Augmented O-GlcNAc signaling via glucosamine attenuates oxidative stress and apoptosis following contrast-induced acute kidney injury in rats

Signal pathways involved in contrast-induced acute kidney injury

Contrast-induced acute kidney injury (CI-AKI) has emerged as a global public health concern, ranking as the third most prevalent cause of hospital-acquired acute kidney injury, which is related to adverse outcomes. However, its precise pathogenesis remains elusive. Consequently, researchers are dedicated to uncovering CI-AKI's pathophysiology and signaling pathways, including inflammation, oxidative stress, apoptosis, and ferroptosis, to improve prevention and treatment. This review thoroughly analyzes the signaling pathways and their interactions associated with CI-AKI, assesses the impact of various research models on pathway analysis, and explores more precise targeted treatment and prevention approaches. Aims to furnish a robust theoretical foundation for the molecular mechanisms underpinning clinical treatments.

O-GlcNAcylation in ischemic diseases

Protein glycosylation is an extensively studied field, with the most studied forms being oxygen or nitrogen-linked N-acetylglucosamine (O-GlcNAc or N-GlcNAc) glycosylation. Particular residues on proteins are targeted by O-GlcNAcylation, which is among the most intricate post-translational modifications. Significantly contributing to an organism's proteome, it influences numerous factors affecting protein stability, function, and subcellular localization. It also modifies the cellular function of target proteins that have crucial responsibilities in controlling pathways related to the central nervous system, cardiovascular homeostasis, and other organ functions. Under conditions of acute stress, changes in the levels of O-GlcNAcylation of these proteins may have a defensive function. Nevertheless, deviant O-GlcNAcylation nullifies this safeguard and stimulates the advancement of several ailments, the prognosis of which relies on the cellular milieu. Hence, this review provides a concise overview of the function and comprehension of O-GlcNAcylation in ischemia diseases, aiming to facilitate the discovery of new therapeutic targets for efficient treatment, particularly in patients with diabetes.

Roles of O-GlcNAcylation in Mitochondrial Homeostasis and Cardiovascular Diseases

Protein posttranslational modifications are important factors that mediate the fine regulation of signaling molecules. O-linked β-N-acetylglucosamine-modification (O-GlcNAcylation) is a monosaccharide modification on N-acetylglucosamine linked to the hydroxyl terminus of serine and threonine of proteins. O-GlcNAcylation is responsive to cellular stress as a reversible and posttranslational modification of nuclear, mitochondrial and cytoplasmic proteins. Mitochondrial proteins are the main targets of O-GlcNAcylation and O-GlcNAcylation is a key regulator of mitochondrial homeostasis by directly regulating the mitochondrial proteome or protein activity and function. Disruption of O-GlcNAcylation is closely related to mitochondrial dysfunction. More importantly, the O-GlcNAcylation of cardiac proteins has been proven to be protective or harmful to cardiac function. Mitochondrial homeostasis is crucial for cardiac contractile function and myocardial cell metabolism, and the imbalance of mitochondrial homeostasis plays a crucial role in the pathogenesis of cardiovascular diseases (CVDs). In this review, we will focus on the interactions between protein O-GlcNAcylation and mitochondrial homeostasis and provide insights on the role of mitochondrial protein O-GlcNAcylation in CVDs.

Functional significance of O-linked N-acetylglucosamine protein modification in regulating autophagy

Autophagy is a core molecular pathway that preserves cellular and organismal homeostasis. Being susceptible to nutrient availability and stress, eukaryotic cells recycle or degrade internal components via membrane transport pathways to provide sustainable biological molecules and energy sources. The dysregulation of this highly conserved physiological process has been strongly linked to human disease. Post-translational modification, a mechanism that regulates protein function, plays a crucial role in autophagy regulation. O-linked N-acetylglucosamine protein modification (O-GlcNAcylation), a monosaccharide post-translational modification of intracellular proteins, is essential in nutritional and stress regulatory mechanisms. O-GlcNAcylation has emerged as an essential regulatory mechanism of autophagy. It regulates autophagy throughout its lifetime by targeting the core components of the autophagy regulatory network. This review provides an overview of the O-GlcNAcylation of autophagy-associated proteins and their regulation and function in the autophagy pathway. Therefore, this article may contribute to further understanding of the role of O-GlcNAc-regulated autophagy and provide new perspectives for the treatment of human diseases.

Nicorandil attenuates cisplatin-induced acute kidney injury in rats via activation of PI3K/AKT/mTOR signaling cascade and inhibition of autophagy

Cisplatin is a highly effective antitumor agent, but its clinical use is limited due to critical adverse reactions including acute kidney injury (AKI). Nicorandil is an approved antianginal agent decreasing ischemia by potassium channel opening. The aim of this study was to investigate the nephroprotective effects of nicorandil and the possible role of activating PI3K/AKT/mTOR pathway in ameliorating cisplatin-induced AKI. Forty male Wistar rats were randomly allocated in 4 groups (n = 10). Group I: rats received the vehicle and served as control. Group II: rats received a single dose of cisplatin (7 mg/kg, i.p) on the 10th day of the experiment and served as AKI group. Group III: rats received cisplatin as in group II and nicorandil (3 mg/kg/day, p.o) for 14 days. Group IV: rats received cisplatin and nicorandil as in group III as well as wortmannin (15 μg/kg, i.v) for 14 days. Nicorandil exhibited obvious nephroprotective effects via the activation of PI3K/AKT/mTOR pathway. Moreover, nicorandil succeed to reduce the expression of the autophagy markers beclin-1 and LC-3II/I. In parallel, nicorandil showed anti-inflammatory and antiapoptotic effects via inhibition of NF-κB inflammatory pathway and depression of Bax/Bcl-2 ratio. Wortmannin, the PI3K inhibitor, was used to demonstrate the proposed pathway. Our study showed the nephroprotective effects of nicorandil in cisplatin-induced AKI in rats via activation of PI3K/AKT/mTOR signaling cascade, inhibition of autophagy, anti-inflammatory, anti-apoptotic, anti-oxidant activities. Thus, nicorandil could represent a promising renoprotective agent in cancer patients treated with cisplatin.

Effects of astragaloside IV on glucocorticoid-induced avascular necrosis of the femoral head via regulating Akt-related pathways

We investigated the role of astragaloside IV (AS-IV) in preventing glucocorticoid-induced avascular necrosis of the femoral head (ANFH) and the underlying molecular mechanisms. Network pharmacology was used to predict the molecular targets of AS-IV. Molecular dynamic simulations were performed to explore the binding mechanism and interaction mode between AS-IV and Akt. Rat models of glucocorticoid-induced ANFH with AS-IV intervention were established, and osteogenesis, angiogenesis, apoptosis and oxidative stress were evaluated before and after blocking the PI3K/Akt pathway with LY294002. The effects of glucocorticoid and AS-IV on bone marrow mesenchymal stem cells and human umbilical vein endothelial cells incubated with and without LY294002 were determined. Downregulated p-Akt expression could be detected in the femoral heads of glucocorticoid-induced ANFH patients and rats. AS-IV increased trabecular bone integrity and vessel density of the femoral head in the model rats. AS-IV increased Akt phosphorylation and upregulated osteogenesis-, angiogenesis-, apoptosis- and oxidative stress-related proteins and mRNA and downregulated Bax, cleaved caspase-3 and cytochrome c levels. AS-IV promoted human umbilical vein endothelial cell migration, proliferation and tube formation ability; bone marrow mesenchymal stem cell proliferation; and osteogenic differentiation under glucocorticoid influence. AS-IV inhibited apoptosis. LY294002 inhibited these effects. AS-IV prevented glucocorticoid-induced ANFH by promoting osteogenesis and angiogenesis via the Akt/Runx2 and Akt/HIF-1α/VEGF pathways, respectively, and suppressing apoptosis and oxidative stress via the Akt/Bad/Bcl-2 and Akt/Nrf2/HO-1 pathways, respectively.

