• Acetylation of the Pro-Apoptotic Factor, p53 in the Hippocampus following Cerebral Ischemia and Modulation by Estrogen

      Raz, Limor; Zhang, Quan-Guang; Han, Dong; Dong, Yan; De Sevilla, Liesl; Brann, Darrell W; Institute of Molecular Medicine and Genetics (2011-10-26)
      Background: Recent studies demonstrate that acetylation of the transcription factor, p53 on lysine373 leads to its enhanced stabilization/activity and increased susceptibility of cells to stress. However, it is not known whether acetylation of p53 is altered in the hippocampus following global cerebral ischemia (GCI) or is regulated by the hormone, 17b-estradiol (17b2E2), and thus, this study examined these issues.
    • Enhanced glutamatergic and decreased GABAergic synaptic appositions to GnRH neurons on proestrus in the rat: modulatory effect of aging.

      Khan, Mohammad; De Sevilla, Liesl; Mahesh, Virendra B; Brann, Darrell W; Institute of Molecular Medicine and Genetics (2010-04-26)
      BACKGROUND: Previous work by our lab and others has implicated glutamate as a major excitatory signal to gonadotropin hormone releasing hormone (GnRH) neurons, with gamma amino butyric acid (GABA) serving as a potential major inhibitory signal. However, it is unknown whether GABAergic and/or glutamatergic synaptic appositions to GnRH neurons changes on the day of the proestrous LH surge or is affected by aging. METHODOLOGY/PRINCIPAL FINDINGS: To examine this question, synaptic terminal appositions on GnRH neurons for VGAT (vesicular GABA transporter) and VGLUT2 (vesicular glutamate transporter-2), markers of GABAergic and glutamatergic synaptic terminals, respectively, was examined by immunohistochemistry and confocal microscopic analysis in young and middle-aged diestrous and proestrous rats. The results show that in young proestrous rats at the time of LH surge, we observed reciprocal changes in the VGAT and VGLUT2 positive terminals apposing GnRH neurons, where VGAT terminal appositions were decreased and VGLUT2 terminal appositions were significantly increased, as compared to young diestrus control animals. Interestingly, in middle-aged cycling animals this divergent modulation of VGAT and VGLUT2 terminal apposition was greatly impaired, as no significant differences were observed between VGAT and VGLUT2 terminals apposing GnRH neurons at proestrous. However, the density of VGAT and VGLUT2 terminals apposing GnRH neurons were both significantly increased in the middle-aged animals. CONCLUSIONS/SIGNIFICANCE: In conclusion, there is an increase in glutamatergic and decrease in GABAergic synaptic terminal appositions on GnRH neurons on proestrus in young animals, which may serve to facilitate activation of GnRH neurons. In contrast, middle-aged diestrous and proestrous animals show a significant increase in both VGAT and VGLUT synaptic terminal appositions on GnRH neurons as compared to young animals, and the cycle-related change in these appositions between diestrus and proestrus that is observed in young animals is lost.
    • Estrogen-astrocyte interactions: implications for neuroprotection.

      Dhandapani, Krishnan M.; Brann, Darrell W; Institute of Molecular Medicine and Genetics; Department of Neurology (2003-03-31)
      BACKGROUND: Recent work has suggested that the ovarian steroid 17beta-estradiol, at physiological concentrations, may exert protective effects in neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and acute ischemic stroke. While physiological concentrations of estrogen have consistently been shown to be protective in vivo, direct protection upon purified neurons is controversial, with many investigators unable to show a direct protection in highly purified primary neuronal cultures. These findings suggest that while direct protection may occur in some instances, an alternative or parallel pathway for protection may exist which could involve another cell type in the brain. PRESENTATION OF THE HYPOTHESIS: A hypothetical indirect protective mechanism is proposed whereby physiological levels of estrogen stimulate the release of astrocyte-derived neuroprotective factors, which aid in the protection of neurons from cell death. This hypothesis is attractive as it provides a potential mechanism for protection of estrogen receptor (ER)-negative neurons through an astrocyte intermediate. It is envisioned that the indirect pathway could act in concert with the direct pathway to achieve a more widespread global protection of both ER+ and ER- neurons. TESTING THE HYPOTHESIS: We hypothesize that targeted deletion of estrogen receptors in astrocytes will significantly attenuate the neuroprotective effects of estrogen. IMPLICATIONS OF THE HYPOTHESIS: If true, the hypothesis would significantly advance our understanding of endocrine-glia-neuron interactions. It may also help explain, at least in part, the reported beneficial effects of estrogen in neurodegenerative disorders. Finally, it also sets the stage for potential extension of the hypothetical mechanism to other important estrogen actions in the brain such as neurotropism, neurosecretion, and synaptic plasticity.
    • Extranuclear estrogen receptors mediate the neuroprotective effects of estrogen in the rat hippocampus.

