Gas6 induces mesangial cell proliferation via latent transcription factor STAT3

Co-targeting JAK1/STAT6/GAS6/TAM signaling improves chemotherapy efficacy in Ewing sarcoma

Ewing sarcoma is a pediatric bone and soft tissue tumor treated with chemotherapy, radiation, and surgery. Despite intensive multimodality therapy, ~50% patients eventually relapse and die of the disease due to chemoresistance. Here, using phospho-profiling, we find Ewing sarcoma cells treated with chemotherapeutic agents activate TAM (TYRO3, AXL, MERTK) kinases to augment Akt and ERK signaling facilitating chemoresistance. Mechanistically, chemotherapy-induced JAK1-SQ phosphorylation releases JAK1 pseudokinase domain inhibition allowing for JAK1 activation. This alternative JAK1 activation mechanism leads to STAT6 nuclear translocation triggering transcription and secretion of the TAM kinase ligand GAS6 with autocrine/paracrine consequences. Importantly, pharmacological inhibition of either JAK1 by filgotinib or TAM kinases by UNC2025 sensitizes Ewing sarcoma to chemotherapy in vitro and in vivo. Excitingly, the TAM kinase inhibitor MRX-2843 currently in human clinical trials to treat AML and advanced solid tumors, enhances chemotherapy efficacy to further suppress Ewing sarcoma tumor growth in vivo. Our findings reveal an Ewing sarcoma chemoresistance mechanism with an immediate translational value.

Gas6/AXL pathway: immunological landscape and therapeutic potential

Cancer is a disease with ecological and evolutionary unity, which seriously affects the survival and quality of human beings. Currently, many reports have suggested Gas6 plays an important role in cancer. Binding of gas6 to TAM receptors is associated with the carcinogenetic mechanisms of multiple malignancies, such as in breast cancer, chronic lymphocytic leukemia, non-small cell lung cancer, melanoma, prostate cancer, etc., and shortened overall survival. It is accepted that the Gas6/TAM pathway can promote the malignant transformation of various types of cancer cells. Gas6 has the highest affinity for Axl, an important member of the TAM receptor family. Knockdown of the TAM receptors Axl significantly affects cell cycle progression in tumor cells. Interestingly, Gas6 also has an essential function in the tumor microenvironment. The Gas6/AXL pathway regulates angiogenesis, immune-related molecular markers and the secretion of certain cytokines in the tumor microenvironment, and also modulates the functions of a variety of immune cells. In addition, evidence suggests that the Gas6/AXL pathway is involved in tumor therapy resistance. Recently, multiple studies have begun to explore in depth the importance of the Gas6/AXL pathway as a potential tumor therapeutic target as well as its broad promise in immunotherapy; therefore, a timely review of the characteristics of the Gas6/AXL pathway and its value in tumor treatment strategies is warranted. This comprehensive review assessed the roles of Gas6 and AXL receptors and their associated pathways in carcinogenesis and cancer progression, summarized the impact of Gas6/AXL on the tumor microenvironment, and highlighted the recent research progress on the relationship between Gas6/AXL and cancer drug resistance.

AXL Inhibitors: Status of Clinical Development

PURPOSE OF REVIEW

The AXL signaling pathway is associated with tumor growth as well as poor prognosis in cancer. Here, we highlight recent strategies for targeting AXL in the treatment of solid and hematological malignancies.

RECENT FINDINGS

AXL is a key player in survival, metastasis, and therapeutic resistance in many cancers. A range of AXL-targeted therapies, including tyrosine kinase inhibitors, monoclonal antibodies, antibody-drug conjugates, and soluble receptors, have entered clinical development. Notably, AXL inhibitors in combination with immune checkpoint inhibitors demonstrate early promise; however, further understanding of predictive biomarkers and treatment sequencing is necessary. Based on its role in tumor growth and drug resistance, AXL represents a promising therapeutic target in oncology. Results from ongoing clinical trials will provide valuable insights into the role of AXL inhibitors, both as single agents and in combination with other therapies.

Triton modified polyethyleneimine conjugates assembled with growth arrest-specific protein 6 for androgenetic alopecia transdermal gene therapy

Androgenetic alopecia is an androgen-dependent skin disorder that commonly affects hair follicle growth and hair loss. Gene therapy that can promote the proliferation and survival of hair follicle cells can be a potential choice for its cure. While transdermal application of therapeutic functional nucleic acids across the stratum corneum is quite difficult. Here, we first develop a transdermal agent for functional nucleic acid delivery using Triton X-100-modified low molecular weight polyethyleneimine (PEI-Triton-N, N ​= ​6 or 8). In vitro cell experiments demonstrate that the PEI-Triton-N conjugates can stably encapsulate and efficiently deliver plasmid DNA to hard-to-transfect keratinocyte HaCaT cells. Further mouse model studies show that PEI-Triton-6 can encapsulate and deliver growth arrest-specific protein 6 (Gas6) plasmid through transdermal administration. The transfected Gas6 prolongs the anagen status, inhibits the apoptosis of hair follicle cells, and further promotes the proliferation and differentiation of hair follicle cells. The PEI-Triton-6/pDNA_Gas6 complexes can obviously alleviate hair loss in androgenetic alopecia mice and provides a promising strategy for gene therapy via transdermal administration.

The Role of JAK/STAT Pathway in Fibrotic Diseases: Molecular and Cellular Mechanisms

There are four members of the JAK family and seven of the STAT family in mammals. The JAK/STAT molecular pathway could be activated by broad hormones, cytokines, growth factors, and more. The JAK/STAT signaling pathway extensively mediates various biological processes such as cell proliferation, differentiation, migration, apoptosis, and immune regulation. JAK/STAT activation is closely related to growth and development, homeostasis, various solid tumors, inflammatory illness, and autoimmune diseases. Recently, with the deepening understanding of the JAK/STAT pathway, the relationship between JAK/STAT and the pathophysiology of fibrotic diseases was noticed, including the liver, renal, heart, bone marrow, and lung. JAK inhibitor has been approved for myelofibrosis, and subsequently, JAK/STAT may serve as a promising target for fibrosis in other organs. Therefore, this article reviews the roles and mechanisms of the JAK/STAT signaling pathway in fibrotic diseases.

AXL inhibition improves BRAF-targeted treatment in melanoma

More than half of metastatic melanoma patients receiving standard therapy fail to achieve a long-term survival due to primary and/or acquired resistance. Tumor cell ability to switch from epithelial to a more aggressive mesenchymal phenotype, attributed with AXL^high molecular profile in melanoma, has been recently linked to such event, limiting treatment efficacy. In the current study, we investigated the therapeutic potential of the AXL inhibitor (AXLi) BGB324 alone or in combination with the clinically relevant BRAF inhibitor (BRAFi) vemurafenib. Firstly, AXL was shown to be expressed in majority of melanoma lymph node metastases. When treated ex vivo, the largest reduction in cell viability was observed when the two drugs were combined. In addition, a therapeutic benefit of adding AXLi to the BRAF-targeted therapy was observed in pre-clinical AXL^high melanoma models in vitro and in vivo. When searching for mechanistic insights, AXLi was found to potentiate BRAFi-induced apoptosis, stimulate ferroptosis and inhibit autophagy. Altogether, our findings propose AXLi as a promising treatment in combination with standard therapy to improve therapeutic outcome in metastatic melanoma.

Axl regulated survival/proliferation network and its therapeutic intervention in mouse models of glomerulonephritis

BACKGROUND

Lupus nephritis (LN) is the most common and serious complication of systemic lupus erythematosus (SLE). LN pathogenesis is not fully understood. Axl receptor tyrosine kinase is upregulated and contributes to the pathogenic progress in LN. We have reported that Axl disruption attenuates nephritis development in mice.

METHODS

In this study, we analyzed the gene expression profiles with RNA-seq using renal cortical samples from nephritic mice. Axl-KO mice were bred onto a B6.lpr spontaneous lupus background, and renal disease development was followed and compared to the Axl-sufficient B6.lpr mice. Finally, anti-glomerular basement membrane (anti-GBM) Ab-induced nephritic mice were treated with Axl small molecule inhibitor, R428, at different stages of nephritis development. Blood urine nitrogen levels and renal pathologies were evaluated.

