Inhibiting p53 pathways in microglia attenuates microglial-evoked neurotoxicity following exposure to Alzheimer peptides

Amyloids and brain cancer: molecular linkages and crossovers

Amyloids are high-order proteinaceous formations deposited in both intra- and extracellular spaces. These aggregates have tendencies to deregulate cellular physiology in multiple ways; for example, altered metabolism, mitochondrial dysfunctions, immune modulation, etc. When amyloids are formed in brain tissues, the endpoint often is death of neurons. However, interesting but least understood is a close connection of amyloids with another set of conditions in which brain cells proliferate at an extraordinary rate and form tumor inside brain. Glioblastoma is one such condition. Increasing number of evidence indicate a possible link between amyloid formation and depositions in brain tumors. Several proteins associated with cell cycle regulation and apoptotic pathways themselves have shown to possess high tendencies to form amyloids. Tumor suppressor protein p53 is one prominent example that mutate, oligomerize and form amyloids leading to loss- or gain-of-functions and cause increased cell proliferation and malignancies. In this review article, we present available examples, genetic links and common pathways that indicate that possibly the two distantly placed pathways: amyloid formation and developing cancers in the brain have similarities and are mechanistically intertwined together.

Microglial cannabinoid receptor type 1 mediates social memory deficits in mice produced by adolescent THC exposure and 16p11.2 duplication

Adolescent cannabis use increases the risk for cognitive impairments and psychiatric disorders. Cannabinoid receptor type 1 (Cnr1) is expressed not only in neurons and astrocytes, but also in microglia, which shape synaptic connections during adolescence. However, the role of microglia in mediating the adverse cognitive effects of delta-9-tetrahydrocannabinol (THC), the principal psychoactive constituent of cannabis, is not fully understood. Here, we report that in mice, adolescent THC exposure produces microglial apoptosis in the medial prefrontal cortex (mPFC), which was exacerbated in a model of 16p11.2 duplication, a representative copy number variation (CNV) risk factor for psychiatric disorders. These effects are mediated by microglial Cnr1, leading to reduction in the excitability of mPFC pyramidal-tract neurons and deficits in social memory in adulthood. Our findings suggest the microglial Cnr1 may contribute to adverse effect of cannabis exposure in genetically vulnerable individuals.

Microglial cannabinoid receptor type 1 mediates social memory deficits produced by adolescent THC exposure and 16p11.2 duplication

Adolescent cannabis use increases the risk for cognitive impairments and psychiatric disorders. Cannabinoid receptor type 1 (Cnr1) is expressed not only in neurons and astrocytes, but also in microglia, which shape synaptic connections during adolescence. Nonetheless, until now, the role of microglia in mediating the adverse cognitive effects of delta-9-tetrahydrocannabinol (THC), the principal psychoactive constituent of cannabis, has been unexplored. Here, we report that adolescent THC exposure produces microglial apoptosis in the medial prefrontal cortex (mPFC), which was exacerbated in the mouse model of 16p11.2 duplication, a representative copy number variation (CNV) risk factor for psychiatric disorders. These effects are mediated by microglial Cnr1, leading to reduction in the excitability of mPFC pyramidal-tract neurons and deficits in social memory in adulthood. Our findings highlight the importance of microglial Cnr1 to produce the adverse effect of cannabis exposure in genetically vulnerable individuals.

Redox dysregulation as a driver for DNA damage and its relationship to neurodegenerative diseases

Redox homeostasis refers to the balance between the production of reactive oxygen species (ROS) as well as reactive nitrogen species (RNS), and their elimination by antioxidants. It is linked to all important cellular activities and oxidative stress is a result of imbalance between pro-oxidants and antioxidant species. Oxidative stress perturbs many cellular activities, including processes that maintain the integrity of DNA. Nucleic acids are highly reactive and therefore particularly susceptible to damage. The DNA damage response detects and repairs these DNA lesions. Efficient DNA repair processes are therefore essential for maintaining cellular viability, but they decline considerably during aging. DNA damage and deficiencies in DNA repair are increasingly described in age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease. Furthermore, oxidative stress has long been associated with these conditions. Moreover, both redox dysregulation and DNA damage increase significantly during aging, which is the biggest risk factor for neurodegenerative diseases. However, the links between redox dysfunction and DNA damage, and their joint contributions to pathophysiology in these conditions, are only just emerging. This review will discuss these associations and address the increasing evidence for redox dysregulation as an important and major source of DNA damage in neurodegenerative disorders. Understanding these connections may facilitate a better understanding of disease mechanisms, and ultimately lead to the design of better therapeutic strategies based on preventing both redox dysregulation and DNA damage.

Human myeloid progenitor glucocorticoid receptor activation causes genomic instability, type 1 IFN- response pathway activation and senescence in differentiated microglia; an early life stress model

One form of early life stress, prenatal exposure to glucocorticoids (GCs), confers a higher risk of psychiatric and neurodevelopmental disorders in later life. Increasingly, the importance of microglia in these disorders is recognized. Studies on GCs exposure during microglial development have been limited, and there are few, if any, human studies. We established an in vitro model of ELS by continuous pre-exposure of human iPS-microglia to GCs during primitive hematopoiesis (the critical stage of iPS-microglial differentiation) and then examined how this exposure affected the microglial phenotype as they differentiated and matured to microglia, using RNA-seq analyses and functional assays. The iPS-microglia predominantly expressed glucocorticoid receptors over mineralocorticoid receptors, and in particular, the GR-α splice variant. Chronic GCs exposure during primitive hematopoiesis was able to recapitulate in vivo ELS effects. Thus, pre-exposure to prolonged GCs resulted in increased type I interferon signaling, the presence of Cyclic GMP-AMP synthase-positive (cGAS) micronuclei, cellular senescence and reduced proliferation in the matured iPS-microglia. The findings from this in vitro ELS model have ramifications for the responses of microglia in the pathogenesis of GC- mediated ELS-associated disorders such as schizophrenia, attention-deficit hyperactivity disorder and autism spectrum disorder.

