Enhancement of endothelial permeability by free fatty acid through lysosomal cathepsin B-mediated Nlrp3 inflammasome activation

Abstract

Obesity is an important risk factor for exacerbating chronic diseases such as cardiovascular disease and cancer. High serum level of saturated free fatty acids such as palmitate is an important contributor for obesity-induced diseases. Here, we examined the contribution of inflammasome activation in vascular cells to free fatty acid-induced endothelial dysfunction and vascular injury in obesity. Our findings demonstrated that high fat diet-induced impairment of vascular integrity and enhanced vascular permeability in the myocardium in mice were significantly attenuated by Nlrp3 gene deletion. In microvascular endothelial cells (MVECs), palmitate markedly induces Nlrp3 inflammasome complex formation leading to caspase-1 activation and IL1β production. By fluorescence microscopy and flow cytometry, we observed that such palmitate-induced Nlrp3 inflammasome activated was accompanied by a reduction in inter-endothelial tight junction proteins ZO-1/ZO-2. Such palmitate-induced decrease of ZO-1/ZO-2 was also correlated with an increase in the permeability of endothelial monolayers treated with palmitates. Moreover, palmitate-induced alterations in ZO-1/ZO-2 or permeability were significantly reversed by an inflammasome activity inhibitor, YVAD, or a high mobility group box 1 (HMGB1) activity inhibitor glycyrrhizin. Lastly, blockade of cathepsin B with Ca-074Me significantly abolished palmitate-induced activation of Nlrp3 inflammasomes, down-regulation of ZO-1/ZO-2, and enhanced permeability in MVECs or their monolayers. Together, these data strongly suggest that activation of endothelial inflammasomes due to increased free fatty acids produces HMGB1, which disrupts inter-endothelial junctions and increases paracellular permeability of endothelium contributing to early onset of endothelial injury during obesity.

Trimethylamine-N-Oxide Instigates NLRP3 Inflammasome Activation and Endothelial Dysfunction

“…For example bacterial endotoxin LPS, environmental toxins, high fat diet can contribute to endothelial dysfunction by increasing endothelial permeability and subsequently arterial lipid accumulation in the subendothelial space, thereby initiating atherosclerotic plaque development. Other injurious stimuli like thrombin, histamine and other acute inflammatory mediators can act on endothelium to stimulate opening of their intercellular junctions at the level of adherens and tight junctional complexes [57, 58]. It has been well established that loss of the integrity of inter-endothelial tight junctions contributes to enhanced paracellular endothelial permeability and plasma proteins including albumin and visfatin can impair renal tubular or endothelial tight junctions via activation of Nlrp3 inflammasomes [23, 24, 57, 58].…”

“…Other injurious stimuli like thrombin, histamine and other acute inflammatory mediators can act on endothelium to stimulate opening of their intercellular junctions at the level of adherens and tight junctional complexes [57, 58]. It has been well established that loss of the integrity of inter-endothelial tight junctions contributes to enhanced paracellular endothelial permeability and plasma proteins including albumin and visfatin can impair renal tubular or endothelial tight junctions via activation of Nlrp3 inflammasomes [23, 24, 57, 58]. Consistent with these studies, the present study demonstrates that TMAO treatment induces increases in permeability to dextrans in CAECs, via activation of Nlrp3 inflammasomes (Fig.…”

Staphylococcus aureus α-Toxin Induces Inflammatory Cytokines via Lysosomal Acid Sphingomyelinase and Ceramides

“…For instance, it has been previously shown that infection of endothelial cells with Lactobacillus casei results in increased lysosomal permeability and a release of cathepsin B into the cytoplasm, finally mediating stimulation of the Nlrp3 inflammasome and arteritis [64]. Interestingly, free fatty acids such as palmitate also triggered a cathepsin B-mediated activation of the inflammasome [65] and it remains to be determined whether treatment with S. aureus α-toxin also mediates an intracellular release of free fatty acids contributing to increased lysosomal permeability. However, only a few studies report that bacterial toxins trigger an activation of the inflammasome via cathepsin B [66, 67] and none of these studies has linked the acid sphingomyelinase/ceramide pathway to the inflammasome.…”

Role of free fatty acids in endothelial dysfunction

“…UA also upregulates RAGE expression and other inflammatory cytokines, possibly via the activation of NF-κB transcription factor [45]. A role of HMGB1 in inducement of ED, triggered by FFAs, has also been shown in a previous study [46] , which will be further discussed later in Section 4.3 ; other mechanisms by which FFAs can mediate ED have been discussed in Section 4 . Drug-induced generation of ROS and inflammation also play a major role in the onset of ED.…”