Doublecortin mutation leads to persistent defects in the Golgi apparatus and mitochondria in adult hippocampal pyramidal cells
Ontology highlight
ABSTRACT: Human doublecortin (DCX) mutations are associated with severe brain malformations leading to aberrant neuron positioning (heterotopia), intellectual disability and epilepsy. DCX is a microtubule-associated protein which plays a key role during neurodevelopment in neuronal migration and differentiation. Dcx knockout (KO) mice show disorganized hippocampal pyramidal neurons. The CA2/CA3 pyramidal cell layer is present as two abnormal layers and disorganized CA3 KO pyramidal neurons are also more excitable than wild-type (WT) cells. To further identify abnormalities, we characterized Dcx KO hippocampal neurons at subcellular, molecular and ultrastructural levels. Severe defects were observed in mitochondria, affecting number and distribution. Also, the Golgi apparatus was visibly abnormal, increased in volume and abnormally organized. Transcriptome analyses from laser microdissected hippocampal tissue at postnatal day 60 (P60) highlighted organelle abnormalities. Ultrastructural studies of CA3 cells performed in P60 (young adult) and > 9 months (mature) tissue showed that organelle defects are persistent throughout life. Locomotor activity and fear conditioning behavior of young and mature adults was also abnormal: KO mice consistently performed less well than WT littermates, with defects becoming more severe with age. Thus, we show that disruption of a neurodevelopmentally-regulated gene can lead to permanent organelle anomalies contributing to abnormal adult behavior
Project description:Human doublecortin (DCX) mutations are associated with severe brain malformations leading to aberrant neuron positioning (heterotopia), intellectual disability and epilepsy. The Dcx protein plays a key role in neuronal migration, and hippocampal pyramidal neurons in Dcx knockout (KO) mice are disorganized. The single CA3 pyramidal cell layer observed in wild type (WT) is present as two abnormal layers in the KO, and CA3 KO pyramidal neurons are more excitable than WT. Dcx KO mice also exhibit spontaneous epileptic activity originating in the hippocampus. It is unknown however, how hyperexcitability arises and why two CA3 layers are observed. Transcriptome analyses were performed to search for perturbed postnatal gene expression, comparing Dcx KO CA3 pyramidal cell layers with WT. Gene expression changes common to both KO layers indicated mitochondria and Golgi apparatus anomalies, as well as increased cell stress. Intriguingly, gene expression analyses also suggested that the KO layers differ significantly from each other, particularly in terms of maturity. Layer-specific molecular markers and BrdU birthdating to mark the final positions of neurons born at distinct timepoints revealed inverted layering of the CA3 region in Dcx KO animals. Notably, many early-born ‘outer boundary’ neurons are located in an inner position in the Dcx KO CA3, superficial to other pyramidal neurons. This abnormal positioning likely affects cell morphology and connectivity, influencing network function. Dissecting this Dcx KO phenotype sheds light on coordinated developmental mechanisms of neuronal subpopulations, as well as gene expression patterns contributing to a bi-layered malformation associated with epilepsy. Expression profiling by array
Project description:Neurological diseases can lead to the denervation of brain regions caused by demyelination, traumatic injury or cell death. Nevertheless, the molecular and structural mechanisms underlying lesion-induced reorganization of denervated brain regions are a matter of ongoing investigation. In order to address this issue, we performed an entorhinal cortex lesion (ECL) in mouse organotypic entorhino-hippocampal tissue cultures of both sexes and studied denervation-induced plasticity of mossy fiber synapses, which connect dentate granule cells (dGCs) with CA3 pyramidal cells (CA3-PCs) and play important roles in spatial learning. Partial denervation caused a strengthening of excitatory neurotransmission in dGCs, in CA3-PCs, and their direct synaptic connections as revealed by paired recordings (GC-to-CA3). These functional changes were accompanied by ultrastructural reorganization of mossy fiber synapses, which regularly contain the plasticity-related protein synaptopodin and the spine apparatus organelle. We demonstrate that the spine apparatus organelle and its integral protein synaptopodin are associated with ribosomes in close proximity to synaptic sites and unravel a synaptopodin-related transcriptome. Notably, synaptopodin-deficient tissue preparations that lack the spine apparatus organelle, failed to express lesion-induced synaptic adjustments. Hence, synaptopodin and the spine apparatus organelle play a crucial role in regulating lesion-induced synaptic plasticity at hippocampal mossy fiber synapses.
