Min Kyoo Shin

WIP1, a Homeostatic Regulator of the DNA Damage Response, Is Targeted by HIPK2 for Phosphorylation and Degradation

WIP1 (wild-type p53-induced phosphatase 1) functions as a homeostatic regulator of the ataxia telangiectasia mutated (ATM)-mediated signaling pathway in response to ionizing radiation (IR). Here we identify homeodomain-interacting protein kinase 2 (HIPK2) as a protein kinase that targets WIP1 for phosphorylation and proteasomal degradation. In unstressed cells, WIP1 is constitutively phosphorylated by HIPK2 and maintained at a low level by proteasomal degradation. In response to IR, ATM-dependent AMPKα2-mediated HIPK2 phosphorylation promotes inhibition of WIP1 phosphorylation through dissociation of WIP1 from HIPK2, followed by stabilization of WIP1 for termination of the ATM-mediated double-strand break (DSB) signaling cascade. Notably, HIPK2 depletion impairs IR-induced γ-H2AX foci formation, cell-cycle checkpoint activation, and DNA repair signaling, and the survival rate of hipk2+/- mice upon γ-irradiation is markedly reduced compared to wild-type mice. Taken together, HIPK2 plays a critical role in the initiation of DSB repair signaling by controlling WIP1 levels in response to IR.

Effects of treadmill exercise on hypoactivity of the hypothalamo-pituitary-adrenal axis induced by chronic administration of corticosterone in rats

The stress response alters behavior, autonomic function and secretion of multiple hormones, including CRF, ACTH, and glucocorticoid, through the HPA axis. Consecutive stress exposures lead to HPA axis dysregulation such as hyperactivity in Alzheimers disease and depression, and hypoactivity in post-traumatic stress disorder. In the present study, we established a model of hypoactivated HPA axis in rat through chronic administration of corticosterone (40mg/kg, s.c.) for 19 consecutive days. In this model, CRF mRNA expression in the hypothalamus and ACTH levels in serum were significantly decreased by chronic administration of corticosterone. In addition, the effect of treadmill exercise was investigated in our hypoactivated HPA axis rat model. Treadmill exercise recovered the dysregulated hypoactivity of the HPA axis induced by corticosterone administration for 19 days. The results of the present study suggest that treadmill exercise may aid recovery of hypoactivated HPA axis dysregulation in psychological diseases such as post-traumatic stress disorder.

The effect of ganglioside GQ1b on the NMDA receptor signaling pathway in H19-7 cells and rat hippocampus.

Gangliosides, sialic acid-containing glycosphingolipids, are related to various synaptic functions in the rat brain. Previously, we investigated the behavioral effects of the ganglioside GQ1b on learning and memory using the Y-maze and Morris water maze test. GQ1b-treated rats showed highly increased memory performance on the Y-maze and the Morris water maze test. In this study, we determined the role of GQ1b on the activation of the N-methyl-d-aspartate (NMDA) receptor signaling pathway in H19-7 rat hippocampal cells and the hippocampus of rats. After 12 h of treatment with GQ1b, the expression levels of NMDA receptor subunit 2A and 2B were increased in H19-7 cells and the hippocampus of rats. In addition, treatment of GQ1b increased the tyrosine phosphorylation of NR2B that may enhance NMDA receptor synaptic activation and enhancement of NMDA receptors. Also, following GQ1b treatment, the phosphorylation of extracellular signal-regulated kinases (ERK1/2) and protein kinase A, a cAMP activated protein kinase (PKA) increased in H19-7 cells and the hippocampus of rats. These increases resulted in an increase in the phosphorylation of cAMP response element binding protein (CREB). These results suggest that GQ1b might facilitate the activation of the NMDA receptor signaling pathway in the hippocampus of rats, an effect which is dependent on ERK1/2, PKA and CREB phosphorylation. Also, these data support our previous result that GQ1b improves the learning and memory of rats.

A novel trimeric peptide, Neuropep‐1‐stimulating brain‐derived neurotrophic factor expression in rat brain improves spatial learning and memory as measured by the Y‐maze and Morris water maze

J. Neurochem. (2011) 116, 205–216.

A novel brain-derived neurotrophic factor-modulating peptide attenuates Aβ1-42-induced neurotoxicity in vitro

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family, which plays important roles in learning and memory formation and in protecting neurons from diverse neurotoxic insults, such as amyloid-beta (Aβ). Since BDNF expression is decreased in patients with Alzheimers disease, various strategies have attempted to increase BDNF levels. In a previous study, we screened and identified a novel BDNF-modulating peptide (consisting of methionine-valine-glycine, named Neuropep-1) by a positional scanning-synthetic peptide combinatorial library (PS-SPCL). Neuropep-1 exhibited neuroprotective effects against in vitro and in vivo Alzheimers disease models. Based on the previous PS-SPCL data, we modified the amino acid sequence of Neuropep-1 in this study to identify a more potent novel BDNF-modulating peptide. By replacing the valine in the second position with aspartic acid, the resulting Neuropep-4 was found to be highly effective in inducing BDNF expression even at concentrations of 1pM in the SH-SY5Y cell line and rat primary cortical neurons. In addition, among the tested peptides, Neuropep-4 provided neurons with the strongest protection against oligomeric and/or fibrillar Aβ1-42-induced cell death through BDNF upregulation. These results suggest the potential of Neuropep-4 as a therapeutic candidate for treating neurodegenerative diseases, such as AD.

Chronic Stress Decreases Cerebrovascular Responses During Rat Hindlimb Electrical Stimulation.

Repeated stress is one of the major risk factors for cerebrovascular disease, including stroke, and vascular dementia. However, the functional alterations in the cerebral hemodynamic response induced by chronic stress have not been clarified. Here, we investigated the in vivo cerebral hemodynamic changes and accompanying cellular and molecular changes in chronically stressed rats. After 3 weeks of restraint stress, the elicitation of stress was verified by behavioral despair in the forced swimming test and by physical indicators of stress. The evoked changes in the cerebral blood volume and pial artery responses following hindpaw electrical stimulation were measured using optical intrinsic signal imaging. We observed that, compared to the control group, animals under chronic restraint stress exhibited a decreased hemodynamic response, with a smaller pial arterial dilation in the somatosensory cortex during hindpaw electrical stimulation. The effect of chronic restraint stress on vasomodulator enzymes, including neuronal nitric oxide synthase (nNOS) and heme oxygenase-2 (HO-2), was assessed in the somatosensory cortex. Chronic restraint stress downregulated nNOS and HO-2 compared to the control group. In addition, we examined the subtypes of cells that can explain the environmental changes due to the decreased vasomodulators. The expression of parvalbumin in GABAergic interneurons and glutamate receptor-1 in neurons were decreased, whereas the microglial activation was increased. Our results suggest that the chronic stress-induced alterations in cerebral vascular function and the modulations of the cellular expression in the neuro-vasomodulatory system may be crucial contributing factors in the development of various vascular-induced conditions in the brain.