Transglutaminase-1 protects renal epithelial cells from hydrogen peroxide-induced apoptosis through activation of STAT3 and AKT signaling pathways

Transglutaminase 1: Emerging Functions beyond Skin

Transglutaminase enzymes catalyze Ca2+- and thiol-dependent posttranslational modifications of glutamine-residues that include esterification, hydrolysis and transamidation, which results in covalent protein-protein crosslinking. Among the eight transglutaminase family members in mammals, transglutaminase 1 (TG1) plays a crucial role in skin barrier formation via crosslinking and insolubilizing proteins in keratinocytes. Despite this established function in skin, novel functions have begun merging in normal tissue homeostasis as well as in pathologies. This review summarizes our current understanding of the structure, activation, expression and activity patterns of TG1 and discusses its putative novel role in other tissues, such as in vascular integrity, and in diseases, such as cancer and fibrosis.

Increased Osteoclastogenesis in Absence of TG2 Is Reversed by Transglutaminase Inhibition-Evidence for the Role for TG1 in Osteoclast Formation

Osteoclasts are multinucleated, bone-resorbing giant cells derived from monocyte-macrophage cell lines. Increased bone resorption results in loss of bone mass and osteoporosis. Osteoclast and bone marrow macrophages have been shown to express three TG enzymes (TG2, Factor XIII-A, and TG1) and TG activity to regulate osteoclast differentiation from bone marrow macrophages in vitro. In vivo and in vitro studies have demonstrated that the deletion of TG2 causes increased osteoclastogenesis and a significant loss of bone mass in mice (Tgm2-/- mice). Here, we confirm that TG2 deficiency results in increased osteoclastogenesis in vitro and show that this increase can be reversed by a TG inhibitor, NC9, suggesting that other TGs are responsible for driving osteoclastogenesis in the absence of TG2. An assessment of total TG activity with 5-(biotinamido)-pentylamine, as well as TG1 and FXIII-A activities using TG-specific Hitomi peptides (bK5 and bF11) in Tgm2-/- bone marrow flushes, bone marrow macrophages, and osteoclasts, showed a significant increase in total TG activity and TG1 activity. Factor XIII-A activity was unchanged. Aspartate proteases, such as cathepsins, are involved in the degradation of organic bone matrix and can be produced by osteoclasts. Moreover, Cathepsin D was shown in previous work to be increased in TG2-null cells and is known to activate TG1. We show that Pepstatin A, an aspartate protease inhibitor, blocks osteoclastogenesis in wild-type and Tgm2-/- cells and decreases TG1 activity in Tgm2-/- osteoclasts. Cathepsin D protein levels were unaltered in Tgm2-/-cells and its activity moderately but significantly increased. Tgm2-/- and Tgm2+/+ bone marrow macrophages and osteoclasts also expressed Cathepsin E, and Renin of the aspartate protease family, suggesting their potential involvement in this process. Our study brings further support to the observation that TGs are significant regulators of osteoclastogenesis and that the absence of TG2 can cause increased activity of other TGs, such as TG1.

Inhibition of Transglutaminase 2 Reduces Peritoneal Injury in a Chlorhexidine-Induced Peritoneal Fibrosis Model

Long-term peritoneal dialysis (PD) is often associated with peritoneal dysfunction leading to withdrawal from PD. The characteristic pathologic features of peritoneal dysfunction are widely attributed to peritoneal fibrosis and angiogenesis. The detailed mechanisms remain unclear, and treatment targets in clinical settings have yet to be identified. We investigated transglutaminase 2 (TG2) as a possible novel therapeutic target for peritoneal injury. TG2 and fibrosis, inflammation, and angiogenesis were investigated in a chlorhexidine gluconate (CG)-induced model of peritoneal inflammation and fibrosis, representing a noninfectious model of PD-related peritonitis. Transforming growth factor (TGF)-β type I receptor (TGFβR-I) inhibitor and TG2-knockout mice were used for TGF-β and TG2 inhibition studies, respectively. Double immunostaining was performed to identify cells expressing TG2 and endothelial-mesenchymal transition (EndMT). In the rat CG model of peritoneal fibrosis, in situ TG2 activity and protein expression increased during the development of peritoneal fibrosis, as well as increases in peritoneal thickness and numbers of blood vessels and macrophages. TGFβR-I inhibitor suppressed TG2 activity and protein expression, as well as peritoneal fibrosis and angiogenesis. TGF-β1 expression, peritoneal fibrosis, and angiogenesis were suppressed in TG2-knockout mice. TG2 activity was detected by α-smooth muscle actin-positive myofibroblasts, CD31-positive endothelial cells, and ED-1-positive macrophages. CD31-positive endothelial cells in the CG model were α-smooth muscle actin-positive, vimentin-positive, and vascular endothelial-cadherin-negative, suggesting EndMT. In the CG model, EndMT was suppressed in TG2-knockout mice. TG2 was involved in the interactive regulation of TGF-β. As inhibition of TG2 reduced peritoneal fibrosis, angiogenesis, and inflammation associated with TGF-β and vascular endothelial growth factor-A suppression, TG2 may provide a new therapeutic target for ameliorating peritoneal injuries in PD.

