Derivation and transcriptional reprogramming of border-forming wound repair astrocytes after spinal cord injury or stroke in mice.

Central nervous system (CNS) lesions become surrounded by neuroprotective borders of newly proliferated reactive astrocytes; however, fundamental features of these cells are poorly understood. Here we show that following spinal cord injury or stroke, 90% and 10% of border-forming astrocytes derive, respectively, from proliferating local astrocytes and oligodendrocyte progenitor cells in adult mice of both sexes. Temporal transcriptome analysis, single-nucleus RNA sequencing and immunohistochemistry show that after focal CNS injury, local mature astrocytes dedifferentiate, proliferate and become transcriptionally reprogrammed to permanently altered new states, with persisting downregulation of molecules associated with astrocyte-neuron interactions and upregulation of molecules associated with wound healing, microbial defense and interactions with stromal and immune cells. These wound repair astrocytes share morphologic and transcriptional features with perimeningeal limitans astrocytes and are the predominant source of neuroprotective borders that re-establish CNS integrity around lesions by separating neural parenchyma from stromal and immune cells as occurs throughout the healthy CNS.

Reactive astrocytes transduce inflammation in a blood-brain barrier model through a TNF-STAT3 signaling axis and secretion of alpha 1-antichymotrypsin.

Astrocytes are critical components of the neurovascular unit that support blood-brain barrier (BBB) function. Pathological transformation of astrocytes to reactive states can be protective or harmful to BBB function. Here, using a human induced pluripotent stem cell (iPSC)-derived BBB co-culture model, we show that tumor necrosis factor (TNF) transitions astrocytes to an inflammatory reactive state that causes BBB dysfunction through activation of STAT3 and increased expression of SERPINA3, which encodes alpha 1-antichymotrypsin (α1ACT). To contextualize these findings, we correlated astrocytic STAT3 activation to vascular inflammation in postmortem human tissue. Further, in murine brain organotypic cultures, astrocyte-specific silencing of Serpina3n reduced vascular inflammation after TNF challenge. Last, treatment with recombinant Serpina3n in both ex vivo explant cultures and in vivo was sufficient to induce BBB dysfunction-related molecular changes. Overall, our results define the TNF-STAT3-α1ACT signaling axis as a driver of an inflammatory reactive astrocyte signature that contributes to BBB dysfunction.

CRISPRi screens in human iPSC-derived astrocytes elucidate regulators of distinct inflammatory reactive states.

Astrocytes become reactive in response to insults to the central nervous system by adopting context-specific cellular signatures and outputs, but a systematic understanding of the underlying molecular mechanisms is lacking. In this study, we developed CRISPR interference screening in human induced pluripotent stem cell-derived astrocytes coupled to single-cell transcriptomics to systematically interrogate cytokine-induced inflammatory astrocyte reactivity. We found that autocrine-paracrine IL-6 and interferon signaling downstream of canonical NF-κB activation drove two distinct inflammatory reactive signatures, one promoted by STAT3 and the other inhibited by STAT3. These signatures overlapped with those observed in other experimental contexts, including mouse models, and their markers were upregulated in human brains in Alzheimer's disease and hypoxic-ischemic encephalopathy. Furthermore, we validated that markers of these signatures were regulated by STAT3 in vivo using a mouse model of neuroinflammation. These results and the platform that we established have the potential to guide the development of therapeutics to selectively modulate different aspects of inflammatory astrocyte reactivity.

Divergent transcriptional regulation of astrocyte reactivity across disorders.

