Journal of Neuroinflammation

Although effective antiretroviral therapy (ART) has substantially reduced the severity of human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND), the condition remains highly prevalent. Understanding HAND has been a challenge due to the lack of small animal models capable of supporting productive HIV infection in the brain. Recent advances in humanized mouse models with engrafted human glial cells now enable systemic HIV infection that extends to the central nervous system, offering a powerful platform to study HAND pathogenesis. In this study, we investigated behavioral alterations and neuropathological changes associated with HIV infection. Using home-cage monitoring, we observed that HIV-infected mice exhibited reduced feeding efficiency, consuming less food despite increased time spent at the feeder, compared to uninfected controls. Additionally, infected animals displayed disrupted circadian rhythms, with a significant correlation between central nervous system viral load and increased locomotor activity during the light cycle. Neuropathological analyses revealed region-specific vulnerability, with the cortex exhibiting pronounced inflammatory and neurodegenerative changes. These findings were supported by transcriptomic profiling, which demonstrated heightened inflammatory and antiviral gene expression in the cortex associated with differentially expressed genes related to neuropathology and behavior deficits. Together, these results highlight distinct region-specific responses to HIV infection in the brain and establish this humanized mouse model as a valuable tool for elucidating the mechanisms underlying HAND and its associated behavioral deficits.

The neuronal mechanisms driving progression in neuroinflammatory disorders from early relapse-remitting phases to later neurodegenerative phases remain largely elusive. Functional brain state shifts towards hyperactivity, persisting beyond relapses, represent an early maladaptive response. Here, in remission stage of an experimental autoimmune encephalitis (EAE) mouse model of RRMS, we identified a reduced excitability upon optogenetic stimulation in the brain stem, the area of active disease, while in the cortex a persistent cortical neuronal hyperactivity and synaptic remodeling emerged, accompanied with an increase of markers of early apoptosis. In contrast, hippocampal circuits, which undergo a functional state shift without hyperactivity, do not show increased apoptosis. Visual cortical networks showed a deterioration of the accuracy of encoding visual information and a decrease in the behavioural visual discrimination ability in mice. In RRMS patients in remission, we identified a reduced visual colour discrimination, indicating both the presence and the clinical relevance of early brain state maladaptation that may contribute to progression independent from relapse activity (PIRA). SummaryIn a RRMS model and in patients, impaired visual processing was reported, indicating brain state maladaptations, associated with persistent cortical hyperactivity, brain stem hypoactivity, synaptic remodeling, and apoptosis. These maladaptations might contribute to relapse-independent disease progression through sustained network dysfunction.

Traumatic brain injury (TBI) induces rapid neuroinflammatory responses not only in the brain but also in anatomically and immunologically connected central nervous system (CNS) compartments, including the retina. In our study, we investigated retinal microglial activation, retinal ganglion cell (RGC) calcium dynamics, and caspase-3 activation in adult mice subjected to severe traumatic brain injury using the Marmarou impact-acceleration model at 24 and 48 h post-injury. Carrying out Ca{superscript 2}-imaging, immunohistochemistry, and ex vivo time-lapse microscopy, we found robust microglial activation in both the superficial and deep retinal layers following TBI, accompanied by increased microglial motility. RGCs exhibited a transient surge in degeneration-induced spontaneous activity at 24 h, followed by a marked reduction below control levels at 48 h, consistent with early degenerative changes. Activated caspase-3 levels were significantly elevated in both microglia and other retinal cell types at both time points, indicating ongoing apoptotic effects. Together, these findings demonstrate that TBI rapidly triggers inflammatory and apoptotic mechanisms in the retina, which are detectable within the first 48 hours. Our results highlight the retina as a sensitive indicator of early CNS pathology after traumatic injury and underscore the potential of retinal analysis for monitoring TBI-induced neurodegeneration for future clinical implementation. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=78 SRC="FIGDIR/small/734783v1_ufig1.gif" ALT="Figure 1"> View larger version (14K): org.highwire.dtl.DTLVardef@5bc694org.highwire.dtl.DTLVardef@14a4ce4org.highwire.dtl.DTLVardef@fe2d32org.highwire.dtl.DTLVardef@149419d_HPS_FORMAT_FIGEXP M_FIG C_FIG

