BMC veterinary research2026; 22(1); 555; doi: 10.1186/s12917-026-05691-6

Endometritis and endometrial fibrosis are associated with alterations in mare endometrial proteome.

Leal, M
·
Silva, E
·
Alpoim-Moreira, J
·
Pinto-Bravo, P
·
Rebordão, MR
·
Quaresma, M
·
Jalali, B
·
Molcan, T
·
Szóstek-Mioduchowska, A
·
Skarzynski, D
·
Ferreira-Dias, G

Abstract: Equine persistent post-breeding endometritis may lead to endometrosis, characterized by excessive fibrosis, which is a major cause of subfertility/infertility. Endometrial proteomic changes induced by endometritis, when associated with fibrosis, were investigated to identify the biological processes (BP) involved. Cyclic mares´ endometrial biopsies were histologically classified (Kenney and Doig's) as: category IIA (n = 5), category IIA with endometritis (IIA-E; n = 4), category IIB (n = 5), or category IIB with endometritis (IIB-E; n = 5). Proteome was assessed by LC-MS/MS. In total, 62 differentially abundant proteins (DAPs) were identified in IIA-E endometria, compared to IIA; and 46 in IIB-E endometria, compared to IIB. The DAPs in endometria with endometritis (IIA-E vs. IIA; IIB-E vs. IIB) were mostly enriched in BP related to immune/inflammatory response, DNA-related process and cell cycle. Inflammatory-related proteins (serpin proteins and several phospholipases) were upregulated in endometritis, regardless of the degree of fibrosis and inflammation, suggesting the activation of conserved innate immune mechanisms. Nevertheless, fibrosis severity determined the expression pattern of histone H2A, which was upregulated in IIA-E endometria, and downregulated in IIB-E endometria. Additionally, other inflammatory-related proteins (azurocidin 1, eosinophil peroxidase and secreted phosphoprotein 1) were differently abundant only in endometritis associated with endometrosis (IIB-E), indicating that moderate fibrosis and endometrial degeneration may influence the inflammatory and tissue remodelling response. In conclusion, although conserved innate immune mechanisms operate independently of fibrosis severity and of endometrial inflammatory state, other processes activated during endometritis are influenced by the endometrium milieu, namely by the progression of endometrial fibrosis, which might modulate specific molecular responses.

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Publication Date: 2026-07-08 PubMed ID: 42421099PubMed Central: PMC13602558DOI: 10.1186/s12917-026-05691-6Google Scholar: Lookup

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Summary
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MeSH
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Journal Article

Summary

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Overview

This study investigates how the protein composition of the mare’s uterine lining (endometrium) changes in response to post-breeding inflammation (endometritis) and related scarring (fibrosis), which together can cause infertility.
It identifies specific proteins and biological processes involved in inflammation and fibrosis, highlighting how the severity of fibrosis influences molecular responses in the endometrium.

Background

Equine persistent post-breeding endometritis (PPBE) is a condition where the mare’s uterus develops prolonged inflammation after breeding.
PPBE can lead to endometrosis, a condition characterized by excessive fibrotic scarring of the endometrium.
Endometrosis is a common cause of subfertility or infertility in mares due to impaired uterine function.
Understanding the molecular and cellular changes during endometritis and fibrosis is crucial for developing treatments and managing fertility issues.

Objectives

To study the changes in the proteome (complete set of proteins) of mare endometrial tissue during endometritis with and without fibrosis.
To identify which biological processes are affected and how the severity of fibrosis influences these processes.
To determine whether certain immune and inflammatory proteins are consistently involved regardless of fibrosis severity.

Methods

Mares in the estrous cycle were sampled via endometrial biopsy.
Endometrial tissue samples were classified using established histological categories based on Kenney and Doig’s system:
- Category IIA: mild changes, no endometritis
- Category IIA-E: mild changes with endometritis
- Category IIB: moderate changes (more fibrosis), no endometritis
- Category IIB-E: moderate changes with endometritis
Protein profiles were analyzed using liquid chromatography with tandem mass spectrometry (LC-MS/MS) to identify and quantify proteins in the tissue.
Differentially abundant proteins (DAPs) were determined by comparing endometritic samples with their corresponding controls in each fibrosis category.
Bioinformatic analysis was used to relate DAPs to biological processes.

