NLRP3 Inflammasome and Physical Therapy in ICU-Acquired Weakness

Critical illness myopathy (CIM) is a frequent complication in patients admitted to intensive care units (ICUs), characterized by symmetric proximal muscle weakness and respiratory muscle involvement. It has been linked to increased mortality, prolonged hospital stays, and long-term physical disability. CIM may also contribute to post-intensive care syndrome (PICS), which includes persistent cognitive, psychological, and physical impairments. In Chile, approximately 40% of patients with critical illness due to COVID-19 developed this syndrome.

Although several molecular mechanisms have been proposed, the precise etiopathogenesis of CIM remains unclear. Muscle atrophy and contractile dysfunction are hallmark features of CIM. The ubiquitin-proteasome system (UPS) and the upregulation of atrogenes such as MuRF1 and Atrogin-1 have been implicated in its development. In murine models of denervation and sepsis, the NLRP3 inflammasome-a multiprotein complex involved in innate immunity and IL-1β/IL-18 secretion-has been shown to promote muscle atrophy via activation of atrophy-related genes.

Evidence suggests that physical therapy can modulate inflammation at the skeletal muscle level, including downregulation of NLRP3 inflammasome components and IL-1β expression. Mechanical silencing, a major modifiable risk factor in CIM, can be mitigated by early mobilization strategies. However, it remains unknown whether physical therapy directly reduces NLRP3 inflammasome activation and associated muscle atrophy in patients with CIM.

This clinical trial is designed to test the hypothesis that physical therapy decreases NLRP3 inflammasome activity and reduces skeletal muscle atrophy in critically ill patients with CIM. In the early stage of ICU admission, sixteen patients at risk of CIM will be randomized to receive either conventional physical therapy or an enhanced protocol that includes servo-assisted motorized movement therapy (Motomed Letto®), twice daily for 60 minutes. In addition, eight patients without CIM will serve as non-CIM controls.

Muscle biopsy samples from the vastus lateralis will be analyzed to assess histological evidence of muscle atrophy, structural alterations in cellular organelles, and expression of atrophy-related genes. Quantitative real-time PCR (RT-qPCR) will be used to measure mRNA levels of atrogenes, and Western blot will assess protein expression of key mediators of NLRP3 inflammasome signaling. Transcriptomic analysis will be conducted using microarray profiling.

This study will address the following specific aims:

To evaluate the effect of physical therapy on NLRP3 inflammasome activation in skeletal muscle and compare it with non-CIM controls.

To assess the impact of physical therapy on muscle atrophy and explore its relationship with inflammasome activation.

To characterize the gene expression profile of signaling pathways involved in muscle degradation in CIM patients.

To analyze the association between molecular alterations in skeletal muscle and the clinical/ultrasound diagnosis of CIM.

It is expected that enhanced physical therapy will reduce NLRP3 inflammasome activity, attenuate muscle atrophy, and modify gene expression profiles involved in the progression of CIM. These molecular findings are anticipated to correlate with clinical assessments of muscle strength and ultrasound-based diagnosis, supporting the role of early mobilization as a non-pharmacological intervention in the management and prevention of CIM.

Inclusion criteria

• Medical diagnosis of sepsis upon ICU admission.
• Receiving invasive mechanical ventilation with a projected requirement ≥7 days.
• SOFA score ≥8 for three consecutive days within the first five days of ICU admission.

Exclusion criteria

• Neurocritical illness.
• Prior malnutrition or cachexia.
• Pre-existing neuromuscular disease.
• Coagulopathy (severe liver disease or continuous dialysis).
• Thrombocytopenia <20,000 platelets/μL.
• Prior Clinical Frailty Scale ≥4.
• Lower limb amputation or fractures.
• Ongoing chemotherapy.
• Pregnancy.
• BMI >35.
• Uncontrolled epilepsy.
• Allergy to ultrasound gel.
• Prior prolonged corticosteroid therapy.
• Expected ICU stay <7 days.
• Imminent death.
• Legal guardian refusal to provide informed consent.