Hyperglycemic Memory of Innate Immune Cells Promotes In Vitro Proinflammatory Responses of Human Monocytes and Murine Macrophages

It has been well established that the presence of diabetes is accompanied by a chronic inflammatory state promoting various diabetes-associated complications. One potential driver of this enhanced inflammatory state in patients with diabetes is hyperglycemia. Even after blood glucose control is achieved, diabetes-associated complications persist, suggesting the presence of a "hyperglycemic memory." Innate immune cells, critically involved in various complications associated with diabetes, can build nonspecific, immunological memory (trained immunity) via epigenetic regulation. We examine the potential involvement of hyperglycemia-induced trained immunity in promoting inflammation. Our results show that hyperglycemia induces a trained phenotype in vivo in mice and in vitro in human monocytes, representative by an increased TNF-α secretion after ex vivo stimulation with LPS. These effects were largely mediated by epigenetic changes controlled by the mixed lineage leukemia (MLL) family because treatment with the MLL inhibitor menin-MLL during the process of trained immunity acquisition repressed the proinflammatory phenotype. Collectively, our results identify a novel link between hyperglycemia and inflammation in innate immune cells that might explain the increased proinflammatory state during diabetes potentially contributing to the development of various diabetes-associated complications.

A High Glycemic Burden Relates to Functional and Metabolic Alterations of Human Monocytes in Patients With Type 1 Diabetes

Diabetes is associated with increased cardiovascular risk and higher occurrence of infections. These complications suggest altered responses of the innate immune system. Recent studies have shown that energy metabolism of monocytes is crucial in determining their functionality. Here we investigate whether monocyte metabolism and function are changed in patients with diabetes and aim to identify diabetes-associated factors driving these alterations. Patients with type 1 diabetes (T1D) (n = 41) and healthy age-, sex-, and BMI-matched control subjects (n = 20) were recruited. Monocytes were isolated from peripheral blood to determine immune functionality, metabolic responses, and transcriptome profiles. Upon ex vivo stimulation with Toll-like receptor (TLR) 4 or TLR-2 agonists, monocytes of patients with T1D secreted lower levels of various cytokines and showed lower glycolytic rates compared with monocytes isolated from matched control subjects. Stratification based on HbA_1c levels revealed that lower cytokine secretion was coupled to higher glycolytic rate of monocytes in patients with a higher glycemic burden. Circulating monocytes displayed an enhanced inflammatory gene expression profile associated with high glycemic burden. These results suggest that a high glycemic burden in patients with T1D is related to expression of inflammatory genes of monocytes and is associated with an impaired relationship between metabolism and inflammatory function upon activation.

Akkermansia muciniphila Exerts Lipid-Lowering and Immunomodulatory Effects without Affecting Neointima Formation in Hyperlipidemic APOE*3-Leiden.CETP Mice

SCOPE

Akkermansia muciniphila (A. muciniphila) is an intestinal commensal with anti-inflammatory properties both in the intestine and other organs. The aim is to investigate the effects of oral administration of A. muciniphila on lipid metabolism, immunity, and cuff-induced neointima formation in hyperlipidemic APOE*3-Leiden (E3L).CETP mice.

METHODS AND RESULTS

Hyperlipidemic male E3L.CETP mice are daily treated with 2 × 108 CFU A. muciniphila by oral gavage for 4 weeks and the effects are determined on plasma lipid levels, immune parameters, and cuff-induced neointima formation and composition. A. muciniphila administration lowers body weight and plasma total cholesterol and triglycerides levels. A. muciniphila influences the immune cell composition in mesenteric lymph nodes, as evident from an increased total B cell population, while reducing the total T cell and neutrophil populations. Importantly, A. muciniphila reduces the expression of the activation markers MHCII on dendritic cells and CD86 on B cells. A. muciniphila also increases whole blood ex vivo lipopolysaccharide-stimulated IL-10 release. Finally, although treatment with A. muciniphila improves lipid metabolism and immunity, it does not affect neointima formation or composition.

CONCLUSIONS

Four weeks of treatment with A. muciniphila exerts lipid-lowering and immunomodulatory effects, which are insufficient to inhibit neointima formation in hyperlipidemic E3L.CETP mice.

Correction to: Rewiring of glucose metabolism defines trained immunity induced by oxidized low-density lipoprotein

The correct name of the 17th Author is presented in this paper.

Deletion of haematopoietic Dectin-2 or CARD9 does not protect from atherosclerosis development under hyperglycaemic conditions

BACKGROUND

C-type lectin receptors, including Dectin-2, are pattern recognition receptors on monocytes and macrophages that mainly recognize sugars and sugar-like structures present on fungi. Activation of C-type lectin receptors induces downstream CARD9 signalling, leading to the production of cytokines. We hypothesized that under hyperglycaemic conditions, as is the case in diabetes mellitus, glycosylated protein (sugar-like) structures activate C-type lectin receptors, leading to immune cell activation and increased atherosclerosis development.

METHODS

Low-density lipoprotein receptor-deficient mice were lethally irradiated and transplanted with bone marrow from control wild-type, Dectin-2^-/- or Card9^-/- mice. After 6 weeks of recovery, mice received streptozotocin injections (50 mg/g BW; 5 days) to induce hyperglycaemia. After an additional 2 weeks, mice were fed a Western-type diet (0.1% cholesterol) for 10 weeks.

RESULTS AND CONCLUSION

Deletion of haematopoietic Dectin-2 reduced the number of circulating Ly6C^hi monocytes, increased pro-inflammatory cytokine production, but did not affect atherosclerosis development. Deletion of haematopoietic CARD9 tended to reduce macrophage and collagen content in atherosclerotic lesions, again without influencing the lesion size. Deletion of haematopoietic Dectin-2 did not influence atherosclerosis development under hyperglycaemic conditions, despite some minor effects on inflammation. Deletion of haematopoietic CARD9 induced minor alterations in plaque composition under hyperglycaemic conditions, without affecting lesion size.

