Elevated muscle TLR4 expression and metabolic endotoxemia in human aging

Area of Science:

• Immunology
• Metabolism
• Aging Research

Background:

• Aging is linked to impaired glucose metabolism and sarcopenia, increasing type 2 diabetes risk.
• Aging is characterized by low-grade inflammation, with toll-like receptor 4 (TLR4) as a key immune mediator.
• Metabolic endotoxemia, elevated plasma endotoxin levels, is associated with metabolic diseases.

Purpose of the Study:

• To investigate altered toll-like receptor 4 (TLR4) signaling in healthy older adults.
• To determine if aerobic exercise reduces TLR4 expression and signaling, mitigating inflammation.
• To explore the relationship between TLR4 signaling, insulin resistance, and sarcopenia in aging.

Main Methods:

• Compared muscle and plasma markers of TLR4 signaling between young and older adults.
• Assessed the impact of a 4-month aerobic exercise program on these markers.
• Measured insulin sensitivity, quadriceps muscle volume, and muscle strength.

Main Results:

• Older adults exhibited elevated muscle TLR4, NF-κB, JNK phosphorylation, and plasma lipopolysaccharide (LPS) and LPS-binding protein, indicating metabolic endotoxemia.
• These changes in older adults correlated with decreased insulin sensitivity, muscle volume, and strength.
• Exercise improved insulin sensitivity but did not affect muscle TLR4 signaling or plasma endotoxin levels.

Conclusions:

• Insulin resistance and sarcopenia in aging are associated with increased TLR4 expression and signaling.
• Elevated TLR4 signaling may be a consequence of metabolic endotoxemia in older individuals.
• Aerobic exercise enhances insulin sensitivity but does not reverse age-related TLR4 pathway alterations.