Results

In mild fibrosis (IIA), 62 proteins were found to vary significantly between inflamed (IIA-E) and non-inflamed (IIA) tissues.
In moderate fibrosis (IIB), 46 proteins differed significantly between inflamed (IIB-E) and non-inflamed (IIB) tissues.
Proteins related to immune and inflammatory responses, DNA processes, and cell cycle were enriched in both comparisons, suggesting involvement of these biological processes during endometritis.
Serpin family proteins and various phospholipases were upregulated consistently in endometritis regardless of fibrosis severity, indicating activation of core innate immune pathways.
Histone H2A, involved in DNA packaging and gene regulation, was:
- Upregulated in mild fibrosis with endometritis (IIA-E)
- Downregulated in moderate fibrosis with endometritis (IIB-E)
- This suggests fibrosis severity affects how cellular DNA and gene expression respond to inflammation.
Additional inflammatory proteins such as azurocidin 1, eosinophil peroxidase, and secreted phosphoprotein 1 showed altered abundance only in moderate fibrosis with endometritis (IIB-E), implying that more advanced fibrotic changes influence specific inflammatory and tissue remodeling proteins.

Conclusions

The mare endometrium activates conserved innate immune mechanisms in response to endometritis, independent of fibrosis degree.
However, progression of fibrosis modulates specific molecular responses, particularly those involving tissue remodeling and inflammatory proteins.
This differential expression pattern emphasizes that the uterine tissue environment, shaped by fibrosis severity, influences how the uterus reacts to inflammation.
Understanding these molecular changes provides insight into the pathophysiology of endometrial diseases affecting fertility and may guide development of targeted therapies for mares with persistent endometritis and fibrosis.

Cite This Article

APA

Leal M, Silva E, Alpoim-Moreira J, Pinto-Bravo P, Rebordão MR, Quaresma M, Jalali B, Molcan T, Szóstek-Mioduchowska A, Skarzynski D, Ferreira-Dias G. (2026). Endometritis and endometrial fibrosis are associated with alterations in mare endometrial proteome. BMC Vet Res, 22(1), 555. https://doi.org/10.1186/s12917-026-05691-6

Publication

BMC veterinary research

ISSN: 1746-6148

NlmUniqueID: 101249759

Country: England

Language: English

Volume: 22

Issue: 1

PII: 555

Researcher Affiliations

Leal, Mariana

Faculty of Veterinary Medicine, CIISA, University of Lisbon, Lisbon, Portugal.
Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), Lisbon, Portugal.

Silva, Elisabete

Faculty of Veterinary Medicine, CIISA, University of Lisbon, Lisbon, Portugal.
Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), Lisbon, Portugal.

Alpoim-Moreira, Joana

Faculty of Veterinary Medicine, CIISA, University of Lisbon, Lisbon, Portugal.
Faculty of Veterinary Medicine, Lusófona University, Lisbon, Portugal.

Pinto-Bravo, Pedro

Polytechnic University of Coimbra, Coimbra Agriculture School, Bencanta, Coimbra, 3045-601, Portugal.
Research Center for Natural Resources, Environment (CERNAS), Polytechnic University of Coimbra, Bencanta, Coimbra, 3045-601, Portugal.

Rebordão, Maria Rosa

Faculty of Veterinary Medicine, CIISA, University of Lisbon, Lisbon, Portugal.
Polytechnic University of Coimbra, Coimbra Agriculture School, Bencanta, Coimbra, 3045-601, Portugal.
Research Center for Natural Resources, Environment (CERNAS), Polytechnic University of Coimbra, Bencanta, Coimbra, 3045-601, Portugal.

Quaresma, Miguel

Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), Lisbon, Portugal.
Animal and Veterinary Research Center (CECAV), University of Trás-os-Montes e Alto Douro (UTAD), Quinta de Prados, Vila Real, 5000-801, Portugal.

Jalali, Beenu

Institute of Animal Reproduction and Food Research Polish Academy of Sciences, Olsztyn, 10-643, Poland.

Molcan, Tomasz

Institute of Animal Reproduction and Food Research Polish Academy of Sciences, Olsztyn, 10-643, Poland.

Szóstek-Mioduchowska, Anna

Institute of Animal Reproduction and Food Research Polish Academy of Sciences, Olsztyn, 10-643, Poland.

Skarzynski, Dariusz

Institute of Animal Reproduction and Food Research Polish Academy of Sciences, Olsztyn, 10-643, Poland.
Faculty of Veterinary Medicine, University of Environmental and Live Sciences, Wroclaw, Poland.

Ferreira-Dias, Graça

Faculty of Veterinary Medicine, CIISA, University of Lisbon, Lisbon, Portugal. gmlfdias@fmv.ulisboa.pt.
Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), Lisbon, Portugal. gmlfdias@fmv.ulisboa.pt.