Fluoxetine plus lithium for treatment of mental health impairment in Long Covid

Purposes

(1) To summarize the mental conditions that may accompany persistent symptoms following acute infection by SARS-CoV-2, often termed Long Covid; (2) to formulate treatment based upon the brain cells that are dominantly affected.

Methods

(1) Review the reports relating to the mental symptoms occurring in Long Covid. (2) Review the drugs that address the brain cells affected in Long Covid, and suggest pharmacotherapy for those patients whose response to psychotherapy is suboptimal.

Results

Long Covid affects ~ 10% of patients infected by SARS-CoV-2, and mental symptoms affect ~ 20% of persons with Long Covid. The brain cell-types that have been demonstrated as dominantly affected in Long Covid are astrocytes, oligodendrocytes, neurons, endothelial cells/pericytes, and microglia. Lithium and fluoxetine each address all of those four cell-types. Low dosage of each is likely to be well-tolerated and to cause neither clinically important adverse events (AE) nor serious adverse events (SAE).

Conclusion

For those patients whose response to psychotherapy is suboptimal, lithium and fluoxetine should be administered in combination for both depth of benefit and reduction of dosages.

The Complex Mechanisms by Which Neurons Die Following DNA Damage in Neurodegenerative Diseases

Human cells are exposed to numerous exogenous and endogenous insults every day. Unlike other molecules, DNA cannot be replaced by resynthesis, hence damage to DNA can have major consequences for the cell. The DNA damage response contains overlapping signalling networks that repair DNA and hence maintain genomic integrity, and aberrant DNA damage responses are increasingly described in neurodegenerative diseases. Furthermore, DNA repair declines during aging, which is the biggest risk factor for these conditions. If unrepaired, the accumulation of DNA damage results in death to eliminate cells with defective genomes. This is particularly important for postmitotic neurons because they have a limited capacity to proliferate, thus they must be maintained for life. Neuronal death is thus an important process in neurodegenerative disorders. In addition, the inability of neurons to divide renders them susceptible to senescence or re-entry to the cell cycle. The field of cell death has expanded significantly in recent years, and many new mechanisms have been described in various cell types, including neurons. Several of these mechanisms are linked to DNA damage. In this review, we provide an overview of the cell death pathways induced by DNA damage that are relevant to neurons and discuss the possible involvement of these mechanisms in neurodegenerative conditions.

Lithium inhibits tryptophan catabolism via the inflammation-induced kynurenine pathway in human microglia

Despite its decades' long therapeutic use in psychiatry, the biological mechanisms underlying lithium's mood-stabilizing effects have remained largely elusive. Here, we investigated the effect of lithium on tryptophan breakdown via the kynurenine pathway using immortalized human microglia cells, primary human microglia isolated from surgical specimens, and microglia-like cells differentiated from human induced pluripotent stem cells. Interferon (IFN)-γ, but not lipopolysaccharide, was able to activate immortalized human microglia, inducing a robust increase in indoleamine-2,3-dioxygenase (IDO1) mRNA transcription, IDO1 protein expression, and activity. Further, chromatin immunoprecipitation verified enriched binding of both STAT1 and STAT3 to the IDO1 promoter. Lithium counteracted these effects, increasing inhibitory GSK3β^S9 phosphorylation and reducing STAT1^S727 and STAT3^Y705 phosphorylation levels in IFN-γ treated cells. Studies in primary human microglia and hiPSC-derived microglia confirmed the anti-inflammatory effects of lithium, highlighting that IDO activity is reduced by GSK3 inhibitor SB-216763 and STAT inhibitor nifuroxazide via downregulation of P-STAT1^S727 and P-STAT3^Y705 . Primary human microglia differed from immortalized human microglia and hiPSC derived microglia-like cells in their strong sensitivity to LPS, resulting in robust upregulation of IDO1 and anti-inflammatory cytokine IL-10. While lithium again decreased IDO1 activity in primary cells, it further increased release of IL-10 in response to LPS. Taken together, our study demonstrates that lithium inhibits the inflammatory kynurenine pathway in the microglia compartment of the human brain.

Anti-Oxidative, Anti-Inflammatory and Anti-Apoptotic Effects of Flavonols: Targeting Nrf2, NF-κB and p53 Pathways in Neurodegeneration

Neurodegenerative diseases are one of the leading causes of disability and death worldwide. Intracellular transduction pathways that end in the activation of specific transcription factors are highly implicated in the onset and progression of pathological changes related to neurodegeneration, of which those related to oxidative stress (OS) and neuroinflammation are particularly important. Here, we provide a brief overview of the key concepts related to OS- and neuroinflammation-mediated neuropathological changes in neurodegeneration, together with the role of transcription factors nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF-κB). This review is focused on the transcription factor p53 that coordinates the cellular response to diverse genotoxic stimuli, determining neuronal death or survival. As current pharmacological options in the treatment of neurodegenerative disease are only symptomatic, many research efforts are aimed at uncovering efficient disease-modifying agents. Natural polyphenolic compounds demonstrate powerful anti-oxidative, anti-inflammatory and anti-apoptotic effects, partially acting as modulators of signaling pathways. Herein, we review the current understanding of the therapeutic potential and limitations of flavonols in neuroprotection, with emphasis on their anti-oxidative, anti-inflammatory and anti-apoptotic effects along the Nrf2, NF-κB and p53 pathways. A better understanding of cellular and molecular mechanisms of their action may pave the way toward new treatments.

Mitophagy pathways and Alzheimer's disease: From pathogenesis to treatment

Alzheimer's disease (AD) is an age-dependent, incurable mental illness that is associated with the accumulation of aggregates of amyloid-beta (Aβ) and hyperphosphorylated tau fragments (p-tau). Detailed studies on postmortem AD brains, cell lines, and mouse models of AD have shown that numerous cellular alterations, including mitochondrial deficits, synaptic disruption and glial/astrocytic activation, are involved in the disease process. Mitophagy is a cellular process by which damaged/weakened mitochondria are selectively eliminated from the cell. In AD, impairments in mitophagy trigger the gradual accumulation of defective mitochondria. This review will focus on the recent progress in understanding the molecular mechanisms and pathological role of mitophagy and its implications for AD pathogenesis. We will also discuss the novel concept of the regulation of mitophagy as a therapeutic avenue for the prevention and treatment of AD.

