AGEs activate mesangial TGF-beta-Smad signaling via an angiotensin II type I receptor interaction

Unveiling Novel Molecules and Therapeutic Targets in Hypertension - A Narrative Review

Hypertension is a prevalent non-communicable disease with serious cardiovascular complications, including heart failure, myocardial infarction, and stroke, often resulting from uncontrolled hypertension. While current treatments primarily target the renin-angiotensin-aldosterone pathway, the therapeutic response remains modest in many patients, with some developing resistant hypertension. Newer therapeutic approaches aim to address hypertension from various aspects beyond conventional drugs, including targeting central nervous system pathways, inflammatory pathways, vascular smooth muscle function, and baroreceptors. Despite these advancements, each therapy faces unique clinical and mechanistic challenges that influence its clinical translatability and long-term viability. This review explores the mechanisms of novel molecules in preclinical and clinical development, highlights potential therapeutic targets, and discusses the challenges and ethical considerations related to hypertension therapeutics and their development.

Decoding the role of aldosterone in glycation-induced diabetic complications

Diabetes-mediated development of micro and macro-vascular complications is a global concern. One of the factors is hyperglycemia induced the non-enzymatic formation of advanced glycation end products (AGEs). Accumulated AGEs bind with receptor of AGEs (RAGE) causing inflammation, oxidative stress and extracellular matrix proteins (ECM) modifications responsible for fibrosis, cell damage and tissue remodeling. Moreover, during hyperglycemia, aldosterone (Aldo) secretion increases, and its interaction with mineralocorticoid receptor (MR) through genomic and non-genomic pathways leads to inflammation and fibrosis. Extensive research on individual involvement of AGEs-RAGE and Aldo-MR pathways in the development of diabetic nephropathy (DN), cardiovascular diseases (CVDs), and impaired immune system has led to the discovery of therapeutic drugs. Despite mutual repercussions, the cross-talk between AGEs-RAGE and Aldo-MR pathways remains unresolved. Hence, this review focuses on the possible interaction of Aldo and glycation in DN and CVDs, considering the clinical significance of mutual molecular targets.

Network pharmacology and molecular docking combined with widely targeted metabolomics to elucidate the potential compounds and targets of Euphorbia helioscopia seeds for the treatment of pulmonary fibrosis

BACKGROUND

The whole herb of Euphorbia helioscopia has been traditionally used for treating pulmonary tuberculosis, malaria, warts, lung cancer and bacillary dysentery for a long time in China. However, E. helioscopia seeds are often discarded and its medicinal value is often ignored, resulting in a waste of resources.

METHOD

In this work, widely targeted metabolomics based on UPLC-ESI-QTRAP-MS/MS methods and metware database (MWDB) were firstly used to identify the chemical compositions of EHS. Besides, network pharmacology, molecular docking and molecular dynamics simulation were performed for elucidating the potential compounds and targets of E. helioscopia seeds for the treatment of pulmonary fibrosis via common database (like TCMSP, Genecards, DAVID, STRING) and common software (like Sybyl, Cytoscape, Pymol and Schrödinger).

RESULT

The results of widely targeted metabolomics showed 231 compounds including 12 categories were identified. The highest content compositions are lipids (33.89%) followed by amino acids and derivatives (21.78%), nucleotides and derivatives (15.73%), as well as the content of functional ingredients like phenolic acids (7.33%), alkaloids (7.03%) and flavonoids (4.51%) are relatively high. Besides, the results of network pharmacology and molecular docking showed that EHS presented anti-pulmonary fibrosis medicinal value through multi-ingredients, multi-targets and multi-pathways approach. Key ingredients including 9-Hydroxy-12-oxo-15(Z)-octadecenoic acid, Nordihydrocapsiate, 1-O-Salicyl-d-glucose, 9-(Arabinosyl)hypoxanthine, Xanthosine and Galangin-7-O-glucoside. Key targets including SRC, HSP90AA1, AKT1, EGFR, JUN, EP300 and VEGFA, and key signaling pathways mainly related to AGE-RAGE, EGFR tyrosine kinase inhibitor resistance, VEGF and HIF-1 signaling pathway. Molecular dynamics simulation showed that HSP90AA1 and 9-Hydroxy-12-oxo-15(Z)-octadecenoic complex (with the highest docking score) have a stable combination effect.

CONCLUSION

In conclusion, this study revealed the chemical compositions of EHS and its anti-pulmonary fibrosis medicinal effect for the first time, it will provide scientific insight for the development of EHS as medicinal resource.

RAGE signaling regulates the progression of diabetic complications

Diabetes, the ninth leading cause of death globally, is expected to affect 642 million people by 2040. With the advancement of an aging society, the number of patients with diabetes having multiple underlying diseases, such as hypertension, obesity, and chronic inflammation, is increasing. Thus, the concept of diabetic kidney disease (DKD) has been accepted worldwide, and comprehensive treatment of patients with diabetes is required. Receptor for advanced glycation endproducts (RAGE), a multiligand receptor, belonging to the immunoglobulin superfamily is extensively expressed throughout the body. Various types of ligands, including advanced glycation endproducts (AGEs), high mobility group box 1, S100/calgranulins, and nucleic acids, bind to RAGE, and then induces signal transduction to amplify the inflammatory response and promote migration, invasion, and proliferation of cells. Furthermore, the expression level of RAGE is upregulated in patients with diabetes, hypertension, obesity, and chronic inflammation, suggesting that activation of RAGE is a common denominator in the context of DKD. Considering that ligand–and RAGE–targeting compounds have been developed, RAGE and its ligands can be potent therapeutic targets for inhibiting the progression of DKD and its complications. Here, we aimed to review recent literature on various signaling pathways mediated by RAGE in the pathogenesis of diabetic complications. Our findings highlight the possibility of using RAGE–or ligand–targeted therapy for treating DKD and its complications.

RAGE pathway activation and function in chronic kidney disease and COVID-19

The multi-ligand receptor for advanced glycation end-products (RAGE) and its ligands are contributing factors in autoimmunity, cancers, and infectious disease. RAGE activation is increased in chronic kidney disease (CKD) and coronavirus disease 2019 (COVID-19). CKD may increase the risk of COVID-19 severity and may also develop in the form of long COVID. RAGE is expressed in essentially all kidney cell types. Increased production of RAGE isoforms and RAGE ligands during CKD and COVID-19 promotes RAGE activity. The downstream effects include cellular dysfunction, tissue injury, fibrosis, and inflammation, which in turn contribute to a decline in kidney function, hypertension, thrombotic disorders, and cognitive impairment. In this review, we discuss the forms and mechanisms of RAGE and RAGE ligands in the kidney and COVID-19. Because various small molecules antagonize RAGE activity in animal models, targeting RAGE, its co-receptors, or its ligands may offer novel therapeutic approaches to slowing or halting progressive kidney disease, for which current therapies are often inadequate.

Pharmacological activation of estrogenic receptor G protein-coupled receptor 30 attenuates angiotensin II-induced atrial fibrosis in ovariectomized mice by modulating TGF-β1/smad pathway

BACKGROUND

G-protein-coupled ER (GPR30) plays an important role in cardioprotection. Recent studies have shown that the GPR30-specific agonist G-1 reduces the degree of myocardial fibrosis in rats with myocardial infarction, reduces the morbidity associated with atrial fibrillation, and inhibits the proliferation of cardiac fibroblasts in animal experiments. Nevertheless, the underlying mechanism of myocardial fibrosis and atrial fibrillation remains unclear. In this study, we explored the mechanism underlying the effect of GPR30 on atrial fibrosis and atrial fibrillation in OVX mice.