Antioxidant activity of glucosamine and its effects on ROS production, Nrf2, and O-GlcNAc expression in HMEC-1 cells

Glucosamine (GlcN) is the most used supplement for osteoarthritis treatment. In vitro studies have related GlcN to beneficial and detrimental effects on health. The aim of this study was to evaluate the effects of O-linked-N-acetylglucosaminylation (O-GlcNAc) on GlcN-induced ROS production and Nrf2 expression in human dermal microvascular endothelial cells-1 (HMEC-1) and to evaluate the antioxidant capacity of GlcN compared to well-known antioxidants. For this, we evaluate the antioxidant capacity by in vitro assays. Besides, the GlcN (5-20 mM) effects on cell viability, reactive oxygen species (ROS) production, O-GlcNAc, and nuclear factor erythroid-2-related factor 2 (Nrf2) expression with and without the O-GlcNAc inhibitor OSMI-1 (10 μM) in HMEC-1 were evaluated. GlcN showed high inhibitory concentration (low scavenging activity) against superoxide (O2•─, IC20 = 47.67 mM), 2,2-diphenyl-1-picrylhydrazyl (DPPH•, IC50 = 21.32 mM), and hydroxyl (HO•, IC50 = 14.04 mM) radicals without scavenging activity against hydrogen peroxide (H2O2) and low antioxidant capacity determined by oxygen radical absorbance capacity (ORAC, 0.001 mM Trolox equivalent) and ferric reducing antioxidant power (FRAP, 0.046 mM Trolox equivalent). In cell culture, GlcN (20 mM) reduced cell viability up to 26 % and induced an increase in ROS production (up to 70 %), O-GlcNAc (4-fold-higher vs. control), and Nrf2 expression (56 %), which were prevented by OSMI-1. These data suggest an association between O-GlcNAc, ROS production, and Nrf2 expression in HMEC-1 cells stimulated with GlcN.

Fetal Reprogramming of Nutrient Surplus Signaling, O-GlcNAcylation, and the Evolution of CKD

ABSTRACT

Fetal kidney development is characterized by increased uptake of glucose, ATP production by glycolysis, and upregulation of mammalian target of rapamycin (mTOR) and hypoxia-inducible factor-1 alpha (HIF-1 α ), which (acting in concert) promote nephrogenesis in a hypoxic low-tubular-workload environment. By contrast, the healthy adult kidney is characterized by upregulation of sirtuin-1 and adenosine monophosphate-activated protein kinase, which enhances ATP production through fatty acid oxidation to fulfill the needs of a normoxic high-tubular-workload environment. During stress or injury, the kidney reverts to a fetal signaling program, which is adaptive in the short term, but is deleterious if sustained for prolonged periods when both oxygen tension and tubular workload are heightened. Prolonged increases in glucose uptake in glomerular and proximal tubular cells lead to enhanced flux through the hexosamine biosynthesis pathway; its end product-uridine diphosphate N -acetylglucosamine-drives the rapid and reversible O-GlcNAcylation of thousands of intracellular proteins, typically those that are not membrane-bound or secreted. Both O-GlcNAcylation and phosphorylation act at serine/threonine residues, but whereas phosphorylation is regulated by hundreds of specific kinases and phosphatases, O-GlcNAcylation is regulated only by O-GlcNAc transferase and O-GlcNAcase, which adds or removes N-acetylglucosamine, respectively, from target proteins. Diabetic and nondiabetic CKD is characterized by fetal reprogramming (with upregulation of mTOR and HIF-1 α ) and increased O-GlcNAcylation, both experimentally and clinically. Augmentation of O-GlcNAcylation in the adult kidney enhances oxidative stress, cell cycle entry, apoptosis, and activation of proinflammatory and profibrotic pathways, and it inhibits megalin-mediated albumin endocytosis in glomerular mesangial and proximal tubular cells-effects that can be aggravated and attenuated by augmentation and muting of O-GlcNAcylation, respectively. In addition, drugs with known nephroprotective effects-angiotensin receptor blockers, mineralocorticoid receptor antagonists, and sodium-glucose cotransporter 2 inhibitors-are accompanied by diminished O-GlcNAcylation in the kidney, although the role of such suppression in mediating their benefits has not been explored. The available evidence supports further work on the role of uridine diphosphate N -acetylglucosamine as a critical nutrient surplus sensor (acting in concert with upregulated mTOR and HIF-1 α signaling) in the development of diabetic and nondiabetic CKD.

A NOVEL RAT MODEL OF CONTRAST-INDUCED ACUTE KIDNEY INJURY BASED ON RENAL CONGESTION AND THE RENO-PROTECTION OF MITOCHONDRIAL FISSION INHIBITION

ABSTRACT

Contrast-induced acute kidney injury (CI-AKI) is a serious and common complication in patients receiving intravenous iodinated contrast medium (CM). Clinically, congestive heart failure is the most critical risk factor for CI-AKI and always leads to renal congestion for increased central venous pressure and fluid overload. Here, we aimed to investigate a novel CI-AKI rat model based on renal congestion. After the exploratory testing phase, we successfully constructed a CI-AKI rat model by inducing renal congestion by clamping the unilateral renal vein, removing the contralateral kidney, and a single tail vein injection of iohexol. This novel CI-AKI rat model showed elevated serum creatinine, urea nitrogen, and released tubular injury biomarkers (KIM-1 and NGAL), reduced glomerular filtration rate, and typical pathologic features of CM-induced tubular injury with extensive foamy degeneration, tubular edema, and necrosis. Electron microscopy and confocal laser scanning revealed excessive mitochondrial fission and increased translocation of Drp1 from the cytoplasm to the mitochondrial surface in tubular epithelial cells. As a Drp1 inhibitor, Mdivi-1 attenuated excessive mitochondrial fission and exerted reno-protection against CM injury. Simultaneously, Mdivi-1 alleviated oxidative stress, apoptosis, and inflammatory responses induced by CM toxicity. We concluded that renal congestion exacerbated CM toxicity and presented a novel CI-AKI rat model. Excessive mitochondrial fission plays a crucial role in CM reno-toxicity and is a promising target for preventing and treating CI-AKI.