Insights into diet-associated oxidative pathomechanisms in inflammatory bowel disease and protective effects of functional amino acids

There has been a substantial rise in the incidence and prevalence of clinical patients presenting with inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis. Accumulating evidence has corroborated the view that dietary factors (particularly diets with high levels of saturated fat or sugar) are involved in the development and progression of IBD, which is predominately associated with changes in the composition of the gut microbiota and an increase in the generation of reactive oxygen species. Notably, the ecological imbalance of the gut microbiome exacerbates oxidative stress and inflammatory responses, leading to perturbations of the intestinal redox balance and immunity, as well as mucosal integrity. Recent findings have revealed that functional amino acids, including L-glutamine, glycine, L-arginine, L-histidine, L-tryptophan, and hydroxyproline, are effectively implicated in the maintenance of intestinal redox and immune homeostasis. These amino acids and their metabolites have oxygen free-radical scavenging and inflammation-relieving properties, and they participate in modulation of the microbial community and the metabolites in the gut. The principal focus of this article is a review of recent advances in the oxidative pathomechanisms of IBD development and progression in relation to dietary factors, with a particular emphasis on the redox and signal transduction mechanisms of host cells in response to unbalanced diets and enterobacteria. In addition, an update on current understanding of the protective effects of functional amino acids against IBD, together with the underlying mechanisms for this protection, have been provided.

Pharmacological effects of natural medicine ginsenosides against Alzheimer's disease

Ginsenosides are the most important pharmacological active ingredient of ginseng, with multiple biological therapeutic targets, mild action and no side effects. It is having shown beneficial effects in vitro and in vivo models of AD. In this review, we analyze large literature, summarize the inhibition of ginsenosides fibrous extracellular deposition of β-amyloid (Aβ) and neurofibrillary tangles (NFTs) of possible mechanisms, and explain the effects of ginsenosides on AD neuroprotection from the aspects of antioxidant, anti-inflammatory, and anti-apoptosis, prove the potential of ginsenosides as a new class of drugs for the treatment of AD. In addition, according to the current clinical application status of natural drugs, this paper analysis the delivery route and delivery mode of ginsenosides from the perspective of pharmacokinetics, providing a deeper insight into the clinical application of ginsenosides in the treatment of AD.

JAK2 deficiency improves erectile function in diabetic mice through attenuation of oxidative stress, apoptosis, and fibrosis

Background

Janus kinase 2 (JAK2) is activated in diabetic mellitus (DM) conditions and may enhance oxidative stress, apoptosis and fibrosis in many tissues. Whether JAK2 activation is involved in the occurrence of diabetic erectile dysfunction (ED) is unknown.

Objectives

We performed this study to investigate the effect of JAK2 deficiency on diabetic ED.

Materials and methods

Conditional JAK2 gene knockout mice (Cre^+/+‐JAK2^fl/fl) were used, in which JAK2 gene knockout could be induced by tamoxifen. Mice fell into four groups: control, JAK2 knockout (JAK2^−/−), DM, and DM with JAK2^−/−. DM was induced by intraperitoneal injection of streptozotocin. Two months later, JAK2 gene knockout was induced with tamoxifen in Cre^+/+‐JAK2^fl/fl mice. After another 2 months, erectile function was measured by electrical stimulation of the cavernous nerve, and penile tissues were harvested. Ratio of maximal intracavernosal pressure (MIP) to mean arterial blood pressure (MAP), expression and phosphorylation of JAK2, oxidative stress level, NO/Cyclic Guanosine Monophosphate (cGMP) pathway, apoptosis, fibrosis, and transforming growth factor beta 1 (TGF‐β1)/Smad/Collagen IV pathway in corpus cavernosum, were measured.

Results

JAK2 expression was remarkably decreased after induction with tamoxifen. JAK2 was activated in penile tissues of diabetic mice, and JAK2 deficiency could improve the impaired erectile function caused by DM. However, in mice without DM, JAK2 deficiency had no apparent influence on erectile function. Levels of oxidative stress, apoptosis, fibrosis, and TGF‐β1/Smad/Collagen IV pathway were all elevated by DM, whereas JAK2 deficiency lessened these alterations in diabetic mice. Moreover, JAK2 deficiency improved the expression of the down‐regulated NO/cGMP pathway in diabetic mice. In non‐diabetic mice, no apparent changes were found in aforementioned parameters after JAK2 gene knockout.

