The mood stabilizers lithium and valproate are both effective in the treatment of bipolar disorder; however, their therapeutic mechanisms remain unclear. Because of the delayed onset of clinical efficacy (days to weeks), it has been proposed that adaptive changes in gene expression, rather than initial pharmacological actions, may be directly responsible. Using cDNA microarray as the initial screening method, we discovered that chronic administration of both agents at therapeutic doses increased the expression of BAG-1 (bcl-2 associated athanogene) in rat hippocampus. Furthermore, these findings were validated in the hippocampus at the protein level, the effects were seen in a time frame consistent with therapeutic effects, and were specific for mood stabilizers. BAG -1 is an important chaperone of bcl-2 (B-cell CLL/lymphoma 2), and enhances bcl-2_s anti-apoptotic functions; furthermore, through interaction with raf (v-raf-1 murine leukemia viral oncogene homolog 1), BAG-1 is able to activate ERK (extracellular signal-regulated protein kinase) MAP (mitogen-activated protein) kinases. Consistent with this, we previously found that lithium and valproate activate ERK MAP kinases. Bag-1 also inhibits GR (glucocorticoid receptor) activation, which may counteract the deleterious effects of hypercortisolemia seen in bipolar disorder. Anti-GR antibody immunostaining plus double staining with DAPI (4',6-Diamidino-2-phenylindole) showed either lithium or VPA, at therapeutically relevant levels, inhibited dexamethasone induced GR nuclear translocation. In addition, glucocorticoid response element (GRE) transfection assay showed lithium, at therapeutically relevant levels, inhibited GR activity in cultured human cells. Evaluated through siRNA (short interference RNA) silencing of BAG-1, the inhibition of mood stabilizers to GR nuclear translocation and to GR activity is mediated, at least in part, by BAG-1. The effect that BAG-1 inhibits glucocorticoid activation suggests mood stabilizers may counteract the deleterious effects of hypercortisolemia seen in bipolar disorder by up-regulating BAG-1. The role of BAG-1 in behavioral plasticity relevant to mood disorders was further investigated in wild-type, neuron-selective BAG-1 transgenic, BAG-1 heterozygous knockout (KO) mice using a battery of behavioral tests. The BAG1 mutant mice appeared normal in growth and in neurological and sensory tests. On mania-related tests, BAG1 TG mice recovered much faster than wild-type (WT) mice in the amphetamine-induced hyperlocomotion test and displayed a clear resistance to cocaine-induced behavioral sensitization. In contrast, BAG1+/- mice displayed an enhanced response to cocaine-induced behavioral sensitization. The BAG1 TG mice showed less anxious-like behavior on the elevated plus maze test and had higher spontaneous recovery rates from helplessness behavior compared with WT mice. In contrast, fewer BAG1+/- mice recovered from helplessness behavior compared with their WT controls. BAG1 TG mice also exhibited specific alterations of hippocampal proteins known to regulate GR function, including Hsp70 and FKBP51. These data suggest that BAG1 plays a key role in affective resilience and in regulating recovery from both manic-like and depression-like behavioral impairments.? We furthermore studied the effects of mood stabilizers on cell proliferation and survival in the adult CNS with an emphasis on adult hippocampal neurogenesis. We found that both drugs reliably increase the number of proliferating and young (survival time 1week) neural progenitors cells while leaving the number of cells surviving long-term (4wk and longer) unaffected. Interestingly, heterozygous Bcl-2 KO mice show the reverse phenotype in that they have significantly decreased young progenitor cells as measured by immunohistochemistry for BrdU (1 wk survival) and doublecortin (marker for neuroblasts). To further understand the impact of adult neurogenesis on mood and anxiety as well as its relevance for treatment with mood stabilizing drugs we (in collaboration with the Unit on Neural Plasticity, Dr. Heather Cameron) developed a mouse model that allows for the conditional ablation of adult neural progenitors. Conditional ablation of adult neural progenitor cell proliferation in this model is achieved by expression of herpes simplex virus thymidine kinase (HSV-tk) under the control of the human GFAP promoter. Administration of the antiviral drug valganciclovir (VGCV) causes prevention of cells expressing HSV-tk from re-entering the cell cycle. Baseline physiological and pathological observations of this mouse model revealed no differences indicating adverse side effects by the treatment or a combination of treatment and insertion of the transgene. Further, behavioral observations did not show increases in baseline anxiety or depressive-like behavior in animals without neurogenesis. However, in a study conducted in collaboration with the Laboratory of Cellular and Molecular Regulation we did show that recovery from psychosocial stress, which can be achieved by housing animals in an enriched environment, is dependent on intact adult neurogenesis.? In order to further our studies on the molecular regulation underlying the effects of the mood stabilizers lithium and VPA, as well as on the development of anxiety- and depressive-like behaviors as a result of various chronic stressors. In order to gain insight into these molecular regulations we have developed both a candidate gene approach and a genome-wide approach to study the epigenetic regulation of those genes underlying both the susceptibility and therapeutic behaviors. Using candidates identified both in our own laboratories as well as well-characterized candidates from other laboratories we have begun studying the epigenetic profiles of these candidate genes. This profile includes studying histone methylation, histone acetylation as well as DNA cytosine methylation. Taking a genome-wide approach we are looking at the epigenetic regulation using promoter chips to look at genome-wide differences at proximal promoters in histone acetylation (ChIP on chip technology) as well as DNA cytosine methylation (m-DIP technology).