Emerging field: O-GlcNAcylation in ferroptosis

In 2012, researchers proposed a non-apoptotic, iron-dependent form of cell death caused by lipid peroxidation called ferroptosis. During the past decade, a comprehensive understanding of ferroptosis has emerged. Ferroptosis is closely associated with the tumor microenvironment, cancer, immunity, aging, and tissue damage. Its mechanism is precisely regulated at the epigenetic, transcriptional, and post-translational levels. O-GlcNAc modification (O-GlcNAcylation) is one of the post-translational modifications of proteins. Cells can modulate cell survival in response to stress stimuli, including apoptosis, necrosis, and autophagy, through adaptive regulation by O-GlcNAcylation. However, the function and mechanism of these modifications in regulating ferroptosis are only beginning to be understood. Here, we review the relevant literature within the last 5 years and present the current understanding of the regulatory function of O-GlcNAcylation in ferroptosis and the potential mechanisms that may be involved, including antioxidant defense system-controlled reactive oxygen species biology, iron metabolism, and membrane lipid peroxidation metabolism. In addition to these three areas of ferroptosis research, we examine how changes in the morphology and function of subcellular organelles (e.g., mitochondria and endoplasmic reticulum) involved in O-GlcNAcylation may trigger and amplify ferroptosis. We have dissected the role of O-GlcNAcylation in regulating ferroptosis and hope that our introduction will provide a general framework for those interested in this field.

Nanosystems for oxidative stress regulation in the anti-inflammatory therapy of acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome that results from a rapid decline in renal structure or renal functional impairment with the main pathological feature of sublethal and lethal damage to renal tubular cells. However, many potential therapeutic agents cannot achieve the desired therapeutic effect because of their poor pharmacokinetics and short retention time in the kidneys. With the recent emergence and progress of nanotechnology, nanodrugs with unique physicochemical properties could prolong circulation time, enhance efficient targeted delivery, and elevate the accumulation of therapeutics that can cross the glomerular filtration barrier and indicate comprehensive application prospects in the prevention and treatment of AKI. In this review, various types of nanosystems (such as liposomes, polymeric nanosystems, inorganic nanoparticles and cell-derived extracellular vesicles) are designed and applied to improve the pharmacokinetics of drug formation, which could further relieve the burden on the kidneys caused by the final cumulative dose of drugs in conventional treatments. Moreover, the passive or active targeting effect of nanosystems can also reduce the total therapeutic dose and off-target adverse effects on other organs. Nanodelivery systems for treating AKI that alleviate oxidative stress-induced renal cell damage and regulate the inflammatory kidney microenvironment are summarized.

An in vivo and in vitro model on the protective effect of cilnidipine on contrast-induced nephropathy via regulation of apoptosis and CaMKⅡ/mPTP pathway

Contrast-induced nephropathy (CIN) is an acute kidney injury (AKI) observed after the administration of contrast media. Calcium channel blockers (CCBs) have been reported to exert a renal protective effect. This study aims to investigate the role of cilnidipine, a novel CCBs, on CIN by regulating the calcium/calmodulin-dependent protein kinase Ⅱ(CaMKⅡ)/mitochondrial permeability transition pore (mPTP) pathway. Here, iohexol, a representative contrast media, was used to establish CIN model. KN-93 (CaMKⅡ inhibitor) and atractyloside (mPTP opener) were administered in rats, and CaMKⅡ overexpression was used in Human proximal tubular epithelial cells. Markers of renal injury (serum creatinine, blood urea nitrogen, and urinary NAGL), hematoxylin-eosin stain, oxidative stress (ROS, superoxide dismutase [SOD], and malondialdehyde [MDA] levels), cell death (MTT and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling [TUNEL]), mitochondrial function (mPTP, mitochondrial membrane potential [MMP], and ATP) were assessed. Western blots were used to measure the expression levels of Bax/Bcl-2, caspase-3, CaMKⅡ/mPTP signaling pathways. Results showed that cilnidipine markedly improved kidney function, and alleviated tubular cell apoptosis, oxidative stress and mitochondrial damage induced by iohexol in vitro and in vivo. The underlying mechanism may be that cilnidipine relieved CaMKⅡ activation and mPTP opening induced by iohexol. All of these protective effects of cilnidipine were attenuated by CaMKⅡ overexpression and atractyloside (mPTP opener) pretreatment. Moreover, KN-93 (CaMKⅡ inhibitor) treatment showed a similar renal protective effect with cilnidipine, while the protective effect of cilnidipine on kidney in CIN rats was not further suppressed by KN-93 cotreatment. These in vitro and in vivo results point toward the fact that cilnidipine might be a novel therapeutic drug against contrast-induced nephrotoxicity in a CaMKⅡ-dependent manner.

Glucosamine inhibits extracellular matrix accumulation in experimental diabetic nephropathy

INTRODUCTION

Glucosamine, the intermediate metabolite of the hexosamine biosynthesis pathway (HBP), is widely used as a supplementary drug in patients with osteoarthritis. However, its consequences in such patients concomitantly suffering from diabetic nephropathy is unknown.

METHODS

The aim of the study was to investigate the effect of exogenous administration of glucosamine in the diabetic kidney. A mouse model of streptozotocin-induced diabetic nephropathy in vivo and cultured endothelial cells in vitro were used in the study. The mice were treated with glucosamine for 6 months. Renal function was evaluated by metabolic cage, and histology of the kidney was estimated by periodic acid-schiff (PAS) staining. The expression of related genes was assessed by real-time PCR, immunofluorescence staining, immunoblotting and ELISA.

RESULTS

There was no significant difference in urinary albumin secretion, relative kidney weight, or creatinine clearance between the groups treated with glucosamine and controls. Assessment of the kidney demonstrated reduction in mesangial expansion and fibronectin expression in the diabetic glomeruli treated with glucosamine. Glucosamine treatment significantly decreased α-smooth muscle actin (α-SMA) protein expression in both diabetic and control kidneys, whereas the expression of other fibrosis-related genes and inflammatory factors was unaltered. Moreover, α-SMA colocalized with the endothelial marker CD31 in the diabetic and control kidneys, and glucosamine reduced α-SMA+ ECs in the diabetic glomeruli. In addition, glucosamine suppressed α-SMA expression in endothelial cells treated with or without high glucose.

DISCUSSION

In summary, this is the first report to show that glucosamine reduces mesangial expansion and inhibits endothelial-mesenchymal transition in diabetic nephropathy. The underlying mechanisms need to be further investigated.

Glucosamine delays the progression of osteoporosis in senile mice by promoting osteoblast autophagy

Background

Senile osteoporosis (SOP) is one of the most prevalent diseases that afflict the elderly population, which characterized by decreased osteogenic ability. Glucosamine (GlcN) is an over-the-counter dietary supplement. Our previous study reported that GlcN promotes osteoblast proliferation by activating autophagy in vitro. The purpose of this study is to determine the effects and mechanisms of GlcN on senile osteoporosis and osteogenic differentiation in vivo.

Methods

Aging was induced by subcutaneous injection of d-Galactose (d-Gal), and treated with GlcN or vehicle. The anti-senile-osteoporosis effect of GlcN was explored by examining changes in micro-CT, serum indicators, body weight, protein and gene expression of aging and apoptosis. Additionally, the effects of GlcN on protein and gene expression of osteogenesis and autophagy were observed by inhibiting autophagy with 3-methyladenine (3-MA).

Results

GlcN significantly improved bone mineral density (BMD) and bone micro-architecture, decreased skeletal senescence and apoptosis and increased osteogenesis in d-Gal induced osteoporotic mice. While all effect was reversed with 3-MA.

Conclusion

GlcN effectively delayed the progression of osteoporosis in senile osteoporotic mice by promoting osteoblast autophagy. This study suggested that GlcN may be a prospective candidate drug for the treatment of SOP.

