CDK/GSK-3 inhibitors as therapeutic agents for parenchymal renal diseases

Mechanisms that potentially contribute to the development of post-streptococcal glomerulonephritis

Post-streptococcal glomerulonephritis (PSGN) is primarily associated with preceding group A streptococcal skin or throat infections, now mainly observed in economically disadvantaged communities. This condition significantly predisposes individuals to later-life chronic kidney disease and concurrent renal complications, with the elderly experiencing increased severity and less favourable outcomes. Streptococcal pyrogenic exotoxin B and nephritis-associated plasmin receptor are identified nephritogenic antigens (nephritogens). Pathogenesis of PSGN is multifactorial. It can involve the formation of antigen-antibody immune complexes, causing inflammatory damage to renal glomeruli. Deposition of circulating immune complexes or in situ formation of immune complexes in glomeruli, or both, results in glomerulonephritis. Additionally, molecular mimicry is hypothesized as a mechanism, wherein cross-reactivity between anti-streptococcal antibodies and glomerular intrinsic matrix proteins leads to glomerulonephritis. Besides, as observed in clinical studies, streptococcal inhibitor of complement, a streptococcal-secreted protein, can also be associated with PSGN. However, the interplay between these streptococcal antigens in the pathogenesis of PSGN necessitates further investigation. Despite the clinical significance of PSGN, the lack of credible animal models poses challenges in understanding the association between streptococcal antigens and the disease process. This review outlines the postulated mechanisms implicated in the development of PSGN with possible therapeutic approaches.

Lessons Learned from Past Cyclin-Dependent Kinase Drug Discovery Efforts

Inhibition of cyclin-dependent kinases (CDKs) has become an effective therapeutic strategy for treating various diseases, especially cancer. Over almost three decades, although great efforts have been made to discover CDK inhibitors, many of which have entered clinical trials, only four CDK inhibitors have been approved. In the process of CDK inhibitor development, many difficulties and misunderstandings have hampered their discovery and clinical applications, which mainly include inadequate understanding of the biological functions of CDKs, less attention paid to pan- and multi-CDK inhibitors, nonideal isoform selectivity of developed selective CDK inhibitors, overlooking the metabolic stability of early discovered CDK inhibitors, no effective resistance solutions, and a lack of available combination therapy and effective biomarkers for CDK therapies. After reviewing the mechanisms of CDKs and the research progress of CDK inhibitors, this perspective summarizes and discusses these difficulties or lessons, hoping to facilitate the successful discovery of more useful CDK inhibitors.

The Oxindole Derivatives, New Promising GSK-3β Inhibitors as One of the Potential Treatments for Alzheimer's Disease-A Molecular Dynamics Approach

Simple Summary

Enzymatic overexpression is a determinant of the development of many diseases. Increased activity of the GSK-3β enzyme is a factor that manifests itself in the development of numerous disease entities such as Alzheimer’s disease, schizophrenia, diabetes and cancers. An important medical procedure in such cases is the inhibition of enzyme activity. Based on the comprehensive use of computational chemistry methods, a group of new compounds derived from 2-oxindole was designed. The conducted research allowed the assessment of the conformational properties of the ligand molecules in the GSK-3β active site, the dynamic stability of the obtained complexes and their exact energetic characteristics. Taking into account the obtained data, a narrow group of derivatives showing an affinity for the active site of the GSK-3β enzyme was selected. The comparison of binding properties of selected 2-oxindole derivatives with an inhibitor with confirmed pharmacological activity indicates the high application potential of the newly developed compounds.

Abstract

The glycogen synthase kinase 3β (GSK-3β) is a protein kinase involved in regulating numerous physiological processes such as embryonic development, transcription, insulin action, cell division cycle and multiple neuronal functions. The overexpression of this enzyme is related to many diseases such as schizophrenia, Alzheimer’s disease, diabetes and cancer. One of the basic methods of treatment in these cases is the usage of ATP-competitive inhibitors. A significant group of such compounds are indirubin and its analogs, e.g., oxindole derivatives. The compounds considered in this work are 112 newly designed oxindole derivatives. In the first stage, such molecular properties of considered compounds as toxicity and LogP were estimated. The preliminary analysis of the binding capabilities of considered compounds towards the GSK-3β active site was conducted with the use of the docking procedure. Based on obtained molecular properties and docking simulations, a selected group of complexes that were analyzed in the molecular dynamics stage was nominated. The proposed procedure allowed for the identification of compounds such as Oxind_4_9 and Oxind_13_10, which create stable complexes with GSK-3β enzyme and are characterized by the highest values of binding affinity. The key interactions responsible for stabilization of considered ligand–protein complexes were identified, and their dynamic stability was also determined. Comparative analysis including analyzed compounds and reference molecule 3a, which is also an oxindole derivative with a confirmed inhibitory potential towards GSK3B protein, clearly indicates that the proposed compounds exhibit an analogous binding mechanism, and the obtained binding enthalpy values indicate a slightly higher binding potential than the reference molecule.

