Aims/hypothesis Diabetic patients are at increased risk of cardiomyopathy, acute myocardial infarction and loss of cardiac progenitor cells (CPCs), but the aetiology is poorly understood. We hypothesised a significant role for mannose-binding lectin (MBL) in cardiomyopathies associated with hyperglycaemia. Methods The role of MBL in myocardial ischaemia and reperfusion (MI/R) injury was investigated in wild-type (WT) and MBL-null mice following 2 weeks of streptozotocin-induced hyperglycaemia. Results Hyperglycaemic WT mice presented with significantly decreased left ventricular ejection fractions and increased serum troponin I levels and myocardial inflammation compared with non-diabetic WT mice following MI/R. Hyperglycaemic MBL-null mice or insulin-treated diabetic WT mice were significantly protected from MI/R injury compared with diabetic WT mice. In an additional study using diabetic WT mice, echocardiographic measurements demonstrated signs of dilative cardiomyopathy, whereas heart:body weight ratios suggested hypertrophic cardiac remodelling after 2 weeks of hyperglycaemia. Immunohistochemical analysis of CPCs showed significantly lower numbers in diabetic WT hearts compared with non-diabetic hearts. Insulin-treated diabetic WT or untreated diabetic MBL-null mice were protected from dilative cardiomyopathy, hypertrophic remodelling and loss of CPCs.
Conclusions/interpretationThese data demonstrate that MBL may play a critical role in diabetic MI/R injury. Further, the absence of MBL appears to inhibit hypertrophic remodelling and hyperglycaemia-induced loss of CPCs after just 2 weeks of hyperglycaemia in mice.
Inflammation plays a critical role in promoting smooth muscle migration and proliferation during vascular diseases such as post-angioplasty restenosis and atherosclerosis. Another common feature of many vascular diseases is the contribution of reactive oxygen (ROS) and nitrogen (RNS) species to vascular injury. Primary sources of ROS and RNS in smooth muscle are several isoforms of NADPH oxidase (Nox) and the cytokine-regulated inducible nitric oxide (NO) synthase (iNOS). One important example of the interaction between NO and ROS is the reaction of NO with superoxide to yield peroxynitrite, which may contribute to the pathogenesis of hypertension. In this review, we discuss the literature that supports an alternate possibility: Nox-derived ROS modulate NO bioavailability by altering the expression of iNOS. We highlight data showing co-expression of iNOS and Nox in vascular smooth muscle and demonstrating the functional consequences of iNOS and Nox during vascular injury. We describe the relevant literature demonstrating that the mitogen activated protein kinases (MAP kinases) are important modulators of pro-inflammatory cytokinedependent expression of iNOS. A central hypothesis discussed is that ROS-dependent regulation of the serine/threonine kinase protein kinase Cδ (PKCδ) is essential to understanding how Nox may regulate signaling pathways leading to iNOS expression. Overall, the integration of non-phagocytic NADPHoxidase with cytokine signaling in general and in vascular smooth muscle in particular is poorly understood and merit further investigation.
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