Involvement of Muscle Mitochondrial Dysfunction in Frailty in Older Adults. Role of Exercise

This study aims to investigate the role of skeletal muscle mitochondrial dysfunction in the development of frailty in older adults and to evaluate whether a short-term, supervised resistance training intervention can improve skeletal muscle health and physical function. Frailty is a common age-related condition associated with increased vulnerability to disability, hospitalisation, and loss of independence. It is characterised by features that may include weakness, fatigue, reduced physical activity, and slower walking speed. Mitochondrial dysfunction in skeletal muscle may contribute to the development of frailty and may be further influenced by chronic conditions such as type 2 diabetes mellitus (T2DM), which are associated with metabolic alterations, inflammation, oxidative stress, and insulin resistance. Resistance training is an effective strategy to counteract age-related declines in muscle strength and physical function. However, the cellular and molecular mechanisms linking resistance training to improvements in mitochondrial function, skeletal muscle health, and resilience in older adults remain incompletely understood. The study will include approximately 120 participants comprising older adults with T2DM, healthy older adults, and young healthy controls. All participants will complete a 6-week supervised resistance training intervention, consisting of two sessions per week. Assessments performed before and after the intervention will include body composition, muscle morphology, physical performance, muscle strength, frailty, and blood-based biomarkers. Peripheral blood mononuclear cells (PBMCs) will be used to assess mitochondrial function, and plasma samples will be used for proteomic profiling. Stool samples will be collected for analysis of gut microbiota. A subset of participants will undergo skeletal muscle biopsies of the vastus lateralis at baseline and after the intervention. Muscle samples will be used to assess mitochondrial oxidative phosphorylation capacity, mitochondrial quality-control proteins, muscle fibre morphology, cell-type-specific transcriptomic profiles using single-nucleus RNA sequencing, and chromatin accessibility using ATAC-seq. The study will provide an integrated assessment of the effects of resistance training on mitochondrial function, skeletal muscle biology, physical function, frailty, circulating biomarkers, and gut microbiota. These findings may help clarify the biological mechanisms through which resistance training influences muscle health and resilience during ageing and in older adults with T2DM.

Inclusion Criteria: * Inclusion criteria for young controls * Healthy young adults (18-35 years old) * Without any pathology or treatment * Inclusion criteria for older controls * Healthy older adults (65 years or older) * Not currently enrolled in a resistance training program * Inclusion criteria for cases * Age over 65 years * Diagnosis of frailty or robustness * Diagnosis of type 2 diabetes mellitus * Glycosylated hemoglobin (HbA1c) less than 9% * Treatment with metformin * Not currently enrolled in a resistance training program Exclusion Criteria: * Exclusion criteria for young controls * Pregnancy or suspected pregnancy * Body mass index greater than 35 kg/m2 * Treatment within the last 30 days with oral corticosteroids * Edema or severe fluid regulation disorders that could alter bioimpedance results * Allergy to the local anesthetic mepivacaine * Prostheses, metal implants, or surgical staples lodinated or barium contrast for other imaging tests within the last 7 days * Exclusion criteria for older controls * Decompensated and uncontrolled chronic diagnoses * Body mass index greater than 35 kg/m2 * Treatment within the last 30 days with oral corticosteroids * Systemic diseases, active oncological disease, liver cirrhosis, untreated hypothyroidism, or severe chronic obstructive pulmonary disease (COPD). * Severe edema or fluid regulation disorders that could alter bioimpedance results * Allergy to the local anesthetic mepivacaine * Prostheses, metal implants, or surgical staples Iodinated or barium contrast for other imaging tests in the last 7 days * Exclusion criteria for cases * Diagnosis of pre-frailty * Age over 80 years * Body mass index greater than 35 kg/m2 * Time since onset of diabetes mellitus type 2 less than 10 years * Treatment with insulin * Treatment with allopurinol * Treatment with anticoagulant or antiplatelet drugs * Treatment within the last 30 days with oral corticosteroids * Advanced chronic complications of diabetes mellitus type 2 : Renal failure (clearance \ or = 4, etc.) * Senile dementia * Edema or severe fluid regulation disorders that may alter bioimpedance results * Allergy to the local anesthetic mepivacaine * Pacemaker, metallic prostheses or implants, surgical staples, and radiopaque tubes or catheters Iodinated or barium contrast for other imaging tests within the last 7 days