Mitochondrial Diseases, Mitochondrial Disorders, Mitochondrial Myopathies
Conditions
Keywords
Mitochondrial disease, Muscle metabolism, Insulin resistance
Brief summary
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
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.
Interventions
None listed
Sponsors
University of Copenhagen
Rigshospitalet, Denmark
Study design
Observational model
CASE_CONTROL
Time perspective
CROSS_SECTIONAL
Eligibility
Sex/Gender
ALL
Age
18 Years to No maximum
Healthy volunteers
Yes
Inclusion criteria
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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Muscle mitochondrial respiration | Baseline | Mitochondrial O2 flux is measured by high-resolution respirometry in permeabilized fibers from muscle biopsy samples |
| Skeletal muscle insulin sensitivity | 90-150 minutes after initiation of the hyperinsulinemic euglycemic clamp | 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 |
| Whole-body insulin sensitivity | 90-150 minutes after initiation of the hyperinsulinemic euglycemic clamp | Whole-body insulin sensitivity is determined by the hyperinsulinemic-euglycemic clamp method |
| Muscle mitochondrial proteome | Baseline | Mitochondrial proteome signatures are determined by mass spectrometry-based proteomics in muscle biopsy samples |
| Muscle mitochondrial reactive oxygen species (ROS) production | Baseline | Mitochondrial H2O2 emission rates are measured by high-resolution fluorometry in permeabilized fibers from muscle biopsy samples |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Muscle integrated stress response genes | Baseline | mRNA content of genes governing the integrated stress response pathway is measured by Real-Time PCR in muscle biopsy samples. |
| Muscle release of FGF21 and GDF15 | Before (baseline) and 0-150 minutes after initiation of a hyperinsulinemic-euglycemic clamp | Skeletal muscle production of FGF21 and GDF15 is determined by measurements of femoral artery blood flow and arteriovenous difference of plasma FGF21 and GDF15 |
| Muscle insulin signaling | Before (baseline) and 0-150 minutes after initiation of a hyperinsulinemic-euglycemic clamp | Insulin-mediated changes in the abundance of (phosphorylated) proteins modulating insulin action are measured by immunoblotting in muscle and fat biopsy samples |
| Glucose tolerance | 0-180 minutes after ingestion of an oral glucose solution | Glucose tolerance is determined by the plasma glucose response curve measured during an oral glucose tolerance test |
| Beta cell function | 0-180 minutes after ingestion of an oral glucose solution | Beta cell function is determined by measurements of plasma insulin and insulin C-peptide during an oral glucose tolerance test |
| Muscle mtDNA heteroplasmy | Baseline | mtDNA mutation load is measured in muscle biopsy samples from the patients with mitochondrial myopathy |
| Muscle integrated stress response signaling proteins | Baseline | Abundance of (phosphorylated) proteins modulating the integrated stress response pathway is measured by immunoblotting in muscle biopsy samples. |
Other
| Measure | Time frame | Description |
|---|---|---|
| Body composition | Baseline | Whole-body fat free mass and fat mass are determined by dual-energy X-ray absorptiometry |
| Cardiorespiratory fitness | Baseline | Pulmonary maximal oxygen uptake (VO2max) is determined during an incremental exercise test to exhaustion |
| Self-reported physical activity | Baseline | Self-reported physical activity is measured by the International Physical Activity Questionnaire - Short Form (IPAQ-SF) |
| Physical activity level | Baseline | Physical activity is measured by wrist-worn accelerometers |
| Leg muscle mass | Baseline | Leg muscle mass is determined by dual-energy X-ray absorptiometry |
Countries
Denmark
Outcome results
None listed