MeSH Terms

Animals
Female
Horses
Endometritis / veterinary
Endometritis / metabolism
Endometritis / pathology
Endometrium / pathology
Endometrium / metabolism
Horse Diseases / metabolism
Horse Diseases / pathology
Proteome / metabolism
Fibrosis / veterinary
Fibrosis / metabolism

Grant Funding

2023.LT3.3 (LA/P/0059/2020) / Associated Laboratory for Animal and Veterinary Science (AL4AnimalS))
https://doi.org/10.54499/CEECINST/00140/2021/CP2807/CT0001 / Associated Laboratory for Animal and Veterinary Science (AL4AnimalS)
UID/276/2025 / Fundação para a Ciência e a Tecnologia

Conflict of Interest Statement

Declarations. Ethics approval and consent to participate: The endometrial biopsies were collected by certified veterinarians as part of breeding examination of the mares, and for diagnostic purpose. A written informed consent was obtained from all mares’ owners before to sample collection. Therefore, ethical approval from the Ethics Committee for Research and Teaching from the Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal was not required. All clinical procedures were also conducted in accordance with EU and national legislation (Directive 2010/63/EU and Decree-Law No. 113/2013). Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

References

This article includes 41 references

Canisso IF, Stewart J, da Silva MC. Endometritis: Managing Persistent Post-Breeding Endometritis. Veterinary Clin North America: Equine Pract 2016;32(3):465–80.
doi: 10.1016/j.cveq.2016.08.004pubmed: 27810036google scholar: lookup
Katila T. Evaluation of diagnostic methods in equine endometritis. Reprod Biol 2016;16:189–96.
doi: 10.1016/j.repbio.2016.06.002pubmed: 27692361google scholar: lookup
Woodward EM, Troedsson MH. Inflammatory mechanisms of endometritis. Equine Vet J 2015;47(4):384–9.
doi: 10.1111/evj.12403pubmed: 25537084google scholar: lookup
Katila T, Ferreira-Dias G. Evolution of the Concepts of Endometrosis, Post Breeding Endometritis, and Susceptibility of Mares. Anim (Basel) 2022;12(6):779.
doi: 10.3390/ani12060779pmc: PMC8944725pubmed: 35327176google scholar: lookup
Da Silva E, Martín-Cano FE, Gómez-Arrones V, Gaitskell-Phillips G, Alonso JM, Rey J. Bacterial endometritis-induced changes in the endometrial proteome in mares: Potential uterine biomarker for bacterial endometritis. Theriogenology 2024;226:202–12.
doi: 10.1016/j.theriogenology.2024.06.009pubmed: 38909435google scholar: lookup
Christoffersen M, Woodward E, Bojesen AM, Jacobsen S, Petersen MR, Troedsson. Inflammatory responses to induced infectious endometritis in mares resistant or susceptible to persistent endometritis. BMC Vet Res 2012;8:41.
doi: 10.1186/1746-6148-8-41pmc: PMC3368729pubmed: 22458733google scholar: lookup
Kenney RM. Cyclic and pathologic changes of the mare endometrium as detected by biopsy, with a note on early embryonic death. J Am Vet Med Assoc 1978;172(3):241–62.
doi: 10.2460/javma.1978.172.03.241pubmed: 621166google scholar: lookup
Ricketts SW, Alonso S. The effect of age and parity on the development of equine chronic endometrial disease. Equine Vet J 1991;23(3):189–92.
doi: 10.1111/j.2042-3306.1991.tb02752.xpubmed: 1884699google scholar: lookup
Kenney RM, Doig PA. Equine endometrial biopsy. Current Therapy in Volume 2. Philadelphia: WB Saunders; 1986. pp. 723–9.
Lehmann J, Ellenberger C, Hoffmann C, Bazer FW, Klug J, Allen WR. Morpho-functional studies regarding the fertility prognosis of mares suffering from equine endometrosis. Theriogenology 2011;76(7):1326–36.
doi: 10.1016/j.theriogenology.2011.06.001pubmed: 21855986google scholar: lookup