RESULTS

Transcriptome analysis revealed that renal Axl activation contributed to cell proliferation, survival, and motility through regulation of the Akt, c-Jun, and actin pathways. Spontaneous lupus-prone B6.lpr mice with Axl deficiency showed significantly reduced kidney damages and decreased T cell infiltration compared to the renal damage and T cell infiltration in Axl-sufficient B6.lpr mice. The improved kidney function was independent of autoAb production. Moreover, R428 significantly reduced anti-GBM glomerulonephritis at different stages of GN development compared to the untreated nephritic control mice. R428 administration reduced inflammatory cytokine (IL-6) production, T cell infiltration, and nephritis disease activity.

CONCLUSIONS

Results from this study emphasize the important role of Axl signaling in LN and highlight Axl as an attractive target in LN.

A review on the role of GAS6 and GAS6-AS1 in the carcinogenesis

Growth arrest specific 6 (GAS6) encodes a protein that serves as a ligand for AXL receptor tyrosine kinase and stimulates cell proliferation. Notably, an antisense RNA, namely GAS6-AS1 is transcribed from chromosome 13q34, near GAS6 gene. In vitro functional experiments have demonstrated that GAS6-AS1 can promote proliferation, migration and invasive properties of transformed cells through enhancing entry into S-phase. Notably, mechanistic investigations have shown that GAS6-AS1 can regulate expression of GAS6 at the transcriptional or translational stages through constructing a RNA-RNA duplex, thus enhancing expression of AXL and inducing AXL signaling. Both GAS6 and its antisense transcript contribute in the pathogenesis of human malignancies. In the current review, we provide a summary of studies that appraised the role of these genes in the carcinogenesis.

Deficiency of Axl aggravates pulmonary arterial hypertension via BMPR2

Pulmonary arterial hypertension (PAH), is a fatal disease characterized by a pseudo-malignant phenotype. We investigated the expression and the role of the receptor tyrosine kinase Axl in experimental (i.e., monocrotaline and Su5416/hypoxia treated rats) and clinical PAH. In vitro Axl inhibition by R428 and Axl knock-down inhibited growth factor-driven proliferation and migration of non-PAH and PAH PASMCs. Conversely, Axl overexpression conferred a growth advantage. Axl declined in PAECs of PAH patients. Axl blockage inhibited BMP9 signaling and increased PAEC apoptosis, while BMP9 induced Axl phosphorylation. Gas6 induced SMAD1/5/8 phosphorylation and ID1/ID2 increase were blunted by BMP signaling obstruction. Axl association with BMPR2 was facilitated by Gas6/BMP9 stimulation and diminished by R428. In vivo R428 aggravated right ventricular hypertrophy and dysfunction, abrogated BMPR2 signaling, elevated pulmonary endothelial cell apoptosis and loss. Together, Axl is a key regulator of endothelial BMPR2 signaling and potential determinant of PAH.

Therapeutic aspects of the Axl/Gas6 molecular system

Axl receptor tyrosine kinase (RTK) and its ligand, growth arrest-specific protein 6 (Gas6), are involved in several biological functions and participate in the development and progression of a range of malignancies and autoimmune disorders. In this review, we present this molecular system from a drug discovery perspective, highlighting its therapeutic implications and challenges that need to be addressed. We provide an update on Axl/Gas6 axis biology, exploring its role in fields ranging from angiogenesis, cancer development and metastasis, immune response and inflammation to viral infection. Finally, we summarize the molecules that have been developed to date to target the Axl/Gas6 molecular system for therapeutic and diagnostic applications.

Markers of epithelial-mesenchymal transition in an experimental breast cancer model induced by organophosphorous pesticides and estrogen

Breast cancer is a major health problem and accounted for 11.6% of all new cancer cases and 6.6% of all cancer deaths among women worldwide in 2018. However, its etiology has remained elusive. According to epidemiological studies, environmental factors are influencing the increase in the incidence of breast cancer risk. Components such as chemicals, including pesticides, are agents that produce deleterious effects on wildlife and humans. Among them, the organophosphorus pesticides, such as malathion, have largely been considered in this etiology. The epithelial-mesenchymal transition serves a key role in tumor progression and it is proposed that malathion is closely associated with the origin of this transition, among other causes. Moreover, proteins participating in this process are primordial in the transformation of a normal cell to a malignant tumor cell. The aim of the current study was to evaluate markers that indicated oncogenic properties. The results indicated greater expression levels of proteins associated with the epithelial-to-mesenchymal transition, including E-cadherin, Vimentin, Axl, and Slug in the rat mammary glands treated with malathion alone and combined with estrogen. Atropine was demonstrated to counteract the malathion effect as a muscarinic antagonist. The understanding of the use of markers in experimental models is crucial to identify different stages in the cancer process. The alteration of these markers may serve as a predicting factor that can be used to indicate whether a person has altered ducts or lobules in breast tissue within biopsies of individuals exposed to OPs or other environmental substances.

Novel AXL-specific inhibitor ameliorates kidney dysfunction through the inhibition of epithelial-to-mesenchymal transition of renal tubular cells

Chronic kidney diseases affect more than 800 million people globally and remain a high unmet need. Various therapeutic targets are currently under evaluation in pre-clinical and clinical studies. Because the growth arrest specific gene 6 (Gas6)/AXL pathway has been implicated in the pathogenesis of kidney diseases, we generated a novel selective and potent AXL inhibitor, CH5451098, and we evaluated its efficacy and elucidated its mechanism in an NEP25 mouse model that follows the clinical course of glomerular nephritis. In this model, CH5451098 significantly ameliorated the excretion of urinary albumin and elevation of serum creatinine. Additionally, it also inhibited tubulointerstitial fibrosis and tubular damage. To elucidate the mechanism behind these changes, we analyzed the effect of CH5451098 against transforming growth factor β1 (TGFβ1) and Gas6, which is a ligand of AXL receptor, in NRK-52E renal tubular epithelial cells. CH5451098 inhibited epithelial-to-mesenchymal transition (EMT) caused by the synergistic effects of TGFβ1 and Gas6 in NRK-52E cells. This inhibition was also observed in NEP25 mice. Taken together, these results suggest that CH5451098 could ameliorate kidney dysfunction in glomerular nephritis by inhibiting EMT in tubular cells. These results reveal that AXL strongly contributes to the disease progression of glomerular nephritis.

Axl Inhibitor R428 Enhances TRAIL-Mediated Apoptosis Through Downregulation of c-FLIP and Survivin Expression in Renal Carcinoma

R428, a selective small molecule Axl inhibitor, is known to have anti-cancer effects, such as inhibition of invasion and proliferation and induction of cell death in cancer cells. The Axl receptor tyrosine kinase is highly expressed in cancer cells and the level of Axl expression is associated with survival, metastasis, and drug resistance of many cancer cells. However, the effect of Axl inhibition on overcoming anti-cancer drugs resistance is unclear. Therefore, we investigated the capability of Axl inhibition as a therapeutic agent for the induction of TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) sensitivity. In this study, R428 markedly sensitized cancer cells to TRAIL-induced apoptotic cell death, but not in normal human skin fibroblast (HSF) and human umbilical vein cells (EA.hy926). Moreover, knockdown of Axl by siRNA also increased TRAIL-induced apoptosis. R428 decreased c-FLIP proteins levels via induction of miR-708 expression and survivin protein levels at the post-translational level, and we found that knockdown of Axl also decreased both c-FLIP and survivin protein expression. Overexpression of c-FLIP and survivin markedly inhibited R428 plus TRAIL-induced apoptosis. Furthermore, R428 sensitized cancer cells to multiple anti-cancer drugs-mediated cell death. Our results provide that inhibition of Axl could improve sensitivity to TRAIL through downregulation of c-FLIP and survivin expression in renal carcinoma cells. Taken together, Axl may be a tempting target to overcome TRAIL resistance.