Project description:Despite widespread interest in using human stem cells in neurological disease modeling, a suitable model system to study human neuronal connectivity is lacking. Here, we report a protocol for efficient differentiation of hippocampal pyramidal neurons and an in vitro model for hippocampal neuronal connectivity. We developed an embryonic stem cell (ESC)- and induced pluripotent stem cell (iPSC)-based protocol to differentiate human CA3 pyramidal neurons from patterned hippocampal neural progenitor cells (NPCs). This differentiation induces a comprehensive patterning and generates multiple CA3 neuronal subtypes. The differentiated CA3 neurons are functionally active and readily form neuronal connection with dentate granule (DG) neurons in vitro, recapitulating the synaptic connectivity within the hippocampus. When we applied this neuronal co-culture approach to study connectivity in schizophrenia, we found deficits in spontaneous activity in patient iPSC derived DG–CA3 co-culture by multi-electrode array recording. In addition, both multi-electrode array recording and whole cell patch clamp electrophysiology revealed a reduction in spontaneous and evoked neuronal activity in CA3 neurons derived from schizophrenia patients. Altogether these results underscore the relevance of this new model in studying diseases with hippocampal vulnerability.
Project description:Despite widespread interest in using human stem cells in neurological disease modeling, a suitable model system to study human neuronal connectivity is lacking. Here, we report a protocol for efficient differentiation of hippocampal pyramidal neurons and an in vitro model for hippocampal neuronal connectivity. We developed an embryonic stem cell (ESC)- and induced pluripotent stem cell (iPSC)-based protocol to differentiate human CA3 pyramidal neurons from patterned hippocampal neural progenitor cells (NPCs). This differentiation induces a comprehensive patterning and generates multiple CA3 neuronal subtypes. The differentiated CA3 neurons are functionally active and readily form neuronal connection with dentate granule (DG) neurons in vitro, recapitulating the synaptic connectivity within the hippocampus. When we applied this neuronal co-culture approach to study connectivity in schizophrenia, we found deficits in spontaneous activity in patient iPSC derived DG–CA3 co-culture by multi-electrode array recording. In addition, both multi-electrode array recording and whole cell patch clamp electrophysiology revealed a reduction in spontaneous and evoked neuronal activity in CA3 neurons derived from schizophrenia patients. Altogether these results underscore the relevance of this new model in studying diseases with hippocampal vulnerability.
Project description:Neurodegenerative brain disorders become more common in the aged. Most of these disorders are associated with or caused by selective death of certain neuronal subpopulations. The mechanisms underlying the differential vulnerability of certain neuronal populations are still largely unexplored and few neuroprotective treatments are available to date. Elucidation of these mechanisms may lead to a greater understanding of the pathogenesis and treatment of neurodegenerative diseases. Moreover, preconditioning by a short seizure confers neuroprotection following a subsequent prolonged seizure. Our goal is to identify pathways that confer vulnerability and resistance to neurotoxic conditions by comparing the basal and preconditioned gene expression profiles of three differentially vulnerable hippocampal neuron populations. Hippocampal CA1 and CA3 pyramidal neurons are highly susceptible to seizures and ischemia, whereas dentate gyrus granule cells are relatively resistant. A brief preconditioning seizure confers protection to the pyramidal cells. We will first determine gene expression profiles of untreated rat CA1 and CA3 pyramidal cells, and dentate granule cells, using laser capture microscopy to obtain region-specific neuronal mRNA. We will then determine the effect of a brief preconditioning seizure, which is neuroprotective in CA1 and CA3, on these expression profiles. We hypothesize that common molecular mechanisms exist in neurons that determine their susceptibility to seizure-induced injury. Intrinsic differences in gene expression exist between hippocampal glutamatergic CA1 and CA3 pyramidal neurons, on the one hand, and dentate granule cells on the other, which contribute to the greater susceptibility of pyramidal neurons to degeneration in experimental stroke and epilepsy. We specifically hypothesize that differences in basal energy metabolism genes may confer differential susceptibility to neurodegeneration produced by seizures and ischemia. Anesthetized animals will be sacrificed by decapitation, and frozen 10 micron sections will be lightly stained with cresyl violet to identify cell layers in the hippocampus. Approximately 1000 neurons from each of the three cell layers will be isolated by LCM. Poly-A RNA will be amplified using a modified Eberwine protocol. The quality of our aRNA will be evaluated by quantitative RT-PCR of GluR6 and KA2 mRNA levels before we send the samples to the Center for labeling and hybridization to Affymetrix rat 230A arrays. We will provide a one-round amplification cDNA product to the center for labeling and hybridization. This protocol is identical to a previously approved study by Jim Greene in our laboratory.
