Faculty Bibliography

Exquisite regulation of energy homeostasis protects from nutrient deprivation but causes metabolic dysfunction upon nutrient excess. In human and murine adipose tissue, the accumulation of ligands of the receptor for advanced glycation end products (RAGE) accompanies obesity, implicating this receptor in energy metabolism. Here, we demonstrate that mice bearing global- or adipocyte-specific deletion of Ager, the gene encoding RAGE, display superior metabolic recovery after fasting, a cold challenge, or high-fat feeding. The RAGE-dependent mechanisms were traced to suppression of protein kinase A (PKA)-mediated phosphorylation of its key targets, hormone-sensitive lipase and p38 mitogen-activated protein kinase, upon β-adrenergic receptor stimulation-processes that dampen the expression and activity of uncoupling protein 1 (UCP1) and thermogenic programs. This work identifies the innate role of RAGE as a key node in the immunometabolic networks that control responses to nutrient supply and cold challenges, and it unveils opportunities to harness energy expenditure in environmental and metabolic stress.

Incense burning is common worldwide and produces environmental toxicants that may influence health; however, biologic effects have been little studied. In 303 Emirati adults, we tested the hypothesis that incense use is linked to compositional changes in the oral microbiota that can be potentially significant for health. The oral microbiota was assessed by amplification of the bacterial 16S rRNA gene from mouthwash samples. Frequency of incense use was ascertained through a questionnaire and examined in relation to overall oral microbiota composition (PERMANOVA analysis), and to specific taxon abundances, by negative binomial generalized linear models. We found that exposure to incense burning was associated with higher microbial diversity (p < 0.013) and overall microbial compositional changes (PERMANOVA, p = 0.003). Our study also revealed that incense use was associated with significant changes in bacterial abundances (i.e. depletion of the dominant taxon Streptococcus), even in occasional users (once/week or less) implying that incense use impacts the oral microbiota even at low exposure levels. In summary, this first study suggests that incense burning alters the oral microbiota, potentially serving as an early biomarker of incense-related toxicities and related health consequences. Although a common indoor air pollutant, guidelines for control of incense use have yet to be developed.

Background/UNASSIGNED:(the gene encoding RAGE), have been reported to be associated with T2D and its complications, we tested for potential relationships between these factors and T2D status in Emirati subjects. Methods/UNASSIGNED:In a case-control study, we recruited Emirati subjects with T2D and controls from the Sheikh Khalifa Medical City in Abu Dhabi. Anthropomorphic characteristics, levels of plasma sRAGE and esRAGE, and routine chemistry variables were measured. Results/UNASSIGNED: = 0.01, after adjustment for age and sex). Conclusion/discussion/UNASSIGNED:Levels of sRAGE, but not esRAGE, were associated with T2D status in Abu Dhabi, but not after correction for eGFR. Elevated levels of plasma insulin in both control and T2D subjects suggests the presence of metabolic dysfunction, even in subjects without diabetes.

Macrophages play an essential role in regression of diabetic atherosclerosis. A key player in these processes is Receptor for Advanced Glycation End Products (RAGE), which binds specific ligands enriched in atherosclerotic plaques. Here, we sought to test the mechanisms by which deletion of Ager in diabetic mice accelerates regression of atherosclerosis in an aorta transplantation model in which donor aortic arches from diabetic Ldlr null Western diet-fed mice (CD45.2) are transplanted into diabetic wild-type (WT) or homozygous Ager null mice (CD45.1), thereby effecting lipid lowering and promoting regression, which was improved in Ager null vs. WT mice. We employed RNA sequencing to identify the transcriptional events by which RAGE mediates its effects in donor (CD45.2) and/or recipient (CD45.1) macrophages in diabetic regressing plaques. Our results suggest that critical gene expression profiles, including those genes involved in interferon signaling, particularly the gene encoding interferon regulating factor-7 (Irf7), monocyte/macrophage fate (recruitment, proliferation, apoptosis), and lipid metabolism, are beneficially modulated, at least in part, via Ager deletion particularly in the recipient CD45.1 macrophages in atherosclerosis regression. We tested the role of the IRF7 pathway and our findings, to date, include: 1) There is a decrease in IRF7+/ macrophage area in plaques retrieved from diabetic Ager null vs. diabetic WT mice; 2) Levels of IFN-gamma are lower in diabetic Ager null vs. WT diabetic recipient mice after transplantation; 3) Bone marrow derived macrophages (BMDMs) treated with 2% serum from Ldlr null mice fed Western diet resulted in significant upregulation of Irf7 in WT but not in Ager null BMDMs; and 4) Upon treatment with 2% serum from Ldlr mice fed Western diet, significant upregulation of genes involved in cholesterol transport (Abca1 and Abcg1) was only observed in Ager null but not WT BMDMs compared to treatment with serum from WT normolipidemic mice. These findings suggest that RAGE may affect lipid driven regulation of the interferon-signaling pathway to impair regression of diabetic atherosclerosis. These data may provide avenues for therapeutic strategies to accelerate regression of diabetic atherosclerosis