Systemic inflammation drives neurodegeneration, yet its differential effects across neural tissues and genetic backgrounds remain poorly understood. We performed RNA-sequencing on brain, optic nerve head (ONH), and retina from four genetically diverse mouse strains (B6, CAST, NZO, WSB) following lipopolysaccharide (LPS)-induced systemic inflammation. The ONH mounted the largest response to LPS (9510 DEGs), followed by retina (5152) and brain (4586). A conserved core of 1444 DEGs across all tissues was enriched for innate immune and acute-phase pathways. Tissue-specific responses were apparent; the retina downregulated phototransduction and visual perception genes; ONH exhibited bidirectional remodeling with upregulated proteasome and ribosome biogenesis and suppressed lipid metabolism and lysosomal function; yet the brain displayed no significant pathway level enrichment. Genetic background strongly modulated the LPS response across the three tissues; the retina exhibited the greatest strain-dependent divergence. Interestingly, differing genetic context affected the ONH response to LPS the least despite its markedly larger response to LPS overall. In totality, both genetic and physical context dictate the neuroinflammatory response to LPS.

Heat stroke is characterized by profound central nervous system dysfunction and vascular abnormalities. Previous studies have demonstrated the marked vulnerability of the CNS to thermal stress, resulting in neuronal injury and glial activation. However, the metabolic mechanisms linking acute injury to chronic neurological long-term effects remain understood. The neuropathological changes are closely associated with neuroinflammatory and metabolic disturbances, including dysregulation of the kynurenine pathway, whose metabolites modulate neurotoxicity, neuroprotection, and immune responses. Here, we present the first comprehensive characterization of kynurenine pathway metabolomic profile across both plasma and brain tissue in a mouse model of heat stroke. Using a validated and sensitive LC-MS/MS method, we simultaneously measured and quantified 13 analytes (kynurenine, kynurenic acid, quinolinic acid, nicotinic acid, picolinic acid, xanthurenic acid, anthranilic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, indole-3-acetic acid, indole-3-lactic acid, 5-hydroxyindoleacetic acid and neopterin). The findings reveal a biphasic metabolic response, characterized by an acute serotonergic disruption and reduced neuroprotective capacity, followed by chronic activation of the kynurenine pathway, depletion of central serotonin metabolites, and metabolic signatures consistent with gut microbiota dysbiosis. The acute phase is marked by a transient imbalance favoring neurotoxic kynurenine pathway metabolites, whereas the chronic phase reflects sustained pathway activation. Notably, the plasma-brain dissociation of 5-hydroxyindoleacetic acid emerged as the most prominent cross-compartment finding, suggesting a potential biomarker of central serotonergic depletion and a mechanistic link between peripheral and central metabolic changes, with implications for therapeutic targeting during the subacute recovery phase.

Traumatic brain injury (TBI) is one of the leading causes of emergency room visits in children under 10. Children are potentially more vulnerable to the adverse effects of TBI, given that their brains are still developing at the time of injury. Indeed, early life TBI has been linked to cognitive, social, and mood-related impairments later in life. The neuroimmune system has been implicated in adult TBI mechanisms and plays numerous key roles in brain development, making it an interesting candidate for linking pediatric TBI and prolonged behavioral alterations. Here we establish a rat model of mild pediatric TBI to investigate the relationship between early life TBI, acute responses of neuroimmune cells, and chronic behavioral dysregulation. At postnatal day 15, which is roughly equivalent to toddler age, male and female rat pups received a TBI via lateral fluid percussion injury. At 3 days post injury, TBI increased microglia and astrocyte coverage locally in the Perilesional Cortex but not in more distant corticolimbic regions. However, the hippocampus and prefrontal cortex did exhibit increased expression of the phagocytic marker CD68 in microglia, suggesting widespread glial activation even in the absence of gross coverage change. TBI also impacted mast cells, early-response innate immune cells, increasing their number and degranulation in multiple regions. In the juvenile and early adult periods, TBI impaired cognitive function, reduced sociability, and increased avoidance, with no change in anxiety-like behavior. Later in adulthood, TBI continued to impact cognitive behavior, increasing risky decision-making and impairing optimization months after injury. Together, these results suggest that pediatric TBI causes lasting cognitive and social dysregulation, possibly via acute neuroimmune alterations following injury at a critical period of brain development.

