Cytosolic dopamine determines hypersensitivity to blunt force trauma.

The selective vulnerability of dopaminergic neurons to trauma-induced neurodegeneration is conserved across species, from nematodes to humans. However, the molecular mechanisms underlying this hypersensitivity to blunt force trauma remain elusive. We find that extravesicular dopamine, a key driver of Parkinson's disease, extends its toxic role to the acute challenges associated with injury. Ectopic dopamine synthesis in serotonergic neurons sensitizes this resilient neuronal subtype to trauma-induced degeneration. While dopaminergic neurons normally maintain dopamine in a functional and benign state, trauma-induced subcellular redox imbalances elicit dopamine-dependent cytotoxicity. Cytosolic dopamine accumulation, through perturbations to its synthesis, metabolism, or packaging, is necessary and sufficient to drive neurodegeneration upon injury and during aging. Additionally, degeneration is further exacerbated by rapid upregulation of the rate-limiting enzyme in dopamine synthesis, cat-2, via the FOS-1 transcription factor. Fundamentally, our study in C. elegans unravels the molecular intricacies rendering dopaminergic neurons uniquely prone to physical perturbation across evolutionary lines.

Blood Markers in Relation to a History of Traumatic Brain Injury Across Stages of Cognitive Impairment in a Diverse Cohort.

BACKGROUND: Traumatic brain injury (TBI) has been linked to multiple pathophysiological processes that could increase risk for Alzheimer's disease and related dementias (ADRD). However, the impact of prior TBI on blood biomarkers for ADRD remains unknown. OBJECTIVE: Using cross-sectional data, we assessed whether a history of TBI influences serum biomarkers in a diverse cohort (approximately 50% Hispanic) with normal cognition, mild cognitive impairment, or dementia. METHODS: Levels of glial fibrillary acidic protein (GFAP), neurofilament light (NFL), total tau (T-tau), and ubiquitin carboxy-terminal hydrolase-L1 (UCHL1) were measured for participants across the cognitive spectrum. Participants were categorized based on presence and absence of a history of TBI with loss of consciousness, and study samples were derived through case-control matching. Multivariable general linear models compared concentrations of biomarkers in relation to a history of TBI and smoothing splines modelled biomarkers non-linearly in the cognitively impaired groups as a function of time since symptom onset. RESULTS: Each biomarker was higher across stages of cognitive impairment, characterized by clinical diagnosis and Mini-Mental State Examination performance, but these associations were not influenced by a history of TBI. However, modelling biomarkers in relation to duration of cognitive symptoms for ADRD showed differences by history of TBI, with only GFAP and UCHL1 being elevated. CONCLUSIONS: Serum GFAP, NFL, T-tau, and UCHL1 were higher across stages of cognitive impairment in this diverse clinical cohort, regardless of TBI history, though longitudinal investigation of the timing, order, and trajectory of the biomarkers in relation to prior TBI is warranted.

Loss of heat shock factor initiates intracellular lipid surveillance by actin destabilization.

Cells sense stress and initiate response pathways to maintain lipid and protein homeostasis. However, the interplay between these adaptive mechanisms is unclear. Herein, we demonstrate how imbalances in cytosolic protein homeostasis affect intracellular lipid surveillance. Independent of its ancient thermo-protective properties, the heat shock factor, HSF-1, modulates lipid metabolism and age regulation through the metazoan-specific nuclear hormone receptor, NHR-49. Reduced hsf-1 expression destabilizes the Caenorhabditis elegans enteric actin network, subsequently disrupting Rab GTPase-mediated trafficking and cell-surface residency of nutrient transporters. The ensuing malabsorption limits lipid availability, thereby activating the intracellular lipid surveillance response through vesicular release and nuclear translocation of NHR-49 to both increase nutrient absorption and restore lipid homeostasis. Overall, cooperation between these regulators of cytosolic protein homeostasis and lipid surveillance ensures metabolic health and age progression through actin integrity, endocytic recycling, and lipid sensing.

