Feed-forward Cycle Research Articles

CNSC-13. CROSSTALK BETWEEN SENSORY NEURONAL ACTIVITY AND TUMOR CELLS PROMOTES MALIGNANCY AND CANCER PAIN

Abstract BACKGROUND Nerve infiltration of solid tumors is associated with poor prognosis in multiple cancer types. Understanding the role of neuronal activity in cancer progression offers innovative approaches for treating malignancies and cancer-associated neurological issues such as pain. Pain perception is mediated by the activity of peripheral sensory neurons. Many cancer types induce pain, and sensory innervation could support tumor growth, raising the interesting hypothesis that cancer pain-associated neuronal activity promotes malignancies. Our study aims to test the hypothesis using malignant peripheral nerve sheath tumor (MPNST) as the experimental platform. METHODS in vivo allograft models were established by implanting mouse MPNST cells into the sciatic nerves of male and female mice, followed by performing pain behavior assays (von Frey, Hargreaves, and conditioned place preference tests) and tumor growth measurements. Primary mouse dorsal root ganglion (DRG) sensory neuron cultures were prepared for calcium imaging and neuron-tumor co-culture experiments. RESULTS MPNST tumor-bearing mice exhibited hypersensitivity to noxious and non-noxious stimuli (evoked pain) and ongoing pain, compared to the sham controls. MPNST-conditioned media increased intracellular calcium concentration and ATF3 (indicator for nerve injury/stress) expression in primary sensory neuron culture, suggesting that MPNST tumor cell secretory factors may induce pain by triggering sensory neuron injury/stress responses that increase sensory neuron activity/sensitivity. Reciprocally, we found that stimulation of sensory neuron activity accelerates MPNST tumor growth. The conditioned media from stimulated sensory neurons increased tumor proliferation (EdU assay) in vitro, suggesting that sensory neuron activity-induced paracrine factors increase MPNST cell growth. CONCLUSIONS MPNST is a devastating cancer that grows within peripheral nerves which induce intractable pain. Our findings demonstrate a feedforward cycle where the cancer cells induce sensory neuron hypersensitivity/hyperactivity (pain) which in turn further accelerates tumor growth. Future studies will identify the molecular mechanisms underlying this crosstalk between MPNST and sensory neuron activity.

Cellular Senescence and Extracellular Vesicles in the Pathogenesis and Treatment of Obesity-A Narrative Review.

This narrative review explores the pathophysiology of obesity, cellular senescence, and exosome release. When exposed to excessive nutrients, adipocytes develop mitochondrial dysfunction and generate reactive oxygen species with DNA damage. This triggers adipocyte hypertrophy and hypoxia, inhibition of adiponectin secretion and adipogenesis, increased endoplasmic reticulum stress and maladaptive unfolded protein response, metaflammation, and polarization of macrophages. Such feed-forward cycles are not resolved by antioxidant systems, heat shock response pathways, or DNA repair mechanisms, resulting in transmissible cellular senescence via autocrine, paracrine, and endocrine signaling. Senescence can thus affect preadipocytes, mature adipocytes, tissue macrophages and lymphocytes, hepatocytes, vascular endothelium, pancreatic β cells, myocytes, hypothalamic nuclei, and renal podocytes. The senescence-associated secretory phenotype is closely related to visceral adipose tissue expansion and metaflammation; inhibition of SIRT-1, adiponectin, and autophagy; and increased release of exosomes, exosomal micro-RNAs, pro-inflammatory adipokines, and saturated free fatty acids. The resulting hypernefemia, insulin resistance, and diminished fatty acid β-oxidation lead to lipotoxicity and progressive obesity, metabolic syndrome, and physical and cognitive functional decline. Weight cycling is related to continuing immunosenescence and exposure to palmitate. Cellular senescence, exosome release, and the transmissible senescence-associated secretory phenotype contribute to obesity and metabolic syndrome. Targeted therapies have interrelated and synergistic effects on cellular senescence, obesity, and premature aging.