Astrocytes respond to injury and disease in the central nervous system with reactive changes that influence the outcome of the disorder1-4. These changes include differentially expressed genes (DEGs) whose contextual diversity and regulation are poorly understood. Here we combined biological and informatic analyses, including RNA sequencing, protein detection, assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) and conditional gene deletion, to predict transcriptional regulators that differentially control more than 12,000 DEGs that are potentially associated with astrocyte reactivity across diverse central nervous system disorders in mice and humans. DEGs associated with astrocyte reactivity exhibited pronounced heterogeneity across disorders. Transcriptional regulators also exhibited disorder-specific differences, but a core group of 61 transcriptional regulators was identified as common across multiple disorders in both species. We show experimentally that DEG diversity is determined by combinatorial, context-specific interactions between transcriptional regulators. Notably, the same reactivity transcriptional regulators can regulate markedly different DEG cohorts in different disorders; changes in the access of transcriptional regulators to DNA-binding motifs differ markedly across disorders; and DEG changes can crucially require multiple reactivity transcriptional regulators. We show that, by modulating reactivity, transcriptional regulators can substantially alter disorder outcome, implicating them as therapeutic targets. We provide searchable resources of disorder-related reactive astrocyte DEGs and their predicted transcriptional regulators. Our findings show that transcriptional changes associated with astrocyte reactivity are highly heterogeneous and are customized from vast numbers of potential DEGs through context-specific combinatorial transcriptional-regulator interactions.

Liquiritin inhibits proliferation and induces apoptosis in HepG2 hepatocellular carcinoma cells via the ROS-mediated MAPK/AKT/NF-κB signaling pathway.

Liquiritin (LIQ), a major constituent of Glycyrrhiza Radix, exhibits various pharmacological activities. In this study, to explore the potential anti-cancer effects and its underlying molecular mechanisms of LIQ in hepatocellular carcinoma (HCC) cells. LIQ significantly decreased viability and induced apoptosis in HepG2 cells by decreasing mitochondrial membrane potential and regulating Bcl-2 family proteins, cytochrome c, cle-caspase-3, and cle-PARP. The cell cycle analysis and western blot analysis revealed that LIQ induced G2/M phase arrest through increased expression of p21 and decreased levels of p27, cyclin B, and CDK1/2. The flow cytometry and western blot analysis also suggested that LIQ promoted the accumulation of ROS in HepG2 cells and up-regulated the phosphorylation expression levels of p38 kinase, c-Jun N-terminal kinase (JNK), and inhibitor of NF-κB (IκB-α); the phosphorylation levels of extracellular signal-regulated kinase (ERK), protein kinase B (AKT), signal transducer activator of transcription 3 (STAT3), and nuclear factor kappa B (NF-κB) were down-regulated. However, these effects were reversed by N-acetyl-L-cysteine (NAC), MAPK, and AKT inhibitors. The findings demonstrated that LIQ induced cell cycle arrest and apoptosis via the ROS-mediated MAPK/AKT/NF-κB signaling pathway in HepG2 cells, and the LIQ may serve as a potential therapeutic agent for the treatment of human HCC.

Two novel 1,4­naphthoquinone derivatives induce human gastric cancer cell apoptosis and cell cycle arrest by regulating reactive oxygen species­mediated MAPK/Akt/STAT3 signaling pathways.

1,4­Naphthoquinone derivatives have superior anticancer effects, but their use has been severely limited in clinical practice due to adverse side effects. To reduce the side effects and extend the anticancer effects of 1,4­naphthoquinone derivatives, 2­(butane­1­sulfinyl)­1,4­naphthoquinone (BQ) and 2­(octane­1­sulfinyl)­1,4­naphthoquinone (OQ) were synthesized, and their anticancer activities were investigated. The anti­proliferation effects, determined by MTT assays, showed that BQ and OQ significantly inhibited the viability of gastric cancer cells and had no significant cytotoxic effect on normal cell lines. The apoptotic effect was determined by flow cytometry, and the results showed that BQ and OQ induced cell apoptosis by regulating the mitochondrial pathway and cell cycle arrest at the G2/M phase via inhibition of the Akt signaling pathway in AGS cells. Furthermore, BQ and OQ significantly increased the levels of reactive oxygen species (ROS) and this effect was blocked by the ROS scavenger NAC in AGS cells. BQ and OQ induced apoptosis by upregulating the protein expression of p38 and JNK and downregulating the levels of ERK and STAT3. Furthermore, expression levels of these proteins were also blocked after NAC treatment. These results demonstrated that BQ and OQ induced apoptosis and cell cycle arrest at the G2/M phase in AGS cells by stimulating ROS generation, which caused subsequent activation of MAPK, Akt and STAT3 signaling pathways. Thus, BQ and OQ may serve as potential therapeutic agents for the treatment of human gastric cancer.