Reduced bone morphogenic protein signaling along the gut-neuron axis by heat shock factor promotes longevity.

Aging is a complex and highly regulated process of interwoven signaling mechanisms. As an ancient transcriptional regulator of thermal adaptation and protein homeostasis, the Heat Shock Factor, HSF-1, has evolved functions within the nervous system to control age progression; however, the molecular details and signaling dynamics by which HSF-1 modulates age across tissues remain unclear. Herein, we report a nonautonomous mode of age regulation by HSF-1 in the Caenorhabditis elegans nervous system that works through the bone morphogenic protein, BMP, signaling pathway to modulate membrane trafficking in peripheral tissues. In particular, HSF-1 represses the expression of the neuron-specific BMP ligand, DBL-1, and initiates a complementary negative feedback loop within the intestine. By reducing receipt of DBL-1 in the periphery, the SMAD transcriptional coactivator, SMA-3, represses the expression of critical membrane trafficking regulators including Rab GTPases involved in early (RAB-5), late (RAB-7), and recycling (RAB-11.1) endosomal dynamics and the BMP receptor binding protein, SMA-10. This reduces cell surface residency and steady-state levels of the type I BMP receptor, SMA-6, in the intestine and further dampens signal transmission to the periphery. Thus, the ability of HSF-1 to coordinate BMP signaling along the gut-brain axis is an important determinate in age progression.

Intracellular lipid surveillance by small G protein geranylgeranylation.

Imbalances in lipid homeostasis can have deleterious effects on health1,2. Yet how cells sense metabolic demand due to lipid depletion and respond by increasing nutrient absorption remains unclear. Here we describe a mechanism for intracellular lipid surveillance in Caenorhabditis elegans that involves transcriptional inactivation of the nuclear hormone receptor NHR-49 through its cytosolic sequestration to endocytic vesicles via geranylgeranyl conjugation to the small G protein RAB-11.1. Defective de novo isoprenoid synthesis caused by lipid depletion limits RAB-11.1 geranylgeranylation, which promotes nuclear translocation of NHR-49 and activation of rab-11.2 transcription to enhance transporter residency at the plasma membrane. Thus, we identify a critical lipid sensed by the cell, its conjugated G protein, and the nuclear receptor whose dynamic interactions enable cells to sense metabolic demand due to lipid depletion and respond by increasing nutrient absorption and lipid metabolism.

Mild Traumatic Brain Injury Is Related to Elevated Cerebrospinal Fluid Tau in Alzheimer's Disease Dementia.

Few studies have examined an association between mild traumatic brain injury (mTBI) and Alzheimer's disease (AD). For this reason, we compared an AD dementia group with an mTBI history (n = 10) to a matched AD control group (n = 20) on measures of cognitive function, cerebral glucose metabolism, and markers of amyloid and tau deposition. Only a trend and medium-to-large effect size for higher phosphorylated and total tau was identified for the mTBI group. A history of mTBI may be associated with greater tau in AD, indicating a potential pathway for increasing risk for AD, though further evaluation with larger samples is needed.

The impact of spatially varying wetland source signatures on the atmospheric variability of δD-CH4.

We present the first spatially resolved distribution of the [Formula: see text] signature of wetland methane emissions and assess its impact on atmospheric [Formula: see text]. The [Formula: see text] signature map is derived by relating [Formula: see text] of precipitation to measured [Formula: see text] of methane wetland emissions at a variety of wetland types and locations. This results in strong latitudinal variation in the wetland [Formula: see text] source signature. When [Formula: see text] is simulated in a global atmospheric model, little difference is found in global mean, inter-hemispheric difference and seasonal cycle if the spatially varying [Formula: see text] source signature distribution is used instead of a globally uniform value. This is because atmospheric [Formula: see text] is largely controlled by OH fractionation. However, we show that despite these small differences, using atmospheric records of [Formula: see text] to infer changes in the wetland emissions distribution requires the use of the more accurate spatially varying [Formula: see text] source signature. We find that models will only be sensitive to changes in emissions distribution if spatial information can be exploited through the spatially resolved source signatures. In addition, we also find that on a regional scale, at sites measuring excursions of [Formula: see text] from background levels, substantial differences are simulated in atmospheric [Formula: see text] if using spatially varying or uniform source signatures. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

Glycolytic preconditioning in astrocytes mitigates trauma-induced neurodegeneration.

