Publisher Correction: Dietary salt promotes cognitive impairment through tau phosphorylation.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Dietary salt promotes cognitive impairment through tau phosphorylation.

Dietary habits and vascular risk factors promote both Alzheimer's disease and cognitive impairment caused by vascular factors1-3. Furthermore, accumulation of hyperphosphorylated tau, a microtubule-associated protein and a hallmark of Alzheimer's pathology4, is also linked to vascular cognitive impairment5,6. In mice, a salt-rich diet leads to cognitive dysfunction associated with a nitric oxide deficit in cerebral endothelial cells and cerebral hypoperfusion7. Here we report that dietary salt induces hyperphosphorylation of tau followed by cognitive dysfunction in mice, and that these effects are prevented by restoring endothelial nitric oxide production. The nitric oxide deficiency reduces neuronal calpain nitrosylation and results in enzyme activation, which, in turn, leads to tau phosphorylation by activating cyclin-dependent kinase 5. Salt-induced cognitive impairment is not observed in tau-null mice or in mice treated with anti-tau antibodies, despite persistent cerebral hypoperfusion and neurovascular dysfunction. These findings identify a causal link between dietary salt, endothelial dysfunction and tau pathology, independent of haemodynamic insufficiency. Avoidance of excessive salt intake and maintenance of vascular health may help to stave off the vascular and neurodegenerative pathologies that underlie dementia in the elderly.

RSK2 inactivation cooperates with AXIN1 inactivation or ß-catenin activation to promote hepatocarcinogenesis.

BACKGROUND & AIMS: Recurrent somatic mutations of the RPS6KA3 gene encoding for the serine/threonine kinase RSK2 were identified in hepatocellular carcinomas (HCCs), suggesting its tumour-suppressive function. Our goal was to demonstrate the tumour suppressor role of RSK2 in the liver and investigate the functional consequences of its inactivation. METHODS: We analysed a series of 1,151 human HCCs for RSK2 mutations and 20 other driver genetic alterations. We then modelled RSK2 inactivation in mice in various mutational contexts recapitulating or not those naturally found in human HCC, using transgenic mice and liver-specific carcinogens. These models were monitored for liver tumour appearance and subjected to phenotypic and transcriptomic analyses. Functional consequences of RSK2 rescue were also investigated in a human RSK2-deficient HCC cell line. RESULTS: RSK2-inactivating mutations are specific to human HCC and frequently co-occur with AXIN1-inactivating or ß-catenin-activating mutations. Modelling of these co-occurrences in mice showed a cooperative effect in promoting liver tumours with transcriptomic profiles recapitulating those of human HCCs. By contrast, there was no cooperation in liver tumour induction between RSK2 loss and BRAF-activating mutations chemically induced by diethylnitrosamine. In human liver cancer cells, we also showed that RSK2 inactivation confers some dependency to the activation of RAS/MAPK signalling that can be targeted by MEK inhibitors. CONCLUSIONS: Our study demonstrates the tumour suppressor role of RSK2 and its specific synergistic effect in hepatocarcinogenesis when its loss of function is specifically combined with AXIN1 inactivation or ß-catenin activation. Furthermore, we identified the RAS/MAPK pathway as a potential therapeutic target for RSK2-inactivated liver tumours. IMPACT AND IMPLICATIONS: This study demonstrated the tumour suppressor role of RSK2 in the liver and showed that its inactivation specifically synergises with AXIN1 inactivation or ß-catenin activation to promote the development of HCC with similar transcriptomic profiles as found in humans. Furthermore, this study highlights that activation of the RAS/MAPK pathway is one of the key signalling pathways mediating the oncogenic effect of RSK2 inactivation that can be targeted with already available anti-MEK therapies.

Meningeal interleukin-17-producing T cells mediate cognitive impairment in a mouse model of salt-sensitive hypertension.

