Amniotic mesenchymal cells from pre‐eclamptic placentae maintain immunomodulatory features as healthy controls

Pre‐eclampsia (PE) is one of the most severe syndromes in human pregnancy, and the underlying mechanisms of PE have yet to be determined. Pre‐eclampsia is characterized by the alteration of the immune system's activation status, an increase in inflammatory Th1/Th17/APC cells, and a decrease in Th2/Treg subsets/cytokines. Moreover, inflammatory infiltrates have been detected in the amniotic membranes of pre‐eclamptic placentae, and to this date limited data are available regarding the role of amniotic membrane cells in PE. Interestingly, we and others have previously shown that human amniotic mesenchymal stromal cells (hAMSC) possess anti‐inflammatory properties towards almost all immune cells described to be altered in PE. In this study we investigated whether the immunomodulatory properties of hAMSC were altered in PE. We performed a comprehensive study of cell phenotype and investigated the in vitro immunomodulatory properties of hAMSC isolated from pre‐eclamptic pregnancies (PE‐hAMSC), comparing them to hAMSC from normal pregnancies (N‐hAMSC). We demonstrate that PE‐hAMSC inhibit CD4/CD8 T‐cell proliferation, suppress Th1/Th2/Th17 polarization, induce Treg and block dendritic cells and M1 differentiation switching them to M2 cells. Notably, PE‐hAMSC generated a more prominent induction of Treg and higher suppression of interferon‐γ when compared to N‐hAMSC, and this was associated with higher transforming growth factor‐β1 secretion and PD‐L2/PD‐L1 expression in PE‐hAMSC. In conclusion, for the first time we demonstrate that there is no intrinsic impairment of the immunomodulatory features of PE‐hAMSC. Our results suggest that amniotic mesenchymal stromal cells do not contribute to the disease, but conversely, could participate in offsetting the inflammatory environment which characterizes PE.     

Complement component 3 inhibition by an antioxidant is neuroprotective after cerebral ischemia and reperfusion in mice

Oxidative stress after stroke is associated with the inflammatory system activation in the brain. The complement cascade, especially the degradation products of complement component 3, is a key inflammatory mediator of cerebral ischemia. We have shown that pro‐inflammatory complement component 3 is increased by oxidative stress after ischemic stroke in mice using DNA array. In this study, we investigated whether up‐regulation of complement component 3 is directly related to oxidative stress after transient focal cerebral ischemia in mice and oxygen‐glucose deprivation in brain cells. Persistent up‐regulation of complement component 3 expression was reduced in copper/zinc‐superoxide dismutase transgenic mice, and manganese‐superoxide dismutase knock‐out mice showed highly increased complement component 3 levels after transient focal cerebral ischemia. Antioxidant N‐tert‐butyl‐α‐phenylnitrone treatment suppressed complement component 3 expression after transient focal cerebral ischemia. Accumulation of complement component 3 in neurons and microglia was decreased by N‐tert‐butyl‐α‐phenylnitrone, which reduced infarct volume and impaired neurological deficiency after cerebral ischemia and reperfusion in mice. Small interfering RNA specific for complement component 3 transfection showed a significant increase in brain cells viability after oxygen‐glucose deprivation. Our study suggests that the neuroprotective effect of antioxidants through complement component 3 suppression is a new strategy for potential therapeutic approaches in stroke.     

