Nitric Oxide Upregulates Proteasomal Protein Degradation in Neurons.

Nitric oxide (NO) is involved in many neuronal functions such as neuromodulation and intracellular signaling. Recent studies have demonstrated that nitric oxide is involved in regulation of proteasomal protein degradation. However, its role in neuronal protein degradation still remains unclear. In our study, we investigated the influence of endogenous nitric oxide production in this process. We have shown that nitric oxide synthase blockade prevents decline of the UbG76V-GFP fluorescence (GFP-based proteasomal protein degradation reporter) in neuronal processes of the cultured hippocampal neurons. It suggests that nitric oxide may regulate ubiquitin-dependent proteasomal protein degradation in neurons. Also, we have confirmed that the NO synthesis blockade alone significantly impairs long-term potentiation, and demonstrated for the first time that simultaneous blockade of the NO and proteins synthesis leads to the long-term potentiation amplitude rescue to the control values. Obtained results suggest that nitric oxide is involved in the protein degradation in proteasomes in physiological conditions.

Lentiviral Modulation of Wnt/ß-Catenin Signaling Affects In Vivo LTP.

Wnt signaling is involved in hippocampal development and synaptogenesis. Numerous recent studies have been focused on the role of Wnt ligands in the regulation of synaptic plasticity. Inhibitors and activators of canonical Wnt signaling were demonstrated to decrease or increase, respectively, in vitro long-term potentiation (LTP) maintenance in hippocampal slices (Chen et al. in J Biol Chem 281:11910-11916, 2006; Vargas et al. in J Neurosci 34:2191-2202, 2014, Vargas et al. in Exp Neurol 264:14-25, 2015). Using lentiviral approach to down- and up-regulate the canonical Wnt signaling, we explored whether Wnt/ß-catenin signaling is critical for the in vivo LTP. Chronic suppression of Wnt signaling induced an impairment of in vivo LTP expression 14 days after lentiviral suspension injection, while overexpression of Wnt3 was associated with a transient enhancement of in vivo LTP magnitude. Both effects were related to the early phase LTP and did not affect LTP maintenance. A loss-of-function study demonstrated decreased initial paired pulse facilitation ratio, ß-catenin, and phGSK-3ß levels. A gain-of-function study revealed not only an increase in PSD-95, ß-catenin, and Cyclin D1 protein levels, but also a reduced phGSK-3ß level and enhanced GSK-3ß kinase activity. These results suggest a presynaptic dysfunction predominantly underlying LTP impairment while postsynaptic modifications are primarily involved in transient LTP amplification. This study is the first demonstration of the involvement of Wnt/ß-catenin signaling in synaptic plasticity regulation in an in vivo LTP model.

Lentiviral-mediated overexpression of nerve growth factor (NGF) prevents beta-amyloid [25-35]-induced long term potentiation (LTP) decline in the rat hippocampus.

We have explored the potential neuroprotective effect of local lentiviraly-mediated overexpression of nerve growth factor (NGF) on in vivo long-term potentiation (LTP) in the rat hippocampus under pathological conditions. The suspension of lentiviral particles was prepared using a genetic construct containing the human NGF gene under the control of a neuron-specific CaMKII promoter. Two weeks after the viral injection NGF concentration in the hippocampus doubled. In vivo recordings of total electrical activity in the dentate gyrus were performed. While the increased expression of NGF did not affect the amplitude of evoked postsynaptic potentials recorded after a high-frequency stimulation of the perforant path, it prevented the LTP decline induced by the i.c.v. administration of 50 nM beta-amyloid (25-35) 1h prior to tetanization. Our results demonstrate that increased endogenous NGF concentration can rescue hippocampal neuronal function from beta-amyloid peptide induced impairment.

Transient disturbances in contextual fear memory induced by Aß(25-35) in rats are accompanied by cholinergic dysfunction.

Damage to the medial septum (MS) or disruption of the septo-hippocampal pathway is often considered as a basis for memory impairments, manifesting in the hippocampus-dependent behavioral paradigms. In the present study, we have examined the effects of intracerebroventricular administration of aggregated amyloid-ß (25-35) (Aß(25-35)) on contextual fear conditioning and the condition of cholinergic neurons in the MS using immunohistochemical detection of choline acetyltransferase (ChAT) and expression of the "cholinergic locus genes" (ChAT and vesicular acetylcholine transporter (VaChT) mRNA). A single injection of Aß(25-35) induced transient moderate impairments in contextual fear conditioning accompaniedby a decrease in ChAT expression. However, the long-term decline in ChAT and VaChT expression was not associated with stable impairments in contextual fear memory. An Aß(25-35)-induced progressive decrease in the number of ChAT expressing neurons in the MS was revealed, but no gross neuronal cell loss in the MS could be detected (as judged by the density of NeuN-immunoreactive cells). Thus, Aß(25-35) induced a loss of the cholinergic phenotype of septal neurons without neuronal cell death in MS. The data give an additional support to the concept of early impairments in the synthesis of proteins related to the cholinergic system as an important mechanism in amyloid-induced neuronal damage.

