Hiroko Nomaru

Galectin-1 promotes basal and kainate-induced proliferation of neural progenitors in the dentate gyrus of adult mouse hippocampus

We examined the expression of galectin-1, an endogenous lectin with one carbohydrate-binding domain, in the adult mouse hippocampus after systemic kainate administration. We found that the expression of galectin-1 was remarkably increased in activated astrocytes of the CA3 subregion and dentate gyrus of the hippocampus, and in nestin-positive neural progenitors in the dentate gyrus. Quantitative reverse transcription PCR (RT-PCR) analysis revealed that the galectin-1 mRNA level in hippocampus began to increase 1 day after kainate administration and that a 13-fold increase was attained within 3 days. Western blotting analysis confirmed that the level of galectin-1 protein increased to more than three-fold a week after the exposure. We showed that isolated astrocytes express and secrete galectin-1. To clarify the significance of the increased expression of galectin-1 in hippocampus, we compared the levels of hippocampal cell proliferation in galectin-1 knockout and wild-type mice after saline or kainate administration. The number of 5-bromo-2′-deoxyuridine (BrdU)-positive cells detected in the subgranular zone (SGZ) of galectin-1 knockout mice decreased to 62% with saline, and to 52% with kainate, as compared with the number seen in the wild-type mice. Most of the BrdU-positive cells in SGZ expressed doublecortin and neuron-specific nuclear protein, indicating that they are immature neurons. We therefore concluded that galectin-1 promotes basal and kainate-induced proliferation of neural progenitors in the hippocampus.

fosB-Null Mice Display Impaired Adult Hippocampal Neurogenesis and Spontaneous Epilepsy with Depressive Behavior

Patients with epilepsy are at high risk for major depression relative to the general population, and both disorders are associated with changes in adult hippocampal neurogenesis, although the mechanisms underlying disease onset remain unknown. The expression of fosB, an immediate early gene encoding FosB and ΔFosB/Δ2ΔFosB by alternative splicing and translation initiation, is known to be induced in neural progenitor cells within the subventricular zone of the lateral ventricles and subgranular zone of the hippocampus, following transient forebrain ischemia in the rat brain. Moreover, adenovirus-mediated expression of fosB gene products can promote neural stem cell proliferation. We recently found that fosB-null mice show increased depressive behavior, suggesting impaired neurogenesis in fosB-null mice. In the current study, we analyzed neurogenesis in the hippocampal dentate gyrus of fosB-null and fosBd/d mice that express ΔFosB/Δ2ΔFosB but not FosB, in comparison with wild-type mice, alongside neuropathology, behaviors, and gene expression profiles. fosB-null but not fosBd/d mice displayed impaired neurogenesis in the adult hippocampus and spontaneous epilepsy. Microarray analysis revealed that genes related to neurogenesis, depression, and epilepsy were altered in the hippocampus of fosB-null mice. Thus, we conclude that the fosB-null mouse is the first animal model to provide a genetic and molecular basis for the comorbidity between depression and epilepsy with abnormal neurogenesis, all of which are caused by loss of a single gene, fosB.

FosB is essential for the enhancement of stress tolerance and antagonizes locomotor sensitization by ΔfosB

BACKGROUND Molecular mechanisms underlying stress tolerance and vulnerability are incompletely understood. The fosB gene is an attractive candidate for regulating stress responses, because ΔFosB, an alternative splice product of the fosB gene, accumulates after repeated stress or antidepressant treatments. On the other hand, FosB, the other alternative splice product of the fosB gene, expresses more transiently than ΔFosB but exerts higher transcriptional activity. However, the functional differences of these two fosB products remain unclear. METHODS We established various mouse lines carrying three different types of fosB allele, wild-type (fosB(+)), fosB-null (fosB(G)), and fosB(d) allele, which encodes ΔFosB but not FosB, and analyzed them in stress-related behavioral tests. RESULTS Because fosB(+/d) mice show enhanced ΔFosB levels in the presence of FosB and fosB(d/d) mice show more enhanced ΔFosB levels in the absence of FosB, the function of FosB can be inferred from differences observed between these lines. The fosB(+/d) and fosB(d/d) mice showed increased locomotor activity and elevated Akt phosphorylation, whereas only fosB(+/d) mice showed antidepressive-like behaviors and increased E-cadherin expression in striatum compared with wild-type mice. In contrast, fosB-null mice showed increased depression-like behavior and lower E-cadherin expression. CONCLUSIONS These findings indicate that FosB is essential for stress tolerance mediated by ΔFosB. These data suggest that fosB gene products have a potential to regulate mood disorder-related behaviors.

Fosb gene products contribute to excitotoxic microglial activation by regulating the expression of complement C5a receptors in microglia.

The Fosb gene encodes subunits of the activator protein‐1 transcription factor complex. Two mature mRNAs, Fosb and ΔFosb, encoding full‐length FOSB and ΔFOSB proteins respectively, are formed by alternative splicing of Fosb mRNA. Fosb products are expressed in several brain regions. Moreover, Fosb‐null mice exhibit depressive‐like behaviors and adult‐onset spontaneous epilepsy, demonstrating important roles in neurological and psychiatric disorders. Study of Fosb products has focused almost exclusively on neurons; their function in glial cells remains to be explored. In this study, we found that microglia express equivalent levels of Fosb and ΔFosb mRNAs to hippocampal neurons and, using microarray analysis, we identified six microglial genes whose expression is dependent on Fosb products. Of these genes, we focused on C5ar1 and C5ar2, which encode receptors for complement C5a. In isolated Fosb‐null microglia, chemotactic responsiveness toward the truncated form of C5a was significantly lower than that in wild‐type cells. Fosb‐null mice were significantly resistant to kainate‐induced seizures compared with wild‐type mice. C5ar1 mRNA levels and C5aR1 immunoreactivity were increased in wild‐type hippocampus 24 hours after kainate administration; however, such induction was significantly reduced in Fosb‐null hippocampus. Furthermore, microglial activation after kainate administration was significantly diminished in Fosb‐null hippocampus, as shown by significant reductions in CD68 immunoreactivity, morphological change and reduced levels of Il6 and Tnf mRNAs, although no change in the number of Iba‐1‐positive cells was observed. These findings demonstrate that, under excitotoxicity, Fosb products contribute to a neuroinflammatory response in the hippocampus through regulation of microglial C5ar1 and C5ar2 expression. GLIA 2014;62:1284–1298

Characterization of galectin-1-positive cells in the mouse hippocampus.