FK506 ameliorates cell death features in Huntington's disease striatal cell models

Huntington’s disease (HD) is a genetic neurodegenerative disorder characterized by striatal neurodegeneration, involving apoptosis. FK506, an inhibitor of calcineurin (or protein phosphatase 3, formerly known as protein phosphatase 2B), has shown neuroprotective effects in several cellular and animal models of HD. In the present study, we show the protective effects of FK506 in two striatal HD models, primary rat striatal neurons treated with 3-nitropropionic acid (3-NP) and immortalized striatal STHdh cells derived from HD knock-in mice expressing normal (STHdh^7/7) or full-length mutant huntingtin (FL-mHtt) with 111 glutamines (STHdh^111/111), under basal conditions and after exposure to 3-NP or staurosporine (STS). In rat striatal neurons, FK506 abolished 3-NP-induced increase in caspase-3 activation, DNA fragmentation/condensation and necrosis. Nevertheless, in STHdh^111/111 cells under basal conditions, FK506 did not prevent, in a significant manner, the release of cytochrome c and apoptosis inducing factor (AIF) from mitochondria, or alter Bax/Bcl-2 ratio, but significantly reverted caspase-3 activation. In STHdh^111/111 cells treated with 0.3 mM 3-NP or 25 nM STS, linked to high necrosis, exposure to FK506 exerted no significant effects on caspase-3 activation. However, treatment of STHdh^111/111 cells exposed to 10 nM STS with FK506 effectively prevented cell death by apoptosis and moderate necrosis. The results suggest that FK506 may be neuroprotective against apoptosis and necrosis under mild cell death stimulus in the presence of FLmHtt.     

Human amniotic mesenchymal stem cells inhibit hepatocellular carcinoma in tumour‐bearing mice

Hepatocellular carcinoma (HCC) is the third leading cause of the cancer‐related death in the world. Human amniotic mesenchymal stem cells (hAMSCs) have been characterized with a pluripotency, low immunogenicity and no tumorigenicity. Especially, the immunosuppressive and anti‐inflammatory effects of hAMSCs make them suitable for treating HCC. Here, we reported that hAMSCs administrated by intravenous injection significantly inhibited HCC through suppressing cell proliferation and inducing cell apoptosis in tumour‐bearing mice with Hepg2 cells. Cell tracking experiments with GFP‐labelled hAMSCs showed that the stem cells possessed the ability of migrating to the tumorigenic sites for suppressing tumour growth. Importantly, both hAMSCs and the conditional media (hAMSC‐CM) have the similar antitumour effects in vitro, suggesting that hAMSCs‐derived cytokines might be involved in their antitumour effects. Antibody array assay showed that hAMSCs highly expressed dickkopf‐3 (DKK‐3), dickkopf‐1 (DKK‐1) and insulin‐like growth factor‐binding protein 3 (IGFBP‐3). Furthermore, the antitumour effects of hAMSCs were further confirmed by applications of the antibodies or the specific siRNAs of DKK‐3, DKK‐1 and IGFBP‐3 in vitro. Mechanically, hAMSCs‐derived DKK‐3, DKK‐1 and IGFBP‐3 markedly inhibited cell proliferation and promoted apoptosis of Hepg2 cells through suppressing the Wnt/β‐catenin signalling pathway and IGF‐1R‐mediated PI3K/AKT signalling pathway, respectively. Taken together, our study demonstrated that hAMSCs possess significant antitumour effects in vivo and in vitro and might provide a novel strategy for HCC treatment clinically.     

Conditioned media from adipocytes promote proliferation,migration, and invasion in melanoma and colorectal cancer cells

Epidemiological evidence suggests that obesity can significantly increase the risk of various cancers, although the mechanisms underlying this link are completely unknown. Here, we analyzed the effect of adipocytes on melanoma and colon cancer cells proliferation, migration, and invasion. The potential effects of conditioned media (CM) obtained from differentiated mouse 3T3-L1 cells and human adipose tissue-derived mesenchymal stem cells (hAMSC) on the proliferation, migration, and invasion of B16BL6 melanoma and colon 26-L5 cancer cells were investigated. The 3T3-L1 and hAMSC CM increased cell proliferation, migration, and invasion in both the cell lines. In addition, adipocytes CM increased matrix metalloproteinase 9 (MMP-9) and MMP-2 activity in both B16BL6 and colon 26-L5 cells. These effects were found to be associated with an increased expression of various oncogenic proteins in B16BL6 and colon 26-L5 cells. Also, adipocyte CM induced Akt and mTOR activation in both tumor cell lines, and the pharmacological inhibition of Akt and mTOR blocked the CM induced Akt as well as mTOR activation and CM-stimulated melanoma and colon cancer cell proliferation, migration, and invasion. These data suggest that adipocyte promotes melanoma and colon cancer progression through modulating the expression of diverse proteins associated with cancer growth and metastasis as well as modulation of the Akt/mTOR signaling.     

