Biology subjects

Carmichael, S. T.

Publications and source records attributed to Carmichael, S. T..

11 recordsLinked to original sources

bioRxiv2026

Astrocytic chordin-like 1 (Chrdl1) is re-engaged early after ischemic stroke to regulate region-dependent GluA2 levels and neuronal vulnerability

Neuronal vulnerability to ischemic stroke varies markedly across brain regions, yet the mechanisms underlying this selective susceptibility remain poorly understood. Here, we show that the developmental astrocytic protein Chordin-like 1 (Chrdl1) is repurposed after ischemic injury to regulate neuronal vulnerability. Chrdl1 expression stabilizes GluA2-containing AMPA receptors, limits delayed apoptotic neuronal death, and preserves hippocampal function early after focal ischemic stroke, whereas sustained Chrdl1 expression does not improve long-term recovery. These findings identify an unexpected neuroprotective role for Chrdl1 during acute ischemia that contrasts with its previously described function as a limiter of synaptic plasticity during recovery. Our work reveals that developmental astrocyte-derived signaling can be redeployed after brain injury, with distinct functions depending on the stage of stroke and region-dependent endogenous expression that together determine whether a conserved neuroprotective mechanism is engaged after ischemic stroke.

neuroscience↗

bioRxiv2025

Loss of Sarm1 Mitigates Axonal and Neuronal Degeneration and Promotes Neuronal Repair After Ischemic Stroke

Axonal degeneration is a core feature of ischemic brain injury that limits functional recovery. The pro-degenerative molecule Sarm1 is required for Wallerian axon degeneration after traumatic and chemotoxic nerve injuries, however it is unclear if a similar mechanism mediates axonal degradation after ischemic injury. Here we show that loss of Sarm1 results in profound attenuation of axonal degeneration after focal ischemia to the subcortical white matter as well as to the cortex. Moreover, absence of Sarm1 significantly promotes the survival of neurons remote from but connected to the infarct after ischemic injuries to the subcortical white matter as well as to the cortex. Notably, loss of Sarm1 also significantly ameliorates early and late motor as well as cognitive deficits following white matter stroke. To further understand the mechanism of Sarm1-/- mediated neuronal protection, we performed differential gene expression analyses of wildtype and Sarm1-/- stroke-injured neurons and found that the loss of Sarm1 activates a pro-growth molecular program that promotes gene expression programs involved in axonogenesis and synaptogenesis after white matter ischemia. Using a functional genomics approach to recapitulate such a molecular program in Sarm1-/- neurons, we identify molecular compounds sufficient to enhance cortical neurite outgrowth in vitro, and all of which elicit a conserved epigenetic signature promoting axonogenesis. These results indicate that Sarm1 promotes axonal degeneration and concurrently inhibits an axonal reparative program encoded at the level of the epigenome that can be modulated pharmacologically. Our findings thus reveal a novel role for Sarm1 as a crucial regulator of both axonal degeneration and axonal repair after ischemic stroke.

neuroscience↗

bioRxiv2025

Clustered VEGF Nanoparticles in Microporous Annealed Particle (MAP) Hydrogel Accelerates Functional Recovery and Brain Tissue Repair after Stroke

Ischemic stroke, a blockage in the vasculature of the brain that results in insufficient blood flow, is one of the worlds leading causes of disability. The cascade of inflammation and cell death that occurs immediately following stroke drives vascular and functional loss that does not fully recover over time, and no FDA-approved therapies exist that stimulate regeneration post-stroke. We have previously developed a hydrogel scaffold that delivered heparin nanoparticles with and without VEGF bound to their surface to promote angiogenesis and reduce inflammation, respectively. However, the inclusion of the naked heparin nanoparticles warranted concern over the development of bleeding complications. Here, we explore how microporous annealed particle (MAP) scaffolds functionalized with VEGF coated heparin nanoparticles can both reduce inflammation and promote angiogenesis - without the inclusion of free heparin nanoparticles. We show that our updated design not only successfully promotes de novo tissue formation, including the development of mature vessels and neurite sprouting, but it also leads to functional improvement in a photothrombotic stroke model. In addition, we find increased astrocyte infiltration into the infarct site correlated with mature vessel formation. This work demonstrates how our biomaterial design can enhance endogenous regeneration post-stroke while eliminating the need for excess heparin.

bioengineering↗

bioRxiv2024

Intercellular Signaling Pathways as Therapeutic Targets for Vascular Dementia Repair

