The miRNA transcriptome of cerebrospinal fluid in preterm infants reveals the signaling pathways that promote reactive gliosis following cerebral hemorrhage

Introduction

Germinal Matrix-Intraventricular Haemorrhage (GM-IVH) is one of the most common neurological complications in preterm infants, which can lead to accumulation of cerebrospinal fluid (CSF) and is a major cause of severe neurodevelopmental impairment in preterm infants. However, the pathophysiological mechanisms triggered by GM-IVH are poorly understood. Analyzing the CSF that accumulates following IVH may allow the molecular signaling and intracellular communication that contributes to pathogenesis to be elucidated. Growing evidence suggests that miRs, due to their key role in gene expression, have a significant utility as new therapeutics and biomarkers.

Methods

The levels of 2,083 microRNAs (miRs) in 15 CSF samples from 10 infants with IVH were measured using miRNA whole transcriptome sequencing. Gene ontology (GO) and miR family analysis were used to uncover dysregulated signalling which were then validated in vitro in human foetal neural progenitor cells treated with IVH-CSF.

Results

Five hundred eighty-seven miRs were differentially expressed in the CSF extracted at least 2 months after injury, compared to CSF extracted within the first month of injury. GO uncovered key pathways targeted by differentially expressed miRs including the MAPK cascade and the JAK/STAT pathway. Astrogliosis is known to occur in preterm infants, and we hypothesized that this could be due to abnormal CSF-miR signaling resulting in dysregulation of the JAK/STAT pathway - a key controller of astrocyte differentiation. We then confirmed that treatment with IVH-CSF promotes astrocyte differentiation from human fetal NPCs and that this effect could be prevented by JAK/STAT inhibition. Taken together, our results provide novel insights into the CSF/NPCs crosstalk following perinatal brain injury and reveal novel targets to improve neurodevelopmental outcomes in preterm infants.

Podocyte GSK3 is an evolutionarily conserved critical regulator of kidney function

Albuminuria affects millions of people, and is an independent risk factor for kidney failure, cardiovascular morbidity and death. The key cell that prevents albuminuria is the terminally differentiated glomerular podocyte. Here we report the evolutionary importance of the enzyme Glycogen Synthase Kinase 3 (GSK3) for maintaining podocyte function in mice and the equivalent nephrocyte cell in Drosophila. Developmental deletion of both GSK3 isoforms (α and β) in murine podocytes causes late neonatal death associated with massive albuminuria and renal failure. Similarly, silencing GSK3 in nephrocytes is developmentally lethal for this cell. Mature genetic or pharmacological podocyte/nephrocyte GSK3 inhibition is also detrimental; producing albuminuric kidney disease in mice and nephrocyte depletion in Drosophila. Mechanistically, GSK3 loss causes differentiated podocytes to re-enter the cell cycle and undergo mitotic catastrophe, modulated via the Hippo pathway but independent of Wnt-β-catenin. This work clearly identifies GSK3 as a critical regulator of podocyte and hence kidney function.

Exosomes populate the cerebrospinal fluid of preterm infants with post-haemorrhagic hydrocephalus

BACKGROUND

Preterm infants are at risk of germinal matrix haemorrhage-intraventricular haemorrhage (GMH-IVH) which leads to post-haemorrhagic hydrocephalus (PHH) in 30% of infants; this is associated with moderate-severe neurodevelopmental impairment and confers significant risk of cerebral palsy. There are however no predictive indicators of the severity or long-term outcome after GMH-IVH. In recent years, endosome-derived extracellular vesicles (EVs) or exosomes have been isolated from biofluids and shown to mediate intercellular communication via selective enrichment in proteins and micro-RNAs.

METHODS

This study aimed to isolate and characterise EVs from the cerebrospinal fluid (CSF) of 3 preterm infants with PHH using nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM) with immunogold protein labelling, and micro-RNA analysis.

RESULTS

NTA of unaltered CSF revealed a heterogeneous and dynamic population of EVs. Exosomal-sized EVs were isolated by differential ultracentrifugation and TEM confirmed the presence of CD63⁺ and CD81⁺ exosomes. The micro-RNAs miR-9, miR-17, miR-26a, miR-124 and miR-1911 were detected within the exosome-enriched fraction and profiled over time.

CONCLUSION

This is the first reported characterisation of exosomes from the CSF of preterm infants with post-haemorrhagic hydrocephalus.

