DNA array analysis of the developing rat cerebellum: transforming growth factor-beta2 inhibits constitutively activated NF-kappaB in granule neurons

The Transcription Factor NF-κB in Stem Cells and Development

NF-κB (nuclear factor kappa B) belongs to a family of transcription factors known to regulate a broad range of processes such as immune cell function, proliferation and cancer, neuroprotection, and long-term memory. Upcoming fields of NF-κB research include its role in stem cells and developmental processes. In the present review, we discuss one role of NF-κB in development in Drosophila, Xenopus, mice, and humans in accordance with the concept of evo-devo (evolutionary developmental biology). REL domain-containing proteins of the NF-κB family are evolutionarily conserved among these species. In addition, we summarize cellular phenotypes such as defective B- and T-cell compartments related to genetic NF-κB defects detected among different species. While NF-κB proteins are present in nearly all differentiated cell types, mouse and human embryonic stem cells do not contain NF-κB proteins, potentially due to miRNA-dependent inhibition. However, the mesodermal and neuroectodermal differentiation of mouse and human embryonic stem cells is hampered upon the repression of NF-κB. We further discuss NF-κB as a crucial regulator of differentiation in adult stem cells such as neural crest-derived and mesenchymal stem cells. In particular, c-REL seems to be important for neuronal differentiation and the neuroprotection of human adult stem cells, while RELA plays a crucial role in osteogenic and mesodermal differentiation.

Canonical TGF-β pathway activity is a predictor of SHH-driven medulloblastoma survival and delineates putative precursors in cerebellar development

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Very little is known about aggressive forms of this disease, such as metastatic or recurrent MBs. In order to identify pathways involved in aggressive MB pathophysiology, we performed unbiased, whole genome microarrays on MB tumors at both the human and murine levels. Primary human MBs were compared, transcriptomically, to their patient-matched recurrent or metastatic tumors. Expression profiling was also performed on murine tumors from two spontaneously developing MB mouse models (Ptch+/- and Smo/Smo) that present with differing clinical severities. At both the human and murine levels we identified transforming growth factor-beta (TGF-β) as a potential contributor to MB progression/metastasis. Smad3, a major downstream component of the TGF-β pathway, was also evaluated using immunohistochemistry in malignant human tissues and was shown to correlate with MB metastasis and survival. Similarly, Smad3 expression during development identified a subset of cerebellar neuronal precursors as putative cells of origin for the Smad3-positive MBs. To our knowledge, this is the first study that links TGF-β to MB pathogenesis. Our research suggests that canonical activation of this pathway leads to better prognosis for patients.

Inhibition of nuclear factor kappa-B signaling reduces growth in medulloblastoma in vivo

Background

Medulloblastoma is a highly malignant pediatric brain tumor that requires surgery, whole brain and spine irradiation, and intense chemotherapy for treatment. A more sophisticated understanding of the pathophysiology of medulloblastoma is needed to successfully reduce the intensity of treatment and improve outcomes. Nuclear factor kappa-B (NFκB) is a signaling pathway that controls transcriptional activation of genes important for tight regulation of many cellular processes and is aberrantly expressed in many types of cancer.

Methods

To test the importance of NFκB to medulloblastoma cell growth, the effects of multiple drugs that inhibit NFκB, pyrrolidine dithiocarbamate, diethyldithiocarbamate, sulfasalazine, curcumin and bortezomib, were studied in medulloblastoma cell lines compared to a malignant glioma cell line and normal neurons. Expression of endogenous NFκB was investigated in cultured cells, xenograft flank tumors, and primary human tumor samples. A dominant negative construct for the endogenous inhibitor of NFκB, IκB, was prepared from medulloblastoma cell lines and flank tumors were established to allow specific pathway inhibition.

