Abstract
Background: NLRP3 inflammasome activation in response to several signals, including mitochondrial DNA (mDNA), regulates inflammatory responses by caspase-1 activation and interleukin-1β (IL-1β) release. Circulating mDNA is linked to micro and macrovascular complications in diabetes. However, a role for mDNA in endothelial dysfunction is not clear. We tested the hypothesis that mDNA contributes to diabetes-associated endothelial dysfunction and vascular inflammation via NLRP3 activation.Methods: Vascular reactivity, reactive oxygen species (ROS) generation, calcium (Ca2+) influx and caspase-1 and IL-1β activation were determined in mesenteric resistance arteries from normoglicemic and streptozotocin-induced diabetic C57BL/6 and NLRP3 knockout (Nlrp3–/–) mice. Endothelial cells and mesenteric arteries were stimulated with mDNA from control (cmDNA) and diabetic (dmDNA) mice.Results: Diabetes reduced endothelium-dependent vasodilation and increased vascular ROS generation and caspase-1 and IL-1β activation in C57BL/6, but not in Nlrp3–/– mice. Diabetes increased pancreatic cytosolic mDNA. dmDNA decreased endothelium-dependent vasodilation. In endothelial cells, dmDNA activated NLRP3 via mitochondrial ROS and Ca2+ influx. Patients with type 1 diabetes exhibited increased circulating mDNA as well as caspase-1 and IL-1β activation.Conclusion: dmDNA activates endothelial NLRP3 inflammasome by mechanisms that involve Ca2+ influx and mitochondrial ROS generation. NLRP3 deficiency prevents diabetes-associated vascular inflammatory damage and endothelial dysfunction. Our study highlights the importance of NLRP3 inflammasome in diabetes-associated vascular dysfunction, which is key to diabetic complications.
Highlights
The NLRP3 inflammasome is a multi-protein complex present in cells of the adaptive and innate immune system
Reduced vasodilation in WT diabetic mice was partially reverted by MCC950, a selective NLRP3 inhibitor (Figure 2B), and completely reverted by the superoxide anion scavenger Tiron (Figure 2C) and by peg-catalase
The present study shows that Nlrp3−/− mice are protected from diabetes-associated inflammatory vascular damage and endothelial dysfunction
Summary
The NLRP3 inflammasome is a multi-protein complex present in cells of the adaptive and innate immune system. In addition to its role on inflammation, IL1β is involved in endothelial dysfunction, a hallmark of several cardiovascular and metabolic diseases, including diabetes (Rizzoni et al, 2001; Beckman et al, 2003). Increased availability of reactive oxygen species (ROS) is a very important mechanism that triggers endothelial dysfunction, being involved in the onset of many diseases. Increased ROS is a classical mechanism that induces NLRP3 inflammasome activation. Many other stimuli, such as lysosomal damage, potassium (K+) efflux, calcium (Ca2+) influx, and DAMPs (damage-associated molecular patterns) induce NLRP3 oligomerization (Brough et al, 2003; Petrilli et al, 2007; Chu et al, 2009; Zhou et al, 2010). We tested the hypothesis that mDNA contributes to diabetesassociated endothelial dysfunction and vascular inflammation via NLRP3 activation
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