N-Wasp Regulates Oligodendrocyte Myelination.

Oligodendrocyte myelination depends on actin cytoskeleton rearrangement. Neural Wiskott-Aldrich syndrome protein(N-Wasp) is an actin nucleation factor that promotes polymerization of branched actin filaments. N-Wasp activity is essential for myelin membrane wrapping by Schwann cells, but its role in oligodendrocytes and CNS myelination remains unknown. Here we report that oligodendrocytes-specific deletion of N-Wasp in mice of both sexes resulted in hypomyelination (i.e., reduced number of myelinated axons and thinner myelin profiles), as well as substantial focal hypermyelination reflected by the formation of remarkably long myelin outfolds. These myelin outfolds surrounded unmyelinated axons, neuronal cell bodies, and other myelin profiles. The latter configuration resulted in pseudo-multimyelin profiles that were often associated with axonal detachment and degeneration throughout the CNS, including in the optic nerve, corpus callosum, and the spinal cord. Furthermore, developmental analysis revealed that myelin abnormalities were already observed during the onset of myelination, suggesting that they are formed by aberrant and misguided elongation of the oligodendrocyte inner lip membrane. Our results demonstrate that N-Wasp is required for the formation of normal myelin in the CNS. They also reveal that N-Wasp plays a distinct role in oligodendrocytes compared with Schwann cells, highlighting a difference in the regulation of actin dynamics during CNS and PNS myelination.SIGNIFICANCE STATEMENT Myelin is critical for the normal function of the nervous system by facilitating fast conduction of action potentials. During the process of myelination in the CNS, oligodendrocytes undergo extensive morphological changes that involve cellular process extension and retraction, axonal ensheathment, and myelin membrane wrapping. Here we present evidence that N-Wasp, a protein regulating actin filament assembly through Arp2/3 complex-dependent actin nucleation, plays a critical role in CNS myelination, and its absence leads to several myelin abnormalities. Our data provide an important step into the understanding of the molecular mechanisms underlying CNS myelination.

The effects of reboxetine treatment on depression-like behavior, brain neurotrophins, and ERK expression in rats exposed to chronic mild stress.

Chronic mild stress (CMS) in rats is an established rodent depression model. Antidepressants attenuate the depression-like symptoms and prevent the biochemical changes caused by stress. In the present study, we examined the effect of CMS and the selective norepinephrine reuptake inhibitor (NRI) reboxetine (REB) treatment on behavioral parameters in rats and on hippocampal and cortical neurotrophic factors. Male Sprague Dawley rats were exposed for 5 weeks to a variety of mild stressors. REB (5 mg/kg/i.p.) was daily injected to half of the stressed and unstressed groups. Animal behavior following CMS was tested using the Morris Water Maze (MWM) cognitive paradigm and by monitoring sucrose intake and weight gain. After 5 weeks of CMS, stressed rats showed decreased sucrose intake, and REB treatment normalized this decrease. CMS reduced hippocampal brain-derived neurotrophic factor (BDNF) levels, and REB treatment reversed this alteration and increased BDNF receptor (TrkB) levels. REB elevated hippocampal extracellular signal-regulated kinase (ERK) phosphorylation of both stressed and unstressed rats. In conclusion, our study shows that BDNF, its receptor TrkB, and ERK participate in the neurobiological response to chronic stress and in the molecular and cellular activities of REB in the hippocampus.

The effects of fluoxetine treatment in a chronic mild stress rat model on depression-related behavior, brain neurotrophins and ERK expression.

Depression is associated with hippocampus (HC) volume loss. Chronic mild stress (CMS) in rats is a model of depression. Antidepressants attenuate HC volume loss and reverse the depression-like symptoms of stressed animals. We evaluated the effect of CMS and the selective serotonin reuptake inhibitor, fluoxetine (FLX) treatment on behavioral and cognitive parameters in rats, and on HC and frontal cortex (FC) neurotrophic factors levels. Male rats were exposed sequentially, over a period of 5 weeks, to a variety of mild stressors. FLX (5 mg/kg/day ip) was administered to the stressed group and controls (unstressed). After 5 of CMS, animals were tested using the Morris Water Maze (MWM). In the MWM, we observed that FLX had a transitory effect on unstressed rats. CMS reduced insulin-like growth factor-1 receptor (IGF-1R) levels in the HC whereas after FLX treatment these levels reverted to normal range. CMS rats revealed a significant decrease in extracellular signal-regulated kinase (ERK) phosphorylation in both HC and FC regions, while FLX normalized these levels. This study suggests that IGF-1R and ERK may have a role in mediating the neural stress response and the mode of action of FLX. This role seems to be independent of the BDNF alterations.