P-303 Calcitonin Gene-Related Protein as a key driver of myometrial fibrogenesis in adenomyosis pathology

Abstract Study question Does CGRP play a role in the fibrosis of adenomyosis lesions? Summary answer CGRP converts fibroblasts to myofibroblasts in adenomyosis lesions via the RAMP1 receptor and participates in the inflammatory activation processes. What is known already Adenomyosis is a prevalent and challenging disease in gynecology. It is characterized by the invasion of endometrial glands and mesenchyme into the myometrium, resulting in the development of limited or diffuse lesions. These lesions interact with in situ fibroblasts and recruit immune cells, leading to a chronic and persistent inflammatory microenvironment, which ultimately contributes to myometrial fibrosis. One of the typical clinical symptoms of adenomyosis is secondary progressive dysmenorrhea. Accumulated research suggests that sensory nerves, which are implicated in dysmenorrhea, and neuropeptides such as CGRP play a role in the development of ectopic lesions, thus establishing a feed-forward cycle. Study design, size, duration This study employed a laboratory-based experimental design. The in vitro experiment included a total of 67 clinical samples and the in vivo part included 57 ICR mice as subjects, conducted over 20 weeks, with data collection taking place between August 2023 and December 2023. Participants/materials, setting, methods Myometrium samples were collected from 37 women with adenomyosis, while control samples were obtained from 30 women without adenomyosis. Among them, the tissues from three adenomyosis patients and three control patients were subjected to scRNA-seq, and the other 61 samples were for validation. A mouse model of adenomyosis was established by administering tamoxifen. The mice were divided into three groups: a control group, a model group, and a treatment group that received Rimegepant via gavage. Main results and the role of chance In adenomyosis tissue, an enrichment of sensory nerve fibers, elevated expression of nerve-related proteins（NGF, PGP9.5）, and increased CGRP expression and its receptor RAMP1 were observed. Furthermore, the qRT-PCR results demonstrated that the adenomyosis lesions were in a chronic inflammatory state which is consistent with the scRNA-seq result. Moreover, the scRNA-seq data suggested a high expression of the CGRP receptor (RAMP1) on fibroblasts, which plays a critical role in causing fibrosis in adenomyosis. Additionally, it was found that CGRP prompted the transition of fibroblasts to myofibroblasts (FMT), and the activated fibroblasts, in turn, attracted macrophages and stimulated their shift towards an M1 phenotype. These significant findings were further confirmed through experimental animal studies. The fertility outcome indicated a positive trend, with the Rimegepant group showing an increased embryo implantation rate. Limitations, reasons for caution In the present experiment, while we have confirmed the involvement of CGRP in the fibrogenesis of adenomyosis, further investigation is needed to understand the specific biological processes occurring in fibroblasts following CGRP administration. Wider implications of the findings Limited research has been conducted on the association between adenomyosis and sensory nerves. This study adds the existing evidence by demonstrating the crucial role of sensory nerves and CGRP in promoting fibrosis. The findings of this study offer new perspectives on the treatment and understanding of the pathogenesis of adenomyosis. Trial registration number not applicable

Amyloid β accelerates age-related proteome-wide protein insolubility

Loss of proteostasis is a highly conserved feature of aging across model organisms and results in the accumulation of insoluble protein aggregates. Protein insolubility is also a unifying feature of major age-related neurodegenerative diseases, including Alzheimer's Disease (AD), in which hundreds of insoluble proteins associate with aggregated amyloid beta (Aβ) in senile plaques. Despite the connection between aging and AD risk, therapeutic approaches to date have overlooked aging-driven generalized protein insolubility as a contributing factor. However, proteins that become insoluble during aging in model organisms are capable of accelerating Aβ aggregation in vitro and lifespan in vivo. Here, using an unbiased proteomics approach, we questioned the relationship between Aβ and age-related protein insolubility. Specifically, we uncovered that Aβ expression drives proteome-wide protein insolubility in C. elegans, even in young animals, and this insoluble proteome is highly similar to the insoluble proteome driven by normal aging, this vulnerable sub-proteome we term the core insoluble proteome (CIP). We show that the CIP is enriched with proteins that modify Aβ toxicity in vivo, suggesting the possibility of a vicious feedforward cycle in the context of AD. Importantly, using human genome-wide association studies (GWAS), we show that the CIP is replete with biological processes implicated not only in neurodegenerative diseases but also across a broad array of chronic, age-related diseases (CARDs). This provides suggestive evidence that age-related loss of proteostasis could play a role in general CARD risk. Finally, we show that the geroprotective, gut-derived metabolite, Urolithin A, relieves Aβ toxicity, supporting its use in clinical trials for dementia and age-related diseases.

