Biology subjects

Johnson, G. V.

Publications and source records attributed to Johnson, G. V..

15 recordsLinked to original sources

bioRxiv2026

Transglutaminase 2 Deletion Enhances Astrocyte-to-Neuron Metabolic Support and Attenuates Subacute Pathology Following Repetitive Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) is the most common form of central nervous system (CNS) injury and is often characterized by persistent neuroinflammation, metabolic dysregulation, and oxidative stress. Repetitive injuries compound these pathologies and lead to multifocal axonal injuries and long-term functional deficits. Despite the prevalence of mTBIs, the cellular mechanisms that facilitate or prevent recovery following injury remain poorly defined. Here, we extend our previous work on the role of the protein transglutaminase 2 (TG2) in CNS injury and we hypothesize that transcriptional regulation by TG2 restricts metabolic versatility in astrocytes following TBI, thereby impairing neuronal energetic support and worsening pathological outcomes. We utilized an established weight-drop model of repetitive mTBI followed by multi-parametric analysis of TBI pathology in complete TG2 knockout (TG2-/-) and wild type mice. At 28 days post-injury, TG2-/- mice showed marked attenuation of TBI pathology, compared to wild type mice, in vulnerable white matter and default mode network (DMN) regions, as assessed by diffusion magnetic resonance imaging (MRI), resting-state functional MRI, and immunohistochemistry. Integrated epigenomic, proteomic, and metabolomic profiling of cortical astrocytes isolated 28 days after injury revealed a pronounced metabolic restriction in wild type astrocytes which was remarkably attenuated in the TG2-/- mice. This rescue was associated with a de-repression of gene networks involved in glutamate recycling, lipid metabolism, and metabolic homeostasis. Together, these studies provide novel mechanistic insights into the metabolic dysregulation that characterizes persistent TBI pathology, and establish a foundation for evaluating TG2 as a therapeutic target for TBI.

neuroscience↗

bioRxiv2026

Tunable Tau Expression in C. elegans Neurons Reveals that Early-AD Tau Phosphorylation Selectively Impacts Behavior and Mitochondrial Quality Control

Tau protein accumulates myriad post-translational modifications as Alzheimers disease (AD) progresses, and early-disease tau modifications such as phosphorylation at threonine 231 (T231) likely play a key role in AD pathogenesis. Here, a series of "tunable tau" strains was developed in C. elegans to test the relative impact of tau pseudo-phosphorylation of T231 (T231E) compared to protein expression level as a driver of phenotypic penetrance and severity. Multiple copies of a cassette coding for pan-neuronal wildtype tau or T231E were inserted at a genomic safe harbor loci to create a repertoire of strains expressing tau from low to high levels. In stereotypical behavioral assays of locomotory activity, T231E selectively impacted phenotypic severity compared to wild-type human tau controls, which further tracked with age and tau expression level. However, deficits in associative memory were non-selective between tau and T231E. Moreover, genetic, pharmacologic, and molecular approaches indicated that mitophagy modulation could suppress T231E phenotypes. Additionally, a robust mitochondrial unfolded protein response (UPRmt) occurred in T231E, and loss of atfs-1, a transcription factor central to the UPRmt suppressed T231E toxicity. These results demonstrate that phenotypic severity is invariably associated with tau dosage, while early-AD relevant modifications can be causative drivers of selective deficits. Consistent with recent findings, enhancing mitophagy or suppressing potentially maladaptive consequences of persistent UPRmt induction can be beneficial. This provides a solid foundation for further interrogation into mitochondrial quality control disruption as a potential root cause for AD pathogenesis. HighlightsO_LIMatched sets of pan-neuronal, multi-copy tau strains enhance experimental control C_LIO_LIPhosphomimetic tau elicits selective behavioral and neuronal dysfunction C_LIO_LIPhosphomimetic tau triggers a unique mitochondrial unfolded response C_LIO_LITau depletion and mitochondrial interventions rescue observed deficits C_LI Visual Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=168 SRC="FIGDIR/small/701793v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@c5afb3org.highwire.dtl.DTLVardef@921b6corg.highwire.dtl.DTLVardef@466f8borg.highwire.dtl.DTLVardef@45452f_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