Results

We report high constitutive activity of the canonical NFκB pathway, as seen by Western analysis of the NFκB subunit p65, in medulloblastoma tumors compared to normal brain. The p65 subunit of NFκB is extremely highly expressed in xenograft tumors from human medulloblastoma cell lines; though, conversely, the same cells in culture have minimal expression without specific stimulation. We demonstrate that pharmacological inhibition of NFκB in cell lines halts proliferation and leads to apoptosis. We show by immunohistochemical stain that phosphorylated p65 is found in the majority of primary tumor cells examined. Finally, expression of a dominant negative form of the endogenous inhibitor of NFκB, dnIκB, resulted in poor xenograft tumor growth, with average tumor volumes 40% smaller than controls.

Conclusions

These data collectively demonstrate that NFκB signaling is important for medulloblastoma tumor growth, and that inhibition can reduce tumor size and viability in vivo. We discuss the implications of NFκB signaling on the approach to managing patients with medulloblastoma in order to improve clinical outcomes.

TGF-β1 induces podocyte injury through Smad3-ERK-NF-κB pathway and Fyn-dependent TRPC6 phosphorylation

TGF-β1 plays an important role on podocyte injury and glomerular diseases, while the underlying molecular mechanisms are still elusive. Here, the potential role of the ion channel TRPC6 and the proximal signaling was explored in TGF-β1-treated mouse podocyte. Our results showed that TGF-β1 significantly increased podocyte apoptosis and induced obvious disorganization of actin filaments in a time-dependent pattern. In TGF-β1-treated podocyte, TRPC6 protein, especially the phosphorylated TRPC6, and the cytosolic free Ca(2+) level upregulated, which was evidently inhibited by the specific knockdown of TRPC6. TRPC6 knockdown also alleviated TGF-β1-induced podocyte apoptosis. Moreover, the Src kinase Fyn increased obviously in TGF-β1-treated podocyte, displaying increment of the active form pY418 and reduction of the inactive form pY530. Immunoprecipitation assay revealed that Fyn interacts with TRPC6 in podocyte. Notably, Fyn knockdown blocked TRPC6 phosphorylation and intracellular Ca(2+) increment following TGF-β1 stimulation, but not affect the expression of TRPC6 protein. In addition, Western blot showed that TGF-β1 induced significant activation of p-Smad3, p-ERK and RelA/p65. Importantly, obvious translocation of ERK and RelA/p65 to nuclei was observed in TGF-β1-treated podocyte, which was reduced by ERK inhibitor U0126. Both U0126 and NF-κB inhibitor PDTC obviously inhibited the increment of TRPC6 protein and the flux of cytosolic free Ca(2+) induced by TGF-β1. Together, we provide evidences that TGF-β1 induces podocyte damage by upregulating TRPC6 protein most possibly through Smad3-ERK-NF-κB pathway, in which Fyn-dependent tyrosine phosphorylation of TRPC6 might exert a crucial role on the activation of its channel function.

Role of nitric oxide produced by iNOS through NF-κB pathway in migration of cerebellar granule neurons induced by Lipopolysaccharide

Inflammatory stimulus during development increases the risk for adverse neurologic outcome. One possible mechanism is disrupting neuronal migration. Using lipopolysaccharide (LPS)-treatment to assess inflammatory stimulus on neuronal migration of cerebellar granule neurons, we previously found that LPS-activation increased the neuronal migration. The precise mechanisms behind these effects have not been investigated. Independently, it was shown that nitric oxide (NO(•-)) regulates neuronal migration during development, that NO(•-) is produced by inducible nitric oxide synthase (iNOS) in response to LPS through the activation of nuclear factor (NF)-κB, and that LPS induce the expression of genes under the transcriptional control of NF-κB in primary cultures from developing mouse cerebellum. To investigate the relationship between these events, we used this culture model to study the role of NO(•-) produced by iNOS through NF-κB signaling pathway, in the effect of LPS on neuron migration. LPS increased NO(•-) production, iNOS protein levels and NF-κB nuclear levels; concomitantly with NO(•-) production, LPS increased the neuronal migration as compared to non stimulated cultures. The necessary roles of the NO(•-) and iNOS were demonstrated by chelating of NO(•-) with hemoglobin and the inhibition of iNOS by 1400W. Each of these treatments reduced neuronal migration induced by LPS. The role of NF-κB was showed by using the inhibitor JSH-23, which decreased NO(•-) production and neuronal migration in LPS activated cultures. These results suggest that neuronal migration during development is susceptible to be modified by pro-inflammatory stimulus such as LPS through intracellular pathways associated with their receptors.

