Clinical risk factors of intensive care unit acquired weakness predicted by human muscle microtissue response to humoral factors
1.ICUAW is an acquired phenomenon in the critically ill patient that is characterized by severe muscle weakness and atrophy. It results from both myopathic and neuropathic injury and is associated with heightened patient morbidity and mortality. Critical illness survivors exhibit variable functional outcomes following ICUAW, ranging from full recovery to persistent weakness with a significant negative impact on quality of life. Despite clinical importance, the mechanistic understanding of ICUAW remains incomplete, in part due to a paucity of tractable, species-specific experimental models. Previous studies have suggested a potential causative role of bloodborne factors, though this remains a matter of debate. To address these technological and knowledge gaps, we leveraged a 3-D human skeletal muscle microtissue (hMMT) culture platform to investigate the ability of humoral factors to directly impact pathogenesis of the myopathic component of ICUAW; critical illness myopathy (CIM). Blood serum collected from ICU patients within 72 hours of ICU admission was used to treat hMMTs for 6 days starting at a time-point when the myotubes were multinucleated, striated, and capable of generating force. hMMTs treated with serum from patients that survived the ICU stay exhibited several hallmarks of CIM including; significant reductions in myotube diameter (atrophy) and striation density, alongside functional declines in calcium release, peak force, and force kinetics. The in vitro profiles of ICU serum treated hMMTs displayed significant associations with known ICUAW and CIM clinical risk factors (e.g. age, length of ICU stay) such that individual patient risk factors could be predicted from serum-induced hMMT responses. An evaluation of hMMT responses enabled delineation of ICU non-survivors from healthy control and ICU survivors. This study offers an enabling technology for studies of CIM biology in the context of human cells while also delivering compelling evidence that humoral factors directly influence ICU-associated skeletal muscle pathogenesis. Together, these advances may inform strategies for preventing or treating ICUAW.