O-GlcNAcylation in Renal (Patho)Physiology

Kidneys maintain internal milieu homeostasis through a well-regulated manipulation of body fluid composition. This task is performed by the correlation between structure and function in the nephron. Kidney diseases are chronic conditions impacting healthcare programs globally, and despite efforts, therapeutic options for its treatment are limited. The development of chronic degenerative diseases is associated with changes in protein O-GlcNAcylation, a post-translation modification involved in the regulation of diverse cell function. O-GlcNAcylation is regulated by the enzymatic balance between O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) which add and remove GlcNAc residues on target proteins, respectively. Furthermore, the hexosamine biosynthetic pathway provides the substrate for protein O-GlcNAcylation. Beyond its physiological role, several reports indicate the participation of protein O-GlcNAcylation in cardiovascular, neurodegenerative, and metabolic diseases. In this review, we discuss the impact of protein O-GlcNAcylation on physiological renal function, disease conditions, and possible future directions in the field.

Ttc21b deficiency attenuates autosomal dominant polycystic kidney disease in a kidney tubular- and maturation-dependent manner

Primary cilia are sensory organelles built and maintained by intraflagellar transport (IFT) multiprotein complexes. Deletion of several IFT-B genes attenuates polycystic kidney disease (PKD) severity in juvenile and adult autosomal dominant polycystic kidney disease (ADPKD) mouse models. However, deletion of an IFT-A adaptor, Tulp3, attenuates PKD severity in adult mice only. These studies indicate that dysfunction of specific cilia components has potential therapeutic value. To broaden our understanding of cilia dysfunction and its therapeutic potential, we investigate the role of global deletion of an IFT-A gene, Ttc21b, in juvenile and adult mouse models of ADPKD. Both juvenile (postnatal day 21) and adult (six months of age) ADPKD mice exhibited kidney cysts, increased kidney weight/body weight ratios, lengthened kidney cilia, inflammation, and increased levels of the nutrient sensor, O-linked β-N-acetylglucosamine (O-GlcNAc). Deletion of Ttc21b in juvenile ADPKD mice reduced cortical collecting duct cystogenesis and kidney weight/body weight ratios, increased proximal tubular and glomerular dilations, but did not reduce cilia length, inflammation, nor O-GlcNAc levels. In contrast, Ttc21b deletion in adult ADPKD mice markedly attenuated kidney cystogenesis and reduced cilia length, inflammation, and O-GlcNAc levels. Thus, unlike IFT-B, the effect of Ttc21b deletion in mouse models of ADPKD is development-specific. Unlike an IFT-A adaptor, deleting Ttc21b in juvenile ADPKD mice is partially ameliorative. Thus, our studies suggest that different microenvironmental factors, found in distinct nephron segments and in developing versus mature stages, modify ciliary homeostasis and ADPKD pathobiology. Further, elevated levels of O-GlcNAc, which regulates cellular metabolism and ciliogenesis, may be a pathological feature of ADPKD.

The glyco-redox interplay: Principles and consequences on the role of reactive oxygen species during protein glycosylation

Reactive oxygen species (ROS) carry out prime physiological roles as intracellular signaling agents, yet pathologically high concentrations of ROS cause irreversible damage to biomolecules, alter cellular programs and contribute to various diseases. While decades of intensive research have identified redox-related patterns and signaling pathways, very few addressed how the glycosylation machinery senses and responds to oxidative stress. A common trait among ROS and glycans residing on glycoconjugates is that they are both highly dynamic, as they are quickly fine-tuned in response to stressors such as inflammation, cancer and infectious diseases. On this account, the delicate balance of the redox potential, which is tightly regulated by dozens of enzymes including NOXs, and the mitochondrial electron transport chain as well as the fluidity of glycan biosynthesis resulting from the cooperation of glycosyltransferases, glycosidases, and nucleotide sugar transporters, is paramount to cell survival. Here, we review the broad spectrum of the interplay between redox changes and glycosylation with respect to their principle consequences on human physiology.

O-GlcNAc / Akt pathway regulates glucose metabolism and reduces apoptosis in liver of piglets with acute cold stress

Cold stress is one of the serious factors restricting the development of animal husbandry in cold areas. Cold exposure can easily lead to cold stress, slow growth and even death of newborn animals. O-GlcNAcylation modification can act as type of "stress receptor" and"nutrition sensor" in a variety of stress responses, however, it is not clear how O-GlcNAcylation can regulate glucose metabolism in the liver of piglets under cold stress. In this study, piglets 21 days of age were exposed to 4 °C for 4 h or 8 h in a phytotron. Serum cortisol and other stress hormones were used to assess body status to establish a cold stress piglet model. The changes of glycogen in liver were detected by PAS. FDP and PA were also measured to study the glycolysis level of liver. To characterize potential mechanisms of O-GlcNAcylation on the livers of cold stress piglets, AKT, GSK3β, GS, PFKFB2, AS160 and their corresponding phosphorylation were determined by Western blotting. Results show O-GlcNAcylation increased and apoptosis levels increased in the liver following cold exposure during excessive CORT or metabolic dysfunction. It is suggested that the acute cold exposure of piglets induced a sequential change in the level of O-GlcNAcylation, which may be one of the factors mediating liver cell apoptosis and glucose metabolism regulation by the O-GlcNAc/AKT pathway. These findings provide new insight into the mechanisms of the cold stress response, which can facilitate the development of new strategies to combat the effects of hypothermia.

Novel biomarkers for post-contrast acute kidney injury identified from long non-coding RNA expression profiles

Background: Post-contrast acute kidney injury (PC-AKI) is a severe complication of cardiac catheterization. Emerging evidence indicated that long non-coding RNAs (lncRNAs) could serve as biomarkers for various diseases. However, the lncRNA expression profile and potential biomarkers in PC-AKI remain unclear. This study aimed to investigate novel lncRNA biomarkers for the early detection of PC-AKI. Methods: lncRNA profile in the kidney tissues of PC-AKI rats was evaluated through RNA sequencing. Potential lncRNA biomarkers were identified through human-rat homology analysis, kidney and blood filtering in rats and verified in 112 clinical samples. The expression patterns of the candidate lncRNAs were detected in HK-2 cells and rat models to evaluate their potential for early detection. Results: In total, 357 lncRNAs were found to be differentially expressed in PC-AKI. We identified lnc-HILPDA and lnc-PRND were conservative and remarkably upregulated in both kidneys and blood from rats and the blood of PC-AKI patients; these lncRNAs can precisely distinguish PC-AKI patients (area under the curve (AUC) values of 0.885 and 0.875, respectively). The combination of these two lncRNAs exhibited improved accuracy for predicting PC-AKI, with 100% sensitivity and 83.93% specificity. Time-course experiments showed that the significant difference was first noted in the blood of PC-AKI rats at 12 h for lnc-HILPDA and 24 h for lnc-PRND. Conclusion: Our study revealed that lnc-HILPDA and lnc-PRND may serve as the novel biomarkers for early detection and profoundly affect the clinical stratification and strategy guidance of PC-AKI.