SIRT1 activation by minocycline on regulation of microglial polarization homeostasis

Sirtuin 1 (SIRT1) has been reported to be involved in the mechanisms underlying longevity and has also been indicated as a valuable regulator of age-related neurological disorders. Some natural products increase SIRT1 activity and stimulate deacetylation of various proteins. In the present study, SIRT1 overexpression by genetic modification or treatment with SIRT1 activators significantly inhibited the secretion of nitric oxide and expression of inducible nitric oxide synthase, cyclooxygenase 2, and proinflammatory mediator-interleukin 1β-in microglia. SIRT1 activation also decreased the levels of K379 acetyl-p53 and the protein inhibitor of activated Stat 1 expression in microglial cells. In addition, it dramatically promoted M2 polarization of microglia, which enhanced cell motility and altered phagocytic ability. We also used minocycline, a well-known inhibitor of microglial activation, to study the mechanism of SIRT1 signaling. Minocycline treatment decreased neuroinflammatory responses and promoted M2 polarization of microglia. It also reduced the acetyl-p53 level in the brain tissues in an inflammatory mouse model. Our findings demonstrated that SIRT1 participates in the maintenance of microglial polarization homeostasis and that minocycline exerts regulatory effects on SIRT1 activation. Therefore, our results indicate that SIRT1 activation may be a useful therapeutic target for the treatment of neuroinflammation-associated disorders.

Mitochondrial Dysfunction and Alzheimer's Disease: Role of Microglia

In 1907, Alois Alzheimer observed, as he quoted, development of "numerous fibers" and "adipose saccules" in the brain of his diseased patient Auguste Deter. The neurodegenerative disease became known as Alzheimer's disease (AD) and is the most common cause of dementia worldwide. AD normally develops with aging and is mostly initiated because of the imbalance between the formation and clearance of amyloid-β (Aβ). Formation of neurofibrillary tangles (NFTs) of hyperphosphorylated tau is another hallmark of AD. Neuroinflammation plays a significant role in the development and pathology of AD. This chapter explores the role of mitochondrial dysfunction in microglia in case of AD. Mitochondrial oxidative stress in microglia has been linked to the development of AD. Elevated generation of reactive oxygen species (ROS) and loss of mitochondrial membrane potential through various mechanisms have been observed in AD. Aβ interacts with microglial receptors, such as triggering receptor expressed in myeloid cells 2 (TREM2), activating downstream pathways causing mitochondrial damage and aggravating inflammation and cytotoxicity. Fibrillar Aβ activates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in microglia leading to elevated induction of mitochondrial ROS which further causes neurotoxicity. Elevated ROS in microglia causes activation of inflammatory and cell death pathways. Production of ATP, regulation of mitochondrial health, autophagy, and mitophagy in microglia play significant roles in the AD pathology. Understanding microglial physiology and mitochondrial dysfunction will enable better therapeutic interventions.

Secretory granule protein chromogranin B (CHGB) forms an anion channel in membranes

The CHGB subfamily of secretory granule proteins forms a new family of anion-selective channels by interacting with membranes via two amphipathic α-helices. The channel exhibits higher anion selectivity, larger conductance, higher DIDS-binding affinity, and higher Cl⁻ sensitivity than other known anion channels.

Regulated secretion is an intracellular pathway that is highly conserved from protists to humans. Granin family proteins were proposed to participate in the biogenesis, maturation and release of secretory granules in this pathway. However, the exact molecular mechanisms underlying the intracellular functions of the granin family proteins remain unclear. Here, we show that chromogranin B (CHGB), a secretory granule protein, inserts itself into membrane and forms a chloride-conducting channel. CHGB interacts strongly with phospholipid membranes through two amphipathic α helices. At a high local concentration, CHGB insertion in membrane causes significant bilayer remodeling, producing protein-coated nanoparticles and nanotubules. Fast kinetics and high cooperativity for anion efflux from CHGB vesicles suggest that CHGB tetramerizes to form a functional channel with a single-channel conductance of ∼125 pS (150/150 mM Cl⁻). The CHGB channel is sensitive to an anion channel blocker and exhibits higher anion selectivity than the other six known families of Cl⁻ channels. Our data suggest that the CHGB subfamily of granin proteins forms a new family of organelle chloride channels.

The p53 Family in Brain Disease

SIGNIFICANCE

The p53 family of transcription factors, including p53, p63, and p73, plays key roles in both biological and pathological processes, including cancer and neural development. Recent Advances: In recent years, a growing body of evidence has indicated that the entire p53 family is involved in the regulation of the central nervous system (CNS) functions as well as in the pathogenesis of several neurological disorders. Mechanistically, the p53 proteins control neuronal cell fate, terminal differentiation, and survival, via a complex interplay among the family members.

CRITICAL ISSUES

In this article, we discuss the involvement of the p53 family in neurobiology and in pathological conditions affecting the CNS, including neuroinflammation.

FUTURE DIRECTIONS

Understanding the molecular mechanism(s) underlying the function of the p53 family could improve our general knowledge of the pathogenesis of brain disorders and potentially pave the road for new therapeutic intervention. Antioxid. Redox Signal. 29, 1-14.

Neuroprotective effects of pifithrin-α against traumatic brain injury in the striatum through suppression of neuroinflammation, oxidative stress, autophagy, and apoptosis

Cortical and hippocampal neuronal damages caused by traumatic brain injury (TBI) are associated with motor and cognitive impairments; however, only little attention paid to the striatal damage. It is known that the p53 tumor-suppressor transcription factor participated in TBI-induced secondary brain damage. We investigated how the p53 inactivator pifithrin (PFT)-α affected TBI-induced striatal neuronal damage at 24 h post-injury. Sprague-Dawley rats subjected to a controlled cortical impact were used as TBI models. We observed that p53 mRNA significantly increased, whereas p53 protein expression was distributed predominantly in neurons but not in glia cells in striatum after TBI. PFT-α improved motor deficit following TBI. PFT-α suppressed TBI-induced striatal glial activation and expression of proinflammatory cytokines. PFT-α alleviated TBI-induced oxidative damage TBI induced autophagy was evidenced by increased protein expression of Beclin-1 and shift of microtubule-associated light chain (LC)3-I to LC3-II, and decreased p62. These effects were reduced by PFT-α. Post-injury PFT-α treatment reduced the number of degenerating (FJC-positive) and apoptotic neurons. Our results suggest that PFT-α may provide neuroprotective effects via p53-dependent or -independent mechanisms depending on the cell type and timing after the TBI and can possibly be developed into a novel therapy to ameliorate TBI-induced neuronal damage.