p5RHH nanoparticle-mediated delivery of AXL siRNA inhibits metastasis of ovarian and uterine cancer cells in mouse xenografts

Ovarian and uterine serous cancers are extremely lethal diseases that often present at an advanced stage. The late-stage diagnosis of these patients results in the metastasis of their cancers throughout the peritoneal cavity leading to death. Improving survival for these patients will require identifying therapeutic targets, strategies to target them, and means to deliver therapies to the tumors. One therapeutic target is the protein AXL, which has been shown to be involved in metastasis in both ovarian and uterine cancer. An effective way to target AXL is to silence its expression with small interfering RNA (siRNA). We investigate the ability of the novel siRNA delivery platform, p5RHH, to deliver anti-AXL siRNA (siAXL) to tumor cells both in vitro and in vivo as well as examine the phenotypic effects of this siRNA interference. First, we present in vitro assays showing p5RHH-siAXL treatment reduces invasion and migration ability of ovarian and uterine cancer cells. Second, we show p5RHH nanoparticles target to tumor cells in vivo. Finally, we demonstrate p5RHH-siAXL treatment reduces metastasis in a uterine cancer mouse xenograft model, without causing an obvious toxicity. Collectively, these findings suggest that this novel therapy shows promise in the treatment of ovarian and uterine cancer patients.

Gas6 is dispensable for pubertal mammary gland development

Mammary gland development is a complex and dynamic process that occurs mainly postnatally. Ductal elongation and branching morphogenesis are regulated by a plethora of factors, including cytokines, hormones, growth factors and the extracellular matrix. Gas6 is a secreted gamma-carboxylated protein that binds to a family of receptors tyrosine kinase receptors known as the TAMR family (Tyro3, Axl, Mer). Gas6 function in developmental processes has been shown in nervous, reproductive and immune systems. In this study, we found that Gas6 is highly expressed in virgin adult mammary glands but declines during pregnancy and lactation. Specifically, Gas6 is highly expressed in luminal and basal mammary epithelial cells during puberty and adulthood, while TAMR expression is low. Mammary whole mount analysis revealed that Gas6 germline deletion does not impact ductal elongation, branching morphogenesis or terminal end bud formation. Masson's trichrome staining showed that collagen deposition is similar in Gas6-/- mice as compared to wildtype mice. Gas6-/- mammary glands presented an organized luminal and myoepithelial bilayer of cells, and the proportion of mammary stem cells was unchanged in Gas6-/- mammary glands as compared to wildtype. Finally, proliferation of epithelial cells and macrophage number were similar in both groups. These studies suggest that Gas6 is not essential for pubertal mammary gland development in nulliparous mice.

Stromal Gas6 promotes the progression of premalignant mammary cells

Tumor progression is regulated by a complex interplay between neoplastic cells and the tumor microenvironment. Tumor associated macrophages have been shown to promote breast cancer progression in advanced disease and more recently, in early stage cancers. However, little is known about the macrophage-derived factors that promote tumor progression in early stage lesions. Using a p53-null model of early stage mammary tumor progression, we found that Gas6 is highly expressed in pre-invasive lesions associated with increased infiltrating macrophages, as compared to those with few recruited macrophages. We show that F4/80⁺CD11b⁺ macrophages produce Gas6 in premalignant lesions in vivo, and that macrophage-derived Gas6 induces a tumor-like phenotype ex vivo. Using a 3-D co-culture system, we show that macrophage-derived Gas6 activates its receptor Axl and downstream survival signals including Akt and STAT3, which was accompanied by altered E-cadherin expression to induce a malignant morphology. In vivo studies demonstrated that deletion of stromal Gas6 delays early stage progression and decreases tumor formation, while tumor growth in established tumors remains unaffected. These studies suggest that macrophage-derived Gas6 is a critical regulator of the transition from premalignant to invasive cancer, and may lead to the development of unique biomarkers of neoplastic progression for patients with early stage breast cancer, including ductal carcinoma in situ.

In glomerular cells of puromycin aminonucleoside nephrosis rats both phosphorylated and total STAT3 levels increased during proteinuria

Recent studies showed that JAK/STAT pathway plays role in glomerular damages. The fact that STAT3 could be activated also by oxidative stress make Puromycin Aminonucleoside (PAN) Nephrosis model very appropriate for examination of STAT3 expression changes in glomerular pathology. Along with a control group, three PAN groups sacrificed on different days were formed by the i.p. injection of PAN for 5 consecutive days. Throughout the experiment, 24-hour-urines were collected on specific days and proteinuria levels were monitored. At the end of the experiments, tissue specimens were stained immunohistochemically for both total and phosphorylated STAT3 and evaluated subjectively. They were also examined ultrastructurally in transmission electron microscope. The proteinuria levels did not increase significantly on 5th day but showed a dramatic increase on 10th and 15th days. On 20th and 25th days, urinary protein levels gradually decreased. Ultrastructural examinations showed glomerular damages such as significant decrease in slit pore number, a significant gradual increase in glomerular basement membrane thickness and podocyte hypertrophy on 5th and 15th days; besides significant increase in mesangial matrix. The first significant increases in phosphorylated and total STAT3 levels occurred in 5th day and 15th day groups respectively. These increases diminished in 25th day group. Regarding all the findings, it was deduced that STAT3 is one of the active factors in glomerular pathologies.

Discovery of N-[4-(Quinolin-4-yloxy)phenyl]benzenesulfonamides as Novel AXL Kinase Inhibitors

The overexpression of AXL kinase has been described in many types of cancer. Due to its role in proliferation, survival, migration, and resistance, AXL represents a promising target in the treatment of the disease. In this study we present a novel compound family that successfully targets the AXL kinase. Through optimization and detailed SAR studies we developed low nanomolar inhibitors, and after further biological characterization we identified a potent AXL kinase inhibitor with favorable pharmacokinetic profile. The antitumor activity was determined in xenograft models, and the lead compounds reduced the tumor size by 40% with no observed toxicity as well as lung metastasis formation by 66% when compared to vehicle control.

AXL modulates extracellular matrix protein expression and is essential for invasion and metastasis in endometrial cancer

The receptor tyrosine kinase AXL promotes migration, invasion, and metastasis. Here, we evaluated the role of AXL in endometrial cancer. High immunohistochemical expression of AXL was found in 76% (63/83) of advanced-stage, and 77% (82/107) of high-grade specimens and correlated with worse survival in uterine serous cancer patients. In vitro, genetic silencing of AXL inhibited migration and invasion but had no effect on proliferation of ARK1 endometrial cancer cells. AXL-deficient cells showed significantly decreased expression of phospho-AKT as well as uPA, MMP-1, MMP-2, MMP-3, and MMP-9. In a xenograft model of human uterine serous carcinoma with AXL-deficient ARK1 cells, there was significantly less tumor burden than xenografts with control ARK1 cells. Together, these findings underscore the therapeutic potentials of AXL as a candidate target for treatment of metastatic endometrial cancer.

Targeting Gas6/TAM in cancer cells and tumor microenvironment

Growth arrest-specific 6, also known as Gas6, is a human gene encoding the Gas6 protein, which was originally found to be upregulated in growth-arrested fibroblasts. Gas6 is a member of the vitamin K-dependent family of proteins expressed in many human tissues and regulates several biological processes in cells, including proliferation, survival and migration, by binding to its receptors Tyro3, Axl and Mer (TAM). In recent years, the roles of Gas6/TAM signalling in cancer cells and the tumour microenvironment have been studied, and some progress has made in targeted therapy, providing new potential directions for future investigations of cancer treatment. In this review, we introduce the Gas6 and TAM receptors and describe their involvement in different cancers and discuss the roles of Gas6 in cancer cells, the tumour microenvironment and metastasis. Finally, we introduce recent studies on Gas6/TAM targeting in cancer therapy, which will assist in the experimental design of future analyses and increase the potential use of Gas6 as a therapeutic target for cancer.

