Effect of dietary nonstructural carbohydrate content on activation of 5'-adenosine monophosphate-activated protein kinase in liver, skeletal muscle, and digital laminae of lean and obese ponies.
BACKGROUND
In EMS-associated laminitis, laminar failure may occur in response to energy failure related to insulin resistance (IR) or to the effect of hyperinsulinemia on laminar tissue. 5'-Adenosine-monophosphate-activated protein kinase (AMPK) is a marker of tissue energy deprivation, which may occur in IR.


HYPOTHESIS/OBJECTIVES
To characterize tissue AMPK regulation in ponies subjected to a dietary carbohydrate (CHO) challenge.


ANIMALS
Twenty-two mixed-breed ponies.


METHODS
Immunohistochemistry and immunoblotting for total AMPK and phospho(P)-AMPK and RT-qPCR for AMPK-responsive genes were performed on laminar, liver, and skeletal muscle samples collected after a 7-day feeding protocol in which ponies stratified on body condition score (BCS; obese or lean) were fed either a low-CHO diet (ESC + starch, approximately 7% DM; n = 5 obese, 5 lean) or a high-CHO diet (ESC + starch, approximately 42% DM; n = 6 obese, 6 lean).


RESULTS
5'-Adenosine-monophosphate-activated protein kinase was immunolocalized to laminar keratinocytes, dermal constituents, and hepatocytes. A high-CHO diet resulted in significantly decreased laminar [P-AMPK] in lean ponies (P = .03), but no changes in skeletal muscle (lean, P = .33; obese, P = .43) or liver (lean, P = .84; obese, P = .13) [P-AMPK]. An inverse correlation existed between [blood glucose] and laminar [P-AMPK] in obese ponies on a high-CHO diet.


CONCLUSIONS AND CLINICAL IMPORTANCE
Laminar tissue exhibited a normal response to a high-CHO diet (decreased [P-AMPK]), whereas this response was not observed in liver and skeletal muscle in both lean (skeletal muscle, P = .33; liver, P = .84) and obese (skeletal muscle, P = .43; liver, P = .13) ponies.
['Burns|T A|TA|', 'Watts|M R|MR|', 'Weber|P S|PS|', 'McCutcheon|L J|LJ|', 'Geor|R J|RJ|', 'Belknap|J K|JK|']
D055372:AMP-Activated Protein Kinases D000818:Animals D001786:Blood Glucose D015153:Blotting, Western D004040:Dietary Carbohydrates D004789:Enzyme Activation D006724:Hoof and Claw D006734:Horse Diseases D006736:Horses D007328:Insulin D008099:Liver D018482:Muscle, Skeletal D009765:Obesity D060888:Real-Time Polymerase Chain Reaction D013851:Thinness
Laminitis Insulin resistance Energy regulation Equine metabolic syndrome