Neuroinflammatory transcriptional programs induced in rhesus pre-frontal cortex white matter during acute SHIV infection.

BACKGROUND: Immunosurveillance of the central nervous system (CNS) is vital to resolve infection and injury. However, immune activation within the CNS in the setting of chronic viral infections, such as HIV-1, is strongly linked to progressive neurodegeneration and cognitive decline. Establishment of HIV-1 in the CNS early following infection underscores the need to delineate features of acute CNS immune activation, as these early inflammatory events may mediate neurodegenerative processes. Here, we focused on elucidating molecular programs of neuroinflammation in brain regions based on vulnerability to neuroAIDS and/or neurocognitive decline. To this end, we assessed transcriptional profiles within the subcortical white matter of the pre-frontal cortex (PFCw), as well as synapse dense regions from hippocampus, superior temporal cortex, and caudate nucleus, in rhesus macaques following infection with Simian/Human Immunodeficiency Virus (SHIV.C.CH505). METHODS: We performed RNA extraction and sequenced RNA isolated from 3 mm brain punches. Viral RNA was quantified in the brain and cerebrospinal fluid by RT-qPCR assays targeting SIV Gag. Neuroinflammation was assessed by flow cytometry and multiplex ELISA assays. RESULTS: RNA sequencing and flow cytometry data demonstrated immune surveillance of the rhesus CNS by innate and adaptive immune cells during homeostasis. Following SHIV infection, viral entry and integration within multiple brain regions demonstrated vulnerabilities of key cognitive and motor function brain regions to HIV-1 during the acute phase of infection. SHIV-induced transcriptional alterations were concentrated to the PFCw and STS with upregulation of gene expression pathways controlling innate and T-cell inflammatory responses. Within the PFCw, gene modules regulating microglial activation and T cell differentiation were induced at 28 days post-SHIV infection, with evidence for stimulation of immune effector programs characteristic of neuroinflammation. Furthermore, enrichment of pathways regulating mitochondrial respiratory capacity, synapse assembly, and oxidative and endoplasmic reticulum stress were observed. These acute neuroinflammatory features were substantiated by increased influx of activated T cells into the CNS. CONCLUSIONS: Our data show pervasive immune surveillance of the rhesus CNS at homeostasis and reveal perturbations of important immune, neuronal, and synaptic pathways within key anatomic regions controlling cognition and motor function during acute HIV infection. These findings provide a valuable framework to understand early molecular features of HIV associated neurodegeneration.

Oligomeric Aß in the monkey brain impacts synaptic integrity and induces accelerated cortical aging.

As the average age of the population continues to rise, the number of individuals affected with age-related cognitive decline and Alzheimer's disease (AD) has increased and is projected to cost more than $290 billion in the United States in 2019. Despite significant investment in research over the last decades, there is no effective treatment to prevent or delay AD progression. There is a translational gap in AD research, with promising drugs based on work in rodent models failing in clinical trials. Aging is the leading risk factor for developing AD and understanding neurobiological changes that affect synaptic integrity with aging will help clarify why the aged brain is vulnerable to AD. We describe here the development of a rhesus monkey model of AD using soluble oligomers of the amyloid beta (Aß) peptide (AßOs). AßOs infused into the monkey brain target a specific population of spines in the prefrontal cortex, induce neuroinflammation, and increase AD biomarkers in the cerebrospinal fluid to similar levels observed in patients with AD. Importantly, AßOs lead to similar dendritic spine loss to that observed in normal aging in monkeys, but so far without detection of amyloid plaques or tau pathology. Understanding the basis of synaptic impairment is the most effective route to early intervention and prevention or postponement of age-related cognitive decline and transition to AD. These initial findings support the use of monkeys as a platform to understand age-related vulnerabilities of the primate brain and may help develop effective disease-modifying therapies for treatment of AD and related dementias.

Towards developing a rhesus monkey model of early Alzheimer's disease focusing on women's health.