Neuroprotection of microglial conditioned medium on 6-hydroxydopamine-induced neuronal death: role of transforming growth factor beta-2

Microglia, the immune cells of the CNS, play essential roles in both physiological and pathological brain states. Here we have used an in vitro model to demonstrate neuroprotection of a 48 h-microglial conditioned medium (MCM) towards cerebellar granule neurons (CGNs) challenged with the neurotoxin 6-hydroxydopamine, which induces a Parkinson-like neurodegeneration, and to identify the protective factor(s). MCM nearly completely protects CGNs from 6-hydroxydopamine neurotoxicity and at least some of the protective factor(s) are peptidic in nature. While the fraction of the medium containing molecules < 30 kDa completely protects CGNs, fractions containing molecules < 10 kDa or > 10 kDa are not neuroprotective. We further demonstrate that microglia release high amounts of transforming growth factor-beta2 (TGF-beta2) and that its exogenous addition to the fraction of the medium not containing it (< 10 kDa) fully restores the neuroprotective action. Moreover, MCM neuroprotection is significantly counteracted by an inhibitor of TGF-beta2 transduction pathway. Our results identify TGF-beta2 as an essential neuroprotective factor released by microglia in its culture medium that requires to be fully effective the concomitant presence of other factor(s) of low molecular weight.

Modulation of NFkappaB activity and E-cadherin by the type III transforming growth factor beta receptor regulates cell growth and motility

Transforming growth factor beta is growth-inhibitory in non-transformed epithelial cells but becomes growth-promoting during tumorigenesis. The role of the type I and II receptors in tumorigenesis has been extensively studied, but the role of the ubiquitously expressed type III receptor (TbetaRIII) remains elusive. We developed short hairpin RNAs directed against TbetaRIII to investigate the role of this receptor in breast cancer tumorigenesis. Nontumorigenic NMuMG mouse cells stably expressing short hairpin RNA specific to mouse TbetaRIII (NM-kd) demonstrated increased cell growth, motility, and invasion as compared with control cells expressing shRNA to human TbetaRIII (NM-con). Reconstitution of TbetaRIII expression with rat TbetaRIII abrogated the increased growth and motility seen in the NM-kd cells. In addition, the NM-kd cells exhibited marked reduction in the expression of the adherens junction protein, E-cadherin. This loss of E-cadherin was due to increased NFkappaB activity that, in turn, resulted in increased expression of the transcriptional repressors of E-cadherin such as Snail, Slug, Twist, and Sip1. Finally, NMuMG cells in which TbetaRIII had been knocked down formed invasive tumors in athymic nude mice, whereas the control cells did not. These data indicate that TbetaRIII acts as a tumor suppressor in nontumorigenic mammary epithelial cells at least in part by inhibiting NFkappaB-mediated repression of E-cadherin.

NF-kappaB functions in the nervous system: from development to disease

The transcription factor nuclear factor-kappaB (NF-kappaB) is an ubiquitously expressed dimeric molecule with post-translationally regulated activity. Its role in the immune system and host defense has been well characterized over the last two decades. In contrast, our understanding of the function of this transcription factor in the nervous system (NS) is only emerging. Given their cytoplasmic retention and nuclear translocation upon stimulus, NF-kappaB members are likely to exert an important role in transduction of signals from synaptic terminals to nucleus, to initiate transcriptional responses. This report describes recent findings deciphering the diverse functions of NF-kappaB in NS development and activity, which range from the control of cell growth, survival and inflammatory response to synaptic plasticity, behavior and cognition. Particular attention is given to the specific roles of NF-kappaB in the various cells of the NS, e.g. neurons and glia. Current knowledge of the contribution of NF-kappaB to several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases is also summarized.