2-(4-methoxyphenylthio)-5,8-dimethoxy-1,4-naphthoquinone induces apoptosis via ROS-mediated MAPK and STAT3 signaling pathway in human gastric cancer cells.

The 1,4-naphthoquinones and their derivatives have garnered great interest due to their antitumor pharmacological properties in various cancers; however, their clinical application is limited by side effects. In this study, to reduce side effects and improve therapeutic efficacy, a novel 1,4-naphthoquinone derivative-2-(4-methoxyphenylthio)-5,8-dimethoxy-1,4-naphthoquinone (MPTDMNQ) was synthesized. We investigated the effects and underlying mechanisms of MPTDMNQ on cell viability, apoptosis, and reactive oxygen species (ROS) generation in human gastric cancer cells. Our results showed that MPTDMNQ decreased cell viability in nine human gastric cancer cell lines. MPTDMNQ significantly induced apoptosis accompanied by the accumulation of ROS in GC cells. However, pre-treatment with the ROS scavenger N-acetyl-L-cysteine (NAC) attenuated the MPTDMNQ-induced apoptosis. Moreover, MPTDMNQ decreased the phosphorylation levels of extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription 3 (STAT3); and increased the phosphorylation levels of c-Jun N-terminal kinase (JNK) and p38 kinase. However, phosphorylation was inhibited by NAC and a mitogen-activated protein kinase (MAPK) inhibitor. These findings showed that MPTDMNQ induced AGS cell apoptosis via ROS-mediated MAPK and STAT3 signaling pathways. Thus, MPTDMNQ may be a promising candidate for treating gastric cancer.

New naphthalene derivatives induce human lung cancer A549 cell apoptosis via ROS-mediated MAPKs, Akt, and STAT3 signaling pathways.

1,4-Naphthoquinone compounds are a class of organic compounds derived from naphthalene. They exert a wide variety of biological effects, but when used as anticancer drugs, have varying levels of side effects. In the present study, in order to reduce toxicity and improve the antitumor activity, we synthesized two novel 1,4-naphthoquinone derivatives, 2-(butane-1-sulfinyl)-1,4-naphthoquinone (BSQ) and 2-(octane-1-sulfinyl)-1,4-naphthoquinone (OSQ). We investigated the antitumor effects of BSQ and OSQ in human lung cancer cells and the underlying molecular mechanisms of these effects, focusing on the relationship between these compounds and reactive oxygen species (ROS) production. MTT assay and trypan blue exclusion assay results showed that BSQ and OSQ had significant cytotoxic effects in human lung cancer cells. Flow cytometry results indicated that the number of apoptotic cells and the intracellular ROS levels significantly increased after treatment with BSQ and OSQ. However, cell apoptosis was inhibited by pretreatment with the ROS scavenger N-acetyl-l-cysteine (NAC). Western blotting results showed that BSQ and OSQ increased the expression levels of p-p38 kinase and p-c-Jun N-terminal kinase (p-JNK), and decreased the expression levels of p-extracellular signal-regulated kinase (p-ERK), p-protein kinase B (p-Akt), and p-signal transducer and activator of transcription-3 (p-STAT3). These phenomena were blocked by mitogen-activated protein kinase (MAPK) inhibitors, Akt inhibitors and NAC. In conclusion, BSQ and OSQ induce human lung cancer A549 cell apoptosis by ROS-mediated MAPKs, Akt, and STAT3 signaling pathways. Therefore, BSQ and OSQ may be therapeutic potential agents for the treatment of human lung cancer.

Mechanisms underlying isoliquiritigenin-induced apoptosis and cell cycle arrest via ROS-mediated MAPK/STAT3/NF-κB pathways in human hepatocellular carcinoma cells.