Concussion is associated with a myriad of deleterious immediate and long-term consequences. Yet the molecular mechanisms and genetic targets promoting the selective vulnerability of different neural subtypes to dysfunction and degeneration remain unclear. Translating experimental models of blunt force trauma in C. elegans to concussion in mice, we identify a conserved neuroprotective mechanism in which reduction of mitochondrial electron flux through complex IV suppresses trauma-induced degeneration of the highly vulnerable dopaminergic neurons. Reducing cytochrome C oxidase function elevates mitochondrial-derived reactive oxygen species, which signal through the cytosolic hypoxia inducing transcription factor, Hif1a, to promote hyperphosphorylation and inactivation of the pyruvate dehydrogenase, PDHE1α. This critical enzyme initiates the Warburg shunt, which drives energetic reallocation from mitochondrial respiration to astrocyte-mediated glycolysis in a neuroprotective manner. These studies demonstrate a conserved process in which glycolytic preconditioning suppresses Parkinson-like hypersensitivity of dopaminergic neurons to trauma-induced degeneration via redox signaling and the Warburg effect.

Concussion is a type of traumatic brain injury that results from a sudden blow or jolt to the head. Symptoms can include a passing headache, dizziness, confusion or sensitivity to light, but experiencing multiple concussions can have drastic repercussions in later life. Studies of professional athletes have shown that those who experience one or more concussions are prone to developing Alzheimer's and Parkinson's disease, two well-known neurodegenerative diseases. Both conditions involve the progressive loss or breakdown of nerve cells, called neurons. But exactly how this so-called neurodegeneration of brain cells stems from the original, physical injury remains unclear. Head trauma may cause damage to the structural support of a cell or disrupt the flow of electrical impulses through neurons. Energy use and production in damaged cells could shift into overdrive to repair the damage. The chemical properties of different types of brain cells could also make some more vulnerable to trauma than others. Besides neurons, star-shaped support cells in the brain called astrocytes, which may have some protective ability, could also be affected. To investigate which cells may be more susceptible to traumatic injuries, Solano Fonseca et al. modelled the impacts of concussion-like head trauma in roundworms (C. elegans) and mice. In both animals, one type of neuron was extremely vulnerable to cell death after trauma. Neurons that release dopamine, a chemical involved in cell-to-cell communication and the brain's reward system, showed signs of cell damage and deteriorated after injury. Dopaminergic cells, as these cells are called, are involved in motor coordination, and the loss of dopaminergic cells has been linked to both Alzheimer's and Parkinson's disease. Astrocytes, however, had a role in reducing the death of dopaminergic neurons after trauma. In experiments, astrocytes appeared to restore the balance of energy production to meet the increased energy demands of impacted neurons. Single-cell analyses showed that genes involved in metabolism were switched on in astrocytes to produce energy via an alternative pathway. This energetic shift facilitated via astrocytes may help mitigate against some damage to dopamine-producing neurons after trauma, reducing cell death. This work furthers our understanding of cellular changes in the concussed brain. More research will be required to better characterise how this immediate trauma to cells, and the subsequent loss of dopaminergic neurons, impacts brain health long-term. Efforts to design effective therapies to slow or reverse these changes could then follow.

Quantitative pupillometry in patients with traumatic brain injury and loss of consciousness: A prospective pilot study.