Ranolazine alleviates contrast-associated acute kidney injury through modulation of calcium independent oxidative stress and apoptosis

This study investigates the role of ranolazine in contrast-associated acute kidney injury (CA-AKI) and potential mechanisms. For in vivo studies, mouse models of CA-AKI and control mice were treated with ranolazine or vehicle. Blood urea nitrogen (BUN) and serum creatinine were detected by spectrophotometry. Anti-T-cell immunoglobulin and mucin domain 1 (TIM 1) and anti-lipocalin 2 antibody (LCN2) were detected by immunofluorescence. Hemodynamic parameters were detected via invasive blood pressure measurement and renal artery color doppler ultrasound, capillary density was measured by CD31 immunofluorescence, vascular permeability assay was performed by Evans blue dye. The expressions of oxidative stress and apoptotic markers were measured and analyzed by immunofluorescence and western blotting. For in vitro studies, intracellular calcium concentration of HUVECs was measured with Fluo 3-AM under confocal microscopy. Results show that compared with control mice, serum BUN, creatinine, TIM 1 and LCN2 levels were elevated in CA-AKI mice, but this effect was alleviated by ranolazine-pretreatment. Safe doses of ranolazine (less than 64 mg/kg) had no significant effect on overall blood pressure, but substantially improved renal perfusion, reduced contrast-induced microcirculation disturbance, improved renal capillary density and attenuated renal vascular permeability in ranolazine-pretreated CA-AKI mice. Mechanistically, ranolazine markedly down-regulated oxidative stress and apoptosis markers compared to CA-AKI mice. Intracellularly, ranolazine attenuated calcium overload in HUVECs. These results indicate that ranolazine alleviates CA-AKI through modulation of calcium independent oxidative stress and apoptosis.

A Novel Antioxidant Protects Against Contrast Medium-Induced Acute Kidney Injury in Rats

Many studies proposed that oxidative stress and apoptosis are key mechanisms in the pathogenesis of contrast-induced acute kidney injury (CI-AKI). Xylose-pyrogallol conjugate (XP) is an original effective antioxidant that showed decent antioxidant and anti-apoptosis effect before. Thus the therapeutic effect and mechanism of XP in preventing CI-AKI in the short and long term were investigated in this research. Renal function and histological grade were evaluated to determine the severity of renal injury. Kidney samples were then collected for the measurement of oxidative stress markers and the detection of apoptosis. Transmission electron microscopy (TEM) and western blot of mitochondrial protein were utilized for the analysis of the mitochondrial conditions. The results demonstrated that the CI-AKI rats caused a significant decrease in renal function accompanied by a remarkable increase in Malondialdehyde (MDA), bax, caspase-3, cytochrome c (Cyt C) level, TdT-mediated dUTP nick end labeling (TUNEL) positive apoptotic cells, and damaged mitochondria, while a decline in antioxidase activities and mitochondrial superoxide dismutase 2 (SOD2) expression compared with the control rats. However, when XP (50 or 100 or 200 mg/kg/day) was given orally for consecutive 7 days before CI-AKI modeling, XP (200 mg/kg) showed a better capability to restore renal dysfunction, histopathological appearance, the level of apoptosis, mitochondrial damage, oxidative stress, and fibrosis generation without interference in computed tomographic imaging. Our study indicated that antioxidant XP played a nephroprotective role probably via antiapoptotic and antioxidant mechanisms. Besides, XP may regulate the mitochondria pathway via decreasing the ratio of bax/bcl-2, inhibiting caspase-3 expression, cytochrome c release, and superoxide dismutase 2 activity. Overall, XP as a high-efficient antioxidant may have the potentials to prevent CI-AKI.

Glucosamine/Chondroitin and Mortality in a US NHANES Cohort

BACKGROUND

Limited previous studies in the United Kingdom or a single US state have demonstrated an association between intake of glucosamine/chondroitin and mortality. This study sought to investigate the association between regular consumption of glucosamine/chondroitin and overall and cardiovascular (CVD) mortality in a national sample of US adults.

METHODS

Combined data from 16,686 participants in National Health and Nutrition Examination Survey 1999 to 2010, merged with the 2015 Public-use Linked Mortality File. Cox proportional hazards models were conducted for both CVD and all-cause mortality.

RESULTS

In the study sample, there were 658 (3.94%) participants who had been taking glucosamine/chondroitin for a year or longer. During followup (median, 107 months), there were 3366 total deaths (20.17%); 674 (20.02%) were due to CVD. Respondents taking glucosamine/chondroitin were less likely to have CVD mortality (hazard ratio [HR] = 0.51; 95% CI, 0.28-0.92). After controlling for age, use was associated with a 39% reduction in all-cause (HR = 0.61; 95% CI, 0.49-0.77) and 65% reduction (HR = 0.35; 95% CI, 0.20-0.61) in CVD mortality. Multivariable-adjusted HR showed that the association was maintained after adjustment for age, sex, race, education, smoking status, and physical activity (all-cause mortality, HR = 0.73; 95% CI, 0.57-0.93; CVD mortality, HR = 0.42; 95% CI, 0.23-0.75).

CONCLUSIONS

Regular intake of glucosamine/chondroitin is associated with lower all-cause and CVD mortality in a national US cohort and the findings are consistent with previous studies in other populations. Prospective studies to confirm the link may be warranted.

Efficacy of the N-acetylglucosamine in experimental therapy of chronic kidney disease

The efficacy of N-acetylglucosamine in rats with chronic kidney disease is described in this article. The results of the study show that N-acetylglucosamine significantly increased (p<0.05) the excretion of nitrogen compounds (creatinine by 100.4% and urea by 46.6%) and as a result de-creased the level of azotemia. The intensity of free radical oxidation was significantly decreased (p<0.05) (blood conjugated dienes by 32.9%, blood thiobarbituric acid reactive substances – by 14.1%, kidney conjugated dienes – by 40.1% and kidney thiobarbituric acid reactive substances – by 26.3%) and the balance of kidney antioxidant system was restored. N-acetylglucosamine was significantly superior (p<0.05) to comparator quercetin in renal excretory function and nitro-gen metabolism by the most of indicators and was not inferior to the influence on the free radical oxidation and kidney oxidative stress. Thus, N-acetylglucosamine is advisable to further experimental studies at i.m. administration as a chronic kidney disease treatment.

Nrf-2 as a therapeutic target in acute kidney injury

Multifaceted cellular pathways exhibit a crucial role in the preservation of homeostasis at the molecular, cellular, and organism levels. One of the most important of these protective cascades is Nuclear factor E2-related factor (Nrf-2) that regulates the expression of several genes responsible for cellular detoxification, antioxidant function, anti-inflammation, drug/xenobiotic transportation, and stress-related factors. A growing body of evidence provides information regarding the protective role of Nrf-2 against a number of kidney diseases. Acute kidney injury (AKI) is a substantial clinical problem that causes a huge social burden. In the kidneys, Nrf-2 exerts a dynamic role in improving the injury triggered by inflammation and oxidative stress. Understanding of the exact molecular mechanisms underlying AKI is vital in order to determine the equilibrium between renal adaptation and malfunction and thus reduce disease progression. This review highlights the role of Nrf-2 targeting against AKI and provides evidence that targeting Nrf-2 to prevail oxidative damage and its consequences might exhibit protective effects in kidney diseases.

