PKB/SGK-resistant GSK-3 signaling following unilateral ureteral obstruction

Isoandrographolide from Andrographis paniculata ameliorates tubulointerstitial fibrosis in ureteral obstruction-induced mice, associated with negatively regulating AKT/GSK-3β/β-cat signaling pathway

Tubulointerstitial fibrosis (TIF) is a prominent pathological manifestation for the progression of almost all chronic kidney diseases (CKDs) to end-stage renal failure. However, there exist few efficient therapies to cure TIF. Our recent results showed that (8R, 12S)-isoandrographolide (ISA), a diterpenoid lactone ingredient of traditional Chinese herbal Andrographis paniculata (Burm.f.) Nees, exhibited anti-pulmonary fibrosis in silica-induced mice. Herein, we investigated the therapeutic effect of ISA on TIF, using mice subjected to unilateral ureteral obstruction (UUO) and human kidney proximal tubular epithelial (HK-2) cells treated with transforming growth factor-β1 (TGF-β1) or tumor necrosis factor-α (TNF-α). The pathological changes and collagen deposition results displayed that ISA administration significantly attenuated inflammatory response, ameliorated TIF, and protected the kidney injury. Interestingly, ISA revealed much lower cytotoxicity on HK-2 cells, but exhibited stronger inhibitory effect on tubular epithelial mesenchymal transformation (EMT) and inflammation, as compared to andrographolide (AD), the major ingredient of A. paniculata extract that has been reported to ameliorate TIF in diabetic nephropathy mice. It was further clarified that the amelioration of TIF by ISA was associated with suppressing the aberrant activation of AKT/GSK-3β/β-catenin pathway through network pharmacology analysis and experimental validation. Taken together, these findings indicate that ISA is a promising lead compound for development of anti-TIF, and even broad-spectrum anti-fibrotic drugs.

Role of SGK1 in the Osteogenic Transdifferentiation and Calcification of Vascular Smooth Muscle Cells Promoted by Hyperglycemic Conditions

In diabetes mellitus, hyperglycemia promotes the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) to enhance medial vascular calcification, a common complication strongly associated with cardiovascular disease and mortality. The mechanisms involved are, however, still poorly understood. Therefore, the present study explored the potential role of serum- and glucocorticoid-inducible kinase 1 (SGK1) during vascular calcification promoted by hyperglycemic conditions. Exposure to high-glucose conditions up-regulated the SGK1 expression in primary human aortic VSMCs. High glucose increased osteogenic marker expression and activity and, thus, promoted the osteogenic transdifferentiation of VSMCs, effects significantly suppressed by additional treatment with the SGK1 inhibitor EMD638683. Moreover, high glucose augmented the mineralization of VSMCs in the presence of calcification medium, effects again significantly reduced by SGK1 inhibition. Similarly, SGK1 knockdown blunted the high glucose-induced osteogenic transdifferentiation of VSMCs. The osteoinductive signaling promoted by high glucose required SGK1-dependent NF-kB activation. In addition, advanced glycation end products (AGEs) increased the SGK1 expression in VSMCs, and SGK1 inhibition was able to interfere with AGEs-induced osteogenic signaling. In conclusion, SGK1 is up-regulated and mediates, at least partly, the osteogenic transdifferentiation and calcification of VSMCs during hyperglycemic conditions. Thus, SGK1 inhibition may reduce the development of vascular calcification promoted by hyperglycemia in diabetes.

Glycogen synthase kinase-3β: a promising candidate in the fight against fibrosis

Fibrosis exists in almost all organs/tissues of the human body, plays an important role in the occurrence and development of diseases and is also a hallmark of the aging process. However, there is no effective prevention or therapeutic method for fibrogenesis. As a serine/threonine (Ser/Thr)-protein kinase, glycogen synthase kinase-3β (GSK-3β) is a vital signaling mediator that participates in a variety of biological events and can inhibit extracellular matrix (ECM) accumulation and the epithelial-mesenchymal transition (EMT) process, thereby exerting its protective role against the fibrosis of various organs/tissues, including the heart, lung, liver, and kidney. Moreover, we further present the upstream regulators and downstream effectors of the GSK-3β pathway during fibrosis and comprehensively summarize the roles of GSK-3β in the regulation of fibrosis and provide several potential targets for research. Collectively, the information reviewed here highlights recent advances vital for experimental research and clinical development, illuminating the possibility of GSK-3β as a novel therapeutic target for the management of tissue fibrosis in the future.