METHODS

We established an animal model of atrial fibrillation induced by Ang II (derived from OVX C57BL/6 female mice) and observed the role of G-1 in cardiac function by echocardiography, hemodynamics, morphology and fibrosis-related and apoptosis-related protein expression by Masson's trichrome, immunofluorescence, western blotting and TUNEL staining.

RESULTS

Echocardiography and body surface ECG showed that G-1 combined with Ang II significantly reduced atrial fibrosis and atrial fibrillation compared to Ang II alone. The G-1 treatment group exhibited changes in the mRNA and protein expression of apoptosis-related genes. Moreover, G-1 treatment also altered the levels of inflammation-related proteins and mRNAs. In primary cultured cardiac fibroblasts (CFSs), proliferation was significantly increased in response to Ang II, and G-1 inhibited cell proliferation and apoptosis.

CONCLUSION

GPR30 is a potential therapeutic target for alleviating atrial fibrosis in OVX mice by upregulating Smad7 expression to inhibit the TGF-β/Smad pathway.

Modification of Fibronectin by Non-Enzymatic Glycation Impairs K+ Channel Function in Rat Cerebral Artery Smooth Muscle Cells

Fibronectin (FN) enhances K+ channel activity by integrin-mediated mechanisms. As vascular smooth muscle (VSM) K+ channels mediate vasodilation, we hypothesized that modification of fibronectin, via advanced non-enzymatic glycation, would alter signaling of this extracellular matrix protein through these channels. Bovine FN (1 mg/ml) was glycated (gFN) for 5 days using methylglyoxal (50 mM), and albumin was similarly glycated as a non-matrix protein control. VSM cells were isolated from rat cerebral arteries for measurement of macroscopic K+ channel activity using whole cell patch clamp methodology. Pharmacological inhibitors, iberiotoxin (0.1 μM) and 4-aminopyridine (0.1 mM), were used to identify contributions of large-conductance, Ca2+-activated, K+ channels and voltage-gated K+ channels, respectively. Compared with baseline, native FN enhanced whole cell K+ current in a concentration-dependent manner, whereas gFN inhibited basal current. Furthermore, native albumin did not enhance basal K+ current, but the glycated form (gAlb) caused inhibition. gFN was shown to impair both the Kv and BKCa components of total macroscopic K+ current. Anti-integrin α5 and β1 antibodies attenuated the effects of both FN and gFN on macroscopic K+ current at +70 mV. Consistent with an action on BKCa activity, FN increased, whereas gFN decreased the frequency of spontaneous transient outward current (STOCs). In contrast, gAlb inhibited whole cell K+ current predominantly through Kv, showing little effect on STOCs. A function-blocking, anti-RAGE antibody partially reversed the inhibitory effects of gFN, suggesting involvement of this receptor. Further, gFN caused production of reactive oxygen species (ROS) by isolated VSMCs as revealed by the fluorescent indicator, DHE. Evoked ROS production was attenuated by the RAGE blocking antibody. Collectively, these studies identify ion channel-related mechanisms (integrin and ROS-mediated) by which protein glycation may modify VSMC function.

Effects of Smoking on Diabetic Nephropathy

Diabetes is a systemic metabolic disease with serious complications that cause significant stress on the healthcare system. Diabetic kidney disease is the primary cause of end stage renal disease globally and its progression is accelerated by various factors. Another major healthcare hazard is tobacco consumption and smoking has deleterious effects on renal physiology. Prominent factors are defined as sympathetic activity, atherosclerosis, oxidative stress and dyslipidemia. This review aims to enlighten the mechanism underlying the cumulative negative effect of simultaneous exposure to hyperglycemia and nicotine.

The combination of ursolic acid and empagliflozin relieves diabetic nephropathy by reducing inflammation, oxidative stress and renal fibrosis

Studies have shown that ursolic acid (UA) and empagliflozin (EM) exert therapeutic effects in the treatment of diabetic nephropathy (DN), but both drugs have disadvantages. This study explores the effect of combining these drugs compared to that of either monotherapy. A diabetic rat model was established by feeding a high-fat diet (HFD) with high-sugar content and administering a low dose of streptozotocin (STZ) via intraperitoneal injection. UA (50 mg/kg/day, po), EM (10 mg/kg/day, po) or both were administered for 8 weeks. The development of DN was determined by observing increases in urine protein, serum creatinine, urea nitrogen, and uric acid and abnormal changes in kidney morphology. UA and EM either alone or in combination can alleviate the increases in blood glucose, glycosylated haemoglobin, blood lipid levels, inflammatory factors (TNF-α, IL-1β, IL-6), oxidation factors (SOD, MDA, GSH, CAT, NO), renal fibrosis and pro-fibrosis factors (FN, E-cad, MMP-9, TIMP-1, SMA-α, TGF-β1, SMAD, MAPK). The treatments could also ameliorate DN by preventing the abnormal proliferation of glomerular mesangial cells under high-glucose conditions, aberrant apoptosis and excessive production of reactive oxygen species (ROS). In addition, UA reduces the increase in LDL-L, reverses abnormal bladder morphology and mitigates the increase in colony count caused by EM, and the combination treatment can overcome the disadvantages of the slow hypoglycaemic effect of UA. In short, UA combined with empagliflozin is more effective than either monotherapy in the treatment of DN and can cancel the adverse effects of each other. The protective effect of this regimen on the kidney may be related to reducing inflammation, oxidative stress and renal fibrosis.

A comprehensive review on RAGE-facilitated pathological pathways connecting Alzheimer’s disease, diabetes mellitus, and cardiovascular diseases

Background

Alzheimer’s disease (AD), cardiovascular disease (CVD), and diabetes are some of the most common causes of morbidity and mortality among the aging populations and cause a heavy burden on the worldwide healthcare system. In this review, we briefly highlighted cellular inflammation-based pathways of diabetes mellitus and CVD through receptor for advanced glycation end products AGEs or RAGE leading to Alzheimer’s disease and interrelation between these vascular and metabolic disorders. The articles were retrieved from Google Scholar, Science Direct, and PubMed databases using the following terms: Alzheimer’s; AGEs; RAGE; RAGE in Alzheimer’s; AGEs in Alzheimer’s; RAGE in diabetes; RAGE related pathways of CVD; RAGE in hypertension; RAGE and RAS system; RAGE and oxidative stress.

Main body of the abstract

AD is a neurodegenerative disease characterized by cognitive dysfunction and neuronal cell death. Vascular complications like hypertension, coronary artery disease, and atherosclerosis as well as metabolic syndromes like obesity and diabetes are related to the pathophysiology of AD. RAGE plays significant role in the onset and progression of AD. Amyloid plaques and neurofibrillary tangles (NFT) are two main markers of AD that regulates via RAGE and other RAGE/ligands interactions which also induces oxidative stress and a cascade of other cellular inflammation pathways leading to AD. Though AD and diabetes are two different disorders but may be inter-linked by AGEs and RAGE. In long-term hyperglycemia, upregulated AGEs interacts with RAGE and produces reactive oxygen species which induces further inflammation and vascular complications. Aging, hypercholesterolemia, atherosclerosis, hypertension, obesity, and inflammation are some of the main risk factors for both diabetes and dementia. Chronic hypertension and coronary artery disease disrupt the functions of the blood-brain barrier and are responsible for the accumulation of senile plaques and NFTs.

Short conclusion

RAGE plays a role in the etiology of Aβ and tau hyperphosphorylation, both of which contribute to cognitive impairment. So far, targeting RAGE may provide a potential sight to develop therapies against some metabolic disorders.

