High-fat diet activates splenic NOD1 and enhances neutrophil recruitment and neutrophil extracellular traps release in the spleen of ApoE-deficient mice

Abstract

In the course of atherogenesis, the spleen plays an important role in the regulation of extramedullary hematopoiesis, and in the control of circulating immune cells, which contributes to plaque progression. Here, we have investigated the role of splenic nucleotide-binding oligomerization domain 1 (NOD1) in the recruitment of circulating immune cells, as well as the involvement of this immune organ in extramedullary hematopoiesis in mice fed on a high-fat high-cholesterol diet (HFD). Under HFD conditions, the absence of NOD1 enhances the mobilization of immune cells, mainly neutrophils, from the bone marrow to the blood. To determine the effect of NOD1-dependent mobilization of immune cells under pro-atherogenic conditions, Apoe−/− and Apoe−/−Nod1−/− mice fed on HFD for 4 weeks were used. Splenic NOD1 from Apoe−/− mice was activated after feeding HFD as inferred by the phosphorylation of the NOD1 downstream targets RIPK2 and TAK1. Moreover, this activation was accompanied by the release of neutrophil extracellular traps (NETs), as determined by the increase in the expression of peptidyl arginine deiminase 4, and the identification of citrullinated histone H3 in this organ. This formation of NETs was significantly reduced in Apoe−/−Nod1−/− mice. Indeed, the presence of Ly6G+ cells and the lipidic content in the spleen of mice deficient in Apoe and Nod1 was reduced when compared to the Apoe−/− counterparts, which suggests that the mobilization and activation of circulating immune cells are altered in the absence of NOD1. Furthermore, confirming previous studies, Apoe−/−Nod1−/− mice showed a reduced atherogenic disease, and diminished recruitment of neutrophils in the spleen, compared to Apoe−/− mice. However, splenic artery ligation reduced the atherogenic burden in Apoe−/− mice an effect that, unexpectedly was lost in Apoe−/−Nod1−/− mice. Together, these results suggest that neutrophil accumulation and activity in the spleen are driven in part by NOD1 activation in mice fed on HFD, contributing in this way to regulating atherogenic progression.

NOD1 cooperates with HAX‐1 to promote cell migration in a RIPK2‐ and NF‐ĸB‐independent manner

“…and Kasimetty et al . reported diminished chemotaxis of neutrophils into the spleen of Nod1 knockout mice in high‐fat diet‐induced atherosclerosis, and into the kidneys in ischemic kidney disease respectively [50,51]. This effect of NOD1 on chemotaxis was cell type specific, as monocyte/macrophage recruitment to the spleen was not affected [50].…”

“…reported diminished chemotaxis of neutrophils into the spleen of Nod1 knockout mice in high‐fat diet‐induced atherosclerosis, and into the kidneys in ischemic kidney disease respectively [50,51]. This effect of NOD1 on chemotaxis was cell type specific, as monocyte/macrophage recruitment to the spleen was not affected [50]. Chan et al ., however, showed that the reason for reduced high‐fat diet‐induced neutrophil infiltration in adipose tissue in Nod1 knockout mice likely is a diminished Cxcl1 production, as they did not observe changes in neutrophil chemotaxis towards Cxcl1 in Nod1 ‐depleted neutrophils [52].…”

High‐fat‐diet induced obesity and diabetes mellitus in Th1 and Th2 biased mice strains: A brief overview and hypothesis

“…43 It is possible that the effects could have been mediated by both T cells and other immune cells or in other tissues such as the spleen. [44][45][46][47][48][49][50] Hence, the absence of Tbet did not prevent the mice from developing obesity but prevented insulin resistance which resembles the phenotype observed in Th2-biased Balbc mice and metabolic healthy humans. [10][11][12] Similarly, deviation to Th2 responses or promoting Th2 biased responses in C57bl/6 mice by administering helminths or products derived from helminths led to improvement in symptoms of diabetes mellitus.…”

“…When Tbet, the major transcription factor for the elicitation of Th1‐type immune responses was knocked out in the C57bl/6 background it led to the dissociation of visceral adiposity and insulin resistance 43 . It is possible that the effects could have been mediated by both T cells and other immune cells or in other tissues such as the spleen 44–50 . Hence, the absence of Tbet did not prevent the mice from developing obesity but prevented insulin resistance which resembles the phenotype observed in Th2‐biased Balbc mice and metabolic healthy humans 10–12 .…”

The perspectives of NETosis on the progression of obesity and obesity-related diseases: mechanisms and applications

“…Feeding an HFD induces neutrophil recruitment into adipose tissue and increases NET formation ( Moorthy et al, 2016 ; Wang et al, 2018a ). NOD1 in HFD-fed mice drives NETosis, which contributes to the regulation of atherogenesis progression ( Fernández-García et al, 2022 ). In recent years, the gut microbiota was found to be strongly associated with NETosis formation.…”