Transforming growth factor-beta1 differentially mediates fibronectin and inflammatory cytokine expression in kidney tubular cells

Transforming growth factor-beta(1) (TGF-beta(1)) is not only an important fibrogenic but also immunomodulatory cytokine in the human kidney. We have recently demonstrated that TGF-beta(1) induces interleukin-8 (IL-8), macrophage chemoattractant protein-1 (MCP-1), and fibronectin production in renal proximal tubular (HK-2) cells. However, the unique dependence of IL-8, MCP-1, and fibronectin on TGF-beta(1) expression is unknown. The TGF-beta(1) gene was effectively silenced in HK-2 cells using small-interference (si) RNA. Basal secretion of IL-8 and MCP-1 decreased (both P < 0.05) but, paradoxically, fibronectin increased (P < 0.05) in TGF-beta(1)-silenced cells compared with cells transfected with nonspecific siRNA. Significant increases were observed in mRNA for the TGF-beta(2) (P < 0.05), TGF-beta(3) (P < 0.05) isoforms and pSmad2 (P < 0.05), which were reflected in protein expression. Concurrent exposure to pan-specific TGF-beta antibody reversed the observed increase in fibronectin expression, suggesting that TGF-beta(2) and TGF-beta(3) isoforms mediate the increased fibronectin expression in TGF-beta(1)-silenced cells. An increase in the DNA binding activity of activator protein-1 (AP-1; P < 0.05) was also observed in TGF-beta(1)-silenced cells. In contrast, nuclear factor-kappaB (NF-kappaB) DNA binding activity was significantly decreased (P < 0.0005). These studies demonstrate that TGF-beta(1) is a key regulator of IL-8 and MCP-1, whereas fibronectin expression is regulated by a complex interaction between the TGF-beta isoforms in the HK-2 proximal tubular cell line. Decreased expression of TGF-beta(1) reduces chemokine production in association with reduced NF-kappaB DNA binding activity, suggesting that immunomodulatory pathways in the kidney are specifically dependent on TGF-beta(1). Conversely, decreased expression of TGF-beta(1) results in increased TGF-beta(2), TGF-beta(3), AP-1, and pSmad2 that potentially mediates the observed increase in fibronectin.

Signaling via NF-κB in the nervous system

Nuclear factor kappa B (NF-kappaB) is an inducible transcription factor present in neurons and glia. Recent genetic models identified a role for NF-kappaB in neuroprotection against various neurotoxins. Furthermore, genetic evidence for a role in learning and memory is now emerging. This review highlights our current understanding of neuronal NF-kappaB in response to synaptic transmission and summarizes potential physiological functions of NF-kappaB in the nervous system. This article contains a listing of NF-kappaB activators and inhibitors in the nervous system, furthermore specific target genes are discussed. Synaptic NF-kappaB activated by glutamate and Ca2+ will be presented in the context of retrograde signaling. A controversial role of NF-kappaB in neurodegenerative diseases will be discussed. A model is proposed explaining this paradox as deregulated physiological NF-kappaB activity, where novel results are integrated, showing that p65 could be turned from an activator to a repressor of anti-apoptotic genes.

TGF-{beta}1 activates two distinct type I receptors in neurons: implications for neuronal NF-{kappa}B signaling

Transforming growth factor-βs (TGF-βs) are pleiotropic cytokines involved in development and maintenance of the nervous system. In several neural lesion paradigms, TGF-β1 exerts potent neuroprotective effects. Neurons treated with TGF-β1 activated the canonical TGF-β receptor I/activin-like kinase receptor 5 (ALK5) pathway. The transcription factor nuclear factor-κB (NF-κB) plays a fundamental role in neuroprotection. Treatment with TGF-β1 enhanced NF-κB activity in gelshift and reporter gene analyses. However, ectopic expression of a constitutively active ALK5 failed to mimic these effects. ALK1 has been described as an alternative TGF-β receptor in endothelial cells. Interestingly, we detected significant basal expression of ALK1 and its injury-induced up-regulation in neurons. Treatment with TGF-β1 also induced a pronounced increase in downstream Smad1 phosphorylation. Overexpression of a constitutively active ALK1 mimicked the effect of TGF-β1 on NF-κB activation and neuroprotection. Our data suggest that TGF-β1 simultaneously activates two distinct receptor pathways in neurons and that the ALK1 pathway mediates TGF-β1–induced NF-κB survival signaling.