      Yang, Li-cai; Zhang, Quan-Guang; Zhou, Cai-feng; Yang, Fang; Zhang, Yi-dong; Wang, Rui-min; Brann, Darrell W; Institute of Molecular Medicine and Genetics (2010-05-18)
      BACKGROUND: 17beta-estradiol (E2) has been implicated to exert neuroprotective effects in the brain following cerebral ischemia. Classically, E2 is thought to exert its effects via genomic signaling mediated by interaction with nuclear estrogen receptors. However, the role and contribution of extranuclear estrogen receptors (ER) is unclear and was the subject of the current study. METHODOLOGY/PRINCIPAL FINDINGS: To accomplish this goal, we employed two E2 conjugates (E2 dendrimer, EDC, and E2-BSA) that can interact with extranuclear ER and exert rapid nongenomic signaling, but lack the ability to interact with nuclear ER due to their inability to enter the nucleus. EDC or E2-BSA (10 microM) was injected icv 60 min prior to global cerebral ischemia (GCI). FITC-tagged EDC or E2-BSA revealed high uptake in the hippocampal CA1 region after icv injection, with a membrane (extranuclear) localization pattern in cells. Both EDC and E2-BSA exerted robust neuroprotection in the CA1 against GCI, and the effect was blocked by the ER antagonist, ICI182,780. EDC and E2-BSA both rapidly enhanced activation of the prosurvival kinases, ERK and Akt, while attenuating activation of the proapoptotic kinase, JNK following GCI, effects that were blocked by ICI182,780. Administration of an MEK or PI3K inhibitor blocked the neuroprotective effects of EDC and E2-BSA. Further studies showed that EDC increased p-CREB and BDNF in the CA1 region in an ERK- and Akt-dependent manner, and that cognitive outcome after GCI was preserved by EDC in an ER-dependent manner. CONCLUSIONS/SIGNIFICANCE: In conclusion, the current study demonstrates that activation of extranuclear ER results in induction of ERK-Akt-CREB-BDNF signaling in the hippocampal CA1 region, which significantly reduces ischemic neuronal injury and preserves cognitive function following GCI. The study adds to a growing literature that suggests that extranuclear ER can have important actions in the brain.
    • A New Antifibrotic Target of Ac-SDKP: Inhibition of Myofibroblast Differentiation in Rat Lung with Silicosis

      Xu, Hong; Yang, Fang; Sun, Ying; Yuan, Yuan; Cheng, Hua; Wei, Zhongqiu; Li, Shuyu; Cheng, Tan; Brann, Darrell W; Wang, Ruimin; et al. (2012-07-3)
      Background: Myofibroblast differentiation, characterized by a-smooth muscle actin (a-SMA) expression, is a key process in organ fibrosis, and is induced by TGF-b. Here we examined whether an anti-fibrotic agent, N-acetyl-seryl-aspartyllysylproline (Ac-SDKP), can regulate induction of TGF-b signaling and myofibroblast differentiation as a potential key component of its anti-fibrotic mechanism in vivo and in vitro.
    • Role of Rac1 GTPase in NADPH Oxidase Activation and Cognitive Impairment Following Cerebral Ischemia in the Rat

      Raz, Limor; Zhang, Quan-Guang; Zhou, Cai-feng; Han, Dong; Gulati, Priya; Yang, Li-cai; Yang, Fang; Wang, Rui-min; Brann, Darrell W; Institute of Molecular Medicine and Genetics (2010-09-7)
      Background: Recent work by our laboratory and others has implicated NADPH oxidase as having an important role in reactive oxygen species (ROS) generation and neuronal damage following cerebral ischemia, although the mechanisms controlling NADPH oxidase in the brain remain poorly understood. The purpose of the current study was to examine the regulatory and functional role of the Rho GTPase, Rac1 in NADPH oxidase activation, ROS generation and neuronal cell death/cognitive dysfunction following global cerebral ischemia in the male rat.
    • VPS35 haploinsufficiency increases Alzheimerâ s disease neuropathology

      Wen, Lei; Tang, Fu-Lei; Hong, Yan; Luo, Shi-Wen; Wang, Chun-Lei; He, Wanxia; Shen, Chengyong; Jung, Ji-Ung; Xiong, Fei; Lee, Dae-hoon; et al. (2011-11-28)
      VPS35, a major component of the retromer complex, is important for endosome-to-Golgi retrieval of membrane proteins. Although implicated in Alzheimerâ s disease (AD), how VPS35 regulates AD-associated pathology is unknown. In this paper, we show that hemizygous deletion of Vps35 in the Tg2576 mouse model of AD led to earlier-onset AD-like phenotypes, including cognitive memory deficits, defective long-term potentiation, and impaired postsynaptic glutamatergic neurotransmission in young adult age. These deficits correlated well with an increase of β-amyloid peptide (Aβ) level in the mutant hippocampus. We further demonstrate that VPS35 is predominantly expressed in pyramidal neurons of young adult hippocampus and interacts with BACE1, a protease responsible for Aβ production. Loss of VPS35 function in the mouse hippocampus increased BACE1 activity. Suppression of VPS35 expression in culture decreased BACE1 trans-Golgi localization but enriched it in endosomes. These results demonstrate an essential role for VPS35 in suppression of AD neuropathology and in inhibition of BACE1 activation and Aβ production by promoting BACE1 endosome-to-Golgi retrieval.