Alzheimer's disease (AD) is the most common cause of elderly dementia, affecting nearly 50 million people worldwide, with two-thirds of the cases in the USA in women. Despite considerable investment, this prevalence is expected to increase further in the coming decades, based on the projected demographics of the population. Currently, most of the preclinical AD studies rely on transgenic mice carrying mutations associated with the early onset familiar form of AD, although the vast majority of cases are sporadic. A prevailing current hypothesis is that the cascade of events leading to AD starts with the accumulation of small soluble oligomers of the Aß peptide (AßOs) that target and disrupt synapses. Taking advantage of the high translational power of rhesus monkeys due to their physiological and genetic similarities to humans, we recently developed a female rhesus monkey model of early AD pathogenesis based on exogenous administration AßOs. Here we review and discuss how soluble oligomers of Aß can target vulnerable spines in the neocortex and hippocampus of female middle-aged monkeys and induce neuroinflammatory responses, similar to what is known to occur in the human brain. Developing a rhesus monkey model of early AD focusing on women's health is critical for the understanding of how hormonal changes during menopause transition affect brain health and ultimately may contribute to AD neurodegeneration.

A novel tau-based rhesus monkey model of Alzheimer's pathogenesis.

INTRODUCTION: Alzheimer's disease (AD) is a devastating condition with no effective treatments, with promising findings in rodents failing to translate into successful therapies for patients. METHODS: Targeting the vulnerable entorhinal cortex (ERC), rhesus monkeys received two injections of an adeno-associated virus expressing a double tau mutation (AAV-P301L/S320F) in the left hemisphere, and control AAV-green fluorescent protein in the right ERC. Noninjected aged-matched monkeys served as additional controls. RESULTS: Within 3 months we observed evidence of misfolded tau propagation, similar to what is hypothesized to occur in humans. Viral delivery of human 4R-tau also coaptates monkey 3R-tau via permissive templating. Tau spreading is accompanied by robust neuroinflammatory response driven by TREM2+ microglia, with biomarkers of inflammation and neuronal loss in the cerebrospinal fluid and plasma. DISCUSSION: These results highlight the initial stages of tau seeding and propagation in a primate model, a more powerful translational approach for the development of new therapies for AD.

Construction and reconstruction of brain circuits: normal and pathological axon guidance.

Perception of our environment entirely depends on the close interaction between the central and peripheral nervous system. In order to communicate each other, both systems must develop in parallel and in coordination. During development, axonal projections from the CNS as well as the PNS must extend over large distances to reach their appropriate target cells. To do so, they read and follow a series of axon guidance molecules. Interestingly, while these molecules play critical roles in guiding developing axons, they have also been shown to be critical in other major neurodevelopmental processes, such as the migration of cortical progenitors. Currently, a major hurdle for brain repair after injury or neurodegeneration is the absence of axonal regeneration in the mammalian CNS. By contrasts, PNS axons can regenerate. Many hypotheses have been put forward to explain this paradox but recent studies suggest that hacking neurodevelopmental mechanisms may be the key to promote CNS regeneration. Here we provide a seminar report written by trainees attending the second Flagship school held in Alpbach, Austria in September 2018 organized by the International Society for Neurochemistry (ISN) together with the Journal of Neurochemistry (JCN). This advanced school has brought together leaders in the fields of neurodevelopment and regeneration in order to discuss major keystones and future challenges in these respective fields.

Cross Talk Between Brain Innate Immunity and Serotonin Signaling Underlies Depressive-Like Behavior Induced by Alzheimer's Amyloid-ß Oligomers in Mice.

Considerable clinical and epidemiological evidence links Alzheimer's disease (AD) and depression. However, the molecular mechanisms underlying this connection are largely unknown. We reported recently that soluble Aß oligomers (AßOs), toxins that accumulate in AD brains and are thought to instigate synapse damage and memory loss, induce depressive-like behavior in mice. Here, we report that the mechanism underlying this action involves AßO-induced microglial activation, aberrant TNF-α signaling, and decreased brain serotonin levels. Inactivation or ablation of microglia blocked the increase in brain TNF-α and abolished depressive-like behavior induced by AßOs. Significantly, we identified serotonin as a negative regulator of microglial activation. Finally, AßOs failed to induce depressive-like behavior in Toll-like receptor 4-deficient mice and in mice harboring a nonfunctional TLR4 variant in myeloid cells. Results establish that AßOs trigger depressive-like behavior via a double impact on brain serotonin levels and microglial activation, unveiling a cross talk between brain innate immunity and serotonergic signaling as a key player in mood alterations in AD. SIGNIFICANCE STATEMENT: Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the main cause of dementia in the world. Brain accumulation of amyloid-ß oligomers (AßOs) is a major feature in the pathogenesis of AD. Although clinical and epidemiological data suggest a strong connection between AD and depression, the underlying mechanisms linking these two disorders remain largely unknown. Here, we report that aberrant activation of the brain innate immunity and decreased serotonergic tonus in the brain are key players in AßO-induced depressive-like behavior in mice. Our findings may open up new possibilities for the development of effective therapeutics for AD and depression aimed at modulating microglial function.