OBJECTIVE: Loss of consciousness (LOC) is a hallmark feature in Traumatic Brain Injury (TBI), and a strong predictor of outcomes after TBI. The aim of this study was to describe associations between quantitative infrared pupillometry values and LOC, intracranial hypertension, and functional outcomes in patients with TBI. METHODS: We conducted a prospective study of patients evaluated at a Level 1 trauma center between November 2019 and February 2020. Pupillometry values including the Neurological Pupil Index (NPi), constriction velocity (CV), and dilation velocity (DV) were obtained. RESULTS: Thirty-six consecutive TBI patients were enrolled. The median (range) age was 48 (range 21-86) years. The mean Glasgow Coma Scale score on arrival was 11.8 (SD = 4.0). DV trichotomized as low (<0.5 mm/s), moderate (0.5-1.0 mm/s), or high (>1.0 mm/s) was significantly associated with LOC (P = .02), and the need for emergent intervention (P < .01). No significant association was observed between LOC and NPi (P = .16); nor between LOC and CV (P = .07). CONCLUSIONS: Our data suggests that DV, as a discrete variable, is associated with LOC in TBI. Further investigation of the relationship between discrete pupillometric variables and NPi may be valuable to understand the clinical significance of the pupillary light reflex findings in acute TBI.

Trauma-induced regulation of VHP-1 modulates the cellular response to mechanical stress.

Mechanical stimuli initiate adaptive signal transduction pathways, yet exceeding the cellular capacity to withstand physical stress results in death. The molecular mechanisms underlying trauma-induced degeneration remain unclear. In the nematode C. elegans, we have developed a method to study cellular degeneration in response to mechanical stress caused by blunt force trauma. Herein, we report that physical injury activates the c-Jun kinase, KGB-1, which modulates response elements through the AP-1 transcriptional complex. Among these, we have identified a dual-specificity MAPK phosphatase, VHP-1, as a stress-inducible modulator of neurodegeneration. VHP-1 regulates the transcriptional response to mechanical stress and is itself attenuated by KGB-1-mediated inactivation of a deubiquitinase, MATH-33, and proteasomal degradation. Together, we describe an uncharacterized stress response pathway in C. elegans and identify transcriptional and post-translational components comprising a feedback loop on Jun kinase and phosphatase activity.

Simultaneous Control of Endogenous and User-Defined Genetic Pathways Using Unique ecDHFR Pharmacological Chaperones.

Destabilizing domains (DDs), such as a mutated form of Escherichia coli dihydrofolate reductase (ecDHFR), confer instability and promote protein degradation. However, when combined with small-molecule stabilizers (e.g., the antibiotic trimethoprim), DDs allow positive regulation of fusion protein abundance. Using a combinatorial screening approach, we identified and validated 17 unique 2,4-diaminopyrimidine/triazine-based ecDHFR DD stabilizers, at least 15 of which were ineffective antibiotics against E. coli and S. aureus. Identified stabilizers functioned in vivo to control an ecDHFR DD-firefly luciferase in the mouse eye and/or the liver. Next, stabilizers were leveraged to perform synergistic dual functions in vitro (HeLa cell death sensitization) and in vivo (repression of ocular inflammation) by stabilizing a user-defined ecDHFR DD while also controlling endogenous signaling pathways. Thus, these newly identified pharmacological chaperones allow for simultaneous control of compound-specific endogenous and user-defined genetic pathways, the combination of which may provide synergistic effects in complex biological scenarios.

Age-Onset Phosphorylation of a Minor Actin Variant Promotes Intestinal Barrier Dysfunction.

Age-associated decay of intercellular interactions impairs the cells' capacity to tightly associate within tissues and form a functional barrier. This barrier dysfunction compromises organ physiology and contributes to systemic failure. The actin cytoskeleton represents a key determinant in maintaining tissue architecture. Yet, it is unclear how age disrupts the actin cytoskeleton and how this, in turn, promotes mortality. Here, we show that an uncharacterized phosphorylation of a low-abundant actin variant, ACT-5, compromises integrity of the C. elegans intestinal barrier and accelerates pathogenesis. Age-related loss of the heat-shock transcription factor, HSF-1, disrupts the JUN kinase and protein phosphatase I equilibrium which increases ACT-5 phosphorylation within its troponin binding site. Phosphorylated ACT-5 accelerates decay of the intestinal subapical terminal web and impairs its interactions with cell junctions. This compromises barrier integrity, promotes pathogenesis, and drives mortality. Thus, we provide the molecular mechanism by which age-associated loss of specialized actin networks impacts tissue integrity.