Advanced glycation end productions and tendon stem/progenitor cells in pathogenesis of diabetic tendinopathy

Tendinopathy is a challenging complication observed in patients with diabetes mellitus. Tendinopathy usually leads to chronic pain, limited joint motion, and even ruptured tendons. Imaging and histological analyses have revealed pathological changes in various tendons of patients with diabetes, including disorganized arrangement of collagen fibers, microtears, calcium nodules, and advanced glycation end product (AGE) deposition. Tendon-derived stem/ progenitor cells (TSPCs) were found to maintain hemostasis and to participate in the reversal of tendinopathy. We also discovered the aberrant osteochondrogenesis of TSPCs in vitro. However, the relationship between AGEs and TSPCs in diabetic tendinopathy and the underlying mechanism remain unclear. In this review, we summarize the current findings in this field and hypothesize that AGEs could alter the properties of tendons in patients with diabetes by regulating the proliferation and differentiation of TSPCs in vivo.

The perplexing role of RAGE in pulmonary fibrosis: causality or casualty?

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease in which most patients die within 3 years of diagnosis. With an unknown etiology, IPF results in progressive fibrosis of the lung parenchyma, diminishing normal lung function, which results in respiratory failure, and eventually, death. While few therapies are available to reduce disease progression, patients continue to advance toward respiratory failure, leaving lung transplantation the only viable option for survival. As incidence and mortality rates steadily increase, the need for novel therapeutics is imperative. The receptor for advanced glycation endproducts (RAGE) is most highly expressed in the lungs and plays a significant role in a number of chronic lung diseases. RAGE has long been linked to IPF; however, confounding data from both human and experimental studies have left an incomplete and perplexing story. This review examines the present understanding of the role of RAGE in human and experimental models of IPF, drawing parallels to recent advances in RAGE biology. Moreover, this review discusses the role of RAGE in lung injury response, type 2 immunity, and cellular senescence, and how such mechanisms may relate to RAGE as both a biomarker of disease progression and potential therapeutic target in IPF.The reviews of this paper are available via the supplemental material section.

Inhibition of double stranded RNA dependent protein kinase (PKR) abrogates isoproterenol induced myocardial ischemia in vitro in cultured cardiomyocytes and in vivo in wistar rats

Protein kinase R (PKR) plays a main role in inflammation, insulin resistance, and glucose balance. It is activated by various stress signals and is key mediators of diabetes and associated complications. In the present study, we investigated the effect of PKR inhibition on myocardial dysfunction, inflammatory, cell death and interrelated signalling pathways in isoproterenol induced myocardial ischemia in vivo in wistar rats and in vitro in cultured cardiomyocytes. H9C2 rat cardiomyocytes were treated with 10 μM Isoproterenol (ISO). For in vivo studies, rats were divided into 4 groups: control, ischemic group (ISO), preventive group, curative group and each group consist of 8 rats. Myocardial Ischemia (MI) was induced with two subsequent doses of ISO (100 mg/kg, s.c.). The rats were treated with PKR inhibitor, C16 (166.5 μg/kg, i.p.) for 14 days. Heart rate, systolic, diastolic and mean arterial pressures were measured by non-invasive BP apparatus. Cardiac biomarkers were measured by commercial kits. Ischemic Zone, Morphological abnormalities and fibrosis of heart was detected by TTC, haematoxylin & eosin staining, Masson's and Sirius red staining respectively. Protein expression was done by western blotting and immune histochemistry. mRNA expression was done by RT-PCR. MI was characterized by declined myocardial performance along with elevation of cardiac biomarkers and associated with increased expression of PKR, oxidative-nitrosative stress, activated various inflammatory pathways (nuclear factor kappa light chain enhancer of activated B cells -NF-κB); Mitogen-activated protein kinases-MAPK; c-Jun N-terminal kinase-JNK), increased expression of inflammatory markers (Tumour necrosis factor alpha-TNF-α), markers of fibrosis (Alpha smooth muscle actin -α-SMA; Transforming growth factor beta-TGF-β), enhanced cell death (Ischemic zone) and increased expression of extracellular regulated-kinases (ERK-1/2) and advanced glycation end products (AGE's). Interestingly, inhibition of PKR attenuated myocardial dysfunction, cardiac fibrosis, oxidative/nitrosative stress, inflammation, cell death, and inter-related signalling pathways. Our findings report that inhibition of PKR improves the ischemic mediated inflammation, apoptosis, cardiac hypertrophy and fibrosis in MI induced rats. Hence, inhibition of PKR might be one of intervention therapy for the treatment of myocardial ischemia.

The axis of the receptor for advanced glycation endproducts in asthma and allergic airway disease

Asthma is a generalized term that describes a scope of distinct pathologic phenotypes of variable severity, which share a common complication of reversible airflow obstruction. Asthma is estimated to affect almost 400 million people worldwide, and nearly ten percent of asthmatics have what is considered "severe" disease. The majority of moderate to severe asthmatics present with a "type 2-high" (T2-hi) phenotypic signature, which pathologically is driven by the type 2 cytokines Interleukin-(IL)-4, IL-5, and IL-13. However, "type 2-low" (T2-lo) phenotypic signatures are often associated with more severe, steroid-refractory neutrophilic asthma. A wide range of clinical and experimental studies have found that the receptor for advanced glycation endproducts (RAGE) plays a significant role in the pathogenesis of asthma and allergic airway disease (AAD). Current experimental data indicates that RAGE is a critical mediator of the type 2 inflammatory reactions which drive the development of T2-hi AAD. However, clinical studies demonstrate that increased RAGE ligands and signaling strongly correlate with asthma severity, especially in severe neutrophilic asthma. This review presents an overview of the current understandings of RAGE in asthma pathogenesis, its role as a biomarker of disease, and future implications for mechanistic studies, and potential therapeutic intervention strategies.

Proteomic Investigation of Glyceraldehyde-Derived Intracellular AGEs and Their Potential Influence on Pancreatic Ductal Cells

Glyceraldehyde-derived advanced glycation end products (AGEs) play an important role in the pathogenesis of many diseases including cancer. Accumulation of intracellular AGEs could stimulate cancer induction and facilitate cancer progression. We evaluated the toxic effect of glyceraldehyde-derived intracellular AGEs on normal and malignant pancreatic ductal cells by assessing the cell viability, toxicity, and oxidative stress, followed by proteomic analysis. Our functional studies showed that pancreatic cancer cells (PANC-1 and MIA PaCa-2) were more resistant to glyceraldehyde treatment compared to normal pancreatic ductal epithelial cells (HPDE), while cytotoxicity effects were observed in all cell types. Furthermore, using ¹³C isotopic labeled glyceraldehyde, the proteomic data revealed a dose-dependent increment of the number of glycation adducts in both these cell types. HPDE cells showed a higher number of intracellular AGEs compared to cancer cells. At a molecular level, the glycations in the lysine residues of proteins showed a concurrent increase with the concentration of the glyceraldehyde treatment, while the arginine glycations appeared to be less affected by the glyceraldehyde doses. Further pathway analysis of these glycated proteins suggested that the glycated proteins participate in important biological processes that are major hallmarks of cancer initiation and progression, including metabolic processes, immune response, oxidative stress, apoptosis, and S100 protein binding.