Vascular dementia (VaD) is a white matter ischemic disease and the second-leading cause of dementia, with no direct therapy. Within the lesion site, cell-cell interactions dictate the trajectory towards disease progression or repair. To elucidate the underlying intercellular signaling pathways, a VaD mouse model was developed for transcriptomic and functional studies. The mouse VaD transcriptome was integrated with a human VaD snRNA-Seq dataset. A custom-made database encompassing 4053 human and 2032 mouse ligand-receptor (L-R) interactions identified significantly altered pathways shared between human and mouse VaD. Two intercellular L-R systems, Serpine2-Lrp1 and CD39-A3AR, were selected for mechanistic study as both the ligand and receptor were dysregulated in VaD. Decreased Seprine2 expression enhances OPC differentiation in VaD repair. A clinically relevant drug that reverses the loss of CD39-A3AR function promotes tissue and behavioral recovery in the VaD model. This study presents novel intercellular signaling targets and may open new avenues for VaD therapies.

neuroscience↗

bioRxiv2024

Supervised deep machine learning models predict forelimb movement from excitatory neuronal ensembles and suggest distinct pattern of activity in CFA and RFA networks

Neuronal networks in the motor cortex are crucial for driving complex movements. Yet it remains unclear whether distinct neuronal populations in motor cortical subregions encode complex movements. Using in vivo two-photon calcium imaging (2P) on head- fixed grid-walking animals, we tracked the activity of excitatory neuronal networks in layer 2/3 of caudal forelimb area (CFA) and rostral forelimb area (RFA) in motor cortex. Employing supervised deep machine learning models, a support vector machine (SVM) and feed forward deep neural networks (FFDNN), we were able to decode the complex grid-walking movement at the level of excitatory neuronal ensembles. This study indicates significant differences between RFA and CFA decoding accuracy in both models. Our data demonstrate distinct temporal-delay decoding patterns for movements in CFA and RFA, as well as a selective ensemble of movement responsive neurons with higher distribution in CFA, suggesting specific patterns of activity-induced movement in these two networks.

neuroscience↗

bioRxiv2023

A toolbox of astrocyte-specific, serotype-independent adeno-associated viral vectors using microRNA targeting sequences.

Astrocytes, one of the most prevalent cell types in the central nervous system (CNS), are critically involved in neural function in both health and disease. Genetically manipulating astrocytes is an essential tool in understanding and affecting their roles. Adeno-associated viruses (AAVs) enable rapid genetic manipulation; however, astrocyte specificity of AAVs can be limited, with high off-target expression in neurons and sparsely in endothelial cells. Here, we report the development of a cassette of four copies of six miRNA targeting sequences (4x6T) which triggers transgene degradation specifically in neurons and endothelial cells. When used in combination with the GfaABC1D promoter, 4x6T increases astrocytic specificity of Cre with a viral reporter from <50% to >99% in multiple serotypes in mice, and confers astrocyte specificity in two inducible forms of Cre; Dre; and reporters. We also present empty vectors to add 4x6T to other cargo, independently and in Cre/Dre-dependent forms. This toolbox of AAVs provides a way to rapidly manipulate astrocytes throughout the CNS, is compatible with different AAV serotypes, and demonstrates the efficacy of using multiplexed miRNA targeting sequences to decrease expression in multiple off-target cell populations simultaneously.

neuroscience↗

bioRxiv2022

Reactive astrocyte derived extracellular vesicles promote functional repair post stroke

Reactive astrocytes are both neurotoxic and pro-regenerative. Their reparative roles after injury have been demonstrated, but how they play a contributing role to regeneration remains question. Here, we investigate the use of astrocytic extracellular vesicles from primary astrocytes cultured in reactive conditions in promoting repair after ischemic stroke. Our studies show that extracellular vesicles derived from reactive astrocytes that co-express a significant number of reactive genes (155 upregulated including log2 of 9.61 for Lcn2) and axonal outgrowth genes (59 upregulated including log2 of 3.49 Ntn1) are necessary for improved regenerative outcomes, including axonal infiltration, vascularization, and improved behavioral recovery. Proteomic analysis of the extracellular vesicles show that astrocytes enrich pro-reparative proteins in extracellular vesicles with only 30 proteins relating to inflammatory or complement pathways loaded out of a total of 1073 proteins. Further, we show that the use of a biomaterial scaffold is necessary for the improved regeneration observed from reactive astrocyte extracellular vesicles. These studies show that reactive astrocytes use extracellular vesicles enriched with pro-repair proteins to promote recovery after injury.

neuroscience↗

bioRxiv2021

Generation of a molecular interactome of the glioblastoma perivascular niche reveals Integrin Binding Sialoprotein as a key mediator of tumor cell migration