Prion Protein Modulates Monoaminergic Systems and Depressive-like Behavior in Mice.

We sought to examine interactions of the prion protein (PrP(C)) with monoaminergic systems due to: the role of PrP(C) in both Prion and Alzheimer diseases, which include clinical depression among their symptoms, the implication of monoamines in depression, and the hypothesis that PrP(C) serves as a scaffold for signaling systems. To that effect we compared both behavior and monoaminergic markers in wild type (WT) and PrP(C)-null (PrP(-/-)) mice. PrP(-/-) mice performed poorly when compared with WT in forced swimming, tail suspension, and novelty suppressed feeding tests, typical of depressive-like behavior, but not in the control open field nor rotarod motor tests; cyclic AMP responses to stimulation of D1 receptors by dopamine was selectively impaired in PrP(-/-) mice, and responses to serotonin, but not to norepinephrine, also differed between genotypes. Contents of dopamine, tyrosine hydroxylase, and the 5-HT5A serotonin receptor were increased in the cerebral cortex of PrP(-/-), as compared with WT mice. Microscopic colocalization, as well as binding in overlay assays were found of PrP(C) with both the 5HT5A and D1, but not D4 receptors. The data are consistent with the scaffolding of monoaminergic signaling modules by PrP(C), and may help understand the pathogenesis of clinical depression and neurodegenerative disorders.

Microglial dysfunction connects depression and Alzheimer's disease.

Alzheimer's disease (AD) and major depressive disorder (MDD) are highly prevalent neuropsychiatric conditions with intriguing epidemiological overlaps. Depressed patients are at increased risk of developing late-onset AD, and around one in four AD patients are co-diagnosed with MDD. Microglia are the main cellular effectors of innate immunity in the brain, and their activation is central to neuroinflammation - a ubiquitous process in brain pathology, thought to be a causal factor of both AD and MDD. Microglia serve several physiological functions, including roles in synaptic plasticity and neurogenesis, which may be disrupted in neuroinflammation. Following early work on the 'sickness behavior' of humans and other animals, microglia-derived inflammatory cytokines have been shown to produce depressive-like symptoms when administered exogenously or released in response to infection. MDD patients consistently show increased circulating levels of pro-inflammatory cytokines, and anti-inflammatory drugs show promise for treating depression. Activated microglia are abundant in the AD brain, and concentrate around senile plaques, hallmark lesions composed of aggregated amyloid-ß peptide (Aß). The Aß burden in affected brains is regulated largely by microglial clearance, and the complex activation state of microglia may be crucial for AD progression. Intriguingly, recent reports have linked soluble Aß oligomers, toxins that accumulate in AD brains and are thought to cause memory impairment, to increased brain cytokine production and depressive-like behavior in mice. Here, we review recent findings supporting the inflammatory hypotheses of AD and MDD, focusing on microglia as a common player and therapeutic target linking these devastating disorders.

Chronic SIV-Induced neuroinflammation disrupts CCR7+ CD4+ T cell immunosurveillance in the rhesus macaque brain.

CD4+ T cells survey and maintain immune homeostasis in the brain, yet their differentiation states and functional capabilities remain unclear. Our approach, combining single-cell transcriptomic analysis, ATAC-Seq, spatial transcriptomics, and flow cytometry, revealed a distinct subset of CCR7+ CD4+ T cells resembling lymph node central memory (TCM) cells. We observed chromatin accessibility at the CCR7, CD28, and BCL-6 loci, defining molecular features of TCM. Brain CCR7+ CD4+ T cells exhibited recall proliferation and interleukin-2 production ex vivo, showcasing their functional competence. We identified the skull bone marrow as a local niche for these cells alongside CNS border tissues. Sequestering TCM cells in lymph nodes using FTY720 led to reduced CCR7+ CD4+ T cell frequencies in the cerebrospinal fluid, accompanied by increased monocyte levels and soluble markers indicating immune activation. In macaques chronically infected with SIVCL757 and experiencing viral rebound due to cessation of antiretroviral therapy, a decrease in brain CCR7+ CD4+ T cells was observed, along with increased microglial activation and initiation of neurodegenerative pathways. Our findings highlight a role for CCR7+ CD4+ T cells in CNS immune surveillance, and their decline during chronic SIV highlights their responsiveness to neuroinflammation.