Hypertension (HTN), a disease afflicting over one billion individuals worldwide, is a leading cause of cognitive impairment, the mechanisms of which remain poorly understood. In the present study, in a mouse model of HTN, we find that the neurovascular and cognitive dysfunction depends on interleukin (IL)-17, a cytokine elevated in individuals with HTN. However, neither circulating IL-17 nor brain angiotensin signaling can account for the dysfunction. Rather, IL-17 produced by T cells in the dura mater is the mediator released in the cerebrospinal fluid and activating IL-17 receptors on border-associated macrophages (BAMs). Accordingly, depleting BAMs, deleting IL-17 receptor A in brain macrophages or suppressing meningeal T cells rescues cognitive function without attenuating blood pressure elevation, circulating IL-17 or brain angiotensin signaling. Our data unveil a critical role of meningeal T cells and macrophage IL-17 signaling in the neurovascular and cognitive dysfunction in a mouse model of HTN.

A cell-autonomous role for border-associated macrophages in ApoE4 neurovascular dysfunction and susceptibility to white matter injury.

Apolipoprotein E4 (ApoE4), the strongest genetic risk factor for sporadic Alzheimer's disease, is also a risk factor for microvascular pathologies leading to cognitive impairment, particularly subcortical white matter injury. These effects have been attributed to alterations in the regulation of the brain blood supply, but the cellular source of ApoE4 and the underlying mechanisms remain unclear. In mice expressing human ApoE3 or ApoE4, we report that border-associated macrophages (BAMs), myeloid cells closely apposed to neocortical microvessels, are both sources and effectors of ApoE4 mediating the neurovascular dysfunction through reactive oxygen species. ApoE4 in BAMs is solely responsible for the increased susceptibility to oligemic white matter damage in ApoE4 mice and is sufficient to enhance damage in ApoE3 mice. The data unveil a new aspect of BAM pathobiology and highlight a previously unrecognized cell-autonomous role of BAM in the neurovascular dysfunction of ApoE4 with potential therapeutic implications.

Cell autonomous role of border associated macrophages in ApoE4 neurovascular dysfunction and susceptibility to white matter injury.

Apolipoprotein-E4 (ApoE4), the strongest genetic risk factor for sporadic Alzheimer's disease, is also a risk factor for microvascular pathologies leading to cognitive impairment, particularly subcortical white matter injury. These effects have been attributed to alterations in the regulation of the brain blood supply, but the cellular source of ApoE4 and the underlying mechanisms remain unclear. In mice expressing human ApoE3 or ApoE4 we report that border associated macrophages (BAM), myeloid cells closely apposed to neocortical microvessels, are both the source and the target of the ApoE4 mediating the neurovascular dysfunction through reactive oxygen species. ApoE4 in BAM is solely responsible for the increased susceptibility to oligemic white matter damage in ApoE4 mice and is sufficient to enhance damage in ApoE3 mice. The data unveil a new aspect of BAM pathobiology and highlight a previously unrecognized cell autonomous role of BAM in the neurovascular dysfunction of ApoE4 with potential therapeutic implications.

Seizure reduction in TSC2-mutant mouse model by an mTOR catalytic inhibitor.

OBJECTIVE: Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder caused by autosomal-dominant pathogenic variants in either the TSC1 or TSC2 gene, and it is characterized by hamartomas in multiple organs, such as skin, kidney, lung, and brain. These changes can result in epilepsy, learning disabilities, and behavioral complications, among others. The mechanistic link between TSC and the mechanistic target of the rapamycin (mTOR) pathway is well established, thus mTOR inhibitors can potentially be used to treat the clinical manifestations of the disorder, including epilepsy. METHODS: In this study, we tested the efficacy of a novel mTOR catalytic inhibitor (here named Tool Compound 1 or TC1) previously reported to be more brain-penetrant compared with other mTOR inhibitors. Using a well-characterized hypomorphic Tsc2 mouse model, which displays a translationally relevant seizure phenotype, we tested the efficacy of TC1. RESULTS: Our results show that chronic treatment with this novel mTOR catalytic inhibitor (TC1), which affects both the mTORC1 and mTORC2 signaling complexes, reduces seizure burden, and extends the survival of Tsc2 hypomorphic mice, restoring species typical weight gain over development. INTERPRETATION: Novel mTOR catalytic inhibitor TC1 exhibits a promising therapeutic option in the treatment of TSC.

Revisiting the neurovascular unit.

