Fiona Kerr

As a gatekeeper of antioxidant and anti-inflammatory cell protection, the transcription factor Nrf2 is a promising therapeutic target for several neurodegenerative diseases, leading to the development of Nrf2 activators targeting Keap1-dependent and independent regulatory mechanisms. Astrocytes play a crucial role in regulating neuronal physiology in health and disease, including Nrf2 neuroprotective responses. As neurons require specific conditions for their differentiation and maintenance, most 2D and 3D co-culture systems use medias that are compatible with neuronal differentiation and function, but also ensure astrocyte survival. Few studies, however, assess the molecular adaptations of astrocytes to changes from astrocyte maintenance medias alone, and their subsequent effects on neurons which may represent technical rather than physiological responses. Our findings show that while Nrf2 can be effectively activated by the Keap1-Nrf2 protein-protein interaction disruptor 18e, and classical Nrf2 activators dimethylfumarate and CDDO-Me, in human primary cortical astrocyte monocultures, their efficacy is lost in LUHMES neuron-astrocyte co-cultures. Further investigation revealed that the Advanced DMEM/F12-based LUHMES differentiation media maximally induced basal Nrf2 activity in astrocytes alone, compared to astrocyte maintenance media, thus preventing pharmacological activation. Although Neurobasal slightly activated basal Nrf2, this was not significant and did not prevent further activation by dimethylfumarate, suggesting that this media has less impact on astrocytic Nrf2 activity relative to Advanced DMEM/F12. As Nrf2 is a key regulator of oxidative damage and neuroinflammation, modelling these common features of neurodegenerative diseases may be confounded by environments that maximally activate basal Nrf2. Our findings thus suggest caution in media selection for neuron-astrocyte co-culture in disease modelling and therapeutic Nrf2 activator discovery, and suggest use of Neurobasal over Advanced DMEM/F12 medias for this purpose.

Molecular landscapes associated with aging and specific neurodegenerative diseases, such as Parkinson's disease (PD).Together, these studies enhance our understanding of the molecular mechanisms underlying age-related pathologies and neurodegeneration, laying the groundwork for future studies to determine their therapeutic potential for both prevention and treatment of neurodegenerative conditions. Mechmet et al. explore age-related olfactory decline in microphthalmia-associated transcription factor (Mitf) mutant mice. MITF is a basic helix-loop-helix leucine zipper transcription factor that regulates immune function and neuronal homeostasis through transcriptional control of genes involved in lysosomal biogenesis and autophagy -central processes in microglia -and macrophage-driven inflammatory responses. While olfactory decline is a well-known marker of aging and an early sign of neurodegenerative disorders, this study examines whether Mitf deficiency leads to neurodegeneration and olfactory dysfunction with age. Interestingly, aging Mitf mutant mice exhibit olfactory decline compared to wild-type controls without evidence of neurodegeneration or major morphological or inflammatory changes in the olfactory bulb. Moreover, the researchers identified compensatory mechanisms, such as the upregulation of potassium channel subunits, as potential buffers against hyperexcitability, a precursor of neurodegeneration. These findings raise important questions about MITF's role in neuronal stability across sensory systems during aging. The Lobon et al. explore the emerging hypothesis that somatic mutations contribute to sporadic cases of PD. By employing whole exome sequencing and developing a Combined Or Single sample MOSaicism (COSMOS) detection approach to computationally identify somatic mutations from bulk sequencing data, their study identified somatic single nucleotide variants (sSNVs) across four brain regions and blood samples from ten PD patients. sSNVs were enriched in genes related to synaptic and neuronal functions, such as GRIP1 and KCNK2, ubiquitination, including UBE2U, and glucose transport, DENND4A, all of which have been linked to several neurodegenerative diseases, including PD and Alzheimer's disease. These findings suggest that many sSNVs may have a developmental origin, contributing to brain mosaicism and potentially influencing PD pathology, and underscore the relevance of somatic mutations in the molecular landscape of sporadic PD. While the correlation between deleterious sSNVs and clinical manifestations remains an area for future exploration, these findings provide a robust framework for further investigations into the molecular underpinnings of PD.Coenen et al. compile a plasma proteome of aging using bioinformatic approaches to integrate four large-scale human plasma SOMAscan proteomic datasets from individuals aged 16 to 95 years. They identified changes in levels of 273 proteins associated with aging across these cohorts, with 56 forming an interconnected protein-protein interaction subnetwork enriched in diverse functions, including growth factor binding, metabolic disease and TNF receptor activation. Creating proteomic clocks, they found that 15 of these aging-associated proteins were sufficient to accurately predict an individual's biological age. Clustering aging proteins that follow a similar expression trajectory revealed that enrichment of these proteins aligned with aging-dependent alterations in specific biological functions including extracellular matrix, insulin-like growth factor and coagulation signalling cascades, as well as regulation of neurodevelopment and GABA receptor binding -processes relevant to nervous system function. Compared to the rest of the plasma proteome, aging-associated proteins were more frequently linked to diseases, such as heart failure, pneumonia, kidney disease, and dementia. GDF15 and TNFRSF1A/1B were associated with the highest number of diseases, while the top 10 proteins shared links to 32 conditions, suggesting that aging proteins may serve as broad biomarkers of multiple diseases. Overall, this study identified a plasma proteome signature that associates with aging across independent cohorts, correlates with disease presence, and pinpoints a subset of proteins capable of accurately predicting biological age.Taken together, these studies exemplify the broad range of research approaches required to understand how aging predisposes the nervous system to some of the most costly and devastating diseases in modern medicine. Spanning powerhouse genetic studies in invertebrate models, meticulous characterisation of mouse models, and bioinformatic studies of both focused and broad human cohorts, these findings open new avenues for future investigation, with the ultimate goal of developing treatments to preserve brain health and reduce disease burden during ageing.