Hsa_circ_0056558 regulates cyclin-dependent kinase 6 by sponging microRNA-1290 to suppress the proliferation and differentiation in ankylosing spondylitis

The aims of this study was to investigate the influences of hsa_circ_0056558/miR-1290/CDK6 axis in ankylosing spondylitis (AS). The differentially expressed has_circ_0056558 and miR-1290 in AS tissue were analysed based on RNA-seq data and microarray data, respectively. qRT-PCR was performed for detection of relative expression levels of hsa_circ_0056558, miR-1290, CDK6, osteogenic differentiation markers (Runx2 and Osterix) and other inflammatory factors (TNF-α, IL-1β, and IL-6). Western blotting analysis was conducted to test the protein levels of CDK6, osteogenic differentiation markers (Runx2 and Osterix), and PI3K/AKT/NF-κB pathway-associated proteins. CCK8 assay and flow cytometry were conducted to determine cell proliferation and cell apoptotic ability, respectively. Targeted relationships were predicted by bioinformatic analysis and verified by dual-luciferase reporter assay. The differentiation of fibroblast cells was analysed by alkaline phosphatase (ALP) activity assay. Our findings revealed that the expression levels of both circ_0056558 and CDK6 in AS tissue were significantly higher than that in normal samples. Besides, hsa_circ_0056558 could suppress cell proliferation and differentiation by facilitating CDK6 expression and suppressing miR-1290 expression in AS. Over-expression of miR-1290 negatively regulated CDK6 expression to enhance cell proliferation. The protein levels of p-AKT, p-NF-κB p65, and p-IκBα were promoted by hsa_circ_0056558 or CDK6 over-expression while suppressed by miR-1290 up-regulation. In conclusion, our study demonstrated that hsa_circ_0056558 and CDK6 suppressed cell proliferation and differentiation while enhanced cell apoptosis by competitive binding to miR-1290 in AS, which might be possibly achieved by PI3K/AKT/NF-κB pathway, providing us novel therapeutic strategy for AS.

Restoring glucose uptake rescues neutrophil dysfunction and protects against systemic fungal infection in mouse models of kidney disease

Disseminated candidiasis caused by the fungus Candida albicans is a major clinical problem in individuals with kidney disease and accompanying uremia; disseminated candidiasis fatality is twice as common in patients with uremia as those with normal kidney function. Many antifungal drugs are nephrotoxic, making treatment of these patients particularly challenging. The underlying basis for this impaired capacity to control infections in uremic individuals is poorly understood. Here, we show in multiple models that uremic mice exhibit an increased susceptibility to systemic fungal infection. Uremia inhibits Glut1-mediated uptake of glucose in neutrophils by causing aberrant activation of GSK3β, resulting in reduced ROS generation and hence impaired killing of C. albicans in mice. Consequently, pharmacological inhibition of GSK3β restored glucose uptake and rescued ROS production and candidacidal function of neutrophils in uremic mice. Similarly, neutrophils isolated from patients with kidney disease and undergoing hemodialysis showed similar defect in the fungal killing activity, a phenotype rescued in the presence of a GSK3β inhibitor. These findings reveal a mechanism of neutrophil dysfunction during uremia and suggest a potentially translatable therapeutic avenue for treatment of disseminated candidiasis.

GSK-3β inhibitor attenuates urinary albumin excretion in type 2 diabetic db/db mice, and delays epithelial-to-mesenchymal transition in mouse kidneys and podocytes

The mechanism underlying epithelial‑to‑mesenchymal transition (EMT) caused by high glucose (HG) stimulation in diabetic nephropathy (DN) remains to be fully elucidated. The present study investigated the effects of HG on EMT and the activity of glycogen synthase kinase 3β (GSK‑3β) in podocytes and the kidneys of db/db mice, and assessed the effects of (2'Z, 3'E)‑6‑bromoindirubin‑3'‑oxime (BIO), an inhibitor of GSK‑3β, on EMT and glomerular injury. The resulting data showed that the activity of GSK‑3β was upregulated by HG and downregulated by BIO in the podocytes and the renal cortex. The expression levels of epithelial markers, including nephrin, podocin and synaptopodin, were decreased by HG and increased by BIO, whereas the reverse were true for mesenchymal markers, including α‑smooth muscle actin (α‑SMA) and fibronectin. The expression levels of β‑catenin and Snail, in contrast to current understanding of the Wnt signaling pathway, were increased by HG and decreased by BIO. In addition, expression of the vitamin D receptor (VDR) was decreased by HG and increased by BIO. In conclusion, the present study revealed that the mechanism by which BIO inhibited HG‑mediated EMT in podocytes and the renal cortex was primarily due to the VDR. Treatment with BIO protected renal function by maintaining the integrity of the filtration membrane and decreasing UAE, but not by regulating blood glucose. Therefore, GSK‑3β may be used as a sensitive biomarker of DN, and its inhibition by BIO may be effective in the treatment of DN.

Lithium in the Kidney: Friend and Foe?

Trace amounts of lithium are essential for our physical and mental health, and administration of lithium has improved the quality of life of millions of patients with bipolar disorder for >60 years. However, in a substantial number of patients with bipolar disorder, long-term lithium therapy comes at the cost of severe renal side effects, including nephrogenic diabetes insipidus and rarely, ESRD. Although the mechanisms underlying the lithium-induced renal pathologies are becoming clearer, several recent animal studies revealed that short-term administration of lower amounts of lithium prevents different forms of experimental AKI. In this review, we discuss the knowledge of the pathologic and therapeutic effects of lithium in the kidney. Furthermore, we discuss the underlying mechanisms of these seemingly paradoxical effects of lithium, in which fine-tuned regulation of glycogen synthase kinase type 3, a prime target for lithium, seems to be key. The new discoveries regarding the protective effect of lithium against AKI in rodents call for follow-up studies in humans and suggest that long-term therapy with low lithium concentrations could be beneficial in CKD.

Glycogen synthase kinase-3β inhibitor ameliorates imbalance of connexin 43 in an acute kidney injury model

This study was designed to evaluate whether glycogen synthase kinase-3β (GSK-3β) inhibitor, 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8) induced the the expression of connexin 43 (Cx43) to protect against renal ischemia–reperfusion (I/R) injury (RI/RI) in rats. Rats were subjected to 45 min ischemia followed 2 h reperfusion with TDZD-8 (1 mg/kg) for 5 min prior to reperfusion. The results indicated that TDZD-8 improved the recovery of renal function, reduced oxidative stress and inflammation injury, and upregulated the expression of (Cx43) as compared to I/R group. Therefore, our study demonstrated that TDZD-8 provided a protection to the kidney against I/R injury in rats through inducing the expression of (Cx43).