CCR7+ CD4 T Cell Immunosurveillance Disrupted in Chronic SIV-Induced Neuroinflammation in Rhesus Brain.

CD4 T cells survey and maintain immune homeostasis in the brain, yet their differentiation states and functional capabilities remain unclear. Our approach, combining single-cell transcriptomic analysis, ATAC-seq, spatial transcriptomics, and flow cytometry, revealed a distinct subset of CCR7+ CD4 T cells resembling lymph node central memory (T CM ) cells. We observed chromatin accessibility at the CCR7, CD28, and BCL-6 loci, defining molecular features of T CM . Brain CCR7+ CD4 T cells exhibited recall proliferation and interleukin-2 production ex vivo, showcasing their functional competence. We identified the skull bone marrow as a local niche for these cells alongside other CNS border tissues. Sequestering T CM cells in lymph nodes using FTY720 led to reduced CCR7+ CD4 T cell frequencies in the cerebrospinal fluid, accompanied by increased monocyte levels and soluble markers indicating immune activation. In macaques chronically infected with SIVCL57 and experiencing viral rebound due to cessation of antiretroviral therapy, a decrease in brain CCR7+ CD4 T cells was observed, along with increased microglial activation and initiation of neurodegenerative pathways. Our findings highlight a role for CCR7+ CD4 T cells in CNS immune surveillance and their decline during chronic SIV-induced neuroinflammation highlights their responsiveness to neuroinflammatory processes. In Brief: Utilizing single-cell and spatial transcriptomics on adult rhesus brain, we uncover a unique CCR7+ CD4 T cell subset resembling central memory T cells (T CM ) within brain and border tissues, including skull bone marrow. Our findings show decreased frequencies of this subset during SIV- induced chronic neuroinflammation, emphasizing responsiveness of CCR7+ CD4 T cells to CNS disruptions. Highlights: CCR7+ CD4 T cells survey border and parenchymal CNS compartments during homeostasis; reduced presence of CCR7+ CD4 T cells in cerebrospinal fluid leads to immune activation, implying a role in neuroimmune homeostasis. CNS CCR7+ CD4 T cells exhibit phenotypic and functional features of central memory T cells (T CM ) including production of interleukin 2 and the capacity for rapid recall proliferation. Furthermore, CCR7+ CD4 T cells reside in the skull bone marrow. CCR7+ CD4 T cells are markedly decreased within the brain parenchyma during chronic viral neuroinflammation.

Neuroanatomical abnormalities in a nonhuman primate model of congenital Zika virus infection.

We evaluated neuropathological consequences of fetal ZIKV exposure in rhesus monkeys, a translatable animal model for human neural development, by carrying out quantitative neuroanatomical analyses of the nearly full-term brains of fetuses infected with ZIKV and procedure-matched controls. For each animal, a complete cerebral hemisphere was evaluated using immunohistochemical (IHC) and neuroanatomical techniques to detect virus, identify affected cell types, and evaluate gross neuroanatomical abnormalities. IHC staining revealed the presence of ZIKV in the frontal lobe, which contained activated microglia and showed increased apoptosis of immature neurons. ZIKV-infected animals exhibited macrostructural changes within the visual pathway. Regional differences tracked with the developmental timing of the brain, suggesting inflammatory processes related to viral infiltration swept through the cortex, followed by a wave of cell death resulting in morphological changes. These findings may help explain why some infants born with normal sized heads during the ZIKV epidemic manifest developmental challenges as they age.

SARS-CoV-2 infects neurons and induces neuroinflammation in a non-human primate model of COVID-19.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiologic agent of coronavirus disease 2019 (COVID-19), can induce a plethora of neurological complications in some patients. However, it is still under debate whether SARS-CoV-2 directly infects the brain or whether CNS sequelae result from systemic inflammatory responses triggered in the periphery. By using high-resolution microscopy, we investigated whether SARS-CoV-2 reaches the brain and how viral neurotropism can be modulated by aging in a non-human primate model of COVID-19. Seven days after infection, SARS-CoV-2 was detected in the olfactory cortex and interconnected regions and was accompanied by robust neuroinflammation and neuronal damage exacerbated in aged, diabetic animals. Our study provides an initial framework for identifying the molecular and cellular mechanisms underlying SARS-CoV-2 neurological complications, which will be essential to reducing both the short- and long-term burden of COVID-19.

