Abstract
SummaryBackgroundObesity is a common feature of equine metabolic syndrome (EMS). In other species, obese adipose tissue shows pathological features such as adipocyte hypertrophy, fibrosis, inflammation and impaired insulin signalling all of which contribute to whole body insulin dysregulation. Such adipose tissue dysfunction has not been investigated in horses.ObjectivesTo determine if obese horses with EMS have adipose tissue dysfunction characterised by adipocyte hypertrophy, fibrosis, inflammation and altered insulin signalling.Study designCross‐sectional post‐mortem study.MethodsSamples of peri‐renal (visceral) and retroperitoneal adipose tissue were obtained at post‐mortem from healthy horses (n = 9) and horses with EMS (n = 6). Samples were analysed to determine average adipocyte size, fibrotic content and expression of inflammatory and insulin signalling genes.ResultsHorses with metabolic syndrome showed marked adipocyte hypertrophy and increased expression of adipokines (leptin) and inflammatory cytokines (TNFα,IL1β and CCL2) in both adipose tissue depots compared to healthy horses. There were no differences in fibrosis or expression of genes relating to insulin signalling between the groups.Main limitationsCases used in this study had advanced EMS and may represent the end stage of the condition; the design of the study is such that we were unable to relate the identified adipose tissue dysfunction to whole body insulin dysregulation.ConclusionsHorses with obesity and EMS have significant dysfunction of the peri‐renal and retroperitoneal adipose tissue that may contribute to whole body insulin dysregulation.
Highlights
Equine metabolic syndrome (EMS), defined as a collection of risk factors including insulin dysregulation, genetic predisposition and obesity which increase the animal’s susceptibility to laminitis, is common in domesticated horses [1]
We hypothesised that obese horses with EMS have visceral and retroperitoneal adipose tissue dysfunction characterised by adipocyte hypertrophy, fibrosis, inflammation and altered insulin signalling
We hypothesised that adipose tissue from horses with metabolic syndrome would be dysfunctional with adipocyte hypertrophy, fibrosis, inflammation and altered insulin signalling
Summary
Equine metabolic syndrome (EMS), defined as a collection of risk factors including insulin dysregulation, genetic predisposition and obesity which increase the animal’s susceptibility to laminitis, is common in domesticated horses [1]. Adipose tissue expands in response to calorie intake in excess of nutritional requirements either by increasing adipocyte number (hyperplasia) or increasing adipocyte size (hypertrophy) [3]. Hypertrophy of adipocytes is associated with whole body insulin resistance and elevated fasting plasma insulin [4,5], whilst hyperplasia appears to be a protective phenotype associated with better insulin sensitivity and lipid profiles [6]. Human obese adipose tissue is characterised by increased fibrosis [7], infiltration of macrophages and a pro-inflammatory phenotype [8,9]. The adipose tissue can itself become resistant to the effects of insulin but probably more significantly obese adipose tissue can contribute to whole body insulin resistance though the release of free fatty acids, proinflammatory cytokines and adipokines [10]
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