Project description:Triggering receptor expressed on myeloid cells 2 (Trem2) is a myeloid cell-specific gene expressed in microglia, whose variants are associated with multiple neurodegenerative diseases. TREM2 receptor modulates phagocytosis, cytokine production and metabolism, enabling appropriate surveillance of the brain by microglia and ensuring their proper response to damage signals. Here, we demonstrate that TREM2 plays a key role in controlling the bioenergetic profile of pyramidal neurons during development. In the absence of Trem2, developing neurons in hippocampal CA1 -but not in CA3- subfield display compromised energetic metabolism and defective basal, maximal and ATP-dependent respiration, accompanied by reduced mitochondrial mass and abnormal organelle ultrastructure. This is paralleled by a significant transcriptional rearrangement of hippocampal pyramidal neurons at birth, with a pervasive alteration of metabolic, oxidative phosphorylation and mitochondrial signatures. The developmental trajectories of the excitatory lineages indicate that lack of Trem2 causes a delay in the maturation of CA1 neurons, paired with specific alterations in the mitochondrial TOM complex which persist in the mature hippocampus. In addition, the mitochondrial defects and faulty neuronal differentiation are maintained also after neuron isolation from the brain context, suggesting that the lack of TREM2-mediated communication between microglia and neurons at early developmental windows is sufficient to derange the forthcoming maturation of neuronal metabolism. Our results unveil a novel role of TREM2 in controlling neuronal development by regulating the metabolic fitness of neurons in a region-specific manner.
Project description:Complete global brain ischemia (CGBI) and reperfusion occur following resuscitation from cardiac arrest. Different brain neurons are selectively vulnerable to CGBI: pyramidal neurons of hippocampal CA3 survive 10 min CGBI but those of CA1 die at 3 days following 10 min CGBI. CA3 neurons are expected to have more robust stress responses and repair responses than CA1 neurons. We used microarrays to compared total and polysome-bound mRNAs in CA1 and CA3 at 8 hr reperfusion after 10 min CGBI in Long Evans male rats to ascertain differences in total vs polysome-bound gene expression.
Project description:Complete global brain ischemia (CGBI) and reperfusion occur following resuscitation from cardiac arrest. Different brain neurons are selectively vulnerable to CGBI: pyramidal neurons of hippocampal CA3 survive 10 min CGBI but those of CA1 die at 3 days following 10 min CGBI. CA3 neurons are expected to have more robust stress responses and repair responses than CA1 neurons. We used microarrays to compared total and polysome-bound mRNAs in CA1 and CA3 at 8 hr reperfusion after 10 min CGBI in Long Evans male rats to ascertain differences in total vs polysome-bound gene expression. Male Long Evans rats were subjected to (1) sham operation (non-ischemic control, NIC) or normothermic CGBI of 10 min followed by 8 hr reperfusion (8R). Hippocampal CA1 and CA3 were dissected. n = 5 CA1 or CA3 were pooled to give a single replicate and there were 3 or 4 replicates per group. Post-mitochondrial supernatant (PMS) was prepared. Twenty percent of PMS was TRIzol extracted to give total RNA. The remainder was run on a 20% sucrose pad to isolate polysome pellets, which were also TRIzol extracted to give polysome RNA. Total and polysome RNA were then run on Affymetrix Rat Gene 2.0 microarrays.
Project description:Neurodegenerative brain disorders become more common in the aged. Most of these disorders are associated with or caused by selective death of certain neuronal subpopulations. The mechanisms underlying the differential vulnerability of certain neuronal populations are still largely unexplored and few neuroprotective treatments are available to date. Elucidation of these mechanisms may lead to a greater understanding of the pathogenesis and treatment of neurodegenerative diseases. Moreover, preconditioning by a short seizure confers neuroprotection following a subsequent prolonged seizure. Our goal is to identify pathways that confer vulnerability and resistance to neurotoxic conditions by comparing the basal and preconditioned gene expression profiles of three differentially vulnerable hippocampal neuron populations. Hippocampal CA1 and CA3 pyramidal neurons are highly susceptible to seizures and ischemia, whereas dentate gyrus granule cells are relatively resistant. A brief preconditioning seizure confers protection to the pyramidal cells. We will first determine gene expression profiles of untreated rat CA1 and CA3 pyramidal cells, and dentate granule cells, using laser capture microscopy to obtain region-specific neuronal mRNA. We will then determine the effect of a brief preconditioning seizure, which is neuroprotective in CA1 and CA3, on these expression profiles. We hypothesize that common molecular mechanisms exist in neurons that determine their susceptibility to seizure-induced injury. Intrinsic differences in gene expression exist between hippocampal glutamatergic CA1 and CA3 pyramidal neurons, on the one hand, and dentate granule cells on the other, which contribute to the greater susceptibility of pyramidal neurons to degeneration in experimental stroke and epilepsy. We specifically hypothesize that differences in basal energy metabolism genes may confer differential susceptibility to neurodegeneration produced by seizures and ischemia. Anesthetized animals will be sacrificed by decapitation, and frozen 10 micron sections will be lightly stained with cresyl violet to identify cell layers in the hippocampus. Approximately 1000 neurons from each of the three cell layers will be isolated by LCM. Poly-A RNA will be amplified using a modified Eberwine protocol. The quality of our aRNA will be evaluated by quantitative RT-PCR of GluR6 and KA2 mRNA levels before we send the samples to the Center for labeling and hybridization to Affymetrix rat 230A arrays. We will provide a one-round amplification cDNA product to the center for labeling and hybridization. This protocol is identical to a previously approved study by Jim Greene in our laboratory. Keywords: other