Validation of the Oxford classification of IgA nephropathy in cohorts with different presentations and treatments.

The Oxford Classification of IgA Nephropathy (IgAN) identified mesangial hypercellularity (M), endocapillary proliferation (E), segmental glomerulosclerosis (S), and tubular atrophy/interstitial fibrosis (T) as independent predictors of outcome. Whether it applies to individuals excluded from the original study and how therapy influences the predictive value of pathology remain uncertain. The VALIGA study examined 1147 patients from 13 European countries that encompassed the whole spectrum of IgAN. Over a median follow-up of 4.7 years, 86% received renin-angiotensin system blockade and 42% glucocorticoid/immunosuppressive drugs. M, S, and T lesions independently predicted the loss of estimated glomerular filtration rate (eGFR) and a lower renal survival. Their value was also assessed in patients not represented in the Oxford cohort. In individuals with eGFR less than 30 ml/min per 1.73 m(2), the M and T lesions independently predicted a poor survival. In those with proteinuria under 0.5 g/day, both M and E lesions were associated with a rise in proteinuria to 1 or 2 g/day or more. The addition of M, S, and T lesions to clinical variables significantly enhanced the ability to predict progression only in those who did not receive immunosuppression (net reclassification index 11.5%). The VALIGA study provides a validation of the Oxford classification in a large European cohort of IgAN patients across the whole spectrum of the disease. The independent predictive value of pathology MEST score is reduced by glucocorticoid/immunosuppressive therapy.

Learning, AMPA receptor mobility and synaptic plasticity depend on n-cofilin-mediated actin dynamics.

Neuronal plasticity is an important process for learning, memory and complex behaviour. Rapid remodelling of the actin cytoskeleton in the postsynaptic compartment is thought to have an important function for synaptic plasticity. However, the actin-binding proteins involved and the molecular mechanisms that in vivo link actin dynamics to postsynaptic physiology are not well understood. Here, we show that the actin filament depolymerizing protein n-cofilin is controlling dendritic spine morphology and postsynaptic parameters such as late long-term potentiation and long-term depression. Loss of n-cofilin-mediated synaptic actin dynamics in the forebrain specifically leads to impairment of all types of associative learning, whereas exploratory learning is not affected. We provide evidence for a novel function of n-cofilin function in synaptic plasticity and in the control of extrasynaptic excitatory AMPA receptors diffusion. These results suggest a critical function of actin dynamics in associative learning and postsynaptic receptor availability.

Transmitter-receptor mismatch in GABAergic synapses in the absence of activity.

Competition among different axons to reach the somatodendritic region of the target neuron is an important event during development to achieve the final architecture typical of the mature brain. Trasmitter-receptor matching is a critical step for the signaling between neurons. In the cerebellar cortex, there is a persistent competition between the two glutamatergic inputs, the parallel fibers and the climbing fibers, for the innervation of the Purkinje cells. The activity of the latter input is necessary to maintain its own synaptic contacts on the proximal dendritic domain and to confine the parallel fibers in the distal one. Here, we show that climbing fiber activity also limits the distribution of the GABAergic input in the proximal domain. In addition, blocking the activity by tetrodotoxin infusion in Wistar rat cerebellum, a synapse made by GABAergic terminals onto the recently formed Purkinje cell spines appear in the proximal dendrites. The density of GABAergic terminals is increased, and unexpected double symmetric/asymmetric postsynaptic densities add to the typical symmetric phenotype of the GABAergic shaft synapses. Moreover, glutamate receptors appear in these ectopic synapses even in the absence of glutamate transmitter inside the presynaptic terminal and close to GABA receptors. These results suggest that the Purkinje cell has an intrinsic tendency to develop postsynaptic assemblies of excitatory types, including glutamate receptors, over the entire dendritic territory. GABA receptors are induced in these assemblies when contacted by GABAergic terminals, thus leading to the formation of hybrid synapses.

Mesenchymal stem cell-derived microvesicles protect against acute tubular injury.