As a gatekeeper of anti-oxidant and anti-inflammatory cell protection, the transcription factor Nrf2 is a promising therapeutic target for several neurodegenerative diseases, leading to the development of Nrf2 activators targeting Keap1-dependent and independent regulatory mechanisms. Astrocytes play a crucial role in regulating neuronal physiology in health and disease, including Nrf2 neuroprotective responses. As neurons require specific conditions for their differentiation and maintenance, most 2D and 3D co-culture systems use medias that are compatible with neuronal differentiation and function, but also ensure astrocyte survival. Few studies, however, assess the molecular adaptations of astrocytes to changes from astrocyte maintenance medias alone, and their subsequent effects on neurons which may represent technical rather than physiological responses. Our findings show that while Nrf2 can be effectively activated by the Keap1-Nrf2 protein-protein interaction disruptor 18e, and classical Nrf2 activators DMF and CDDO-Me, in human primary cortical astrocyte monocultures, their efficacy is lost in LUHMES neuron-astrocyte co-cultures. Further investigation revealed that the Advanced DMEM/F12-based LUHMES differentiation media maximally induced basal Nrf2 activity in astrocytes alone, compared to astrocyte maintenance media, thus preventing pharmacological activation. Although Neurobasal slightly activated basal Nrf2, this was not significant suggesting that this media has less impact on astrocytic Nrf2 activity relative to Advanced DMEM/F12. As Nrf2 is a key regulator of oxidative damage and neuroinflammation, modelling these common features of neurodegenerative diseases may be confounded by environments that maximally activate basal Nrf2. Our findings thus suggest caution in media selection for neuron-astrocyte co-culture in disease modelling and therapeutic Nrf2 activator discovery.

Throughout the global coronavirus pandemic, we have seen an unprecedented volume of COVID-19 researchpublications. This vast body of evidence continues to grow, making it difficult for research users to keep up with the pace of evolving research findings. To enable the synthesis of this evidence for timely use by researchers, policymakers, and other stakeholders, we developed an automated workflow to collect, categorise, and visualise the evidence from primary COVID-19 research studies. We trained a crowd of volunteer reviewers to annotate studies by relevance to COVID-19, study objectives, and methodological approaches. Using these human decisions, we are training machine learning classifiers and applying text-mining tools to continually categorise the findings and evaluate the quality of COVID-19 evidence.