The brain is supplied by an elaborate vascular network that originates extracranially and reaches deep into the brain. The concept of the neurovascular unit provides a useful framework to investigate how neuronal signals regulate nearby microvessels to support the metabolic needs of the brain, but it does not consider the role of larger cerebral arteries and systemic vasoactive signals. Furthermore, the recently emerged molecular heterogeneity of cerebrovascular cells indicates that there is no prototypical neurovascular unit replicated at all levels of the vascular network. Here, we examine the cellular and molecular diversity of the cerebrovascular tree and the relative contribution of systemic and brain-intrinsic factors to neurovascular function. Evidence supports the concept of a 'neurovascular complex' composed of segmentally diverse functional modules that implement coordinated vascular responses to central and peripheral signals to maintain homeostasis of the brain. This concept has major implications for neurovascular regulation in health and disease and for brain imaging.

Endothelium-Macrophage Crosstalk Mediates Blood-Brain Barrier Dysfunction in Hypertension.

Hypertension is a leading cause of stroke and dementia, effects attributed to disrupting delivery of blood flow to the brain. Hypertension also alters the blood-brain barrier (BBB), a critical component of brain health. Although endothelial cells are ultimately responsible for the BBB, the development and maintenance of the barrier properties depend on the interaction with other vascular-associated cells. However, it remains unclear if BBB disruption in hypertension requires cooperative interaction with other cells. Perivascular macrophages (PVM), innate immune cells closely associated with cerebral microvessels, have emerged as major contributors to neurovascular dysfunction. Using 2-photon microscopy in vivo and electron microscopy in a mouse model of Ang II (angiotensin II) hypertension, we found that the vascular segments most susceptible to increased BBB permeability are arterioles and venules >10 µm and not capillaries. Brain macrophage depletion with clodronate attenuates, but does not abolish, the increased BBB permeability in these arterioles where PVM are located. Deletion of AT1R (Ang II type-1 receptors) in PVM using bone marrow chimeras partially attenuated the BBB dysfunction through the free radical-producing enzyme Nox2. In contrast, downregulation of AT1R in cerebral endothelial cells using a viral gene transfer-based approach prevented the BBB disruption completely. The results indicate that while endothelial AT1R, mainly in arterioles and venules, initiate the BBB disruption in hypertension, PVM are required for the full expression of the dysfunction. The findings unveil a previously unappreciated contribution of resident brain macrophages to increased BBB permeability of hypertension and identify PVM as a putative therapeutic target in diseases associated with BBB dysfunction.

Gut microbiota composition before infection determines the Salmonella super- and low-shedder phenotypes in chicken.

Heterogeneity of infection and extreme shedding patterns are common features of animal infectious diseases. Individual hosts that are super-shedders are key targets for control strategies. Nevertheless, the mechanisms associated with the emergence of super-shedders remain largely unknown. During chicken salmonellosis, a high heterogeneity of infection is observed when animal-to-animal cross-contaminations and reinfections are reduced. We hypothesized that unlike super-shedders, low-shedders would be able to block the first Salmonella colonization thanks to a different gut microbiota. The present study demonstrates that (i) axenic and antibiotic-treated chicks are more prone to become super-shedders; (ii) super or low-shedder phenotypes can be acquired through microbiota transfer; (iii) specific gut microbiota taxonomic features determine whether the chicks develop a low- and super-shedder phenotype after Salmonella infection in isolator; (iv) partial protection can be conferred by inoculation of four commensal bacteria prior to Salmonella infection. This study demonstrates the key role plays by gut microbiota composition in the heterogeneity of infection and pave the way for developing predictive biomarkers and protective probiotics.

Salmonella Typhimurium Invalidated for the Three Currently Known Invasion Factors Keeps Its Ability to Invade Several Cell Models.