Abstract 124: IRG1-Itaconate Axis Protects From Cholesterol-Induced Inflammation And Atherosclerosis

Atherosclerosis, the major underlying cause of cardiovascular disease (CVD) mortality, is fueled by a failure to resolve lipid-driven inflammation within the vessel wall. Understanding the immunometabolic mechanisms underpinning sustained inflammation within this microenvironment is needed for the development of novel targeted therapies. Immune responsive gene 1 (IRG) is an enzyme that diverts the TCA cycle intermediate, cis-aconitate, to produce itaconate, a metabolite with anti-microbial and anti-inflammatory functions. We used a translational approach to investigate the therapeutic potential of the Irg1-itaconate axis for human atherosclerosis. Using single cell RNA-sequencing, we found that IRG1 is upregulated in human coronary atherosclerotic lesions compared to patient-matched healthy vasculature, and is primarily expressed by plaque monocytes and macrophages. In mouse models of atherosclerosis, Irg1 was expressed by plaque monocytes, macrophage and neutrophils, but declined with disease progression. Global or hematopoietic Irg1 -deficiency increased atherosclerosis burden, plaque lipid content, and expression of interleukin (IL)-1b. Mechanistically, absence of Irg1 potentiates lipid accumulation and lipid-mediated inflammation via a feed-forward cycle involving increased neutrophil extracellular trap (NET) formation, NET-induced NLRP3 inflammasome priming in macrophages, and subsequent IL-1b release. Conversely, supplementation of the Irg1 pathway using the derivative 4-octyl itaconate (4-OI) reduced atherosclerotic inflammation and promoted beneficial plaque remodeling in mice. To assess the therapeutic potential of 4-OI in humans, we leveraged a validated systems-immunology approach to investigate CVD-related inflammation ex vivo . Using high dimensional single cell analyses, we showed that 4-OI supplementation attenuated pro-inflammatory phospho-signaling in human peripheral blood mononuclear cells treated with plasma from CVD patients, and caused an anti-inflammatory rewiring of macrophage populations. Our data highlight the relevance of pursuing Irg1 -itaconate axis supplementation as a therapeutic approach to treat atherosclerosis in humans.

Bronchoconstriction damages airway epithelia by crowding-induced excess cell extrusion.

Asthma is deemed an inflammatory disease, yet the defining diagnostic feature is mechanical bronchoconstriction. We previously discovered a conserved process called cell extrusion that drives homeostatic epithelial cell death when cells become too crowded. In this work, we show that the pathological crowding of a bronchoconstrictive attack causes so much epithelial cell extrusion that it damages the airways, resulting in inflammation and mucus secretion in both mice and humans. Although relaxing the airways with the rescue treatment albuterol did not affect these responses, inhibiting live cell extrusion signaling during bronchoconstriction prevented all these features. Our findings show that bronchoconstriction causes epithelial damage and inflammation by excess crowding-induced cell extrusion and suggest that blocking epithelial extrusion, instead of the ensuing downstream inflammation, could prevent the feed-forward asthma inflammatory cycle.

SKA2 regulated hyperactive secretory autophagy drives neuroinflammation-induced neurodegeneration

High levels of proinflammatory cytokines induce neurotoxicity and catalyze inflammation-driven neurodegeneration, but the specific release mechanisms from microglia remain elusive. Here we show that secretory autophagy (SA), a non-lytic modality of autophagy for secretion of vesicular cargo, regulates neuroinflammation-mediated neurodegeneration via SKA2 and FKBP5 signaling. SKA2 inhibits SA-dependent IL-1β release by counteracting FKBP5 function. Hippocampal Ska2 knockdown in male mice hyperactivates SA resulting in neuroinflammation, subsequent neurodegeneration and complete hippocampal atrophy within six weeks. The hyperactivation of SA increases IL-1β release, contributing to an inflammatory feed-forward vicious cycle including NLRP3-inflammasome activation and Gasdermin D-mediated neurotoxicity, which ultimately drives neurodegeneration. Results from protein expression and co-immunoprecipitation analyses of male and female postmortem human brains demonstrate that SA is hyperactivated in Alzheimer’s disease. Overall, our findings suggest that SKA2-regulated, hyperactive SA facilitates neuroinflammation and is linked to Alzheimer’s disease, providing mechanistic insight into the biology of neuroinflammation.