N-WASP is required for membrane wrapping and myelination by Schwann cells.

During peripheral nerve myelination, Schwann cells sort larger axons, ensheath them, and eventually wrap their membrane to form the myelin sheath. These processes involve extensive changes in cell shape, but the exact mechanisms involved are still unknown. Neural Wiskott-Aldrich syndrome protein (N-WASP) integrates various extracellular signals to control actin dynamics and cytoskeletal reorganization through activation of the Arp2/3 complex. By generating mice lacking N-WASP in myelinating Schwann cells, we show that N-WASP is crucial for myelination. In N-WASP-deficient nerves, Schwann cells sort and ensheath axons, but most of them fail to myelinate and arrest at the promyelinating stage. Yet, a limited number of Schwann cells form unusually short internodes, containing thin myelin sheaths, with the occasional appearance of myelin misfoldings. These data suggest that regulation of actin filament nucleation in Schwann cells by N-WASP is crucial for membrane wrapping, longitudinal extension, and myelination.

Evidence for an inhibitory immunomodulatory effect of selected antidepressants on rat splenocytes: possible relevance to depression and hyperactive-immune disorders.

Antidepressants have been found to possess antiproliferative effect. In the immune system depression may activate pro-inflammatory cytokines. Therefore, the aim of this study was to assess the immunomodulatory activity of antidepressants in naïve rat. Rat splenocytes were activated with con A and treated with paroxetine, sertraline or clomipramine ex vivo. We found that the antidepressants inhibit cell viability and proliferation at IC50 of 5-8 microM of mitogen-stimulated rat splenocytes. This inhibitory effect was accompanied by cell cycle arrest and increase in apoptotic events as assayed by FACS. Moreover, antidepressants decrease the secretion of the TH1 factor--TNFalpha. In addition, the antidepressants reduced the expression of the enzyme cyclooxygenase2 which is involved in inflammation. On the cellular level we show the up-regulation of MAPK death signaling pathway and suppression of the anti-apoptotic factor--Bcl-2. These findings reveal the immunomodulatory effect of the selected antidepressants. These data suggest a novel use of antidepressants or their derivatives.

Relationship between antidepressants and IGF-1 system in the brain: possible role in cognition.

Antidepressants facilitate neuroplasticity by stimulating trophic factors. This study evaluated the effect of fluoxetine (FLX) treatment on insulin-like growth factor-1 (IGF-1) in the rat brain and its role in the effect of FLX on cognition. IGF-1 receptor (IGF-1R) protein expression and IGF-1 mRNA levels were assessed in rat frontal cortex (FC) and hippocampus, in FLX-treated [15 mg/kg, orally; 3 (acute) or 21 (repeated) days] male Wistar rats. Rats were subjected to the Morris Water Maze test. Acute FLX administration decreased IGF-1 mRNA levels in the FC and hippocampus and increased IGF-1R levels in the FC. Repeated FLX increased both mRNA and IGF-1R levels in the FC. Repeated, but not acute, FLX treatment decreased IGF-1 mRNA in the hippocampus. FLX did not affect cognitive performance. Thus, repeated FLX treatment leads to upregulation of IGF-1 system is FC. It is possible that FLX affect FC neuroplasticity through activation of the IGF-1 system.

Prostate cancer PET bioprobes: synthesis of [18F]-radiolabeled hydroxyflutamide derivatives.

Approximately 80-90% of prostate cancers are androgen dependent at initial diagnosis. The androgen receptor (AR) is present in most advanced prostate cancer specimens and is believed to have a critical role in its development. Today, treatment of prostate cancer is done by inhibition of AR using antiandrogens such as flutamide (pro-drug of hydroxyflutamide), nilutamide, and bicalutamide. However, there is currently no noninvasive imaging modalities to detect, guide, and monitor specific treatment of AR-positive prostate cancer. (R)-3-Bromo-N-(4-fluoro-3-(trifluoromethyl)phenyl)-2-hydroxy-2-methyl-propanamide [18F]-1 and N-(4-fluoro-3-(trifluoromethyl)phenyl)-2-hydroxy-2-methylpropanamide [18F]-2, derivatives of hydroxyflutamide, were synthesized as a fluorine-containing imaging agent candidates. A three-step fluorine-18 radiosynthesis route was developed, and the compounds were successfully labeled with a 10+/-3% decay corrected radiochemical yield, 95% radiochemical purity, and a specific activity of 1500+/-200 Ci/mmol end of bombardment (n = 10). These labeled biprobes not only may enable for the future quantitative molecular imaging of AR-positive prostate cancer using positron emission tomography but may also allow for image-guided treatment of prostate cancer.