Function of Axl receptor tyrosine kinase in non-small cell lung cancer

Axl receptor tyrosine kinase (hereafter Axl) is a member of the tyrosine-protein kinase receptor Tyro3, Axl and proto-oncogene tyrosine-protein kinase Mer family of receptor tyrosine kinases, possessing multiple different functions in normal cells. Axl is overexpressed and activated in numerous different human cancer types, triggering several signaling pathways and enhancing tumor progression. The present review assesses previous studies on the function of Axl in non-small cell lung cancer (NSCLC). Axl is overexpressed in the tumor tissues of a number of patients with NSCLC and is associated with poorer clinical outcomes; it promotes NSCLC tumor growth, invasion/metastasis, drug resistance and the epithelial-mesenchymal transition, thus providing a survival advantage to tumor cells. Therefore, Axl may be a promising target in NSCLC treatment.

CCR7 Is Important for Mesangial Cell Physiology and Repair

The homeostatic chemokine receptor CCR7 serves as key molecule in lymphocyte homing into secondary lymphoid tissues. Previous experiments from our group identified CCR7 also to be expressed by human mesangial cells. Exposing cultured human mesangial cells to the receptor ligand CCL21 revealed a positive effect on these cells regarding proliferation, migration, and survival. In the present study, we localized CCR7 and CCL21 during murine nephrogenesis. Analyzing wild-type and CCR7 deficient (CCR7^-/-) mice, we observed a retarded glomerulogenesis during renal development and a significantly decreased mesangial cellularity in adult CCR7^-/- mice, as a consequence of less mesangial cell proliferation between embryonic day E17.5 and week 5 postpartum. Cell proliferation assays and cell-wounding experiments confirmed reduced proliferative and migratory properties of mesangial cells cultured from CCR7^-/- kidneys. To further emphasize the role of CCR7 as important factor for mesangial biology, we examined the chemokine receptor expression in rats after induction of a mesangioproliferative glomerulonephritis. Here, we demonstrated for the first time that extra- and intraglomerular mesangial cells that were CCR7-negative in control rats exhibited a strong CCR7 expression during the phase of mesangial repopulation and proliferation.

Pharmacological effects of a vitamin K1 2,3-epoxide reductase (VKOR) inhibitor, 3-acetyl-5-methyltetronic acid, on cisplatin-induced fibrosis in rats

Cisplatin (CDDP) is a chemotherapeutic agent that is widely used in the treatment of lymphomas and solid malignancies. However, its clinical usage is limited by its severe side effects in the kidneys. Glomerular and tubular injuries in the kidneys commonly progress to interstitial fibrosis and, ultimately, the end stage of renal failure. We previously reported that 3-acetyl-5-methyltetronic acid (AMT) had inhibitory effects on rat renal vitamin K₁ 2,3-epoxide reductase (VKOR) in vitro and also suppressed mesangial cell proliferation and, consequently, the formation of fibrosis via the vitamin K-dependent activation of the growth arrest-specific 6 (Gas6)/Axl pathway in anti-Thy-1 glomerulonephritis (Thy-1 GN) in rats. In the present study, we demonstrated that AMT alleviated the progression of renal fibrosis in CDDP-treated rats. The repeated intravenous administration of AMT for 28 days dose-dependently suppressed increases in plasma urea nitrogen and plasma creatinine levels as well as creatinine clearance in CDDP-treated rats. Furthermore, the treatment suppressed the expression of α-smooth muscle actin (SMA)-positive cells and ameliorated the extracellular matrix accumulation of collagen III, indicating an antifibrotic effect. In conclusion, our toxicological and histopathological results demonstrated quantitatively the pharmacological inhibitory effects of AMT on the progression of renal fibrosis in CDDP-treated rats.

Molecular insights of Gas6/TAM in cancer development and therapy

Since growth arrest-specific gene 6 (Gas6) was discovered in 1988, numerous studies have highlighted the role of the Gas6 protein and its receptors Tyro3, Axl and Mer (collectively referred to as TAM), in proliferation, apoptosis, efferocytosis, leukocyte migration, sequestration and platelet aggregation. Gas6 has a critical role in the development of multiple types of cancers, including pancreatic, prostate, oral, ovarian and renal cancers. Acute myelocytic leukaemia (AML) is a Gas6-dependent cancer, and Gas6 expression predicts poor prognosis in AML. Interestingly, Gas6 also has a role in establishing tumour dormancy in the bone marrow microenvironment and in suppressing intestinal tumorigenesis. Numerous studies regarding cancer therapy have targeted Gas6 and TAM receptors with good results. However, some findings have suggested that Gas6 is associated with the development of resistance to cancer therapies. Concerning these significant effects of Gas6 in numerous cancers, we discuss the roles of Gas6 in cancer development in this review. First, we introduce basic knowledge on Gas6 and TAM receptors. Next, we describe and discuss the involvement of Gas6 and TAM receptors in cancers from different organ systems. Finally, we highlight the progress in therapies targeting Gas6 and TAM receptors. This review presents the significant roles of Gas6 in cancers from different systems and may contribute to the continued promotion of Gas6 as a therapeutic target.

Expression of Axl and its prognostic significance in human breast cancer

Breast cancer is the most common malignant cancer and second leading cause of cancer-related death among women, and its prevalence continues to increase. Axl overexpression has been identified in the many types of human cancer, and it has been demonstrated to participate in signaling pathways related to carcinogenesis and cancer development. In the present study, Axl expression was examined by performing immunohistochemical staining in 60 breast cancer tumors and 40 benign breast lesions (25 mammary dysplasia and 15 breast fibroadenoma). In total, 34 (56.67%) cancer tissues and 13 (32.5%) benign breast lesions were classified as exhibiting high levels of Axl expression, indicating a significant association between malignancy and high Axl expression. High Axl expression was also associated with estrogen receptor (ER) positivity (P=0.028), progesterone receptor (PR) positivity (P=0.007), and poor tumor differentiation (P=0.033). No significant associations were observed between Axl expression and age, tumor size, lymph node metastasis, tumor node metastasis staging, human epidermal growth factor receptor 2 and Ki67 antigen. The Kaplan-Meier survival analysis and Cox proportional hazard model both demonstrated that there was no statistical difference between Axl expression and breast cancer prognosis. However, it remains unclear whether the expression of Axl is correlated with the prognosis of luminal type breast cancer patients.

Gas6 Promotes Oligodendrogenesis and Myelination in the Adult Central Nervous System and After Lysolecithin-Induced Demyelination

A key aim of therapy for multiple sclerosis (MS) is to promote the regeneration of oligodendrocytes and remyelination in the central nervous system (CNS). The present study provides evidence that the vitamin K-dependent protein growth arrest specific 6 (Gas6) promotes such repair in in vitro cultures of mouse optic nerve and cerebellum. We first determined expression of Gas6 and TAM (Tyro3, Axl, Mer) receptors in the mouse CNS, with all three TAM receptors increasing in expression through postnatal development, reaching maximal levels in the adult. Treatment of cultured mouse optic nerves with Gas6 resulted in significant increases in oligodendrocyte numbers as well as expression of myelin basic protein (MBP). Gas6 stimulation also resulted in activation of STAT3 in optic nerves as well as downregulation of multiple genes involved in MS development, including matrix metalloproteinase-9 (MMP9), which may decrease the integrity of the blood-brain barrier and is found upregulated in MS lesions. The cytoprotective effects of Gas6 were examined in in vitro mouse cerebellar slice cultures, where lysolecithin was used to induce demyelination. Cotreatment of cerebellar slices with Gas6 significantly attenuated demyelination as determined by MBP immunostaining, and Gas6 activated Tyro3 receptor through its phosphorylation. In conclusion, these results demonstrate that Gas6/TAM signaling stimulates the generation of oligodendrocytes and increased myelin production via Tyro3 receptor in the adult CNS, including repair after demyelinating injury. Furthermore, the effects of Gas6 on STAT3 signaling and matrix MMP9 downregulation indicate potential glial cell repair and immunoregulatory roles for Gas6, indicating that Gas6-TAM signaling could be a potential therapeutic target in MS and other neuropathologies.

