This Key Event Relationship is licensed under the Creative Commons BY-SA license. This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, so long as attribution is given to the creator. The license allows for commercial use. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.

Relationship: 3834

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Epigenetic modification process leads to Impaired, Spermatogenesis

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Epigenetic modification process

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Impaired, Spermatogenesis

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Suppression, Estrogen receptor (ER) activity leads to Impaired, Spermatogenesis via epigenetic modifications	adjacent	Moderate		John Frisch (send email)	Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Term	Scientific Term	Evidence	Link
mammals	mammals	High	NCBI
Vertebrates	Vertebrates	Moderate	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Male	High

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Term	Evidence
Adult, reproductively mature	Moderate

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Epigenetic modifications are alterations that affect gene expression without altering the underlying gene sequence. Among some of the more common processes that lead to epigenetic modifications are DNA methylation and alteration of histone proteins. DNA methylation involves addition of methyl groups to DNA which causes increased or decreased gene expression. Histone proteins are small proteins that assist gene expression, DNA repair, and DNA replication; histones can be modified by the addition of methyl, acetyl, or phosphate groups, which accelerates or slows DNA expression, repair, and replication.

Spermatogenesis is the process in which germ cells develop into mature sperm in testes in male animals and hermaphrodites. Impaired spermatogenesis can result in lower mature sperm counts, problems in proper sperm function such as sperm motility, or other sperm abnormalities. Epigenetic modifications alter the levels of gene expression for loci expressing proteins involved in sperm development, impairing spermatogenesis.

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings. Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

This Key Event Relationship was part of an Environmental Protection Agency effort to develop AOPs that establish scientifically supported causal linkages between alternative endpoints measured using new approach methodologies (NAMs) and guideline apical endpoints measured in Tier 1 and Tier 2 test guidelines (U.S. EPA, 2025) employed by the Endocrine Disruptor Screening Program (EDSP). A series of key events that represent significant, measurable, milestones connecting molecular initiation to apical endpoints indicative of adversity were identified based on scientific review articles and empirical studies. Additionally, scientific evidence supporting the causal relationships between each pair of key events was assembled and evaluated. The present effort focused primarily on empirical studies with mammals.

Empirical studies are focused on epigenetic modifications and resulting impaired spermatogenesis, in support of development of AOP 651.

Authors of KER 3834 did a further evaluation of published peer-reviewed literature to provide additional evidence in support of the key event relationship. The literature used to support this KER began with the test guidelines and followed to primary, secondary, and/or tertiary works concerning the relevant underlying biology. In addition, search engines were used to target journal articles with ‘epigenetic modifications’, ‘sperm motility’, and ‘sperm abnormalities’ in order to locate representative empirical studies that support the key event relationship.

Following initial human effort AOP development, artificial Intelligence (AI)-assisted literature search and synthesis, using EPA-AI GPT5, was used to identify additional literature, and draft Uncertainties and Inconsistencies content of this KER page. Additionally, EPA-AI GPT5 was also used to check for additional text improvement in other sections. All content generated through this process were reviewed and verified by the KER author against literature sources, prior to inclusion.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured. More help

Epigenetic modification of DNA located in germ cells alters the levels of gene expression for loci expressing proteins involved in sperm development, with resulting impaired spermatogenesis causing lower sperm counts, problems in sperm function, and other sperm abnormalities (for review of normal epigenetic modifications in spermatogenesis, see Gunes and Kulac (2013), for review of how disruption of epigenetic modifications disrupts spermatogenesis, see Cui et al. (2025)).

