Mitochondrial Dysfunctions Driving Insulin Resistance

Study Overview
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Brief Summary
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The overarching aim of this observational study is to characterize muscle mitochondrial defects in individuals harboring pathogenic mitochondrial DNA (mtDNA) mutations associated with an insulin-resistant phenotype. In a case-control design, individuals with pathogenic mtDNA mutations will be compared to controls matched for sex, age, and physical activity level. Participants will attend a screening visit and two experimental trials including: An oral glucose tolerance test A hyperinsulinemic-euglycemic clamp combined with measurements of femoral artery blood flow and arteriovenous difference of glucose Muscle biopsy samples

Detailed Description
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Background: Peripheral insulin resistance is a major risk factor for metabolic diseases such as type 2 diabetes. Skeletal muscle accounts for the majority of insulin-stimulated glucose disposal, hence restoring insulin action in skeletal muscle is key in the prevention of type 2 diabetes. Mitochondrial dysfunction is implicated in the etiology of muscle insulin resistance. Also, as mitochondrial function is determined by its proteome quantity and quality, alterations in the muscle mitochondrial proteome may play a critical role in the pathophysiology of insulin resistance. However, insulin resistance is multifactorial in nature and whether mitochondrial derangements are a cause or a consequence of impaired insulin action is unclear. In recent years, the study of humans with genetic mutations has shown enormous potential to establish the mechanistic link between two physiological variables; indeed, if the mutation has a functional impact on one of those variables, then the direction of causality can be readily ascribed. Mitochondrial myopathies are genetic disorders of the mitochondrial respiratory chain affecting predominantly skeletal muscle. Mitochondrial myopathies are caused by pathogenic mutations in either nuclear or mitochondrial DNA (mtDNA), which ultimately lead to mitochondrial dysfunction. Although the prevalence of mtDNA mutations is just 1 in 5,000, the study of patients with mtDNA defects has the potential to provide unique information on the pathogenic role of mitochondrial derangements that is disproportionate to the rarity of affected individuals. The m.3243A>G mutation in the MT-TL1 gene encoding the mitochondrial leucyl-tRNA 1 gene is the most common mutation leading to mitochondrial myopathy in humans. The m.3243A>G mutation is associated with impaired glucose tolerance and insulin resistance in skeletal muscle. Most importantly, insulin resistance precedes impairments of β-cell function in carriers of the m.3243A>G mutation, making these patients an ideal human model to study the causative nexus between muscle mitochondrial dysfunction and insulin resistance. Thus, a comprehensive characterization of mitochondrial functional defects and the associated proteome alterations in patients harboring a mtDNA mutation associated with an insulin-resistant phenotype may elucidate the causal nexus between mitochondrial derangements and insulin resistance. Also, as mitochondrial dysfunction exhibits many faces (e.g. reduced oxygen consumption rate, impaired ATP synthesis, overproduction of reactive oxygen species, altered membrane potential), such an approach may clarify which features of mitochondrial dysfunction play a prominent role in the pathogenesis of insulin resistance. Objective: To characterize muscle mitochondrial defects in individuals harboring pathogenic mitochondrial DNA (mtDNA) mutations associated with an insulin-resistant phenotype. Study design: Case-control study in individuals with pathogenic mtDNA mutations (n=15) and healthy controls (n=15) matched for sex, age, and physical activity level. Endpoint: Differences between individuals with pathogenic mtDNA mutations and controls.

Official Title
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Mitochondrial Derangements Driving Muscle Insulin Resistance in Humans

Conditions
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Mitochondrial Myopathies, Mitochondrial Diseases, Mitochondrial Disorders

Participation Criteria
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Eligibility Criteria
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Eligibility criteria for individuals with pathogenic mtDNA mutations Inclusion criteria: Known m.3243A>G mutation in the MT-TL1 gene encoding the mitochondrial leucyl-tRNA 1 gene Other known mtDNA point mutations Exclusion criteria: Use of antiarrhythmic medications or other medications which, in the opinion of the investigators, have the potential to affect outcome measures. Diagnosed severe heart disease, dysregulated thyroid gland conditions, or other dysregulated endocrinopathies, or other conditions which, in the opinion of the investigators, have the potential to affect outcome measures. Pregnancy Eligibility criteria for controls Exclusion criteria: Current and regular use of antidiabetic medications or other medications which, in the opinion of the investigators, have the potential to affect outcome measures. Diagnosed heart disease, symptomatic asthma, liver cirrhosis or -failure, chronic kidney disease, dysregulated thyroid gland conditions or other dysregulated endocrinopathies, or other conditions which, in the opinion of the investigators, have the potential to affect outcome measures Daily use of tobacco products Excessive alcohol consumption Pregnancy

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Mitochondrial myopathy<br>Individuals with pathogenic mtDNA mutations | |
| Control<br>Individuals without mtDNA mutations | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Skeletal muscle insulin sensitivity | Insulin-stimulated muscle glucose uptake is determined by the hyperinsulinemic-euglycemic clamp method integrated with measurements of femoral artery blood flow and arteriovenous difference of glucose | 90-150 minutes after initiation of the hyperinsulinemic euglycemic clamp | 
| Whole-body insulin sensitivity | Whole-body insulin sensitivity is determined by the hyperinsulinemic-euglycemic clamp method | 90-150 minutes after initiation of the hyperinsulinemic euglycemic clamp | 
| Muscle mitochondrial respiration | Mitochondrial O2 flux is measured by high-resolution respirometry in permeabilized fibers from muscle biopsy samples | Baseline | 
| Muscle mitochondrial reactive oxygen species (ROS) production | Mitochondrial H2O2 emission rates are measured by high-resolution fluorometry in permeabilized fibers from muscle biopsy samples | Baseline | 
| Muscle mitochondrial proteome | Mitochondrial proteome signatures are determined by mass spectrometry-based proteomics in muscle biopsy samples | Baseline | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Glucose tolerance | Glucose tolerance is determined by the plasma glucose response curve measured during an oral glucose tolerance test | 0-180 minutes after ingestion of an oral glucose solution | 
| Beta cell function | Beta cell function is determined by measurements of plasma insulin and insulin C-peptide during an oral glucose tolerance test | 0-180 minutes after ingestion of an oral glucose solution | 
| Muscle mtDNA heteroplasmy | mtDNA mutation load is measured in muscle biopsy samples from the patients with mitochondrial myopathy | Baseline | 
| Muscle insulin signaling | Insulin-mediated changes in the abundance of (phosphorylated) proteins modulating insulin action are measured by immunoblotting in muscle and fat biopsy samples | Before (baseline) and 0-150 minutes after initiation of a hyperinsulinemic-euglycemic clamp | 
| Muscle integrated stress response signaling proteins | Abundance of (phosphorylated) proteins modulating the integrated stress response pathway is measured by immunoblotting in muscle biopsy samples. | Baseline | 
| Muscle integrated stress response genes | mRNA content of genes governing the integrated stress response pathway is measured by Real-Time PCR in muscle biopsy samples. | Baseline | 
| Muscle release of FGF21 and GDF15 | Skeletal muscle production of FGF21 and GDF15 is determined by measurements of femoral artery blood flow and arteriovenous difference of plasma FGF21 and GDF15 | Before (baseline) and 0-150 minutes after initiation of a hyperinsulinemic-euglycemic clamp | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Mitochondrial disease, Muscle metabolism, Insulin resistance