mRNAs and miRNAs in whole blood associated with lung hyperplasia, fibrosis, and bronchiolo-alveolar adenoma and adenocarcinoma after multi-walled carbon nanotube inhalation exposure in mice

Inhalation exposure to multi-walled carbon nanotubes (MWCNT) in mice results in inflammation, fibrosis and the promotion of lung adenocarcinoma; however, the molecular basis behind these pathologies is unknown. This study determined global mRNA and miRNA profiles in whole blood from mice exposed by inhalation to MWCNT that correlated with the presence of lung hyperplasia, fibrosis, and bronchiolo-alveolar adenoma and adenocarcinoma. Six-week-old, male, B6C3F1 mice received a single intraperitoneal injection of either the DNA-damaging agent methylcholanthrene (MCA, 10 µg g(-1) body weight) or vehicle (corn oil). One week after injections, mice were exposed by inhalation to MWCNT (5 mg m(-3), 5 hours per day, 5 days per week) or filtered air (control) for a total of 15 days. At 17 months post-exposure, mice were euthanized and examined for the development of pathological changes in the lung, and whole blood was collected and analyzed using microarray analysis for global mRNA and miRNA expression. Numerous mRNAs and miRNAs in the blood were significantly up- or down-regulated in animals developing pathological changes in the lung after MCA/corn oil administration followed by MWCNT/air inhalation, including fcrl5 and miR-122-5p in the presence of hyperplasia, mthfd2 and miR-206-3p in the presence of fibrosis, fam178a and miR-130a-3p in the presence of bronchiolo-alveolar adenoma, and il7r and miR-210-3p in the presence of bronchiolo-alveolar adenocarcinoma, among others. The changes in miRNA and mRNA expression, and their respective regulatory networks, identified in this study may potentially serve as blood biomarkers for MWCNT-induced lung pathological changes.

Severity and Frequency of Proximal Tubule Injury Determines Renal Prognosis

AKI increases the risk of developing CKD, but the mechanisms linking AKI to CKD remain unclear. Because proximal tubule injury is the mainstay of AKI, we postulated that proximal tubule injury triggers features of CKD. We generated a novel mouse model to induce proximal tubule-specific adjustable injury by inducing the expression of diphtheria toxin (DT) receptor with variable prevalence in proximal tubules. Administration of high-dose DT in mice expressing the DT receptor consistently caused severe proximal tubule-specific injury associated with interstitial fibrosis and reduction of erythropoietin production. Mild proximal tubule injury from a single injection of low-dose DT triggered reversible fibrosis, whereas repeated mild injuries caused sustained interstitial fibrosis, inflammation, glomerulosclerosis, and atubular glomeruli. DT-induced proximal tubule-specific injury also triggered distal tubule injury. Furthermore, injured tubular cells cocultured with fibroblasts stimulated induction of extracellular matrix and inflammatory genes. These results support the existence of proximal-distal tubule crosstalk and crosstalk between tubular cells and fibroblasts. Overall, our data provide evidence that proximal tubule injury triggers several features of CKD and that the severity and frequency of proximal tubule injury determines the progression to CKD.

Axl modulates immune activation of smooth muscle cells in vein graft remodeling

The pathophysiological mechanisms of the immune activation of smooth muscle cells are not well understood. Increased expression of Axl, a receptor tyrosine kinase, was recently found in arteries from patients after coronary bypass grafts. In the present study, we hypothesized that Axl-dependent immune activation of smooth muscle cells regulates vein graft remodeling. We observed a twofold decrease in intimal thickening after vascular and systemic depletion of Axl in vein grafts. Local depletion of Axl had the greatest effect on immune activation, whereas systemic deletion of Axl reduced intima due to an increase in apoptosis in vein grafts. Primary smooth muscle cells isolated from Axl knockout mice had reduced proinflammatory responses by prevention of the STAT1 pathway. The absence of Axl increased suppressor of cytokine signaling (SOCS)1 expression in smooth muscle cells, a major inhibitory protein for STAT1. Ultrasound imaging suggested that vascular depletion of Axl reduced vein graft stiffness. Axl expression determined the STAT1-SOCS1 balance in vein graft intima and progression of the remodeling. The results of this investigation demonstrate that Axl promotes STAT1 signaling via inhibition of SOCS1 in activated smooth muscle cells in vein graft remodeling.

Axl receptor tyrosine kinase is a potential therapeutic target in renal cell carcinoma

Background:

Axl plays multiple roles in tumourigenesis in several cancers. Here we evaluated the expression and biological function of Axl in renal cell carcinoma (RCC).

Methods:

Axl expression was analysed in a tissue microarray of 174 RCC samples by immunostaining and a panel of 11 normal tumour pairs of human RCC tissues by western blot, as well as in RCC cell lines by both western blot and quantitative PCR. The effects of Axl knockdown in RCC cells on cell growth and signalling were investigated. The efficacy of a humanised Axl targeting monoclonal antibody hMAb173 was tested in histoculture and tumour xenograft.

Results:

We have determined by immunohistochemistry (IHC) that Axl is expressed in 59% of RCC array samples with moderate to high in 20% but not expressed in normal kidney tissue. Western blot analysis of 11 pairs of tumour and adjacent normal tissue show high Axl expression in 73% of the tumours but not normal tissue. Axl is also expressed in RCC cell lines in which Axl knockdown reduces cell viability and PI3K/Akt signalling. The Axl antibody hMAb173 significantly induced RCC cell apoptosis in histoculture and inhibited the growth of RCC tumour in vivo by 78%. The hMAb173-treated tumours also had significantly reduced Axl protein levels, inhibited PI3K signalling, decreased proliferation, and induced apoptosis.

Conclusions:

Axl is highly expressed in RCC and critical for RCC cell survival. Targeting Axl is a potential approach for RCC treatment.

Exploring the origin and limitations of kidney regeneration

Epidemiological findings indicate that acute kidney injury (AKI) increases the risk for chronic kidney disease (CKD), although the molecular mechanism remains unclear. Genetic fate mapping demonstrated that nephrons, functional units in the kidney, are repaired by surviving nephrons after AKI. However, the cell population that repairs damaged nephrons and their repair capacity limitations remain controversial. To answer these questions, we generated a new transgenic mouse strain in which mature proximal tubules, the segment predominantly damaged during AKI, could be genetically labelled at desired time points. Using this strain, massive proliferation of mature proximal tubules is observed during repair, with no dilution of the genetic label after the repair process, demonstrating that proximal tubules are repaired mainly by their own proliferation. Furthermore, acute tubular injury caused significant shortening of proximal tubules associated with interstitial fibrosis, suggesting that proximal tubules have a limited capacity to repair. Understanding the mechanism of this limitation might clarify the mechanism of the AKI-to-CKD continuum.

Two enzymes catalyze vitamin K 2,3-epoxide reductase activity in mouse: VKORC1 is highly expressed in exocrine tissues while VKORC1L1 is highly expressed in brain

VKORC1 and VKORC1L1 are enzymes that both catalyze the reduction of vitamin K2,3-epoxide via vitamin K quinone to vitamin K hydroquinone. VKORC1 is the key enzyme of the classical vitamin K cycle by which vitamin K-dependent (VKD) proteins are γ-carboxylated by the hepatic γ-glutamyl carboxylase (GGCX). In contrast, the VKORC1 paralog enzyme, VKORC1L1, is chiefly responsible for antioxidative function by reduction of vitamin K to prevent damage by intracellular reactive oxygen species. To investigate tissue-specific vitamin K 2,3-epoxide reductase (VKOR) function of both enzymes, we quantified mRNA levels for VKORC1, VKORC1L1, GGCX, and NQO1 and measured VKOR enzymatic activities in 29 different mouse tissues. VKORC1 and GGCX are highly expressed in liver, lung and exocrine tissues including mammary gland, salivary gland and prostate suggesting important extrahepatic roles for the vitamin K cycle. Interestingly, VKORC1L1 showed highest transcription levels in brain. Due to the absence of detectable NQO1 transcription in liver, we assume this enzyme has no bypass function with respect to activation of VKD coagulation proteins. Our data strongly suggest diverse functions for the vitamin K cycle in extrahepatic biological pathways.