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Species	Duration	Dose	Epigenetic modfications?	Impaired spermatogenesis?	Summary	Citation
Mice (Mus musculus)	5 weeks	20-40 ug/kg body weight zearalenone (ZEA).	yes	yes	Epigenetic modifications indicated by statistically significant decrease in methylation markers 5mC and 5hmC at all doses and statistically significant increase in the histone methylation marker H3K27 at all doses leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility at high dose and statistically significant increase in abnormal acrosome integrity and spermatozoa abnormality at all doses.	Gao et al. (2019)
Mice (Mus musculus)	5 weeks	1–10 mg/kg body weight carbendazim (CBZ).	yes	yes	Epigenetic modifications indicated by statistically significant decrease in methylation markers 5mC at all doses and 5hmC at high dose and statistically significant increase in the histone methylation marker H3K27 at all doses leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility at all doses and statistically significant decrease in spermatozoa count at high dose.	Liu et al. (2019)
Mice (Mus musculus)	56 days after birth	20-40 ug/kg body weight zearalenone (ZEA).	yes	yes	Epigenetic modifications in offspring indicated by statistically significant decrease in methylation marker 5hmC at high dose and statistically significant increase in the histone methylation marker H3K27 at high dose leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility at all doses, statistically significant decrease in spermatozoa count at high dose, and statistically significant increase in abnormal acrosome integrity at high dose.	Men et al. (2019)
Mice (Mus musculus)	6 weeks	50 mg/kg/body weight/day Bisphenol A (BPA)	yes	yes	Epigenic modifications indicated by statistically significant change in histone mRNA, protein and methylation leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility, concentration, and hyperactivity.	Ryu et al. (2022)

Uncertainties and Inconsistencies

Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Complications due to heterogeneity in tissue type.
- Tissue contains a variety of cell types, particularly reproductive tissue with various ages in germ cells. Care should be taken not to attribute a global pattern in epigenetic modification when there are heterogeneous cell-types present, which can be mitigated by single cell type studies in humans and laboratory rodents (Cui et al. 2025).
Complications due to multiple epigenetic effects.
- Interactions among DNA methylation, histone modifications, and other epigenetic modifications can make it difficult to attribute impaired spermatogenesis to a particular epigenetic effect in humans and laboratory rodents (Cui et al. 2025).

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references. More help

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Time-scale

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

Life Stage: Adult, reproductively mature for process producing fully functional sperm.

Sex: Applies to males as related to sperm.

Taxonomic: Largely studied in lab mammals; plausible for all sexually reproductive animals that have sperm.

References

List of the literature that was cited for this KER description. More help

Cui Y, Deng J, Zhang Y, Du L, Jiang F, Li C, Chen W, Zhang H, He Z. 2025. Epigenetic regulation by DNA methylation, histone modifications and chromatin remodeling complexes in controlling spermatogenesis and their dysfunction with male infertility. Cellular and Molecular Life Sciences 82(1): 343.

Gao Y, Zhao Y, Zhang H, Zhang P, Liu J, Feng Y, Men Y, Li L, Shen W, Sun Z, Min L. 2019. Pubertal exposure to low doses of zearalenone disrupting spermatogenesis through ERα related genetic and epigenetic pathways. Toxicology Letters. 315: 31-38.

Gunes S, Kulac T. 2013. The role of epigenetics in spermatogenesis. Turkish Journal of Urology 39(3): 181-187.

Liu J, Zhang P, Zhao Y, Zhang H. 2019. Low dose carbendazim disrupts mouse spermatogenesis might be through estrogen receptor related histone and DNA methylation. Ecotoxicology and Environmental Safety 176: 242-249.

Men Y, Zhao Y, Zhang P, Zhang H, Gao Y, Liu J, Feng Y, Li L, Shen W, Sun Z, Min L. 2019. Gestational exposure to low-dose zearalenone disrupting offspring spermatogenesis might be through epigenetic modifications. Basic and Clinical Pharmacology and Toxicology 125(4): 382-393.

Ryu DY, Pang WK, Adegoke EO, Rahman MS, Park YJ, Pang MG. 2022. Abnormal histone replacement following BPA exposure affects spermatogenesis and fertility sequentially. Environment International 170: 107617.

U.S. Environmental Protection Agency. 2025. EDSP Test Guidelines and Guidance Document. https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/edsp-test-guidelines-and-guidance-document (retrieved 25 July 2025).

Italics indicate edits from John Frisch July 2026. A full list of updates can be found in the Change Log on the View History page.