Combined effect of high-fat, high-sugar diet and volumetric muscle loss injury on skeletal muscle bioenergetics, pyruvate dehydrogenase activity and post-translational regulation
Authors: HEO Junwon , Schifino Albino , McFaline-Figueroa Jennifer , Greising Sarah , Call Jarrod 
Published: May 2023

INTRODUCTION: Volumetric muscle loss (VML) injury due to trauma or surgery cannot fully rejuvenate muscle mass and function, resulting in pathologic comorbidities, including alteration in whole-body metabolism, and long-term disability. Western diets (WD), i.e., high-fat, high-sugar diets, are associated with metabolic stress in the skeletal muscle because of the excessive fuel supplies regardless of energy demand. The objective of this study was to determine the extent to which WD affects metabolic function following a VML injury, and to interrogate enzyme kinetics as potential mechanistic contributors if metabolic dysfunction is present. METHODS: Male C57BL/6 mice (N=35) were randomized into four groups: Normal Chow (NC), WD, VML, and VML+WD. At age 12 weeks, VML groups underwent unilateral VML surgery to the plantar flexors (gastrocnemius, plantaris, soleus). WD groups received a 60% high-fat diet plus 11% high-fructose corn syrup for 8 weeks ad libitum, and diet was started at age 12 weeks also. Mitochondrial function was assessed by oxygen consumption rate and electron conductance (efficiency of electron flow) in permeabilized gastrocnemius muscle fibers using carbohydrate substrate glutamate/malate; enzyme kinetic function included citrate synthase (CS) and pyruvate dehydrogenase (PDH); PDH post-translational regulation included immunoblots for PDH kinase 4 (PDK4), PDH phosphatase (PDP), total PDH, phospho-PDHser293. Two-way ANOVA was used to detect significant interaction effects between diet and injury, or in the absence of a significant interaction, the main effects of diet or injury. RESULTS: Mice on WD had 51% greater body mass compared to mice on NC (p<0.001), independent of injury and worse blood glucose regulation (ipGTT 83% higher in WD groups compared to NC groups, irrespective of injury, p<0.001). There were significant interaction effects between diet and injury for permeabilized muscle fiber maximal JO2 (p=0.014) and conductance (p=0.027). Especially, the VML+WD group had 48% lower maximal JO2, and 47% reduced conductance compared to the VML group. PDH enzyme activity was 20% less in WD groups, independent of injury (p<0.001), and 24% lower in VML-injured groups, independent of diets (p<0.001). CS activity was 23% greater in WD groups compared to NC groups, regardless of injury (p=0.005). WD had 48% greater phospho-to-total PDH at the inhibitor site ser293 compared to NC groups, irrespective of injury (p=0.041). CONCLUSIONS: PDH plays an important role in glucose-dependent NADH-linked mitochondrial function as it converts glycolysis end-product pyruvate into acetyl-CoA for Krebs cycle entry. This study demonstrates WD exacerbates carbohydrate-supported mitochondrial function after VML injury. PDH regulation and enzymatic function may influence this phenomenon and future research is required to further define the cellular mechanisms. W81XWH-20-1-0885 to JAC and SMG, R01-AR078903 to JAC and SMG This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.