Lamellar leukocyte infiltration and involvement of IL-6 during oligofructose-induced equine laminitis development.

The research study examines the role of leukocyte infiltration and the gene expression of IL-6 in the development of laminitis, a painful hoof disease in horses, induced by oligofructose. The findings suggest that an increase in IL-6 gene expression may precede leukocyte infiltration, and IL-6 plays a key role in increasing proMMP-9 levels, a protease involved in tissue remodeling and inflammation.

Study Methodology and Process

• To investigate leukocyte infiltration and the gene expression of Interleukin-6 (IL-6) in the lamellae (thin layers of tissue in horses’ hooves), an oligofructose-induced laminitis model was applied in normal standardbred horses. This model was selected because, although leukocyte infiltration has been well-studied in other laminitis models, the oligofructose-induced model has not been previously investigated in this regard.
• Biopsies of lamellar tissues were taken from horses at various times post oligofructose dosing. Real-time polymerase chain reaction (PCR), immunohistochemistry, and zymography methods were used to test and monitor the development and progression of laminitis.
• In vitro experiments were conducted using lamellar explants and keratinocytes, cells that produce keratin, to assess the role of IL-6 in protease regulation, a process linked to the degradation of tissue during laminitis development.

Key Findings

• After 18-24 hours post oligofructose dosing, infiltration of calprotectin-positive leukocytes, specifically monocytes and neutrophils, were ascendant. This signifies the initiation of the horse’s immunologic response to the oligofructose-induced laminitis.
• Leukocyte infiltration was found to occur later than the increase in IL-6 gene expression, which became noticeable as early as 12 hours after dosing. This suggests that IL-6 gene expression may precede and possibly trigger leukocyte infiltration in laminitis development.
• In vitro tests revealed that IL-6 did not cause significant damage to the basement membrane (BM), a part of the lamellae. However, the presence of IL-6 resulted in increased levels of pro Matrix Metalloprotease-9 (proMMP-9), another protease involved in inflammation and tissue remodelling associated with laminitis development. Notably, IL-6’s role in increasing the proMMP-9 levels does not seem to involve keratinocytes.

Conclusion

• The research findings indicate that during oligofructose-induced laminitis development, leukocyte infiltration happens, potentially stimulated by an earlier increase in IL-6 gene expression.
• The study also suggests a role for IL-6 in raising proMMP-9 levels in vivo. This could contribute to our understanding of how inflammation and tissue remodelling processes are regulated during the development of laminitis, providing a basis for further study and potential therapeutic targets for this painful equine condition.