Discussion and conclusion

Our study showed that JAK2 deficiency could improve erectile function in diabetic mice, which might be mediated by reduction in oxidative stress, apoptosis, and fibrosis in corpus cavernosum.

Transcriptional modulation of the T helper 17/interleukin 17 axis ameliorates renal ischemia-reperfusion injury

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) is a latent transcription factor critical for T-cell function. Although inhibition of the Janus kinase 2 (JAK2)/STAT3 pathway has been reported to be protective against ischemia-reperfusion injury (IRI), the role of T cell-associated STAT3 in the pathogenesis of renal IRI has not been specifically defined.

METHODS

We induced renal IRI in both mice with T cell-specific STAT3 knockout (Lck-Cre;STAT3flox/flox) and wild-type controls (C57BL/6) and assessed renal damage and inflammation at 48 h after IRI. Human proximal tubular epithelial cells grown under hypoxia were treated with a JAK2 inhibitor, caffeic acid 3,4-dihydroxy-phenylethyl ester, to determine the effect of JAK2/STAT3 inhibition on renal epithelia. Independently, we disrupted Cln 3-requiring 9 (Ctr9) to inhibit T helper 17 (Th17) activation via RNA interference and determined if Ctr9 inhibition aggravates renal injury through upregulated Th17 activation.

RESULTS

The Lck-Cre;STAT3flox/flox mice exhibited significantly reduced kidney damage compared with controls. This protective effect was associated with reduced intrarenal Th17 infiltration and proinflammatory cytokines. Human proximal tubular epithelial cells under hypoxia exhibited significant upregulation of interleukin 17 receptors, and pharmacologic inhibition of JAK2 significantly ameliorated this change. RNA interference with Ctr9 in splenocytes enhanced differentiation into Th17 cells. In vivo knockdown of Ctr9 in mice with renal IRI further aggravated Th17-associated inflammation and kidney injury.

CONCLUSIONS

STAT3 in T cells contributes to renal IRI through Th17 activation. Inhibition of Ctr9 further enhances Th17 activation and aggravates kidney injury, further supporting the role of Th17 cells in renal IRI.

Increased transcription of transglutaminase 1 mediates neuronal death in in vitro models of neuronal stress and Aβ1-42-mediated toxicity

Alzheimer's disease (AD) is the most common cause of dementia. At the pre-symptomatic phase of the disease, the processing of the amyloid precursor protein (APP) produces toxic peptides, called amyloid-β 1-42 (Aβ 1-42). The downstream effects of Aβ 1-42 production are not completely uncovered. Here, we report the involvement of transglutaminase 1 (TG1) in in vitro AD models of neuronal toxicity. TG1 was increased at late stages of the disease in the hippocampus of a mouse model of AD and in primary cortical neurons undergoing stress. Silencing of TGM1 gene was sufficient to prevent Aβ-mediated neuronal death. Conversely, its overexpression enhanced cell death. TGM1 upregulation was mediated at the transcriptional level by an activator protein 1 (AP1) binding site that when mutated halted TGM1 promoter activation. These results indicate that TG1 acts downstream of Aβ-toxicity, and that its stress-dependent increase makes it suitable for pharmacological intervention.

γ-Oryzanol mitigates oxidative stress and prevents mutant SOD1-Related neurotoxicity in Drosophila and cell models of amyotrophic lateral sclerosis

Oxidative stress plays a critical role in mutant copper/zinc superoxide dismutase 1 (SOD1)-linked amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease characterized by selective loss of motor neurons. Thus, an anti-oxidative stress remedy might be a promising means for the treatment of ALS. The aim of the present study is to investigate the neuroprotective effects of γ-oryzanol (Orz) and elucidate its relevant molecular mechanisms in mutant hSOD1-linked Drosophila and cell models of ALS. Orz treatment provided neuroprotection in flies with expression of hSOD1-G85R in motor neurons, as demonstrated by the prolonged survival, improvement of motor deficits, reduced oxidative damage and regulated redox homeostasis when compared with those in controls. Moreover, Orz significantly decreased neuronal apoptosis and upregulated the nuclear factor erythroid 2-related factor 2 (Nrf2)/glutamate-cysteine ligase catalytic subunit (GCLC) antioxidant pathway via activating Akt in hSOD1-G93A-expressing NSC-34 cells. In addition, our results showed that both in vivo and in vitro, Akt served as an upstream regulator of signal transducers and activators of transcription (Stat) 3 stimulated by Orz, which further increased the level of another anti-oxidative stress factor heat-shock protein 70 (HSP70). Altogether, these findings provide evidence that Orz has potential neuroprotective effects that may be beneficial in the treatment of ALS disease with SOD1 mutations.