RAGE ligands stimulate angiotensin II type I receptor (AT1) via RAGE/AT1 complex on the cell membrane

The receptor for advanced glycation end-products (RAGE) and the G protein-coupled angiotensin II (AngII) type I receptor (AT1) play a central role in cardiovascular diseases. It was recently reported that RAGE modifies AngII-mediated AT1 activation via the membrane oligomeric complex of the two receptors. In this study, we investigated the presence of the different directional crosstalk in this phenomenon, that is, the RAGE/AT1 complex plays a role in the signal transduction pathway of RAGE ligands. We generated Chinese hamster ovary (CHO) cells stably expressing RAGE and AT1, mutated AT1, or AT2 receptor. The activation of two types of G protein α-subunit, Gq and Gi, was estimated through the accumulation of inositol monophosphate and the inhibition of forskolin-induced cAMP production, respectively. Rat kidney epithelial cells were used to assess RAGE ligand-induced cellular responses. We determined that RAGE ligands activated Gi, but not Gq, only in cells expressing RAGE and wildtype AT1. The activation was inhibited by an AT1 blocker (ARB) as well as a RAGE inhibitor. ARBs inhibited RAGE ligand-induced ERK phosphorylation, NF-κB activation, and epithelial-mesenchymal transition of rat renal epithelial cells. Our findings suggest that the activation of AT1 plays a central role in RAGE-mediated cellular responses and elucidate the role of a novel molecular mechanism in the development of cardiovascular diseases.

Establishment of a Nanopatterned Renal Disease Model by Mimicking the Physical and Chemical Cues of a Diseased Mesangial Cell Microenvironment

Modulation of mesangial cell (MC) response by in vitro disease models offers therapeutic strategies for the treatment of several glomerular diseases. However, traditional cell culture models lack the nanostructured extracellular matrix (ECM), which has unique physical and chemical properties, so they poorly reflect the complexities of the native microenvironment. Therefore, a cell disease model with ECM nanostructures is required to better mimic the in vivo diseased nanoenvironment. To establish a renal disease model, we used a titanium dioxide-based disease-mimic nanopattern as the physical cues and transforming growth factor-beta 1 (TGF-β1) as a chemical cue. The effects of this renal disease model on proliferation and mesangial matrix (MM) component changes in the SV40MES13 (MES13) mouse mesangial cell line were evaluated. Our results showed that both the presence of the disease-mimic nanopattern and TGF-β1 intensified proliferation and resulted in increased type I collagen and fibronectin and decreased type IV collagen expressions in MES13 cells. These effects could be involved in increased TGF-β type I receptor expression in MES13 cells. The intracellular reactive oxygen species (ROS) level as a biomarker of this renal disease model indicated that the cells were in a diseased state. A small molecule A83-01 and known drug dexamethasone markedly attenuated the intracellular ROS production in MES13 that was induced by the disease-mimic nanopattern and TGF-β1. These results highlight the significant effects of physical and chemical cues in facilitating disease-like behavior in MES13 cells, providing an important theoretical basis for developing a drug screening platform for glomerular diseases.

Fibrosis in Chronic Kidney Disease: Pathogenesis and Consequences

Fibrosis is a process characterized by an excessive accumulation of the extracellular matrix as a response to different types of tissue injuries, which leads to organ dysfunction. The process can be initiated by multiple and different stimuli and pathogenic factors which trigger the cascade of reparation converging in molecular signals responsible of initiating and driving fibrosis. Though fibrosis can play a defensive role, in several circumstances at a certain stage, it can progressively become an uncontrolled irreversible and self-maintained process, named pathological fibrosis. Several systems, molecules and responses involved in the pathogenesis of the pathological fibrosis of chronic kidney disease (CKD) will be discussed in this review, putting special attention on inflammation, renin-angiotensin system (RAS), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, microRNAs (miRs), and the vitamin D hormonal system. All of them are key factors of the core and regulatory pathways which drive fibrosis, having a great negative kidney and cardiac impact in CKD.

Association of advanced glycation end products with sarcopenia and frailty in chronic kidney disease

Prevalence of sarcopenia is high in patients with chronic kidney disease (CKD), especially in those with dialysis. Various pathological conditions related to CKD, such as chronic inflammation, insulin resistance, and endothelial dysfunction, are thought to be associated with the development and progression of sarcopenia. Advanced glycation end products (AGE), one of the representative uremic toxins, have been shown to contribute to various CKD-associated complications. This study investigated the role of AGE in frailty and sarcopenia in patients and animals with CKD, respectively. In patients undergoing dialysis, serum AGE levels were significantly increased according to the frailty status and inversely associated with physical performance and activity. AGE accumulated in the gastrocnemius muscle of 5/6 nephrectomy mice in association with morphological abnormalities, capillary rarefaction, and mitochondrial dysfunction, all of which were completely inhibited by DNA-aptamer raised against AGE. Our present findings may suggest the pathological role of AGE in sarcopenia and frailty in CKD.

Stochastic non-enzymatic modification of long-lived macromolecules - A missing hallmark of aging

Damage accumulation in long-living macromolecules (especially extracellular matrix (ECM) proteins, nuclear pore complex (NPC) proteins, and histones) is a missing hallmark of aging. Stochastic non-enzymatic modifications of ECM trigger cellular senescence as well as many other hallmarks of aging affect organ barriers integrity and drive tissue fibrosis. The importance of it for aging makes it a key target for interventions. The most promising of them can be AGE inhibitors (chelators, O-acetyl group or transglycating activity compounds, amadorins and amadoriases), glucosepane breakers, stimulators of elastogenesis, and RAGE antagonists.

Glucose and Blood Pressure-Dependent Pathways-The Progression of Diabetic Kidney Disease

The major clinical associations with the progression of diabetic kidney disease (DKD) are glycemic control and systemic hypertension. Recent studies have continued to emphasize vasoactive hormone pathways including aldosterone and endothelin which suggest a key role for vasoconstrictor pathways in promoting renal damage in diabetes. The role of glucose per se remains difficult to define in DKD but appears to involve key intermediates including reactive oxygen species (ROS) and dicarbonyls such as methylglyoxal which activate intracellular pathways to promote fibrosis and inflammation in the kidney. Recent studies have identified a novel molecular interaction between hemodynamic and metabolic pathways which could lead to new treatments for DKD. This should lead to a further improvement in the outlook of DKD building on positive results from RAAS blockade and more recently newer classes of glucose-lowering agents such as SGLT2 inhibitors and GLP1 receptor agonists.

Dynamic Phenotypes and Molecular Mechanisms to Understand the Pathogenesis of Diabetic Nephropathy in Two Widely Used Animal Models of Type 2 Diabetes Mellitus

Objective

We aimed to characterize the pathogenesis of diabetic nephropathy (DN) in two commonly used type 2 diabetes mellitus (T2DM) animal models and explore the preliminary molecular mechanisms underlying DN in two models.

Methods

To verify the effect of hyperglycemia on renal tissue, we observed the cell growth inhibition rate by adding different concentration of glucose to cell supernatant. After that, a chemically-induced T2DM model was established by administering streptozotocin (STZ) to Sprague Dawley (SD) rats in combination with high fat feeding. In addition, a spontaneous T2DM model was established by feeding 8 weeks old KK-Ay mice a high-fat diet during a period of over 20 weeks. Animal body weight, fasting blood glucose (FBG), insulin tolerance, lipid metabolism, renal function, and renal pathology were periodically measured (once every 2 or 4 weeks) over a duration of 20 weeks. At the 12th week, an Affymetrix gene chip assay was performed on the renal tissues extracted from the T2DM animal models and control animals. Through screening for the differentially expressed genes, some key genes were selected for PCR validation.

Results

High level of glucose could inhibit the growth of kidney cells. Besides, KK-Ay mice were found to have high FBG and abnormal insulin tolerance. Renal dysfunction and pathology were observed at the 4th week following the start of model creation, which increased in severity over the length of the experiment. The T2DM SD rats also showed high FBG, abnormal glucose tolerance and abnormal lipid metabolism, but the renal function and renal pathology changed only slightly within 20 weeks. Gene profiling in animal kidneys and subsequent analyses and validation revealed differentially expressed genes and enriched pathways in DN.