An antioxidant feedforward cycle coordinated by linker histone variant H1.2 and NRF2 that drives nonsmall cell lung cancer progression

Nonsmall cell lung cancer (NSCLC) is highly malignant with limited treatment options, platinum-based chemotherapy is a standard treatment for NSCLC with resistance commonly seen. NSCLC cells exploit enhanced antioxidant defense system to counteract excessive reactive oxygen species (ROS), which contributes largely to tumor progression and resistance to chemotherapy, yet the mechanisms are not fully understood. Recent studies have suggested the involvement of histones in tumor progression and cellular antioxidant response; however, whether a major histone variant H1.2 (H1C) plays roles in the development of NSCLC remains unclear. Herein, we demonstrated that H1.2 was increasingly expressed in NSCLC tumors, and its expression was correlated with worse survival. When crossing the H1c knockout allele with a mouse NSCLC model (KrasLSL-G12D/+), H1.2 deletion suppressed NSCLC progression and enhanced oxidative stress and significantly decreased the levels of key antioxidant glutathione (GSH) and GCLC, the catalytic subunit of rate-limiting enzyme for GSH synthesis. Moreover, high H1.2 was correlated with the IC50 of multiple chemotherapeutic drugs and with worse prognosis in NSCLC patients receiving chemotherapy; H1.2-deficient NSCLC cells presented reduced survival and increased ROS levels upon cisplatin treatment, while ROS scavenger eliminated the survival inhibition. Mechanistically, H1.2 interacted with NRF2, a master regulator of antioxidative response; H1.2 enhanced the nuclear level and stability of NRF2 and, thus, promoted NRF2 binding to GCLC promoter and the consequent transcription; while NRF2 also transcriptionally up-regulated H1.2. Collectively, these results uncovered a tumor-driving role of H1.2 in NSCLC and indicate an "H1.2-NRF2" antioxidant feedforward cycle that promotes tumor progression and chemoresistance.

Calcium Dyshomeostasis Drives Pathophysiology and Neuronal Demise in Age-Related Neurodegenerative Diseases.

This review postulates that age-related neurodegeneration entails inappropriate activation of intrinsic pathways to enable brain plasticity through deregulated calcium (Ca2+) signalling. Ca2+ in the cytosol comprises a versatile signal controlling neuronal cell physiology to accommodate adaptive structural and functional changes of neuronal networks (neuronal plasticity) and, as such, is essential for brain function. Although disease risk factors selectively affect different neuronal cell types across age-related neurodegenerative diseases (NDDs), these appear to have in common the ability to impair the specificity of the Ca2+ signal. As a result, non-specific Ca2+ signalling facilitates the development of intraneuronal pathophysiology shared by age-related NDDs, including mitochondrial dysfunction, elevated reactive oxygen species (ROS) levels, impaired proteostasis, and decreased axonal transport, leading to even more Ca2+ dyshomeostasis. These core pathophysiological processes and elevated cytosolic Ca2+ levels comprise a self-enforcing feedforward cycle inevitably spiralling toward high levels of cytosolic Ca2+. The resultant elevated cytosolic Ca2+ levels ultimately gear otherwise physiological effector pathways underlying plasticity toward neuronal demise. Ageing impacts mitochondrial function indiscriminately of the neuronal cell type and, therefore, contributes to the feedforward cycle of pathophysiology development seen in all age-related NDDs. From this perspective, therapeutic interventions to safely restore Ca2+ homeostasis would mitigate the excessive activation of neuronal destruction pathways and, therefore, are expected to have promising neuroprotective potential.

Structural snapshots along K48-linked ubiquitin chain formation by the HECT E3 UBR5.