Understanding podocytopathy and its relevance to clinical nephrology

Podocytopathies are the most common group of glomerular disorder leading to proteinuria. On the basis of pathophysiology, light microscopic and ultrastructural evaluation, the podocytopathies include minimal change disease, diffuse mesangial sclerosis, focal segmental glomerulosclerosis and collapsing glomerulopathy. The present review summarizes the basic etiopathogenesis of podocytopthies, highlights the common genetic and acquired factors in its causation, puts forth various diagnostic modalities and discusses the role of emerging agents or treatment.

Cell cycle control in the kidney

Proper control of the cell cycle is mandatory during homeostasis and disease. The balance of p53 and MDM2 integrates numerous signalling pathways to regulate the cell cycle, which is executed by multiple proteins including the cyclins, cyclin kinases and cyclin kinase inhibitors. Mutations or environmental factors that affect cell cycle control can lead to inappropriate hyperplasia or cancer as well as to cell loss and tissue atrophy. Normal kidney function is maintained largely by post-mitotic quiescent cells in the G0 phase with a low turnover. Early cell cycle activation during kidney injury contributes to cell death via mitotic catastrophe, i.e. death via mitosis, e.g. of cell with significant DNA damage. At later stages, cell cycle entry supports tissue regeneration and functional reconstitution via cell hypertrophy and/or cell proliferation. It is of note that so-called proliferation markers such as Ki67, PCNA or BrdU identify only cell cycle entry without telling whether this results in cell hypertrophy, cell division or mitotic catastrophe. With this in mind, some established concepts on kidney injury and regeneration are to be re-evaluated. Here, we discuss the components and functional roles of p53/MDM2-mediated cell cycle regulation in kidney homeostasis and disease.

Glycogen synthase kinase 3β orchestrates microtubule remodeling in compensatory glomerular adaptation to podocyte depletion

Reminiscent of neural repair, following podocyte depletion, remnant-surviving podocytes exhibit a considerable adaptive capacity to expand and cover the denuded renal glomerular basement membrane. Microtubules, one of the principal cytoskeletal components of podocyte major processes, play a crucial role in podocyte morphogenesis and podocyte process outgrowth, branching, and elongation. Here, we demonstrated that the microtubule-associated proteins Tau and collapsin response mediator protein (CRMP) 2, key regulators of microtubule dynamics, were abundantly expressed by glomerular podocytes in vivo and in vitro, interacted with glycogen synthase kinase (GSK)3β, and served as its putative substrates. GSK3β overactivity induced by adriamycin injury or by a constitutively active mutant of GSK3β augmented phosphorylation of Tau and CRMP2, concomitant with microtubule depolymerization, cell body shrinkage, and shortening of podocyte processes. Conversely, inhibition of GSK3β by a dominant negative mutant or by lithium, a Food and Drug Administration-approved neuroprotective mood stabilizer, diminished Tau and CRMP2 phosphorylation, resulting in microtubule polymerization, podocyte expansion, and lengthening of podocyte processes. In a mouse model of adriamycin-induced podocyte depletion and nephropathy, delayed administration of a single low dose of lithium attenuated proteinuria and ameliorated progressive glomerulosclerosis despite no correction of podocytopenia. Mechanistically, lithium therapy obliterated GSK3β overactivity, mitigated phosphorylation of Tau and CRMP2, and enhanced microtubule polymerization and stabilization in glomeruli in adriamycin-injured kidneys, associated with elongation of podocyte major processes. Collectively, our findings suggest that the GSK3β-dictated podocyte microtubule dynamics might serve as a novel therapeutic target to reinforce the compensatory glomerular adaptation to podocyte loss.

Silencing of p53 RNA through transarterial delivery ameliorates renal tubular injury and downregulates GSK-3β expression after ischemia-reperfusion injury

p53, a pivotal protein in the apoptotic pathway, has been identified as a mediator of transcriptional responses to ischemia-reperfusion (IR) injury. The characteristics and functional significance of the p53 response in vivo are largely unknown in IR-induced kidney injury. Therapeutic opportunities of delivering small interfering RNA (siRNA) via venous injection have gained recognition; however, systemic adverse effects of siRNA therapy should be considered. To prevent IR-induced kidney injury, we tested the efficacy of transarterial administration of siRNA targeting p53 (p53 siRNA). Female C57BL/6 mice underwent unilateral renal artery ischemia for 30 min, followed by reperfusion. siRNA experiments utilized short hairpin (sh) RNA plasmid-based approaches. Transfection of shRNA was performed using cationic polymer transfection reagent. Injection of synthetic p53 shRNA into the left renal artery just after ischemia improved tubular injury, apoptosis, and the swelling of mitochondria in cells of the thick ascending limb of Henle (mTALH) at the outer medullary regions. Staining of upregulated p53 was colocalized with the inducible expression of glycogen synthase kinase-3β (GSK-3β) at mTALH after IR injury. p53 shRNA inhibited GSK-3β expression and restored β-catenin expression at mTALH. For IR-induced kidney injury, transarterial delivery of p53 siRNA is an effective pharmacological intervention. Targeting siRNA to p53 leads to an attenuation of apoptosis and mitochondrial damage through the downregulation of GSK-3β expression and upregulation of β-catenin. Local delivery of vectors such as p53 siRNA through a transaortic catheter is clinically useful in reducing the adverse effect of siRNA-related therapy.