Galectin-1 (gal-1) is one of several well-studied proteins from the galectin families. It is a 14.5 kDa glycoprotein with a single carbohydrate-binding domain. To examine the distribution and properties of gal-1 in the mouse hippocampus, we performed immunohistochemistry using an anti-gal-1 antibody. We found that most gal-1-positive cells showed both NeuN and &bgr;-tubulin III (Tuj-1) immunoreactivity (NeuN: 93%, &bgr;-tubulin III: 88%). Furthermore, we clarified that 77% of gal-1-positive cells expressed somatostatin, 79% of gal-1-positive cells expressed GAD67, 34% of gal-1-positive cells expressed parvalbumin, 5% of gal-1-positive cells expressed calretinin, 2% of gal-1-positive cells expressed calbindin, and 31% of gal-1-positive cells expressed neuropeptide Y in the mouse hippocampus. These results indicate that gal-1 is expressed in interneurons that also express &bgr;-tubulin III and gal-1 may be a novel marker for interneuron subpopulations in the hippocampus.

Erratum: FosB-null mice display impaired adult hippocampal neurogenesis and spontaneous epilepsy with depressive behavior (Neuropsychopharmacology (2013) 38 (1374-1375) DOI: 10.1038/npp.2013.56)

In this article, the parenthetical text in lines 10 and 11 of the Acknowledgments should read ‘(Cell-fate Decision: Function and Dysfunction in Homeostasis).’ In page 899, left column, line 17 should read ‘The remainder of BrdU-positive cells mostly expressed either DCX or NeuN.’ Corrections were made in Figure 4c; a revised version with caption is provided in the next page. In page 904, left column, line 35 should read ‘fosB-null mice exhibited abnormalities in hippocampal structures, which were similar to hippocampal sclerosis observed in the brains of rodent models and human patients with epilepsy (Fahrner et al, 2007).’ In page 904, right column, line 36 should read ‘The 10 genes listed in Table 1 are expressed in hippocampal neurons.’ In page 904, right column, line 39 should read ‘As VGF, TRH, GAL, DLK1, and PENK are secretory molecules.’ Neuropsychopharmacology (2013) 38, 1374–1375

Molecular Histochemistry Identifies Peptidomic Organization and Reorganization Along Striatal Projection Units

Matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) (MALDI-IMS) provides a technical means for simultaneous analysis of precise anatomic localization and regulation of peptides. We explored the technical capability of matrix-assisted laser desorption ionization mass spectrometry for characterization of peptidomic regulation by an addictive substance along two distinct projection systems in the mouse striatum. The spatial expression patterns of substance P and proenkephalin, marker neuropeptides of two distinct striatal projection neurons, were negatively correlated at baseline. We detected 768 mass/charge (m/z) peaks whose expression levels were mostly negatively and positively correlated with expression levels of substance P and proenkephalin A (amino acids 218-228), respectively, within the dorsal striatum. After nicotine administration, there was a positive shift in correlation of mass/charge peak expression levels with substance P and proenkephalin A (218-228). Our exploratory analyses demonstrate the technical capacity of MALDI-IMS for comprehensive identification of peptidomic regulation patterns along histochemically distinguishable striatal projection pathways.

Deletion size analysis of 1680 22q11.2DS subjects identifies a new recombination hotspot on chromosome 22q11.2

Recurrent, de novo, meiotic non-allelic homologous recombination events between low copy repeats, termed LCR22s, leads to the 22q11.2 deletion syndrome (22q11.2DS; velo-cardio-facial syndrome/DiGeorge syndrome). Although most 22q11.2DS patients have a similar sized 3 million base pair (Mb), LCR22A-D deletion, some have nested LCR22A-B or LCR22A-C deletions. Our goal is to identify additional recurrent 22q11.2 deletions associated with 22q11.2DS, serving as recombination hotspots for meiotic chromosomal rearrangements. Here, using data from Affymetrix 6.0 microarrays on 1680 22q11.2DS subjects, we identified what appeared to be a nested proximal 22q11.2 deletion in 38 (2.3%) of them. Using molecular and haplotype analyses from 14 subjects and their parent(s) with available DNA, we found essentially three types of scenarios to explain this observation. In eight subjects, the proximal breakpoints occurred in a small sized 12 kb LCR distal to LCR22A, referred to LCR22A+, resulting in LCR22A+-B or LCR22A+-D deletions. Six of these eight subjects had a nested 22q11.2 deletion that occurred during meiosis in a parent carrying a benign 0.2 Mb duplication of the LCR22A-LCR22A+ region with a breakpoint in LCR22A+. Another six had a typical de novo LCR22A-D deletion on one allele and inherited the LCR22A-A+ duplication from the other parent thus appearing on microarrays to have a nested deletion. LCR22A+ maps to an evolutionary breakpoint between mice and humans and appears to serve as a local hotspot for chromosome rearrangements on 22q11.2.