Toll-like receptor 4 (TLR4) mediates innate immune responses following endotoxemia and myocardial ischaemia-reperfusion (I/R) injury. Pre-treatment with the major TLR4 ligand lipopolysaccharide (LPS) reduces infarct size. Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) play a crucial role in endotoxemia possibly also determining I/R injury.
Aims: We investigated the influence of TLR4 on infarct size and assessed the influence of MMP and TIMP regulation on I/R injury.
Methods: Left anterior descending artery (LAD) occlusion was performed on wild-type (C3H/HeN) and TLR4-deficient (C3H/HeJ) mice. Animals were stimulated with LPS (1 mg/kg) or PBS 16 h ahead of 60 min LAD ligation. After 24 h of reperfusion, triphenyltetrazolium chloride staining was performed and infarct size was measured by planimetry. MMP- and TIMP-mRNA expression were determined by RPA after 3 h of reperfusion. MMP zymographic activity was monitored 6 h after occlusion.
Results: TLR4-deficient mice and LPS-treated wild-type mice showed significantly reduced infarct areas. LPS-stimulation significantly increased the overall MMP/TIMP mRNA expression ratio due to elevated MMP-3, -8, -9, and TIMP-1 in wild-type mice. I/R overall reduced the MMP/TIMP ratio due to increased MMP-1, TIMP-1, and -3 mRNA expression.
Conclusions: LPS pre-treatment and TLR4-deficiency led to a decreased infarct size. However, infarct area and MMP/TIMP ratio were not correlated. This means that in TLR4-deficient mice MMP/TIMP ratios are not determining the infarct size.