Cerebrospinal Fluid Neurotransmitters, Cytokines, and Chemokines in Alzheimer's and Lewy Body Diseases.

BACKGROUND: Alzheimer's disease (AD) and Lewy body disease (LBD) are complex neurodegenerative disorders that have been associated with brain inflammation and impaired neurotransmission. OBJECTIVE: We aimed to determine concentrations of multiple cytokines, chemokines, and neurotransmitters previously associated with brain inflammation and synapse function in cerebrospinal fluid (CSF) from AD and LBD patients. METHODS: We examined a panel of 50 analytes comprising neurotransmitters, cytokines, chemokines, and hormones in CSF in a cohort of patients diagnosed with mild cognitive impairment (MCI), AD, LBD, or non-demented controls (NDC). RESULTS: Among neurotransmitters, noradrenaline (NA) was increased in AD CSF, while homovanillic acid (HVA), a dopamine metabolite, was reduced in both AD and LBD CSF relative to NDC. Six cytokines/chemokines out of 30 investigated were reliably detected in CSF. CSF vascular endothelial growth factor (VEGF) was significantly reduced in LBD patients relative to NDC. CONCLUSIONS: CSF alterations in NA, HVA, and VEGF in AD and LBD may reflect pathogenic features of these disorders and provide tools for improved diagnosis. Future studies are warranted to replicate current findings in larger, multicenter cohorts.

Exercise-linked FNDC5/irisin rescues synaptic plasticity and memory defects in Alzheimer's models.

Defective brain hormonal signaling has been associated with Alzheimer's disease (AD), a disorder characterized by synapse and memory failure. Irisin is an exercise-induced myokine released on cleavage of the membrane-bound precursor protein fibronectin type III domain-containing protein 5 (FNDC5), also expressed in the hippocampus. Here we show that FNDC5/irisin levels are reduced in AD hippocampi and cerebrospinal fluid, and in experimental AD models. Knockdown of brain FNDC5/irisin impairs long-term potentiation and novel object recognition memory in mice. Conversely, boosting brain levels of FNDC5/irisin rescues synaptic plasticity and memory in AD mouse models. Peripheral overexpression of FNDC5/irisin rescues memory impairment, whereas blockade of either peripheral or brain FNDC5/irisin attenuates the neuroprotective actions of physical exercise on synaptic plasticity and memory in AD mice. By showing that FNDC5/irisin is an important mediator of the beneficial effects of exercise in AD models, our findings place FNDC5/irisin as a novel agent capable of opposing synapse failure and memory impairment in AD.

The effects of metergoline and 8-OH-DPAT injections into arcuate nucleus and lateral hypothalamic area on feeding in female rats during the estrous cycle.

The present study examined the effects of local injections of metergoline (MET, an antagonist of 5-HT1/2 receptors, 2 and 20 nmol) and 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT, selective 5-HT1A receptor agonist, 0.6 and 6 nmol) into the arcuate nucleus (ARC) and the lateral hypothalamus (LH), on ingestive and non-ingestive behaviors of female rats. These effects were examined during the diurnal periods of diestrus and estrus in rats adapted to eat a wet mash diet (enriched with 10% sucrose) during 1h for 3 consecutive days at the recording chamber. The results showed that 8-OH-DPAT injected into the LH significantly reduced food intake at all doses and both cycle stages, while in the ARC these treatments evoked hypophagia only at the highest 8-OH-DPAT dose and only at the estrous phase. MET administered into the ARC (at all doses) failed to affect food intake during both estrous stages. On the other hand, food intake decreased after injection of both doses of MET into the LH of rats during estrous and diestrus phases. In estrus stage, injections of the higher dose of 8-OH-DPAT into the ARC and into the LH decreased the duration of feeding. Latency to start feeding, drinking, and non-ingestive behaviors were not affected by 8-OH-DPAT or MET treatments in the ARC or the LH in both cycle phases. These results indicated that 5-HT1A receptors participate in the serotonergic control of feeding-related mechanisms located at the ARC and the LH. These feeding-related serotonergic circuits in both areas are possibly affected by ovarian hormones that could increase sensitivity of ARC neurons to the hypophagic effects of 8-OH-DPAT or increase the efficacy of satiety signals that terminate feeding. In addition, the present data indicated that serotonergic inputs do not exert a tonic inhibitory activity on the ARC and the LH feeding-related circuits.