Microglia are essential for sculpting the developing brain, yet the molecular mechanisms that select beneficial overreactive phagocytosis remain incompletely understood. Connexin 43 (Cx43, encoded by GJA1 in humans) is best known as a gap junction and hemichannel protein, although its non canonical, channel independent functions are increasingly recognized. We found that Cx43 is highly expressed in microglia during the perinatal period in human and mouse, whereas proportion of full length multimeric Cx43 unexpectedly localizes to the nucleoplasm. Deletion of microglial Cx43 in mice during development instigates a transient neurotoxic state with microgliosis, upregulated phagocytic and complement pathways, excessive neuronal apoptosis, translating into depressive like and cognitive deficits in the adulthood. Notably, neither microglia-specific deletion of Cx43 in adulthood nor hemichannel blockade recapitulate these changes, indicating a channel independent, developmental stage-specific neuroprotective mechanism. Nucleus targeted Cx43 overexpression suppresses neurotoxic markers and neural apoptosis. Nuclear Cx43 interacts with transcriptional regulators to restrain proinflammatory gene programs, nuclear import of Cx43 is driven by neurogenic niche derived bFGF, which triggers AKT mediated phosphorylation of a C terminal nucleus localization signal (NLS), 14 3 3 binding, and importin dependent nucleus translocation. These findings reveal a developmentally restricted nuclear Cx43 function that restrains microglial neurotoxicity while promoting microglial physiological functions thus expanding connexin biology to transcriptional co regulation and pointing to a potential avenue for therapeutic intervention.

Multiple sclerosis (MS) is a chronic T cell-mediated autoimmune disease characterized by blood-brain barrier (BBB) disruption, neuroinflammation, and demyelination of the central nervous system (CNS). Emerging evidence links gut microbiota to disease pathogenesis, but the microbial factors that regulate pathogenic microRNA (miRNA) programs are largely unknown. Here, using experimental autoimmune encephalomyelitis (EAE, a MS mouse model), we investigated whether gut microbiota exacerbate EAE pathogenesis by modulating host miRNA expression. Antibiotic-induced depletion of the gut microbiota markedly attenuated EAE scores and reduced circulating inflammatory miRNAs, with miR-21 emerging as the dominant pathogenic candidate. Functional inhibition of miR-21 significantly ameliorated disease severity and reduced CNS T-cell infiltration. Mechanistically, miR-21 enhanced IL-17 and GM-CSF production by CD4 T cells and promoted immune-cell entry into the CNS through endothelial activation and blood-brain barrier dysfunction. We identified a transient expansion of Akkermansia muciniphila during the prodromal phase of EAE that positively correlated with circulating miR-21 levels. Colonization of antibiotic-treated mice with A. muciniphila exacerbated EAE and increased serum miR-21, whereas monocolonization of germ-free mice was insufficient to induce systemic miR-21, indicating a requirement for an inflammatory host environment. Further analyses revealed that atypical lipopolysaccharides (LPS) derived from A. muciniphila induce epithelial miR-21 production through coordinated TLR2/TLR4 signaling. Circulating miR-21 subsequently promoted endothelial dysfunction through the TIMP3-ADAM17 pathway, facilitating pathogenic T-cell migration into the CNS. Importantly, circulating miR-21 was also elevated in patients with MS. Collectively, these findings identify a previously unrecognized A. muciniphila-LPS-miR-21 axis linking gut dysbiosis to neuroinflammation and suggest that host-derived miRNAs function as systemic mediators through which microbial signals influence CNS autoimmunity.