Axl is a novel target of withaferin A in the induction of apoptosis and the suppression of invasion

Withaferin A, a withanolide derived from the medicinal plant Withania somnifera, has been reported to exhibit anti-tumorigenic activity against various cancer cells. In this study, we show that withaferin A inhibits the constitutive and recombinant human growth-arrest-specific protein 6 (rhGas6)-induced phosphorylation of Axl and STAT3. In addition, withaferin A also induces the down-regulation of Axl protein expression in a lysosome-dependent manner and inhibits rhGas6-induced wound healing and cell migration. Furthermore, the overexpression of Axl attenuates withaferin A-induced apoptosis. Taken together, the data from the present study indicate that the withaferin A-mediated down-regulation of the Gas6/Axl signaling pathway mediates the inhibition of cell migration and the induction of apoptosis.

Growth arrest-specific gene 6 protein promotes the proliferation and migration of endothelial progenitor cells through the PI3K/AKT signaling pathway

Endothelial progenitor cells (EPCs) play an important role in endothelial repair and vascular regeneration. Growth arrest-specific gene 6 (Gas6) is a novel key regulator of the vascular system, which is linked to a number of cardiovascular diseases. However, the effects of Gas6 on EPCs have not been elucidated to date. The present study was designed to determine the biological function of EPCs treated with Gas6 and to eludicate the underlying mechanisms. EPCs were isolated from umbilical cord blood and treated with various concentrations (25, 50, 100 and 200 ng/ml) of Gas6. The proliferation, migration and angiogenesis of the Gas6-treated EPCs were evaluated by MTT assay, Transwell assay and in vitro tube formation assay, respectively. The phosphorylation status of AKT and ERK was evaluated by western blot analysis. The results demonstrated that treatment with Gas6 enhanced the proliferation and migration of the EPCs in a dose-dependent manner. However, Gas6 did not promote the differentiation of EPCs on Matrigel. Gas6 induced the phosphorylation of AKT, but not that of ERK. The enhanced proliferation and migration induced by Gas6 was markedly suppressed by the inhibitor of PI3K but not by that of ERK. These results suggest that Gas6 activates the AKT signaling pathway, which, in turn, promotes the proliferation and migration of EPCs.

Bmp7 maintains undifferentiated kidney progenitor population and determines nephron numbers at birth

The number of nephrons, the functional units of the kidney, varies among individuals. A low nephron number at birth is associated with a risk of hypertension and the progression of renal insufficiency. The molecular mechanisms determining nephron number during embryogenesis have not yet been clarified. Germline knockout of bone morphogenetic protein 7 (Bmp7) results in massive apoptosis of the kidney progenitor cells and defects in early stages of nephrogenesis. This phenotype has precluded analysis of Bmp7 function in the later stage of nephrogenesis. In this study, utilization of conditional null allele of Bmp7 in combination with systemic inducible Cre deleter mice enabled us to analyze Bmp7 function at desired time points during kidney development, and to discover the novel function of Bmp7 to inhibit the precocious differentiation of the progenitor cells to nephron. Systemic knockout of Bmp7 in vivo after the initiation of kidney development results in the precocious differentiation of the kidney progenitor cells to nephron, in addition to the prominent apoptosis of progenitor cells. We also confirmed that in vitro knockout of Bmp7 in kidney explant culture results in the accelerated differentiation of progenitor population. Finally we utilized colony-forming assays and demonstrated that Bmp7 inhibits epithelialization and differentiation of the kidney progenitor cells. These results indicate that the function of Bmp7 to inhibit the precocious differentiation of the progenitor cells together with its anti-apoptotic effect on progenitor cells coordinately maintains renal progenitor pool in undifferentiated status, and determines the nephron number at birth.

IL-18 induces profibrotic renal tubular cell injury via STAT3 activation

IL-18 is an important mediator of obstruction-induced renal fibrosis and renal tubular epithelial cell (TEC) injury. IL-18's proinflammatory properties have been attributed, in part, to NF-κB activation and the stimulation of cytokine gene expression; however, STAT3 has increasingly been shown to mediate renal fibrotic injury. We therefore hypothesized that IL-18 mediates profibrotic TEC injury via STAT3 activation. Male C57BL6 wild-type mice and transgenic mice for human IL-18-binding protein were subjected to unilateral ureteral obstruction or sham operation. The kidneys were harvested 1 or 2 wk afterward and analyzed for active STAT3 (p-STAT3) expression (Western blotting, immunohistochemistry) and suppressor of cytokine signaling 3 (SOCS3) expression. In a separate arm, renal tubular cells (HK-2) were directly stimulated with IL-18 for 2 days with or without the STAT3 inhibitor S3I-201 (50 μM). Cell lysates were then analyzed for p-STAT3 and SOCS3 expression, profibrotic cellular changes (collagen and α-SMA expression), and tubular cell apoptosis. p-STAT3 and SOCS3 expression increased significantly in response to obstruction; however, a significant reduction in p-STAT3 and SOCS3 expression occurred following 1 wk, but not 2 wk, of obstruction in the presence of IL-18 neutralization. In vitro results similarly demonstrate increased p-STAT3, SOCS3, α-SMA, and collagen III expression, and increased collagen production and TEC apoptosis in response to IL-18 stimulation, but the response was significantly diminished in the presence of STAT3 inhibition. These results demonstrate that IL-18-induces profibrotic cellular changes and collagen production in TECs via STAT3 activation.

Glycoxidised LDL induced the upregulation of Axl receptor tyrosine kinase and its ligand in mouse mesangial cells

Aim/Hypothesis

Low-density lipoprotein (LDL) is subjected to glycoxidation in diabetes, and a novel signalling mechanism by which glycoxidised LDL functions in glomerular mesangial cells remains to be ascertained.

Methods

We performed gene expression analysis in mouse glomerular mesangial cells treated with LDL modified by glycation and oxidation (GO-LDL, 100 µg/ml) for 48 h by using DNA microarray analysis and quantitative real-time PCR. We examined the GO-LDL-specific changes in gene and protein expression in mesangial cells and glomeruli of type 2 diabetic Zucker diabetic fatty (ZDF) rats.

Results

By microarray profiling, we noted that GO-LDL treatment increased Axl receptor tyrosine kinase (Axl) mRNA expression (∼2.5-fold, p<0.05) compared with normal LDL (N-LDL) treatment in mesangial cells. Treatment with GO-LDL also increased the protein levels of Axl and its ligand Gas6 as measured by Western blotting. These increases were inhibited by neutralising Axl receptor-specific antibody. Silencing Gas6 by siRNA inhibited GO-LDL-induced Axl expression in mesangial cells. Axl and Gas6 protein were also increased in cells cultured in high glucose (30 mM) or methylglyoxal (200 µM). Gas6 treatment increased the expression and secretion of TGF-β1 protein, a key regulator of extracellular matrix expression in the glomeruli of diabetic kidneys. Immunohistochemical analyses of glomeruli from 20-week-old ZDF rats exhibited increased Axl protein expression. Rottlerin, a selective PKC-δ inhibitor, completely blocked Gas6-induced TGF-β1 expression.

Conclusions/Interpretation

These data suggest that LDL modified by glycoxidation may mediate Axl/Gas6 pathway activation, and this mechanism may play a significant role in the pathogenesis of diabetic nephropathy.