IL-17A Enhances Microglial Response to OGD by Regulating p53 and PI3K/Akt Pathways with Involvement of ROS/HMGB1

Cerebral ischemia-reperfusion injury (IRI) has a complex pathogenesis, and interleukin-17 (IL-17) is a newly identified class of the cytokine family that plays an important role in ischemic inflammation. An oxygen-glucose deprivation (OGD) model showed that IL-17A expression was significantly up-regulated in microglial cells. After IL-17A siRNA transfection, the inhibition of proliferation, and the increased apoptosis in microglial cells, induced by OGD/reperfusion, was improved, and the elevation of Caspase-3, Caspase-8, Caspase-9, and poly ADP ribose polymerase (PARP) activities was inhibited. Mass spectrometry demonstrated that IL-17A functioned through a series of factors associated with oxidative stress and apoptosis and regulated Caspase-3 activity and apoptosis in microglial cells via the p53 and PI3K/Akt signaling pathways. IL-17A, HMGB1, and ROS were regulated mutually to exhibit a synergistic effect in the OGD model of microglial cells, but the down-regulation of IL-17A or HMGB1 expression did not completely inhibit the production of ROS. These findings demonstrated that ROS might be located upstream of IL-17A and HMGB1 so that ROS can regulate HMGB1/IL-17A expression to affect the p53 and PI3K/Akt signaling pathways and therefore promote the occurrence of apoptosis in microglial cells. These findings provide a novel evidence for the role of IL-17A in ischemic cerebral diseases.

Transcriptional control of microglia phenotypes in health and disease

Microglia are the main resident macrophage population of the CNS and perform numerous functions required for CNS development, homeostasis, immunity, and repair. Many lines of evidence also indicate that dysregulation of microglia contributes to the pathogenesis of neurodegenerative and behavioral diseases. These observations provide a compelling argument to more clearly define the mechanisms that control microglia identity and function in health and disease. In this Review, we present a conceptual framework for how different classes of transcription factors interact to select and activate regulatory elements that control microglia development and their responses to internal and external signals. We then describe functions of specific transcription factors in normal and pathological contexts and conclude with a consideration of open questions to be addressed in the future.

Regulation of microglial activation in stroke

When ischemic stroke occurs, oxygen and energy depletion triggers a cascade of events, including inflammatory responses, glutamate excitotoxicity, oxidative stress, and apoptosis that result in a profound brain injury. The inflammatory response contributes to secondary neuronal damage, which exerts a substantial impact on both acute ischemic injury and the chronic recovery of the brain function. Microglia are the resident immune cells in the brain that constantly monitor brain microenvironment under normal conditions. Once ischemia occurs, microglia are activated to produce both detrimental and neuroprotective mediators, and the balance of the two counteracting mediators determines the fate of injured neurons. The activation of microglia is defined as either classic (M1) or alternative (M2): M1 microglia secrete pro-inflammatory cytokines (TNFα, IL-23, IL-1β, IL-12, etc) and exacerbate neuronal injury, whereas the M2 phenotype promotes anti-inflammatory responses that are reparative. It has important translational value to regulate M1/M2 microglial activation to minimize the detrimental effects and/or maximize the protective role. Here, we discuss various regulators of microglia/macrophage activation and the interaction between microglia and neurons in the context of ischemic stroke.

The Plant-Derived Chalcone 2,2',5'-Trihydroxychalcone Provides Neuroprotection against Toll-Like Receptor 4 Triggered Inflammation in Microglia

Chalcones are plant metabolites with potential for therapeutic exploitation as antioxidant, anti-inflammatory, and antiproliferative agents. Here we explored the neuroprotective effects of 2,2',5'-trihydroxychalcone (225THC), a potent antioxidant with radical-scavenging properties. 225THC was found to be a potent inhibitor of apoptosis in stimulated primary rat neuronal cultures. This was likely mediated by an anti-inflammatory effect on microglial cells since 225THC inhibited LPS-stimulated TNF-α and IL-6 secretion from primary rat microglia and modulated the cytokine/chemokine profile of BV2 microglial cells. Additionally, 225THC inhibited LPS-evoked inducible nitric oxide synthase expression but did not influence endogenous superoxide generation. Microglial flow cytometric analyses indicated the 225THC treatment induced a shift from an M1-like phenotype to a more downregulated microglial profile. Taken together these data suggest that the chalcone 2,2',5'-trihydroxychalcone can modulate neuroinflammatory activation in brain-derived microglia and holds promise as a therapeutic in neuroinflammatory conditions.

The associations between Parkinson's disease and cancer: the plot thickens

Epidemiological studies support a general inverse association between the risk of cancer development and Parkinson’s disease (PD). In recent years however, increasing amount of eclectic evidence points to a positive association between PD and cancers through different temporal analyses and ethnic groups. This positive association has been supported by several common genetic mutations in SNCA, PARK2, PARK8, ATM, p53, PTEN, and MC1R resulting in cellular changes such as mitochondrial dysfunction, aberrant protein aggregation, and cell cycle dysregulation. Here, we review the epidemiological and biological advances of the past decade in the association between PD and cancers to offer insight on the recent and sometimes contradictory findings.