TGF-beta2 neutralization inhibits proliferation and activates apoptosis of cerebellar granule cell precurors in the developing cerebellum

Transforming growth factor beta 2 (TGF-beta2) plays a critical role in growth, differentiation and cell death, but its function in the developing cerebellum is still uncertain. In this study we analyzed the effects of TGF-beta2 on ex vivo developing cerebellar slice cultures. Proliferation of granule cell precursors peaked ex vivo in the same developmental window as in vivo (P8-P14). Addition of recombinant TGF-beta2 could extent the proliferation of granule cell precursors and induced a second late proliferation wave. In contrast, antibody neutralization of TGF-beta2 strongly reduced proliferation and induced neurodegeneration. TGF-beta2 neutralization resulted in apoptotic cells, which showed caspase 3 activation. Taken together our results demonstrate that TGF-beta2 is a novel growth and survival factor for granule cells precursors in the developing cerebellum.

Neuroprotection by transforming growth factor-beta1 involves activation of nuclear factor-kappaB through phosphatidylinositol-3-OH kinase/Akt and mitogen-activated protein kinase-extracellular-signal regulated kinase1,2 signaling pathways

Prevention of neuronal apoptosis has been introduced as a new therapeutic strategy for neurodegenerative disorders. We have previously reported anti-apoptotic effects of transforming growth factor-beta1 (TGF-beta1), a multifunctional cytokine, in models of cerebral ischemia and in cultured neurons and recently focused on the mechanisms underlying the anti-apoptotic effect of TGF-beta1. The anti-apoptotic transcriptional factor nuclear factor kappa B (NF-kappaB) shows high impact in the cell survival function of multiple cytokines and growth factors. The present study explored whether NF-kappabeta is a target of TGF-beta1 and which signaling pathways involved in the activation of NF-kappabeta are triggered by TGF-beta1. We demonstrated that TGF-beta1 increased the transcriptional activity of NF-kappabeta in cultured hippocampal neurons in a time- and concentration-dependent manner. Furthermore, TGF-beta1 induced translocation of p65/NF-kappabeta to the nucleus and enhanced NF-kappabeta transcriptional activity in the presence of apoptotic stimuli. TGF-beta1-mediated NF-kappabeta activation was blocked by wortmannin and U0126, indicating the involvement of both phosphatidylinositol-3-OH kinase (PI3k)/Akt and mitogen-activated protein kinase (MAPK)/extracellular-signal regulated kinase (Erk)1,2 pathways in the action of TGF-beta1. TGF-beta1 produced a concomitant increase in the phosphorylations of Ikappabeta kinase (IKKalpha/beta) and Ikappabetaalpha with a subsequent degradation of Ikappabetaalpha. Interestingly, the increased phosphorylation of IKKalpha/beta and Ikappabetaalpha was abrogated by wortmannin, but not by U0126, suggesting that PI3k/Akt and MAPK/Erk1,2 pathways triggered by TGF-beta1 regulated the activation of NF-kappabeta through different mechanisms. Of note, wortmannin and U0126, as well as kappabeta-decoy DNA, abolished the anti-apoptotic effect of TGF-beta1, corroborating the notion that both PI3k/Akt and MAPK/Erk1,2 pathways, and NF-kappabeta activity are necessary for the anti-apoptotic activity of TGF-beta1.

