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.

Abstract 441: Macrophage CD40 in Atherosclerosis, Obesity and Multiple Sclerosis

Introduction: The co-stimulatory dyad CD40-CD40L plays a central role in fine-tuning immune reactions in atherosclerosis, obesity-induced inflammation and multiple sclerosis (MS). Inhibition of CD40 in atherosclerosis and experimental autoimmune encephalomyelitis (EAE) ameliorates disease outcome, whereas CD40-deficiency in a diet induced obesity (DIO) model worsens insulin resistance and induces excessive adipose tissue inflammation. Although inhibition of CD40 has powerful effects, we do not know which CD40 expressing cell-type is responsible for the amelioration/aggravation of disease. As myeloid CD40 is known to play a role in leukocyte trafficking, which is important in atherosclerosis, obesity and neuro-inflammation, we hypothesize that myeloid CD40 is important in these disease modalities.

Methods: To investigate the role of myeloid CD40 in atherosclerosis, obesity and EAE we have generated macrophage specific LysM-CD40flfl - (ApoE-/-), and dendritic cell/adipose tissue macrophage specific CD11C-CD40flfl). Atherosclerosis was induced by aging the LysM-CD40flfl - ApoE-/- mice until 30 weeks. EAE was induced in LysM-CD40flfl mice by subjecting them to myelin oligodendrocyte glycoprotein peptide (MOG35-55), and LysM-CD40flfl and CD11c-CD40flfl mice were subjected to a 60% high fat diet for 18 wks.

Results: LysM-CD40flfl - ApoE-/- mice showed a significant reduction in atherosclerotic plaque area, with a reduced macrophage accumulation. Loss of macrophage CD40 in EAE results in a significant decrease in the neurological symptoms of EAE, and a majority of the LysM-CD40flfl mice were fully protected against EAE. LysM-CD40flfl mice subjected to DIO showed an increase in macrophage accumulation in the visceral adipose tissue, but did not affect adipose tissue mass, insulin tolerance, or plasma triglyceride concentrations. The CD11CcreCD40flfl mice exhibited a decrease in visceral adipose tissue weight, an increased lipid content in the liver and slightly decreases leukocyte numbers and pro-inflammatory gene expression in the adipose tissue.

Conclusions: Macrophage CD40 is an important driver of atherosclerosis and EAE. Macrophage CD40 is protective in obesity-induced inflammation, but is probably not the key player.

Scattered Deletion of PKD1 in Kidneys Causes a Cystic Snowball Effect and Recapitulates Polycystic Kidney Disease

In total, 1 in 1000 individuals carries a germline mutation in the PKD1 or PKD2 gene, which leads to autosomal dominant polycystic kidney disease (ADPKD). Cysts can form early in life and progressively increase in number and size during adulthood. Extensive research has led to the presumption that somatic inactivation of the remaining allele initiates the formation of cysts, and the progression is further accelerated by renal injury. However, this hypothesis is primarily on the basis of animal studies, in which the gene is inactivated simultaneously in large percentages of kidney cells. To mimic human ADPKD in mice more precisely, we reduced the percentage of Pkd1-deficient kidney cells to 8%. Notably, no pathologic changes occurred for 6 months after Pkd1 deletion, and additional renal injury increased the likelihood of cyst formation but never triggered rapid PKD. In mildly affected mice, cysts were not randomly distributed throughout the kidney but formed in clusters, which could be explained by increased PKD-related signaling in not only cystic epithelial cells but also, healthy-appearing tubules near cysts. In the majority of mice, these changes preceded a rapid and massive onset of severe PKD that was remarkably similar to human ADPKD. Our data suggest that initial cysts are the principal trigger for a snowball effect driving the formation of new cysts, leading to the progression of severe PKD. In addition, this approach is a suitable model for mimicking human ADPKD and can be used for preclinical testing.

Blocking CD40-TRAF6 signaling is a therapeutic target in obesity-associated insulin resistance

The immune system plays an instrumental role in obesity and insulin resistance. Here, we unravel the role of the costimulatory molecule CD40 and its signaling intermediates, TNF receptor-associated factors (TRAFs), in diet-induced obesity (DIO). Although not exhibiting increased weight gain, male CD40(-/-) mice in DIO displayed worsened insulin resistance, compared with wild-type mice. This worsening was associated with excessive inflammation of adipose tissue (AT), characterized by increased accumulation of CD8(+) T cells and M1 macrophages, and enhanced hepatosteatosis. Mice with deficient CD40-TRAF2/3/5 signaling in MHCII(+) cells exhibited a similar phenotype in DIO as CD40(-/-) mice. In contrast, mice with deficient CD40-TRAF6 signaling in MHCII(+) cells displayed no insulin resistance and showed a reduction in both AT inflammation and hepatosteatosis in DIO. To prove the therapeutic potential of inhibition of CD40-TRAF6 in obesity, DIO mice were treated with a small-molecule inhibitor that we designed to specifically block CD40-TRAF6 interactions; this compound improved insulin sensitivity, reduced AT inflammation, and decreased hepatosteatosis. Our study reveals that the CD40-TRAF2/3/5 signaling pathway in MHCII(+) cells protects against AT inflammation and metabolic complications associated with obesity whereas CD40-TRAF6 interactions in MHCII(+) cells aggravate these complications. Inhibition of CD40-TRAF6 signaling by our compound may provide a therapeutic option in obesity-associated insulin resistance.