Human-specific endogenous retroviral insert serves as an enhancer for the schizophrenia-linked gene PRODH.

Using a systematic, whole-genome analysis of enhancer activity of human-specific endogenous retroviral inserts (hsERVs), we identified an element, hsERVPRODH, that acts as a tissue-specific enhancer for the PRODH gene, which is required for proper CNS functioning. PRODH is one of the candidate genes for susceptibility to schizophrenia and other neurological disorders. It codes for a proline dehydrogenase enzyme, which catalyses the first step of proline catabolism and most likely is involved in neuromediator synthesis in the CNS. We investigated the mechanisms that regulate hsERVPRODH enhancer activity. We showed that the hsERVPRODH enhancer and the internal CpG island of PRODH synergistically activate its promoter. The enhancer activity of hsERVPRODH is regulated by methylation, and in an undermethylated state it can up-regulate PRODH expression in the hippocampus. The mechanism of hsERVPRODH enhancer activity involves the binding of the transcription factor SOX2, whch is preferentially expressed in hippocampus. We propose that the interaction of hsERVPRODH and PRODH may have contributed to human CNS evolution.

Knocking down of the KCC2 in rat hippocampal neurons increases intracellular chloride concentration and compromises neuronal survival.

KCC2 is a neuron-specific potassium-chloride co-transporter controlling intracellular chloride homeostasis in mature and developing neurons. It is implicated in the regulation of neuronal migration, dendrites outgrowth and formation of the excitatory and inhibitory synaptic connections. The function of KCC2 is suppressed under several pathological conditions including neuronal trauma, different types of epilepsies, axotomy of motoneurons, neuronal inflammations and ischaemic insults. However, it remains unclear how down-regulation of the KCC2 contributes to neuronal survival during and after toxic stress. Here we show that in primary hippocampal neuronal cultures the suppression of the KCC2 function using two different shRNAs, dominant-negative KCC2 mutant C568A or DIOA inhibitor, increased the intracellular chloride concentration [Cl⁻]i and enhanced the toxicity induced by lipofectamine-dependent oxidative stress or activation of the NMDA receptors. The rescuing of the KCC2 activity using over-expression of the active form of the KCC2, but not its non-active mutant Y1087D, effectively restored [Cl⁻]i and enhanced neuronal resistance to excitotoxicity. The reparative effects of KCC2 were mimicked by over-expression of the KCC3, a homologue transporter. These data suggest an important role of KCC2-dependent potassium/chloride homeostasis under neurototoxic conditions and reveal a novel role of endogenous KCC2 as a neuroprotective molecule.

A family of human zinc finger proteins that bind methylated DNA and repress transcription.

In vertebrates, densely methylated DNA is associated with inactive transcription. Actors in this process include proteins of the MBD family that can recognize methylated CpGs and repress transcription. Kaiso, a structurally unrelated protein, has also been shown to bind methylated CGCGs through its three Krüppel-like C2H2 zinc fingers. The human genome contains two uncharacterized proteins, ZBTB4 and ZBTB38, that contain Kaiso-like zinc fingers. We report that ZBTB4 and ZBTB38 bind methylated DNA in vitro and in vivo. Unlike Kaiso, they can bind single methylated CpGs. When transfected in mouse cells, the proteins colocalize with foci of heavily methylated satellite DNA and become delocalized upon loss of DNA methylation. Chromatin immunoprecipitation suggests that both of these proteins specifically bind to the methylated allele of the H19/Igf2 differentially methylated region. ZBTB4 and ZBTB38 repress the transcription of methylated templates in transfection assays. The two genes have distinct tissue-specific expression patterns, but both are highly expressed in the brain. Our results reveal the existence of a family of Kaiso-like proteins that bind methylated CpGs. Like proteins of the MBD family, they are able to repress transcription in a methyl-dependent manner, yet their tissue-specific expression pattern suggests nonoverlapping functions.

Kaiso-deficient mice show resistance to intestinal cancer.

Kaiso is a BTB domain protein that associates with the signaling molecule p120-catenin and binds to the methylated sequence mCGmCG or the nonmethylated sequence CTGCNA to modulate transcription. In Xenopus laevis, xKaiso deficiency leads to embryonic death accompanied by premature gene activation in blastulae and upregulation of the xWnt11 gene. Kaiso has also been proposed to play an essential role in mammalian synapse-specific transcription. We disrupted the Kaiso gene in mice to assess its role in mammalian development. Kaiso-null mice were viable and fertile, with no detectable abnormalities of development or gene expression. However, when crossed with tumor-susceptible Apc(Min/+) mice, Kaiso-null mice showed a delayed onset of intestinal tumorigenesis. Kaiso was found to be upregulated in murine intestinal tumors and is expressed in human colon cancers. Our data suggest that Kaiso plays a role in intestinal cancer and may therefore represent a potential target for therapeutic intervention.