Adult hippocampal neurogenesis Flashcards
(6 cards)
identifying neural stem cells
Neural Stem Cell Markers - In vivo several transcription factors are expressed during early neural cell development and persist in adult NSC - Early NSC markers: Sox genes e.g. Sox2 are among the earliest genes expressed everywhere in the early neural plate - Late NSC markers: Nestin (intermediate filament protein), Musashi (RNA-binding protein) appear after Sox proteins and persist during embryo development and Adult NSC ¥ Sox2, Nestin, and Musashi are used as NSC markers but they can be expressed in restricted progenitors (e.g. neuronal or glial restricted progenitors) ¥ No exclusive antigens have been identified for NSCs so presence of Sox2 alone, does not confirm neural stem cells ¥ Combinations of positive and negative markers are required to better identify NSCs ¥ Also starting to use single cell RNA extraction to see if a gene is expressed that would identify NSC.
Identification of Dividing/New-born Cells BrdU Labelling: - Technology used to label cells that are dividing with NSC marker - BrdU is injected systemically - Integrates into DNA as cell is dividing - Add BrdU antibody to act as NSC marker - Allows us to see the fate of the cells e.g. becoming a neuron - Advantageous in quantitative studies e.g. to see which mouse is producing more of a cell
Retroviral labelling: - Engineer retrovirus to express GFP and add to cell - Inject it locally - Entire cell body, dendrites and synapses can be seen - Advantageous because it only integrates into dividing cells and allows qualitative studies - you can see where the cells are migrating
adult neurogenesis
Adult Neurogenesis Originally believed that once development ended everything dies and nothing can be regenerated but a study in 1965 (Altman & Das) found evidence of new neuronal growth in the rat hippocampus using autoradiographic techniques. Neurogenesis in the adult hippocampus evidence = in 60’s nuclear bomb caused increased C14 atmospheric level but since then the levels have been decreasing. Measure c14 label from a single hippocampal neuron found in post mortem tissue. Woman born in 1910 had neurons with C14 level, still some labelled neurons at 15 years and continued to produce them until death showing that neurons are produced throughout life. Neurogenesis is limited to 2 specific neurogenic regions i.e. SVZ and DG. Adult Subventricular Zone (Lateral Ventricle) Neurogenesis: in mice, NSC migrate to the olfactory bulb as they differentiate. Humans have a different niche – NSC more likely migrate to the striatum
Adult Hippocampal Neurogenesis: NSCs proliferate within the granular cell layer of the dentate gyrus and then migrate a bit whilst differentiating into neurons. They receive input from the Entorhinal cortex and then project to the CA3 so are functional. It takes between 4- 6 weeks to go from NSC to neuron in the mouse. How Much Neuron is Produced? - 700 new neurons formed in adult human hippocampus/day - 70% of bulbar neurons are replaced during 6-week period in adult rodent - Granule cells born during adulthood become integrated into circuits and survive at least 8 months in rodents and 2 years in humans Environment of Adult Neurogenesis Neurogenesis only occurs in these 2 niches (DG or SVZ). To test this, we take NSC from the CNS and observe what happens when they are placed in other regions
adult neorgenic microenvironment
Adult neurogenic microenvironment - Spinal cord stem cells are grown in dish to expand them - Transplanted cells into DG/SVZ à become neurons and control: transfer cells from same dish to spinal cord to show dish environment doesn’t cause them to become neurons. They cannot become neurons in the spinal cord as it is not the correct environment. - Cells from a place where they can make neurons transferred to spinal cord still do not produce neurons because lack of appropriate nice - Shows that cells become neurons depending on their niche environment, rather than the change coming from the cells themselves. The niche is what is important in pushing stem cells into becoming neurons - Well vascularised; proximity to blood vessels - Surrounded by astrocytes and endothelial cells - Astrocytes are important for producing factor that induces neurogenesis; study involved extracting astrocytes from hippocampus and then from spinal cord. They did co-culture with neural stem cells from hippocampus. Neurons were only formed in the cultures with astrocytes. NSCs (green) are packed by astrocytes (red
molecular control of adult neuroigenesis