Isoliquiritigenin (ISL), a natural flavonoid isolated from plant licorice, has various pharmacological properties, including anticancer, anti-inflammatory, and antiviral effects. However, the underlying mechanisms and signaling pathways of ISL in human hepatocellular carcinoma (HCC) cells remain unknown. In this study, we evaluated the effects of ISL on the apoptosis of human HCC cells with a focus on reactive oxygen species (ROS) production. Our results showed that ISL exhibited cytotoxic effects on two human liver cancer cells in a dose-dependent manner. ISL significantly induced mitochondrial-related apoptosis and cell cycle arrest at the G2/M phase, which was accompanied by ROS accumulation in HepG2 cells. However, pretreatment with an ROS scavenger, N-acetyl-l-cysteine (NAC), inhibited ISL-induced apoptosis. In addition, ISL increased the phosphorylation levels of c-Jun N-terminal kinase (JNK), p38 kinase and inhibitor of NF-κB (IκB), and decreased the phosphorylation levels of extracellular signal-regulated kinase (ERK), signal transducer and activator of transcription 3 (STAT3), nuclear factor-kappa B (NF-κB), these effects were blocked by NAC and mitogen-activated protein kinase (MAPK) inhibitors. Taken together, the findings of this study indicate that ISL induced HepG2 cell apoptosis via ROS-mediated MAPK, STAT3, and NF-κB signaling pathways. Therefore, ISL may be a potential treatment for human HCC, as well as other cancer types.

Novel 1,4­naphthoquinone derivatives induce reactive oxygen species­mediated apoptosis in liver cancer cells.

Derivatives of 1,4­naphthoquinone have excellent anti­cancer effects, but their use has been greatly limited due to their serious side effects. To develop compounds with decreased side effects and improved anti­cancer activity, two novel types of 1,4­naphthoquinone derivatives, 2,3­dihydro­2,3­epoxy­2­propylsulfonyl­5,8­dimethoxy­1,4­naphthoquinone (EPDMNQ) and 2,3­dihydro­2,3­epoxy­2­nonylsulfonyl­5,8­dimethoxy­1,4­naphthoquinone (ENDMNQ) were synthesized and their anti­tumor activities were investigated. The effects of EPDMNQ and ENDMNQ on cell viability, apoptosis and accumulation of reactive oxygen species (ROS) in liver cancer cells were determined by MTT cell viability assay and flow cytometry. The expression levels of mitochondrial, mitogen activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) signaling pathway­associated proteins in Hep3B liver cancer cells were analyzed by western blot analysis. The results demonstrated that EPDMNQ and ENDMNQ inhibited the proliferation of liver cancer Hep3B, HepG2, and Huh7 cell lines but not that of normal liver L­02, normal lung IMR­90 and stomach GES­1 cell lines. The number of apoptotic cells and ROS levels were significantly increased following treatment with EPDMNQ and ENDMNQ, and these effects were blocked by the ROS inhibitor N­acetyl­L­cysteine (NAC) in Hep3B cells. EPDMNQ and ENDMNQ induced apoptosis by upregulating the protein expression of p38 MAPK and c­Jun N­terminal kinase and downregulating extracellular signal­regulated kinase and STAT3; these effects were inhibited by NAC. The results of the present study demonstrated that EPDMNQ and ENDMNQ induced apoptosis through ROS­modulated MAPK and STAT3 signaling pathways in Hep3B cells. Therefore, these novel 1,4­naphthoquinone derivatives may be useful as anticancer agents for the treatment of liver cancer.

Y-box protein-1 is a transcriptional regulator of BMP7.

