Abstract
AIMS/HYPOTHESIS: Previous studies reporting lower skeletal muscle mitochondrial function in type 1 diabetes did not account for cardiorespiratory fitness, a key confounder when assessing mitochondrial function. We hypothesised that, compared with healthy individuals, muscle mitochondrial phenotypic differences would be abolished in individuals with type 1 diabetes when matched for age, sex, BMI and maximal oxygen uptake ( V˙O2max ). METHODS: Seventeen individuals with type 1 diabetes and seventeen healthy control individuals matched for age, sex, BMI and V˙O2max participated and underwent a muscle biopsy from the vastus lateralis. Mitochondrial respiration was assessed by high-resolution respirometry, and mitochondrial density and morphology were assessed by transmission electron microscopy. RESULTS: V˙O2max (individuals with type 1 diabetes 40±10 kg(-1) min(-1); control individuals 41±8 ml kg(-1) min(-1); p=0.51) and mitochondrial oxidative phosphorylation capacity (individuals with type 1 diabetes 101±35 [pmol O(2)] s(-1) mg(-1); control individuals 99±23 [pmol O(2)] s(-1) mg(-1), p=0.82) did not differ between groups. Both intermyofibrillar (individuals with type 1 diabetes 6.07±2.16%; control individuals 6.01±1.11%; p=0.92) and subsarcolemmal (individuals with type 1 diabetes 18.70±8.16%; control individuals 19.29±7.36%; p=0.83) mitochondrial densities were not different between groups. Mitochondrial respiration normalised by density did not differ between groups. However, individuals with type 1 diabetes and higher HbA(1c) displayed lower rates of mitochondrial respiration than those with lower HbA(1c), whereas those with higher BMI displayed lower mitochondrial densities than those with lower BMI. CONCLUSIONS/INTERPRETATION: Collectively, our study demonstrates that when matched for age, sex, BMI and V˙O2max , maximal muscle mitochondrial respiration and morphology in people with type 1 diabetes are not impaired. These findings highlight the importance of habitual exercise, optimal glucose management and a healthy BMI in maintaining mitochondrial health in individuals with type 1 diabetes.