Timing of the cell cycle exit of differentiating hippocampal neural stem cells

Daily high doses of atorvastatin alter neuronal morphology in a juvenile songbird model

Statins are highly effective and widely prescribed cholesterol lowering drugs. However, statins cross the blood-brain barrier and decrease neural cholesterol in animal models, raising concern that long-term statin use may impact cholesterol-dependent structures and functions in the brain. Cholesterol is a fundamental component of cell membranes and experimentally decreasing membrane cholesterol has been shown to alter cell morphology in vitro. In addition, brain regions that undergo adult neurogenesis rely on local brain cholesterol for the manufacture of new neuronal membranes. Thus neurogenesis may be particularly vulnerable to long-term statin use. Here we asked whether oral statin treatment impacts neurogenesis in juveniles, either by decreasing numbers of new cells formed or altering the structure of new neurons. The use of statins in children and adolescents has received less attention than in older adults, with few studies on potential unintended effects in young brains. We examined neurons in the juvenile zebra finch songbird in telencephalic regions that function in song perception and memory (caudomedial nidopallium, NCM) and song production (HVC). Birds received either 40 mg/kg of atorvastatin in water or water vehicle once daily for 2-3 months until they reached adulthood. We labeled newborn cells using systemic injections of bromodeoxyuridine (BrdU) and quantified cells double-labeled with antibodies for BrdU and the neuron-specific protein Hu 30-32 days post mitosis. We also quantified a younger cohort of new neurons in the same birds using antibody to the neuronal protein doublecortin (DCX). We then compared numbers of new neurons and soma morphology of BrdU + /Hu+ neurons between statin-treated and control birds. We did not find an effect of statins on the density of newly formed neurons in either brain region, suggesting that statin treatment did not impact neurogenesis or young neuron survival in our paradigm. However, we found that neuronal soma morphology differed significantly between statin-treated and control birds. Somata of BrdU + /Hu+ (30-32 day old) neurons were flatter and had more furrowed contours in statin-treated birds relative to controls. In a larger, heterogeneous cohort of non-birthdated BrdU-/Hu+ neurons, largely born prior to statin treatment, somata were smaller in statin-treated birds than in controls. Our findings indicate that atorvastatin may affect neural cytoarchitecture in both newly formed and mature neurons, perhaps as a consequence of decreased cholesterol availability in the brain.

Methionine-Choline Deprivation Impairs Adult Hippocampal Neurogenesis in C57BL/6 Mice

Methionine and choline, which are essential nutrients for mammalian animals, are important for cell composition, as metabolic factors, and for the synthesis of other biochemical compounds for cell metabolism. Methionine and choline, which are methyl group donors, play key roles in the homocysteine cycle and neuronal development and maintenance. In this study, we investigated the effects of methionine and choline deficiency on adult hippocampal neurogenesis and neural stem cell (NSC) lineage in the adult stage. For this study, we divided C57BL/6 mice into three groups as follows: normal chow (NC)-fed, methionine choline sufficient (MCS) diet-fed, and methionine choline deficient (MCD) diet-fed mice. The mice were fed the NC, MCS, and MCD diets for 4 weeks from the age of 8 weeks. MCD diet-fed mice showed significantly decreased proliferation and differentiation of NSCs when compared with the NC diet-fed or MCS diet-fed mice. In addition, the survival of newly generated neurons was critically impaired in the MCD diet-fed mice. We confirmed a decrease in the proliferation and differentiation of NSCs after 4 weeks of MCD diet administration, compared with that in NC- and MCS diet-fed mice. MCD diet critically impaired NSCs survival and survival of neurons during the 4 weeks. The number of phosphorylated cyclic AMP response element binding (pCREB) protein immunoreactive nuclei was decreased in the MCD diet-fed mice compared with that in the NC- or MCS diet-fed group. These results suggest that suitable levels of methionine and choline are essential for the maintenance of hippocampal neurogenesis in mice and affect NSC proliferation and differentiation through phosphorylation of CREB.