CaMKII as a key regulator of contrast-induced nephropathy through mPTP opening in HK-2 cells

Contrast-induced nephropathy (CIN), refers to acute kidney injury observed after administration of contrast media during angiographic or other medical procedures such as urography, and accounting for 12% of all causes of acute renal failure, but no specific prevention or treatment strategy exists for its obscure pathophysiology. The aim of our study was to explore the influence of calcium/calmodulin-dependent protein kinase II (CaMKII) in CIN by using HK-2 cells. Knockdown of CypD was achieved by lentivirus, and CaMKII overexpression by transfection with the plasmid. In this study, we have demonstrated that CypD-mediated mPTP opening triggered mitochondrial dysfunction and tubule cells apoptosis in CIN. We also found that iohexol treatment was associated with mitochondrial ROS overloading, ATP depletion and LDH release. Inhibition of CypD with the pharmacologic inhibitor or knockdown of CypD abrogated mPTP opening, oxidative stress, mitochondria damage, and cell apoptosis induced by iohexol. In addition, we found that inhibition of the CaMKII activity alleviated iohexol-induced CypD expression, whereas also decreased mPTP opening, oxidative stress, mitochondria damage, and cell apoptosis, similarly to the inhibition of CypD did. Moreover, CaMKII overexpression enhanced iohexol-induced mPTP opening, mitochondrial damage and renal tubular epithelial cells apoptosis. These findings first identified the novel role of CaMKII in iohexol-induced tubular cells apoptosis and delineated the CaMKII-CypD/mPTP pathway during contrast-induced tubular cell damage. Hence, these results could provide a new strategy for CIN protection.

Tripterygium glycoside fraction n2 ameliorates adriamycin-induced nephrotic syndrome in rats by suppressing apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Tripterygium wilfordii Hook F. (TwHF), a traditional Chinese herb medicine, has been widely used for clinical treatment of various rheumatic immune diseases. Tripterygium glycosides (TG) extracted from TwHF has been verified to process multiple bioactivities, including immunosuppressive, anti-inflammatory and anti-cancer effects. However, the clinical application of TG is limited due to its severe toxicity and narrow therapeutic window. For the clinical safety of TG usage, attenuation of toxicity is the key issue to be solved.

PURPOSE

Tripterygium glycoside fraction n2 (TG-n2) is a detoxified mixture obtained from TG using a new preparation method. In our previous study, we have demonstrated that TG-n2 has a lower toxicity than TG. The aim of the present study was to screen the renal protective effect of TG-n2 in nephrotic syndrome (NS) induced by adriamycin (ADR) in rats and its effect on apoptosis, as well as the effective difference between TG-n2 and TG.

MATERIALS AND METHODS

The ADR-induced NS rat model was established. Rats were intravenously injected with ADR (6 mg/kg), then treated with either TG-n2 (10 mg/kg/day) or TG (10 mg/kg/day) by oral gavage for 4 weeks. Clinical indexes in each group were determined. HE staining and electron microscopic analysis were used to evaluate renal histopathological damage. Caspase-3 activity reagent and TUNEL staining were used to estimate renal apoptosis. Protein levels of caspase-3, caspase-9, caspase-8, caspase-12, Bax, Bcl-2, p53, TNF-R1, FLIP and podocin were measured by Western Blot.

RESULTS

TG-n2 and TG intervention ameliorated renal function as assessed by the levels of 24-h proteinuria, Cr, BUN, TC, TG, ALB and LDL-c. TG-n2 and TG alleviated the decrease of podocin protein expression and morphological injury of podocyte as screened by Western Blot and electron microscopic analysis. Besides, renal tubular injury was reduced as inspected by light microscopic analysis. TG-n2 and TG could significantly inhibit the apoptosis and activity of caspase-3 in kidney tissues as examined by fluorescence microscopic analysis and reagent. After intervention of TG-n2 and TG, protein levels of cleaved caspase-3, cleaved caspase-8, cleaved caspase-9, Bax, p53 and TNF-R1 in renal issues were significantly decreased compared with ADR group. In contrast, protein level of Bcl-2 was elevated remarkedly.

CONCLUSIONS

Our data suggested that attenuated TG-n2 may have a similar protective effect with TG in ADR-induced NS in rats by inhibiting activation of apoptosis.

O-GlcNAc impairs endothelial function in uterine arteries from virgin but not pregnant rats: The role of GSK3β

Increased O-Linked β-N-acetylglucosamine (O-GlcNAc) is observed in several pathologies, and unbalanced O-GlcNAcylation levels favor endothelial dysfunction. Whether augmented O-GlcNAc impacts the uterine artery (UA) function and how it affects the UA during pregnancy remains to be elucidated. We hypothesized that glucosamine treatment increases O-GlcNAc, leading to uterine artery dysfunction and this effect is prevented by pregnancy. Pregnant (P) and non-pregnant (NP) Wistar rats were treated with glucosamine (300 mg/kg; i.p.) for 21 days. Concentration response-curves (CRC) to acetylcholine (in the presence or absence of L-NAME) and sodium nitroprusside were performed in UAs. In NP rats, glucosamine treatment increased O-GlcNAc expression in UAs accompanied by decreased endothelium-dependent relaxation, which was abolished by L-NAME. Endothelial nitric oxide synthase (eNOS) activity and total Akt expression were decreased by glucosamine-treatment in NP rats. Further, NP rats treated with glucosamine displayed increased glycogen synthase kinase 3 beta (GSK3β) activation and O-GlcNAc-transferase (OGT) expression in the UA. P rats treated with glucosamine displayed decreased O-GlcNAc in UAs and it was accompanied by improved relaxation to acetylcholine, whereas eNOS and GSK3β activity and total Akt and OGT expression were unchanged. Sodium nitroprusside-induced relaxation was not changed in all groups, indicating that glucosamine treatment led to endothelial dysfunction in NP rats. The underlying mechanism is, at least in part, dependent on Akt/GSK3β/OGT modulation. We speculate that during pregnancy, hormonal alterations play a protective role in preventing O-GlcNAcylation-induced endothelial dysfunction in the UAs.

O-GlcNAc stimulation: A new metabolic approach to treat septic shock

Septic shock is a systemic inflammation associated with cell metabolism disorders and cardiovascular dysfunction. Increases in O-GlcNAcylation have shown beneficial cardiovascular effects in acute pathologies. We used two different rat models to evaluate the beneficial effects of O-GlcNAc stimulation at the early phase of septic shock. Rats received lipopolysaccharide (LPS) to induce endotoxemic shock or saline (control) and fluid resuscitation (R) with or without O-GlcNAc stimulation (NButGT-10 mg/kg) 1 hour after shock induction. For the second model, rats received cecal ligature and puncture (CLP) surgery and fluid therapy with or without NButGT. Cardiovascular function was evaluated and heart and blood samples were collected and analysed. NButGT treatment efficiently increased total O-GlcNAc without modification of HBP enzyme expression.Treatment improved circulating parameters and cardiovascular function in both models, and restored SERCA2a expression levels. NButGT treatment also reduced animal mortality. In this study, we demonstrate that in septic shock O-GlcNAc stimulation improves global animal and cardiovascular function outcomes associated with a restoration of SERCA2a levels. This pre-clinical study opens avenues for a potential therapy of early-stage septic shock.

Redox signaling in aging kidney and opportunity for therapeutic intervention through natural products

Kidney diseases are serious public problems with high morbidity and mortality in the general population and heavily retard renal function with aging regardless of the cause. Although myriad strategies have been assigned to prevent or harness disease progression, unfortunately, thus far, there is a paucity of effective therapies partly due to an insufficient knowledge of underlying pathological mechanisms, indicating deeper studies are urgently needed. Additionally, natural products are increasingly recognized as an alternative source for disease intervention owing to the potent safety and efficacy, which might be exploited for novel drug discovery. In this review, we primarily expatiate the new advances on mediators that might be amenable to targeting aging kidney and kidney diseases, including nicotinamide adenine dinucleotide phosphate oxidase (NOX), transforming growth factor-β (TGF-β), renin-angiotensin system (RAS), nuclear factor-erythroid 2 related factor 2 (Nrf2), peroxisome proliferator-activated γ receptor (PPARγ), advanced glycation endproducts (AGEs) as well as microRNAs and vitagenes. Of note, we conclude by highlighting some natural products which have the potential to facilitate the development of novel treatment for patients with myriad renal diseases.

