistic core of the study lies in the relationship between AKAP12 and Src, a kinase with a well-known appetite for adding phosphate groups to tyrosine residues on target proteins. The researchers found that AKAP12 normally sequesters Src kinase, holding it in check. In the absence of AKAP12, Src becomes hyperactive, as indicated by increased phosphorylation at tyrosine 416, a hallmark of the enzyme’s activated state. That hyperactivity has a specific and damaging consequence: Src phosphorylates zonula occludens-1, or ZO-1, a central scaffolding component of tight junctions, on tyrosine residues. Phosphorylated ZO-1 is then marked for ubiquitin-dependent degradation, and its loss destabilizes the wider tight junction complex, dragging down associated proteins including Occludin and Claudin-11.

In other words, the study traces a complete signaling chain from gene to barrier failure: without AKAP12 to restrain Src, the kinase phosphorylates ZO-1, ubiquitin machinery degrades the phosphorylated protein, tight junction components fall away, and the blood-testis barrier loosens. The evidence for this pathway is strengthened by a rescue experiment. When the researchers administered a Src inhibitor to Akap12-deficient Sertoli cells, the drug effectively reversed the ZO-1 phosphorylation and degradation triggered by AKAP12 loss, confirming that Src activity is the proximate cause of the junctional collapse rather than a bystander effect. This pharmacological reversal also hints at a potential intervention strategy, although the authors’ experiments were conducted in cells and mice rather than in a clinical setting.

Beyond the tight junctions themselves, the study uncovered a second layer of vulnerability. AKAP12 deficiency also disrupted the homeostasis of the extracellular matrix and integrins, the receptor systems that anchor Sertoli cells to their surrounding basement membrane. This matters because the blood-testis barrier is not simply a row of tight junctions floating in isolation; it is embedded in a structural context in which cell-matrix adhesion and cell-cell junctions are functionally intertwined. Destabilizing the integrin-linked framework may compound the damage caused by ZO-1 loss, further weakening the tubule’s ability to withstand chemical stress.

The choice of BPAF as the environmental challenge gives the findings contemporary relevance. Bisphenol AF is a fluorinated analog of bisphenol A that has been increasingly adopted in polymers, seals and other industrial applications as manufacturers move away from BPA amid regulatory and consumer pressure. The study’s results suggest that so-called BPA substitutes are not automatically benign for male reproduction, and that their impact depends partly on the genetic endowment of the exposed individual. This is where the concept of gene-environment interactions becomes concrete: the same dose of BPAF produced very different reproductive outcomes depending on whether Sertoli cells carried a functional Akap12 gene, implying that variation in such protective genes could help explain why some individuals appear more susceptible to endocrine-disrupting chemicals than others.

The authors frame their conclusions as an extension of AKAP12 biology into reproductive toxicology and as new insight into how genes and environments interact to shape fertility. The work received ethics approval from the Animal Care and Use Committee of Fudan University and from the Ethics Committee of Shanghai Tenth People’s Hospital, which provided human testicular tissue specimens used in the research, and it was supported by grants from the National Natural Science Foundation of China, the National Key R&D Program of China, the Natural Science Foundation of Shanghai and other Shanghai science programs. The article was published on 15 September 2026 as a peer-reviewed, open-access paper carrying the DOI 10.1007/s00018-026-06424-6.

For a field searching for ways to protect male fertility from the growing inventory of endocrine-disrupting chemicals, the study offers two takeaways. First, the blood-testis barrier is not a passive target; it is actively defended by scaffold proteins such as AKAP12 that keep destructive kinases away from the junctional machinery, and understanding that defense system opens the door to measuring or even bolstering it. Second, the demonstration that a Src inhibitor can reverse ZO-1 phosphorylation and degradation in AKAP12-deficient Sertoli cells identifies a druggable node in the pathway, suggesting that pharmacological protection of tight junctions might one day complement efforts to reduce environmental exposure. Whether such strategies can be translated safely to humans remains an open question, but the study makes clear that the battle between plastic chemicals and sperm production is fought, at least in part, at the molecular seams that hold the testis together.

Subject of Research: The role of AKAP12 in maintaining blood-testis barrier integrity and protecting male fertility from BPAF-induced reproductive toxicity

Article Title: AKAP12 maintains blood-testis barrier integrity and resists BPAF-induced male fertility impairment by inhibiting Src-mediated ZO-1 degradation

Article References: Bao, M., Guo, S., Xue, D., Mao, S., Han, L., Wang, S., Lu, S., Xiong, Y., Gu, G., Hu, Z., Liu, S., Cao, D., Xie, L., Li, T., Shen, S., Hu, J., Tang, S., Zhang, F., Wang, H., … Chen, L. (2026). AKAP12 maintains blood-testis barrier integrity and resists BPAF-induced male fertility impairment by inhibiting Src-mediated ZO-1 degradation. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06424-6

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06424-6

Keywords: AKAP12, blood-testis barrier, BPAF, Sertoli cells, Src kinase, ZO-1, tight junctions, male fertility, reproductive toxicology, endocrine disruptors, spermatogenesis, gene-environment interaction