Deletion of hematopoietic Dectin-2 or CARD9 does not protect against atherosclerotic plaque formation in hyperlipidemic mice

Inflammatory reactions activated by pattern recognition receptors (PRRs) on the membrane of innate immune cells play an important role in atherosclerosis. Whether the PRRs of the C-type lectin receptor (CLR) family including Dectin-2 may be involved in the pathogenesis of atherosclerosis remains largely unknown. Recently, the CLR-adaptor molecule caspase recruitment domain family member 9 (CARD9) has been suggested to play a role in cardiovascular pathologies as it provides the link between CLR activation and transcription of inflammatory cytokines as well as immune cell recruitment. We therefore evaluated whether hematopoietic deletion of Dectin-2 or CARD9 reduces inflammation and atherosclerosis development. Low-density lipoprotein receptor (Ldlr)-knockout mice were transplanted with bone marrow from wild-type, Dectin-2- or Card9-knockout mice and fed a Western-type diet containing 0.1% (w/w) cholesterol. After 10 weeks, lipid and inflammatory parameters were measured and atherosclerosis development was determined. Deletion of hematopoietic Dectin-2 or CARD9 did not influence plasma triglyceride and cholesterol levels. Deletion of hematopoietic Dectin-2 did not affect atherosclerotic lesion area, immune cell composition, ex vivo cytokine secretion by peritoneal cells or bone marrow derived macrophages. Unexpectedly, deletion of hematopoietic CARD9 increased atherosclerotic lesion formation and lesion severity. Deletion of hematopoietic CARD9 did also not influence circulating immune cell composition and peripheral cytokine secretion. Besides a tendency to a reduced macrophage content within these lesions, plasma MCP-1 levels decreased upon WTD feeding. Deletion of hematopoietic Dectin-2 did not influence atherosclerosis development in hyperlipidemic mice. The absence of CARD9 unexpectedly increased atherosclerotic lesion size and severity, suggesting that the presence of CARD9 may protect against initiation of atherosclerosis development.

Diabetes propels the risk for cardiovascular disease: sweet monocytes becoming aggressive?

Diabetes strongly predisposes to cardiovascular disease (CVD), the leading cause of mortality in these patients, as well as in the entire population. Hyperglycemia is an important cardiovascular risk factor as shown by the observation that even transient periods of hyperglycemia, despite return to normoglycemia during follow-up, increase the risk for CVD, a phenomenon termed 'hyperglycemic memory'. The molecular mechanisms underlying this phenomenon remain largely unknown. As inflammation plays an important role in the pathogenesis of atherosclerosis, we propose that long-term functional reprogramming of monocytes and macrophages, induced by hyperglycemia, plays an important role in the phenomenon of hyperglycemic memory leading to cardiovascular complications in patients with diabetes. In this review, we discuss recent insights showing that innate immune cells possess the capacity to reprogram their function through epigenetically mediated rewiring of gene transcription, a process termed 'trained immunity'. The long-term reprogramming of monocytes can be induced by microbial as well as metabolic products, and involves a shift in cellular metabolism from oxidative phosphorylation to aerobic glycolysis. We hypothesize that hyperglycemia in diabetes patients induces long-term activation of monocytes and macrophages through similar mechanisms, thereby contributing to plaque development and subsequent macrovascular complications.

[Cheyne-Stokes respiration in patients with chronic heart failure: only a diagnostic marker or also a cardiovascular risk factor?]

Sleep disordered breathing with predominant obstructive or central apnea is an under-recognized but highly prevalent comorbidity in patients with chronic heart failure. As the severity of heart failure increases the prevalence of central sleep apnea (CSA) and Cheyne-Stokes respiration (CSR) is also much more frequent. Cheyne-Stokes respiration is characterized by alternating periods of crescendo and decrescendo respiration followed by central apnea. Present data indicate that CSA-CSR is not only a compensatory response to severe heart failure but also a predictor of worse prognosis. However the results on long-term mortality are not consistent. The prognostic importance of night- and daytime CSR has to be further elucidated. Increased sympathetic nervous activity has been proposed to play a mayor role concerning progression and outcome of chronic heart failure by CSA-CSR.

Tumour necrosis factor-alpha increases intracellular Ca2+ and induces a depolarization in cultured astroglial cells

Tumour necrosis factor (TNF)-alpha, a strong immune mediator, is released within the brain during inflammatory diseases and contributes to immunological activation of glial cells. Here we report that, in astrocytes, TNF-alpha also affects the intracellular Ca2+ homeostasis and basic electrophysiological properties such as the membrane potential. Using the Ca2+ indicator dye fura-2 in a cell culture model, we found that TNF-alpha (10-1000 U ml-1), but not interleukin 1 or 6, induced a slow but more than two-fold increase of the intracellular Ca2+ concentration, which could be blocked by Co2+ (1.0 mM), verapamil (100 microM) or omission of external Ca2+. This intracellular Ca2+ increase was accompanied by a marked decrease of the membrane potential by 35 mV. CSF of patients with bacterial meningitis, known to contain large amounts of TNF-alpha, induced a similar depolarization of astrocytes, which was markedly reduced by a neutralizing anti-TNF-alpha antibody. We conclude that TNF-alpha induces an increase of intracellular Ca2+ and a depolarization in astrocytes with the consequence of disturbing voltage-dependent glial functions such as regulation of local ion concentrations and glutamate uptake. During inflammatory CNS diseases this immuno-electrical coupling may contribute to an impairment of neuronal function.