The p53 Transcriptional Network Influences Microglia Behavior and Neuroinflammation

The tumor-suppressor protein p53 belongs to a family of proteins that play pivotal roles in multiple cellular functions including cell proliferation, cell death, genome stability, and regulation of inflammation. Neuroinflammation is a common feature of central nervous system (CNS) pathology, and microglia are the specialized resident population of CNS myeloid cells that initiate innate immune responses. Microglia maintain CNS homeostasis through pathogen containment, phagocytosis of debris, and initiation of tissue-repair cascades. However, an unregulated pro-inflammatory response can lead to tissue injury and dysfunction in both acute and chronic inflammatory states. Therefore, regulation of the molecular signals that control the induction, magnitude, and resolution of inflammation are necessary for optimal CNS health. We and others have described a novel mechanism by which p53 transcriptional activity modulates microglia behaviors in vitro and in vivo. Activation of p53 induces expression of microRNAs (miRNAs) that support microglia pro-inflammatory functions and suppress anti-inflammatory and tissue repair behaviors. In this review, we introduce the previously described roles of the p53 signaling network and discuss novel functions of p53 in the microglia-mediated inflammatory response in CNS health and disease. Ultimately, improved understanding of the molecular regulators modulated by p53 transcriptional activity in microglia will enhance the development of rational therapeutic strategies to harness the homeostatic and tissue repair functions of microglia.

NADPH oxidase- and mitochondria-derived reactive oxygen species in proinflammatory microglial activation: a bipartisan affair?

Microglia are the resident immune cells of the brain and play major roles in central nervous system development, maintenance, and disease. Brain insults cause microglia to proliferate, migrate, and transform into one or more activated states. Classical M1 activation triggers the production of proinflammatory factors such as tumor necrosis factor-α, interleukin-1β (IL-1β), nitric oxide, and reactive oxygen species (ROS), which, in excess, can exacerbate brain injury. The mechanisms underlying microglial activation are not fully understood, yet reactive oxygen species are increasingly implicated as mediators of microglial activation. In this review, we highlight studies linking reactive oxygen species, in particular hydrogen peroxide derived from NADPH oxidase-generated superoxide, to the classical activation of microglia. In addition, we critically evaluate controversial evidence suggesting a specific role for mitochondrial reactive oxygen species in the activation of the NLRP3 inflammasome, a multiprotein complex that mediates the production of IL-1β and IL-18. Finally, the limitations of common techniques used to implicate mitochondrial ROS in microglial and inflammasome activation, such as the use of the mitochondrially targeted ROS indicator MitoSOX and the mitochondrially targeted antioxidant MitoTEMPO, are also discussed.

Redox control of microglial function: molecular mechanisms and functional significance

Neurodegenerative diseases are characterized by chronic microglial over-activation and oxidative stress. It is now beginning to be recognized that reactive oxygen species (ROS) produced by either microglia or the surrounding environment not only impact neurons but also modulate microglial activity. In this review, we first analyze the hallmarks of pro-inflammatory and anti-inflammatory phenotypes of microglia and their regulation by ROS. Then, we consider the production of reactive oxygen and nitrogen species by NADPH oxidases and nitric oxide synthases and the new findings that also indicate an essential role of glutathione (γ-glutamyl-l-cysteinylglycine) in redox homeostasis of microglia. The effect of oxidant modification of macromolecules on signaling is analyzed at the level of oxidized lipid by-products and sulfhydryl modification of microglial proteins. Redox signaling has a profound impact on two transcription factors that modulate microglial fate, nuclear factor kappa-light-chain-enhancer of activated B cells, and nuclear factor (erythroid-derived 2)-like 2, master regulators of the pro-inflammatory and antioxidant responses of microglia, respectively. The relevance of these proteins in the modulation of microglial activity and the interplay between them will be evaluated. Finally, the relevance of ROS in altering blood brain barrier permeability is discussed. Recent examples of the importance of these findings in the onset or progression of neurodegenerative diseases are also discussed. This review should provide a profound insight into the role of redox homeostasis in microglial activity and help in the identification of new promising targets to control neuroinflammation through redox control of the brain.

Mice lacking chromogranins exhibit increased aggressive and depression-like behaviour

Chromogranins are acidic proteins; both chromogranins A and B constitute the main protein component in the vesicular matrix of large dense core vesicles. Chromogranins are a natural source of peptides with different physiological activities that have been associated with vascular and neurological diseases. We have used three different genetic mutant models of mice lacking chromogranin A, chromogranin B and both all on the same C57BL/6J background, to characterize the physiological roles of these proteins using metabolic, cardiovascular and behavioural tests. In mice from 3 to 18 months of age, the lack of any chromogranin promoted age-dependent hypersensitivity to insulin, while the lack of both chromogranins provoked progressive lack of response to stress, as restriction did not promote tachycardia in old mice. Moreover, the lack of chromogranin B produced a depressive-like and aggressive phenotype, while the lack either or both chromogranins increased barbering behaviour. In addition, we observed no effects on light-dark box or RotaRod tests. Mice lacking chromogranin B exhibited lower exploratory activity. Based on this extensive phenotyping with more than 2800 mice, these findings support roles of chromogranins, or the peptides derived from them, in the control of aggressive behaviour along with changes in their metabolic profile beyond their previously described activities in the secretory pathway.

STAT1-induced ASPP2 transcription identifies a link between neuroinflammation, cell polarity, and tumor suppression

Inflammation and loss of cell polarity play pivotal roles in neurodegeneration and cancer. A central question in both diseases is how the loss of cell polarity is sensed by cell death machinery. Here, we identify apoptosis-stimulating protein of p53 with signature sequences of ankyrin repeat-, SH3 domain-, and proline-rich region-containing protein 2 (ASPP2), a haploinsufficient tumor suppressor, activator of p53, and regulator of cell polarity, as a transcriptional target of signal transducer and activator of transcription 1 (STAT1). LPS induces ASPP2 expression in murine macrophage and microglial cell lines, a human monocyte cell line, and primary human astrocytes in vitro. LPS and IFNs induce ASPP2 transcription through an NF-κB RELA/p65-independent but STAT1-dependent pathway. In an LPS-induced maternal inflammation mouse model, LPS induces nuclear ASPP2 in vivo at the blood-cerebral spinal fluid barrier (the brain's barrier to inflammation), and ASPP2 mediates LPS-induced apoptosis. Consistent with the role of ASPP2 as a gatekeeper to inflammation, ASPP2-deficient brains possess enhanced neuroinflammation. Elevated ASPP2 expression is also observed in mouse models and human neuroinflammatory disease tissue, where ASPP2 was detected in GFAP-expressing reactive astrocytes that coexpress STAT1. Because the ability of ASPP2 to maintain cellular polarity is vital to CNS development, our findings suggest that the identified STAT1/ASPP2 pathway may connect tumor suppression and cell polarity to neuroinflammation.