Dl‐3‐n‐butylphthalide attenuates acute inflammatory activation in rats with spinal cord injury by inhibiting microglial TLR4/NF‐κB signalling

In this study, we examined the neuroprotective effects and anti‐inflammatory properties of Dl‐3‐n‐butylphthalide (NBP) in Sprague‐Dawley (SD) rats following traumatic spinal cord injury (SCI) as well as microglia activation and inflammatory response both in vivo and in vitro. Our results showed that NBP improved the locomotor recovery of SD rats after SCI an significantly diminished the lesion cavity area of the spinal cord, apoptotic activity in neurons, and the number of TUNEL‐positive cells at 7 days post‐injury. NBP inhibited activation of microglia, diminished the release of inflammatory mediators, and reduced the upregulation of microglial TLR4/NF‐κB expression at 1 day post‐injury. In a co‐culture system with BV‐2 cells and PC12 cells, NBP significantly reduced the cytotoxicity of BV‐2 cells following lipopolysaccharide (LPS) stimulation. In addition, NBP reduced the activation of BV‐2 cells, diminished the release of inflammatory mediators, and inhibited microglial TLR4/NF‐κB expression in BV‐2 cells. Our findings demonstrate that NBP may have neuroprotective and anti‐inflammatory properties in the treatment of SCI by inhibiting the activation of microglia via TLR4/NF‐κB signalling.     

Folic acid deficiency enhanced microglial immune response via the Notch1/nuclear factor kappa B p65 pathway in hippocampus following rat brain I/R injury and BV2 cells

Recent studies revealed that folic acid deficiency (FD) increased the likelihood of stroke and aggravated brain injury after focal cerebral ischaemia. The microglia‐mediated inflammatory response plays a crucial role in the complicated pathologies that lead to ischaemic brain injury. However, whether FD is involved in the activation of microglia and the neuroinflammation after experimental stroke and the underlying mechanism is still unclear. The aim of the present study was to assess whether FD modulates the Notch1/nuclear factor kappa B (NF‐κB) pathway and enhances microglial immune response in a rat middle cerebral artery occlusion‐reperfusion (MCAO) model and oxygen‐glucose deprivation (OGD)‐treated BV‐2 cells. Our results exhibited that FD worsened neuronal cell death and exaggerated microglia activation in the hippocampal CA1, CA3 and Dentate gyrus (DG) subregions after cerebral ischaemia/reperfusion. The hippocampal CA1 region was more sensitive to ischaemic injury and FD treatment. The protein expressions of proinflammatory cytokines such as tumour necrosis factor‐α, interleukin‐1β and interleukin‐6 were also augmented by FD treatment in microglial cells of the post‐ischaemic hippocampus and in vitro OGD‐stressed microglia model. Moreover, FD not only dramatically enhanced the protein expression levels of Notch1 and NF‐κB p65 but also promoted the phosphorylation of pIkBα and the nuclear translocation of NF‐κB p65. Blocking of Notch1 with N‐[N‐(3, 5‐difluorophenacetyl)‐l‐alanyl]‐S‐phenylglycine t‐butyl ester partly attenuated the nuclear translocation of NF‐κB p65 and the protein expression of neuroinflammatory cytokines in FD‐treated hypoxic BV‐2 microglia. These results suggested that Notch1/NF‐κB p65 pathway‐mediated microglial immune response may be a molecular mechanism underlying cerebral ischaemia‐reperfusion injury worsened by FD treatment.     

