Microglial morphology in Alzheimer’s disease and after Aβ immunotherapy

Microglia are the brain immune cells and their function is highly dependent on cell motility. It was hypothesised that morphological variability leads to differences in motility, ultimately impacting on the microglial function. Here, we assessed microglial morphology in 32 controls, 44 Alzheimer’s disease (AD) cases and 16 AD cases from patients immunised against Aβ42 (iAD) using 2D and 3D approaches. Our 2D assessment showed an increased number of microglia in iAD vs. AD (P = 0.032) and controls (P = 0.018). Ramified microglia were fewer in AD vs. controls (P = 0.041) but increased in iAD compared to AD (P < 0.001) and controls (P = 0.006). 3D reconstructions highlighted larger cell bodies in AD vs. controls (P = 0.049) and increased total process length in iAD vs. AD (P = 0.032), with negative correlations detected for pan-Aβ load with total process length (P < 0.001) in AD and number of primary processes (P = 0.043) in iAD. In summary, reactive/amoeboid microglia are the most represented population in the aged human brain. AD does not affect the number of microglia, but the ramified population is decreased adopting a more reactive morphology. Aβ removal by immunotherapy leads to increased ramified microglia, implying that the cells retain plasticity in an aged disease brain meriting further investigation.

The Role of Microglia in the Polycystic Ovary Syndrome (PCOS)-Like Brain

Polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility, affecting roughly 1 in 8 women of reproductive age. Accumulating evidence from animal models suggests that the brain plays a key role in the development and maintenance of PCOS. In a well-characterised prenatally androgenised (PNA) mouse model of PCOS, aberrant neuronal wiring associated with PCOS deficits in adulthood are detected as early as postnatal day (P) 25, prior to disease onset. However, the mechanisms by which prenatal androgen exposure alters brain wiring remains unknown. Microglia, the immune cells of the brain, are active sculptors of neuronal wiring across development, mediating both the formation and removal of neuronal inputs. Therefore, microglia may play an important role in driving the abnormal neuronal wiring that leads to PCOS-like features in the PNA brain. Here, to assess whether microglia are altered in the brain of PNA mice, microglia number and morphology-associated activation states were quantified in two hypothalamic regions implicated in fertility regulation. Microglia were identified by immunolabelling for the microglia-specific marker, Iba-1, across developmental timepoints, including embryonic day 17.5, P0, P25, P40 and P60 (n = 7–14/group). At P0, PNA mice had significantly fewer “activated” amoeboid microglia compared to controls (P &lt; 0.05). Later in development at P25, PNA mice exhibited significantly fewer “sculpting” microglia (P &lt; 0.001), whereas at P60, PNA mice possessed a greater number of “activated” amoeboid microglia relative to controls (P &lt; 0.01). This study demonstrates time-specific changes in the number and morphology of microglia in a mouse model of PCOS and suggests a role for microglia in driving the brain wiring abnormalities associated with PCOS. These findings support the need for future functional experiments to determine the relative importance of microglia function in shaping the PCOS-like brain and associated reproductive dysfunction.

Effects of Early-Life Stress, Postnatal Diet Modulation and Long-Term Western-Style Diet on Peripheral and Central Inflammatory Markers

Early-life stress (ES) exposure increases the risk of developing obesity. Breastfeeding can markedly decrease this risk, and it is thought that the physical properties of the lipid droplets in human milk contribute to this benefit. A concept infant milk formula (IMF) has been developed that mimics these physical properties of human milk (Nuturis®, N-IMF). Previously, we have shown that N-IMF reduces, while ES increases, western-style diet (WSD)-induced fat accumulation in mice. Peripheral and central inflammation are considered to be important for obesity development. We therefore set out to test the effects of ES, Nuturis® and WSD on adipose tissue inflammatory gene expression and microglia in the arcuate nucleus of the hypothalamus. ES was induced in mice by limiting the nesting and bedding material from postnatal day (P) 2 to P9. Mice were fed a standard IMF (S-IMF) or N-IMF from P16 to P42, followed by a standard diet (STD) or WSD until P230. ES modulated adipose tissue inflammatory gene expression early in life, while N-IMF had lasting effects into adulthood. Centrally, ES led to a higher microglia density and more amoeboid microglia at P9. In adulthood, WSD increased the number of amoeboid microglia, and while ES exposure increased microglia coverage, Nuturis® reduced the numbers of amoeboid microglia upon the WSD challenge. These results highlight the impact of the early environment on central and peripheral inflammatory profiles, which may be key in the vulnerability to develop metabolic derangements later in life.