Myotrophin/V-1, a protein up-regulated in the failing human heart and in postnatal cerebellum, converts NFkappa B p50-p65 heterodimers to p50-p50 and p65-p65 homodimers

Myotrophin/V-1 is a cytosolic protein found at elevated levels in failing human hearts and in postnatal cerebellum. We have previously shown that it disrupts nuclear factor of kappaB (NFkappaB)-DNA complexes in vitro. In this study, we demonstrated that in HeLa cells native myotrophin/V-1 is predominantly present in the cytoplasm and translocates to the nucleus during sustained NFkappaB activation. Three-dimensional alignment studies indicate that myotrophin/V-1 resembles a truncated IkappaBalpha without the signal response domain (SRD) and PEST domains. Co-immunoprecipitation studies reveal that myotrophin/V-1 interacts with NFkappaB proteins in vitro; however, it remains physically associated only with p65 and c-Rel proteins in vivo during NFkappaB activation. In vitro studies indicate that myotrophin/V-1 can promote the formation of p50-p50 homodimers from monomeric p50 proteins and can convert the preformed p50-p65 heterodimers into p50-p50 and p65-p65 homodimers. Furthermore, adenovirus-mediated overexpression of myotrophin/V-1 resulted in elevated levels of both p50-p50 and p65-p65 homodimers exceeding the levels of p50-p65 heterodimers compared with Adbetagal-infected cells, where the levels of p50-p65 heterodimers exceeded the levels of p50-p50 and p65-p65 homodimers. Thus, overexpression of myotrophin/V-1 during NFkappaB activation resulted in a qualitative shift by quantitatively reducing the level of transactivating heterodimers while elevating the levels of repressive p50-p50 homodimers. Correspondingly, overexpression of myotrophin/V-1 resulted in significantly reduced kappaB-luciferase reporter activity. Because myotrophin/V-1 is found at elevated levels during NFkappaB activation in postnatal cerebellum and in failing human hearts, this study cumulatively suggests that myotrophin/V-1 is a regulatory protein for modulating the levels of activated NFkappaB dimers during this period.

Cerebellar granule cells as a model to study mechanisms of neuronal apoptosis or survival in vivo and in vitro

Granule cells of the cerebellum constitute the largest homogeneous neuronal population of mammalian brain. Due to their postnatal generation and the feasibility of well characterized primary in vitro cultures, cerebellar granule cells are a model of election for the study of cellular and molecular correlates of mechanisms of survival/apoptosis and neurodegeneration/neuroprotection. The present review mainly deals with recent data on mechanisms and factors promoting survival or apoptotic elimination of cerebellar granule neurons, with a particular focus on the molecular correlates at the level of gene expression and induction of cellular signal pathways. The in vivo development is first analysed with particular reference to the role played by several neurotrophic factors and by the NMDA subtype of glutamate receptor. Then, mechanisms of survival/apoptosis are examined in the model of primary in vitro cultures, where the role of neurotrophins acting on cerebellar granule cells is followed by the large deal of data coming from the paradigm of potassium/serum withdrawal. The role of some key genes of the Bcl family, of some kinase systems and of transcriptional factors is primarily highlighted. Furthermore, the involvement of mitochondria, free radicals and proteases of the caspase family is considered. Finally, the use of cerebellar granule neurons in primary culture to experimentally address the issue of neurodegeneration and pharmacological neuroprotection is considered, with some comments on models at the borderline between necrosis and apoptosis, such as the excitotoxic neuronal damage. The overlapping of cellular signal pathways activated in granule neurons by apparently unrelated stimuli, such as neurotrophins and neurotransmitters/neuromodulators is stressed to put into light the special 'trophic' role played by activity in neurons. Finally, the advantage of designing and performing conceptually equivalent experiments on cerebellar granule neurons during development in vivo and in vitro, is stressed. On the basis of the reviewed material, it is concluded that cerebellar granule neurons have acquired a special position in modern neuroscience as one of the most reliable models for the study of neural development, function and pathology.