Transplantation of canine olfactory ensheathing cells producing chondroitinase ABC promotes chondroitin sulphate proteoglycan digestion and axonal sprouting following spinal cord injury

Olfactory ensheathing cell (OEC) transplantation is a promising strategy for treating spinal cord injury (SCI), as has been demonstrated in experimental SCI models and naturally occurring SCI in dogs. However, the presence of chondroitin sulphate proteoglycans within the extracellular matrix of the glial scar can inhibit efficient axonal repair and limit the therapeutic potential of OECs. Here we have used lentiviral vectors to genetically modify canine OECs to continuously deliver mammalian chondroitinase ABC at the lesion site in order to degrade the inhibitory chondroitin sulphate proteoglycans in a rodent model of spinal cord injury. We demonstrate that these chondroitinase producing canine OECs survived at 4 weeks following transplantation into the spinal cord lesion and effectively digested chondroitin sulphate proteoglycans at the site of injury. There was evidence of sprouting within the corticospinal tract rostral to the lesion and an increase in the number of corticospinal axons caudal to the lesion, suggestive of axonal regeneration. Our results indicate that delivery of the chondroitinase enzyme can be achieved with the genetically modified OECs to increase axon growth following SCI. The combination of these two promising approaches is a potential strategy for promoting neural regeneration following SCI in veterinary practice and human patients.

Control of epigenetic states by WT1 via regulation of de novo DNA methyltransferase 3A

Although tumour suppressor gene hypermethylation is a universal feature of cancer cells, little is known about the necessary molecular triggers. Here, we show that Wilms' tumour 1 (WT1), a developmental master regulator that can also act as a tumour suppressor or oncoprotein, transcriptionally regulates the de novo DNA methyltransferase 3A (DNMT3A) and that cellular WT1 levels can influence DNA methylation of gene promoters genome-wide. Specifically, we demonstrate that depletion of WT1 by short-interfering RNAs leads to reduced DNMT3A in Wilms' tumour cells and human embryonal kidney-derived cell lines. Chromatin immunoprecipitation assays demonstrate WT1 recruitment to the DNMT3A promoter region and reporter assays confirm that WT1 directly transactivates DNMT3A expression. Consistent with this regulatory role, immunohistochemical analysis shows co-expression of WT1 and DNMT3A proteins in nuclei of blastemal cells in human fetal kidney and Wilms' tumours. Using genome-wide promoter methylation arrays, we show that human embryonal kidney cells over-expressing WT1 acquire DNA methylation changes at specific gene promoters where DNMT3A recruitment is increased, with hypermethylation being associated with silencing of gene expression. Elevated DNMT3A is also demonstrated at hypermethylated genes in Wilms' tumour cells, including a region of long-range epigenetic silencing. Finally, we show that depletion of WT1 in Wilms' tumour cells can lead to reactivation of gene expression from methylated promoters, such as TGFB2, a key modulator of epithelial-mesenchymal transitions. Collectively, our work defines a new regulatory modality for WT1 involving elicitation of epigenetic alterations which is most likely crucial to its functions in development and disease.

Fusion between human mesenchymal stem cells and rodent cerebellar Purkinje cells

AIMS

we explored whether cellular fusion and heterokaryon formation between human and rodent cells in the cerebellum of mice occurs after intravenous injection of human bone marrow-derived mesenchymal stem cells (MSCs). The influence of central nervous system inflammation on this process was also assessed. In addition, we examined whether tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma, factors associated with inflammation, increase cellular fusion between human MSCs and rodent cerebellar neurons in vitro.

METHODS AND RESULTS

human MSCs were intravenously injected into mice with experimental autoimmune encephalomyelitis (EAE) and control mice. After 22 days, mouse Purkinje cells expressing human Golgi Zone were found within the Purkinje cell layer of the cerebellum, indicating that fusion and heterokaryon formation had occurred. The numbers of heterokaryons in the cerebellum were markedly increased in mice with EAE compared with control mice. Rodent cerebellar neuronal cells labelled with enhanced green fluorescent proteinin vitro were co-cultured with human bone marrow-derived MSCs in the presence of TNF-alpha and/or IFN-gamma to determine their influence on fusion events. We found that fusion between MSCs and cerebellar neurons did occur in vitro and that the frequency of cellular fusion increased in the presence of TNF-alpha and/or IFN-gamma.

CONCLUSIONS

we believe that this is the first paper to define fusion and heterokaryon formation between human MSCs and rodent cerebellar neurons in vivo. We have also demonstrated that fusion between these cell populations occurs in vitro. These findings indicate that MSCs may be potential therapeutic agents for cerebellar diseases, and other neuroinflammatory and neurodegenerative disorders.