Internalization of nanopolymeric tracers does not alter characteristics of placental cells

In the cell therapy scenario, efficient tracing of transplanted cells is essential for investigating cell migration and interactions with host tissues. This is fundamental to provide mechanistic insights which altogether allow for the understanding of the translational potential of placental cell therapy in the clinical setting. Mesenchymal stem/stromal cells (MSC) from human placenta are increasingly being investigated for their potential in treating patients with a variety of diseases. In this study, we investigated the feasibility of using poly (methyl methacrylate) nanoparticles (PMMA‐NPs) to trace placental MSC, namely those from the amniotic membrane (hAMSC) and early chorionic villi (hCV‐MSC). We report that PMMP‐NPs are efficiently internalized and retained in both populations, and do not alter cell morphofunctional parameters. We observed that PMMP‐NP incorporation does not alter in vitro immune modulatory capability of placental MSC, a characteristic central to their reparative/therapeutic effects in vitro. We also show that in vitro, PMMP‐NP uptake is not affected by hypoxia. Interestingly, after in vivo brain ischaemia and reperfusion injury achieved by transient middle cerebral artery occlusion (tMCAo) in mice, iv hAMSC treatment resulted in significant improvement in cognitive function compared to PBS‐treated tMCAo mice. Our study provides evidence that tracing placental MSC with PMMP‐NPs does not alter their in vitro and in vivo functions. These observations are grounds for the use of PMMP‐NPs as tools to investigate the therapeutic mechanisms of hAMSC and hCV‐MSC in preclinical models of inflammatory‐driven diseases.     

TRPV1介导H4组蛋白乳酸化调控AD炎症激活小胶质细胞

摘要 目的：阿尔茨海默病（AD）中小胶质细胞的免疫监测和吞噬功能逐渐减弱并发生炎症激活。以往研究报道瞬时受体电位香草素1型（TRPV1）通道的激活可以缓解3xTg小鼠脑内小胶质细胞的炎症激活和吞噬功能障碍,作用机制尚不清楚。方法：首先,通过蛋白印迹法和免疫荧光实验测量3xTg小鼠大脑细胞核内组蛋白H4的12位赖氨酸乳酸化（H4K12la）的表达水平和细胞定位情况。其次,验证TRPV1的激活是否可以调控3xTg小鼠大脑细胞核内H4K12la的表达水平。最后,使用Imaris软件和流式细胞术分析TRPV1的激活对小胶质细胞炎症激活形态和生物标志物的影响。结果：蛋白印迹法显示3xTg小鼠大脑细胞核内H4K12la的表达水平上升,免疫荧光实验证明H4K12la与小胶质细胞共定位。TRPV1的激活可以减少3xTg小鼠脑内小胶质细胞中H4K12la的表达水平,缓解3xTg小鼠脑内小胶质细胞炎症激活。结论：TRPV1可以通过抑制组蛋白H4K12la表达缓解AD小胶质细胞炎症激活。     

The NKCC1 ion transporter modulates microglial phenotype and inflammatory response to brain injury in a cell-autonomous manner

The NKCC1 ion transporter contributes to the pathophysiology of common neurological disorders, but its function in microglia, the main inflammatory cells of the brain, has remained unclear to date. Therefore, we generated a novel transgenic mouse line in which microglial NKCC1 was deleted. We show that microglial NKCC1 shapes both baseline and reactive microglia morphology, process recruitment to the site of injury, and adaptation to changes in cellular volume in a cell-autonomous manner via regulating membrane conductance. In addition, microglial NKCC1 deficiency results in NLRP3 inflammasome priming and increased production of interleukin-1β (IL-1β), rendering microglia prone to exaggerated inflammatory responses. In line with this, central (intracortical) administration of the NKCC1 blocker, bumetanide, potentiated intracortical lipopolysaccharide (LPS)-induced cytokine levels. In contrast, systemic bumetanide application decreased inflammation in the brain. Microglial NKCC1 KO animals exposed to experimental stroke showed significantly increased brain injury, inflammation, cerebral edema and worse neurological outcome. Thus, NKCC1 emerges as an important player in controlling microglial ion homeostasis and inflammatory responses through which microglia modulate brain injury. The contribution of microglia to central NKCC1 actions is likely to be relevant for common neurological disorders.

