Faculty Bibliography

Our studies have shown the cytoplasmic domain of the receptor for advanced glycation endproducts (RAGE) binds to the formin molecule, diaphanous-1 (mDia1). mDia1 is a member of the formin family of intracellular molecules involved in cellular migration which act as effectors of Rho GTPase signaling. In RAGE-expressing cells devoid of Drf1 (gene encoding mDia1), incubation with RAGE ligands failed to generate reactive oxygen species or activate key signaling cellular stress pathways. Here, we sought to determine if mDia1 plays key roles in a murine model of diabetic nephropathy (DN). Our preliminary data reveal that mDia1 expression is increased in human and murine diabetic podocytes and parietal epithelial cells in a diffuse and global pattern compared to age-matched controls. Furthermore, expression patterns of mDia1 are highly analogous to those of RAGE. While the role of RAGE has been shown to play a key role in the development of DN, the potential contribution of mDia1 has yet to be elucidated. Therefore, we tested the hypothesis that mDia1 contributes to the development and progression of diabetic renal disease in a murine model. Male wild-type and Drf1-null (WT, Drf1KO; all in the C57BL/6 background) mice were rendered diabetic at 6 weeks of age with streptozotocin and sacrificed after 3 or 6 months of diabetes. Kidneys were harvested and processed for histology and gene expression and stained with periodic-acid Schiff (PAS) and semi-quantitative scoring was used to determine the degree of mesangial sclerosis by average findings in >100 glomeruli/mouse (scale 0-3+; 0=absent, 1=mild, 2=moderate, 3=severe). Glomerular basement membrane (GBM) thickness and podocyte foot process effacement (FPE) were measured by ultrastructural analysis (>8 glomeruli/mouse). Gene expression of inflammatory markers (transforming growth factor beta; Tgfb, interleukin 6; Il6, and monocyte chemoattractant protein 1; Ccl2) were assessed by quantitative real time PCR using RNA prepared from whole kidney cortex and normalized to beta-actin. This preliminary study suggests that deletion of Drf1 in mice results in a substantial protection against indices of DN by reducing podocyte effacement, inflammation and fibrosis in type 1 DM. View this table: In this window In a new window Table 1 Histological and microscopic observations show that mDiaKO mice have a reduced GBM, less podocyte FPE and a decrease in mesangial sclerosis compared to WT mice after 6 months of diabetes. (Table Presented)

Post-translational modification of proteins imparts diversity to protein functions. The process of glycation represents a complex set of pathways that mediates advanced glycation endproduct (AGE) formation, detoxification, intracellular disposition, extracellular release, and induction of signal transduction. These processes modulate the response to hyperglycemia, obesity, aging, inflammation, and renal failure, in which AGE formation and accumulation is facilitated. It has been shown that endogenous anti-AGE protective mechanisms are thwarted in chronic disease, thereby amplifying accumulation and detrimental cellular actions of these species. Atop these considerations, receptor for advanced glycation endproducts (RAGE)-mediated pathways downregulate expression and activity of the key anti-AGE detoxification enzyme, glyoxalase-1 (GLO1), thereby setting in motion an interminable feed-forward loop in which AGE-mediated cellular perturbation is not readily extinguished. In this review, we consider recent work in the field highlighting roles for glycation in obesity and atherosclerosis and discuss emerging strategies to block the adverse consequences of AGEs. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Histone deacetylase 3 (HDAC3), a chromatin-modifying enzyme, requires association with the deacetylase-containing domain (DAD) of the nuclear receptor corepressors NCOR1 and SMRT for its stability and activity. Here, we show that aldose reductase (AR), the rate-limiting enzyme of the polyol pathway, competes with HDAC3 to bind the NCOR1/SMRT DAD. Increased AR expression leads to HDAC3 degradation followed by increased PPARgamma signaling, resulting in lipid accumulation in the heart. AR also downregulates expression of nuclear corepressor complex cofactors including Gps2 and Tblr1, thus affecting activity of the nuclear corepressor complex itself. Though AR reduces HDAC3-corepressor complex formation, it specifically derepresses the retinoic acid receptor (RAR), but not other nuclear receptors such as the thyroid receptor (TR) and liver X receptor (LXR). In summary, this work defines a distinct role for AR in lipid and retinoid metabolism through HDAC3 regulation and consequent derepression of PPARgamma and RAR.

