Pro-Inflammatory Cytokine and Chemokine Expression Profiles of Various Adipose Tissue Depots of Insulin-Resistant and Insulin-Sensitive Light Breed Horses
Expression of pro-inflammatory cytokines is higher in nuchal adipose tissue (AT) than in other depots of adult horses.
Introduction
Insulin resistance (IR) is associated with laminitis in equids. In humans and rodents, omental AT expresses pro-inflammatory cytokines at higher levels than other depots, correlating with systemic insulin resistance. While this has been suggested to contribute to IR in horses, no published data currently support or refute this hypothesis.
Materials and Methods
Eleven mares, categorized as IR (n = 5) or IS (n = 6) based on results of a FSIGTT, were studied. Under general anesthesia, omental, retroperitoneal, and mesocolonic AT was collected via celiotomy; nuchal ligament and tail head AT was collected via incisional biopsy. Total RNA was extracted; cDNA was analyzed via rt-PCR to quantify expression of TNF-α, IL-1β, IL-6, plasminogen activator inhibitor-1 (PAI-1), and monocyte chemoattractant protein-1 (MCP-1). Data were analyzed using a Kruskal-Wallis test and Dunnett's post-test (p = 0.05).
Results
No differences in expression of TNF-α, IL-1β, IL-6, PAI-1, or MCP-1 were noted between IR and IS groups for each depot. When data from IR and IS groups were pooled, the expression of IL-1β (p = 0.009) and IL-6 (p = 0.023) was significantly higher in nuchal AT than in other depots.
Discussion
Nuchal AT appears to have different biological behavior (displaying an inflammatory phenotype) than other depots.
Clinical Relevance
Nuchal AT is an appropriate non-invasive sample for the study of adipobiology of obesity and IR in adult horses.
Conclusion
Visceral AT may not be as important to the pathophysiology of IR in the horse as in other species.
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