Impact of hyperlipidemia on alloimmunity

The role of IL-6 in hyperlipidemia-induced accelerated rejection

Hyperlipidemia induces accelerated rejection of cardiac allografts and resistance to tolerance induction using costimulatory molecule blockade in mice due in part to anti-donor Th17 responses and reduced regulatory T cell function. Accelerated rejection in hyperlipidemic mice is also associated with increased serum levels of IL-6. Here, we examined the role of IL-6 in hyperlipidemia-induced accelerated rejection and resistance to tolerance. Genetic ablation of IL-6 prevented hyperlipidemia-induced accelerated cardiac allograft rejection. Using Th17-lineage fate tracking mice, we observed that IL-6 is required to promote the development of anti-donor Th17 lineage cells independently of antigen challenge. In contrast, the frequency of alloreactive T cells producing IL-2 or IFN-γ remained increased in hyperlipidemic IL-6-deficient mice. Ablation of IL-6 overcame hyperlipidemia-induced changes in Tregs, but was not sufficient to overcome resistance to costimulatory molecule blockade induced tolerance. We suggest that accelerated rejection in hyperlipidemic mice results from IL-6 driven anti-donor Th17 responses. While alterations in Tregs were overcome by ablation of IL-6, the reversal of hyperlipidemia-induced changes in Tregs was not sufficient to overcome increased Th1-type anti-donor T cell responses, suggesting that hyperlipidemia induced IL-6-independent effects on recipient immunity prevent tolerance induction.

Obesity-related IL-18 Impairs Treg Function and Promotes Lung Ischemia-reperfusion Injury

RATIONALE

Primary graft dysfunction (PGD) is a severe form of acute lung injury, leading to increased early morbidity and mortality after lung transplantation. Obesity is a major health problem, and recipient obesity is one of the most significant risk factors for developing PGD.

OBJECTIVES

We hypothesized that T-regulatory (Treg) cells are able to dampen early ischemia/reperfusion events and thereby decrease risk of PGD, whereas that action is impaired in obese recipients.

METHODS

We evaluated Treg, T cells and inflammatory markers, plus clinical data, in 79 lung and 41 liver or kidney transplant recipients and studied two groups of mice on high fat diet (HFD), who developed ("inflammatory" HFD) or not ("healthy" HFD) low-grade inflammation with decreased Treg function.

RESULTS

We identified increased levels of IL-18 as a previously unrecognized mechanism that impairs Treg suppressive function in obese individuals. IL-18 decreases levels of FOXP3, the key Treg transcription factor, decreases FOXP3 di- and oligomerization and increases the ubiquitination and proteasomal degradation of FOXP3. IL-18-treated Tregs or Treg from obese mice fail to control PGD, while IL-18 inhibition ameliorates lung inflammation. The IL-18 driven impairment in Treg suppressive function pre-transplant was associated with increased risk and severity of PGD in clinical lung transplant recipients.

CONCLUSION

Obesity-related IL-18 induces Treg dysfunction that may contribute to the pathogenesis of PGD. Evaluation of Treg suppressive function along with IL-18 levels may serve as screening tools to identify pre-transplant obese recipients with increased risk of PGD.

Effects of Huatan Jiangzhuo decoction on diet-induced hyperlipidemia and gene expressions in rats

Huatan Jiangzhuo decoction (HJD) is a combination of six traditional Chinese medicines that were used for lipid metabolism-related disorders, but its efficacy and underlying mechanisms have not been explored by modern research strategies. This study aimed to investigate the therapeutic role of HJD in determining the transcriptome level. Hyperlipidemia model was established by feeding Sprague-Dawley rats with high-fat diet. Differentially expressed genes (DEGs) were detected by high-through transcriptome sequencing, followed by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. The total cholesterol (TC) and triglyceride (TG) levels in hyperlipidemia model rats were significantly increased, whereas high-density lipoprotein (HDL) concentration decreased when compared to normal rats, and HJD significantly downregulated TC concentrations and liver coefficient in the hyperlipidemia rats. Histology staining showed that HDJ greatly recovered the lipid accumulation in rat hepatic stellate cells and aortic arch vascular wall thickness of hyperlipidemia rats. One thousand nine hundred and thirty-six DEGs were identified in the HJD-treated hyperlipidemia rats, which were associated with various biological processes and signaling pathways such as peroxisome proliferator-activated receptors, AMP-activated Protein Kinase , and insulin signaling pathways. Quantitative reverse transcription-polymerase chain reaction further confirmed the downregulated expression of cholesterol 7-α-hydroxylase(CYP7A1), liver orphan receptor(LXRα),peroxisome proliferator-activated receptor gamma(PPARγ),andSterol Response Element-Binding Protein 1c(SREBP1c) genes in hyperlipidemia rats treated with HJD. Our data first elucidated the gene expression profile of high-fat diet-induced hyperlipidemia in rats after HJD treatment, and lipid metabolism-related genes (CYP7A1, LXRα, PPARγ, and SREBP1c) may be potentially biomarkers for HJD-alleviated hyperlipidemia.

Interactions between dyslipidemia and the immune system and their relevance as putative therapeutic targets in atherosclerosis

Cardiovascular disease (CVD) continues to be a leading cause of death worldwide with atherosclerosis being the major underlying pathology. The interplay between lipids and immune cells is believed to be a driving force in the chronic inflammation of the arterial wall during atherogenesis. Atherosclerosis is initiated as lipid particles accumulate and become trapped in vessel walls. The subsequent immune response, involving both adaptive and immune cells, progresses plaque development, which may be exacerbated under dyslipidemic conditions. Broad evidence, especially from animal models, clearly demonstrates the effect of lipids on immune cells from their development in the bone marrow to their phenotypic switching in circulation. Interestingly, recent research has also shown a long-lasting epigenetic signature from lipids on immune cells. Traditionally, cardiovascular therapies have approached atherosclerosis through lipid-lowering medications because, until recently, anti-inflammatory therapies have been largely unsuccessful in clinical trials. However, the recent Canakinumab Antiinflammatory Thrombosis Outcomes Study (CANTOS) provided pivotal support of the inflammatory hypothesis of atherosclerosis in man spurring on anti-inflammatory strategies to treat atherosclerosis. In this review, we describe the interactions between lipids and immune cells along with their specific outcomes as well as discuss their future perspective as potential cardiovascular targets.