Acute increases in O-GlcNAc indirectly impair mitochondrial bioenergetics through dysregulation of LonP1-mediated mitochondrial protein complex turnover

The attachment of O-linked β-N-acetylglucosamine (O-GlcNAc) to the serine and threonine residues of proteins in distinct cellular compartments is increasingly recognized as an important mechanism regulating cellular function. Importantly, the O-GlcNAc modification of mitochondrial proteins has been identified as a potential mechanism to modulate metabolism under stress with both potentially beneficial and detrimental effects. This suggests that temporal and dose-dependent changes in O-GlcNAcylation may have different effects on mitochondrial function. In the current study, we found that acutely augmenting O-GlcNAc levels by inhibiting O-GlcNAcase with Thiamet-G for up to 6 h resulted in a time-dependent decrease in cellular bioenergetics and decreased mitochondrial complex I, II, and IV activities. Under these conditions, mitochondrial number was unchanged, whereas an increase in the protein levels of the subunits of several electron transport complex proteins was observed. However, the observed bioenergetic changes appeared not to be due to direct increased O-GlcNAc modification of complex subunit proteins. Increases in O-GlcNAc were also associated with an accumulation of mitochondrial ubiquitinated proteins; phosphatase and tensin homolog induced kinase 1 (PINK1) and p62 protein levels were also significantly increased. Interestingly, the increase in O-GlcNAc levels was associated with a decrease in the protein levels of the mitochondrial Lon protease homolog 1 (LonP1), which is known to target complex IV subunits and PINK1, in addition to other mitochondrial proteins. These data suggest that impaired bioenergetics associated with short-term increases in O-GlcNAc levels could be due to impaired, LonP1-dependent, mitochondrial complex protein turnover.

The Role of O-GlcNAcylation for Protection against Ischemia-Reperfusion Injury

Ischemia reperfusion injury (IR injury) associated with ischemic heart disease contributes significantly to morbidity and mortality. O-linked β-N-acetylglucosamine (O-GlcNAc) is a dynamic posttranslational modification that plays an important role in numerous biological processes, both in normal cell functions and disease. O-GlcNAc increases in response to stress. This increase mediates stress tolerance and cell survival, and is protective. Increasing O-GlcNAc is protective against IR injury. Experimental cellular and animal models, and also human studies, have demonstrated that protection against IR injury by ischemic preconditioning, and the more clinically applicable remote ischemic preconditioning, is associated with increases in O-GlcNAc levels. In this review we discuss how the principal mechanisms underlying tissue protection against IR injury and the associated immediate elevation of O-GlcNAc may involve attenuation of calcium overload, attenuation of mitochondrial permeability transition pore opening, reduction of endoplasmic reticulum stress, modification of inflammatory and heat shock responses, and interference with established cardioprotective pathways. O-GlcNAcylation seems to be an inherent adaptive cytoprotective response to IR injury that is activated by mechanical conditioning strategies.

Camel milk attenuates methotrexate-induced kidney injury via activation of PI3K/Akt/eNOS signaling and intervention with oxidative aberrations

Methotrexate (MTX) is a classical chemotherapeutic agent with nephrotoxicity as the most disturbing adverse effect. So far, its underlying molecular mechanisms, particularly PI3K/Akt/eNOS transduction, are inadequately explored. Several antioxidant modalities have been characterized to ameliorate MTX-induced renal injury. In this regard, Camel milk (CM) is a natural product with recognized antioxidant and anti-inflammatory features. Thus, the current study aimed to investigate the potential ameliorating effects of CM in MTX-induced kidney injury in rats. Renal tissues were studied in terms of renal injury markers, histopathology, oxidative stress, apoptosis and PI3K/Akt/eNOS signaling. CM was orally administered (10 ml kg-1) and the renal injury was induced by a single i.p. injection of MTX (20 mg kg-1). Interestingly, CM dose-dependently attenuated MTX-triggered increase of BUN and serum creatinine and renal Kim-1 expression and mitigated the renal histopathological changes. CM counteracted renal oxidative stress as manifested by lowering of lipid peroxides, restoration of NOX-1 levels and augmentation of the antioxidant defenses e.g., GSH, SOD, GPx and total antioxidant capacity. With respect to apoptosis, CM curbed the cleavage of PARP and caspase-3, downregulated p53, Bax and Cyt C proapoptotic signals and enhanced Bcl-2 and PCNA levels. In the same context, CM activated the prosurvival PI3K/Akt/eNOS pathway via enhancing PI3K p110, phospho-Akt and phospho-eNOS levels. Equally important, CM preconditioning did not interfere with MTX cytotoxicity in TK-10 or PC-3 cancer cells. Together, the current findings demonstrate, for the first time, the renoprotective effects of CM in MTX-induced kidney injury via activation of PI3K/Akt/eNOS signaling and combating oxidative stress and apoptosis.

Effects of Acute Cold Stress on Liver O-GlcNAcylation and Glycometabolism in Mice

Protein O-linked β-N-acetylglucosamine glycosylation (O-GlcNAcylation) regulates many biological processes. Studies have shown that O-GlcNAc modification levels can increase during acute stress and suggested that this may contribute to the survival of the cell. This study investigated the possible effects of O-GlcNAcylation that regulate glucose metabolism, apoptosis, and autophagy in the liver after acute cold stress. Male C57BL/6 mice were exposed to cold conditions (4 °C) for 0, 2, 4, and 6 h, then their livers were extracted and the expression of proteins involved in glucose metabolism, apoptosis, and autophagy was determined. It was found that acute cold stress increased global O-GlcNAcylation and protein kinase B (AKT) phosphorylation levels. This was accompanied by significantly increased activation levels of the glucose metabolism regulators 160 kDa AKT substrate (AS160), 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 2 (PFKFB2), and glycogen synthase kinase-3β (GSK3β). The levels of glycolytic intermediates, fructose-1,6-diphosphate (FDP) and pyruvic acid (PA), were found to show a brief increase followed by a sharp decrease. Additionally, adenosine triphosphate (ATP), as the main cellular energy source, had a sharp increase. Furthermore, the B-cell lymphoma 2(Bcl-2)/Bcl-2-associated X (Bax) ratio was found to increase, whereas cysteine-aspartic acid protease 3 (caspase-3) and light chain 3-II (LC3-II) levels were reduced after acute cold stress. Therefore, acute cold stress was found to increase O-GlcNAc modification levels, which may have resulted in the decrease of the essential processes of apoptosis and autophagy, promoting cell survival, while altering glycose transport, glycogen synthesis, and glycolysis in the liver.

O-GlcNAc Modification During Pregnancy: Focus on Placental Environment

Successful placentation is a key event for fetal development, which commences following embryo implantation into the uterine wall, eliciting decidualization, placentation, and remodeling of blood vessels to provide physiological exchange between embryo-fetus and mother. Several signaling pathways are recruited to modulate such important processes and specific proteins that regulate placental function are a target for the glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAc), or O-GlcNAcylation. This is a reversible post-translational modification on nuclear and cytoplasmic proteins, mainly controlled by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). O-GlcNAcylation has been implicated as a modulator of proteins, both in physiological and pathological conditions and, more recently, O-GlcNAc has also been shown to be an important modulator in placental tissue. In this mini-review, the interplay between O-GlcNAcylation of proteins and placental function will be addressed, discussing the possible implications of this post-translational modification through placental development and pregnancy.