Cyclin-dependent kinase inhibitors closer to market launch?

INTRODUCTION

Interest in cyclin-dependent kinase (CDK) inhibitors was stimulated by the demonstration that their pharmacological activities could lead to therapies for numerous diseases. Until now, despite the clinical introduction of a dozen compounds belonging to other classes of kinase inhibitors, no CDK inhibitor has reached the marketplace.

AREAS COVERED

This review covers CDK inhibitor patents published between 2009 and September 2012. It presents compounds currently undergoing clinical development, along with our earlier (2010) review of the same topic, as well as descriptions of recently published compounds not disclosed in the patent literature. It provides the reader with an update of all chemical structures of current interest in the CDK inhibitor field.

EXPERT OPINION

Though cancer remains the most obvious application for CDK inhibition, other indications, such as HIV infection, could potentially be treated with CDK inhibitors.

Regulatory role of GSK-3 β on NF- κ B, nitric oxide, and TNF- α in group A streptococcal infection

Group A streptococcus (GAS) imposes a great burden on humans. Efforts to minimize the associated morbidity and mortality represent a critical issue. Glycogen synthase kinase-3β (GSK-3β) is known to regulate inflammatory response in infectious diseases. However, the regulation of GSK-3β in GAS infection is still unknown. The present study investigates the interaction between GSK-3β, NF-κB, and possible related inflammatory mediators in vitro and in a mouse model. The results revealed that GAS could activate NF-κB, followed by an increased expression of inducible nitric oxide synthase (iNOS) and NO production in a murine macrophage cell line. Activation of GSK-3β occurred after GAS infection, and inhibition of GSK-3β reduced iNOS expression and NO production. Furthermore, GSK-3β inhibitors reduced NF-κB activation and subsequent TNF-α production, which indicates that GSK-3β acts upstream of NF-κB in GAS-infected macrophages. Similar to the in vitro findings, administration of GSK-3β inhibitor in an air pouch GAS infection mouse model significantly reduced the level of serum TNF-α and improved the survival rate. The inhibition of GSK-3β to moderate the inflammatory effect might be an alternative therapeutic strategy against GAS infection.

[Cell cycle and molecular targets: CDK inhibition]

Protein phosphorylation is a fundamental post-translational modification. It regulates a large number of critical cellular processes (differentiation, division, proliferation, apoptosis). Cell division is a process including a series of phases by which a parent cell divides into two daughter cells. The cells enter these stages then progress within the cell division under an accurate control by many proteins. These proteins are activated by phosphorylation. Cyclin-dependent kinases are responsible for this phosphorylation and therefore represent potential therapeutic targets especially in oncology.

Expression of GSK-3β in renal allograft tissue and its significance in pathogenesis of chronic allograft dysfunction

Objective

To explore the expression of Glycogen synthase kinase 3 beta (GSK-3β) in renal allograft tissue and its significance in the pathogenesis of chronic allograft dysfunction.

Methods

Renal allograft biopsy was performed in all of the renal allograft recipients with proteinuria or increased serum creatinine level who came into our hospital from January 2007 to December 2009. Among them 28 cases was diagnosed as chronic allograft dysfunction based on pahtological observation, including 21 males with a mean age of 45 ± 10 years old and 7 females with a mean age of 42 ± 9 years old. The time from kidney transplantation to biopsy were 1-9 (3.5) years. Their serum creatinine level were 206 ± 122 umol/L. Immunohistochemical assay and computer-assisted genuine color image analysis system (imagepro-plus 6.0) were used to detect the expression of GSK-3β in the renal allografts of 28 cases of recipients with chronic allograft dysfunction. Mean area and mean integrated optical density of GSK-3β expression were calculated. The relationship between expression level of GSK-3β and either the grade of inflammatory cell infiltration or interstitial fibrosis/tubular atrophy in renal allograft was analyzed. Five specimens of healthy renal tissue were used as controls.

Results

The expression level of the GSK-3β was significantly increased in the renal allograft tissue of recipients with chronic allograft dysfunction, compared to normal renal tissues, and GSK-3β expression became stronger along with the increasing of the grade of either inflammatory cell infiltration or interstitial fibrosis/tubular atrophy in renal allograft tissue.

Conclusion

There might be a positive correlation between either inflammatory cell infiltration or interstitial fibrosis/tubular atrophy and high GSK-3β expression in renal allograft tissue.

Virtual slides

The virtual slide(s) for this article can be found here:

http://www.diagnosticpathology.diagnomx.eu/vs/9924478946162998.

Deconstructing GSK-3: The Fine Regulation of Its Activity

Glycogen synthase kinase-3 (GSK-3) unique position in modulating the function of a diverse series of proteins in combination with its association with a wide variety of human disorders has attracted significant attention to the protein both as a therapeutic target and as a means to understand the molecular basis of these disorders. GSK-3 is ubiquitously expressed and, unusually, constitutively active in resting, unstimulated cells. In mammals, GSK-3α and β are each expressed widely at both the RNA and protein levels although some tissues show preferential levels of some of the two proteins. Neither gene appears to be acutely regulated at the transcriptional level, whereas the proteins are controlled posttranslationally, largely through protein-protein interactions or by posttranslational regulation. Control of GSK-3 activity thus occurs by complex mechanisms that are each dependent upon specific signalling pathways. Furthermore, GSK-3 appears to be a cellular nexus, integrating several signalling systems, including several second messengers and a wide selection of cellular stimulants. This paper will focus on the different ways to control GSK-3 activity (phosphorylation, protein complex formation, truncation, subcellular localization, etc.), the main signalling pathways involved in its control, and its pathological deregulation.

