Inducible Nitric Oxide Synthase Deficiency Impairs Matrix Metalloproteinase-9 Activity and Disrupts Leukocyte Migration in Hepatic Ischemia/Reperfusion Injury

Abstract

Matrix metalloproteinase 9 (MMP-9) is a critical mediator of leukocyte migration in hepatic ischemia/ reperfusion (I/R) injury. To test the relevance of inducible nitric oxide synthase (iNOS) expression on the regulation of MMP-9 activity in liver I/R injury, our experiments included both iNOS-deficient mice and mice treated with ONO-1714, a specific iNOS inhibitor. The inability of iNOS-deficient mice to generate iNOS-derived nitric oxide (NO) profoundly inhibited MMP-9 activity and depressed leukocyte migration in livers after I/R injury. While macrophages expressed both iNOS and MMP-9 in damaged wild-type livers, neutrophils expressed MMP-9 and were virtually negative for iNOS; however, exposure of isolated murine neutrophils and macrophages to exogenous NO increased MMP-9 activity in both cell types, suggesting that NO may activate MMP-9 in leukocytes by either autocrine or paracrine mechanisms. Furthermore, macrophage NO production through the induction of iNOS was capable of promoting neutrophil transmigration across fibronectin in a MMP-9-dependent manner. iNOS expression in liver I/R injury was also linked to liver apoptosis, which was reduced in the absence of MMP-9. These results suggest that MMP-9 activity induced by iNOS-derived NO may also lead to detachment of hepatocytes from the extracellular matrix and cell death, in addition to regulating leukocyte migration across extracellular matrix barriers. These data provide evidence for a novel mechanism by which MMP-9 can mediate iNOS-induced liver I/R injury.

Ex vivo induced regulatory T cells regulate inflammatory response of Kupffer cells by TGF-beta and attenuate liver ischemia reperfusion injury

“…Furthermore, in the current study, we found that the activation of MMP-9 in KCs was decreased markedly in TGF-β-treated animals. Taken together with the findings in other IRI models [35,36], the results support a protective role of TGF-β in liver IRI.…”

Nitric oxide in liver diseases

“…The role of iNOS-derived NO in I/R injury is not straightforward because studies reported on its protective [141], harmful [142] or no [141, 143] effects. These studies differ in the length of ischemia or reperfusion, which may account for the observed different roles of iNOS in liver I/R injury.…”

Uropod elongation is a common final step in leukocyte extravasation through inflamed vessels

“…Mouse neutro phils were isolated from bone marrow (Hamada et al, 2009). In brief, femurs and tibias were harvested and stripped of all muscle and sinew.…”