PET Imaging of Peripheral Benzodiazepine Receptor Standard Uptake Value Increases After Controlled Cortical Impact, a Rodent Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a chronic, life threatening injury for which few effective interventions are available. Evidence in animal models suggests un-checked immune activation may contribute to the pathophysiology. Changes in regional density of active brain microglia can be quantified in vivo with positron emission topography (PET) with the relatively selective radiotracer, peripheral benzodiazepine receptor 28 (11 C-PBR28). Phenotypic assessment (activated vs resting) can subsequently be assessed (ex vivo) using morphological techniques. To elucidate the mechanistic contribution of immune cells in due to TBI, we employed a hybrid approach involving both in vivo (11 C-PBR28 PET) and ex vivo (morphology) to elucidate the role of immune cells in a controlled cortical impact (CCI), a rodent model for TBI. Density of activated brain microglia/macrophages was quantified 120 hours after injury using the standardized uptake value (SUV) approach. Ex vivo morphological analysis from specific brain regions using IBA-1 antibodies differentiated ramified (resting) from amoeboid (activated) immune cells. Additional immunostaining of PBRs facilitated co-localization of PBRs with IBA-1 staining to further validate PET data. Injured animals displayed greater PBR28suv when compared to sham animals. Immunohistochemistry demonstrated elevated density of amoeboid microglia/macrophages in the ipsilateral dentate gyrus, corpus callosum, thalami and injury penumbra of injured animals compared to sham animals. PBR co-stained with amoeboid microglia/macrophages in the injury penumbra and not with astrocytes. These data suggest the technologies evaluated may serve as bio-signatures of neuroinflammation following severe brain injury in small animals, potentially enabling in vivo tracking of neuroinflammation following TBI and cellular-based therapies.

Purinergic Signaling Participates in a Transition Between Functional States of Reactive Microglia and Controls Astrocyte-Driven Neuroinflammation in the Model of Trimethyltin-Induced Neurodegeneration

BackgroundThe present study aims to explore the involvement of purinergic signaling in the rodent model of hippocampal degeneration induced by trimethyltin (TMT), which results in behavioral and neurological dysfunction similar to Alzheimer’s disease. Our study has provided novel evidence that TMT induced extracellular depositions of amyloid β, which might be the cause of the well-defined progressive hippocampal neurodegeneration and gliosis. MethodsWe have applied enzyme histochemistry and immunohistochemistry to study spatial and temporal patterns of ectonucleotidase NTPDase1/CD39 and eN/CD73 expression, gene expression analysis and immunochemistry to analyze cellular localization of select purinoreceptors and pro-inflammatory cytokines previously associated with microglia and astrocytes activation. ResultsOur study demonstrated that all Iba1-ir microglial cells, irrespective of the cell shape and localization, upregulated NTPDase1/CD39, while the induction of eN/CD73 has been observed only at amoeboid microglia, localized within the hippocampal layers with pronounced cell death. Marked induction of P2Y12R and P2Y6R at amoeboid microglia might reflect the transition from rod to amoeboid microglia and the adaptation to the migratory and phagocytic properties of the latter. Based on the expression of the microglial polarization markers, the majority of microglia belonged to the M2-like functional state. A significant change in purinergic signaling components accompanied the response of reactive astrocytes, which occupied the areas with pronounced cell death. Reactive astrocytes, which markedly expressed adenosine A2A and P2Y1 receptors, showed massive induction of complement component C3, NF-kB and IL-1β, suggesting that astrocyte-derived inflammation might be responsible for prolonged and spreading neurodegeneration in TMT model.ConclusionThis study put glia-associated purinergic signaling in the center of molecular pathogenesis of AD-like disease. Our findings suggest that the ectonucleotidases and purinergic signaling play significant role in microgliosis, astrocyte-driven neuroinflammation and prolonged neurodegeneration in the TMT model.