Two non-invasive GFR-estimation methods in rat models of polycystic kidney disease: 3.0 Tesla dynamic contrast-enhanced MRI and optical imaging

BACKGROUND

The aim of this study was the assessment of kidney morphology and glomerular filtration rate (GFR) in rat models of polycystic kidney disease and a healthy control group of Sprague-Dawley rats (SD rats). The performance of two non-invasive GFR estimation methods-3.0 Tesla magnetic resonance imaging (MRI) and optical imaging were investigated. Data of GFR assessment was compared to surrogate markers of kidney function and renal histology.

METHODS

Optical imaging of GFR was performed transcutaneously in a small animal imaging system with the fluorescent renal marker fluorescein-isothiocyanate-labelled-sinistrin. Morphologic and dynamic renal imaging was done on a clinical 3.0T MR scanner. Renal perfusion analysis was performed with a two-compartment filtration model.

RESULTS

The healthy SD rats showed physiological levels of creatinine and urea, indicating normal kidney function. These parameters were elevated in the small animal groups of polycystic kidney disease. For the calculation of perfusion and filtration parameters of kidney function in MRI, a 2D turbo FLASH sequence was performed and allowed to distinguish between normal GFR of healthy rats and reduced GFR of rats with polycystic kidney disease. Also, MRI GFR varied among two different rat strains of polycystic kidney disease, according to their status of renal function impairment. Optical imaging GFR confirmed higher GFR values in healthy rats compared to ill rats but did not show different results among the two rat strains of polycystic kidney disease. For this reason, MRI and optical imaging GFR estimation presented an intra-method bias.

CONCLUSIONS

Both non-invasive estimation methods of GFR, MRI and optical imaging, can differentiate between healthy rats and animals with limited kidney function. Furthermore, optical imaging, unlike MRI, seems to consider that disease progression with increase of renal polycystic deterioration does not correlate with decrease of GFR in the initial stage of compensatory hyperfiltration.

Conditional ablation of glycogen synthase kinase 3β in postnatal mouse kidney

Glycogen synthase kinase (GSK)3 is a ubiquitously expressed serine/threonine kinase existing in two isoforms, namely GSK3α and GSK3β. Aside from the long-recognized role in insulin signal transduction and glycogen biosynthesis, GSK3β has been recently coined as a master control molecule in nuclear factor-κB activation and inflammatory kidney injury. Nevertheless, previous studies are less conclusive because they relied greatly on small molecule inhibitors, which lack selectivity and barely distinguish between the GSK3 isoforms. In addition, early embryonic lethality after global knockout of GSK3β precludes interrogation of the biological role of GSK3β in the adult kidney. To circumvent these issues, the Cre/loxP system was used to generate a conditional knockout mouse model in which the GSK3β gene was specifically deleted in kidney cortical tubules at postnatal mature stage. Kidney-specific ablation of GSK3β resulted in a phenotype no different from control littermates. Knockout mice (KO) were viable and exhibited normal development and normal kidney physiology in terms of kidney function, urine albumin excretion, and urine-concentrating ability. It is noteworthy that apart from normal glomerular and tubulointerstitial morphology, the kidneys from KO demonstrated more glycogen accumulation in the renal cortical tubules as assessed by both periodic acid-Schiff staining for light microscopy and direct biochemical assay, consistent with an elevated glycogen synthetic activity as evidenced by diminished inhibitory phosphorylation of glycogen synthase that occurred subsequent to GSK3β ablation. This finding was further validated by electron microscopic observations of increased deposition of glycogen particles in the renal tubules of KO, suggesting that GSK3α could not fully compensate for the loss of GSK3β in regulating glycogen metabolism in the kidney. Collectively, our study suggests that kidney-specific ablation of GSK3β barely affects kidney function and histology under normal circumstances. Extended examinations of these KO under diseased conditions are merited to understand the role of GSK3β in renal pathophysiology.

Cyclin-dependent kinase inhibitors: a survey of recent patent literature

IMPORTANCE OF THE FIELD

Abnormalities in protein phosphorylation by cyclin-dependent kinases (CDKs) have been observed in numerous major human diseases, which has strongly encouraged the search for pharmacological inhibitors. Almost 10 years after the first compounds entered clinical studies, numerous CDK inhibitors with differing selectivity profiles are now undergoing preclinical and clinical evaluation. Nevertheless, these intensive searches have not yet resulted in drug approvals.

AREAS COVERED IN THIS REVIEW

This paper reviews patent activity associated with these efforts during the 2005 - 2008 period.

WHAT THE READER WILL GAIN

Readers will rapidly obtain an overview of the majority of CDK inhibitor scaffolds; they will discover which companies are the main players in the field and acquire information on products that have reached the clinical phases.

TAKE HOME MESSAGE

In most cases, applications have been claimed in the field of cancer; however, potential applications of CDK inhibitors in other therapeutic areas are regularly reported and could herald therapeutic introduction over the next few years.

GSK3beta promotes apoptosis after renal ischemic injury

The mechanism by which the serine-threonine kinase glycogen synthase kinase-3beta (GSK3beta) affects survival of renal epithelial cells after acute stress is unknown. Using in vitro and in vivo models, we tested the hypothesis that GSK3beta promotes Bax-mediated apoptosis, contributing to tubular injury and organ dysfunction after acute renal ischemia. Exposure of renal epithelial cells to metabolic stress activated GSK3beta, Bax, and caspase 3 and induced apoptosis. Expression of a constitutively active GSK3beta mutant activated Bax and decreased cell survival after metabolic stress. In contrast, pharmacologic inhibition (4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione [TDZD-8]) or RNA interference-mediated knockdown of GSK3beta promoted cell survival. Furthermore, RNA interference-mediated knockdown of Bax abrogated the cell death induced by constitutively active GSK3beta. In a cell-free assay, TDZD-8 inhibited the phosphorylation of a peptide containing the Bax serine(163) site targeted by stress-activated GSK3beta. In rats, TDZD-8 inhibited ischemia-induced activation of GSK3beta, Bax, and caspase 3; ameliorated tubular and epithelial cell damage; and significantly protected renal function. Taken together, GSK3beta-mediated Bax activation induces apoptosis and tubular damage that contribute to acute ischemic kidney injury.