Traumatic brain injury (TBI) is a characteristic feature of neurodegenerative diseases such as Alzheimers disease and chronic traumatic encephalopathy. Small animal models have been used to establish clinically relevant biomarkers of neuropathology, however, they show significant anatomical differences from humans and are affected by artificial experimental manipulations, making them often unsuitable for longitudinal study of repetitive mild TBI. Building on a previous study of neuropathology in headbutting bovids in the wild, this pilot study investigated whether freely headbutting domestic goats, which naturally engage in low-intensity, high-frequency head impacts, accumulate measurable biomarkers of neurodegeneration in cerebrospinal fluid (CSF) and brain tissue. Over a six-month period, three male goats (Capra hircus) were allowed to freely headbutt under continuous video surveillance. Monthly CSF samples were collected, and concentrations of key neurodegeneration biomarkers were measured via multiplex immunoassays, including amyloid {beta} ; peptides (A {beta} 40, A {beta} 42), total and phosphorylated tau (tTau and pTau), glial fibrillary acidic protein (GFAP), S100 calcium-binding protein B (S100B), and neurofilament M (NF-M). Postmortem immunohistochemistry was conducted on prefrontal cortical tissues using antibodies targeting pTau, GFAP, and S100B. Head impact kinematics were quantified using horn-mounted accelerometer and inclinometer sensors that recorded linear acceleration, rotational velocity, and head orientation during naturally occurring headbutting events. Several notable trends were observed. Phosphorylated tau as well as reactive astrocytes were detected in the brain tissue, mirrored by elevated GFAP detected in the CSF. PET TSPO was unsuccessful, however, FDG PET revealed frontal-dominant activity in all goats, and one with asymmetrical activation. Overall, the goats sustained 5,000-7,000 head impacts each over six months, with forces up to 388 N and peak acceleration up to 16.5 g. This multi-modal observational study is the first to characterize neurodegeneration biomarkers and kinematics in headbutting goats. Even at one year old, the combination of pTau and gliosis in both the brain tissue and CSF indicates that the goat s repetitive head impacts begin to show neurodegenerative consequences early in life. Likely, the severity of these consequences increases with headbutts and age, eventually resulting in chronic neurodegeneration. This system shows promise as a large-animal model for the longitudinal study of the onset and progression of neurodegenerative disease.

Long non-coding RNAs (lncRNAs) are increasingly recognized as regulators of cellular identity and disease associated gene expression programs, yet their role in astrocyte reactivity remains poorly understood. Here, we profiled lncRNA expression in primary mouse astrocytes exposed to inflammatory activation paradigms that model microglia driven signaling. This identified a conserved set of activation responsive lncRNAs, among which Gm16685 emerged as one of the most strongly induced candidates. Gm16685 and its human homolog MITA1 were enriched in the nucleus, and MITA1 expression was increased in selected human datasets from Alzheimer's disease, Parkinson's disease and frontotemporal dementia patients. Functional depletion of Gm16685 attenuated inflammatory gene expression and several activation associated astrocyte phenotypes, including reactive oxygen species production, glutamate handling, phagocytic activity and proliferation. Time-resolved transcriptomic analysis indicated that Gm16685 is required for the timely induction of inflammatory response genes. Mechanistically, Gm16685/MITA1 interacted with the RNA binding protein PCBP2, and Gm16685 depletion was associated with reduced PCBP2 protein abundance, altered splicing of Inhibitor of NF-{kappa}B Kinase Subunit Beta (IKK{beta}) and a shift in downstream inflammatory signaling. Together, our findings identify Gm16685/MITA1 as a conserved lncRNA regulator of astrocyte reactivity and suggest that non-coding RNA dependent control of RNA binding proteins contributes to inflammatory signaling in neurodegenerative disease relevant contexts.

Perinatal ischemic stroke is an early developmental brain injury caused by obstruction of cerebral blood vessels and is a leading cause of cerebral palsy and cognitive disability in survivors. However, progress in understanding its impact on the brain and other organ systems, as well as in developing effective therapies, remains limited, in part due to the scarcity of relevant preclinical models. Here, we induced ischemic stroke via middle cerebral artery occlusion in perinatal mice and investigated its effects within and beyond the brain across development into adulthood. We found that perinatal stroke disrupted fine motor development and impaired memory. In addition, it induced structural alterations in skeletal muscle and significant changes in gut microbiota composition. Notably, gut-targeted intervention using fecal microbiota transplantation improved fine motor function. Our findings demonstrate, for the first time, the multisystem developmental impact of perinatal stroke, extending beyond the brain, and identify gut microbiota modulation as a promising and potentially safe therapeutic strategy to improve motor outcomes after stroke.