Adult Hippocampal Neurogenesis: NSCs proliferate within the granular cell layer of the dentate gyrus and then migrate a bit whilst differentiating into neurons. They receive input from the Entorhinal cortex and then project to the CA3 so are functional. It takes between 4- 6 weeks to go from NSC to neuron in the mouse. How Much Neuron is Produced? - 700 new neurons formed in adult human hippocampus/day - 70% of bulbar neurons are replaced during 6-week period in adult rodent - Granule cells born during adulthood become integrated into circuits and survive at least 8 months in rodents and 2 years in humans Environment of Adult Neurogenesis Neurogenesis only occurs in these 2 niches (DG or SVZ). To test this, we take NSC from the CNS and observe what happens when they are placed in other regions. Adult neurogenic microenvironment - Spinal cord stem cells are grown in dish to expand them - Transplanted cells into DG/SVZ à become neurons and control: transfer cells from same dish to spinal cord to show dish environment doesn’t cause them to become neurons. They cannot become neurons in the spinal cord as it is not the correct environment. - Cells from a place where they can make neurons transferred to spinal cord still do not produce neurons because lack of appropriate nice - Shows that cells become neurons depending on their niche environment, rather than the change coming from the cells themselves. The niche is what is important in pushing stem cells into becoming neurons - Well vascularised; proximity to blood vessels - Surrounded by astrocytes and endothelial cells - Astrocytes are important for producing factor that induces neurogenesis; study involved extracting astrocytes from hippocampus and then from spinal cord. They did co-culture with neural stem cells from hippocampus. Neurons were only formed in the cultures with astrocytes. NSCs (green) are packed by astrocytes (red) Molecular control of Adult Neurogenesis Growth factors are needed to stimulate proliferation, but we previously did not know which factors were needed for integration and migration etc. - Wnt Signallling Regulates Adult hippocampal neurogenesis - Wnt is secreted by astrocytes - Start culture of dentate gyrus stem cells - Add Wnt and allow growth; many neurons are produced - In control dish where Wnt is dilated there are fewer red neurons. 4x more neurons when wnt is added. In vivo experiment involved injecting antivirus that affects all cells then engineer an antivirus that expresses dominant negative Wnt i.e. blocks Wnt signalling. There is 8x fewer neurons being producing in the hippocampus. Antivirus that overexpressed Wnt produced a twofold increase of neurogenesis.
disorders
Depression Animal model shows reduced neurogenesis in depression; sertoline i.e. Prozac increases neurogenesis and alleviates the symptoms of depression. Antidepressants have no effect in mice that have blocked neurogenesis, however some antidepressants can work independently of neurogenesis.
Neurodegenerative Disorders Many neurons are lost and cannot be replenished at the same rate. In these diseases neurogenesis is altered. AD patients usually experience depression and depressed patients have higher risk of developing AD possibly because of reduced neurogenesis but levels shown in results are dependent on factors including age, gender, genetic background, neuropathology state (end of AD = very low neurogenesis), method of AHN detection and post mortem studies are also contradictory. Alterations in AHN occur at very early state of AD progression; prior to processes such as neuronal loss, amyloid deposition and inflammation that may secondarily affect neurogenesis. This shows AHN is integral to AD pathology. Stimulate neurogenesis to slow the progression of AD even if global repair of AD causing molecules is not possible. Presently there are no drugs capable of doing this.
modulation of neuroigenesis
Modulation of Adult Neurogenesis - Learning, fireworks and running: increased neurogenesis - Stress, sleep deprivation and ageing: decrease neurogenesis Test: Mice with running wheels in the cage have increased cell proliferation compared to mice without the wheels. - They are given a water maze task to test their spatial learning - The water is milky so mice cannot see through it - There is a platform under the water - Mice do not like swimming so they will try to find the platform - At first, they take long random path as they don’t know where the platform is. Once it finds the platform allow rest so it can become spatially aware - Repeat; over time mouse takes a much shorter route to the path - Running mice are faster than control mice and take a shorter path because they are learning faster and have better strategy due to increase neurogenesis
Parabiosis Experiment - Fuse circulatory system of two mice for 3 months - 2 young (ctronol), young and old, and 2 old (control) - Observe dentate gyrus and neurogenesis levels - 2 young have good level of neurogenesis, old have low levels and young/old have decreased level because blood sharing - Injection of old mouse blood into a young mouse can also cause reduced neurogenesis. Young blood injected into the old mouse can rejuvenate neurogenesis The effect of diet on mood and cognition could be mediated by its effect on neurogenesis.