Administration of mesenchymal stem cells (MSCs) improves the recovery from acute kidney injury (AKI). The mechanism may involve paracrine factors promoting proliferation of surviving intrinsic epithelial cells, but these factors remain unknown. In the current study, we found that microvesicles derived from human bone marrow MSCs stimulated proliferation in vitro and conferred resistance of tubular epithelial cells to apoptosis. The biologic action of microvesicles required their CD44- and beta1-integrin-dependent incorporation into tubular cells. In vivo, microvesicles accelerated the morphologic and functional recovery of glycerol-induced AKI in SCID mice by inducing proliferation of tubular cells. The effect of microvesicles on the recovery of AKI was similar to the effect of human MSCs. RNase abolished the aforementioned effects of microvesicles in vitro and in vivo, suggesting RNA-dependent biologic effects. Microarray analysis and quantitative real time PCR of microvesicle-RNA extracts indicate that microvesicles shuttle a specific subset of cellular mRNA, such as mRNAs associated with the mesenchymal phenotype and with control of transcription, proliferation, and immunoregulation. These results suggest that microvesicles derived from MSCs may activate a proliferative program in surviving tubular cells after injury via a horizontal transfer of mRNA.

Glutamate receptor delta2 subunit in activity-dependent heterologous synaptic competition.

In the adult cerebellum, the glutamate receptor delta2 subunit (GluRdelta2) is selectively targeted to the spines of the distal Purkinje cell dendrites, the spiny branchlets, that are innervated by the parallel fibers. Although GluRdelta2 has no known channel function, it is presumed to be involved in the formation and stabilization of these synapses. After block of electrical activity by tetrodotoxin, GluRdelta2s appear in the postsynaptic densities of the proximal dendritic spines, which then lose their contact with climbing fibers and become ectopically innervated by parallel fibers. This phenomenon suggests that climbing fiber activity prevents GluRdelta2 targeting to proximal dendrites and that GluRdelta2s admitted to the postsynaptic density of the spine cause withdrawal of the silent climbing fiber. To test this hypothesis, we studied the distribution of GluRdelta2s in the rat cerebellum by immunoelectron microscopy during the recovery period that follows removal of the electrical block, and during the sprouting of climbing fibers that follows subtotal deletion of the parent inferior olivary neurons by administration of the drug 3-acetylpyridine. We found that after removal of the electrical block, the climbing fibers reinnervate proximal spines that bear GluRdelta2s and these subunits are successively repressed. Similarly, after subtotal lesion of the inferior olive, reinnervation of denervated Purkinje cells occurs on spines bearing GluRdelta2s. Thus, GluRdelta2s are not responsible for displacing silent climbing fibers. We propose instead that GluRdelta2s are associated with climbing fiber-to-Purkinje cell synapses, during development or at early stages of climbing fiber regeneration or sprouting, and are downregulated during the process of synapse maturation.

Spontaneous electrical activity and structural plasticity in the mature cerebellar cortex.

The Purkinje cell of the cerebellar cortex presents two distinct dendritic domains: a distal one, with spiny branchlets and a high density of spines innervated by many parallel fibers, and a proximal one, with a few clusters of spines innervated by a single climbing fiber terminal arbor. In adult rats, after 7 days of blocked electrical activity by the administration of TTX into the cerebellar parenchyma, the proximal dendritic domain of the Purkinje cell shows a remarkable growth of new spines that are innervated by parallel fibers. At the same time, the climbing fiber terminal arbor tends to become atrophic. In contrast, in the branchlets, spine density remains unmodified. These changes are reversible when TTX is removed. TTX treatment also leads to a decrease in spine size both in the branchlets and in the new spines of the proximal dendritic compartment. Spontaneous electrical activity should therefore be regarded not simply as noise, but as a significant signal for maintaining the typical profile of afferent innervation of the Purkinje cell and for preventing spines from shrinking.