Neurodegeneration is a major determinant of disability progression in multiple sclerosis (MS), yet the pathophysiological mechanisms associating inflammation to neuronal insult remain poorly understood. We recently identified Dendritic Syntaphilin Intrusion (DSI), a novel excitoxicity pathway in which the axonal mitochondrial anchor syntaphilin (SNPH) aberrantly translocates into dendrites, causing neurodegeneration in a non-inflammatory model of MS. However, whether this protein intrudes abruptly into dendrites in inflammatory MS pathology is still not clear. Here, we investigated the role of synaptic and extrasynaptic NMDA receptors (NMDAR) in regulating the intrusion of Syntaphilin into dendrites. Using primary hippocampal neuronal cultures, we examined how the balance between synaptic GluN2A-containing and extrasynaptic GluN2B-containing NMDARs influences DSI under inflammatory conditions. Pharmacological and viral-mediated approaches were employed to manipulate NMDAR subtype activity and evaluate their impact on DSI. Inflammatory cytokines discernibly sensitized neurons to DSI. Our results revealed that blockade of synaptic NMDARs significantly increased DSI, whereas inhibition of extrasynaptic NMDARs reduced DSI. These findings demonstrate opposing roles of NMDAR subtypes, with GluN2A-containing synaptic receptors inhibiting DSI and fostering neuronal survival, while GluN2B-containing extrasynaptic receptors enhancing DSI and neurodegenerative signaling. Manipulation of the GluN2A/GluN2B balance showed opposite effect on DSI, suggesting a relationship between NMDAR subtype signaling and SNPH mislocalization. Overall, our findings extend the relevance of DSI from non-inflammatory MS to inflammatory MS and identify DSI as a downstream convergence point linking inflammatory cytokines and excitotoxic NMDAR signaling to neuronal insult. These results reveal DSI as a potential mechanistic link between inflammatory signaling and excitotoxic neuronal injury and indicate that modulation of GluN2B-dependent pathways warrants further investigation in inflammatory neurodegenerative disorders.

Epileptogenesis is accompanied by robust neuroinflammation, yet the molecular pathways linking innate immune activation to neuronal dysfunction remain incompletely defined. Given the established pro-inflammatory role of the stimulator of interferon genes (STING), we initially hypothesized that its loss would attenuate neuroinflammatory responses during epileptogenesis. Contrary to our expectation, we found that STING deficiency instead amplified microglial activation. Using a kainic acid mouse model of temporal lobe epilepsy (TLE), we show that STING-deficient microglia exhibit pronounced lysosomal expansion and enhanced phagocytic engulfment of neurons, leading to increased hippocampal neuronal loss and cognitive impairment. Mechanistically, STING deficiency increased the expression and altered the subcellular distribution of stromal interaction molecule 1 (STIM1), an endoplasmic reticulum Ca2+ sensor that mediates store-operated calcium entry (SOCE), resulting in dysregulated intracellular calcium dynamics and elevated SOCE activity. Pharmacological inhibition of SOCE reduced microglia-neuron interactions and microglial phagocytic engulfment, improved neuronal survival in the CA3 region of the hippocampus, and rescued cognitive deficits following status epilepticus. Collectively, these findings redefine STING as a negative regulator of microglial activation and identify a previously unrecognized STING-STIM1-SOCE axis that constrains calcium-dependent microglial phagocytosis during epileptogenesis, highlighting microglial calcium signaling as a potential therapeutic target in TLE.