Targeted inhibition of STAT3 as a potential treatment strategy for atherosclerosis

Atherosclerosis is the main pathological basis of ischemic cardiovascular and cerebrovascular diseases and has attracted more attention in recent years. Multiple studies have demonstrated that the signal transducer and activator of transcription 3 (STAT3) plays essential roles in the process of atherosclerosis. Moreover, aberrant STAT3 activation has been shown to contribute to the occurrence and development of atherosclerosis. Therefore, the study of STAT3 inhibitors has gradually become a focal research topic. In this review, we describe the crucial roles of STAT3 in endothelial cell dysfunction, macrophage polarization, inflammation, and immunity during atherosclerosis. STAT3 in mitochondria is mentioned as well. Then, we present a summary and classification of STAT3 inhibitors, which could offer potential treatment strategies for atherosclerosis. Furthermore, we enumerate some of the problems that have interfered with the development of mature therapies utilizing STAT3 inhibitors to treat atherosclerosis. Finally, we propose ideas that may help to solve these problems to some extent. Collectively, this review may be useful for developing future STAT3 inhibitor therapies for atherosclerosis.

Development and Validation of Conditions for Extracting Flavonoids Content and Evaluation of Antioxidant and Cytoprotective Activities from Bougainvillea x buttiana Bracteas (var. Rose)

In this study the effect of the ethanol concentration of Bougainvillea x buttiana extracts on the flavonoids content, and its antioxidant and cytoprotective activities in vitro were determined and compared. For the elucidation of the chemical constituents, the high-performance liquid chromatography method (HPLC) was used, and verification of the antioxidant activity was carried out using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical method. The cytoprotective effects of extracts were determined by exposure to hydrogen peroxide. The HPLC analysis showed the presence of rutin, quercetin-3-glucoside and quercetin rhamnoside. Among the extracts investigated the best recuperation of the rutin content was observed in extracts with 80% ethanol (83 ± 5 mg/mL). The amounts of rutin present in all extracts contribute to the antioxidant capacity and the IC50 was 427.49 (0%), 275.41 (50%), 271.61 (80%), and 272.14 (100%) µg/mL. The lowest percentage of viability was found in the cultures exposed to 100% ethanol (92%). In cultures exposed to hydrogen peroxide the percentages of protection were 25%, 33%, 78%, and 65% for cultures treated for 72 h at 0%, 50%, 80%, and 100% ethanol, respectively. The ethanolic extract of B. x buttiana was confirmed to have high rutin content with potent antioxidant activity, low cytotoxic and strong cytoprotective effects.

Isozyme-specific comprehensive characterization of transglutaminase-crosslinked substrates in kidney fibrosis

Chronic kidney disease is characterized by prolonged decline in renal function, excessive accumulation of ECM, and progressive tissue fibrosis. Transglutaminase (TG) is a crosslinking enzyme that catalyzes the formation of covalent bonds between glutamine and lysine residues, and is involved in the induction of renal fibrosis via the stabilization of ECM and the activation of TGF-β1. Despite the accumulating evidences indicating that TG2 is a key enzyme in fibrosis, genetic knockout of TG2 reduced by only 50% the elevated protein crosslinking and fibrous protein in renal fibrosis model, whereas treatment with TG inhibitor almost completely reduced these levels. Here, we also clarified the distributions of TG isozymes and their in situ activities and identified the isozyme-specific crosslinked substrates for both TG1 and TG2 in fibrotic kidney. We found that TG1 activity was markedly enhanced in renal tubular epithelium and interstitial areas, whereas TG2 activity increased only in the extracellular space. In total, 47 and 67 possible candidates were identified as TG1 and TG2 substrates, respectively, only in fibrotic kidney. Among them, several possible substrates related to renal disease and fibrosis were identified. These findings provide novel insights into the mechanisms of renal fibrosis through the targeting of isozyme-specific TG substrates.