The role of the Janus kinase family/signal transducer and activator of transcription signaling pathway in fibrotic renal disease

Over the past several years, a number of cytokines and growth factors including transforming growth factor β1, tumor necrosis factor α, and angiotensin II have been shown to play a crucial role in renal fibrosis. The Janus kinase family (JAK) and signal transducers and activators of transcription (STATs) constitute one of the primary signaling pathways that regulate cytokine expression, and the JAK/STAT signaling pathway has increasingly been implicated in the pathophysiology of renal disease. This review examines the role of the JAK/STAT signaling pathway in fibrotic renal disease. The JAK/STAT signaling pathway is activated in a variety of renal diseases and has been implicated in the pathophysiology of renal fibrosis. Experimental evidence suggests that inhibition of the JAK/STAT signaling pathway, in particular JAK2 and STAT3, may suppress renal fibrosis and protect renal function. However, it is incompletely understood which cells activate the JAK/STAT signaling pathway and which JAK/STAT signaling pathway is activated in each renal disease. Research regarding JAK/STAT signaling and its contribution to renal disease is still ongoing in humans. Future studies are required to elucidate the potential role of JAK/STAT signaling inhibition as a therapeutic strategy in the attenuation of renal fibrosis.

Cross-phosphorylation, signaling and proliferative functions of the Tyro3 and Axl receptors in Rat2 cells

The dysregulation of receptor protein tyrosine kinase (RPTK) function can result in changes in cell proliferation, cell growth and metastasis leading to malignant transformation. Among RPTKs, the TAM receptor family composed of three members Tyro3, Axl, and Mer has been recognized to have a prominent role in cell transformation. In this study we analyzed the consequences of Tyro3 overexpression on cell proliferation, activation of signaling pathways and its functional interactions with Axl. Overexpression of Tyro3 in the Rat2 cell line that expresses Axl, but not Mer or Tyro3, resulted in a 5 fold increase in cell proliferation. This increase was partially blocked by inhibitors of the mitogen-activated protein kinase (MAPK) signaling pathway but not by inhibitors of the phosphatidylinositol 3-kinase (PI(3)K) signaling pathway. Consistent with these findings, an increase in ERK1/2 phosphorylation was detected with Tyro3 but not with Axl overexpression. In contrast, activation of Axl stimulated the PI(3)K pathway, which was mitigated by co-expression of Tyro3. The overexpression of Tyro3 enhanced Gas6-mediated Axl phosphorylation, which was not detected upon overexpression of a “kinase dead” form of Tyro3 (kdTyro3). In addition, the overexpression of Axl induced kdTyro3 phosphorylation. Co-immunoprecipitation experiments confirmed that the Axl and Tyro3 receptors are closely associated. These findings show that overexpression of Tyro3 in the presence of Axl promotes cell proliferation, and that co-expression of Axl and Tyro3 can affect the outcome of Gas6-initiated signaling. Furthermore, they demonstrate a functional interaction between the members of the TAM receptor family which can shed light on the molecular mechanisms underlying the functional consequences of TAM receptor activation in cell transformation, neural function, immune function, and reproductive function among others.

Loss of the BMP antagonist USAG-1 ameliorates disease in a mouse model of the progressive hereditary kidney disease Alport syndrome

The glomerular basement membrane (GBM) is a key component of the filtering unit in the kidney. Mutations involving any of the collagen IV genes (COL4A3, COL4A4, and COL4A5) affect GBM assembly and cause Alport syndrome, a progressive hereditary kidney disease with no definitive therapy. Previously, we have demonstrated that the bone morphogenetic protein (BMP) antagonist uterine sensitization-associated gene-1 (USAG-1) negatively regulates the renoprotective action of BMP-7 in a mouse model of tubular injury during acute renal failure. Here, we investigated the role of USAG-1 in renal function in Col4a3-/- mice, which model Alport syndrome. Ablation of Usag1 in Col4a3-/- mice led to substantial attenuation of disease progression, normalization of GBM ultrastructure, preservation of renal function, and extension of life span. Immunohistochemical analysis revealed that USAG-1 and BMP-7 colocalized in the macula densa in the distal tubules, lying in direct contact with glomerular mesangial cells. Furthermore, in cultured mesangial cells, BMP-7 attenuated and USAG-1 enhanced the expression of MMP-12, a protease that may contribute to GBM degradation. These data suggest that the pathogenetic role of USAG-1 in Col4a3-/- mice might involve crosstalk between kidney tubules and the glomerulus and that inhibition of USAG-1 may be a promising therapeutic approach for the treatment of Alport syndrome.

Reduction of Stat3 activity attenuates HIV-induced kidney injury

HIV-1 Nef induces podocyte proliferation and dedifferentiation by activating the Stat3 and MAPK1,2 pathways. Activation of Stat3 also occurs in human kidneys affected by HIV-associated nephropathy (HIVAN), but its contribution to the development of HIVAN is unknown. Here, we generated HIV-1 transgenic mice (Tg26) with either 75% Stat3 activity (Tg26-SA/+) or 25% Stat3 activity (Tg26-SA/-). The kidneys of Tg26-SA/+ mice, but not Tg26-SA/- mice, showed increased Stat3 phosphorylation. The Tg26-SA/+ phenotype was not different from Tg26 mice, but Tg26-SA/- mice developed significantly less proteinuria, glomerulosclerosis, and tubulointerstitial injury. Tg26-SA/+ mice exhibited reduced expression of podocyte differentiation markers and increased expression of VEGF and proliferation markers as compared to Tg26-SA/- mice. Primary podocytes isolated from Tg26-SA/+ mice showed increased Stat3 phosphorylation and reduced expression of podocyte differentiation markers. The tubulointerstitial compartment and isolated tubules of Tg26-SA/+ mice also had increased Stat3 phosphorylation and expression of Stat3 target genes. We confirmed that the expression of the HIV-1 transgene and reduction of Stat3 activity did not affect T and B cell development. In conclusion, Stat3 plays a critical role in the pathogenesis of HIVAN.

Inhibition of zymosan-induced kidney dysfunction by tyrphostin AG-490

Background

Zymosan-induced shock has been associated with an increased production of pro-inflammatory cytokines and mediators, causing a generalized dysfunction of liver, lung and kidneys. Herein, we investigate the effects of tyrphostin AG-490 on the early inflammation and on the late renal injury provoked by zymosan injection.

Methods

Shock was induced by intraperitoneal injection of zymosan in a dose of 0.8–1.0 mg/g body weight in BALB/c mice and 0.8 mg/g body weight in SCID mice. Tyrphostin AG-490 was administered intraperitoneally in a dose of 5 mg/kg immediately after shock induction. Blood, peritoneal lavage and kidneys were collected at certain time points after zymosan injection. The levels of MIP-1α, RANTES, IL-6, IL-10, α1-antitrypsin and C5a in plasma were determined by ELISA. The number of IL-10-secreting cells in peritoneum was assayed by ELISPOT. Kidney function was monitored by measurement of urine/plasma creatinine levels and proteinuria. Histological assessment of renal injury was performed in a blinded fashion after hematoxylin/eosin staining. Immunohistochemistry analyses were used to evaluate the expression of C5aR, STAT1, STAT3 and the binding ability of IgGs in kidneys.

Results

Tyrphostin AG-490 attenuated the early phase of zymosan-induced shock via inhibition of MIP-1α, RANTES and C5a plasma levels and via elevation of IL-10 in plasma. The drug increased IL-10 production in peritoneum and the number of IL-10-secreting peritoneal cells. AG-490 was able to retain the time of coagulation and the level of α1-antitrypsin to normal values. At the late stage of shock, AG-490 decreased scores of tubular injury, cell infiltration and glomerular lesions in parallel with diminished creatinine plasma level and protein excretion. These beneficial effects of AG-490 were related to lowered levels of circulating IL-6, MIP-1α and C5a, and to inhibited expression of STAT1, STAT3 and C5aR in kidneys. The drug diminished the production of zymosan-specific IgG antibodies and hindered the glomeruli from IgGs recognition.

Conclusion

Tyrphostin AG-490 reduced the magnitude of the initial inflammatory response in zymosan-induced shock and prevented the development of severe kidney dysfunction. Our data suggest that the drug might be used as a therapeutic approach in cases where shock is combined with acute renal injury.

