Pro-inflammatory cytokines and Toll-like receptor 4: A regulatory link?

摘要

Inflammatory cytokines are associated with an increased risk of cardiovascular disease, diabetes mellitus, cachexia, and osteoporosis and are often increased in older persons. Regular exercise may offset age-associated increases in inflammatory cytokines, and reduce the risk of developing diseases with an inflammatory etiology. Toll-like receptor 4 (TLR4) is the primary signaling receptor for lipopolysaccharide and TLR4 signaling stimulates innate immunity and inflammatory cytokine production. To determine the effects of chronic and acute resistance exercise on TLR4 expression, three phases were completed: Phase I (mRNA for whole blood), Phase II (mRNA for muscle), and Phase III (mRNA and cell-surface markers for whole blood). RT-PCR was used to determine mRNA for TLR4, CD14, IL-6, IL-1beta, and TNF-alpha in all phases. Dilute blood cultures (1:10 in RPMI 1640) were stimulated with LPS to determine IL-6, IL-1beta, and TNF-alpha production in phase III. Finally, cell-surface expression of CD14 and TLR4 were determined in phase III using 2-color flow cytometry. Phase III subjects were also divided into high and low groups based on TLR4 cell-surface expression and LPS-stimulated cytokine production was compared. Exercise trained (TR) subjects expressed significantly less mRNA (phase I) and cell-surface (phase III) TLR4 than untrained (UT) subjects. No significant effects were found between TR and UT for TLR4, CD14, IL-6, IL-1beta, or TNF-alpha expression in skeletal muscle (phase II). In phase III, TR and UT had similar LPS-stimulated production of IL-6, IL-1beta and TNF-alpha. High TLR4 expressers produced significantly more IL-6, IL-1beta, and TNF-alpha than low TLR4 expressers. Trained subjects appear to express less TLR4 than untrained older subjects, yet this difference did not consistently result in a difference in LPS-stimulated cytokine production. However, TLR4 was significantly correlated to mRNA and LPS-stimulated production of IL-6, IL-1beta, and TNF-alpha. In conclusion, TLR4 was lower in the blood of trained compared to untrained subjects measured by two different methods (RT-PCR and flow cytometry), but differences in inflammatory cytokines were not consistently observed.