Cyclin-dependent kinase inhibitor drugs as potential novel anti-inflammatory and pro-resolution agents

The cyclin-dependent kinase inhibitor (CDKi) drugs such as R-roscovitine have emerged as potential anti-inflammatory, pharmacological agents that can influence the resolution of inflammation. Usually, once an inciting inflammatory stimulus has been eliminated, resolution proceeds by prompt, safe removal of dominant inflammatory cells. This is accomplished by programmed cell death (apoptosis) of prominent effector, inflammatory cells typified by the neutrophil. Apoptosis of neutrophils ensures that toxic neutrophil granule contents are securely packaged in apoptotic bodies and expedites phagocytosis by professional phagocytes such as macrophages. A panel of CDKi drugs have been shown to promote neutrophil apoptosis in a concentration- and time-dependent manner and the archetypal CDKi drug, R-roscovitine, overrides the anti-apoptotic effects of powerful survival factors [including lipopolysaccharide (LPS) and granulocyte macrophage-colony stimulating factor (GM-CSF)]. Inflammatory cell longevity and survival signalling is integral to the inflammatory process and any putative anti-inflammatory agent must unravel a complex web of redundancy in order to be effective. CDKi drugs have also been demonstrated to have significant effects on other cell types including lymphocytes and fibroblasts indicating that they may have pleiotropic anti-inflammatory, pro-resolution activity. In keeping with this, CDKi drugs like R-roscovitine have been reported to be efficacious in resolving established animal models of neutrophil-dominant and lymphocyte-driven inflammation. However, the mechanism of action behind these powerful effects has not yet been fully elucidated. CDKs play an integral role in the regulation of the cell cycle but are also recognized as participants in processes such as apoptosis and transcriptional regulation. Neutrophils have functional CDKs, are transcriptionally active and demonstrate augmented apoptosis in response to CDKi drugs, while lymphocyte proliferation and secretory function are inhibited. This review will discuss current understanding of the processes of inflammation and resolution but will focus on CDKis and their potential mechanisms of action.

The cell cycle and acute kidney injury

Acute kidney injury (AKI) activates pathways of cell death and cell proliferation. Although seemingly discrete and unrelated mechanisms, these pathways can now be shown to be connected and even to be controlled by similar pathways. The dependence of the severity of renal-cell injury on cell cycle pathways can be used to control and perhaps to prevent acute kidney injury. This review is written to address the correlation between cellular life and death in kidney tubules, especially in acute kidney injury.

Inhibiting glycogen synthase kinase-3 reduces endotoxaemic acute renal failure by down-regulating inflammation and renal cell apoptosis

BACKGROUND AND PURPOSE

Excessive inflammation and apoptosis are pathological features of endotoxaemic acute renal failure. Activation of glycogen synthase kinase-3 (GSK-3) is involved in inflammation and apoptosis. We investigated the effects of inhibiting GSK-3 on lipopolysaccharide (LPS)-induced acute renal failure, nuclear factor-kappaB (NF-kappaB), inflammation and apoptosis.

EXPERIMENTAL APPROACH

The effects of inhibiting GSK-3 with inhibitors, including lithium chloride (LiCl) and 6-bromo-indirubin-3'-oxime (BIO), on LPS-treated (15 mg x kg(-1)) C3H/HeN mice (LiCl, 40 mg x kg(-1) and BIO, 2 mg x kg(-1)) and LPS-treated (1 microg x mL(-1)) renal epithelial cells (LiCl, 20 mM and BIO, 5 microM) were studied. Mouse survival was monitored and renal function was analysed by histological and serological examination. Cytokine and chemokine production, and cell apoptosis were measured by enzyme-linked immunosorbent assay and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelling staining, respectively. Activation of NF-kappaB and GSK-3 was determined by immunostaining and Western blotting, respectively.

KEY RESULTS

Mice treated with GSK-3 inhibitors showed decreased mortality, renal tubular dilatation, vacuolization and sloughing, blood urea nitrogen, creatinine and renal cell apoptosis in response to endotoxaemia. Inhibiting GSK-3 reduced LPS-induced tumour necrosis factor-alpha (TNF-alpha) and CCL5/RANTES (released upon activation of normal T-cells) in vivo in mice and in vitro in murine kidney cortical collecting duct epithelial M1 cells. Inhibiting GSK-3 did not block TNF-alpha-induced cytotoxicity in rat kidney proximal tubular epithelial NRK52E or in M1 cells.

CONCLUSIONS AND IMPLICATIONS

These results suggest that GSK-3 inhibition protects against endotoxaemic acute renal failure mainly by down-regulating pro-inflammatory TNF-alpha and RANTES.