Amorim M, Khan FA, Chenier TS, Scholtz EL, Hayes MA. Analysis of the uterine flush fluid proteome of healthy mares and mares with endometritis or fibrotic endometrial degeneration. Reprod Fertility 2020;32(6):572–81.
doi: 10.1071/RD19085pubmed: 31987068google scholar: lookup
Teixeira-Soares CM, Viana AG, Carvalho RPR, Barros E, Ramirez-Lopez C, Moura AA. Unraveling the uterine fluid proteome of mares diagnosed with post-breeding and infectious endometritis. J Reprod Immunol 2025;167:104401.
doi: 10.1016/j.jri.2024.104401pubmed: 39616824google scholar: lookup
Cocchia N, Paciello O, Auletta L. Comparison of the cytobrush, cottonswab, and low-volume uterine flush techniques to evaluate endometrial cytology for diagnosing endometritis in chronically infertile mares. Theriogenology 2012;77(1):89–98.
doi: 10.1016/j.theriogenology.2011.07.020pubmed: 21855980google scholar: lookup
Perez-Riverol Y, Bandla C, Kundu DJ, Kamatchinathan S, Bai J, Hewapathirana S. The PRIDE database at 20 years: 2025 update. Nucleic Acids Res 2025; 6;53(D1):D543-D553.
doi: 10.1093/nar/gkae1011pmc: PMC11701690pubmed: 39494541google scholar: lookup
Deutsch EW, Bandeira N, Perez-Riverol Y, Sharma V, Carver J, Mendoza L. The ProteomeXchange Consortium at 10 years: 2023 update. Nucleic Acids Res 2023;51(D1):D1539–48.
doi: 10.1093/nar/gkac1040pmc: PMC9825490pubmed: 36370099google scholar: lookup
Tang D, Chen M, Huang X, Zhang G, Zeng L, Zhang G. SRplot: A free online platform for data visualization and graphing.. PLoS ONE 2023;18(11):e0294236.
doi: 10.1371/journal.pone.0294236pmc: PMC10635526pubmed: 37943830google scholar: lookup
Huang DW, Sherman BT, Lempicki RA. Bioinformatics enrichment tools: paths toward the comprehensive functional analysis of large gene lists.. Nucleic Acids Res 2009;37(1):1–13.
doi: 10.1093/nar/gkn923pmc: PMC2615629pubmed: 19033363google scholar: lookup
Huang DW, Sherman BT, Lempicki RA. Systematic and integrative analysis of large gene lists using DAVID Bioinformatics Resources.. Nat Protoc 2009;4(1):44–57.
doi: 10.1038/nprot.2008.211pubmed: 19131956google scholar: lookup
Goedhart J, Luijsterburg MS. VolcaNoseR is a web app for creating, exploring, labeling and sharing volcano plots.. Sci Rep 2020;10:20560.
doi: 10.1038/s41598-020-76603-3pmc: PMC7689420pubmed: 33239692google scholar: lookup
Li J, Zhao Y, Mi J, Yi Z, Holyoak GR, Wu R. Comparative Proteome Analysis of Serum Uncovers Differential Expression of Proteins in Donkeys (Equus asinus) With Endometritis Caused by Escherichia coli.. J Equine Veterinary Scince 2023;122:104221.
doi: 10.1016/j.jevs.2023.104221pubmed: 36623579google scholar: lookup
Janciauskiene S, Lechowicz U, Pelc M, Olejnicka B, Chorostowska-Wynimko J. Diagnostic and therapeutic value of human serpin family proteins.. Biomed Pharmacother 2024;175:116618.
doi: 10.1016/j.biopha.2024.116618pubmed: 38678961google scholar: lookup
Frey S, Sticht H, Wilsmann-Theis D, Gerschütz A, Wolf K, Löhr S. Rare Loss-of-Function Mutation in SERPINA3 in Generalized Pustular Psoriasis.. J Invest Dermatol 2020;140(7):1451–5.
doi: 10.1016/j.jid.2019.11.024pubmed: 31945348google scholar: lookup
Kantaputra P, Chaowattanapanit S, Kiratikanon S, Chaiwarith R, Choonhakarn C, Intachai W. SERPINA1, generalized pustular psoriasis, and adult-onset immunodeficiency.. J Dermatol 2021;48(10):1597–601.
doi: 10.1111/1346-8138.16081pubmed: 34390020google scholar: lookup
Heutinck KM, ten Berge IJ, Hack CE, Hamann J, Rowshani AT. Serine proteases of the human immune system in health and disease.. Mol Immunol 2010;47(11–12):1943–55.
doi: 10.1016/j.molimm.2010.04.020pubmed: 20537709google scholar: lookup