Cellular Retinoic Acid-Binding Protein 1 Modulates Stem Cell Proliferation to Affect Learning and Memory in Male Mice

Retinoic acid (RA) is the active ingredient of vitamin A. It exerts its canonical activity by binding to nuclear RA receptors (RARs) to regulate gene expression. Increasingly, RA is also known to elicit nongenomic RAR-independent activities, most widely detected in activating extracellular regulated kinase (ERK)1/2. This study validated the functional role of cellular retinoic acid-binding protein 1 (Crabp1) in mediating nongenomic activity in RA, specifically activating ERK1/2 to rapidly augment the cell cycle by expanding the growth 1 phase and slowing down embryonic stem cell and neural stem cell (NSC) proliferation. The study further uncovered the physiological activity of Crabp1 in modulating NSC proliferation and animal behavior. In the Crabp1 knockout mouse hippocampus, where Crabp1 is otherwise detected in the subgranular zone, neurogenesis and NSC proliferation increased and hippocampus-dependent brain functions such as learning and memory correspondingly improved. This study established the physiological role of Crabp1 in modulating stem cell proliferation and hippocampus-dependent brain activities such as learning and memory.

Characterization of slow-cycling cells in the mouse cochlear lateral wall

Cochlear spiral ligament fibrocytes (SLFs) play essential roles in the physiology of hearing including ion recycling and the generation of endocochlear potential. In adult animals, SLFs can repopulate after damages, yet little is known about the characteristics of proliferating cells that support SLFs' self-renewal. Here we report in detail about the characteristics of cycling cells in the spiral ligament (SL). Fifteen P6 mice and six noise-exposed P28 mice were injected with 5-bromo-2'-deoxyuridine (BrdU) for 7 days and we chased BrdU retaining cells for as long as 60 days. Immunohistochemistry revealed that the BrdU positive IB4 (an endotherial marker) negative cells expressed an early SLF marker Pou3f4 but negative for cleaved-Caspase 3. Marker studies revealed that type 3 SLFs displayed significantly higher percentage of BrdU+ cells compared to other subtypes. Notably, the cells retained BrdU until P72, demonstrating they were dividing slowly. In the noise-damaged mice, in contrast to the loss of the other types, the number of type 3 SLFs did not altered and the BrdU incorporating- phosphorylated Histone H3 positive type 3 cells were increased from day 1 to 14 after noise exposure. Furthermore, the cells repopulating type 1 area, where the cells diminished profoundly after damage, were positive for the type 3 SLF markers. Collectively, in the latral wall of the cochlea, type 3 SLFs have the stem cell capacity and may contribute to the endogenous regeneration of lateral wall spiral ligament. Manipulating type 3 cells may be employed for potential regenerative therapies.

The linker histone H1.0 generates epigenetic and functional intratumor heterogeneity

Tumors comprise functionally diverse subpopulations of cells with distinct proliferative potential. Here, we show that dynamic epigenetic states defined by the linker histone H1.0 determine which cells within a tumor can sustain the long-term cancer growth. Numerous cancer types exhibit high inter- and intratumor heterogeneity of H1.0, with H1.0 levels correlating with tumor differentiation status, patient survival, and, at the single-cell level, cancer stem cell markers. Silencing of H1.0 promotes maintenance of self-renewing cells by inducing derepression of megabase-sized gene domains harboring downstream effectors of oncogenic pathways. Self-renewing epigenetic states are not stable, and reexpression of H1.0 in subsets of tumor cells establishes transcriptional programs that restrict cancer cells' long-term proliferative potential and drive their differentiation. Our results uncover epigenetic determinants of tumor-maintaining cells.

The pharmacological stimulation of Nurr1 improves cognitive functions via enhancement of adult hippocampal neurogenesis

The nuclear receptor related-1 (Nurr1) protein plays an important role in both the development of neural precursor cells (NPCs) and cognitive functions. Despite its relevance, the effects of Nurr1 on adult hippocampal neurogenesis have not been thoroughly investigated. Here we used RT-PCR, western blot, and immunocytochemistry to show that adult hippocampal NPCs abundantly express Nurr1. We then examined the effect of Nurr1 activation on adult hippocampal NPCs using amodiaquine (AQ), an anti-malarial drug that was recently discovered to be a Nurr1 agonist. Cell proliferation assay showed that AQ significantly increased cell proliferation. AQ-treated NPCs showed increased levels of phosphorylation of Akt and ERK1/2 whereas AQ-treated Nurr1 siRNA-transfected NPCs showed no changes in those levels. Further immunocytochemical and immunohistochemical analyses confirmed the stimulating effect of Nurr1 agonist on the proliferation and differentiation of adult hippocampal NPCs both in vivo and in vitro. In addition to its effects on proliferation and differentiation of NPCs, AQ-treated mice showed a significant enhancement of both short- and long-term memory in the Y-maze and the novel object recognition test. These data suggest that activation of Nurr1 may enhance cognitive functions by increasing adult hippocampal neurogenesis and also indicate that Nurr1 may be used as a therapeutic target for the treatment of memory disorders and cognitive impairment observed in neurodegenerative diseases.