Blockade of histone deacetylase 6 protects against cisplatin-induced acute kidney injury

Histone deacetylase 6 (HDAC6) has been shown to be involved in various pathological conditions, including cancer, neurodegenerative disorders and inflammatory diseases. Nonetheless, its specific role in drug-induced nephrotoxicity is poorly understood. Cisplatin (dichlorodiamino platinum) belongs to an inorganic platinum - fundamental chemotherapeutic drug utilized in the therapy of various solid malignant tumors. However, the use of cisplatin is extremely limited by obvious side effects, for instance bone marrow suppression and nephrotoxicity. In the present study, we utilized a murine model of cisplatin-induced acute kidney injury (AKI) and a highly selective inhibitor of HDAC6, tubastatin A (TA), to assess the role of HDAC6 in nephrotoxicity and its associated mechanisms. Cisplatin-induced AKI was accompanied by increased expression and activation of HDAC6; blocking HDAC6 with TA lessened renal dysfunction, attenuated renal pathological changes, reduced expression of neutrophil gelatinase-associated lipocalin and kidney injury molecule 1, and decreased tubular cell apoptosis. In cultured human epithelial cells, TA or HDAC6 siRNA treatment also inhibited cisplatin-induced apoptosis. Mechanistic studies demonstrated that cisplatin treatment induced phosphorylation of AKT and loss of E-cadherin in the nephrotoxic kidney, and administration of TA enhanced AKT phosphorylation and preserved E-cadherin expression. HDAC6 inhibition also potentiated autophagy as evidenced by increased expression of autophagy-related gene (Atg) 7 (Atg7), Beclin-1, and decreased renal oxidative stress as demonstrated by up-regulation of superoxide dismutase (SOD) activity and down-regulation of malondialdehyde levels. Moreover, TA was effective in inhibiting nuclear factor-κ B (NF-κB) phosphorylation and suppressing the expression of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Collectively, these data provide strong evidence that HDAC6 inhibition is protective against cisplatin-induced AKI and suggest that HDAC6 may be a potential therapeutic target for AKI treatment.

Ginsenoside Rg1 Decreases Oxidative Stress and Down-Regulates Akt/mTOR Signalling to Attenuate Cognitive Impairment in Mice and Senescence of Neural Stem Cells Induced by D-Galactose

Adult hippocampal neurogenesis plays a pivotal role in learning and memory. The suppression of hippocampal neurogenesis induced by an increase of oxidative stress is closely related to cognitive impairment. Neural stem cells which persist in the adult vertebrate brain keep up the production of neurons over the lifespan. The balance between pro-oxidants and anti-oxidants is important for function and surviving of neural stem cells. Ginsenoside Rg1 is one of the most active components of Panax ginseng, and many studies suggest that ginsenosides have antioxidant properties. This research explored the effects and underlying mechanisms of ginsenoside Rg1 on protecting neural stem cells (NSCs) from oxidative stress. The sub-acute ageing of C57BL/6 mice was induced by subcutaneous injection of D-gal (120 mg kg^-1 day^-1) for 42 day. On the 14th day of D-gal injection, the mice were treated with ginsenoside Rg1 (20 mg kg^-1 day^-1, intraperitoneally) or normal saline for 28 days. The study monitored the effects of Rg1 on proliferation, senescence-associated and oxidative stress biomarkers, and Akt/mTOR signalling pathway in NSCs. Compared with the D-gal group, Rg1 improved cognitive impairment induced by D-galactose in mice by attenuating senescence of neural stem cells. Rg1 also decreased the level of oxidative stress, with increased the activity of superoxide dismutase and glutathione peroxidase in vivo and in vitro. Rg1 furthermore reduced the phosphorylation levels of protein kinase B (Akt) and the mechanistic target of rapamycin (mTOR) and down-regulated the levels of downstream p53, p16, p21 and Rb in D-gal treated NSCs. The results suggested that the protective effect of ginsenoside Rg1 on attenuating cognitive impairment in mice and senescence of NSCs induced by D-gal might be related to the reduction of oxidative stress and the down-regulation of Akt/mTOR signaling pathway.

Biochemical Characterization of Medaka (Oryzias latipes) Transglutaminases, OlTGK1 and OlTGK2, as Orthologues of Human Keratinocyte-Type Transglutaminase

Calcium-dependent transglutaminases (TGs) are a family of enzymes that catalyze protein cross-linking and/or attachment of primary amines in a variety of organisms. Mammalian TGs are implicated in multiple biological events such as skin formation, blood coagulation, and extracellular matrix stabilization. Medaka (Oryzias latipes) has been used as a model fish to investigate the physiological functions of mammalian proteins. By analysis of the medaka genome, we found seven TGs orthologues, some of which apparently corresponded to the mammalian TG isozymes, TG1, TG2, and Factor XIII. All orthologues had preserved amino acid residues essential for enzymatic activity in their deduced primary structures. In this study, we analyzed biochemical properties of two orthologues (OlTGK1 and OlTGK2) of mammalian epithelium-specific TG (TG1) that are significantly expressed at the transcriptional level. Using purified recombinant proteins for OlTGK1 and OlTGK2, we characterized their catalytic reactions. Furthermore, immunohistochemical analyses of fish sections revealed higher expression in the pancreas (OTGK1), intervertebral disk (OlTGK2) and pharyngeal teeth (OlTGK2) as well as in the skin epidermis.

