Single Nuclei Sequencing in Human Skeletal Muscle After Unloading

Overview

Injuries often require people to undergo some degree of limb immobilization. This comes at a high cost in terms of muscle mass and function losses. At the molecular level, it is completely unknown how the different cells in the muscle respond to this complete lack of mechanical stimuli. The investigators will explore cell type specific changes in skeletal muscle after a short period of unloading, and specifically examine the behavior of myogenic stem cells with particular attention to potential unloading-induced maturation into fast- or slow-twitch muscle fibers. Twenty healthy young participants will perform a 5-day Unilateral Lower Limb Suspension (ULLS) intervention, where one leg is continuously subjected to unloading, i.e., lack of mechanical stimuli. Before and after the ULLS period, participants will perform muscle function testing and MRI scans to assess muscle size in the lower limbs. Immediately after the ULLS, two muscle biopsies will be obtained, one from each leg. The tissue will be employed for single-nuclei RNA sequencing analysis and immunohistochemistry experiments. This project will be the first to analyze cell type specific changes induced by complete, short-term lack of mechanical stimuli in skeletal muscle. This will add a new dimension to the understanding of the processes directing this type of muscle atrophy (i.e., muscle loss in otherwise healthy individuals) and thus help to develop effective countermeasures to offset muscle changes.

Interventions

• Other Unilateral lower limb suspension
  Participants will perform a 5-day unloading intervention using the ULLS model. Short-length crutches, aided by handgrip and forearm support distal to the elbow will be used to assist in any upright or ambulatory activity. One foot (randomized in a counterbalance manner) will be equipped with a shoe having a 10-cm thick sole, which permits the unloaded limb to move passively about the hip joint while adopting a near straight position.

Primary outcome measures

• Single nuclei RNA sequencing [Time frame: Immediately after the 5-day unilateral unloading intervention]

Secondary outcome measures (3)

• Muscle mass [Time frame: Before and immediately after the 5-day unloading intervention]
• Concentric isokinetic torque of knee extensor muscles [Time frame: Before and immediately after the 5-day unloading intervention]
• Isometric torque of knee extensor muscles [Time frame: Before and immediately after the 5-day unloading intervention]

Eligibility criteria

Inclusion criteria

• Healthy young adult men and women

Exclusion criteria

• An age younger than 18 or older than 40 years
• Contraindications to magnetic resonance imaging (MRI)
• Contraindications to maximal intensity resistance exercise
• Contraindications to unloading (i.e., ULLS)
• Very high physical activity levels (determined using a standard Godin Leisure-Time Exercise Questionnaire (GLTEQ))
• Hypertension (>140/90 mm Hg)
• History of malignancy
• History of coagulation dysfunction
• History of musculoskeletal or neurological disorders
• History of cardiovascular disease
• History of cerebrovascular disease
• History of respiratory disease
• History of gastrointestinal disease
• History of renal disease
• History of past or present condition requiring long-term drug prescriptions.

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

N/A

Model

Single group

Masking

Open label

Primary purpose

Basic science

Study locations

Sweden · 1 center

• Karolinska Institutet — Huddinge

Identifiers

NCT: NCT05801185 · Dnr 2022-04662-01

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