Epigenetic Aging of Critical Illness Survivors Assessed by the Muscle-Specific "Clock" and Its Relationship With Reduced Long-Term Muscle Strength.

Critically ill patients requiring treatment in the intensive care unit (ICU) suffer from muscle weakness that persists for years. As compared with healthy subjects, skeletal muscle of patients biopsied five years post-ICU revealed an abnormal transcriptome partially associated with poor muscle strength. We now hypothesized that skeletal muscle of long-term ICU survivors is "epigenetically aged", as determined by a muscle-specific epigenetic clock(definition), and that such accelerated epigenetic aging contributes to their long-term muscle weakness. Muscle DNA-methylation data from former ICU patients at 5-year follow-up (N = 118) and healthy controls (N = 160), aged 18-89 years, were analyzed by the MEATv2 epigenetic clock. First, epigenetic age (DNAmAge), epigenetic minus chronological age (AADiff) and epigenetic age acceleration (AAResid) were compared between 97 former patients and 97 controls, propensity score-matched for age and sex. Next, the impact of any muscle-specific epigenetic aging of ICU survivors was investigated, via multivariable models, as a potential contributor to the altered transcriptome and reduced muscle strength. Former ICU patients showed a significantly higher muscle DNAmAge, AADiff, and AAResid than matched controls. In adjusted models, higher muscle DNAmAge, AADiff, or AAResid did not substantially contribute to differentially expressed muscle RNAs in former patients as compared with controls and was not associated with the poor long-term muscle strength. In conclusion, five years after ICU discharge, former patients showed accelerated epigenetic aging in skeletal muscle. However, the muscle-specific epigenetic clock did not capture molecular changes that are associated with long-term muscle weakness, which highlights the need for other muscle-specific biological predictors of age-related physical impairment. Trail Registration: ClinicalTrials.gov: NCT00512122.