Early response as shown by enhancement of transglutaminase 1 expression after cisplatin-induced acute kidney injury

Acute kidney injury (AKI) is caused by drugs and other stimuli, which limits the use of several therapeutic approaches. The AKI mouse model generated by intraperitoneal administration with cisplatin, one of the most widely used anti-cancer drugs, is generally applied to study on this disease. Transglutaminases are posttranslational modifying enzymes that catalyze irreversible cross-linking reactions between proteins in several biological events such as skin formation and blood coagulation. In this study, we found an increase in the expression level of transglutaminase (TG1) in the kidney of mice which had been injected with cisplatin and underwent progressive nephrotoxicity. Before the appearance of the tentative symptoms of renal failure, which is apparent by morphological damage in the kidney and increases in blood creatinine levels, both the expression level and activity of TG1 rapidly increased mainly at the proximal tubule. On the other hand, the protein expression level of another major isozyme (TG2) remained mostly unaltered. This investigation will provide a possible basal-level biomarker and also information on progression of renal failure from the aspect of the protein-modifying enzyme, transglutaminase.

JAK2/STAT3 inhibition attenuates noise-induced hearing loss

Signal transducers and activators of transcription 3 (STAT3) is a stress responsive transcription factor that plays a key role in oxidative stress-mediated tissue injury. As reactive oxygen species (ROS) are a known source of damage to tissues of the inner ear following loud sound exposure, we examined the role of the Janus kinase 2 (JAK2)/STAT3 signaling pathway in noise induce hearing loss using the pathway specific inhibitor, JSI-124. Mice were exposed to a moderately damaging level of loud sound revealing the phosphorylation of STAT3 tyrosine 705 residues and nuclear localization in many cell types in the inner ear including the marginal cells of the stria vascularis, type II, III, and IV fibrocytes, spiral ganglion cells, and in the inner hair cells. Treatment of the mice with the JAK2/STAT3 inhibitor before noise exposure reduced levels of phosphorylated STAT3 Y705. We performed auditory brain stem response and distortion product otoacoustic emission measurements and found increased recovery of hearing sensitivity at two weeks after noise exposure with JAK2/STAT3 inhibition. Performance of cytocochleograms revealed improved outer hair cell survival in JSI-124 treated mice relative to control. Finally, JAK2/STAT3 inhibition reduced levels of ROS detected in outer hair cells at two hours post noise exposure. Together, these findings demonstrate that inhibiting the JAK2/STAT3 signaling pathway is protective against noise-induced cochlear tissue damage and loss of hearing sensitivity.

Class I HDAC activity is required for renal protection and regeneration after acute kidney injury

Activation of histone deacetylases (HDACs) is required for renal epithelial cell proliferation and kidney development. However, their role in renal tubular cell survival and regeneration after acute kidney injury (AKI) remains unclear. In this study, we demonstrated that all class I HDAC isoforms (1, 2, 3, and 8) were expressed in the renal epithelial cells of the mouse kidney. Inhibition of class I HDACs with MS-275, a highly selective inhibitor, resulted in more severe tubular injury in the mouse model of AKI induced by folic acid or rhabdomyolysis, as indicated by worsening renal dysfunction, increased neutrophil gelatinase-associated lipocalin expression, and enhanced apoptosis and caspase-3 activation. Blocking class I HDAC activity also impaired renal regeneration as evidenced by decreased expression of renal Pax-2, vimentin, and proliferating cell nuclear antigen. Injury to the kidney is accompanied by increased phosphorylation of epidermal growth factor receptor (EGFR), signal transducers and activators of transcription 3 (STAT3), and Akt. Inhibition of class I HDACs suppressed EGFR phosphorylation as well as reduced its expression. MS-275 was also effective in inhibiting STAT3 and Akt phosphorylation, but this treatment did not affect their expression levels. Taken together, these data suggest that the class I HDAC activity contributes to renal protection and functional recovery and is required for renal regeneration after AKI. Furthermore, renal EGFR signaling is subject to regulation by this class of HDACs.