Prolyl oligopeptidase binds to GAP-43 and functions without its peptidase activity

Inhibitors of the enzyme prolyl oligopeptidase (PO) improve performance in rodent learning and memory tasks. PO inhibitors are also implicated in the action of drugs used to treat bipolar disorder: they reverse the effects of three mood stabilizers on the dynamic behaviour of neuronal growth cones. PO cleaves prolyl bonds in short peptides, suggesting that neuropeptides might be its brain substrates. PO is located in the cytosol, however, where it would not contact neuropeptides. Here, we show that mice with a targeted PO null-mutation have altered growth cone dynamics. The wild-type phenotype is restored by PO cDNAs encoding either native or a catalytically-dead enzyme. In addition, we show that PO binds to the growth-associated protein GAP-43, which is a key regulator of synaptic plasticity. Taken together, our results show that peptidase activity is not required for PO function in neurons and suggest that PO instead acts by binding to cytosolic proteins that control growth cone and synaptic function.

A novel member of the SAF (scaffold attachment factor)-box protein family inhibits gene expression and induces apoptosis

The SLTM [SAF (scaffold attachment factor)-like transcription modulator] protein contains a SAF-box DNA-binding motif and an RNA-binding domain, and shares an overall identity of 34% with SAFB1 {scaffold attachment factor-B1; also known as SAF-B (scaffold attachment factor B), HET [heat-shock protein 27 ERE (oestrogen response element) and TATA-box-binding protein] or HAP (heterogeneous nuclear ribonucleoprotein A1-interacting protein)}. Here, we show that SLTM is localized to the cell nucleus, but excluded from nucleoli, and to a large extent it co-localizes with SAFB1. In the nucleus, SLTM has a punctate distribution and it does not co-localize with SR (serine/arginine) proteins. Overexpression of SAFB1 has been shown to exert a number of inhibitory effects, including suppression of oestrogen signalling. Although SLTM also suppressed the ability of oestrogen to activate a reporter gene in MCF-7 breast-cancer cells, inhibition of a constitutively active beta-galactosidase gene suggested that this was primarily the consequence of a generalized inhibitory effect on transcription. Measurement of RNA synthesis, which showed a particularly marked inhibition of [(3)H]uridine incorporation into mRNA, supported this conclusion. In addition, analysis of cell-cycle parameters, chromatin condensation and cytochrome c release showed that SLTM induced apoptosis in a range of cultured cell lines. Thus the inhibitory effects of SLTM on gene expression appear to result from generalized down-regulation of mRNA synthesis and initiation of apoptosis consequent upon overexpressing the protein. While indicating a crucial role for SLTM in cellular function, these results also emphasize the need for caution when interpreting phenotypic changes associated with manipulation of protein expression levels.

VEGF and angiopoietin-1 stimulate different angiogenic phenotypes that combine to enhance functional neovascularization in adult tissue

OBJECTIVE

Therapeutic angiogenesis requires an understanding of how growth factors such as vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1) result in physiological neovascularization. This study determined the physiological mechanism by which adenoviral delivery of growth factor combinations alter vascular phenotype and functionality.

METHODS

Adenovirus-mediated gene transfer into the adjacent fat pad of the rat mesentery was used to characterize induction of angiogenesis by VEGF and Ang-1, in a model that permitted a detailed examination of the neovessel phenotype.

RESULTS

Ang-1 combined with VEGF resulted in a distinct vascular phenotype from either factor alone. Microvascular perfusion was significantly enhanced in all groups, but VEGF produced short, narrow, highly branched and sprouting vessels, with normal pericyte coverage. Ang-1 induced broader, longer neovessels, with no increase in branching or sprouting, yet a significantly higher pericyte ensheathment. Combination of Ang-1 and VEGF generated a significantly higher degree of functionally perfused, larger, less branched, and more mature microvessels, resulting from increased efficiency of sprout to vessel formation. Ang-1 and VEGF also caused differential effects on larger compared with smaller blood vessels, a finding reproduced in vitro.

CONCLUSIONS

Ang-1 and VEGF use different physiological mechanisms to enhance neovascularization of relatively avascular tissue. Administration of both growth factors combines these physiological mechanisms to give greater enhancement of neovascularization than either growth factor alone. These results suggest that effective revascularization therapy may require combination growth factor treatment.

cAMP responsive element-binding protein phosphorylation is necessary for perirhinal long-term potentiation and recognition memory

We established the importance of phosphorylation of cAMP responsive element-binding protein (CREB) to both the familiarity discrimination component of long-term recognition memory and plasticity within the perirhinal cortex of the temporal lobe. Adenoviral transduction of perirhinal cortex (and adjacent visual association cortex) with a dominant-negative inhibitor of CREB impaired the preferential exploration of novel over familiar objects at a long (24 h) but not a short (15 min) delay, disrupted the normal reduced activation of perirhinal neurons to familiar compared with novel pictures, and impaired long-term potentiation of synaptic transmission in perirhinal slices. The consistency of these effects across the behavioral, systems, and cellular levels of analysis provides strong evidence for involvement of CREB phosphorylation in synaptic plastic processes within perirhinal cortex necessary for long-term recognition memory.