FAM84B facilitates tau propagation via RYR3-mediated exocytosis in response to neuroinflammation

The increasing prevalence of dementia underscores the pressing need for effective therapeutic interventions. Despite extensive research into A{beta}, the limited efficacy of existing treatment modalities necessitates a paradigm shift toward tau pathology including tau propagation to slow dementia progression. Here, we identified a novel protein, FAM84B (also known as LRATD2), involved in tau propagation. Elevated FAM84B levels were detected in the postmortem cortex, cerebrospinal fluid, and induced pluripotent stem cell-derived cortical neurons of patients with tauopathy. FAM84B facilitates tau secretion through exosome assembly and RYR3-mediated exocytosis, followed by exosomal uptake into neighboring cells via clathrin-mediated endocytosis, thereby driving tau propagation. We confirmed that neuroinflammation induced by heightened STAT3 activity and cytokine treatment upregulated FAM84B expression, stimulating tau propagation, as evidenced by reduced propagation upon RYR3 inhibition. These findings provide invaluable insights into potential avenues for targeting tau propagation to ameliorate disease progression in tauopathies.

neuroscience↗

bioRxiv2025

BAG3 modulates clathrin-mediated endocytosis and tau uptake in astrocytes

In a healthy brain, astrocytes maintain neuronal homeostasis by removing proteins like tau from the extracellular space, preventing their uptake by neurons. In Alzheimers disease (AD), this function is impaired, contributing to tau accumulation. Many AD risk genes are linked to endocytosis pathways, suggesting their role in AD pathogenesis. Astrocytes can internalize, degrade, and release tau, but the mechanisms remain unclear. BAG3, a multifunctional protein, regulates vacuolar processes and interacts with clathrin-mediated endocytosis (CME) components. However, its role in astrocytic CME and tau processing is not fully understood. We show BAG3 depletion in astrocytes reduces clathrin-AP-2 interaction, inhibits CME-dependent epidermal growth factor receptor internalization, and decreases tau uptake. Live-cell imaging reveals BAG3 depletion impairs CME dynamics, increasing clathrin particle lifetimes. BAG3 depletion also alters endolysosomal compartments, increasing Lamp1+ puncta and tau co-localization. These findings highlight BAG3s role in CME, tau trafficking, and vacuolar processes, suggesting its dysfunction may contribute to AD pathogenesis.

neuroscience↗

bioRxiv2025

A Bioinformatic Analysis of BAG Protein Interactors and Pathways in Alzheimers and Parkinsons Disease

Alzheimers disease (AD) and Parkinsons disease (PD) are the two most common neurodegenerative disorders. While the symptoms and general etiology may be different, these two diseases share significant common features in terms of their disease pathogenesis. Within the scope of neurodegenerative disorders, the Bcl-2 associated athanogene (BAG) family proteins and associated interactors have been a key area of focus. The BAG family is a group of proteins that contain at least one evolutionarily conserved BAG domain. Despite this similarity, their interactions and functions can vary widely. So far, research has predominantly scrutinized individual BAG proteins, rather than explore potential cooperative actions among family members. Some BAG family members may function together thereby indicating potential interactions within this family. Although connections among BAG members have been observed, their role in neurodegenerative disorders, such as AD and PD, remains largely uncharacterized. This mini review explores the common pathways, intersections, and differences within these interactions as well as their link to AD and PD. Using computational techniques to mine transcriptomic data, several groupings of pathways that these BAG family members are involved in were identified in the context of AD and PD. Understanding these pathways and their relationships may uncover potential gaps in current research and help identify novel therapeutic targets for the treatment of these neurodegenerative diseases. Significance statementAlthough distinct diseases, Alzheimers disease and Parkinsons disease share common features such as protein aggregation and mitochondrial dysfunction. Members of the BAG family of proteins have been implicated in the pathogenesis of both diseases. Computational techniques were used to mine transcriptomic data of Alzheimers and Parkinsons disease cases to identify common pathways. BAG protein interactors, common to all family members, were analyzed in the context of these common pathways for Alzheimers and Parkinsons disease. These analyses provide insights into the pathways mediated by these BAG protein interactors that are likely at the intersection of Alzheimers disease and Parkinsons disease pathologies.

