IL-10 AND TOLL LIKE RECEPTORS 2 AND 4 IN CARDIAC STRESS CONDITIONS
Pawan K. Singal, Ph.D.,
St. Boniface Hospital Albrechtsen Research Centre, University of Manitoba, Winnipeg, Manitoba, Canada
Aims: It has been suggested that TLR4 promotes IL-10-mediated cardiac cell survival while TLR2 is detrimental. However, the role of these TLRs and their downstream signaling molecules in response to different stresses is not completely known. This study reports a differential role of TLR4 and TLR2 in IL-10 knockout (IL-10 KO) mice and global ischemia/reperfusion (I/R) injury in rat hearts.
Methods and Results: Adult rat ventricular cardiomyocytes as well as cardiac tissue from wild type and IL-10 KO mice (strain C57BL/6) were used. Increase in TLR2 in IL-10 KO hearts indicated its negative regulation by IL-10. Circulating and myocardial levels of TNF-alpha were higher in IL-10 KO hearts. The ex-vivo I/R caused a marked upregulation of TLR2. However, 40min reperfusion with IL-10, triggered an increase in TLR4 expression. Increase in interleukin-1 receptor-associated kinase-M (IRAK-M) and IRAK-2 activity during I/R injury suggested their role in TLR2 signaling. Inhibition of TLR4 activity as a consequence of RNAi-mediated suppression of MyD88 suggests a MyD88-dependent activation of TLR4. IL-10 significantly downregulated the expression of IRAK-2 and TRAIP as well as TGF-beta and its receptor TGF-beta1. IL-10 mitigation of these changes suggests that IL-10 stimulation through TLR4 signaling, dissociates IRAK-4 into IRAK-1 instead of IRAK-2.
Conclusion: Under conditions of stress, an increase in TNF-alpha and upregulation of TLR2 mediated activation of IRAK-M and formation of IRAK-2 from IRAK-4, results in apoptosis and fibrosis. IL-10 significantly reduced TNF-alpha receptor-associated apoptosis during I/R injury and IL-10 KO which reduced TGF-betaRI expression and had an anti-fibrotic action via increase in IL-1beta activity. These data suggest that IL-10, through TLR4 induced innate signaling, restores heart health under conditions of stress due to I/R and a drop in IL-10 in its gene knockout mice.
(Supported by CIHR, Research Manitoba.)