Effects of lithium on inflammation

Lithium is an effective medication for the treatment of bipolar affective disorder. Accumulating evidence suggests that inflammation plays a role in the pathogenesis of bipolar disorder and that lithium has anti-inflammatory effects that may contribute to its therapeutic efficacy. This article summarizes the studies which examined the effects of lithium on pro- and anti-inflammatory mediators. Some of the summarized data suggest that lithium exerts anti-inflammatory effects (e.g., suppression of cyclooxygenase-2 expression, inhibition of interleukin (IL)-1β and tumor necrosis factor-α production, and enhancement of IL-2 and IL-10 synthesis). Nevertheless, there is a large body of data which indicates that under certain experimental conditions lithium also exhibits pro-inflammatory properties (e.g., induction of IL-4, IL-6 and other pro-inflammatory cytokines synthesis). The reviewed studies utilized various experimental model systems, and it is thus difficult to draw an unequivocal conclusion regarding the effect of lithium on specific inflammatory mediators.

p53 functional inhibitors behaving like pifithrin-β counteract the Alzheimer peptide non-β-amyloid component effects in human SH-SY5Y cells

Alzheimer's disease (AD) develops from a complex setting of genetic and biochemical alterations, including an increased level of p53 in the brain. Here, the robust and specific activation of p53 by the fibrillar non-β-amyloid component (NAC) of AD was demonstrated in human neuroblastoma SH-SY5Y cells. For the first time, the increase in the level of p53 target gene transcription, the cell cycle arrest, and the induction of apoptosis elicited by NAC were evidenced. These effects were counterbalanced by pifithrin-β, a small molecule interfering with the p53 functions. Using the structure of a pifithrin-β analogue as a reference, a pharmacophore-based virtual screening of the ZINC database was performed. Among the resulting hits, 20 druglike heterocyclic compounds were selected and evaluated for their neuroprotective activity against fibrillar NAC in the human SH-SY5Y cellular model. Three compounds exhibited neuroprotective effects. In particular, 2-(4-methoxyphenyl)-7-methyl-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine resulted in a promising lead compound for further development of anti-AD agents in terms of neuroprotection, reducing the rate of NAC-induced cell death with an activity higher than that of pifithrin-β, as a result of a more effective functional inhibition of p53 target gene transcription.

The p53 transcription factor modulates microglia behavior through microRNA-dependent regulation of c-Maf

Neuroinflammation occurs in acute and chronic CNS injury, including stroke, traumatic brain injury, and neurodegenerative diseases. Microglia are specialized resident myeloid cells that mediate CNS innate immune responses. Disease-relevant stimuli, such as reactive oxygen species (ROS), can influence microglia activation. Previously, we observed that p53, a ROS-responsive transcription factor, modulates microglia behaviors in vitro and in vivo, promoting proinflammatory functions and suppressing downregulation of the inflammatory response and tissue repair. In this article we describe a novel mechanism by which p53 modulates the functional differentiation of microglia both in vitro and in vivo. Adult microglia from p53-deficient mice have increased expression of the anti-inflammatory transcription factor c-Maf. To determine how p53 negatively regulates c-Maf, we examined the impact of p53 on known c-Maf regulators. MiR-155 is a microRNA that targets c-Maf. We observed that cytokine-induced expression of miR-155 was suppressed in p53-deficient microglia. Furthermore, Twist2, a transcriptional activator of c-Maf, is increased in p53-deficient microglia. We identified recognition sites in the 3' untranslated region of Twist2 mRNA that are predicted to interact with two p53-dependent microRNAs: miR-34a and miR-145. In this article, we demonstrate that miR-34a and -145 are regulated by p53 and negatively regulate Twist2 and c-Maf expression in microglia and the RAW macrophage cell line. Taken together, these findings support the hypothesis that p53 activation induced by local ROS or accumulated DNA damage influences microglia functions and that one specific molecular target of p53 in microglia is c-Maf.

Cognitive impairments accompanying rodent mild traumatic brain injury involve p53-dependent neuronal cell death and are ameliorated by the tetrahydrobenzothiazole PFT-α

With parallels to concussive mild traumatic brain injury (mTBI) occurring in humans, anesthetized mice subjected to a single 30 g weight drop mTBI event to the right parietal cortex exhibited significant diffuse neuronal degeneration that was accompanied by delayed impairments in recognition and spatial memory. To elucidate the involvement of reversible p53-dependent apoptosis in this neuronal loss and associated cognitive deficits, mice were subjected to experimental mTBI followed by the systemic administration of the tetrahydrobenzothiazole p53 inactivator, PFT-α, or vehicle. Neuronal loss was quantified immunohistochemically at 72 hr. post-injury by the use of fluoro-Jade B and NeuN within the dentate gyrus on both sides of the brain, and recognition and spatial memory were assessed by novel object recognition and Y-maze paradigms at 7 and 30 days post injury. Systemic administration of a single dose of PFT-α 1 hr. post-injury significantly ameliorated both neuronal cell death and cognitive impairments, which were no different from sham control animals. Cellular studies on human SH-SY5Y cells and rat primary neurons challenged with glutamate excitotoxicity and H₂O₂ induced oxidative stress, confirmed the ability of PFT-α and a close analog to protect against these TBI associated mechanisms mediating neuronal loss. These studies suggest that p53-dependent apoptotic mechanisms underpin the neuronal and cognitive losses accompanying mTBI, and that these are potentially reversible by p53 inactivation.

p53 in neurodegenerative diseases and brain cancers

More than thirty years elapsed since a protein, not yet called p53 at the time, was detected to bind SV40 during viral infection. Thousands of papers later, p53 evolved as the main tumor suppressor involved in growth arrest and apoptosis. A lot has been done but the protein has not yet revealed all its secrets. Particularly important is the observation that in totally distinct pathologies where apoptosis is either exacerbated or impaired, p53 appears to play a central role. This is exemplified for Alzheimer's and Parkinson's diseases that represent the two main causes of age-related neurodegenerative affections, where cell death enhancement appears as one of the main etiological paradigms. Conversely, in cancers, about half of the cases are linked to mutations in p53 leading to the impairment of p53-dependent apoptosis. The involvement of p53 in these pathologies has driven a huge amount of studies aimed at designing chemical tools or biological approaches to rescue p53 defects or over-activity. Here, we describe the data linking p53 to neurodegenerative diseases and brain cancers, and we document the various strategies to interfere with p53 dysfunctions in these disorders.