Author Correction: Small-molecule TFEB pathway agonists that ameliorate metabolic syndrome in mice and extend C. elegans lifespan.

The originally published version of this Article contained an error in the spelling of the author Nathaniel W. Oswald, which was incorrectly given as Nathaniel W. Olswald. This has now been corrected in both the PDF and HTML versions of the Article.

Small-molecule TFEB pathway agonists that ameliorate metabolic syndrome in mice and extend C. elegans lifespan.

Drugs that mirror the cellular effects of starvation mimics are considered promising therapeutics for common metabolic disorders, such as obesity, liver steatosis, and for ageing. Starvation, or caloric restriction, is known to activate the transcription factor EB (TFEB), a master regulator of lipid metabolism and lysosomal biogenesis and function. Here, we report a nanotechnology-enabled high-throughput screen to identify small-molecule agonists of TFEB and discover three novel compounds that promote autophagolysosomal activity. The three lead compounds include the clinically approved drug, digoxin; the marine-derived natural product, ikarugamycin; and the synthetic compound, alexidine dihydrochloride, which is known to act on a mitochondrial target. Mode of action studies reveal that these compounds activate TFEB via three distinct Ca2+-dependent mechanisms. Formulation of these compounds in liver-tropic biodegradable, biocompatible nanoparticles confers hepatoprotection against diet-induced steatosis in murine models and extends lifespan of Caenorhabditis elegans. These results support the therapeutic potential of small-molecule TFEB activators for the treatment of metabolic and age-related disorders.

The homeodomain-interacting protein kinase HPK-1 preserves protein homeostasis and longevity through master regulatory control of the HSF-1 chaperone network and TORC1-restricted autophagy in Caenorhabditis elegans.

An extensive proteostatic network comprised of molecular chaperones and protein clearance mechanisms functions collectively to preserve the integrity and resiliency of the proteome. The efficacy of this network deteriorates during aging, coinciding with many clinical manifestations, including protein aggregation diseases of the nervous system. A decline in proteostasis can be delayed through the activation of cytoprotective transcriptional responses, which are sensitive to environmental stress and internal metabolic and physiological cues. The homeodomain-interacting protein kinase (hipk) family members are conserved transcriptional co-factors that have been implicated in both genotoxic and metabolic stress responses from yeast to mammals. We demonstrate that constitutive expression of the sole Caenorhabditis elegans Hipk homolog, hpk-1, is sufficient to delay aging, preserve proteostasis, and promote stress resistance, while loss of hpk-1 is deleterious to these phenotypes. We show that HPK-1 preserves proteostasis and extends longevity through distinct but complementary genetic pathways defined by the heat shock transcription factor (HSF-1), and the target of rapamycin complex 1 (TORC1). We demonstrate that HPK-1 antagonizes sumoylation of HSF-1, a post-translational modification associated with reduced transcriptional activity in mammals. We show that inhibition of sumoylation by RNAi enhances HSF-1-dependent transcriptional induction of chaperones in response to heat shock. We find that hpk-1 is required for HSF-1 to induce molecular chaperones after thermal stress and enhances hormetic extension of longevity. We also show that HPK-1 is required in conjunction with HSF-1 for maintenance of proteostasis in the absence of thermal stress, protecting against the formation of polyglutamine (Q35::YFP) protein aggregates and associated locomotory toxicity. These functions of HPK-1/HSF-1 undergo rapid down-regulation once animals reach reproductive maturity. We show that HPK-1 fortifies proteostasis and extends longevity by an additional independent mechanism: induction of autophagy. HPK-1 is necessary for induction of autophagosome formation and autophagy gene expression in response to dietary restriction (DR) or inactivation of TORC1. The autophagy-stimulating transcription factors pha-4/FoxA and mxl-2/Mlx, but not hlh-30/TFEB or the nuclear hormone receptor nhr-62, are necessary for extended longevity resulting from HPK-1 overexpression. HPK-1 expression is itself induced by transcriptional mechanisms after nutritional stress, and post-transcriptional mechanisms in response to thermal stress. Collectively our results position HPK-1 at a central regulatory node upstream of the greater proteostatic network, acting at the transcriptional level by promoting protein folding via chaperone expression, and protein turnover via expression of autophagy genes. HPK-1 therefore provides a promising intervention point for pharmacological agents targeting the protein homeostasis system as a means of preserving robust longevity.