Accumulation of amyloid beta peptides is thought to initiate the pathogenesis of Alzheimer's disease. However, the precise mechanisms mediating their neurotoxicity are unclear. Our microarray analyses show that, in Drosophila models of amyloid beta 42 toxicity, genes involved in the unfolded protein response and metabolic processes are upregulated in brain. Comparison with the brain transcriptome of early-stage Alzheimer's patients revealed a common transcriptional signature, but with generally opposing directions of gene expression changes between flies and humans. Among these differentially regulated genes, lactate dehydrogenase (Ldh) was up-regulated by the greatest degree in amyloid beta 42 flies and the human orthologues (LDHA and LDHB) were down-regulated in patients. Functional analyses revealed that either over-expression or inhibition of Ldh by RNA interference (RNAi) slightly exacerbated climbing defects in both healthy and amyloid beta 42-induced Drosophila. This suggests that metabolic responses to lactate dehydrogenase must be finely-tuned, and that its observed upregulation following amyloid beta 42 production could potentially represent a compensatory protection to maintain pathway homeostasis in this model, with further manipulation leading to detrimental effects. The increased Ldh expression in amyloid beta 42 flies was regulated partially by unfolded protein response signalling, as ATF4 RNAi diminished the transcriptional response and enhanced amyloid beta 42-induced climbing phenotypes. Further functional studies are required to determine whether Ldh upregulation provides compensatory neuroprotection against amyloid beta 42-induced loss of activating transcription factor 4 activity and endoplasmatic reticulum stress. Our study thus reveals dysregulation of lactate dehydrogenase signalling in Drosophila models and patients with Alzheimer's disease, which may lead to a detrimental loss of metabolic homeostasis. Importantly, we observed that down-regulation of ATF4-dependent endoplasmic reticulum-stress signalling in this context appears to prevent Ldh compensation and to exacerbate amyloid beta 42-dependent neuronal toxicity. Our findings, therefore, suggest caution in the use of therapeutic strategies focussed on down-regulation of this pathway for the treatment of Alzheimer's disease, since its natural response to the toxic peptide may induce beneficial neuroprotective effects.

Alzheimer’s disease (AD), the most prevalent form of dementia, is a progressive and devastating neurodegenerative condition for which there are no effective treatments. Understanding the molecular pathology of AD during disease progression may identify new ways to reduce neuronal damage. Here, we present a longitudinal study tracking dynamic proteomic alterations in the brains of an inducible Drosophila melanogaster model of AD expressing the Arctic mutant Aβ42 gene. We identified 3093 proteins from flies that were induced to express Aβ42 and age-matched healthy controls using label-free quantitative ion-mobility data independent analysis mass spectrometry. Of these, 228 proteins were significantly altered by Aβ42 accumulation and were enriched for AD-associated processes. Network analyses further revealed that these proteins have distinct hub and bottleneck properties in the brain protein interaction network, suggesting that several may have significant effects on brain function. Our unbiased analysis provides useful insights into the key processes governing the progression of amyloid toxicity and forms a basis for further functional analyses in model organisms and translation to mammalian systems.

Lowered insulin/insulin-like growth factor (IGF) signaling (IIS) can extend healthy lifespan in worms, flies, and mice, but it can also have adverse effects (the “insulin paradox”). Chronic, moderately lowered IIS rescues age-related decline in neurotransmission through the Drosophila giant fiber system (GFS), a simple escape response neuronal circuit, by increasing targeting of the gap junctional protein innexin shaking-B to gap junctions (GJs). Endosomal recycling of GJs was also stimulated in cultured human cells when IIS was reduced. Furthermore, increasing the activity of the recycling small guanosine triphosphatases (GTPases) Rab4 or Rab11 was sufficient to maintain GJs upon elevated IIS in cultured human cells and in flies, and to rescue age-related loss of GJs and of GFS function. Lowered IIS thus elevates endosomal recycling of GJs in neurons and other cell types, pointing to a cellular mechanism for therapeutic intervention into aging-related neuronal disorders. Insulin and insulin-like growth factors play an important role in the nervous system development and function. Reduced insulin signaling, however, can improve symptoms of neurodegenerative diseases in different model organisms and protect against age-associated decline in neuronal function extending lifespan. Here, we analyze the effects of genetically attenuated insulin signaling on the escape response pathway in the fruit fly Drosophila melanogaster. This simple neuronal circuit is dominated by electrical synapses composed of the gap junctional shaking-B protein, which allows for the transfer of electrical impulses between cells. Transmission through the circuit is known to slow down with age. We show that this functional decline is prevented by systemic or circuit-specific suppression of insulin signaling due to the preservation of the number of gap junctional proteins in aging animals. Our experiments in a human cell culture system reveal increased membrane targeting of gap junctional proteins via small proteins Rab4 and Rab11 under reduced insulin conditions. We also find that increasing the level of these recycling-mediating proteins in flies preserves the escape response circuit output in old flies and suggests ways of improving the function of neuronal circuits dominated by electrical synapses during aging.