Bone morphogenetic protein-7 (BMP7) is an endogenous antifibrogenic protein in the kidney which is down regulated in experimental chronic kidney diseases such as obstructive and diabetic nephropathy in parallel with progressively increasing TGFß. In vitro studies were performed in Madin-Darby Canine Kidney (MDCK)-cells to identify transcriptional regulators of BMP7. Experiments with various BMP7 promoter fragments (465-4,267 bp) identify small proximal promoter segments that are transcriptionally activated by high glucose (3.2-fold) but down regulated by TGFß (0.2-fold) compared to normal glucose. Protein binding to these DNA segments is increased by high glucose and decreased by TGFß in a time-dependent, progressive manner. Analysis of BMP7 promoter-binding proteins with liquid chromatography/tandem mass spectrometry (LC/MS/MS) identifies seven unique, partially overlapping peptides, spanning 25% of the amino acid sequence of Y-box protein-1 (YB1). EMSA-Western blot combination experiments confirm that YB1 is a BMP7 promoter-binding protein. YB1 knock-down reduces transcriptional responses to high glucose and TGFß by about one-half, respectively. In addition, high glucose induces but TGFß reduces nuclear translocation of YB1 from the cytoplasm. These studies identify YB1 as a transcriptional activator of BMP7 and helps to explain the progressive decline in renal BMP7 in diabetic nephropathy and other kidney diseases.

Noncanonical TGF-beta pathways, mTORC1 and Abl, in renal interstitial fibrogenesis.

Renal interstitial fibrosis is a major determinant of renal failure in the majority of chronic renal diseases. Transforming growth factor-beta (TGF-beta) is the single most important cytokine promoting renal fibrogenesis. Recent in vitro studies identified novel non-smad TGF-beta targets including p21-activated kinase-2 (PAK2), the abelson nonreceptor tyrosine kinase (c-Abl), and the mammalian target of rapamycin (mTOR) that are activated by TGF-beta in mesenchymal cells, specifically in fibroblasts but less in epithelial cells. In the present studies, we show that non-smad effectors of TGF-beta including PAK2, c-Abl, Akt, tuberin (TSC2), and mTOR are activated in experimental unilateral obstructive nephropathy in rats. Treatment with c-Abl or mTOR inhibitors, imatinib mesylate and rapamycin, respectively, each blocks noncanonical (non-smad) TGF-beta pathways in the kidney in vivo and diminishes the number of interstitial fibroblasts and myofibroblasts as well as the interstitial accumulation of extracellular matrix proteins. These findings indicate that noncanonical TGF-beta pathways are activated during the early and rapid renal fibrogenesis of obstructive nephropathy. Moreover, the current findings suggest that combined inhibition of key regulators of these non-smad TGF-beta pathways even in dose-sparing protocols are effective treatments in renal fibrogenesis.

Diabetes-relevant regulation of cultured blood outgrowth endothelial cells.

Many cell and tissue abnormalities in diabetes mellitus are mediated by auto- and paracrine TGFbeta which is induced by high ambient glucose and glycated proteins. In most cell types TGFbeta reduces cell proliferation and enhances apoptosis which are mediated through the TGFbeta type I receptor, Alk5. In contrast, early diabetic microangiopathy is characterized by endothelial cell proliferation. Endothelial cells are unique in expressing a second TGFbeta type I receptor, Alk1, as well as the co-receptor, endoglin which increases the affinity of the ligand to Alk1. In differentiated blood outgrowth endothelial cells from normal subjects Alk1 and endoglin are constitutively expressed. Incubation with high glucose (HG) and glycated albumin (gAlb) induces Alk5 and raises TGFbeta secretion 3-fold without affecting Alk1 or endoglin levels. This diabetic milieu accelerates cell proliferation, at least in part, through TGFbeta/Alk1-smad1/5 and probably involving VEGF as well as pro-migratory MMP2 downstream of Alk1. In contrast, HG/gAlb also increases caspase-3 activity (suggesting increased apoptosis) in part but not entirely using a TGFbeta/Alk5-smad2/3 pathway. The findings support pleiotropy of TGFbeta in endothelial cells including proliferative effects (through Alk1-smad1/5) and pro-apoptotic signals (through Alk5-smad2/3).

Osmotic polyuria: an overlooked mechanism in diabetic nephropathy.