Ubiquitin (Ub) chain formation by homologous to E6AP C-terminus (HECT)-family E3 ligases regulates vast biology, yet the structural mechanisms remain unknown. We used chemistry and cryo-electron microscopy (cryo-EM) to visualize stable mimics of the intermediates along K48-linked Ub chain formation by the human E3, UBR5. The structural data reveal a ≈ 620 kDa UBR5 dimer as the functional unit, comprising a scaffold with flexibly tethered Ub-associated (UBA) domains, and elaborately arranged HECT domains. Chains are forged by a UBA domain capturing an acceptor Ub, with its K48 lured into the active site by numerous interactions between the acceptor Ub, manifold UBR5 elements and the donor Ub. The cryo-EM reconstructions allow defining conserved HECT domain conformations catalyzing Ub transfer from E2 to E3 and from E3. Our data show how a full-length E3, ubiquitins to be adjoined, E2 and intermediary products guide a feed-forward HECT domain conformational cycle establishing a highly efficient, broadly targeting, K48-linked Ub chain forging machine.

0085 Peripheral glucose metabolism bidirectionally modulates sleep in a model of Alzheimer's disease

Abstract Introduction Metabolic impairments and sleep disruptions are both recognized as modifiable risk factors in the development of Alzheimer’s disease (AD). A bidirectional relationship exists between sleep and AD where pathology can disrupt sleep, but sleep disturbances can also increase AD-related pathology. This results in a feed-forward cycle of disease progression and further sleep impairments. Sleep fragmentation and poor sleep quality can also cause glucose intolerance and insulin resistance. However, it remains unclear if peripheral metabolic dysfunction alone can impair sleep, particularly in the context of AD-related pathology. Therefore, the goal of this study was to establish mechanisms connecting peripheral metabolic and sleep disruptions and identify potential therapeutic targets for mitigating AD risk. Methods We implanted biosensors measuring interstitial fluid (ISF) levels of glucose and lactate, biomarkers of cerebral metabolism and neuronal activity, respectively, directly into the hippocampus of wildtype and APP/PS1 mice, a model of amyloid-beta (Aβ) overexpression. Biosensors were paired with cortical EEG and EMG recordings for simultaneous sleep/wake analysis. To understand the relationship between metabolic dysfunction and sleep, we altered the peripheral metabolic environment using two paradigms: an acute high-fat, high-sugar diet (HF/HSD) and a pharmacological metabolic rescue. Results We found short-term HF/HSD exposure was sufficient to disrupt ISF glucose and lactate diurnal rhythms, independent of changes to pathology burden. Moreover, we found significant sleep disruptions, particularly decreased delta power, indicating slow wave sleep impairments. These findings were exacerbated in mice with Aβ pathology who have disrupted metabolic and sleep functioning at baseline. Conversely, we found normalizing peripheral glucose tolerance in mice with Aβ pathology was sufficient to rescue impaired ISF glucose and lactate rhythms. We also saw a restoration of normal sleep-wake patterns, specifically within slow wave activity. Conclusion We found modulating peripheral glucose metabolism can bidirectionally alter sleep, particularly slow wave sleep, independent of changes in Aβ burden. This indicates sleep as a mediator in the relationship between metabolic impairments and AD pathophysiology. While impaired sleep increases AD risk, improved sleep slows pathology accumulation. Therefore, this study demonstrates targeting peripheral glucose regulation is a potential avenue for early AD intervention and risk mitigation. Support (if any) F31-AG066302, R01-AG068330, P30-AG072947

Mitochondrial dysfunction, iron accumulation, and ferroptosis in Parkinson’s disease

Iron accumulation and ferroptosis have long been implicated in the pathogenesis and neuronal loss of Parkinson’s disease. With the growing discovery of genes associated with Parkinson’s disease and mitochondrial function, there is emerging evidence of the convergent role of mitochondrial dysfunction, subsequent reactive oxygen species generation and ensuing iron accumulation working in concert to facilitate neuronal loss and injury in Parkinson’s disease. This subsequently leads to a vicious cycle where mitochondrial dysfunction may stimulate iron accumulation and inflammation as part of a synergistic feed-forward cycle resulting in neuronal death after the antioxidant cellular defense systems are overwhelmed. We reviewed the existing literature on mitochondrial and iron homeostasis and described the potential intersections of the disease mechanisms leading to iron accumulation, ferroptosis and dopaminergic cell death, ultimately culminating in the onset and progression of Parkinson’s disease.