Neuroprotective effects of psychotropic drugs in Huntington's disease

Psychotropics (antipsychotics, mood stabilizers, antidepressants, anxiolytics, etc.) are commonly prescribed to treat Huntington’s disease (HD). In HD preclinical models, while no psychotropic has convincingly affected huntingtin gene, HD modifying gene, or huntingtin protein expression, psychotropic neuroprotective effects include upregulated huntingtin autophagy (lithium), histone acetylation (lithium, valproate, lamotrigine), miR-222 (lithium-plus-valproate), mitochondrial protection (haloperidol, trifluoperazine, imipramine, desipramine, nortriptyline, maprotiline, trazodone, sertraline, venlafaxine, melatonin), neurogenesis (lithium, valproate, fluoxetine, sertraline), and BDNF (lithium, valproate, sertraline) and downregulated AP-1 DNA binding (lithium), p53 (lithium), huntingtin aggregation (antipsychotics, lithium), and apoptosis (trifluoperazine, loxapine, lithium, desipramine, nortriptyline, maprotiline, cyproheptadine, melatonin). In HD live mouse models, delayed disease onset (nortriptyline, melatonin), striatal preservation (haloperidol, tetrabenazine, lithium, sertraline), memory preservation (imipramine, trazodone, fluoxetine, sertraline, venlafaxine), motor improvement (tetrabenazine, lithium, valproate, imipramine, nortriptyline, trazodone, sertraline, venlafaxine), and extended survival (lithium, valproate, sertraline, melatonin) have been documented. Upregulated CREB binding protein (CBP; valproate, dextromethorphan) and downregulated histone deacetylase (HDAC; valproate) await demonstration in HD models. Most preclinical findings await replication and their limitations are reviewed. The most promising findings involve replicated striatal neuroprotection and phenotypic disease modification in transgenic mice for tetrabenazine and for sertraline. Clinical data consist of an uncontrolled lithium case series (n = 3) suggesting non-progression and a primarily negative double-blind, placebo-controlled clinical trial of lamotrigine.

Blockage of CR1 prevents activation of rodent microglia

The importance of the complement system in Alzheimer's disease (AD) pathogenesis has been emphasized through recent genome wide association studies. However, the cellular and molecular role of these complement proteins is not fully understood. Microglia express complement receptors and the activation of specific receptors may increase Aβ clearance and reduce neurodegeneration. Here, we investigated the contribution of complement receptor 1 (CR1), the second most significant hit in GWAS studies, on microglia to neuronal damage. We show that microglia displaying an activated phenotype demonstrate an increase in CR1 expression. We also provide evidence that activation of microglial CR1 was detrimental to neurons and this correlated with an increase in microglial intracellular superoxide generation, and tumour necrosis factor-α (TNFα) and interleukin-1 β (IL-1β) secretion. Amyloid-β 42 (Aβ1-42)-treated microglia displayed an increased ability to phagocytose dextran beads following antibody blockage of CR1 but a decreased capacity to phagocytose fluorescent-tagged Aβ1-42. Together, these results indicate that microglial CR1 plays a role in the neuronal death observed in AD and investigating this further may provide a possible strategy to control neurotoxicity in the AD brain.

Wnt3a induces exosome secretion from primary cultured rat microglia

Background

Microglia, the immune effector cells of the CNS and the signaling molecule Wnt, both play critical roles in neurodevelopment and neurological disease. Here we describe the inducible release of exosomes from primary cultured rat microglia following treatment with recombinant carrier-free Wnt3a.

Results

Wnt3a was internalised into microglia, being detectable in early endosomes, and secreted in exosomes through a GSK3-independent mechanism. Electron microscopy demonstrated that exosomes were elliptical, electron-dense (100 nm) vesicles that coalesced with time in vitro. In contrast to microglia, primary cortical neurons released exosomes constitutively and the quantity of exosomes released was not altered by Wnt3a treatment. The proteomic profile of the microglial-derived exosomes was characterised using liquid chromatography-tandem mass spectrometry (LC/MS/MS) and the vesicles were found to be associated with proteins involved in cellular architecture, metabolism, protein synthesis and protein degradation including β-actin, glyceraldehyde-3-phosphate dehydrogenase, ribosomal subunits and ubiquitin (45 proteins in total). Unlike lipopolysaccharide, Wnt3a did not induce a neurotoxic, pro-inflammatory phenotype in primary microglia.

Conclusion

These findings reveal a novel mechanism through which Wnt3a signals in microglia resulting in the release of exosomes loaded with proteinaceous cargo.

Toll-like receptor 2 ligands promote microglial cell death by inducing autophagy

Microglial cells are phagocytes in the central nervous system (CNS) and become activated in pathological conditions, resulting in microgliosis, manifested by increased cell numbers and inflammation in the affected regions. Thus, controlling microgliosis is important to prevent pathological damage to the brain. Here, we evaluated the contribution of Toll-like receptor 2 (TLR2) to microglial survival. We observed that activation of microglial cells with peptidoglycan (PGN) from Staphylococcus aureus and other TLR2 ligands results in cell activation followed by the induction of autophagy and autophagy-dependent cell death. In C57BL/6J mice, intracerebral injection of PGN increased the autophagy of microglial cells and reduced the microglial/macrophage cell number in brain parenchyma. Our results demonstrate a novel role of TLRs in the regulation of microglial cell activation and survival, which are important for the control of microgliosis and associated inflammatory responses in the CNS.