Conclusion

KK-Ay mice with both high fasting glucose and insulin resistance were more likely to develop diabetic nephropathy than STZ-induced diabetic SD rats with low fasting glucose or only insulin resistance. The KK-Ay mice model showed earlier onset of the typical pathological characteristics associated with T2DM and obvious renal lesions suggestive of kidney damage.

Keap1/Nrf2/ARE signaling unfolds therapeutic targets for redox imbalanced-mediated diseases and diabetic nephropathy

Hyperglycemia/oxidative stress has been implicated in the initiation and progression of diabetic complications while the components of Keap1/Nrf2/ARE signaling are being exploited as therapeutic targets for the treatment/management of these pathologies. Antioxidant agents like drugs, nutraceuticals and pure compounds that target the proteins of this pathway and their downstream genes hold the therapeutic strength to put the progression of this disease at bay. Here, we elucidate how the modulation of Keap1/Nrf2/ARE had been exploited for the treatment/management of end-stage diabetic kidney complication (diabetic nephropathy) by looking into (1) Nrf2 nuclear translocation and phosphorylation by some protein kinases at specific amino acid sequences and (2) Keap1 downregulation/Keap1-Nrf2 protein-protein inhibition (PPI) as potential therapeutic mechanisms exploited by Nrf2 activators for the modulation of diabetic nephropathy biomarkers (Collagen IV, Laminin, TGF-β1 and Fibronectin) that ultimately lead to the amelioration of this disease progression. Furthermore, we brought to limelight the relationship between diabetic nephropathy and Keap1/Nrf2/ARE and finally elucidate how the modulation of this signaling pathway could be further explored to create novel therapeutic milestones.

Antidiabetic effects of extracts of red and yellow fruits of cornelian cherries (Cornus mas L.) on rats with streptozotocin-induced diabetes mellitus

The effects of extracts of red and yellow fruits of cornelian cherries have been evaluated in rats with streptozotocin-induced diabetes mellitus.

Transactivation of RAGE mediates angiotensin-induced inflammation and atherogenesis

Activation of the type 1 angiotensin II receptor (AT1) triggers proinflammatory signaling through pathways independent of classical Gq signaling that regulate vascular homeostasis. Here, we report that the AT1 receptor preformed a heteromeric complex with the receptor for advanced glycation endproducts (RAGE). Activation of the AT1 receptor by angiotensin II (Ang II) triggered transactivation of the cytosolic tail of RAGE and NF-κB-driven proinflammatory gene expression independently of the liberation of RAGE ligands or the ligand-binding ectodomain of RAGE. The importance of this transactivation pathway was demonstrated by our finding that adverse proinflammatory signaling events induced by AT1 receptor activation were attenuated when RAGE was deleted or transactivation of its cytosolic tail was inhibited. At the same time, classical homeostatic Gq signaling pathways were unaffected by RAGE deletion or inhibition. These data position RAGE transactivation by the AT1 receptor as a target for vasculoprotective interventions. As proof of concept, we showed that treatment with the mutant RAGE peptide S391A-RAGE362-404 was able to inhibit transactivation of RAGE and attenuate Ang II-dependent inflammation and atherogenesis. Furthermore, treatment with WT RAGE362-404 restored Ang II-dependent atherogenesis in Ager/Apoe-KO mice, without restoring ligand-mediated signaling via RAGE, suggesting that the major effector of RAGE activation was its transactivation.

Cell-Matrix Interactions and Matricrine Signaling in the Pathogenesis of Vascular Calcification

Vascular calcification is a complex pathological process occurring in patients with atherosclerosis, type 2 diabetes, and chronic kidney disease. The extracellular matrix, via matricrine-receptor signaling plays important roles in the pathogenesis of calcification. Calcification is mediated by osteochondrocytic-like cells that arise from transdifferentiating vascular smooth muscle cells. Recent advances in our understanding of the plasticity of vascular smooth muscle cell and other cells of mesenchymal origin have furthered our understanding of how these cells transdifferentiate into osteochondrocytic-like cells in response to environmental cues. In the present review, we examine the role of the extracellular matrix in the regulation of cell behavior and differentiation in the context of vascular calcification. In pathological calcification, the extracellular matrix not only provides a scaffold for mineral deposition, but also acts as an active signaling entity. In recent years, extracellular matrix components have been shown to influence cellular signaling through matrix receptors such as the discoidin domain receptor family, integrins, and elastin receptors, all of which can modulate osteochondrocytic differentiation and calcification. Changes in extracellular matrix stiffness and composition are detected by these receptors which in turn modulate downstream signaling pathways and cytoskeletal dynamics, which are critical to osteogenic differentiation. This review will focus on recent literature that highlights the role of cell-matrix interactions and how they influence cellular behavior, and osteochondrocytic transdifferentiation in the pathogenesis of cardiovascular calcification.

Protective Effects of Kaempferitrin on Advanced Glycation End Products Induce Mesangial Cell Apoptosis and Oxidative Stress

Advanced glycation end products (AGEs) and the receptor for AGEs (RAGE) both play important roles in diabetic nephropathy (DN). Previous studies have identified glomerular mesangial cells (GMCs) injury as a key early risk factor in the development of DN. Kaempferitrin (KM) is a potent antioxidant with hypoglycemic action. Although KM is known to protect against AGE-induced damage in GMCs, the effects and the mechanisms by which they occur are poorly understood. In this study, cultured rat GMCs were exposed to AGE-induced oxidative stress (OS) to model DN in vitro. Reactive oxygen species (ROS) was analyzed by 2',7'-dichlorofluorescin diacetate (DCFH-DA). Superoxide dismutase (SOD) and malondialdehyde (MDA) were studied using commercial kits. Mitochondrial membrane potential (Δψm) was measured by rhodamine 123. Hoechst 33258 and annexin V and propidium iodide (PI) double staining were performed to observe the apoptosis states in GMCs, whereas apoptosis and protective mechanism in AGE-induced GMCs were investigated by Western blot. The data revealed that KM effectively increased SOD activity, decreased MDA levels, suppressed ROS generation, and protected against OS in AGE-induced GMCs. Treatment with KM also inhibited the expression of collagen IV and transforming growth factor-β1 (TGF-β1), improved mitochondrial membrane potential recovery, and suppressed the mitochondrial/cytochrome c-mediated apoptosis pathway through the expression of anti-apoptotic factors in GMCs in vitro. These findings suggest that KM may be a new potential agent in the treatment of DN in future.

Chrysin Inhibits Advanced Glycation End Products-Induced Kidney Fibrosis in Renal Mesangial Cells and Diabetic Kidneys

Advanced glycation end products (AGEs) play a causative role in the development of diabetic nephropathy via induction of matrix protein deposition in kidneys. This study investigated inhibitory effects of chrysin, present in bee propolis and herbs, on glomerulosclerosis in db/db mice and AGEs-exposed renal mesangial cells. The in vivo study explored the demoting effects of 10 mg/kg chrysin on glomerular fibrosis in a type 2 diabetic model. Oral supplementation of chrysin inhibited the collagen fiber accumulation and α-smooth muscle actin (α-SMA) induction in periodic acid schiff-positive renal tissues of db/db mice. Moreover, treating db/db mice with chrysin diminished the level of AGEs increased in diabetic glomeruli. The in vitro study employed human mesangial cells exposed to 100 μg/mL AGE-BSA for 72 h in the presence of 1⁻20 μM chrysin. Glucose increased mesangial AGE production via induction of receptor for AGEs. Chrysin suppressed the induction of collagens, α-SMA, fibroblast-specific protein-1 and matrix metalloproteinases enhanced by AGE-bovine serum albumin. Furthermore, chrysin blunted transforming growth factor-β1 induction and Smad 2/3 activation in AGEs-exposed mesangial cells. These results demonstrate that chrysin attenuated accumulation of myofibroblast-like cells and matrix proteins in AGEs-laden diabetic glomeruli. Therefore, chrysin may be a potential renoprotective agent targeting glucose-mediated AGEs-associated glomerulosclerosis and fibrosis.