This study shows that inflammatory responses of microglial cells are markedly influenced by the ion transporter, NKCC1; blockade or genetic deletion of microglial NKCC1 has broad cell-autonomous effects, leading to changes in morphology, membrane conductance, process recruitment after injury, and cytokine production, with worsened neurological outcome after stroke.     

Aging and sex: Impact on microglia phagocytosis

Microglia dysfunction and activation are important hallmarks of the aging brain and are concomitant with age‐related neurodegeneration and cognitive decline. Age‐associated changes in microglia migration and phagocytic capacity result in maladaptive responses, chronic neuroinflammation, and worsened outcomes in neurodegenerative disorders. Given the sex bias in the incidence, prevalence, and therapy response of most neurological disorders, we have here examined whether the phagocytic activity of aged microglia is different in males and females. With this aim, the phagocytosis activity of male and female cells was compared in an in vitro aged microglia model and in microglia isolated from adult (5‐month‐old) or aged (18‐month‐old) mice. In both models, the phagocytosis of neural debris increased with aging in male and female cells and was higher in aged female microglia than in aged male cells. However, female aged microglia lost its ability to adapt its phagocytic activity to inflammatory conditions. These findings suggest that microglia phagocytosis of neural debris may represent a previously unexplored neuroprotective characteristic of aged microglia that may contribute to the generation of sex differences in the manifestation of neurodegenerative diseases.     

The effect of intrauterine inflammation on mTOR signaling in mouse fetal brain

Fetuses exposed to an inflammatory environment are predisposed to long‐term adverse neurological outcomes. However, the mechanism by which intrauterine inflammation (IUI) is responsible for abnormal fetal brain development is not fully understood. The mechanistic target of rapamycin (mTOR) signaling pathway is closely associated with fetal brain development. We hypothesized that mTOR signaling might be involved in fetal brain injury and malformation when fetuses are exposed to the IUI environment. A well‐established IUI model was utilized by intrauterine injection of lipopolysaccharide (LPS) to explore the effect of IUI on mTOR signaling in mouse fetal brains. We found that microglia activation in LPS fetal brains was increased, as demonstrated by elevated Iba‐1 protein level and immunofluorescence density. LPS fetal brains also showed reduced neuronal cell counts, decreased cell proliferation demonstrated by low Ki67‐positive density, and elevated neuron apoptosis evidenced by high expression of cleaved Caspase 3. Furthermore, we found that mTOR signaling in LPS fetal brains was elevated at 2 hr after LPS treatment, declined at 6 hr and showed overall inhibition at 24 hr. In summary, our study revealed that LPS‐induced IUI leads to increased activation of microglia cells, neuronal damage, and dynamic alterations in mTOR signaling in the mouse fetal brain. Our findings indicate that abnormal changes in mTOR signaling may underlie the development of future neurological complications in offspring exposed to prenatal IUI.     