neuroscience↗

bioRxiv2025

Tau Clearance Reverses Neuronal Dysfunction in Both Young and Aged C. elegans

Alzheimers Disease (AD) is an age-related dementia and presents a growing medical and economic burden as the average human lifespan continues to rise. AD is classically diagnosed via the accumulation and aggregation of two major proteins: amyloid-{beta} and tau. To date, potential and FDA-approved therapies designed to clear these aggregates at best delay rather than prevent disease, indicating that the root cause of AD lay upstream of aggregate formation. Tau proteins phosphorylation is critical for AD progression, and phosphorylation at Threonine 231 is thought to be an early disease-associated, "gatekeeper" event. Previously, we showed that genomic, single-copy insertion of phosphomimetic human tau (T231E) into C. elegans mechanosensory neurons induced age-dependent deficits in light-touch sensation. Herein, we have generated new C. elegans models which express pan-neuronal human tau to assess the idea of selective vulnerability and whether specific neuronal behaviors might be impacted preferentially. We also tested whether tau clearance via an Auxin Inducible Degron (AID) could reverse these deficits. Despite our hypothesis that prolonged stress in older animals would induce irreversible metabolic rewiring or maladaptation, tau depletion rescued known behavioral deficits at all ages tested, including in old worms which displayed the most overt phenotypes. Taken together, our data suggest that neuronal dysfunction induced by phosphorylated tau is reversible and provides reassurance that current early-phase therapeutic efforts aimed at reducing soluble tau levels in AD patients may prove effective.

cell biology↗

bioRxiv2024

Tau phosphorylation suppresses oxidative stress-induced mitophagy via FKBP8 receptor modulation

Neurodegenerative diseases are often characterized by mitochondrial dysfunction. In Alzheimers disease, abnormal tau phosphorylation disrupts mitophagy, a quality control process through which damaged organelles are selectively removed from the mitochondrial network. The precise mechanism through which this occurs remains unclear. Previously, we showed that tau which has been mutated at Thr-231 to glutamic acid to mimic an Alzheimers-relevant phospho-epitope expressed early in disease selectively inhibits oxidative stress-induced mitophagy in C. elegans. Here, we use immortalized mouse hippocampal neuronal cell lines to extend that result into mammalian cells. Specifically, we show that phosphomimetic tau at Ser-396/404 (EC) or Thr-231/Ser-235 (EM) partly inhibits mitophagy induction by paraquat, a potent inducer of mitochondrial oxidative stress. Moreover, a combination of immunologic and biochemical approaches demonstrates that the levels of the mitophagy receptor FKBP8, significantly decrease in response to paraquat in cells expressing EC or EM tau mutants, but not in cells expressing wildtype tau. In contrast, paraquat treatment results in a decrease in the levels of the mitophagy receptors FUNDC1 and BNIP3 in the presence of both wildtype tau and the tau mutants. Interestingly, FKBP8 is normally trafficked to the endoplasmic reticulum during oxidative stress induced mitophagy, and our results support a model where this trafficking is impacted by disease-relevant tau, perhaps through a direct interaction. We provide new insights into the molecular mechanisms underlying tau pathology in Alzheimers disease and highlight FKBP8 receptor as a potential target for mitigating mitochondrial dysfunction in neurodegenerative diseases.

neuroscience↗

bioRxiv2024

Stabilizing transglutaminase 2 in the open conformation results in reactive astrocytes being more neurosupportive