Pharmacological reversion of sphingomyelin-induced dendritic spine anomalies in a Niemann Pick disease type A mouse model.

Understanding the role of lipids in synapses and the aberrant molecular mechanisms causing the cognitive deficits that characterize most lipidosis is necessary to develop therapies for these diseases. Here we describe sphingomyelin (SM) as a key modulator of the dendritic spine actin cytoskeleton. We show that increased SM levels in neurons of acid sphingomyelinase knock out mice (ASMko), which mimic Niemann Pick disease type A (NPA), result in reduced spine number and size and low levels of filamentous actin. Mechanistically, SM accumulation decreases the levels of metabotropic glutamate receptors type I (mGluR1/5) at the synaptic membrane impairing membrane attachment and activity of RhoA and its effectors ROCK and ProfilinIIa. Pharmacological enhancement of the neutral sphingomyelinase rescues the aberrant molecular and morphological phenotypes in vitro and in vivo and improves motor and memory deficits in ASMko mice. Altogether, these data demonstrate the influence of SM and its catabolic enzymes in dendritic spine physiology and contribute to our understanding of the cognitive deficits of NPA patients, opening new perspectives for therapeutic interventions.

Early environmental enrichment moderates the behavioral and synaptic phenotype of MeCP2 null mice.

BACKGROUND: Rett syndrome (RTT) is an X-linked progressive neurodevelopmental disorder characterized by a variety of symptoms including motor abnormalities, mental retardation, anxiety, and autism. Most of RTT cases are caused by mutations of MeCP2. In mice, impaired MeCP2 function results in synaptic deficits associated with motor, cognitive, and emotional alterations. Environmental enrichment (EE) is a rearing condition that enhances synapse formation and plasticity. Previous studies analyzing the effects of postweaning EE found limited effects on motor performance of male MeCP2 mutants. However, EE during early postnatal development produces powerful effects on neural development and plasticity. Thus, we tested whether early EE could ameliorate several phenotypes of male homozygous and female heterozygous MeCP2 mutants. METHODS: We investigated the effects of early EE on motor coordination, structural and functional synaptic plasticity, and brain-derived neurotrophic factor expression in male MeCP2 null mice. Anxiety-related behavior and spatial learning was analyzed in heterozygous MeCP2 female mice. RESULTS: In male mutants, EE modified excitatory and to a lesser extent inhibitory synaptic density in cerebellum and cortex, reversed the cortical long-term potentiation deficit and augmented cortical brain-derived neurotrophic factor levels. Environmental enrichment also ameliorated motor coordination and motor learning. In female heterozygous mice, a model closely mimicking some aspects of RTT symptoms, EE rescued memory deficits in the Morris water maze and decreased anxiety-related behavior. CONCLUSIONS: Early EE dramatically improves several phenotypes of MeCP2 mutants. Thus, environmental factors should be taken into account when analyzing phenotypes of MeCP2 knockout mice, an accepted model of RTT. Early EE might be beneficial in RTT patients.

Synaptic vesicle docking: sphingosine regulates syntaxin1 interaction with Munc18.

Consensus exists that lipids must play key functions in synaptic activity but precise mechanistic information is limited. Acid sphingomyelinase knockout mice (ASMko) are a suitable model to address the role of sphingolipids in synaptic regulation as they recapitulate a mental retardation syndrome, Niemann Pick disease type A (NPA), and their neurons have altered levels of sphingomyelin (SM) and its derivatives. Electrophysiological recordings showed that ASMko hippocampi have increased paired-pulse facilitation and post-tetanic potentiation. Consistently, electron microscopy revealed reduced number of docked vesicles. Biochemical analysis of ASMko synaptic membranes unveiled higher amounts of SM and sphingosine (Se) and enhanced interaction of the docking molecules Munc18 and syntaxin1. In vitro reconstitution assays demonstrated that Se changes syntaxin1 conformation enhancing its interaction with Munc18. Moreover, Se reduces vesicle docking in primary neurons and increases paired-pulse facilitation when added to wt hippocampal slices. These data provide with a novel mechanism for synaptic vesicle control by sphingolipids and could explain cognitive deficits of NPA patients.