The receptor for advanced glycation endproducts (RAGE) binds diverse ligands linked to chronic inflammation and disease. NMR spectroscopy and x-ray crystallization studies of the extracellular domains of RAGE indicate that RAGE ligands bind by distinct charge- and hydrophobicity-dependent mechanisms. The cytoplasmic tail (ct) of RAGE is essential for RAGE ligand-mediated signal transduction and consequent modulation of gene expression and cellular properties. RAGE signaling requires interaction of ctRAGE with the intracellular effector, mammalian diaphanous 1 or DIAPH1. We screened a library of 58,000 small molecules and identified 13 small molecule competitive inhibitors of ctRAGE interaction with DIAPH1. These compounds, which exhibit in vitro and in vivo inhibition of RAGE-dependent molecular processes, present attractive molecular scaffolds for the development of therapeutics against RAGE-mediated diseases, such as those linked to diabetic complications, Alzheimer's disease, and chronic inflammation, and provide support for the feasibility of inhibition of protein-protein interaction (PPI).

INTRODUCTION: This review focuses on the multi-ligand receptor of the immunoglobulin superfamily - receptor for advanced glycation endproducts (RAGE). The accumulation of the multiple ligands of RAGE in cellular stress milieux links RAGE to the pathobiology of chronic disease and natural aging. Areas covered: In this review, we present a discussion on the ligands of RAGE and the implications of these ligand families in disease. We review the recent literature on the role of ligand-RAGE interaction in the consequences of natural aging; the macro- and microvascular complications of diabetes; obesity and insulin resistance; autoimmune disorders and chronic inflammation; and tumors and Alzheimer's disease. We discuss the mechanisms of RAGE signaling through its intracellular binding effector molecule - the formin DIAPH1. Physicochemical evidence of how the RAGE cytoplasmic domain binds to the FH1 (formin homology 1) domain of DIAPH1, and the consequences thereof, are also reviewed. Expert opinion: We discuss the modalities of RAGE antagonism currently in preclinical and clinical studies. Finally, we present the rationale behind potentially targeting the RAGE cytoplasmic domain-DIAPH1 interaction as a logical strategy for therapeutic intervention in the pathological settings of chronic diseases and aging wherein RAGE ligands accumulate and signal.

Diabetes exacerbates cardiovascular disease, at least in part via suppression of macrophage cholesterol efflux and levels of the cholesterol transporters, ATP binding cassette transporters A1 (ABCA1) and ABCG1. The receptor for advanced glycation end products (RAGE) is highly expressed in human and murine diabetic atherosclerotic plaques, particularly in macrophages. We tested the hypothesis that RAGE suppresses macrophage cholesterol efflux and probed the mechanisms by which RAGE downregulates ABCA1 and ABCG1. Macrophage cholesterol efflux to Apolipoprotein A1 (ApoA1) and High Density Lipoprotein (HDL) and reverse cholesterol transport to plasma, liver and feces were reduced in diabetic macrophages via RAGE. In vitro, RAGE ligands suppressed ABCG1 and ABCA1 promoter luciferase activity and transcription of ABCG1 and ABCA1 through PPARG-responsive promoter elements, but not through Liver X Receptor (LXR) elements. Plasma levels of HDL were reduced in diabetic mice in a RAGE-dependent manner. Laser capture microdissected CD68+ macrophages from atherosclerotic plaques of Ldlr-/- mice devoid of Ager (RAGE) displayed higher levels of Abca1, Abcg1 and Pparg mRNA transcripts vs. Ager-expressing Ldlr-/- mice, in a manner independent of glycemia or plasma levels of total cholesterol and triglyceride. Antagonism of RAGE may fill an important therapeutic gap in the treatment of diabetic macrovascular complications.

Ferroptosis has emerged as a new form of regulated necrosis that is implicated in various human diseases. However, the mechanisms of ferroptosis are not well defined. This study reports the discovery of multiple molecular components of ferroptosis and its intimate interplay with cellular metabolism and redox machinery. Nutrient starvation often leads to sporadic apoptosis. Strikingly, we found that upon deprivation of amino acids, a more rapid and potent necrosis process can be induced in a serum-dependent manner, which was subsequently determined to be ferroptosis. Two serum factors, the iron-carrier protein transferrin and amino acid glutamine, were identified as the inducers of ferroptosis. We further found that the cell surface transferrin receptor and the glutamine-fueled intracellular metabolic pathway, glutaminolysis, played crucial roles in the death process. Inhibition of glutaminolysis, the essential component of ferroptosis, can reduce heart injury triggered by ischemia/reperfusion, suggesting a potential therapeutic approach for treating related diseases.