IL-22 ameliorates renal ischemia-reperfusion injury by targeting proximal tubule epithelium

IL-22 is an epithelial cell survival cytokine that is currently under development for the treatment of acute liver damage. Here, we used a mouse model of renal ischemia/reperfusion (I/R) injury to investigate whether IL-22 has therapeutic potential for the treatment of AKI. The action of IL-22 is mediated by binding to IL-22R1 and leads to STAT3 activation. Under physiologic conditions, renal expression of IL-22R1 was detected only in the brush border of the renal proximal tubular epithelial cells (RPTECs). Renal I/R elevated serum IL-22 levels slightly but did not induce STAT3 phosphorylation in RPTECs. IL-22-deficient mice had slightly increased I/R-induced injury compared with wild-type mice. In contrast, treatment with IL-22 or overexpression of IL-22 by either gene targeting (IL-22 transgenic mice) or administration of adenovirus expressing IL-22 increased STAT3 phosphorylation in RPTECs, ameliorated I/R-induced renal inflammation and tubular cell injury, and preserved renal functions. Overexpression of IL-22 increased the phosphorylation of STAT3 and Akt, upregulated antiapoptotic genes (e.g., Bcl-2), and downregulated proapoptotic genes (e.g., Bad) in the kidneys of mice subjected to I/R. Notably, phosphorylation of Akt increased and expression of Bad decreased in proximal tubular cells under these conditions. Furthermore, compared with wild-type mice, IL-22 transgenic mice had increased survival rates, whereas IL-22-deficient mice had reduced survival rates after I/R injury. In summary, renal expression of IL-22R1 is restricted to RPTECs, and treatment with IL-22 protects against renal I/R injury by activating STAT3 and AKT, suggesting that IL-22 has therapeutic potential for the treatment of AKI.

New role of JAK2/STAT3 signaling in endothelial cell oxidative stress injury and protective effect of melatonin

Previous studies have shown that the JAK2/STAT3 signaling pathway plays a regulatory role in cellular oxidative stress injury (OSI). In this study, we explored the role of the JAK2/STAT3 signaling pathway in hydrogen peroxide (H₂O₂)-induced OSI and the protective effect of melatonin against (H₂O₂)-induced injury in human umbilical vein endothelial cells (HUVECs). AG490 (a specific inhibitor of the JAK2/STAT3 signaling pathway) and JAK2 siRNA were used to manipulate JAK2/STAT3 activity, and the results showed that AG490 and JAK2 siRNA inhibited OSI and the levels of p-JAK2 and p-STAT3. HUVECs were then subjected to H₂O₂ in the absence or presence of melatonin, the main secretory product of the pineal gland. Melatonin conferred a protective effect against H₂O₂, which was evidenced by improvements in cell viability, adhesive ability and migratory ability, decreases in the apoptotic index and reactive oxygen species (ROS) production and several biochemical parameters in HUVECs. Immunofluorescence and Western blotting showed that H₂O₂ treatment increased the levels of p-JAK2, p-STAT3, Cytochrome c, Bax and Caspase3 and decreased the levels of Bcl2, whereas melatonin treatment partially reversed these effects. We, for the first time, demonstrate that the inhibition of the JAK2/STAT3 signaling pathway results in a protective effect against endothelial OSI. The protective effects of melatonin against OSI, at least partially, depend upon JAK2/STAT3 inhibition.

Gastrin acting on the cholecystokinin2 receptor induces cyclooxygenase-2 expression through JAK2/STAT3/PI3K/Akt pathway in human gastric cancer cells

Gastrin, cholecystokinin2 receptor (CCK2R), and cyclooxygenase-2 (COX-2) have been implicated in the carcinogenesis and progression of gastric cancer. Our study demonstrated that antagonist or siRNA against CCK2R blocked amidated gastrin (G17)-induced activation of STAT3 and Akt in gastric cancer cell lines. G17-increased COX-2 expression and cell proliferation were effectively blocked by CCK2R antagonist and inhibitors of JAK2 and PI3K. In addition, knockdown of STAT3 expression significantly attenuated G17-induced PI3K/Akt activation, COX-2 expression, and cell proliferation. These results suggest that CCK2R-mediated COX-2 up-regulation via JAK2/STAT3/PI3K/Akt pathway is involved in the proliferative effect of G17 on human gastric cancer cells.

PrLZ protects prostate cancer cells from apoptosis induced by androgen deprivation via the activation of Stat3/Bcl-2 pathway

PrLZ/PC-1 is a newly identified, prostate-specific and androgen-inducible gene. Our previous study showed that PrLZ can enhance the proliferation and invasive capability of LNCaP cells, contributing to the development of prostate cancer. However, its potential role in androgen-independent processes remains elusive. In this study, we showed that PrLZ enhanced in vitro growth and colony formation of prostate cancer cells on androgen deprivation as well as tumorigenicity in castrated nude mice. In addition, PrLZ stabilized mitochondrial transmembrane potential, prevented release of cytochrome c from mitochondria to cytoplasm, and inhibited intrinsic apoptosis induced by androgen depletion. Mechanistically, PrLZ elevated the phosphorylation of Akt and Stat3 and upregulated Bcl-2 expression. Our data indicate that PrLZ protects prostate cancer cells from apoptosis and promotes tumor progression following androgen deprivation. In summary, we propose that PrLZ is a novel antiapoptotic gene that is specifically activated in prostate cancer cells escaping androgen deprivation may offer an appealing therapeutic target to prevent or treat advanced prostate malignancy.