Cytosolic calcium: Judge, jury and executioner of neurodegeneration in Alzheimer's disease and beyond.

This review discusses the driving principles that may underlie neurodegeneration in dementia, represented most dominantly by Alzheimer's disease (AD). While a myriad of different disease risk factors contribute to AD, these ultimately converge to a common disease outcome. Based on decades of research, a picture emerges where upstream risk factors combine in a feedforward pathophysiological cycle, culminating in a rise of cytosolic calcium concentration ([Ca2+ ]c ) that triggers neurodegeneration. In this framework, positive AD risk factors entail conditions, characteristics, or lifestyles that initiate or accelerate self-reinforcing cycles of pathophysiology, whereas negative risk factors or therapeutic interventions, particularly those mitigating elevated [Ca2+ ]c , oppose these effects and therefore have neuroprotective potential.

Abstract 3208: Bone-derived TGF-ß release is associated with cardiac dysfunction due to oxidation of SR calcium gatekeepers, Ca2+ leak and mitochondrial dysfunction

Abstract Cancer patients with bone metastases are associated with cardiac dysfunction. Heart attack was observed in 3.8% of patients within 30 days of diagnosis. Here, we report that bone turnover marker β-CTX (P=0.002) and platelet-poor plasma TGF-ß (P=0.036) from patients with bone metastasis were significantly higher than those without bone metastasis. In patients, serum β-CTX concentration was positively correlated with TGF-ß (R2=0.67, P<0.0001). Excess TGF-ß release caused skeletal muscle weakness by oxidation of the sarcoplasmic reticulum (SR) Ca2+ ryanodine receptor (RyR), induction of SR and oxidative stress in breast cancer patients with bone metastasis. Thus, we hypothesized that the systemic effects of TGF-ß could have similar effects on cardiac muscle to induce heart failure. Mechanistically, we showed that TGF-β1 increased transcription of NADPH oxidases, aberrant Ca2+ signaling, SR stress and ROS production in adult cardiomyocytes. We tested this in a transgenic mouse model of Camurati-Engelmann Disease (CED) in which mutant TGF-ß1 (H222D) is overexpressed in osteoblasts and causes accelerated bone destruction. We found that CED mice had increased cardiac size, dilated left ventricle and reduced ejection fraction, by echocardiography, compared to littermate controls. This was associated with increased phosphorylation of Smad2/3, myocardial necrosis and fibrosis in cardiac tissues. Similarly, SR Ca2+ channel RyR2 and SERCA2 showed a significant increase in oxidation and nitrosylation and reduced binding of the stabilizing subunits as well as upregulated iNOS and NADPH oxidases consistent with depressed SR Ca2+ re-uptake, RyR-mediated Ca2+ leak and oxidative stress in CED mice left ventricular. Mitochondria isolated from ventricular samples showed increased mitochondrial Ca2+ overload, ROS production, release of apoptotic proteins, reduced mitochondrial DNA and ATP reproduction in CED mice. Thus, a feed-forward cycle of pathological Ca2+ handling is created between SR mitochondria, which underlies TGF-ß-driven cardiac muscle dysfunction. These findings are consistent with mitochondrial calcium toxicity induced by SR Ca2+ re-uptake and leak, and heart failure with reduced ATP production. The data suggest that excess TGF-ß release by pathological bone destruction could have significant impact on cardiac muscle to induce oxidative stress, SR Ca2+ leak and heart failure and could explain heart disease observed clinically with bone metastasis. Targeting this pathway may improve survival in patients with bone metastases. Citation Format: Lei Shi, Truc Kuo, Jade Martinez, Sukanya Suresh, Trupti Trivedi, Gabriel M. Pagnotti, Leah D. Guerra, Xu Cao, Theresa A. Guise. Bone-derived TGF-ß release is associated with cardiac dysfunction due to oxidation of SR calcium gatekeepers, Ca2+ leak and mitochondrial dysfunction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3208.

Neuroinflammation with increased glymphatic flow in a murine model of decompression sickness.