Tubulo-interstitial pathology in diabetic nephropathy is thought to be caused by cell injury that is induced by high ambient glucose levels and increased proportions of glycated proteins. Other mechanistic hypotheses engage glomerular ultrafiltration of proteins and bioactive growth factors and their effects on tubular cells. Some scholars promote tubular ischaemia due to reduced peritubular blood flow as a response to glomerular injury. All of these mechanisms contribute to renal tubulo-interstitial injury in diabetic nephropathy. However, they do not well explain observations that have been made in studies of experimental animals and evaluations of human biopsies showing dilated collecting ducts in early diabetic nephropathy. Dilatation of distal nephron segments is routinely seen in human biopsies or in histological sections from experimental diabetic nephropathy and is reminiscent of similar findings in obstructive nephropathy. Moreover, it is these dilated tubules that are the primary source for pro-inflammatory and pro-fibrogenic cytokines and regulators. Based on this large body of observations from this laboratory and the published literature this narrative develops a novel hypothesis where hyperglycaemic, osmotic polyuria play important contributory roles in the initiation and progression of tubulo-interstitial injury in diabetic nephropathy.

Functional symbiosis between endothelium and epithelial cells in glomeruli.

In some capillary beds, pericytes regulate endothelial growth. Capillaries with high filtration capacity, such as those in renal glomeruli, lack pericytes. Glomerular endothelium lies adjacent to visceral epithelial cells (podocytes) that are anchored to and cover the anti-luminal surface of the basement membrane. We have tested the hypothesis that podocytes can function as endothelial supporting cells. Endothelial cells were outgrown from circulating endothelial progenitors of normal subjects and were extensively characterized. These blood outgrowth endothelial cells (BOECs) expressed endothelial markers, lacked stem cell markers, and expressed the angiopoietin-1 receptor, Tie-2, and the vascular endothelial growth factor (VEGF) receptor, Flk-1. Differentiated podocytes in culture expressed and secreted VEGF, which was upregulated 4.5-fold by high glucose. In complete medium, BOECs formed thin cell-cell connections and multicellular tubes on Matrigel, the in vitro correlate of angiogenesis. This was impaired in deficient media but rescued by co-incubation with Transwell Anopore inserts containing differentiated podocytes. To assess whether VEGF was the major podocyte-derived signal that rescued BOEC angiogenesis, we examined angiogenesis of control and Flk-1-deficient BOECs. Co-incubation with podocytes or addition of recombinant VEGF each rescued angiogenesis in control BOECs, but both failed to support maintenance and angiogenesis in Flk-1-deficient BOECs. Finally, co-culture with podocytes increased BOEC-proliferation. In concert, these findings suggest a model in which glomerular visceral epithelial cells function as pericyte-like endothelial supporting cells. Podocyte-derived VEGF is a required and sufficient regulator of vascular endothelial maintenance, and its upregulation in podocytes by high glucose may be the mechanism for the increased glomerular angiogenesis that is observed in vivo in early diabetic glomerular injury.

BMP7 is a podocyte survival factor and rescues podocytes from diabetic injury.

In early diabetic renal injury, there is podocyte drop-out (but no decrease in the number of other glomerular cells) which is thought to cause glomerular proteinuria and subsequent diabetic glomerular injury. We tested the hypothesis that early diabetic podocyte injury is caused, in part, by downregulation of bone morphogenetic protein-7 (BMP7) and loss of its autocrine function in murine podocytes. High glucose (HG; 25 mM) induces rounding of differentiated podocytes and changes in the distribution of F-actin but without quantitative changes in E-cadherin and the podocyte markers podocin, CD2AP, Neph1, or synaptopodin. HG reduces BMP7 secretion and activity but does not affect BMP receptor levels in murine podocytes. In these cells, BMP7 effectively activates smad5 (but not smad1) and raises p38 phosphorylation [which is also increased by transforming growth factor-beta (TGF-beta)]. HG as well as TGF-beta raise caspase-3 activity, increase apoptosis, and reduce cell survival which is, in part, blocked by BMP7. Knockdown and forced expression studies indicate that smad5 is required as well as sufficient for these actions of BMP7. These findings indicate that BMP7 is a differentiation and survival factor for podocytes, requires smad5, and can reduce diabetic podocyte injury.

Renal bone morphogenetic protein-7 protects against diabetic nephropathy.