Cerebral inflammation contributes to encephalopathy and brain edema in acute liver failure: protective effect of minocycline

Encephalopathy and brain edema are serious complications of acute liver failure (ALF). The precise pathophysiologic mechanisms responsible have not been fully elucidated but it has been recently proposed that microglia‐derived proinflammatory cytokines are involved. In the present study we evaluated the role of microglial activation and the protective effect of the anti‐inflammatory drug minocycline in the pathogenesis of hepatic encephalopathy and brain edema in rats with ALF resulting from hepatic devascularisation. ALF rats were killed 6 h after hepatic artery ligation before the onset of neurological symptoms and at coma stages of encephalopathy along with their appropriate sham‐operated controls and in parallel with minocycline‐treated ALF rats. Increased OX‐42 and OX‐6 immunoreactivities confirming microglial activation were accompanied by increased expression of interleukins (IL‐1β, IL‐6) and tumor necrosis factor‐alpha (TNF‐α) in the frontal cortex at coma stage of encephalopathy in ALF rats compared with sham‐operated controls. Minocycline treatment prevented both microglial activation as well as the up‐regulation of IL‐1β, ΙL‐6 and TNF‐α mRNA and protein expression with a concomitant attenuation of the progression of encephalopathy and brain edema. These results offer the first direct evidence for central proinflammatory mechanisms in the pathogenesis of brain edema and its complications in ALF and suggest that anti‐inflammatory agents may be beneficial in these patients.     

Pyrroloquinoline Quinone (PQQ) Inhibits Lipopolysaccharide Induced Inflammation in Part via Downregulated NF-κB and p38/JNK Activation in Microglial and Attenuates Microglia Activation in Lipopolysaccharide Treatment Mice

Therapeutic strategies designed to inhibit the activation of microglia may lead to significant advancement in the treatment of most neurodegenerative diseases. Pyrroloquinoline quinone (PQQ) is a naturally occurring redox cofactor that acts as an essential nutrient, antioxidant, and has been reported to exert potent immunosuppressive effects. In the present study, the anti-inflammatory effects of PQQ was investigated in LPS treated primary microglia cells. Our observations showed that pretreatment with PQQ significantly inhibited the production of NO and PGE2 and suppressed the expression of pro-inflammatory mediators such as iNOS, COX-2, TNF-a, IL-1b, IL-6, MCP-1 and MIP-1a in LPS treated primary microglia cells. The nuclear translocation of NF-κB and the phosphorylation level of p65, p38 and JNK MAP kinase pathways were also inhibited by PQQ in LPS stimulated primary microglia cells. Further a systemic LPS treatment acute inflammation murine brain model was used to study the suppressive effects of PQQ against neuroinflammation in vivo. Mice treated with PQQ demonstrated marked attenuation of neuroinflammation based on Western blotting and immunohistochemistry analysis of Iba1-against antibody in the brain tissue. Indicated that PQQ protected primary cortical neurons against microglia-mediated neurotoxicity. These results collectively suggested that PQQ might be a promising therapeutic agent for alleviating the progress of neurodegenerative diseases associated with microglia activation.     

Microglial activation mediates host neuronal survival induced by neural stem cells

The rational of neural stem cells (NSCs) in the therapy of neurological disease is either to replace dead neurons or to improve host neuronal survival, the latter of which has got less attention and the underlying mechanism is as yet little known. Using a transwell co‐culture system, we reported that, in organotypic brain slice cultures, NSCs significantly improved host neuronal viability. Interestingly, this beneficial effect of NSCs was abrogated by a microglial inhibitor minocycline, while it was mimicked by a microglial agonist, Toll‐like receptor 9 (TLR9) ligand CpG‐ODN, which supports the pro‐vital mediation by microglia on this NSCs‐improved neuronal survival. Moreover, we showed that NSCs significantly induced host microglial movement and higher expression of a microglial marker IBA‐1, the latter of which was positively correlated with TLR9 or extracellular‐regulated protein kinases 1/2 (ERK1/2) activation. Real‐time PCR revealed that NSCs inhibited the expression of pro‐inflammatory molecules, but significantly increased the expression of molecules associated with a neuroprotective phenotype such as CX3CR1, triggering receptor expressed on myeloid cells‐2 (TREM2) and insulin growth factor 1 (IGF‐1). Similarly, in the microglia cells, NSCs induced the same microglial response as that in the slices. Further treatment with TLR9 ligand CpG‐ODN, TLR9 inhibitor chloroquine (CQ) or ERK1/2 inhibitor U0126 demonstrated that TLR9‐ERK1/2 pathway was involved in the NSCs‐induced microglial activation. Collectively, this study indicated that NSCs improve host neuronal survival by switching microglia from a detrimental to a neuroprotective phenotype in adult mouse brain, and the microglial TLR9‐ERK1/2 pathway seems to participate in this NSCs‐mediated rescue action.     