Aging Is Associated With Impaired Activation of Protein Homeostasis-Related Pathways After Cardiac Arrest in Mice

Background The mechanisms underlying worse outcome at advanced age after cardiac arrest ( CA ) and resuscitation are not well understood. Because protein homeostasis (proteostasis) is essential for cellular and organismal health, but is impaired after CA , we investigated the effects of age on proteostasis-related prosurvival pathways activated after CA . Methods and Results Young (2-3 months old) and aged (21-22 months old) male C57Bl/6 mice were subjected to CA and cardiopulmonary resuscitation ( CPR ). Functional outcome and organ damage were evaluated by assessing neurologic deficits, histological features, and creatinine level. CA / CPR -related changes in small ubiquitin-like modifier conjugation, ubiquitination, and the unfolded protein response were analyzed by measuring mRNA and protein levels in the brain, kidney, and spinal cord. Thiamet-G was used to increase O-linked β-N-acetylglucosamine modification. After CA / CPR , aged mice had trended lower survival rates, more severe tissue damage in the brain and kidney, and poorer recovery of neurologic function compared with young mice. Furthermore, small ubiquitin-like modifier conjugation, ubiquitination, unfolded protein response, and O-linked β-N-acetylglucosamine modification were activated after CA / CPR in young mice, but their activation was impaired in aged mice. Finally, pharmacologically increasing O-linked β-N-acetylglucosamine modification after CA improved outcome. Conclusions Results suggest that impaired activation of prosurvival pathways contributes to worse outcome after CA / CPR in aged mice because restoration of proteostasis is critical to the survival of cells stressed by ischemia. Therefore, a pharmacologic intervention that targets aging-related impairment of proteostasis-related pathways after CA / CPR may represent a promising therapeutic strategy.

Remote Ischemic Preconditioning Ameliorates Acute Kidney Injury due to Contrast Exposure in Rats through Augmented O-GlcNAcylation

Remote ischemic preconditioning (RIPC) is an adaptive response, manifesting when local short-term ischemic preconditioning reduces damage to adjacent or distant tissues or organs. O-linked β-N-acetylglucosamine (O-GlcNAc) glycosylation of intracellular proteins denotes a type of posttranslational modification that influences multiple cytoplasmic and nuclear protein functions. Growing evidence indicates that stress can induce an acute increase in O-GlcNAc levels, which can be cytoprotective. The current study aimed to determine whether RIPC can provide renoprotection against contrast-induced acute kidney injury (CI-AKI) by augmenting O-GlcNAc signaling. We established a stable model of CI-AKI using 5/6 nephrectomized rats exposed to dehydration followed by iohexol injection via the tail vein. We found that RIPC increased UDP-GlcNAc levels through the hexosamine biosynthetic pathway as well as global renal O-GlcNAcylation. RIPC-induced elevation of O-GlcNAc signaling ameliorated CI-AKI based on the presence of less tubular damage and apoptosis and the amount of reactive oxygen species. In addition, the use of alloxan, an O-GlcNAc transferase inhibitor, and azaserine, a glutamine fructose-6-phosphate amidotransferase inhibitor, neutralized the protective effect of RIPC against oxidative stress and tubular apoptosis. In conclusion, RIPC attenuates local oxidative stress and tubular apoptosis induced by contrast exposure by enhancing O-GlcNAc glycosylation levels; this can be a potentially useful approach for lowering the risk of CI-AKI.

O-GlcNAcylation reduces proximal tubule protein reabsorption and promotes proteinuria in spontaneously hypertensive rats

Hypertensive individuals are at greater risk for developing chronic kidney disease (CKD). Reducing proteinuria has been suggested as a possible therapeutic approach to treat CKD. However, the mechanisms underlying the development of proteinuria in hypertensive conditions are incompletely understood. Cardiac and vascular dysfunction is associated with changes in the O-GlcNAcylation pathway in hypertensive models. We hypothesized that O-GlcNAcylation is also involved in renal damage, especially development of proteinuria, associated with hypertension. Using the spontaneously hypertensive rat (SHR) model, we observed higher renal cortex O-GlcNAcylation, glutamine-fructose aminotransferase (GFAT), and O-GlcNAc transferase (OGT) protein expression, which positively correlated with proteinuria. Interestingly, this was observed in hypertensive, but not pre-hypertensive, rats. Pharmacological inhibition of GFAT decreased renal cortex O-GlcNAcylation, proteinuria, and albuminuria in SHR. Using a proximal tubule cell line, we observed that increased O-GlcNAcylation reduced megalin surface expression and albumin endocytosis in vitro, and the effects were correlated in vivo Moreover, megalin is O-GlcNAcylated both in vitro and in vivo In conclusion, our results demonstrate a new mechanism involved in hypertension-associated proteinuria.

Protein O-GlcNAcylation in Cardiac Pathologies: Past, Present, Future

O-GlcNAcylation is a ubiquitous and reversible post-translational protein modification that has recently gained renewed interest due to the rapid development of analytical tools and new molecules designed to specifically increase the level of protein O-GlcNAcylation. The level of O-GlcNAc modification appears to have either deleterious or beneficial effects, depending on the context (exposure time, pathophysiological context). While high O-GlcNAcylation levels are mostly reported in chronic diseases, the increase in O-GlcNAc level in acute stresses such as during ischemia reperfusion or hemorrhagic shock is reported to be beneficial in vitro, ex vivo, or in vivo. In this context, an increase in O-GlcNAc levels could be a potential new cardioprotective therapy, but the ambivalent effects of protein O-GlcNAcylation augmentation remains as a key problem to be solved prior to their transfer to the clinic. The emergence of new analytical tools has opened new avenues to decipher the mechanisms underlying the beneficial effects associated with an O-GlcNAc level increase. A better understanding of the exact roles of O-GlcNAc on protein function, targeting or stability will help to develop more targeted approaches. The aim of this review is to discuss the mechanisms and potential beneficial impact of O-GlcNAc modulation, and its potential as a new clinical target in cardiology.

Glycolysis and the Hexosamine Biosynthetic Pathway as Novel Targets for Upper and Lower Airway Inflammation

Glycolysis is a process that rapidly converts glucose to lactate to produce adenosine triphosphate (ATP) under anaerobic conditions and occurs in all eukaryotic and prokaryotic cells. On the other hand, the hexosamine biosynthetic pathway (HBP) converts glucose to intermediate products like UDP-N-acetylglucosamine, which is critical for post-translational modifications of proteins, such as protein glycosylation. These 2 pathways are well known to contribute to glucose metabolism, but recent studies indicate modulation of these pathways can alter immune system function. In this review article, the authors present results suggesting how cellular metabolism, including glycolysis and the HBP, occurs in immune cells, and the immunologic significances of such activities. In addition, they provide a review of the literature on the effects of glycolysis and the HBP on various autoimmune, immunologic, and allergic diseases. Finally, the authors briefly introduce the results of their research on the immunologic effects of HBP supplementation (glucosamine) in animal models of allergic disease.