Longstanding diabetes causes renal injury with early dropout of podocytes, albuminuria, glomerular and tubulointerstitial fibrosis, and progressive renal failure. The renal pathology seems to be driven, in part, by TGF-beta and is associated with a loss of renal bone morphogenic protein-7 (BMP-7) expression. Here, the hypothesis that maintenance of renal (especially podocyte) BMP-7 by transgenic expression reduces diabetic renal injury was tested. Diabetic mice that expressed the phosphoenolpyruvate carboxykinase promoter-driven BMP-7 transgene and nondiabetic, transgenic mice as well as diabetic and nondiabetic wild-type controls were studied for up to 1 yr. Transgenic expression of BMP-7 in glomerular podocytes and proximal tubules prevents podocyte dropout and reductions in nephrin levels in diabetic mice. Maintenance of BMP-7 also reduces glomerular fibrosis and interstitial collagen accumulation as well as collagen I and fibronectin expression. Diabetic wild-type mice develop progressive albuminuria, which is substantially reduced in transgenic mice. These effects of the BMP-7 transgene occur without changing renal TGF-beta levels. It is concluded that maintenance of renal BMP-7 during the evolution of diabetic nephropathy reduces diabetic renal injury, especially podocyte dropout. The findings also establish a role for endogenous glomerular BMP-7 as an autocrine regulator of podocyte integrity in vivo.

Imatinib mesylate blocks a non-Smad TGF-beta pathway and reduces renal fibrogenesis in vivo.

Transforming growth factor-beta (TGF-beta) is the single most important cytokine promoting renal fibrogenesis. p21-activated kinase-2 (PAK2) and activation of abelson nonreceptor tyrosine kinase (c-abl) have been shown recently to be smad-independent, fibroblast-specific targets downstream of the activated TGF-beta receptor. In the current study we show that in cultured NRK49F-renal fibroblasts (but not in tubular or mesangial cells) TGF-beta similarly activates PAK2 as well as c-abl and induces cell proliferation. Inhibition of the c-abl kinase with imatinib mesylate prevents increased proliferation after TGF-beta addition without affecting PAK2. These in vitro findings were extended to rats with unilateral obstructive nephropathy, a disease model of TGF-beta-driven renal fibrogenesis. In obstructed kidneys, PAK2 and c-abl activity were increased but only c-abl activation was blocked by imatinib. Treatment with imatinib did not prevent renal interstitial infiltration of macrophages or phosphorylation and nuclear translocation of smad2/3 in obstructed kidneys. In contrast, imatinib substantially inhibited an increase in the number of interstitial fibroblasts and myofibroblasts and reduced the expression and interstitial accumulation of collagen type III, collagen type IV and fibronectin. These findings indicate that TGF-beta-induced activation of the nonreceptor c-abl tyrosine kinase regulates fibroblast proliferation and, by this means, is a costimulatory signal in TGF-beta-dependent renal fibrogenesis. Inhibition of c-abl activity with imatinib mesylate ameliorates experimental renal fibrosis in rats.

Proteinuria and growth factors in the development of tubulointerstitial injury and scarring in kidney disease.

PURPOSE OF REVIEW: There are ongoing debates as to the role and mechanisms of proteinuria in tubulointerstitial fibrogenesis. Moreover, recent experimental findings have allowed for further insights into mediators and interactions between cells in the renal interstitium during fibrogenesis. RECENT FINDINGS: Proteinuria or albuminuria are likely just markers for the glomerular ultrafiltration and tubular actions of ultrafiltered, biologically active growth factors which 'activate' tubular cells causing basolateral secretion of chemokines and cytokines. Chemokines attract and activate macrophages. Tubular cell-derived platelet-derived growth factor (PDGF) and macrophage-derived transforming growth factor-beta cause fibroblast proliferation. Several growth factors contribute to their transition into extracellular matrix-producing myofibroblasts. This cascade of events provides targets for some currently available and several novel therapies. SUMMARY: Albuminuria or glomerular proteinuria appear to be markers but ultrafiltered, bioactive growth factors are culprits in proteinuria-associated interstitial fibrosis. Interactions of tubular cells with macrophages and fibroblasts in the interstitium via defined growth factor/cytokines provide opportunities for therapeutic interventions.