SGK1-dependent stimulation of vascular smooth muscle cell osteo-/chondrogenic transdifferentiation by interleukin-18

The serum- and glucocorticoid-inducible kinase 1 (SGK1) is a key regulator of osteo-/chondrogenic transdifferentiation and subsequent calcification of vascular smooth muscle cells (VSMCs). The phenotypical transdifferentiation of VSMCs is associated with increased interleukin-18 (IL-18) levels and generalized inflammation. Therefore, the present study investigated the possible involvement of SGK1 in IL-18-induced vascular calcification. Experiments were performed in primary human aortic smooth muscle cells (HAoSMCs) treated with recombinant human IL-18 protein in control or high phosphate conditions and following SGK1 knockdown by siRNA or pharmacological inhibition of SGK1, PI3K, and PDK1. As a result, IL-18 treatment increased SGK1 mRNA and protein expression in HAoSMCs. IL-18 upregulated SGK1 mRNA expression in a dose-dependent manner. This effect was paralleled by upregulation of the mRNA expression of MSX2 and CBFA1, osteogenic transcription factors, and of tissue-nonspecific alkaline phosphatase (ALPL), an osteogenic enzyme, as markers of increased osteo-/chondrogenic transdifferentiation. Phosphate treatment increased SGK1 and osteogenic markers mRNA expression as well as ALPL activity and induced calcification of HAoSMCs, all effects significantly augmented by additional treatment with IL-18. Conversely, silencing of SGK1 or cotreatment with the SGK1 inhibitor EMD638683 blunted the effects of IL-18 on osteo-/chondrogenic transdifferentiation and calcification of HAoSMCs. The procalcific effects of IL-18 were similarly suppressed in the presence of PI3K or PDK1 inhibitors. In conclusion, SGK1 expression is upregulated by IL-18 in VSMCs and SGK1 participates in the intracellular signaling of IL-18-induced osteo-/chondrogenic transdifferentiation of VSMCs. Thus, SGK1 may serve as therapeutic target to limit the progression of medial vascular calcification during vascular inflammation.

Role of PKB/SGK-dependent phosphorylation of GSK-3α/β in vascular calcification during cholecalciferol overload in mice

Medial vascular calcification is a highly regulated process involving osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells. Both, protein kinase B (PKB) and serum- and glucocorticoid-inducible kinase 1 (SGK1) are involved in the intracellular signaling of vascular calcification and both phosphorylate and inactivate glycogen synthase kinase 3 (GSK-3). The present study explored whether PKB/SGK-dependent phosphorylation of GSK-3α/β is involved in vascular calcification. Experiments were performed in Gsk-3α/β double knockin mice lacking functional PKB/SGK phosphorylation sites (gsk-3^KI) and corresponding wild-type mice (gsk-3^WT) following high-dosed cholecalciferol treatment as well as ex vivo in aortic ring explants from gsk-3^KI and gsk-3^WT mice treated without and with phosphate. In gsk-3^WT mice, high-dosed cholecalciferol induced vascular calcification and aortic osteo-/chondrogenic signaling, shown by increased expression of osteogenic markers Msx2, Cbfa1 and tissue-nonspecific alkaline phosphatase (Alpl). All these effects were suppressed in aortic tissue from gsk-3^KI mice. Cholecalciferol decreased aortic Gsk-3α/β phosphorylation (Ser^21/9) in gsk-3^WT mice, while no phosphorylation was observed in gsk-3^KI mice. Moreover, the mRNA expression of type III sodium-dependent phosphate transporter (Pit1) and plasminogen activator inhibitor 1 (Pai1) was increased following cholecalciferol treatment in aortic tissue of gsk-3^WT mice, effects again blunted in gsk-3^KI mice. In addition, phosphate treatment induced mineral deposition and osteogenic markers expression in aortic ring explants from gsk-3^WT mice, effects reduced in aortic ring explants from gsk-3^KI mice. In conclusion, vascular PKB/SGK-dependent phosphorylation of GSK-3α/β contributes to the osteoinductive signaling leading to vascular calcification.