RAGE Deletion Confers Renoprotection by Reducing Responsiveness to Transforming Growth Factor-β and Increasing Resistance to Apoptosis

Signaling via the receptor of advanced glycation end products (RAGE)-though complex and not fully elucidated in the setting of diabetes-is considered a key injurious pathway in the development of diabetic nephropathy (DN). We report here that RAGE deletion resulted in increased expression of fibrotic markers (collagen I and IV, fibronectin) and the inflammatory marker MCP-1 in primary mouse mesangial cells (MCs) and in kidney cortex. RNA sequencing analysis in MCs from RAGE^-/- and wild-type mice confirmed these observations. Nevertheless, despite these gene expression changes, decreased responsiveness to transforming growth factor-β was identified in RAGE^-/- mice. Furthermore, RAGE deletion conferred a more proliferative phenotype in MCs and reduced susceptibility to staurosporine-induced apoptosis. RAGE restoration experiments in RAGE^-/- MCs largely reversed these gene expression changes, resulting in reduced expression of fibrotic and inflammatory markers. This study highlights that protection against DN in RAGE knockout mice is likely to be due in part to the decreased responsiveness to growth factor stimulation and an antiapoptotic phenotype in MCs. Furthermore, it extends our understanding of the role of RAGE in the progression of DN, as RAGE seems to play a key role in modulating the sensitivity of the kidney to injurious stimuli such as prosclerotic cytokines.

Glycated albumin induces lipid infiltration in mice aorta independently of DM and RAS local modulation by inducing lipid peroxidation and inflammation

AIMS

Advanced glycated albumin (AGE-albumin) adversely impairs macrophage lipid homeostasis in vitro, which may be prevented by angiotensin receptor blockers. In vivo studies are inconclusive whether AGE-albumin itself plays important role in early-stage atherogenesis. We aimed at investigating how AGE-albumin by itself drives atherosclerosis development in dyslipidemic non-diabetic mice and if its effects are due to the activation of renin-angiotensin system in the arterial wall and the expression of genes and proteins involved in lipid flux.

METHODS AND RESULTS

Murine albumin glycation was induced by incubation with 10mM glycolaldehyde and C-albumin with PBS alone. Twelve-week-old-male apoE knockout mice were submitted to a daily IP injection of control (C) or AGE-albumin (2mg/mL) during 30days with or without losartan (LOS: 100mg/L; C+LOS and AGE+LOS). Aortic arch was removed, and gene expression was determined by RT-PCR and protein content by immunofluorescence. Plasma lipid and glucose levels were similar among groups. Systolic blood pressure was similarly reduced in both groups treated with LOS. In comparison to C-albumin, aortic lipid infiltration was 5.3 times increased by AGE-albumin, which was avoided by LOS. LOS prevented the enhancement induced by AGE-albumin in Ager, Tnf and Cybb mRNA levels but did not reduce Olr1. Nfkb and Agt mRNA levels were unchanged by AGE-albumin. LOS similarly reduced Agtr1a mRNA level in both C and AGE-albumin groups. In AGE-albumin-treated mice, immunofluorescence for carboxymethyl-lysine, 4-hydroxynonenal and RAGE was respectively, 4.8, 2.6 and 1.7 times enhanced in comparison to C-albumin. These increases were all avoided by LOS.

CONCLUSIONS

AGE-albumin evokes a pre-stage of atherogenesis in dyslipidemic mice independently of the presence of diabetes mellitus or modulation in the RAS in part by the induction of lipid peroxidation and inflammation.

In vitro and in vivo inhibition of mTOR by 1,25-dihydroxyvitamin D3 to improve early diabetic nephropathy via the DDIT4/TSC2/mTOR pathway

We investigated whether 1,25-dihydroxy-vitamin D₃ (1,25(OH)₂D₃) could improve early diabetic nephropathy through the DNA-damage-inducible transcript 4/tuberous sclerosis 2/mammalian target of rapamycin pathway. Rat mesangial cells were cultured in media containing normal glucose or high glucose and were treated with or without 1,25(OH)₂D₃. Mesangial cells proliferation was measured. Streptozotocin-induced diabetic rats were injected intravenously with a recombinant lentivirus against the rat vitamin D receptor gene. Urinary and serum albumin, fasting plasma glucose, serum triglyceride, total cholesterol, calcium, parathyroid hormone and serum 25-dihydroxy-vitamin D (25(OH)D) levels, mean glomerular volume, glomerular basement membrane thickness and total kidney volume were determined. The expressions of vitamin D receptor, DNA-damage-inducible transcript 4, and mammalian target of rapamycin were measured. 1,25(OH)₂D₃ inhibited the proliferation of mesangial cells induced by hyperglycemia. 1,25(OH)₂D₃ also significantly reduced albumin excretion, mean glomerular volume, glomerular basement membrane, and total kidney volume in rats with diabetic nephropathy. The expression of DNA-damage-inducible transcript 4 was elevated by 1,25(OH)₂D₃ treatment. The phosphorylation of mammalian target of rapamycin was reduced by 1,25(OH)₂D₃ treatment. Vitamin D receptor gene silencing blocked all of the above results. The current study demonstrates that 1,25(OH)₂D₃ can effectively inhibit mesangial cells proliferation induced by hyperglycemia, thus suppressing the development of diabetic nephropathy. This study also shows that the nephron-protective effect of 1,25(OH)₂D₃ occurs partly through the DDIT4/TSC2/mTOR pathway.

Knockout of Angiotensin AT2 receptors accelerates healing but impairs quality

Wounds are among the most common, painful, debilitating and costly conditions in older adults. Disruption of the angiotensin type 1 receptors (AT₁R), has been associated with impaired wound healing, suggesting a critical role for AT₁R in this repair process. Biological functions of angiotensin type 2 receptors (AT₂R) are less studied. We investigated effects of genetically disrupting AT₂R on rate and quality of wound healing. Our results suggest that AT₂R effects on rate of wound closure depends on the phase of wound healing. We observed delayed healing during early phase of wound healing (inflammation). An accelerated healing rate was seen during later stages (proliferation and remodeling). By day 12, fifty percent of AT₂R^−/− mice had complete wound closure as compared to none in either C57/BL6 or AT₁R^−/− mice. There was a significant increase in AT₁R, TGFβ₁ and TGFβ₂ expression during the proliferative and remodeling phases in AT₂R^−/− mice. Despite the accelerated closure rate, AT₂R^−/− mice had more fragile healed skin. Our results suggest that in the absence of AT₂R, wound healing rate is accelerated, but yielded worse skin quality. Elucidating the contribution of both of the angiotensin receptors may help fine tune future intervention aimed at wound repair in older individuals.

