Hippocampal Adaptive Response Following Extensive Neuronal Loss in an Inducible Transgenic Mouse Model

<div><p>Neuronal loss is a common component of a variety of neurodegenerative disorders (including Alzheimer's, Parkinson's, and Huntington's disease) and brain traumas (stroke, epilepsy, and traumatic brain injury). One brain region that commonly exhibits neuronal loss in several neurodegenerative disorders is the hippocampus, an area of the brain critical for the formation and retrieval of memories. Long-lasting and sometimes unrecoverable deficits caused by neuronal loss present a unique challenge for clinicians and for researchers who attempt to model these traumas in animals. Can these deficits be recovered, and if so, is the brain capable of regeneration following neuronal loss? To address this significant question, we utilized the innovative CaM/Tet-DT_A mouse model that selectively induces neuronal ablation. We found that we are able to inflict a consistent and significant lesion to the hippocampus, resulting in hippocampally-dependent behavioral deficits and a long-lasting upregulation in neurogenesis, suggesting that this process might be a critical part of hippocampal recovery. In addition, we provide novel evidence of angiogenic and vasculature changes following hippocampal neuronal loss in CaM/Tet-DT_A mice. We posit that angiogenesis may be an important factor that promotes neurogenic upregulation following hippocampal neuronal loss, and both factors, angiogenesis and neurogenesis, can contribute to the adaptive response of the brain for behavioral recovery.</p></div

Upregulated proliferation of new-born neurons following lesion.

<p><b>A</b>) Neuronal proliferation in the dentate of lesion (<b>A1–A3</b>) and non-lesioned (<b>A4–A6</b>) mice was analyzed in the 1 month post lesion group utilizing an alternate thymidine analoge, EdU. The EdU pulse was administered during the last 4 days before sacrifice, labeling newly dividing cells. The immature neuronal marker doublecortin (DCX) was used as a double label to confirm neuronal differentiation. <b>B</b>) Stereologically-based analysis revealed a significant increase in the number of EdU+/DCX+ cells in the dentate gyrus of lesioned mice compared to controls. <b>C</b>) Protein samples purified from lesioned and non-lesioned mice were analyzed by Western blot for levels of the Nestin protein, normalized to GAPDH, and quantified in <b>D</b>. The quantification showed a significant increase of Nestin in Lesion animals compared to control mice. Scale Bar: 50 µm.</p

Neurogenesis is upregulated in CaM/Tet-DT_A mice 1 and 3 months post-lesion.

<p>Hippocampal slices from control (sub panels 1–4) and lesion (sub panels 5–8) mice were stained for the mature neuronal marker NeuN (sub panels 2 and 6), the astrocytic marker S100β (sub panels 3 and 7), and the proliferation marker BrdU (sub panels 1 and 5). The merged images are shown in sub panels 4 and 8. <b>D</b>) At 1 month post lesion, there was a significant increase in the number of BrdU+/NeuN+/S100β− cells in lesion mice, indicating an increase in neurogenesis. We also observed an increase in the number of BrdU+/NeuN/S100β− cells with an unclear differentiation. <b>H</b>) The upregulation of neurogenesis in lesion mice, as indicated by more BrdU+/NeuN+/S100β− cells, persisted for 3 months. Scale Bar: 50 µm.</p

Increased angiogenesis and VEGF expression following lesion in CaM/Tet-DT_A mice.

<p><b>A</b>) Angiogenesis was analyzed in control mice and lesion mice at 0, 2, and 8 weeks post lesion. <b>B</b>) Dextran-Texas red was administered during perfusion, labeling blood vessels in the dentate gyrus and imaged using confocal microscopy. <b>C</b>) Optical density was measured using Image J software, and revealed a step-wise increase in Dextran-Texas Red labeling following lesion. As VEGF has been shown to be a critical regulator of angiogenesis, <b>D</b>) VEGF expression was analyzed by Western blot using brain samples immediately post-lesion and 2 months post lesion. VEGF expression, normalized to actin, was increased in lesion mice compared to control mice, as illustrated in E. Scale Bar: 50 µm.</p

Recovery of 24-hour probe deficits, but not training deficits, 3 months post-lesion in the Barnes maze.

<p><b>A</b>) 6-month old CaM/Tet-DT_A mice, lesion and control, were trained in the Barnes maze for 4 days. Significant learning deficits in the latency to enter the target on day 3 and 4 of training were observed in 1-month post lesion mice compared to control mice. <b>B</b>) In the 24-hour probe trial, 1-month post lesion mice had significantly higher latencies to find the target zone. <b>C</b>) Additionally, 1-month post lesion mice also exhibited significantly less correct head pokes into the target hole. <b>D</b>) CaM/Tet-DT_A lesion mice, exhibited significantly higher latencies to enter the target on day 3 and 4 of training compared to controls. <b>E</b>) 3-months post lesion mice exhibited no significant differences in the latency to find the target hole compared to controls. <b>F</b>) Additionally, 3-months post lesion mice revealed no difference in the total number of target entries. The values represent the mean±SEM (n = 12). *p<0.05, **p<0.01, ***p<0.001.</p

Psychiatric Risk Factor ANK3/Ankyrin-G Nanodomains Regulate the Structure and Function of Glutamatergic Synapses

SummaryRecent evidence implicates glutamatergic synapses as key pathogenic sites in psychiatric disorders. Common and rare variants in the ANK3 gene, encoding ankyrin-G, have been associated with bipolar disorder, schizophrenia, and autism. Here we demonstrate that ankyrin-G is integral to AMPAR-mediated synaptic transmission and maintenance of spine morphology. Using superresolution microscopy we find that ankyrin-G forms distinct nanodomain structures within the spine head and neck. At these sites, it modulates mushroom spine structure and function, probably as a perisynaptic scaffold and barrier within the spine neck. Neuronal activity promotes ankyrin-G accumulation in distinct spine subdomains, where it differentially regulates NMDA receptor-dependent plasticity. These data implicate subsynaptic nanodomains containing a major psychiatric risk molecule, ankyrin-G, as having location-specific functions and open directions for basic and translational investigation of psychiatric risk molecules

Short-term modern life-like stress exacerbates Aβ-pathology and synapse loss in 3xTg-AD mice

Alzheimer's disease (AD) is a progressive neurological disorder that impairs memory and other cognitive functions in the elderly. The social and financial impacts of AD are overwhelming and are escalating exponentially as a result of population aging. Therefore, identifying AD-related risk factors and the development of more efficacious therapeutic approaches are critical to cure this neurological disorder. Current epidemiological evidence indicates that life experiences, including chronic stress, are a risk for AD. However, it is unknown if short-term stress, lasting for hours, influences the onset or progression of AD. Here, we determined the effect of short-term, multi-modal 'modern life-like' stress on AD pathogenesis and synaptic plasticity in mice bearing three AD mutations (the 3xTg-AD mouse model). We found that combined emotional and physical stress lasting 5 h severely impaired memory in wild-type mice and tended to impact it in already low-performing 3xTg-AD mice. This stress reduced the number of synapse-bearing dendritic spines in 3xTg-AD mice and increased Aβ levels by augmenting AβPP processing. Thus, short-term stress simulating modern-life conditions may exacerbate cognitive deficits in preclinical AD by accelerating amyloid pathology and reducing synapse numbers