SGK1 induces vascular smooth muscle cell calcification through NF-κB signaling

Medial vascular calcification, associated with enhanced mortality in chronic kidney disease (CKD), is fostered by osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells (VSMCs). Here, we describe that serum- and glucocorticoid-inducible kinase 1 (SGK1) was upregulated in VSMCs under calcifying conditions. In primary human aortic VSMCs, overexpression of constitutively active SGK1S422D, but not inactive SGK1K127N, upregulated osteo-/chondrogenic marker expression and activity, effects pointing to increased osteo-/chondrogenic transdifferentiation. SGK1S422D induced nuclear translocation and increased transcriptional activity of NF-κB. Silencing or pharmacological inhibition of IKK abrogated the osteoinductive effects of SGK1S422D. Genetic deficiency, silencing, and pharmacological inhibition of SGK1 dissipated phosphate-induced calcification and osteo-/chondrogenic transdifferentiation of VSMCs. Aortic calcification, stiffness, and osteo-/chondrogenic transdifferentiation in mice following cholecalciferol overload were strongly reduced by genetic knockout or pharmacological inhibition of Sgk1 by EMD638683. Similarly, Sgk1 deficiency blunted vascular calcification in apolipoprotein E-deficient mice after subtotal nephrectomy. Treatment of human aortic smooth muscle cells with serum from uremic patients induced osteo-/chondrogenic transdifferentiation, effects ameliorated by EMD638683. These observations identified SGK1 as a key regulator of vascular calcification. SGK1 promoted vascular calcification, at least partly, via NF-κB activation. Inhibition of SGK1 may, thus, reduce the burden of vascular calcification in CKD.

Syndecan-1 inhibits early stages of liver fibrogenesis by interfering with TGFβ1 action and upregulating MMP14

Increased expression of syndecan-1 is a characteristic feature of human liver cirrhosis. However, no data are available on the significance of this alteration. To address this question we designed a transgenic mouse strain that driven by albumin promoter, expresses human syndecan-1 in the hepatocytes. Liver cirrhosis was induced by thioacetamide in wild type and hSDC1^+/+ mice of the identical strain. The process of fibrogenesis, changes in signal transduction and proteoglycan expression were followed. In an in vitro experiment, the effect of syndecan-1 overexpression on the action of TGFβ1 was determined. Human syndecan-1 and TGFβ1 levels were measured by ELISA in the circulation. Without challenge, no morphological differences were observed between wild type and transgenic mice livers, although significant upregulation of phospho-Akt and FAK was observed in the latter. Fibrogenesis in the transgenic livers, characterized by picrosirius staining, collagen type I, and SMA levels, lagged behind that of control in the first and second months. Changes in signal transduction involved in the process of fibrogenesis, as SMAD, MAPK, Akt and GSK, pointed to the decreased effect of TGFβ1, and this was corroborated by the decreased mRNA expression of TIEG and the growth factor itself. In vitro experiments exposing the LX2 hepatic stellate cell line to conditioned media of wild type and syndecan-1 transfected Hep3B cell lines proved that medium with high syndecan-1 content inhibits TGFβ1-induced upregulation of SMA, TIEG, collagen type I and thrombospondin-1 expression. Detection of liver proteoglycans and heparan sulfate level revealed that their amounts are much higher in control transgenic liver, than that in the wild type. However, it decreases dramatically as a result of shedding after hepatic injury. Shedding is likely promoted by the upregulation of MMP14. As syndecan-1 can bind thrombospondin-1, and as our result demonstrated that the same is true for TGFβ1, shed syndecan-1 can remove the growth factor and its activator together into the systemic circulation.Taking together, our results indicate that the effect of syndecan-1 is accomplished on two levels: a, the shedded syndecan can bind, inhibit and remove TGFβ1; b, interferes with the activation of TGFβ1 by downregulation and binding thrombospondin-1, the activator of the growth factor. However, by the end of the fourth month the protective effect was lost, which is explained by the considerable decrease of syndecan-1 and the almost complete loss of heparan sulfate from the surface of hepatocytes.

