The traditional view of mitochondria as isolated, spherical, energy producing organelles is undergoing a revolutionary transformation. Emerging data show that mitochondria form a dynamic networked reticulum that is regulated by cycles of fission and fusion. The discovery of a number of proteins that regulate these activities has led to important advances in understanding human disease. We have demonstrated that activation of dynamin related protein 1 (Drp1), a protein that controls mitochondrial fission, is reduced following exercise in prediabetes, and the decrease is linked to increased insulin sensitivity and fat oxidation. We now propose to build on this research and test the hypothesis that mitochondrial dynamics is a key mechanism of insulin resistance in type 2 diabetes. Our central hypothesis is that in diabetes elevated mitochondrial lipid metabolism causes recruitment and activation of Drp1 - likely through increased reactive oxygen species, leading to increased mitochondrial fragmentation and opening of the mitochondrial permeability transition pore.
In Aim 1 a we will perform in vivo and in vitro studies of human skeletal muscle mitochondrial dynamics across the metabolic phenotype ranging from patients with type 2 diabetes, to obese, to lean healthy controls. Translational first-in-man studies will use an acute lipid challenge (Aim 1b) and exercise training (Aim 1c) to investigate the physiological significance of altered skeleta muscle mitochondrial dynamics on insulin sensitivity in humans. Insulin resistance will be assessed using euglycemic hyperinsulinemic clamps, and in vivo substrate metabolism will be measured using indirect calorimetry. Mitochondrial fission/fusion, fragmentation, function, membrane potential, mitochondrial reactive oxygen species, and the accumulation of lipid intermediates will be assessed from muscle biopsy tissue and permeabilized muscle fibers.
In Aim 2, we will use inhibition and expression cloning experiments to directly examine the impact of manipulating mitochondrial fragmentation in intact ex vivo cultured human skeletal muscle cells. This research will provide a comprehensive and complementary analysis of skeletal muscle mitochondrial dynamics, and will also generate novel data on the link between exercise and nutrient regulation of mitochondrial dynamics and function in type 2 diabetes. The experimental approach harnesses innovative molecular and cellular tools, interfaced with physiologically significant human studies to obtain meaningful data on insulin resistance, and has the potential to generate insights that will lead to new diabetes therapies for future generations.

Public Health Relevance

Mitochondria are the critical cellular components that regulate glucose and lipid metabolism, and may hold the key to understanding the pathophysiology of insulin resistance in type 2 diabetes. We will carefully examine the role of mitochondria in insulin resistance by investigating the pathways that regulate a process known as mitochondrial dynamics. These studies are expected to generate new insights into mechanisms of type 2 diabetes and eventually lead to novel therapies for the disease.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Clinical and Integrative Diabetes and Obesity Study Section (CIDO)
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Laughlin, Maren R
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Lsu Pennington Biomedical Research Center
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Baton Rouge
United States
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Axelrod, Christopher L; Fealy, CiarĂ¡n E; Mulya, Anny et al. (2018) Exercise training remodels human skeletal muscle mitochondrial fission and fusion machinery towards a pro-elongation phenotype. Acta Physiol (Oxf) :e13216
Mulya, Anny; Haus, Jacob M; Solomon, Thomas P J et al. (2017) Exercise training-induced improvement in skeletal muscle PGC-1?-mediated fat metabolism is independent of dietary glycemic index. Obesity (Silver Spring) 25:721-729
Mulya, Anny; Kirwan, John P (2016) Brown and Beige Adipose Tissue: Therapy for Obesity and Its Comorbidities? Endocrinol Metab Clin North Am 45:605-21