Distribution of insulin receptor and insulin-like growth factor-1 receptor in the digital laminae of mixed-breed ponies: an immunohistochemical study.

This research indicates that a rise in dietary nonstructural carbohydrates (NSCs) increases the amount of insulin receptors (IRc) in laminar endothelial cells of ponies. These receptors, along with insulin-like growth factor-1 receptors (IGF-1R), could potentially be manipulated to treat or prevent laminitis, an inflammation in hooves associated with high levels of insulin.

Study Design and Methods

• Research was conducted with 22 mixed-breed ponies. These ponies were initially fed a diet composed of approximately 6% nonstructural carbohydrates (NSCs), often found in foods like grains and certain vegetables.
• Later, these ponies were divided into two groups based on their body condition score – lean (score ≤ 4) and obese (score ≥ 7). Each group was further bifurcated, with half continuing with the low NSC diet and the other half being switched to a high NSC diet (total diet ~42% NSC).
• This dietary routine was continued for 7 days. After this period, laminae samples from the ponies’ hooves were collected.
• The samples were stained to highlight the insulin receptor (IRc) and insulin-like growth factor-1 receptor (IGF-1R). IRc-positive cells were quantified and the distribution of IGF-1R was recorded.

Key Findings

• Ponies on a high NSC diet had a greater number of IRc-positive cells in their laminae as compared to those on a low NSC diet. This rise in IRc was also positively correlated with an increase in serum insulin levels.
• No epithelial IRc-positive cells were recorded, suggesting that insulin signalling in laminar epithelial cells is regulated by other receptors, possibly IGF-1R.
• IGF-1Rs were found to be more distributed than IRc, present in vascular elements, epithelial cells, and fibroblasts.
• IRc-positive cells were identified as endothelial cells.

Implications

• The increase in IRc expression due to increased NSC in the diet suggests a potential link between diet and laminitis, a painful condition affecting the hooves of horses.
• The findings could pave the way towards new treatments for laminitis. Modifying the signalling pathways downstream of insulin and IGF-1R may offer a method of preventing or managing laminitis, which is believed to be associated with hyperinsulinaemia.