ATP-noncompetitive inhibitors of CDK-cyclin complexes

Progression through the cell division cycle is controlled by a family of cyclin-dependent kinases (CDKs), the activity of which depends on their binding to regulatory partners (cyclins A-H). Deregulation of the activity of CDKs has been associated with the development of infectious, neurodegenerative, and proliferative diseases such as Alzheimer's, Parkinson's, or cancer. Most cancer cells contain mutations in the pathways that control the activity of CDKs. This observation led this kinase family to become a central target for the development of new drugs for cancer therapy. A range of structurally diverse molecules has been shown to inhibit the activity of CDKs through their activity as ATP antagonists. Nevertheless, the ATP binding sites on CDKs are highly conserved, limiting the kinase specificity of these inhibitors. Various genetic and crystallographic approaches have provided essential information about the mechanism of formation and activation of CDK-cyclin complexes, providing new ways to implement novel research strategies toward the discovery of new, more effective and selective drugs. Herein we review the progress made in the development of ATP-noncompetitive CDK-cyclin inhibitors.

Advances in the biology and genetics of the podocytopathies: implications for diagnosis and therapy

CONTEXT

Etiologic factors and pathways leading to altered podocyte phenotype are clearly numerous and involve the activity of different cellular function.

OBJECTIVE

To focus on recent discoveries in podocyte biology and genetics and their relevance to these human glomerular diseases, named podocytopathies.

DATA SOURCES

Genetic mutations in genes encoding for proteins in the nucleus, slit diaphragm, podocyte cytoplasm, and cell membrane are responsible for podocyte phenotype and functional abnormalities. Podocyte injury may also derive from secondary stimuli, such as mechanical stress, infections, or use of certain medications. Podocytes can respond to injury in a limited number of ways, which include (1) effacement, (2) apoptosis, (3) arrest of development, and (4) dedifferentiation. Each of these pathways results in a specific glomerular morphology: minimal change nephropathy, focal segmental glomerulosclerosis, diffuse mesangial sclerosis, and collapsing glomerulopathy.

CONCLUSIONS

Based on current knowledge of podocyte biology, we organized etiologic factors and morphologic features in a taxonomy of podocytopathies, which provides a novel approach to the classification of these diseases. Current and experimental therapeutic approaches are also discussed.

Advances in the biology and genetics of the podocytopathies: implications for diagnosis and therapy

CONTEXT

Etiologic factors and pathways leading to altered podocyte phenotype are clearly numerous and involve the activity of different cellular function.

OBJECTIVE

To focus on recent discoveries in podocyte biology and genetics and their relevance to these human glomerular diseases, named podocytopathies.

DATA SOURCES

Genetic mutations in genes encoding for proteins in the nucleus, slit diaphragm, podocyte cytoplasm, and cell membrane are responsible for podocyte phenotype and functional abnormalities. Podocyte injury may also derive from secondary stimuli, such as mechanical stress, infections, or use of certain medications. Podocytes can respond to injury in a limited number of ways, which include (1) effacement, (2) apoptosis, (3) arrest of development, and (4) dedifferentiation. Each of these pathways results in a specific glomerular morphology: minimal change nephropathy, focal segmental glomerulosclerosis, diffuse mesangial sclerosis, and collapsing glomerulopathy.

CONCLUSIONS

Based on current knowledge of podocyte biology, we organized etiologic factors and morphologic features in a taxonomy of podocytopathies, which provides a novel approach to the classification of these diseases. Current and experimental therapeutic approaches are also discussed.

Present and future drug treatments for chronic kidney diseases: evolving targets in renoprotection

At present, there are no specific cures for most of the acquired chronic kidney diseases, and renal transplantation is limited by organ shortage, therefore present efforts are concentrated on the prevention of progression of renal diseases. There is robust experimental and clinical evidence that progression of chronic nephropathies is multifactorial; however, intraglomerular haemodynamic changes and proteinuria play a key role in this process. With a focus on renoprotection, we first examine more established therapies--such as those that modulate the renin-angiotensin-aldosterone system--that can be used for the treatment of proteinuric renal diseases. We then discuss examples of novel drugs and biologics that might be used to target the inflammatory and profibrotic process, and glomerular injury, highlighting results from recent clinical trials.

Soluble 3',6-substituted indirubins with enhanced selectivity toward glycogen synthase kinase -3 alter circadian period

Glycogen synthase kinase -3 (GSK-3) is a key enzyme involved in numerous physiological events and in major diseases, such as Alzheimer's disease, diabetes, and cardiac hypertrophy. Indirubins are bis-indoles that can be generated from various natural sources or chemically synthesized. While rather potent and selective as GSK-3 inhibitors, most indirubins exhibit low water solubility. To address the issue of solubility, we have designed novel analogues of 6-bromo-indirubin-3'-oxime with increased hydrophilicity based on the GSK-3/indirubins cocrystal structures. The new derivatives with an extended amino side chain attached at position 3' showed potent GSK-3 inhibitory activity, enhanced selectivity, and dramatically increased water solubility. Furthermore, some of them displayed little or no cytotoxicity. The new indirubins inhibit GSK-3 in a cellular reporter model. They alter the circadian period measured in rhythmically expressing cell cultures, suggesting that they might constitute tools to investigate circadian rhythm regulation.

Glycogen synthase kinase 3beta: a novel marker and modulator of inflammatory injury in chronic renal allograft disease

One key cell-signaling event central to inflammation in kidney diseases, including chronic renal allograft dysfunction or disease (CRAD), is the activation of NF-kappaB, which controls transcription of numerous proinflammatory mediators. Glycogen synthase kinase (GSK) 3beta is an indispensable element of NF-kappaB activation, however, the exact role of GSK3beta in the pathogenesis of inflammatory kidney diseases like CRAD is uncertain and was examined. Immunohistochemistry staining of GSK3beta was weak in normal kidneys, but was markedly induced in inflamed allograft kidneys, with prominent cytoplasmic staining of tubular cells in areas of inflammation. Net GSK3beta activity is regulated by inhibitory phosphorylation of its serine 9 residue, and this occurred in CRAD. Thus, the magnitude of GSK3beta inactivation was inversely correlated with the degree of injury as assessed by Banff criteria. In vitro in cultured human tubular epithelial cells, GSK3beta overexpression augmented, while GSK3beta silencing diminished proinflammatory cellular responses to TNF-alpha stimulation, including NF-kappaB activation and expression of chemokines MCP-1 and RANTES. These inflammatory responses were obliterated by GSK3beta inhibitors. Collectively, GSK3beta plays an important role in mediating proinflammatory NF-kappaB activation and renal inflammation. Suppression of GSK3beta activity might represent a novel therapeutic strategy to treat CRAD.