Short Hairpin RNA Knockdown of Connective Tissue Growth Factor by Ultrasound-Targeted Microbubble Destruction Improves Renal Fibrosis

The purpose of this study was to evaluate whether ultrasound-targeted microbubble destruction transfer of interfering RNA against connective tissue growth factor (CTGF) in the kidney would ameliorate renal fibrosis in vivo. A short hairpin RNA (shRNA) targeting CTGF was cloned into a tool plasmid and loaded onto the surface of a cationic microbubble product. A unilateral ureteral obstruction (UUO) model in mice was used to evaluate the effect of CTGF knockdown. Mice were administered the plasmid-carrying microbubble intravenously, and ultrasound was applied locally to the obstructed kidney. Mice undergoing a sham UUO surgery and untreated UUO mice were used as disease controls, and mice administered plasmid alone, plasmid with ultrasound treatment and microbubbles and plasmid without ultrasound were used as treatment controls. Mice were treated once and then evaluated at day 14. CTGF in the kidney was measured by quantitative reverse transcription polymerase chain reaction and Western blot. Expression of CTGF, transforming growth factor β1, α smooth muscle actin and type I collagen in the obstructed kidney was evaluated by immunohistochemistry. The cohort treated with plasmid-carrying microbubbles and ultrasound exhibited reduced mRNA and protein expression of CTGF (p < 0.01). Furthermore, CTGF gene silencing decreased the interstitial deposition of transforming growth factor β1, α smooth muscle actin and type I collagen as assessed in immunohistochemistry, as well as reduced renal fibrosis in pathologic alterations (p < 0.01). No significant changes in target mRNA, protein expression or disease pathology were observed in the control cohorts. A single treatment of ultrasound-targeted microbubble destruction is able to deliver sufficient shRNA to inhibit the expression of CTGF and provide a meaningful reduction in disease severity. This technique may be a potential therapy for treatment of renal fibrosis.

Impact of AMP-Activated Protein Kinase α1 Deficiency on Tissue Injury following Unilateral Ureteral Obstruction

Background

AMP-activated protein kinase (Ampk) is a sensor of the cellular energy status and a powerful regulator of metabolism. Activation of Ampk was previously shown to participate in monocyte-to-fibroblast transition and matrix protein production in renal tissue. Thus, the present study explored whether the catalytic Ampkα1 isoform participates in the regulation of the renal fibrotic response following unilateral ureteral obstruction (UUO).

Methods

UUO was induced in gene-targeted mice lacking functional Ampkα1 (Ampkα1^-/-) and in corresponding wild-type mice (Ampkα1^+/+). In the obstructed kidney and, for comparison, in the non-obstructed control kidney, quantitative RT-PCR, Western blotting and immunostaining were employed to determine transcript levels and protein abundance, respectively.

Results

In Ampkα1^+/+ mice, UUO significantly up-regulated the protein abundance of the Ampkα1 isoform, but significantly down-regulated the Ampkα2 isoform in renal tissue. Phosphorylated Ampkα protein levels were significantly increased in obstructed kidney tissue of Ampkα1^+/+ mice but not of Ampkα1^-/- mice. Renal expression of α-smooth muscle actin was increased following UUO, an effect again less pronounced in Ampkα1^-/- mice than in Ampkα1^+/+ mice. Histological analysis did not reveal a profound effect of Ampkα1 deficiency on collagen 1 protein deposition. UUO significantly increased phosphorylated and total Tgf-ß-activated kinase 1 (Tak1) protein, as well as transcript levels of Tak1-downstream targets c-Fos, Il6, Pai1 and Snai1 in Ampkα1^+/+ mice, effects again significantly ameliorated in Ampkα1^-/- mice. Moreover, Ampkα1 deficiency inhibited the UUO-induced mRNA expression of Cd206, a marker of M2 macrophages and of Cxcl16, a pro-fibrotic chemokine associated with myeloid fibroblast formation. The effects of Ampkα1 deficiency during UUO were, however, paralleled by increased tubular injury and apoptosis.

Conclusions

Renal obstruction induces an isoform shift from Ampkα2 towards Ampkα1, which contributes to the signaling involved in cell survival and fibrosis.