Glioblastoma (GBM) is characterized by extensive microvascular hyperproliferation. In addition to supplying blood to the tumor, GBM vessels also provide trophic support to glioma cells and serve as conduits for migration into the surrounding brain promoting recurrence. Here, we enriched CD31-expressing glioma vascular cells (GVC) and A2B5-expressing glioma tumor cells (GTC) from primary GBM and utilized RNA sequencing to create a comprehensive interaction map of the secreted and extracellular factors elaborated by GVC that can interact with receptors and membrane molecules on GTC. To validate our findings, we utilized functional assays, including a novel hydrogel-based migration assay and in vivo mouse models to demonstrate that one identified factor, the little-studied integrin binding sialoprotein (IBSP) enhances tumor growth and promotes the migration of GTC along the vasculature. This perivascular niche interactome will serve a resource to the research community in defining the potential functions of the GBM vasculature.

cancer biology↗

bioRxiv2019

Hyaluronic acid particle hydrogels decrease cerebral atrophy and promote pro-reparative astrocyte/axonal infiltration after ischemic stroke

The death rate due to stroke is decreasing, resulting in more individuals living with stroke related disabilities. Following stroke, dying cells contribute to the large influx of highly reactive astrocytes and pro-inflammatory microglia that release cytokines and lead to a cytotoxic environment that causes further brain damage and prevents endogenous repair. Paradoxically, these same cells also activate pro-repair mechanisms that contribute to endogenous repair and brain plasticity. Here, we show that the direct injection of a hyaluronic acid based microporous annealed particle (HA-MAP) hydrogel into the stroke core reduces the percent of highly reactive astrocytes and increases the percent of alternatively activated microglia in and around the lesion. Further, we show that HA-MAP hydrogel promotes reparative astrocyte infiltration into the lesion, which directly coincides with axonal penetration into the lesion. Additionally, HA-MAP injection decreases cerebral atrophy and preserves nigrostriatal bundles after stroke. This work shows that the injection of a porous scaffold into the stroke core can lead to clinically relevant decrease in cerebral atrophy and modulates the phenotype of astrocytes and microglia towards a pro-repair phenotype.

bioengineering↗

bioRxiv2019

Click by Click Microporous Annealed Particle (MAP) Scaffolds

Macroporous scaffolds are being increasingly used in regenerative medicine and tissue repair. While our recently developed microporous annealed particle (MAP) scaffolds have overcome issues with injectability and in situ hydrogel formation, limitations with respect to tunability to be able to manipulate hydrogel strength and rigidity for broad applications still exist. To address these key issues, here we synthesized hydrogel microparticles (HMPs) of hyaluronic acid (HA) using the thiol-norbornene click reaction and then subsequently annealed HMPs into a porous scaffold using the tetrazine-norbornene click reaction. This assembly method allowed for straightforward tuning of bulk scaffold rigidity by varying the tetrazine to norbornene ratio, with increasing tetrazine resulting in increasing scaffold storage modulus, Youngs modulus, and maximum stress. These changes were independent of void fraction. Further incorporation of human dermal fibroblasts (HDFs) throughout the porous scaffold revealed the biocompatibility of this annealing strategy as well as differences in proliferation and cell-occupied volume. Finally, injection of porous HA-Tet MAP scaffolds into an ischemic stroke model showed this chemistry is biocompatible in vivo with reduced levels of inflammation and astrogliosis as previously demonstrated for other crosslinking chemistries.

bioengineering↗

bioRxiv2019

Endothelial CXCL5 negatively regulates myelination and repair after white matter stroke

Cerebral small vessel disease and resulting white matter pathologies are worsened by cardiovascular risk factors including obesity. The molecular changes in cerebral endothelial cells caused by chronic cerebrovascular risk factors remain unknown. We developed a novel approach for molecular profiling of chronically injured cerebral endothelial cells using cell-specific translating ribosome affinity purification (RiboTag) with RNA-seq in Tie2-Cre:RiboTag mice. We used this approach to identify the transcriptome of white matter endothelial cells after the onset of diet-induced obesity (DIO). DIO induces an IL-17B signaling pathway that acts on the cerebral endothelia through IL-17Rb to increase levels of both circulating CXCL5 and local endothelial expression of CXCL5 in both the DIO mouse model and in humans with imaging or pathologic evidence of cerebral small vessel disease. In the white matter, endothelial CXCL5 acts as a chemoattractant and promotes the association of oligodendrocyte progenitor cells (OPCs) with cerebral endothelia increasing vessel-associated OPC cell number and triggers OPC gene expression programs regulating migration and chemokine receptor activation. Targeted blockade of IL-17B with peripheral antibody administration reduced the population of vessel-associated OPCs by reducing endothelial CXCL5 expression. CXCL5-mediated sequestration of OPCs to white matter vasculature impairs OPC differentiation after a focal white matter ischemic lesion. DIO promotes a unique white matter endothelial-to-oligodendrocyte progenitor cell signaling pathway that compromises brain repair after stroke.

neuroscience↗