Astrocytes play critical roles in supporting structural and metabolic homeostasis in the central nervous system (CNS). CNS injury leads to the development of a range of reactive phenotypes in astrocytes whose molecular determinants are poorly understood. Finding ways to modulate astrocytic injury responses and leverage a pro-recovery phenotype holds promise in treating CNS injury. Recently, it has been demonstrated that ablation of astrocytic transglutaminase 2 (TG2) modulates the phenotype of reactive astrocytes in a way that improves neuronal injury outcomes both in vitro and in vivo. In an in vivo mouse model, pharmacological inhibition of TG2 with the irreversible inhibitor VA4 phenocopies the neurosupportive effects of TG2 deletion in astrocytes. In this study, we provide insights into the mechanisms by which TG2 deletion or inhibition result in a more neurosupportive astrocytic phenotype. Using a neuron-astrocyte co-culture model, we show that VA4 treatment improves the ability of astrocytes to support neurite outgrowth on an injury-relevant matrix. To better understand how pharmacologically altering TG2 affects its ability to regulate reactive astrocyte phenotypes, we assessed how VA4 inhibition impacts TG2s interaction with Zbtb7a, a transcription factor we have previously identified as a functionally relevant TG2 nuclear interactor. The results of these studies demonstrate that VA4 significantly decreases the interaction of TG2 and Zbtb7a. TG2s interactions with Zbtb7a, as well as a wide range of other transcription factors and chromatin regulatory proteins, suggest that TG2 may act as an epigenetic regulator to modulate gene expression. To begin to understand if TG2-mediated epigenetic modification may impact astrocytic phenotypes in our models, we interrogated the effect of TG2 deletion and VA4 treatment on histone acetylation and found significantly greater acetylation in both experimental groups. Consistent with these findings, previous RNA-sequencing and our present proteomic analysis also supported a predominant transcriptionally suppressive role of TG2 in astrocytes. Our proteomic data additionally unveiled pronounced changes in lipid and antioxidant metabolism in astrocytes with TG2 deletion or inhibition, which likely contribute to the enhanced neurosupportive function of these astrocytes.

neuroscience↗

bioRxiv2023

Site-specific phosphorylation of tau impacts mitochondrial biology and response to stressors

Phosphorylation of tau at sites associated with Alzheimers disease (AD) likely plays a role in the disease progression. Mitochondrial impairment, correlating with increased presence of phosphorylated tau, has been identified as a contributing factor to neurodegenerative processes in AD. However, how tau phosphorylated at specific sites impacts mitochondrial function has not been fully defined. We examined how AD-relevant phosphomimetics of tau impact selected aspects of mitochondrial biology. To mimic phosphorylation at AD-associated sites, the Ser/Thr sites in wild-type GFP tagged-tau (T4) were converted to glutamic acid (E) to make pseudophosphorylated GFP tagged-Ser-396/404 (2EC) and GFP tagged-Thr-231/Ser-235 (2EM) constructs. These constructs were expressed in neuronal HT22 cells and their impact on specific mitochondrial functions and responses to stressors were measured. Phosphomimetic tau altered mitochondrial distribution. Specifically, mitochondria accumulated in the soma of cells expressing either 2EC or 2EM, and neurite-like extensions in 2EC cells were shorter. Additionally, ATP levels were reduced in both 2EC and 2EM expressing cells, and ROS production increased in 2EC cells during oxidation of succinate when compared to T4 expressing cells. Thapsigargin reduced mitochondrial membrane potential ({Psi}m) and increased ROS production in both 2EC and 2EM cells relative to T4 cells, with no significant difference in the effects of rotenone. These results show that tau phosphorylation at specific AD-relevant epitopes negatively affects mitochondria, with the extent of dysfunction and stress response varying according to the sites of phosphorylation. Altogether, these findings extend our understanding of potential mechanisms whereby phosphorylated tau promotes mitochondria dysfunction in tauopathies, including AD. Funding informationR01 AG067617

neuroscience↗

bioRxiv2023

BAG3 regulates the specificity of the recognition of specific MAPT species by NBR1 and SQSTM1