Neuronal regulation by which microglia enhance the production of neurotrophic factors for GABAergic, catecholaminergic, and cholinergic neurons

A phenomenon-in which microglia are activated in axotomized rat facial nucleus suggests that a certain neuronal stimulus triggers the activation of microglia. However, how the microglial characteristics are regulated by this neuronal stimulus has not previously been determined. In this study, therefore, the regulation of microglial properties by neurons was characterized in vitro from a neurotrophic perspective. To evaluate the neurotrophic effects of microglia stimulated with neurons, the effects of conditioned medium (CM) of microglia stimulated with neuronal CM (NCM) were assessed in neuronal cultures. The amounts of tyrosine hydroxylase (TH) in neuronal culture exposed to CM of microglia stimulated with NCM was much more than those in neurons exposed to CM of control microglia, suggesting that neuronal stimulus enhances the production of neurotrophic factors for catecholaminergic neurons in microglia. Therefore, the neurotrophic effects of CM of microglia stimulated with NCM were analyzed in detail. The immunocytochemical and biochemical experiments revealed that the CM of microglia stimulated with NCM enhances the survival/maturation of GABAergic and catecholaminergic neurons. The levels of choline acetyltransferase specific to cholinergic neurons also significantly increased in response to stimulation with the same microglial CM. These results allowed us to investigate the production of neurotrophic factors in the CM of microglia stimulated with NCM. The results indicated that NCM induces nerve growth factor (NGF), and enhances neurotrophin-4/5 (NT-4/5), transforming growth factor beta1 (TGFbeta1), glial cell line-derived neurotrophic factor (GDNF), fibroblast growth factor 2 (FGF2), interleukin-3 (IL-3), and IL-10 in microglia. The promoted neurotrophic effects of CM of microglia stimulated with NCM were significantly abrogated by deprivation of neurotrophic factors by means of an immunoprecipitation method. Taken together, neuronal stimulus was found to activate microglia to produce more neurotrophic factors as above, thereby changing microglia into more neurotrophic cells.     

Microglial Depletion Causes Region‐Specific Changes to Developmental Neuronal Cell Death in the Mouse Brain

Developmental neuronal cell death has been characterized as a cell autonomous “suicide” program, but recent findings suggest that microglia play an active role in determining the survival of developing neurons. Results have been contradictory, however, with some studies concluding that microglia promote cell death, while others report that microglia are neuroprotective. Here, we depleted microglia throughout the newborn mouse brain using intracerebroventricular injections of clodronate liposomes, and examined effects on naturally occurring cell death across multiple brain areas. Microglial density varied significantly by brain region, and clodronate liposome treatment at birth reduced the number of microglia in all regions examined. The effect of microglia reduction on cell death, however, varied by region: the number of dying cells was reduced in the medial septum and medial amygdala in clodronate treated animals, but was increased in the oriens layer of the hippocampus, and unchanged in several other brain regions. In most brain regions, the average size of microglia was greater in microglia‐depleted than in control animals, suggesting that the remaining microglia compensate to some extent for a reduction in microglial number. The hippocampal oriens was exceptional in this regard, in that microglial size was reduced following treatment with clodronate. Microglia produce cytokines which mediate many of their effects, and we found higher expression of inflammatory cytokines in the hippocampus than in the septum, independent of clodronate treatment. Thus, microglial depletion has opposite effects on cell death in different brain regions of the newborn brain, which may be related to regional heterogeneity in microglia.