Apoptosis in podocytes induced by TGF-beta and Smad7

Primary and secondary forms of focal segmental glomerulosclerosis (FSGS) are characterized by depletion of podocytes and constitute a central manifestation of chronic progressive glomerular diseases. Here we report that podocytes undergo apoptosis at early stages in the course of progressive glomerulosclerosis in TGF-beta1 transgenic mice. Apoptosis is associated with progressive depletion of podocytes and precedes mesangial expansion. Smad7 protein expression is strongly induced specifically in damaged podocytes of transgenic mice and in cultured murine podocytes treated with TGF-beta. TGF-beta1 and Smad7 each induce apoptosis in podocytes, and their coexpression has an additive effect. Activation of p38 MAP kinase and caspase-3 is required for TGF-beta-mediated apoptosis, but not for apoptosis induced by Smad7. Unlike TGF-beta, Smad7 inhibits nuclear translocation and transcriptional activity of the cell survival factor NF-kappaB. Our results suggest a novel functional role for Smad7 as amplifier of TGF-beta-induced apoptosis in podocytes and a new pathomechanism for podocyte depletion in progressive glomerulosclerosis.

The functional genomic response of developing embryonic submandibular glands to NF-kappa B inhibition

BACKGROUND

The proper balance between epithelial cell proliferation, quiescence, and apoptosis during development is mediated by the specific temporal and spatial appearance of transcription factors, growth factors, cytokines, caspases, etc. Since our prior studies suggest the importance of transcription factor NF-kappaB during embryonic submandibular salivary gland (SMG) development, we attempted to delineate the emergent dynamics of a cognate signaling network by studying the molecular patterns and phenotypic outcomes of interrupted NF-kappaB signaling in embryonic SMG explants.

RESULTS

SN50-mediated inhibition of NF-kappaB nuclear translocation in E15 SMG explants cultured for 2 days results in a highly significant increase in apoptosis and decrease in cell proliferation. Probabilistic Neural Network (PNN) analyses of transcriptomic and proteomic assays identify specific transcripts and proteins with altered expression that best discriminate control from SN50-treated SMGs. These include PCNA, GR, BMP1, BMP3b, Chk1, Caspase 6, E2F1, c-Raf, ERK1/2 and JNK-1, as well as several others of lesser importance. Increased expression of signaling pathway components is not necessarily probative of pathway activity; however, as confirmation we found a significant increase in activated (phosphorylated/cleaved) ERK 1/2, Caspase 3, and PARP in SN50-treated explants. This increased activity of proapoptotic (caspase3/PARP) and compensatory antiapoptotic (ERK1/2) pathways is consistent with the dramatic cell death seen in SN50-treated SMGs.

CONCLUSIONS

Our morphological and functional genomic analyses indicate that the primary and secondary effects of NF-kappaB-mediated transcription are critical to embryonic SMG developmental homeostasis. Relative to understanding complex genetic networks and organogenesis, our results illustrate the importance of evaluating the gene, protein, and activated protein expression of multiple components from multiple pathways within broad functional categories.

Apoptosis in podocytes induced by TGF-beta and Smad7

Primary and secondary forms of focal segmental glomerulosclerosis (FSGS) are characterized by depletion of podocytes and constitute a central manifestation of chronic progressive glomerular diseases. Here we report that podocytes undergo apoptosis at early stages in the course of progressive glomerulosclerosis in TGF-beta1 transgenic mice. Apoptosis is associated with progressive depletion of podocytes and precedes mesangial expansion. Smad7 protein expression is strongly induced specifically in damaged podocytes of transgenic mice and in cultured murine podocytes treated with TGF-beta. TGF-beta1 and Smad7 each induce apoptosis in podocytes, and their coexpression has an additive effect. Activation of p38 MAP kinase and caspase-3 is required for TGF-beta-mediated apoptosis, but not for apoptosis induced by Smad7. Unlike TGF-beta, Smad7 inhibits nuclear translocation and transcriptional activity of the cell survival factor NF-kappaB. Our results suggest a novel functional role for Smad7 as amplifier of TGF-beta-induced apoptosis in podocytes and a new pathomechanism for podocyte depletion in progressive glomerulosclerosis.