Autophagy receptors are essential for the recognition and clearance of specific cargos by selective autophagy, which is essential for maintaining MAPT proteostasis. Previous studies have implicated different autophagy receptors in directing distinct species of MAPT to autophagy, but the underlying mechanisms have not been fully investigated. Here we examine how the autophagy receptors NBR1 and SQSTM1 differentially engage specific forms of MAPT and facilitate their clearance. In primary neurons depletion of NBR1, unlike depletion of SQSTM1, significantly increased phosphorylated MAPT levels. The specificity of the interactions were confirmed using in vitro binding assays with purified proteins. We provide direct evidence that NBR1 preferentially binds to monomeric MAPT, while SQSTM1 interacts predominantly with oligomeric MAPT, and that the co-chaperone BAG3 regulates the specificity of these interactions. Using an in vitro pulldown assay, we show that SQSTM1 only binds to monomeric MAPT when BAG3 is absent and fails to bind when BAG3 is present. The opposite is true of NBR1; its binding to monomeric MAPT was dependent on the presence of BAG3. Interestingly, in Alzheimers disease brain the association of NBR1 with BAG3 was significantly decreased. In a mouse model, ablation of BAG3 in neural cells disrupted the association of NBR1 with phosphorylated MAPT and lead to increased levels of phosphorylated and oligomeric MAPT. Overall, our results uncover a novel role for BAG3 in regulating the specificity of selective autophagy receptors in targeting different species of MAPT and provide compelling evidence that BAG3 plays a key role in maintaining MAPT proteostasis. HighlightsO_LIFirst direct evidence of the district role of NBR1 and SQSTM1 in binding with monomeric and oligomeric MAPT, respectively. C_LIO_LIDemonstration of a novel mechanism by which BAG3 regulates the specificity of the recognition of monomeric MAPT by NBR1 and oligomeric MAPT by SQSTM1. C_LIO_LIConditional knockout of BAG3 in the brain disrupted the association of NBR1 with phosphorylated MAPT and lead to increased levels of phosphorylated and oligomeric MAPT. C_LI

neuroscience↗

bioRxiv2023

Deletion of transglutaminase 2 from astrocytes significantly improves their ability to promote neurite outgrowth on an inhibitory matrix

neuroscience↗

bioRxiv2023

All-optical spatiotemporal mapping of ROS dynamics across mitochondrial microdomains in situ

Hydrogen peroxide (H2O2) functions as a second messenger to signal metabolic distress through highly compartmentalized production in mitochondria. The dynamics of ROS generation and diffusion between mitochondrial compartments and into the cytosol govern oxidative stress responses and pathology, though our understanding of these processes remains limited. Here, we couple the H2O2 biosensor, HyPer7, with optogenetic stimulation of the ROS-generating protein KillerRed targeted into multiple mitochondrial microdomains. Single mitochondrial photogeneration of H2O2 demonstrates the spatiotemporal dynamics of ROS diffusion and transient hyperfusion of mitochondria due to ROS. Measurement of microdomain-specific H2O2 diffusion kinetics reveals directionally selective diffusion through mitochondrial microdomains. All-optical generation and detection of physiologically-relevant concentrations of H2O2 between mitochondrial compartments provide a map of mitochondrial H2O2 diffusion dynamics in situ. These kinetic details of spatiotemporal ROS dynamics and inter-mitochondrial spreading forms a framework to understand the role of ROS in health and disease.

molecular biology↗

bioRxiv2021

Deletion or inhibition of astrocytic transglutaminase 2 promotes functional recovery after spinal cord injury

Following CNS injury astrocytes become "reactive" and exhibit pro-regenerative or harmful properties. However, the molecular mechanisms that cause astrocytes to adopt either phenotype are not well understood. Transglutaminase 2 (TG2) plays a key role in regulating the response of astrocytes to insults. Here we used mice in which TG2 was specifically deleted in astrocytes (Gfap-Cre+/-TG2fl/fl, referred to here as TG2-A-cKO) in a spinal cord contusion injury (SCI) model. Deletion of TG2 from astrocytes resulted in a significant improvement in motor function following SCI. GFAP and NG2 immunoreactivity, as well as number of SOX9 positive cells, were significantly reduced in TG2-A-cKO_mice. RNA-seq analysis of spinal cords from TG2-A-cKO and control mice 3 days postinjury identified thirty-seven differentially expressed genes, all of which were increased in TG2-A-cKO mice. Pathway analysis reveals a prevalence for fatty acid metabolism, lipid storage and energy pathways, which play essential roles in neuron-astrocyte metabolic coupling. Excitingly, treatment of wild type mice with the selective TG2 inhibitor VA4 significantly improved functional recovery after SCI, similar to what was observed using the genetic model. These findings indicate the use of TG2 inhibitors as a novel strategy for the treatment of SCI and other CNS injuries.