Epigallocatechin-3-gallate Attenuates Renal Damage by Suppressing Oxidative Stress in Diabetic db/db Mice

Epigallocatechin-3-gallate (EGCG), extracted from green tea, has been shown to have antioxidative activity. In the present study, we evaluated the effect of EGCG on the kidney function in db/db mice and also tried to investigate the underlying mechanism of the renoprotective effects of EGCG in both animals and cells. EGCG treatment could decrease the level of urinary protein, 8-iso-PGF2a, and Ang II. Moreover, EGCG could also change the level of several parameters associated with oxidative stress. In addition, the protein expression levels of AT-1R, p22-phox, p47-phox, p-ERK1/2, p-p38 MAPK, TGF-β1, and α-SMA in diabetic db/db mice were upregulated, and all of these symptoms were downregulated with the treatment of EGCG at 50 and 100 mg/kg/d. Furthermore, the pathological changes were ameliorated in db/db mice after EGCG treatment. HK-2 cell-based experiments indicated that EGCG could inhibit the expression of MAPK pathways, which is the downstream effector of Ang II mediated oxidative stress. All these results indicated that EGCG treatment could ameliorate changes of renal pathology and delay the progression of DKD by suppressing hyperglycemia-induced oxidative stress in diabetic db/db mice.

Angiotensin II receptors and peritoneal dialysis-induced peritoneal fibrosis

The vasoactive hormone angiotensin II initiates its major hemodynamic effects through interaction with AT1 receptors, a member of the class of G protein-coupled receptors. Acting through its AT1R, angiotensin II regulates blood pressure and renal salt and water balance. Recent evidence points to additional pathological influences of activation of AT1R, in particular inflammation, fibrosis and atherosclerosis. The transcription factor nuclear factor κB, a key mediator in inflammation and atherosclerosis, can be activated by angiotensin II through a mechanism that may involve arrestin-dependent AT1 receptor internalization. Peritoneal dialysis is a therapeutic modality for treating patients with end-stage kidney disease. The effectiveness of peritoneal dialysis at removing waste from the circulation is compromised over time as a consequence of peritoneal dialysis-induced peritoneal fibrosis. The non-physiological dialysis solution used in peritoneal dialysis, i.e. highly concentrated, hyperosmotic glucose, acidic pH as well as large volumes infused into the peritoneal cavity, contributes to the development of fibrosis. Numerous trials have been conducted altering certain components of the peritoneal dialysis fluid in hopes of preventing or delaying the fibrotic response with limited success. We hypothesize that structural activation of AT1R by hyperosmotic peritoneal dialysis fluid activates the internalization process and subsequent signaling through the transcription factor nuclear factor κB, resulting in the generation of pro-fibrotic/pro-inflammatory mediators producing peritoneal fibrosis.

Polydatin attenuates AGEs-induced upregulation of fibronectin and ICAM-1 in rat glomerular mesangial cells and db/db diabetic mice kidneys by inhibiting the activation of the SphK1-S1P signaling pathway

We previously demonstrated that activation of sphingosine kinase 1 (SphK1)- sphingosine 1- phosphate (S1P) signaling pathway by high glucose (HG) plays a pivotal role in increasing the expression of fibronectin (FN), an important fibrotic component, by promoting the DNA-binding activity of transcription factor activator protein 1 (AP-1) in glomerular mesangial cells (GMCs) under diabetic conditions. As a multi-target anti-oxidative drug, polydatin (PD) has been shown to have renoprotective effects on experimental diabetes. However, whether PD could resist diabetic nephropathy (DN) by regulating SphK1-S1P signaling pathway needs further investigation. Here, we found that PD significantly reversed the upregulated FN and ICAM-1 expression in GMCs exposed to AGEs. Simultaneously, PD dose-dependently inhibited SphK1 levels at the protein expression and kinase activity and attenuated S1P production under AGEs treatment conditions. In addition, PD reduced SphK activity in GMCs transfected with wild-type SphK(WT) plasmid and significantly suppressed SphK1-mediated increase of FN and ICAM-1 levels under normal conditions. Furthermore, we found that the AGEs-induced upregulation of phosphorylation of c-Jun at Ser63 and Ser73 and c-Fos at Ser32, DNA-binding activity and transcriptional activity of AP-1 were blocked by PD. In comparison with db/db model group, PD treatment suppressed SphK1 levels (mRNA, protein expression, and activity) and S1P production, reversed the upregulation of FN, ICAM-1, c-Jun, and c-Fos in the kidney tissues of diabetic mice, and finally ameliorated renal injury in db/db mice. These findings suggested that the downregulation of SphK1-S1P signaling pathway is probably a novel mechanism by which PD suppressed AGEs-induced FN and ICAM-1 expression and improved renal dysfunction of diabetic models.

Malocclusion model of temporomandibular joint osteoarthritis in mice with and without receptor for advanced glycation end products

OBJECTIVE

This study has two aims: 1. Validate a non-invasive malocclusion model of mouse temporomandibular joint (TMJ) osteoarthritis (OA) that we developed and 2. Confirm role of inflammation in TMJ OA by comparing the disease in the presence and absence of the receptor for advanced glycation end products (RAGE).

DESIGN

The malocclusion procedure was performed on eight week old mice, either wild type (WT) or without RAGE.

RESULTS

We observed TMJ OA at two weeks post-misalignment/malocclusion. The modified Mankin score used for the semi-quantitative assessment of OA showed an overall significantly higher score in mice with malocclusion compared to control mice at all times points (2, 4, 6 and 8 weeks). Mice with malocclusion showed a decrease in body weight by the first week after misalignment but returned to normal weight for their ages during the following weeks. The RAGE knock out (KO) mice had statistically lower modified Mankin scores compared to WT mice of the same age. The RAGE KO mice had statistically lower levels of Mmp-13 and HtrA1 but higher Tgf-β1, as measured by immunohistochemistry, compared to WT mice at eight weeks post malocclusion.

CONCLUSIONS

We demonstrate an inexpensive, efficient, highly reproducible and non-invasive model of mouse TMJ OA. The mechanical nature of the malocclusion resembles the natural development of TMJ OA in humans, making this an ideal model in future studies that aim to elucidate the pathogenesis of the disease leading to the discovery of a treatment. The RAGE plays a role in mouse TMJ OA.

Histone Lysine Methylation in TGF-β1 Mediated p21 Gene Expression in Rat Mesangial Cells

Transforming growth factor beta1- (TGF-β1-) induced p21-dependent mesangial cell (MC) hypertrophy plays a key role in the pathogenesis of chronic renal diseases including diabetic nephropathy (DN). Increasing evidence demonstrated the role of posttranscriptional modifications (PTMs) in the event; however, the precise regulatory mechanism of histone lysine methylation remains largely unknown. Here, we examined the roles of both histone H3 lysine 4 and lysine 9 methylations (H3K4me/H3K9me) in TGF-β1 induced p21 gene expression in rat mesangial cells (RMCs). Our results indicated that TGF-β1 upregulated the expression of p21 gene in RMCs, which was positively correlated with the increased chromatin marks associated with active genes (H3K4me1/H3K4me2/H3K4me3) and negatively correlated with the decreased levels of repressive marks (H3K9me2/H3K9me3) at p21 gene promoter. TGF-β1 also elevated the recruitment of the H3K4 methyltransferase (HMT) SET7/9 to the p21 gene promoter. SET7/9 gene silencing with small interfering RNAs (siRNAs) significantly abolished the TGF-β1 induced p21 gene expression. Taken together, these results reveal the key role of histone H3Kme in TGF-β1 mediated p21 gene expression in RMC, partly through HMT SET7/9 occupancy, suggesting H3Kme and SET7/9 may be potential renoprotective agents in managing chronic renal diseases.

