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PloS one2025; 20(11); e0335179; doi: 10.1371/journal.pone.0335179

Collagen composition in equine exuberant granulation tissue reflects tissue immaturity.

Abstract: Exuberant granulation tissue (EGT) is a second intention wound healing disorder. It commonly occurs in the distal limb of horses. EGT causes significant increase in the duration and cost of treatment, potentially leading to the decision not to pursue treatment and euthanize the patient. The underlying pathomechanisms of this fibroproliferative disorder remain unclear, particularly in terms of collagen composition and the association between myofibroblasts and blood vessels. This study investigated the collagen composition in naturally occurring EGT following trimming in 19 horses (EGT group). In both the superficial and deep wound beds of EGT-affected horses, the collagen distribution was assessed and compared to control wounds (n = 6 horses, control group, punch biopsies) using histology. Immunofluorescence was performed to colocalize activated alpha smooth muscle actin-positive myofibroblasts in EGT as well as angiogenic markers. Our histological findings showed significantly higher amounts of immature collagen (type III) in the superficial and deep regions of EGT compared to the controls while the total amount of collagen in both groups did not differ significantly. In EGT, occluded microvessels and endothelial cell hypertrophy were present in the deep layer and myofibroblasts were ubiquitously found in the whole wound bed. Markers for intermediate filaments were reduced in the superficial region. In conclusion, collagen composition in EGT differed significantly from control wounds, indicating tissue immaturity. Consequently, promoting tissue maturation towards a more mature ECM composition could serve as a valuable target for future therapeutic interventions enabling better regeneration.
Copyright: © 2025 Partusch et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Publication Date: 2025-11-06 PubMed ID: 41196884PubMed Central: PMC12591489DOI: 10.1371/journal.pone.0335179Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This research investigated the composition of collagen in exuberant granulation tissue (EGT), a problematic wound healing condition in horse limbs, to understand its tissue maturity and underlying mechanisms.
  • The study compared collagen types and cellular markers in EGT-affected wounds versus normal healing wounds, revealing that EGT tissue remains immature, which may inform future treatment strategies.

Introduction to Exuberant Granulation Tissue (EGT)

  • EGT is a disorder of second intention wound healing, primarily occurring in the distal limbs of horses.
  • It is characterized by excessive fibroproliferation, which delays healing and increases treatment duration and costs.
  • In severe cases, poor prognosis may lead to euthanasia due to the difficulty and expense of treatment.
  • The exact biological mechanisms behind EGT are poorly understood, especially concerning the specific collagen types involved and the roles of myofibroblasts and blood vessels.

Objectives of the Study

  • To analyze the collagen composition specifically in naturally occurring EGT in horses.
  • To compare collagen distribution in EGT wounds versus normal healing wounds (control group).
  • To examine the presence and location of activated myofibroblasts (alpha smooth muscle actin-positive cells) and angiogenic markers (indicators of new blood vessel formation).

Methods

  • Wound samples were collected from 19 horses with EGT (EGT group) following trimming procedures.
  • Control samples were obtained from 6 horses through punch biopsies of normal healing wounds.
  • Histological analysis was used to assess collagen distribution in the superficial and deep layers of the wound beds.
  • Immunofluorescence staining was performed to identify and co-localize activated myofibroblasts and angiogenic markers.

Key Findings

  • EGT tissue contained significantly higher amounts of type III collagen (immature collagen) in both superficial and deep wound regions compared to controls.
  • The overall total collagen amount did not significantly differ between EGT and control wounds, indicating the difference lies in collagen type rather than quantity.
  • In the deep layers of EGT, microvessels were often occluded (blocked), and endothelial cells (lining the blood vessels) showed hypertrophy (enlargement), suggesting vascular abnormalities.
  • Myofibroblasts were found throughout the whole wound bed in EGT, indicating ongoing fibrotic activity.
  • Markers for intermediate filaments, which support cellular structure, were reduced in the superficial region of EGT wounds.

Interpretation and Implications

  • The predominance of immature type III collagen in EGT versus more mature collagen types in normal wounds indicates that EGT tissue is less mature and has not progressed through normal healing stages.
  • Abnormal blood vessel structure and persistent activated myofibroblast presence suggest ongoing pathological remodeling rather than resolution of the wound.
  • These findings highlight the potential of targeting collagen maturation and tissue remodeling processes as therapeutic approaches.
  • Encouraging the transition from immature to mature extracellular matrix (ECM) composition may improve healing outcomes and reduce the burden of EGT in horses.

Conclusion

  • Collagen composition in equine EGT significantly differs from normal wound healing, reflecting tissue immaturity.
  • Future treatments aiming to promote ECM maturation could lead to better regeneration and more effective management of EGT in horses.

Cite This Article

APA
Partusch L, Rutland CS, Martens A, Du Cheyne C, De Spiegelaere W, Michler JK. (2025). Collagen composition in equine exuberant granulation tissue reflects tissue immaturity. PLoS One, 20(11), e0335179. https://doi.org/10.1371/journal.pone.0335179

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 20
Issue: 11
Pages: e0335179
PII: e0335179

Researcher Affiliations

Partusch, Lena
  • Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
Rutland, Catrin Sian
  • School of Veterinary Medicine and Science, Sutton Bonington Campus, Faculty of Medicine and Health Sciences, University of Nottingham, Nottingham, United Kingdom.
Martens, Ann
  • Department of Large Animal Surgery, Anaesthesia and Orthopaedics, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
Du Cheyne, Charis
  • Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
De Spiegelaere, Ward
  • Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
Michler, Jule Kristin
  • Physiology and Pathophysiology, Dpt. of Biological Sciences and Pathobiology, University of Veterinary Medicine Vienna, Vienna, Austria.
  • Institute of Anatomy, Histology and Embryology, Faculty of Veterinary Medicine, Leipzig University, Leipzig, Germany.

MeSH Terms

  • Animals
  • Horses
  • Granulation Tissue / metabolism
  • Granulation Tissue / pathology
  • Wound Healing
  • Collagen / metabolism
  • Myofibroblasts / metabolism
  • Myofibroblasts / pathology
  • Male
  • Horse Diseases / metabolism
  • Horse Diseases / pathology
  • Female

Conflict of Interest Statement

The authors declare no competing interests.

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