Role of transglutaminase 2 in apoptosis induced by hydrogen peroxide in human chondrocytes

Chondrocyte apoptosis has been implicated in the pathogenesis of osteoarthritis. Transglutaminase 2 (TG2), the expression of which is higher in osteoarthritis patients, has been shown to be up-regulated during apoptosis in many experimental models. This study investigated the expression and role of TG2 in human chondrocytes undergoing apoptosis induced by hydrogen peroxide (H₂O₂). Human chondrocytes were obtained from the knee articular cartilage of patients undergoing total joint arthroplasty. Apoptosis was induced by H₂O₂ and was measured with Annexin-V flow cytometry, DNA Fragmentation ELISA and DAPI staining. Western Blot, an in situ activity assay and immunocytochemistry were used to examine TG2 expression. The role of TG2 was evaluated by TG-specific siRNA transfection and monodansylcadaverine (MDC), a competitive substrate for TG2. H₂O₂ induced apoptosis of human chondrocytes in a dose- and time-dependent manner. The level of TG2 expression was higher in the chondrocytes undergoing H₂O₂-induced apoptosis. Inhibition of TG2 by siRNA or MDC increased the level of apoptosis in the H₂O₂-treated chondrocytes. TG2 expression is higher in human chondrocytes undergoing apoptosis, and inhibition of TG2 leads to increased apoptosis. These results may raise the possibility of TG2 as a modulator of cartilage damage in osteoarthritis by offering protection against chondrocyte apoptosis.

E-cadherin and transglutaminase-1 epithelial barrier restoration precedes type IV collagen basement membrane reconstruction following vocal fold mucosal injury

The vocal fold epithelium is critical to upper airway immunologic defense and water/ion transport; therefore, any form of physical trauma or insult increases the vulnerability of this structure to functional impairment and pathogen invasion/infection. In this study, we examined the reestablishment of epithelial and basement membrane barrier structures in a well-established rat model of vocal fold mucosal injury. We observed active cell recruitment culminating in peak hyperplasia at 3 days postinjury, the establishment of robust E-cadherin+ and transglutaminase-1+ biochemical barrier signals along the epithelial surface by 3 days postinjury, and the persistent absence of a type IV collagen+ basement membrane at 7 days postinjury. The distinct spatial and temporal immunoactivity of these molecules is consistent with a programmed repair process driving the restoration of vocal fold mucosal integrity and permeability. These data may inform future efforts to optimize functional mucosal recovery postinjury and avoid undesirable events such as barrier compromise or epithelial metaplasia.

HIV-1 inhibits autophagy in bystander macrophage/monocytic cells through Src-Akt and STAT3

Autophagy is a homeostatic mechanism of lysosomal degradation. Defective autophagy has been linked to various disorders such as impaired control of pathogens and neurodegeneration. Autophagy is regulated by a complex array of signaling pathways that act upstream of autophagy proteins. Little is known about the role of altered regulatory signaling in disorders associated with defective autophagy. In particular, it is not known if pathogens inhibit autophagy by modulation of upstream regulatory pathways. Cells infected with HIV-1 blocked rapamycin-induced autophagy and CD40-induced autophagic killing of Toxoplasma gondii in bystander (non-HIV-1 infected) macrophage/monocytic cells. Blockade of autophagy was dependent on Src-Akt and STAT3 triggered by HIV-1 Tat and IL-10. Neutralization of the upstream receptors VEGFR, beta-integrin or CXCR4, as well as of HIV-1 Tat or IL-10 restored autophagy in macrophage/monocytic cells exposed to HIV-1-infected cells. Defective autophagic killing of T. gondii was detected in monocyte-derived macrophages from a subset of HIV-1(+) patients. This defect was also reverted by neutralization of Tat or IL-10. These studies revealed that a pathogen can impair autophagy in non-infected cells by activating counter-regulatory pathways. The fact that pharmacologic manipulation of cell signaling restored autophagy in cells exposed to HIV-1-infected cells raises the possibility of therapeutic manipulation of cell signaling to restore autophagy in HIV-1 infection.