BackgroundExtracellular matrix (ECM) remodeling is increasingly recognized as an important component of neuroinflammatory pathology in multiple sclerosis (MS), yet the mechanisms by which CNS cells sense and respond to alterations in their mechanical environment and the spatial across which mechanical changes can influence cellular behavior remain poorly understood. Piezo1 is a mechanosensitive ion channel that regulates cellular responses to mechanical stimuli and has recently emerged as a potential modulator of neuroinflammation. MethodsExperimental autoimmune encephalomyelitis (EAE) was induced in C57BL/6 wildtype mice using myelin oligodendrocyte glycoprotein (MOG):35-55. Immunohistochemical analyses were performed in spinal cord gray matter (GM), normal-appearing white matter (NAWM), and white matter lesion (LES) regions to assess ECM remodeling, total Piezo1 expression, and astrocyte-specific Piezo1 expression during acute and chronic EAE stages. Correlations with clinical EAE severity were determined. In parallel, mixed primary murine glial cultures were exposed to substrates of different stiffness and analyzed by transcriptomic profiling to investigate mechanobiological responses in vitro. ResultsECM-associated proteins, including glial fibrillary acidic protein (GFAP), fibronectin-1 and matrix metalloproteinase-3 (MMP3), were regionally upregulated during EAE, indicating widespread tissue remodeling beyond focal inflammatory lesions. Total Piezo1 expression was increased within lesions and transiently elevated in GM, whereas astrocyte-specific Piezo1 remained persistently upregulated during both acute and chronic EAE. Astrocytic Piezo1 expression correlated closely with ECM remodeling and clinical EAE severity, particularly in GM and NAWM. Notably, both total and astrocyte-specific Piezo1 showed stronger associations with clinical disability than classical inflammatory markers. Transcriptomic analysis revealed pronounced stiffness-dependent responses in glial cells, including alterations in extracellular matrix organization, cytokine signaling, cell adhesion, and proliferative pathways. ConclusionsOur findings identify astrocytic Piezo1 as a prominent component of neuroinflammatory tissue remodeling during EAE. The close association of Piezo1 with ECM alterations, clinical disease severity, and stiffness-dependent glial responses supports a link between neuroinflammation and mechanosensory signaling. These results highlight mechanosensation as a potentially important contributor to CNS pathology and establish Piezo1 alteration as a candidate biomarker for neuroinflammatory disease.

Glioblastoma is characterized by spatial heterogeneity, with tumor-core and invasive-edge regions differing in cellular composition, transcriptional state, and metabolic context. Spatial transcriptomics has improved understanding of glioblastoma tissue organization. However, cellular transcriptional programs and metabolic interpretation remain poorly resolved. Here, single-cell matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) with spatial transcriptomics were integrated on the same tissue sections to map lipid and transcriptomic organization across matched tumor-core and invasive-region samples from 10 glioblastoma patients. Common region-dependent cellular organization along the core - versus invasive regions were identified after accounting for patient specific signatures. Tumor cores were enriched with astrocyte-like malignant and immune cell types, whereas invasive regions showed increased contribution from oligodendrocyte (progenitor cells). Despite these compositional differences, tumor and invasive cells had a shared transcriptional state space, indicating that regional identity is shaped by altered spatial organization of shared cell states. Transcriptional programs associated with proliferation, hypoxia, extracellular matrix remodeling, tumor associated macrophages and microglia (TAMs) phagocytic activity, T-cell infiltration, and lipid synthesis were spatially structured and differed between tumor and invasive compartments. MALDI-MSI revealed broad lipidomic remodeling across these regions. Tumor regions were enriched in membrane and storage lipid classes, whereas invasive regions showed relative enrichment of lipid species associated with membrane turnover. Integrating lipid and transcriptomic layers revealed spatial lipid-gene program coupling, with tumor cores showing stronger and more coherent coupling than invasive regions. TAM phagocytic activity co-localized with cholesteryl ester abundance, while lipid synthesis coupled to phosphatidylcholine-rich astrocyte-like tumor niches. Exploratory analysis indicated that MGMT promoter methylation may be associated with this altered lipid-transcriptional coupling, particularly in TAM-associated lipid-handling programs. Together, these findings imply that spatial coordination between lipid states and transcriptional programs is a key feature of glioblastoma metabolic heterogeneity.