The Receptor for Advanced Glycation End Products (RAGE) is expressed by multiple cell types in the brain and spinal cord that are linked to the pathogenesis of neurovascular and neurodegenerative disorders, including neurons, glia (microglia and astrocytes) and vascular cells (endothelial cells, smooth muscle cells and pericytes). Mounting structural and functional evidence implicates the interaction of the RAGE cytoplasmic domain with the formin, Diaphanous1 (DIAPH1), as the key cytoplasmic hub for RAGE ligand-mediated activation of cellular signaling. In aging and diabetes, the ligands of the receptor abound, both in the central nervous system (CNS) and in the periphery. Such accumulation of RAGE ligands triggers multiple downstream events, including upregulation of RAGE itself. Once set in motion, cell intrinsic and cell-cell communication mechanisms, at least in part via RAGE, trigger dysfunction in the CNS. A key outcome of endothelial dysfunction is reduction in cerebral blood flow and increased permeability of the blood brain barrier, conditions that facilitate entry of activated leukocytes into the CNS, thereby amplifying primary nodes of CNS cellular stress. This contribution details a review of the ligands of RAGE, the mechanisms and consequences of RAGE signal transduction, and cites multiple examples of published work in which RAGE contributes to the pathogenesis of neurovascular perturbation. Insights into potential therapeutic modalities targeting the RAGE signal transduction axis for disorders of CNS vascular dysfunction and neurodegeneration are also discussed.

Macrophages accumulate prominently in the visceral adipose tissue (VAT) of obese humans and high fat diet (HFD) fed mice, and this is linked to insulin resistance and type II diabetes. While the mechanisms regulating macrophage recruitment in obesity have been delineated, the signals directing macrophage persistence in VAT are poorly understood. We previously showed that the neuroimmune guidance cue netrin-1 is expressed in the VAT of obese mice and humans, where it promotes macrophage accumulation. To better understand the source of netrin-1 and its effects on adipose tissue macrophage (ATM) fate and function in obesity, we generated mice with myeloid-specific deletion of netrin-1 (Ntn1^fl/flLysMCre^+/-; Ntn1^Δmac). Interestingly, Ntn1^Δmac mice showed a modest decrease in HFD-induced adiposity and adipocyte size, in the absence of changes in food intake or leptin, that was accompanied by an increase in markers of adipocyte beiging (Prdm16, UCP-1). Using single cell RNA-seq, combined with conventional histological and flow cytometry techniques, we show that myeloid-specific deletion of netrin-1 caused a 50% attrition of ATMs in HFD-fed mice, particularly of the resident macrophage subset, and altered the phenotype of residual ATMs to enhance lipid handling. Pseudotime analysis of single cell transcriptomes showed that in the absence of netrin-1, macrophages in the obese VAT underwent a phenotypic switch with the majority of ATMs activating a program of genes specialized in lipid handling, including fatty acid uptake and intracellular transport, lipid droplet formation and lipolysis, and regulation of lipid localization. Furthermore, Ntn1^Δmac macrophages had reduced expression of genes involved in arachidonic acid metabolism, and targeted LCMS/MS metabololipidomics analysis revealed decreases in proinflammatory eicosanoids (5-HETE, 6-trans LTB₄, TXB₂, PGD₂) in the obese VAT. Collectively, our data show that targeted deletion of netrin-1 in macrophages reprograms the ATM phenotype in obesity, leading to reduced adipose inflammation, and improved lipid handling and metabolic function.