Mer tyrosine kinase (MerTK) promotes macrophage survival following exposure to oxidative stress

The MerTK plays several important roles in normal macrophage physiology, including regulation of cytokine secretion and clearance of apoptotic cells. Mer signaling in other cell types, including malignant cells that ectopically overexpress the RTK, leads to downstream prosurvival pathway activation. We explored the hypothesis that Mer has a prosurvival role in macrophages exposed to oxidative stress. H(2)O(2) treatment of peritoneal exudate murine macrophages and J774 cells rapidly stimulated Mer phosphorylation in a concentration-dependent manner. Mer phosphorylation was dependent on the ligand Gas6, as treatment with warfarin or MerFc (a fusion protein of the extracellular domain of Mer and the Fc portion of human Ig), inhibitors of Gas6 activity, blocked H(2)O(2)-mediated activation of Mer. Antiapoptotic signals including pAkt and pErk 1/2 were increased dramatically (threefold and 4.5-fold, respectively) in WT Mer-positive macrophages compared with Mer KO macrophages stimulated with H(2)O(2). In a consistent manner, Mer expression led to decreased cleavage of proapoptotic indicators PARP and Caspase-3. Furthermore, Mer provided up to twofold enhanced cellular survival to primary macrophages exposed to H(2)O(2). These data represent the first report of Mer activation in response to oxidative stress and demonstrate the ability of Mer RTK to promote macrophage survival in disease states that involve an oxidative stress environment.

Knockdown of Stat3 activity in vivo prevents diabetic glomerulopathy

Recent studies suggest that Stat3, a transcription factor that mediates cytokine signaling, plays a critical role in the pathogenesis of diabetic nephropathy. Complete Stat3 gene knockout is embryonic lethal; therefore, we crossed Stat3+/- mice with Stat3 mutant mice (SA/SA) that lack full Stat3 activity. This strategy generated Stat3SA/- mice (25% activity) and Stat3SA/+ mice (75% activity), which were made diabetic using streptozotocin in order to define the role of Stat3 in diabetic kidney disease. While the glomerular number was not different between these two groups of mice, the diabetic SA/- mice had significantly less proteinuria, mesangial expansion, glomerular cell proliferation, and macrophage infiltration than the diabetic SA/+ mice. The reduction in Stat3 activity did not affect glomerular hyperfiltration seen after the induction of diabetes, as it was increased to the same degree in both groups of mice. Phosphorylation of Stat3 was markedly increased in the glomeruli of diabetic SA/+ mice compared to diabetic SA/- mice. The expression of inflammatory markers, IL-6, MCP-1, and activated NF-kappaB; type IV collagen, TGF-beta, and ICAM-1 mRNA; or type IV collagen and TGF-beta protein, were all found to be significantly less in glomeruli isolated from diabetic SA/- mice, as compared with diabetic SA/+ mice. Our study shows that Stat3 plays a critical role in the regulation of inflammation and abnormal matrix synthesis at an early stage of DN.

The Axl/Gas6 pathway is required for optimal cytokine signaling during human natural killer cell development

Interleukin-15 (IL-15) is essential for natural killer (NK) cell differentiation. In this study, we assessed whether the receptor tyrosine kinase Axl and its ligand, Gas6, are involved in IL-15-mediated human NK differentiation from CD34(+) hematopoietic progenitor cells (HPCs). Blocking the Axl-Gas6 interaction with a soluble Axl fusion protein (Axl-Fc) or the vitamin K inhibitor warfarin significantly diminished the absolute number and percentage of CD3(-)CD56(+) NK cells derived from human CD34(+) HPCs cultured in the presence of IL-15, probably resulting in part from reduced phosphorylation of STAT5. In addition, CD3(-)CD56(+) NK cells derived from culture of CD34(+) HPCs with IL-15 and Axl-Fc had a significantly diminished capacity to express interferon-gamma or its master regulator, T-BET. Culture of CD34(+) HPCs in the presence of c-Kit ligand and Axl-Fc resulted in a significant decrease in the frequency of NK precursor cells responding to IL-15, probably the result of reduced c-Kit phosphorylation. Collectively, our data suggest that the Axl/Gas6 pathway contributes to normal human NK-cell development, at least in part via its regulatory effects on both the IL-15 and c-Kit signaling pathways in CD34(+) HPCs, and to functional NK-cell maturation via an effect on the master regulatory transcription factor T-BET.

Altered gene expression in highly purified enterocytes from patients with active coeliac disease

Background

Coeliac disease is a multifactorial inflammatory disorder of the intestine caused by ingestion of gluten in genetically susceptible individuals. Genes within the HLA-DQ locus are considered to contribute some 40% of the genetic influence on this disease. However, information on other disease causing genes is sparse. Since enterocytes are considered to play a central role in coeliac pathology, the aim of this study was to examine gene expression in a highly purified isolate of these cells taken from patients with active disease. Epithelial cells were isolated from duodenal biopsies taken from five coeliac patients with active disease and five non-coeliac control subjects. Contaminating T cells were removed by magnetic sorting. The gene expression profile of the cells was examined using microarray analysis. Validation of significantly altered genes was performed by real-time RT-PCR and immunohistochemistry.

Results

Enterocyte suspensions of high purity (98–99%) were isolated from intestinal biopsies. Of the 3,800 genes investigated, 102 genes were found to have significantly altered expression between coeliac disease patients and controls (p < 0.05). Analysis of these altered genes revealed a number of biological processes that are potentially modified in active coeliac disease. These processes include events likely to contibute to coeliac pathology, such as altered cell proliferation, differentiation, survival, structure and transport.

Conclusion

This study provides a profile of the molecular changes that occur in the intestinal epithelium of coeliac patients with active disease. Novel candidate genes were revealed which highlight the contribution of the epithelial cell to the pathogenesis of coeliac disease.

Activation of signal transducer and activator of transcription 3 correlates with cell proliferation and renal injury in human glomerulonephritis

BACKGROUND

Signal transducer and activator of transcription (STAT) 3 plays an important role in the regulation of cell proliferation. However, the mechanism of STAT3 activation in human glomerulonephritis is unclear.

METHODS

STAT3 activation was determined using immunohistochemistry for phosphorylated STAT3 (p-STAT3) in normal human kidney and various types of glomerulonephritis. We also identified the cell exhibiting activated p-STAT3 expression in human glomerulonephritis and correlated STAT3 activation with renal function and histologic injury.

RESULTS

p-STAT3 staining was identified in glomeruli and some tubules in normal human kidney. p-STAT3 positive glomerular cells were significantly increased in lupus nephritis, IgA nephropathy and vasculitis compared with normal kidney. p-STAT3 positive tubulointerstitial cells were significantly increased in IgA nephropathy and vasculitis compared with normal kidney. Glomerular and tubulointerstitial p-STAT3 staining was significantly decreased after steroid therapy. There was a significant correlation between the number of p-STAT3 positive cells and the number of PCNA positive glomerular and tubulointerstitial cells in all cases of glomerulonephritis. Furthermore, renal function inversely correlated with the number of p-STAT3 positive glomerular and tubulointerstitial cells in all cases of glomerulonephritis.

CONCLUSIONS

The present study has identified STAT3 activation in normal human kidney and a marked increase in STAT3 activation in many forms of glomerulonephritis. The correlation of STAT3 activation with clinical and histologic parameters suggests that this pathway plays an important role in the pathogenesis of kidney disease. Furthermore, localization of STAT3 activation to individual cell types suggests that this pathway may play a pivotal role in promoting renal inflammation and fibrosis.

Vitamin K-dependent actions of Gas6

Gas6 (growth arrest-specific gene 6) is the last addition to the family of plasma vitamin K-dependent proteins. Gas6 was cloned and characterized in 1993 and found to be similar to the plasma anticoagulant protein S. Soon after it was recognized as a growth factor-like molecule, as it interacted with receptor tyrosine kinases (RTKs) of the TAM family; Tyro3, Axl, and MerTK. Since then, the role of Gas6, protein S, and the TAM receptors has been found to be important in inflammation, hemostasis, and cancer, making this system an interesting target in biomedicine. Gas6 employs a unique mechanism of action, interacting through its vitamin K-dependent Gla module with phosphatidylserine-containing membranes and through its carboxy-terminal LG domains with the TAM membrane receptors. The fact that these proteins are affected by anti-vitamin K therapy is discussed in detail.