Pancreatic cancer (PC) exhibits a striking association with depression, with neuropsychiatric symptoms frequently preceding diagnosis. However, the biological mechanisms linking pancreatic tumor development to central nervous system dysfunction remain poorly understood. Here, we investigated the impact of PC progression on adult hippocampal neurogenesis using complementary orthotopic xenograft and genetically engineered mouse models. Tumor-bearing mice developed depressive-like behavioral abnormalities accompanied by reduced adult hippocampal neurogenesis, including depletion of neural stem cell populations and immature neurons in both dorsal and ventral dentate gyrus regions. In the genetic model, neurogenic impairment progressed in parallel with disease severity. Exposure of primary hippocampal neural stem cells to serum derived from tumor-bearing mice selectively impaired cell survival, indicating that circulating factors are sufficient to compromise neurogenic capacity. Consistent with this, cytokine profiling revealed profound systemic inflammatory alterations, with IL-6 emerging as the only cytokine consistently elevated across both models. Together, our findings identify disruption of the adult hippocampal neurogenic niche as a previously unrecognized consequence of pancreatic cancer progression and provide a biological framework for pancreatic cancer-associated depression.

BackgroundPhospholipase C gamma-2 (PLC{gamma}2) catalyzes the hydrolysis of the membrane phosphatidylinositol-4,5-bisphosphate (PIP2) to form diacylglycerol (DAG) and inositol trisphosphate (IP3), feeding into diverse downstream signaling pathways. PLCG2 polymorphisms have been associated with reduced and/or increased risk of Alzheimers disease (AD) and related dementias, longevity, autoinflammation, and immune disorders. In the brain, PLC{gamma}2 is expressed in microglia, and other neuroimmune and vascular interface populations, yet its role in brain homeostasis remains incompletely defined. MethodsWe analyzed the brains of three-month-old Plcg2 wild-type (WT), heterozygous (Het KO) and homozygous knockout (Homo KO) littermate mice modeling human PLCG2 loss-of-function risk alleles linked to AD risk using a multiomic approach that included lipidomics, metabolomics, proteomics, and transcriptomics, together with immunofluorescence, as well as flow-cytometric profiling of peripheral and brain-draining immune compartments. ResultsPlcg2 deficiency substantially impaired early survival and produced splenomegaly without increasing total spleen cellularity, instead shifting spleen composition toward myeloid/innate-enriched cells and away from B cells, with expansion of age-associated B-cell (ABC-like) subsets and parallel reductions in CD4 and CD8 regulatory T cells in spleen and cervical lymph nodes. Brain lipidomics revealed selective depletion of PIP2, despite very low bulk PLC{gamma}2 protein abundance relative to other PLC family members. PLC{gamma}2 loss led to significant reductions in myelin-enriched lipid classes and myelin/paranode-associated proteins, accompanied by compensatory upregulation of oligodendrocyte/myelin genes, and modest shifts in microglial, lysosomal, complement, and oxidative metabolism pathways by NanoString and DIA-MS. Targeted acylcarnitine profiling demonstrated reprogramming of brain oxidative metabolism, with increased short-, medium-, and long-chain acylcarnitines and enrichment of mitochondrial matrix fatty-acid and amino-acid catabolic enzymes in Homo KO brains. ConclusionsLoss of PLC{gamma}2 installs a coordinated program that compromises systemic immune tolerance and subtly erodes central myelin and phosphoinositide homeostasis while enhancing brain oxidative metabolism, effects that extend beyond microglial phagocytic signaling and may underlie increased vulnerability to AD pathology and aging, providing a mechanistic framework for how PLCG2 variation may link systemic immune regulation, white-matter integrity, and neurodegenerative risk. LimitationsBecause constitutive Plcg2 Homo KO mice display high early mortality and intestinal vascular abnormalities, observed phenotypes may reflect developmental compensation and may not fully recapitulate protective human PLCG2 variants.