Purkinje cell spinogenesis during architectural rewiring in the mature cerebellum.

Spines can grow and retract within hours of activity perturbation. We investigated the time course of spine formation in a model of plasticity involving changes in brain architecture where spines of a dendritic domain become innervated by a different neuronal population. Following a lesion of rat olivocerebellar axons, by severing the inferior cerebellar peduncle, new spines grow on the deafferented proximal dendrite of the Purkinje cells (PCs) and these new spines become innervated by parallel fibres (PFs) that normally contact only the distal dendrites. The varicosities of climbing fibre (CF) terminal arbors disappear within 3 days of the lesion. Spine density in the proximal dendritic domain begins to rise within 3 days and continues to increase towards a plateau at 6-8 days. In 'slow Wallerian degeneration' mice, in which axonal degeneration is delayed, climbing fibre varicosities virtually disappear at 14 rather than 3 days. Spine density in the proximal dendritic domain is similar to control Purkinje cells up to 14 days and increases significantly 18 days postlesion. The delayed spinogenesis in the latter mutant is the result of a persistence of the climbing fibre presynaptic structure in the absence of activity. Therefore, climbing fibre activity itself is not directly responsible for the suppression of spine formation, but suppression mechanisms tend to become weaker as long as the structural dismantling of the presynaptic varicosities proceeds. Thus, spinogenesis is guided by two different mechanisms; a rapid one related to changes in homotypic remodeling and a slower one, which requires the removal of a competitive afferent.

Spontaneous electrical activity and dendritic spine size in mature cerebellar Purkinje cells.

Previous experiments have shown that in the mature cerebellum both blocking of spontaneous electrical activity and destruction of the climbing fibres by a lesion of the inferior olive have a similar profound effect on the spine distribution on the proximal dendrites of the Purkinje cells. Many new spines develop that are largely innervated by parallel fibers. Here we show that blocking electrical activity leads to a significant decrease in size of the spines on the branchlets. We have also compared the size of the spines of the proximal dendritic domain that appear during activity block and after an inferior olive lesion. In this region also, the spines in the absence of activity are significantly smaller. In the proximal dendritic domain, the new spines that develop in the absence of activity are innervated by parallel fibers and are not significantly different in size from those of the branchlets, although they are shorter. Thus, the spontaneous activity of the cerebellar cortex is necessary not only to maintain the physiological spine distribution profile in the Purkinje cell dendritic tree, but also acts as a signal that prevents spines from shrinking.

Agmatine inhibits the proliferation of rat hepatoma cells by modulation of polyamine metabolism.

BACKGROUND/AIMS: Previous experiments have shown that agmatine, the product of arginine decarboxylase, is transported in competition with putrescine into quiescent rat hepatocytes, where it promotes several effects, including marked decrease of intracellular polyamines and induction of apoptosis. The primary aim of the present study was to assess the action of agmatine on transformed and proliferating hepatic rat cells. METHODS: To assess the effect of agmatine on hepatoma cells, analysis by flow cytometry, Western blotting, reverse transcription-polymerase chain reaction, scanning and transmission electron microscopy, immunofluorescence detection of beta-actin and alpha-tubulin were performed. RESULTS: The results showed that agmatine has antiproliferative effects on the cell lines studied (HTC, JM2, HepG2). Further experiments were performed on HTC cells. The effect was proportional to agmatine concentration (in a range between 50 and 500 microM). It was not correlated with induction of necrosis or apoptosis and was accompanied by accumulation in G(2)/M cell cycle phase and by dramatic modification of cell morphology. Spermidine reversed these effects, suggesting that the marked decrease of the polyamine pool is the main target of agmatine . CONCLUSIONS: The results obtained show a relationship between the decrease of intracellular polyamine content, the rate of cell growth and the cytoskeleton organization.