Nrf2, a transcriptional activator of cell protection genes, is an attractive therapeutic target for the prevention of neurodegenerative diseases, including Alzheimer’s disease (AD). Current Nrf2 activators, however, may exert toxicity and pathway over-activation can induce detrimental effects. An understanding of the mechanisms mediating Nrf2 inhibition in neurodegenerative conditions may therefore direct the design of drugs targeted for the prevention of these diseases with minimal side-effects. Our study provides the first in vivo evidence that specific inhibition of Keap1, a negative regulator of Nrf2, can prevent neuronal toxicity in response to the AD-initiating Aβ42 peptide, in correlation with Nrf2 activation. Comparatively, lithium, an inhibitor of the Nrf2 suppressor GSK-3, prevented Aβ42 toxicity by mechanisms independent of Nrf2. A new direct inhibitor of the Keap1-Nrf2 binding domain also prevented synaptotoxicity mediated by naturally-derived Aβ oligomers in mouse cortical neurons. Overall, our findings highlight Keap1 specifically as an efficient target for the re-activation of Nrf2 in AD, and support the further investigation of direct Keap1 inhibitors for the prevention of neurodegeneration in vivo. As our population ages the incidence of neurodegenerative diseases, including Alzheimer’s disease (AD), is predicted to increase dramatically. Despite providing important symptomatic relief, existing treatments for such conditions do not slow-down disease progression, and this will cause an overwhelming future burden on our healthcare system and immense suffering for many more patients and their families. Nrf2 is a gene that normally protects cells from stressful conditions. Although we don’t know why, Nrf2 is reduced in the brains of AD patients and this may explain the increased susceptibility of neurons to damage in neurodegenerative diseases. Our research, using a fruit fly model, identifies Keap1, a negative regulator of Nrf2, as a valid target for the rescue of AD-related Nrf2 defects and the subsequent prevention of neuronal degeneration. Moreover, we show that a new compound, which directly blocks the binding between Nrf2 and Keap1, can prevent toxicity of the AD-initiating Aβ peptide in mouse neurons. Hence, our study provides strong evidence that direct Keap1-Nrf2 disruptors can specifically target the defects in Nrf2 activity observed in neurodegenerative diseases, and supports the further development of such compounds as potential new drugs to prevent neuronal decline AD and other neurodegenerative conditions.

Human Tau (hTau) is a highly soluble and natively unfolded protein that binds to microtubules within neurons. Its dysfunction and aggregation into insoluble paired helical filaments is involved in the pathogenesis of Alzheimer’s disease (AD), constituting, together with accumulated β-amyloid (Aβ) peptides, a hallmark of the disease. Deciphering both the loss-of-function and toxic gain-of-function of hTau proteins is crucial to further understand the mechanisms leading to neurodegeneration in AD. As the fruit fly Drosophila melanogaster expresses Tau proteins (dTau) that are homologous to hTau, we aimed to better comprehend dTau functions by generating a specific tau knock-out (KO) fly line using homologous recombination. We observed that the specific removal of endogenous dTau proteins did not lead to overt, macroscopic phenotypes in flies. Indeed, survival, climbing ability and neuronal function were unchanged in tau KO flies. In addition, we did not find any overt positive or negative effect of dTau removal on human Aβ-induced toxicity. Altogether, our results indicate that the absence of dTau proteins has no major functional impact on flies and suggests that our tau KO strain is a relevant model to further investigate the role of dTau proteins in vivo, thereby giving additional insights into hTau functions.