Removal of AMPA receptors (AMPARs) from synapses is preceded by transient endocytosis of extrasynaptic AMPARs

AMPA receptors (AMPARs) are dynamically regulated at synapses, but the time course and location of their exocytosis and endocytosis are not known. Therefore, we have used ecliptic pHluorin-tagged glutamate receptor 2 to visualize changes in AMPAR surface expression in real time. We show that synaptic and extrasynaptic AMPARs respond very differently to NMDA receptor activation; there is a rapid internalization of extrasynaptic AMPARs that precedes the delayed removal of synaptic AMPARs.

A mutant receptor with enhanced dominant-negative activity for the blockade of human prolactin signalling

An effective mechanism for interfering with prolactin signalling would provide a powerful tool for clarifying the importance of prolactin in breast cancer, as well as for investigating functions of prolactin in other tissues. Based on our previous identification of a dominant-negative mutation in the growth hormone receptor that causes familial short stature, we investigated the potential for using a similar truncated mutant of the prolactin receptor (PRLR1-242). Like the mutant growth hormone receptor, PRLR1-242 exerts an exceptionally powerful dominant-negative effect. A probable explanation for the strong dominant-negative activity of this class of mutation is that, lacking internalisation motifs, the truncated mutants accumulate at the cell surface and form non-functional heterodimers with wild-type receptors. In accordance with evidence for heterodimer formation between the two receptors, PRLR1-242 also blocks signalling by the growth hormone receptor. When expressed from an adenoviral vector, PRLR1-242 inhibits activation of STAT5 (signal transducer and activator of transcription 5) by prolactin in T47-D breast cancer cells, and blocks the ability of prolactin to induce proliferation in these cells. Thus PRLR1-242 provides an effective means of blocking the responsiveness of target tissues to human prolactin.

cAMP-dependent protein kinase A mediation of vasopressin gene expression in the hypothalamus of the osmotically challenged rat

We have tested the hypothesis that 3', 5'-cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is involved in the regulation of the vasopressin (VP) gene in the magnocellular neurons of the paraventricular nucleus (PVN) of the osmotically challenged rat. An adenoviral vector expressing a potent peptide inhibitor of PKA, Ad.CMV.PKIalpha, was demonstrated to be highly efficient in vitro. Ad.CMV.PKIalpha was then introduced into the PVN of rats bearing a VP reporter transgene (3-VCAT-3) consisting of the VP structural gene containing an epitope reporter in exon III, flanked by 3 kb of upstream and 3 kb of downstream sequence Robust transgene expression is seen in VP neurons of the PVN, and this increases following 72 h of dehydration. Ad.CMV.PKIalpha significantly blunted 3-VCAT-3 expression in the osmotically stimulated PVN. Our evidence suggests that PKA mediates changes in VP gene expression in response to dehydration through sequences contained within the 3-VCAT-3 transgene.

Ubiquitin, PGP 9.5 and dense body formation in trimethyltin intoxication: differential neuronal responses to chemically induced cell damage

Ubiquitin in normal cells may be important in degrading or transferring short-lived or aberrant proteins to lysosomal dense bodies. To examine its role in degrading proteins produced by a chemical insult, changes in the distribution of ubiquitin and the carboxy-terminal hydrolase, PGP 9.5, have been studied in rat hippocampal neurons and cerebellar Purkinje cells in trimethyltin intoxication. Here tubulovesicular dense bodies (TVBs) form from 12h onwards associated with vacuolation of the Golgi apparatus. Striking accumulations of lysosomal dense bodies follow in hippocampal pyramidal cells but not in cerebellar Purkinje cells; many of the hippocampal neurons later die, while the Purkinje cells generally survive. Ubiquitin immunoreactivity was diffusely increased in hippocampal pyramidal and Purkinje cells 6 h after dosing. By 12 h both diffuse and granular ubiquitin immunoreactivity was present that intensified over 24 and 48 h. Both by light and electron microscopy TVBs showed ubiquitin immunoreactivity, but dense bodies in hippocampal perikarya did not stain with an anti-ubiquitin antibody. PGP 9.5 immunoreactivity was not altered in hippocampal cells at any time, while Purkinje and Golgi cell dendrites and perikarya showed intensified labelling at 3 h that reached a peak of 12 h. At 48 h Western blot analysis of hippocampal homogenates showed significant increases in high molecular weight (HMW) ubiquitin conjugates, while cerebellar homogenates showed an increase in ubiquitin-histone conjugates. Northern blot analyses showed no change in ubiquitin or PGP9.5 gene expression in hippocampus or cerebellum. These findings suggest that the material in the TVBs in hippocampal cells is not being degraded by the ubiquitin system but passes ubiquitinated into the lysosomal system, while material in Purkinje cell TVBs is degraded by the ubiquitin system, suggesting it may have a different composition in each type of neuron.