We showed before that the endogenous peptide Nociceptin blocks the premature differentiation of oligodendrocytes (OLGs), preventing untimely precocious myelination in the developing brain. Consistent with this early function, Nociceptin brain expression is developmentally regulated, sharply decreasing with the initiation and progression of myelination. However, we now found that at difference with controls and relapsing-remitting multiple sclerosis (RRMS), Nociceptin levels are highly elevated in cerebrospinal fluid from patients with the most severe progressive MS (PMS) forms. This questioned whether Nociceptin early developmental effects could be latter recapitulated, interfering with remyelination in PMS. This possibility was tested by inducing experimental autoimmune encephalomyelitis in older mice, at an age equivalent to that with increased risk of RRMS transition into PMS. Older animals develop persistently highly debilitating clinical symptoms, and display both brain and spinal cord demyelination. Importantly, these mice exhibit elevated brain Nociceptin levels, and their treatment with an antagonist of the Nociceptin receptor (NOR) elicits a regression of clinical scoring that is accompanied by higher ratios of OLGs/OLG progenitor cells, increased myelination, and reduction of reactive astrocytes. These findings suggest that Nociceptin may be a crucial player in the age-related progression of MS; interfering with OLG maturation and remyelination, and perhaps further exacerbating neurological dysfunction by targeting astrocyte populations. The upregulation of Nociceptin secretion by human astrocytes in response to proinflammatory cytokines, also points to this peptide as a mediator of microglia-astrocyte interactions supporting MS progression with aging. NOR may offer a novel pharmacological target for ameliorating the devastating effects of MS progression.

Progressive and chronic neuroinflammation is associated with numerous neurodegenerative diseases, including primary tauopathies such as frontotemporal dementia and progressive supranuclear palsy. Unlike Alzheimer's disease, there is no clear genetic association implicating microglial dysfunction as a primary driver of tauopathy. As such, the contributions of microglia to tauopathy pathogenesis have been less well defined. Here, we explore the cell autonomous effects of the pathogenic MAPT-S305N variant on microglial function, across two distinct iPSC-microglia protocols, followed by examination of the non-cell autonomous effects of microglial MAPT genotype on neuronal health and function. We find that different protocols produce cells of equivalent microglial identity, but result in microglia in different functional states, thereby influencing reactivity and detectable phenotypes. Regardless, across both protocols we find that MAPT-S305N induces microglial hypoactivity, evidenced by impaired phagocytosis, reduced cytokine release and diminished regulation of synaptic function. We conclude that microglial hypoactivity may be an early event in disease pathogenesis, where MAPT mutation microglia fail to adequately respond to pathogenic stimuli, thereby contributing to subsequent neuronal vulnerability and susceptibility. Further studies are required to understand how and when this initial hypoactive state may switch to a toxic pro-inflammatory state, and whether early detection and correction may be of therapeutic value.

Microbes residing in the gastrointestinal tract exert immunomodulatory impacts on the brain through the gut-brain axis. Short-chain fatty acids (SCFAs) produced by bacterial fermentation of dietary fiber can enter the brain parenchyma and are implicated in microglia-mediated inflammation. While the gut microbiome is required to maintain microglial homeostasis, the mechanisms by which microbiota-derived metabolites affect microglia remains unknown. We examined the roles of SCFAs, specifically butyrate, propionate and acetate, on microglial function in response to SCFAs both in vitro using BV2 cells and in vivo in mice. We observed in vivo that SCFAs impact microglial transcriptional responses to LPS in a sex- and metabolite-specific manner with butyrate having the strongest effect. Enriched gene sets included signatures associated with LPS responsive microglia, Arg1 positive microglia, microglial cell cycle related genes and genes affiliated with changes in microglial morphology. We observed a similar effect in vitro, where metabolite administration enhanced phagocytosis, blunted proliferation and nitric oxide production. We then evaluated global histone modification levels following metabolite treatment and detected an enhancement of H3K9ac, H3K27ac, and H3K4me3 both in vivo and in BV2 cells treated with butyrate. Finally, we showed that butyrate is a potent HDAC inhibitor possibly contributing to enhanced acetylation. Hence, our findings suggest that SCFAs impact microglial function in a metabolite- and sex-specific manner, and that butyrate blunts inflammation by regulating microglial histone acetylation. Our results provide a more in-depth understanding of gut microbiome-microglia crosstalk, opening the door for new microbiome- and microglia-targeted therapies.