Glycogen synthase kinase-3 inhibition attenuates fibroblast activation and development of fibrosis following renal ischemia-reperfusion in mice

Glycogen synthase kinase-3β (GSK3β) is a serine/threonine protein kinase that plays an important role in renal tubular injury and regeneration in acute kidney injury. However, its role in the development of renal fibrosis, often a long-term consequence of acute kidney injury, is unknown. Using a mouse model of renal fibrosis induced by ischemia-reperfusion injury, we demonstrate increased GSK3β expression and activity in fibrotic kidneys, and its presence in myofibroblasts in addition to tubular epithelial cells. Pharmacological inhibition of GSK3 using TDZD-8 starting before or after ischemia-reperfusion significantly suppressed renal fibrosis by reducing the myofibroblast population, collagen-1 and fibronectin deposition, inflammatory cytokines, and macrophage infiltration. GSK3 inhibition in vivo reduced TGF-β1, SMAD3 activation and plasminogen activator inhibitor-1 levels. Consistently in vitro, TGF-β1 treatment increased GSK3β expression and GSK3 inhibition abolished TGF-β1-induced SMAD3 activation and α-smooth muscle actin (α-SMA) expression in cultured renal fibroblasts. Importantly, overexpression of constitutively active GSK3β stimulated α-SMA expression even in the absence of TGF-β1 treatment. These results suggest that TGF-β regulates GSK3β, which in turn is important for TGF-β–SMAD3 signaling and fibroblast-to-myofibroblast differentiation. Overall, these studies demonstrate that GSK3 could promote renal fibrosis by activation of TGF-β signaling and the use of GSK3 inhibitors might represent a novel therapeutic approach for progressive renal fibrosis that develops as a consequence of acute kidney injury.

Summary: GSK3 promotes renal fibrosis by activation of TGF-β signaling, and the use of GSK3 inhibitors might represent a novel therapeutic approach for progressive renal fibrosis that develops as a consequence of acute kidney injury.

Enhanced Orai1 and STIM1 expression as well as store operated Ca2+ entry in therapy resistant ovary carcinoma cells

Mechanisms underlying therapy resistance of tumor cells include protein kinase Akt. Putative Akt targets include store-operated Ca²⁺-entry (SOCE) accomplished by pore forming ion channel unit Orai1 and its regulator STIM1. We explored whether therapy resistant (A2780cis) differ from therapy sensitive (A2780) ovary carcinoma cells in Akt, Orai1, and STIM1 expression, Ca²⁺-signaling and cell survival following cisplatin (100μM) treatment. Transcript levels were quantified with RT-PCR, protein abundance with Western blotting, cytosolic Ca²⁺-activity ([Ca²⁺]i) with Fura-2-fluorescence, SOCE from increase of [Ca²⁺]i following Ca²⁺-readdition after Ca²⁺-store depletion, and apoptosis utilizing flow cytometry. Transcript levels of Orai1 and STIM1, protein expression of Orai1, STIM1, and phosphorylated Akt, as well as SOCE were significantly higher in A2780cis than A2780 cells. SOCE was decreased by Akt inhibitor III (SH-6, 10μM) in A2780cis but not A2780 cells and decreased in both cell lines by Orai1 inhibitor 2-aminoethoxydiphenyl borate (2-ABP, 50μM). Phosphatidylserine exposure and late apoptosis following cisplatin treatment were significantly lower in A2780cis than A2780 cells, a difference virtually abolished by SH-6 or 2-ABP. In conclusion, Orai1/STIM1 expression and function are increased in therapy resistant ovary carcinoma cells, a property at least in part due to enhanced Akt activity and contributing to therapy resistance in those cells.

Discovery of N-[4-(1H-Pyrazolo[3,4-b]pyrazin-6-yl)-phenyl]-sulfonamides as Highly Active and Selective SGK1 Inhibitors

From a virtual screening starting point, inhibitors of the serum and glucocorticoid regulated kinase 1 were developed through a combination of classical medicinal chemistry and library approaches. This resulted in highly active small molecules with nanomolar activity and a good overall in vitro and ADME profile. Furthermore, the compounds exhibited unusually high kinase and off-target selectivity due to their rigid structure.