This project investigated glial-based lymphatic (glymphatic) function and its role in a murine model of decompression sickness (DCS). DCS pathophysiology is traditionally viewed as being related to gas bubble formation from insoluble gas on decompression. However, a body of work implicates a role for a subset of inflammatory extracellular vesicles, 0.1 to 1 µm microparticles (MPs) that are elevated in human and rodent models in response to high gas pressure and rise further after decompression. Herein, we describe immunohistochemical and Western blot evidence showing that following high air pressure exposure, there are elevations of astrocyte NF-κB and microglial-ionized calcium-binding adaptor protein-1 (IBA-1) along with fluorescence contrast and MRI findings of an increase in glymphatic flow. Concomitant elevations of central nervous system-derived MPs coexpressing thrombospondin-1 (TSP) drain to deep cervical nodes and then to blood where they cause neutrophil activation. A new set of blood-borne MPs are generated that express filamentous actin at the surface that exacerbate neutrophil activation. Blood-brain barrier integrity is disrupted due to activated neutrophil sequestration that causes further astrocyte and microglial perturbation. When postdecompression node or blood MPs are injected into naïve mice, the same spectrum of abnormalities occur and they are blocked with coadministration of antibody to TSP. We conclude that high pressure/decompression causes neuroinflammation with an increased glymphatic flow. The resulting systemic liberation of TSP-expressing MPs sustains the neuroinflammatory cycle lasting for days.NEW & NOTEWORTHY A murine model of central nervous system (CNS) decompression sickness demonstrates that high gas pressure activates astrocytes and microglia triggering inflammatory microparticle (MP) production. Thrombospondin-expressing MPs are released from the CNS via enhanced glymphatic flow to the systemic circulation where they activate neutrophils. Secondary production of neutrophil-derived MPs causes further cell activation and neutrophil adherence to the brain microvasculature establishing a feed-forward neuroinflammatory cycle.

Impaired Awareness of Hypoglycemia in Type 1 Diabetes: A Report of An NIDDK Workshop in October 2021.

Hypoglycemia remains a limiting factor in the optimal treatment of type 1 diabetes. Repeated episodes of hypoglycemia result in impaired awareness of subsequent hypoglycemic events, inducing a vicious feed-forward cycle and increasing the risk of morbidity and mortality. Why this occurs and how to manage the problem in clinical practice remain uncertain. To address the obstacles and barriers that have hindered progress in this clinically important area, the National Institute of Diabetes and Digestive and Kidney Diseases convened a workshop on 14-15 October 2021. This perspective offers a summary of this outstanding meeting, which brought clinical and basic scientists from the fields of diabetes, neuroscience, psychology, psychiatry, and imaging together, on how to best advance the field of impaired awareness of hypoglycemia and hypoglycemia in general in patients with diabetes.

The APP intracellular domain promotes LRRK2 expression to enable feed-forward neurodegenerative mechanisms in Parkinson's disease.

Gain-of-function mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are common in familial forms of Parkinson's disease (PD), which is characterized by progressive neurodegeneration that impairs motor and cognitive function. We previously demonstrated that LRRK2-mediated phosphorylation of β-amyloid precursor protein (APP) triggers the production and nuclear translocation of the APP intracellular domain (AICD). Here, we connected LRRK2 to AICD in a feed-forward cycle that enhanced LRRK2-mediated neurotoxicity. In cooperation with the transcription factor FOXO3a, AICD promoted LRRK2 expression, thus increasing the abundance of LRRK2 that promotes AICD activation. APP deficiency in LRRK2G2019S mice suppressed LRRK2 expression, LRRK2-mediated mitochondrial dysfunction, α-synuclein accumulation, and tyrosine hydroxylase (TH) loss in the brain, phenotypes associated with toxicity and loss of dopaminergic neurons in PD. Conversely, AICD overexpression increased LRRK2 expression and LRRK2-mediated neurotoxicity in LRRK2G2019S mice. In LRRK2G2019S mice or cultured dopaminergic neurons from LRRK2G2019S patients, treatment with itanapraced reduced LRRK2 expression and was neuroprotective. Itanapraced showed similar effects in a neurotoxin-induced PD mouse model, suggesting that inhibiting the AICD may also have therapeutic benefits in idiopathic PD. Our findings reveal a therapeutically targetable, feed-forward mechanism through which AICD promotes LRRK2-mediated neurotoxicity in PD.