To establish an infection, Salmonella has to interact with eukaryotic cells. Invasion of non-phagocytic cells (i.e., epithelial, fibroblast and endothelial cells) involves either a trigger or a zipper mechanism mediated by the T3SS-1 or the invasin Rck, respectively. Another outer membrane protein, PagN, was also implicated in the invasion. However, other unknown invasion factors have been previously suggested. Our goal was to evaluate the invasion capability of a Salmonella Typhimurium strain invalidated for the three known invasion factors. Non-phagocytic cell lines of several animal origins were tested in a gentamicin protection assay. In most cells, we observed a drastic decrease in the invasion rate between the wild-type and the triple mutant. However, in five cell lines, the triple mutant invaded cells at a similarly high level to the wild-type, suggesting the existence of unidentified invasion factors. For the wild-type and the triple mutant, scanning-electron microscopy, confocal imaging and use of biochemical inhibitors confirmed their cellular uptake and showed a zipper-like mechanism of internalization involving both clathrin- and non-clathrin-dependent pathways. Despite a functional T3SS-1, the wild-type bacteria seemed to use the same entry route as the mutant in our cell model. All together, these results demonstrate the existence of unknown Salmonella invasion factors, which require further characterization.

Sensitive Periods for Cerebellar-Mediated Autistic-like Behaviors.

Despite a prevalence exceeding 1%, mechanisms underlying autism spectrum disorders (ASDs) are poorly understood, and targeted therapies and guiding parameters are urgently needed. We recently demonstrated that cerebellar dysfunction is sufficient to generate autistic-like behaviors in a mouse model of tuberous sclerosis complex (TSC). Here, using the mechanistic target of rapamycin (mTOR)-specific inhibitor rapamycin, we define distinct sensitive periods for treatment of autistic-like behaviors with sensitive periods extending into adulthood for social behaviors. We identify cellular and electrophysiological parameters that may contribute to behavioral rescue, with rescue of Purkinje cell survival and excitability corresponding to social behavioral rescue. In addition, using anatomic and diffusion-based MRI, we identify structural changes in cerebellar domains implicated in ASD that correlate with sensitive periods of specific autism-like behaviors. These findings thus not only define treatment parameters into adulthood, but also support a mechanistic basis for the targeted rescue of autism-related behaviors.

mGluR5 Modulation of Behavioral and Epileptic Phenotypes in a Mouse Model of Tuberous Sclerosis Complex.

Drugs targeting metabotropic glutamate receptor 5 (mGluR5) have therapeutic potential in autism spectrum disorders (ASD), including tuberous sclerosis complex (TSC). The question whether inhibition or potentiation of mGluR5 could be beneficial depends, among other factors, on the specific indication. To facilitate the development of mGluR5 treatment strategies, we tested the therapeutic utility of mGluR5 negative and positive allosteric modulators (an mGluR5 NAM and PAM) for TSC, using a mutant mouse model with neuronal loss of Tsc2 that demonstrates disease-related phenotypes, including behavioral symptoms of ASD and epilepsy. This model uniquely enables the in vivo characterization and rescue of the electrographic seizures associated with TSC. We demonstrate that inhibition of mGluR5 corrects hyperactivity, seizures, and elevated de novo synaptic protein synthesis. Conversely, positive allosteric modulation of mGluR5 results in the exacerbation of hyperactivity and epileptic phenotypes. The data suggest a meaningful therapeutic potential for mGluR5 NAMs in TSC, which warrants clinical exploration and the continued development of mGluR5 therapies.

Erratum: Parvalbumin-expressing interneurons coordinate hippocampal network dynamics required for memory consolidation.

This corrects the article DOI: 10.1038/ncomms15039.

Parvalbumin-expressing interneurons coordinate hippocampal network dynamics required for memory consolidation.

Activity in hippocampal area CA1 is essential for consolidating episodic memories, but it is unclear how CA1 activity patterns drive memory formation. We find that in the hours following single-trial contextual fear conditioning (CFC), fast-spiking interneurons (which typically express parvalbumin (PV)) show greater firing coherence with CA1 network oscillations. Post-CFC inhibition of PV+ interneurons blocks fear memory consolidation. This effect is associated with loss of two network changes associated with normal consolidation: (1) augmented sleep-associated delta (0.5-4 Hz), theta (4-12 Hz) and ripple (150-250 Hz) oscillations; and (2) stabilization of CA1 neurons' functional connectivity patterns. Rhythmic activation of PV+ interneurons increases CA1 network coherence and leads to a sustained increase in the strength and stability of functional connections between neurons. Our results suggest that immediately following learning, PV+ interneurons drive CA1 oscillations and reactivation of CA1 ensembles, which directly promotes network plasticity and long-term memory formation.