The stress response paradox: fighting degeneration at the cost of cancer.

In the modern research era, sequencing and high-throughput analysis have linked genetic factors with a multitude of disease states. Often times, the same cellular machinery is implicated in several different diseases and has made it challenging to drug a particular disease with minimal pleotropic consequences. It is intriguing to see how different fields of disease research can present such differing views when describing the same biological process, pathway, or molecule. As observations in one field converge with research in another, we gain a more complete picture of a biological system and can accurately assess the feasibility for translational science. As an example discussed here, modulating latent stress response pathways within the cell provides exciting therapeutic potential, however, opposing views have emerged in the fields of degenerative disease and cancer. This at first glance seems logical as suppression of degenerative disease entails maintaining cell viability, while cancer aims to enhance selective senescence and cell death. As both of these disciplines seek novel therapeutic interventions, we should not overlook how scientific biases involving one biological process may impact different disease paradigms.

Heterotypic Signals from Neural HSF-1 Separate Thermotolerance from Longevity.

Integrating stress responses across tissues is essential for the survival of multicellular organisms. The metazoan nervous system can sense protein-misfolding stress arising in different subcellular compartments and initiate cytoprotective transcriptional responses in the periphery. Several subcellular compartments possess a homotypic signal whereby the respective compartment relies on a single signaling mechanism to convey information within the affected cell to the same stress-responsive pathway in peripheral tissues. In contrast, we find that the heat shock transcription factor, HSF-1, specifies its mode of transcellular protection via two distinct signaling pathways. Upon thermal stress, neural HSF-1 primes peripheral tissues through the thermosensory neural circuit to mount a heat shock response. Independent of this thermosensory circuit, neural HSF-1 activates the FOXO transcription factor, DAF-16, in the periphery and prolongs lifespan. Thus a single transcription factor can coordinate different stress response pathways to specify its mode of protection against changing environmental conditions.

Drought, agricultural adaptation, and sociopolitical collapse in the Maya Lowlands.

Paleoclimate records indicate a series of severe droughts was associated with societal collapse of the Classic Maya during the Terminal Classic period (∼800-950 C.E.). Evidence for drought largely derives from the drier, less populated northern Maya Lowlands but does not explain more pronounced and earlier societal disruption in the relatively humid southern Maya Lowlands. Here we apply hydrogen and carbon isotope compositions of plant wax lipids in two lake sediment cores to assess changes in water availability and land use in both the northern and southern Maya lowlands. We show that relatively more intense drying occurred in the southern lowlands than in the northern lowlands during the Terminal Classic period, consistent with earlier and more persistent societal decline in the south. Our results also indicate a period of substantial drying in the southern Maya Lowlands from ∼200 C.E. to 500 C.E., during the Terminal Preclassic and Early Classic periods. Plant wax carbon isotope records indicate a decline in C4 plants in both lake catchments during the Early Classic period, interpreted to reflect a shift from extensive agriculture to intensive, water-conservative maize cultivation that was motivated by a drying climate. Our results imply that agricultural adaptations developed in response to earlier droughts were initially successful, but failed under the more severe droughts of the Terminal Classic period.