Barman A, Gohain D, Bora U, Tamuli R. Phospholipases play multiple cellular roles including growth, stress tolerance, sexual development, and virulence in fungi.. Microbiol Res 2018;209:55–69.
doi: 10.1016/j.micres.2017.12.012pubmed: 29580622google scholar: lookup
Zhao Y, Aoudjit F, Bourgoin SG. Phospholipase A1 Member A Deficiency Alleviates Mannan-Induced Psoriatic Arthritis in Mice Model.. Int J Mol Sci 2022;23(15):8559.
doi: 10.3390/ijms23158559pmc: PMC9369159pubmed: 35955693google scholar: lookup
Khan MI, Hariprasad G. Human Secretary Phospholipase A2 Mutations and Their Clinical Implications.. J Inflamm Res 2020;13:551–61.
doi: 10.2147/JIR.S269557pmc: PMC7502393pubmed: 32982370google scholar: lookup
Morris L, McCue P, Aurich C. Equine endometritis: a review of challenges and new approaches.. Reproduction 2020;160(5):R95–110.
doi: 10.1530/REP-19-0478pubmed: 32805710google scholar: lookup
Hoeksema M, van Eijk M, Haagsman HP, Hartshorn KL. Histones as mediators of host defense, inflammation and thrombosis.. Future Microbiol 2016;11(3):441–53.
doi: 10.2217/fmb.15.151pmc: PMC5549641pubmed: 26939619google scholar: lookup
Doolin T, Amir HM, Duong L, Rosenzweig R, Urban LA, Bosch M. Mammalian histones facilitate antimicrobial synergy by disrupting the bacterial proton gradient and chromosome organization.. Nat Commun 2020;11(1):3888.
doi: 10.1038/s41467-020-17699-zpmc: PMC7403156pubmed: 32753666google scholar: lookup
Li X, Ye Y, Peng K, Zeng Z, Chen L, Zeng Y. Histones: The critical players in innate immunity.. Front Immunol 2022;13:1030610.
doi: 10.3389/fimmu.2022.1030610pmc: PMC9720293pubmed: 36479112google scholar: lookup
Yin X, Zeng D, Liao Y, Tang C, Li Y. The Function of H2A Histone Variants and Their Roles in Diseases.. Biomolecules 2024;14(8):993.
doi: 10.3390/biom14080993pmc: PMC11352661pubmed: 39199381google scholar: lookup
Soehnlein O, Lindbom L. Neutrophil-derived azurocidin alarms the immune system.. J Leukoc Biol 2009;85:344–51.
doi: 10.1189/jlb.0808495pubmed: 18955543google scholar: lookup
Hemmann P, Kloppenburg L, Breinbauer R, Ehnert S, Blumenstock G, Reumann MK. AZU1: a new promising marker for infection in orthopedic and trauma patients?. EXCLI J 2024;23:53–61.
doi: 10.17179/excli2023-6705pmc: PMC10864703pubmed: 38357095google scholar: lookup
Lee J, Rosenberg H. Chapter 13 - Eosinophils in human disease.. Eosinophils in Health and Disease 2013;431–536.
Wang J, Slungaard A. Role of eosinophil peroxidase in host defense and disease pathology.. Arch Biochem Biophys 2006;445(2):256–60.
doi: 10.1016/j.abb.2005.10.008pubmed: 16297853google scholar: lookup
Grimm AL, Schoon HA, Schöniger S. Histopathological features of endometritis eosinophilica in mares.. Histol Histopathol 2017;32(11):1161–73.
doi: 10.14670/HH-11-872pubmed: 28105630google scholar: lookup
Johnson GA, Burghardt RC, Bazer FW. Osteopontin: a leading candidate adhesion molecule for implantation in pigs and sheep.. Journal of Animal Science and Biotechnology 2014;5(1):56.
doi: 10.1186/2049-1891-5-56pmc: PMC4322467pubmed: 25671104google scholar: lookup
Klein C. Novel equine conceptus–endometrial interactions on Day 16 of pregnancy based on RNA sequencing.. Reprod Fertility Dev 2015.
doi: 10.1071/RD14489pubmed: 25940503google scholar: lookup
Kay J, Thadhani E, Samson L, Engelward B. Inflammation-induced DNA damage, mutations and cancer.. DNA Repair (Amst) 2019;83:102673.
doi: 10.1016/j.dnarep.2019.102673pmc: PMC6801086pubmed: 31387777google scholar: lookup
Pezone A, Olivieri F, Napoli MV, Procopio A, Avvedimento EV, Gabrielli A. Inflammation and DNA damage: cause, effect or both.. Nat Rev Rheumatol 2023;19(4):200–11.
doi: 10.1038/s41584-022-00905-1pubmed: 36750681google scholar: lookup