Biology subjects

Kernie, S. G.

Publications and source records attributed to Kernie, S. G..

3 recordsLinked to original sources

bioRxiv2021

Unique Microglial Transcriptomic Signature within the Hippocampal Neurogenic Niche

Microglia, the resident immune cells of the brain, are crucial in the development of the nervous system. Recent evidence demonstrates that microglia modulate adult hippocampal neurogenesis by inhibiting cell proliferation of neural precursors and survival both in vitro and in vivo, thus maintaining a balance between cell division and cell death in the neural stem cell pool. There are increasing reports suggesting these microglia found in neurogenic niches differ from their counterparts in non-neurogenic areas. Here, we present evidence that microglia in the hippocampal neurogenic niche are a specialized population that express genes known to regulate neurogenesis. By comprehensively profiling myeloid lineage cells in the hippocampus using single cell RNA-sequencing, we resolve transcriptomic differences in microglia originating from the subgranular zone. These cells have lower expression of genes associated with homeostatic microglia and increased expression of genes associated with phagocytosis. Intriguingly, this small yet distinct population expresses a gene signature with substantial overlap with previously characterized phenotypes, including disease associated microglia (DAM), a particularly unique and compelling microglial state.

cell biology↗

bioRxiv2021

Astrocyte-derived ApoE is Required for the Maturation of Injury-induced Hippocampal Neurons and Regulates Cognitive Recovery After Traumatic Brain Injury

Polymorphisms in the apolipoprotein E (ApoE) gene confer a major genetic risk for the development of late-onset Alzheimers disease (AD) and are predictive of outcome following traumatic brain injury (TBI). Alterations in adult hippocampal neurogenesis have long been associated with both the development of AD and recovery following TBI, and ApoE is known to play a role in this process. In order to determine how ApoE might influence hippocampal injury-induced neurogenesis, we developed a novel conditional system whereby functional ApoE from astrocytes was ablated just prior to injury. While successfully ablating 90% of astrocytic ApoE just prior to a closed cortical impact injury in mice, we observed an attenuation in the development of newly born neurons using a GFP-expressing retrovirus, but not in existing hippocampal neurons visualized with a Golgi stain. Intriguingly, animals with a "double-hit", i.e. injury and ApoE conditionally inactivated in astrocytes, demonstrated the most pronounced impairments in the hippocampal-dependent Morris water maze test, failing to exhibit spatial memory after both acquisition and reversal training trials. In comparison, conditional knockout mice without injury displayed impairments but only in the reversal phase of the test, suggesting accumulative effects of astrocytic ApoE deficiency and traumatic brain injury on AD-like phenotypes. Together, these findings demonstrate that astrocytic ApoE is required for functional injury-induced neurogenesis following traumatic brain injury. Significance StatementApoE has long been implicated in the development of Alzheimers disease and recovery from traumatic brain injury via unknown mechanisms. Using a novel conditional ablation model of mouse ApoE and subsequent tracing of individual hippocampal neurons, we demonstrate its requirement in injury-induced neurogenesis for proper dendritic arborization and cognitive function in hippocampal-dependent learning and memory tasks.

neuroscience↗

bioRxiv2020

Upregulated functionality of mitochondria-associated ER membranes in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) can lead to neurodegenerative diseases such as Alzheimers disease (AD) through mechanisms that remain incompletely characterized. Similar to AD, TBI models present with cellular metabolic alterations and modulated cleavage of amyloid precursor protein (APP). Specifically, AD and TBI tissues display increases in amyloid-{beta} as well as its precursor, APP C-terminal fragment of 99 a.a. (C99). Our recent data in cell models of AD indicate that C99, due to its affinity for cholesterol, induces the formation of transient lipid raft domains in the ER known as mitochondria-associated ER membranes ("MAM" domains). The formation of these domains recruits and activates specific lipid metabolic enzymes that regulate cellular cholesterol trafficking and sphingolipid turnover. Increased C99 levels in AD cell models promote MAM formation and significantly modulate cellular lipid homeostasis. Here, these phenotypes were recapitulated in the controlled cortical impact (CCI) model of TBI in adult mice. Specifically, the injured cortex and hippocampus displayed significant increases in C99 and MAM activity, as measured by phospholipid synthesis, sphingomyelinase activity and cholesterol turnover. In addition, our cell type-specific lipidomics analyses revealed significant changes in microglial lipid composition that are consistent with the observed alterations in MAM-resident enzymes. Altogether, we propose that alterations in the regulation of MAM and relevant lipid metabolic pathways could contribute to the epidemiological connection between TBI and AD. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=128 SRC="FIGDIR/small/381756v2_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@12d0989org.highwire.dtl.DTLVardef@1cd1eb2org.highwire.dtl.DTLVardef@19a56caorg.highwire.dtl.DTLVardef@1b7f3e1_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