neuroscience↗

bioRxiv2021

BAG3 regulation of Rab35 mediates the ESCRT/endolysosome pathway and tau clearance

BackgroundDeclining proteostasis with aging contributes to increased susceptibility to neurodegenerative diseases, including Alzheimers disease (AD). Emerging studies implicate impairment of the endosome-lysosome pathway as a significant factor in the pathogenesis of these diseases. Our lab was the first to demonstrate that BAG3 regulates phosphorylated tau clearance. However, we did not fully define how BAG3 regulates endogenous tau proteostasis, especially in the early stages of disease progression. MethodsMass spectrometric analyses were performed to identify neuronal BAG3 interactors. Multiple biochemical assays were used to investigate the BAG3-HSP70-TBC1D10B-Rab35-Hrs regulatory networks. Live-cell imaging was used to study the dynamic of endosomal pathway. Immunohistochemistry and immunoblotting were performed in human AD brains and BAG3 overexpressed P301S tau transgenic mice. ResultsThe primary group of neuronal BAG3 interactors identified are involved in the endocytic pathway. Among them were key regulators of small GTPases, such as the Rab35 GTPase activating protein, TBC1D10B. We demonstrated that a BAG3-HSP70-TBC1D10B complex attenuates the ability of TBC1D10B to inactivate Rab35. Thus, BAG3 interacts with TBC1D10B to support the activation of Rab35 and recruitment of Hrs, initiating ESCRT-mediated endosomal tau clearance. Further, TBC1D10B shows significantly less co-localization with BAG3 in AD brains than in age-matched controls. Overexpression of BAG3 in P301S tau transgenic mice increased the co-localization of phospho-tau with the ESCRT III protein CHMP2B and reduced the levels of the mutant human tau. ConclusionWe identified a novel BAG3-TBC1D10B-Rab35 regulatory axis that modulates ESCRT-dependent protein degradation machinery and tau clearance. Dysregulation of BAG3 could contribute to the pathogenesis of AD.

neuroscience↗

bioRxiv2019

BAG3 and SYNPO (synaptopodin) facilitate phospho-MAPT/Tau degradation via autophagy in neuronal processes

A major cellular catabolic pathway in neurons is macroautophagy/autophagy, through which misfolded or aggregation-prone proteins are sequestered into autophagosomes that fuse with lysosomes, and are subsequently degraded. MAPT (microtubule associated protein tau) is one of the protein clients of autophagy. Given that accumulation of hyperphosphorylated MAPT contributes to the pathogenesis of Alzheimer disease and other tauopathies, decreasing endogenous MAPT levels has been shown to be beneficial to neuronal health in models of these diseases. A previous study demonstrated that the HSPA/HSP70 co-chaperone BAG3 (BCL2 associated athanogene 3) facilitates endogenous MAPT clearance through autophagy. These findings prompted us to further investigate the mechanisms underlying BAG3-mediated autophagy in the degradation of endogenous MAPT. Here we demonstrate for the first time that BAG3 plays an important role in autophagic flux in the neuritic processes of mature neurons (20-24 days in vitro [DIV]) through interaction with the post-synaptic cytoskeleton protein SYNPO (synaptopodin). Loss of either BAG3 or SYNPO impeded the fusion of autophagosomes and lysosomes predominantly in the post-synaptic compartment. A block of autophagy leads to accumulation of the autophagic receptor protein SQSTM1/p62 (sequestosome 1) as well as MAPT phosphorylated at Ser262 (p-Ser262). Furthermore, p-Ser262 appears to accumulate in autophagosomes at post-synaptic densities. Overall these data provide evidence of a novel role for the co-chaperone BAG3 in synapses. In cooperation with SYNPO, it functions as part of a surveillance complex that facilitates the autophagic clearance of MAPT p-Ser262, and possibly other MAPT species at the post-synapse. This appears to be crucial for the maintenance of a healthy, functional synapse.

neuroscience↗