A molecular study of pathways involved in the inhibition of cell proliferation in neuroblastoma B65 cells by the GSK-3 inhibitors lithium and SB-415286

Pharmacological GSK-3 inhibitors are potential drugs for the treatment of neurodegenerative diseases, cancer and diabetes. We examined the antiproliferative effects of two GSK-3 inhibitors, lithium and SB-415286, on B65 neuroblastoma cell line. Treatment of B65 cells with either drug administered separately caused a decrease in cell proliferation that was associated with G₂/M cell cycle arrest. Cell-cycle proteins such as cyclins D, E, A, cdk4 and cdk2 were up-regulated. Since lithium and SB-415286-induced G₂/M arrest we studied changes in the expression of proteins involved in this phase, specifically cyclin B, cdc2 and the phosphorylated form of this protein (tyr15-cdc2). Both drugs increased the expression of tyr15-cdc2, thus inhibiting mitosis. On the other hand, SB-415286 increased the expression of SIRT2, involved in the regulation of proliferation. Moreover, cell-cycle arrest mediated by SB-415286 was accompanied by apoptosis that was not prevented by 100 μM of zVAD-fmk (benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone), a pan-caspase inhibitor. Likewise, GSK-3 inhibitors did not affect the mitochondrial release of apoptosis inducing factor (AIF). We conclude that inhibitors of GSK-3 induced cell-cycle arrest, mediated by the phosphorylation of cdc2 and, in the case of SB-415286, SIRT2 expression, which induced apoptosis in a caspase-independent manner.

Advanced glycation end-product-inhibited cell proliferation and protein expression of beta-catenin and cyclin D1 are dependent on glycogen synthase kinase 3beta in LLC-PK1 cells

Glycogen synthase kinase 3beta (GSK3beta) is increased by high glucose in mesangial cells. Thus, we studied the role of GSK3beta in advanced glycation end-product (AGE)-induced effects in the proximal tubule-like LLC-PK1 cells. We found that AGE (100 microg/ml) time-dependently (8-48 h) increased phospho-GSK3beta-Tyr216 (active GSK3beta) and time-dependently (4-24 h) decreased phospho-GSK3beta-Ser21/9 (inactive GSK3beta) protein expression. Meanwhile, AGE (100 microg/ml) activated GSK3beta kinase at 8-48 h. AGE (100 microg/ml) dose-dependently (75-100 microg/ml) decreased beta-catenin protein expression but AGE did not decrease beta-catenin protein expression until 48 h. SB216763 (a GSK3beta inhibitor) and GSK3beta shRNA attenuated AGE (100 microg/ml)-inhibited cell proliferation and protein expression of beta-catenin and cyclin D1 at 48 h. SB216763 also attenuated AGE-induced type IV collagen. We conclude that AGE activates GSK3beta in LLC-PK1 cells. AGE-inhibited beta-catenin and cyclin D1 protein expression are dependent on GSK3beta. Moreover, AGE-inhibited cell proliferation and AGE-induced type IV collagen protein expression are dependent on GSK3beta.

Overlapping genes in Nalp6/PYPAF5 locus encode two V2-type vasopressin isoreceptors: angiotensin-vasopressin receptor (AVR) and non-AVR

The angiotensin-vasopressin receptor (AVR) responds with equivalent affinities to angiotensin II (ANG II) and vasopressin and is coupled to adenylate cyclase and hence a V2-type vasopressin receptor. AVR maps to the Nalp6 locus and overlaps with the larger Nalp6/PYPAF5 reported to be a T cell/granulocyte-specific, cytoplasmic-specific proapoptotic protein, thus questioning the existence of AVR. Here we confirm, through different experimental modalities, that AVR is distinct from Nalp6/PYPAF5 based on different mRNA and protein sizes, subcellular localization, and tissue-specific expression patterns. Binding studies of PYPAF5-specific Cos1 transfectants detect high-affinity binding to vasopressin but not ANG II, thus assigning PYPAF5 as a non-AVR (NAVR). Signaling array analysis reveals that AVP stimulation of AVR- and NAVR-specific Cos1 transfectants results in diametrical activation as well as coactivation of signaling pathways known to mediate renal sodium and water balance. Likewise, ANG II stimulation of Cos1-AVR transfectants reveals a signaling profile distinct from that of AVP-stimulated Cos1-AVR transfectants. Analysis of genomic organization of the AVR/NAVR locus shows an overlapping gene arrangement with alternative promoter usage resulting in different NH(2) termini for NAVR and AVR. In addition to core promoter elements, androgen and estrogen response elements are detected. Promoter analysis of NAVR/AVR 5'-regulatory region detects transcriptional upregulation by testosterone and synergistic upregulation by testosterone and estrogen, thus suggesting that AVR and/or NAVR contribute to sex-specific V2-type vasopressin-mediated effects. Altogether, confirmation of AVR and identification of NAVR as vasopressin receptors are concordant with emerging vasopressin functions not attributable to V1a, V1b, or V2 receptors and add molecular bases for the multifunctional complexity of vasopressin-mediated functions and regulation.