Dysregulated lipolysis and lipophagy in lipid droplets of macrophages from high fat diet-fed obese mice.

Obesity is associated with lipid droplet (LD) accumulation, dysregulated lipolysis and chronic inflammation. Previously, the caspase recruitment domain‐containing protein 9 (CARD9) has been identified as a potential contributor to obesity‐associated abnormalities including cardiac dysfunction. In the current study, we explored a positive feedback signalling cycle of dysregulated lipolysis, CARD9‐associated inflammation, impaired lipophagy and excessive LD accumulation in sustaining the chronic inflammation associated with obesity. C57BL/6 WT and CARD9−/− mice were fed with normal diet (ND, 12% fat) or a high fat diet (HFD, 45% fat) for 5 months. Staining of LDs from peritoneal macrophages (PMs) revealed a significant increase in the number of cells with LD and the number of LD per cell in the HFD‐fed WT but not CARD9−/− obese mice. Rather, CARD9 KO significantly increased the mean LD size. WT obese mice showed down regulation of lipolytic proteins with increased diacylglycerol (DAG) content, and CARD9 KO normalized DAG with restored lipolytic protein expression. The build‐up of DAG in the WT obese mice is further associated with activation of PKCδ, NF‐κB and p38 MAPK inflammatory signalling in a CARDD9‐dependent manner. Inhibition of adipose triglyceride lipase (ATGL) by Atglistatin (Atg) resulted in similar effects as in CARD9−/− mice. Interestingly, CARD9 KO and Atg treatment enhanced lipophagy. In conclusion, HFD feeding likely initiated a positive feedback signalling loop from dysregulated lipolysis, CARD9‐dependent inflammation, impaired lipophagy, to excessive LD accumulation and sustained inflammation. CARD9 KO and Atg treatment protected against the chronic inflammation by interrupting this feedforward cycle.

When a trophic process turns toxic: Alzheimer's disease as an aberrant recapitulation of a developmental mechanism.

Here we review the idea that Alzheimer's disease (AD) results from aberrant activation of a normal developmental mechanism. This process operates in primarily vulnerable, subcortical nuclei with a distinguishing embryological provenance: the basal rather than the alar plate. All cells are dependent for growth on calcium influx yet these neurons retain a sensitivity to trophic factors into maturity. However, as the brain matures this action becomes detrimental such that the trophic process could turn toxic if triggered in adult brain, in retaliation to an initial insult. The signalling molecule driving this trophic-toxic mechanism is a 14mer peptide (T14) that acts on the alpha-7 receptor to enhance calcium entry, inducing excitotoxicity and proliferation of the receptor, perpetuating a feedforward cycle of neurodegeneration including production of beta-amyloid and p-tau. The T14 system has been previously unrecognised as a basic biological process, yet its pharmaceutical manipulation could have valuable clinical applications.

Alexithymia and its Link to Autism

Alexithymia is common, rather than universal, with notably high rates of overlap with autism spectrum disorder (ASD). Co-occurring autism and alexithymia represent a specific subgroup in the ASD population who may have specific clinical needs. There is evidence of its overlap with ASD in terms of prevalence, etiology, and behaviors. Emerging evidence has found that alexithymia may also play a role as both cause and consequence of ASD in a feedforward cycle between alexithymia and ASD symptomatology. Over the last two decades the association between alexithymia and autism spectrum disorder ASD has attracted significant attention – there has been a surge in the number of studies aimed at investigating the relationship between these conditions, including from a theoretical and etiological point of view, as well as for clinical and therapeutic practices. The ongoing studies and research aiming to understand how autism affects face perception need also to consider the contribution of alexithymia. Here we review the description of Alexithymia and its relationship to ASD. Our first aim is to provide a brief definition then focus on the relationship between ASD and alexithymia, including clarifying when and how they originate, as well as their overlap in terms of etiology and features, and suggest clinically useful constructs and interventions. Key words: Autism, ASD, Alexithymia, Emotions