High Glucose Stimulates Tumorigenesis in Hepatocellular Carcinoma Cells Through AGER-Dependent O-GlcNAcylation of c-Jun

Epidemiologic studies suggest that hepatocellular carcinoma (HCC) has a strong relationship with diabetes. However, the underlying molecular mechanisms still remain unclear. Here, we demonstrated that high glucose (HG), one of the main characteristics of diabetes, was capable of accelerating tumorigenesis in HCC cells. Advanced glycosylation end product-specific receptor (AGER) was identified as a stimulator during this process. Mechanistically, AGER activated a hexosamine biosynthetic pathway, leading to enhanced O-GlcNAcylation of target proteins. Notably, AGER was capable of increasing activity and stability of proto-oncoprotein c-Jun via O-GlcNAcylation of this protein at Ser73. Interestingly, c-Jun can conversely enhance AGER transcription. Thereby, a positive autoregulatory feedback loop that stimulates diabetic HCC was established. Finally, we found that AG490, an inhibitor of Janus kinase, has the ability to impair AGER expression and its functions in HCC cells. In conclusion, AGER and its functions to stimulate O-GlcNAcylation are important during liver tumorigenesis, when high blood glucose levels are inadequately controlled.

Ellagic acid inhibits non-enzymatic glycation and prevents proteinuria in diabetic rats

The formation of advanced glycation end products (AGEs) is a characteristic feature of diabetic tissues and accumulation of AGEs been implicated in the pathogenesis of diabetic nephropathy (DN). Ellagic acid prevented the accumulation of AGEs and in turn ameliorated proteinurea in diabetic rats.

Advanced Glycation End Products: A Molecular Target for Vascular Complications in Diabetes

A nonenzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids contributes to the aging of macromolecules and subsequently alters their structural integrity and function. This process has been known to progress at an accelerated rate under hyperglycemic and/or oxidative stress conditions. Over a course of days to weeks, early glycation products undergo further reactions such as rearrangements and dehydration to become irreversibly cross-linked, fluorescent and senescent macroprotein derivatives termed advanced glycation end products (AGEs). There is a growing body of evidence indicating that interaction of AGEs with their receptor (RAGE) elicits oxidative stress generation and as a result evokes proliferative, inflammatory, thrombotic and fibrotic reactions in a variety of cells. This evidence supports AGEs' involvement in diabetes- and aging-associated disorders such as diabetic vascular complications, cancer, Alzheimer's disease and osteoporosis. Therefore, inhibition of AGE formation could be a novel molecular target for organ protection in diabetes. This report summarizes the pathophysiological role of AGEs in vascular complications in diabetes and discusses the potential clinical utility of measurement of serum levels of AGEs for evaluating organ damage in diabetes.

Advanced glycation end-product expression is upregulated in the gastrointestinal tract of type 2 diabetic rats

AIM: To investigate changes in advanced glycation end products (AGEs) and their receptor (RAGE) expression in the gastrointestinal (GI) tract in type 2 diabetic rats.

METHODS: Eight inherited type 2 diabetic rats Goto-Kakizak (GK) and ten age-matched normal rats were used in the study. From 18 wk of age, the body weight and blood glucose were measured every week and 2 wk respectively. When the rats reached 32 wk, two-centimeter segments of esophagus, duodenum, jejunum, ileum, and colon were excised and the wet weight was measured. The segments were fixed in 10% formalin, embedded in paraffin and five micron sections were cut. The layer thickness was measured in Hematoxylin and Eosin-stained slides. AGE [N epsilon-(carboxymethyl) lysine and N epsilon-(carboxyethyl)lysine] and RAGE were detected by immunohistochemistry staining and image analysis was done using Sigmascan Pro 4.0 image analysis software.

RESULTS: The blood glucose concentration (mmol/L) at 18 wk age was highest in the GK group (8.88 ± 1.87 vs 6.90 ± 0.43, P < 0.001), a difference that continued to exist until the end of the experiment. The wet weight per unit length (mg/cm) increased in esophagus, jejunum and colon from the normal to the GK group (60.64 ± 9.96 vs 68.56 ± 11.69, P < 0.05 for esophagus; 87.01 ± 9.35 vs 105.29 ± 15.45, P < 0.01 for jejunum; 91.37 ± 7.25 vs 97.28 ± 10.90, P < 0.05 for colon). Histologically, the layer thickness of the GI tract was higher for esophagus, jejunum and colon in the GK group [full thickness (μm): 575.37 ± 69.22 vs 753.20 ± 150.41, P < 0.01 for esophagus; 813.51 ± 44.44 vs 884.81 ± 45.31, P < 0.05 for jejunum; 467.12 ± 65.92 vs 572.26 ± 93.60, P < 0.05 for colon]. In esophagus, the AGE and RAGE mainly distributed in striated muscle cells and squamous epithelial cells. The AGE distribution was much stronger in the GK group compared to the normal group both in the striated muscle layer and mucosa layer (immuno-positive area/ total measuring area %: 4.52 ± 0.89 vs 10.96 ± 1.34, P < 0.01 for muscle; 8.90 ± 2.62 vs 22.45 ± 1.26, P < 0.01 for mucosa). No visible difference was found for RAGE distribution between the two groups. In the intestine AGE and RAGE distributed in epithelial cells of villi and crypt. RAGE was also found in neurons in the myenteric and submucosal plexus. The intensity of AGE staining in mucosa of all segments and RAGE staining in neurons in all segments were strongest in the diabetes group. Significant difference for AGE was found in the epithelial cells of villi and crypt in duodenum (immuno-positive area/total measuring area %: 13.37 ± 3.51 vs 37.48 ± 8.43, P < 0.05 for villi; 0.38 ± 0.12 vs 1.87 ± 0.53, P < 0.05 for crypt) and for RAGE in neurons of all segments (e.g., for jejunum: no staining neurons% 0 vs 0, mild 36.0 ± 5.2 vs 28.7 ± 3.5, moderate 53.2 ± 4.8 vs 55.8 ± 5.4, strong 10.7 ± 1.1 vs 15.4 ± 2.0, P < 0.05). In the colon, RAGE was primarily found in neurons in the myenteric and submucosal plexus. It was stronger in the diabetes group than in the normal group (no staining neurons% 6.2 ± 0.2 vs 0.3 ± 0.04, mild 14.9 ± 2.1 vs 17.6 ± 1.5, moderate 53.1 ± 4.6 vs 44.7 ± 4.4, strong 25.6 ± 18 vs 43.6 ± 4.0, P < 0.05). In the rectum, RAGE was primarily found in the mucosa epithelial cells.

CONCLUSION: The AGE and RAGE expression was up-regulated in the GI tract of GK diabetic rats and may contribute to GI dysfunction in type 2 diabetic patients.

Advanced glycation end products and oxidative stress in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a very complex and multifactorial metabolic disease characterized by insulin resistance and β cell failure leading to elevated blood glucose levels. Hyperglycemia is suggested to be the main cause of diabetic complications, which not only decrease life quality and expectancy, but are also becoming a problem regarding the financial burden for health care systems. Therefore, and to counteract the continually increasing prevalence of diabetes, understanding the pathogenesis, the main risk factors, and the underlying molecular mechanisms may establish a basis for prevention and therapy. In this regard, research was performed revealing further evidence that oxidative stress has an important role in hyperglycemia-induced tissue injury as well as in early events relevant for the development of T2DM. The formation of advanced glycation end products (AGEs), a group of modified proteins and/or lipids with damaging potential, is one contributing factor. On the one hand it has been reported that AGEs increase reactive oxygen species formation and impair antioxidant systems, on the other hand the formation of some AGEs is induced per se under oxidative conditions. Thus, AGEs contribute at least partly to chronic stress conditions in diabetes. As AGEs are not only formed endogenously, but also derive from exogenous sources, i.e., food, they have been assumed as risk factors for T2DM. However, the role of AGEs in the pathogenesis of T2DM and diabetic complications—if they are causal or simply an effect—is only partly understood. This review will highlight the involvement of AGEs in the development and progression of T2DM and their role in diabetic complications.