Microglia, Alzheimer's disease, and complement

Microglia, the immune cell of the brain, are implicated in cascades leading to neuronal loss and cognitive decline in Alzheimer's disease (AD). Recent genome-wide association studies have indicated a number of risk factors for the development of late-onset AD. Two of these risk factors are an altered immune response and polymorphisms in complement receptor 1. In view of these findings, we discuss how complement signalling in the AD brain and microglial responses in AD intersect. Dysregulation of the complement cascade, either by changes in receptor expression, enhanced activation of different complement pathways or imbalances between complement factor production and complement cascade inhibitors may all contribute to the involvement of complement in AD. Altered complement signalling may reduce the ability of microglia to phagocytose apoptotic cells and clear amyloid beta peptides, modulate the expression by microglia of complement components and receptors, promote complement factor production by plaque-associated cytokines derived from activated microglia and astrocytes, and disrupt complement inhibitor production. The evidence presented here indicates that microglia in AD are influenced by complement factors to adopt protective or harmful phenotypes and the challenge ahead lies in understanding how this can be manipulated to therapeutic advantage to treat late onset AD.

Mood stabilizers commonly restore staurosporine-induced increase of p53 expression and following decrease of Bcl-2 expression in SH-SY5Y cells

Adult neurogenesis in dentate gyrus (DG) is involved in the action mechanism of mood stabilizers. However, it is poorly understood how mood stabilizers affect adult neurogenesis in DG. Neurogenesis consists of proliferation, survival (anti-apoptosis) and differentiation of neural precursor cells in adult DG. Using in vitro culture of adult rat DG-derived neural precursor cells (ADP), we have already shown that four mood stabilizers, such as lithium (Li), valproate (VPA), carbamazepine (CBZ) and lamotrigine (LTG), commonly decrease staurosporine (STS)-induced apoptosis of ADP. These suggest that the common anti-apoptotic effect of mood stabilizers could be involved in mood-stabilizing effects. Past studies have shown that Li and VPA increase the expression of Bcl-2, an anti-apoptotic gene. In addition, it has been shown that Li decreases the expression of p53, which plays a prominent role in apoptosis and regulates the expression of Bcl-2. Therefore, p53 and Bcl-2 can be considered to mediate the common anti-apoptotic effects of Li, VPA, CBZ and LTG. To elucidate the molecular mechanism underlying the common anti-apoptotic effects of mood stabilizers, we investigated the effects of Li, VPA, CBZ and LTG on STS-induced expression changes of p53, Bcl-2 and other p53-related molecules using SH-SY5Y cells as a model of neural precursor-like cells. STS increased the expression of p53 and decreased that of Bcl-2. These effects of STS on p53 and Bcl-2 are restored by all of Li, VPA, CBZ and LTG. In addition, p53 overexpression decreased the expression of Bcl-2. Taken together, these results suggest that p53 and Bcl-2 may be involved in a part of mood-stabilizing effects.

Neuroprotection by the histone deacetylase inhibitor trichostatin A in a model of lipopolysaccharide-sensitised neonatal hypoxic-ischaemic brain injury

Background

Perinatal brain injury is complex and often associated with both inflammation and hypoxia-ischaemia (HI). In adult inflammatory brain injury models, therapies to increase acetylation are efficacious in reducing inflammation and cerebral injury. Our aim in the present study was to examine the neuropathological and functional effects of the histone deacetylase inhibitor (HDACi) trichostatin A (TSA) in a model of neonatal lipopolysaccharide (LPS)-sensitised HI. We hypothesised that, by decreasing inflammation, TSA would improve injury and behavioural outcome. Furthermore, TSA’s effects on oligodendrocyte development, which is acetylation-dependent, were investigated.

Methods

On postnatal day 8 (P8), male and female mice were exposed to LPS together with or without TSA. On P9 (14 hours after LPS), mice were exposed to HI (50 minutes at 10% O₂). Neuropathology was assessed at 24 hours, 5 days and 27 days post-LPS/HI via immunohistochemistry and/or Western blot analysis for markers of grey matter (microtubule-associated protein 2), white matter (myelin basic protein) and cell death (activated caspase-3). Effects of TSA on LPS or LPS/HI-induced inflammation (cytokines and microglia number) were assessed by Luminex assay and immunohistochemistry. Expression of acetylation-dependent oligodendrocyte maturational corepressors was assessed with quantitative PCR 6 hours after LPS and at 24 hours and 27 days post-LPS/HI. Animal behaviour was monitored with the open-field and trace fear-conditioning paradigms at 25 days post-LPS/HI to identify functional implications of changes in neuropathology associated with TSA treatment.

Results

TSA induced increased Ac-H4 in females only after LPS exposure. Also only in females, TSA reduced grey matter and white matter injury at 5 days post-LPS/HI. Treatment altered animal behaviour in the open field and improved learning in the fear-conditioning test in females compared with LPS/HI-only females at 25 days post-HI. None of the inflammatory mechanisms assessed that are known to mediate neuroprotection by HDACi in adults correlated with improved outcome in TSA-treated neonatal females. Oligodendrocyte maturation was not different between the LPS-only and LPS + TSA-treated mice before or after exposure to HI.

Conclusions

Hyperacetylation with TSA is neuroprotective in the female neonatal mouse following LPS/HI and correlates with improved learning long-term. TSA appears to exert neuroprotection via mechanisms unique to the neonate. Deciphering the effects of age, sex and inflammatory sensitisation in the cerebral response to HDACi is key to furthering the potential of hyperacetylation as a viable neuroprotectant. TSA did not impair oligodendrocyte maturation, which increases the possible clinical relevance of this strategy.

Amyloid neurotoxicity is attenuated by metallothionein: dual mechanisms at work

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of memory and cognition. One of the hallmarks of AD is the accumulation of beta-amyloid (Aβ). Although endoplasmic reticulum stress, mitochondrial dysfunction, and oxidative stress have been implicated in Aβ toxicity, the molecular mechanism(s) of Aβ-induced neurotoxicity are not fully understood. In this study, we present evidence that the glia-derived stress protein metallothionein (MT) attenuates Aβ-induced neurotoxicity by unique mechanisms. MT expression was increased in brain astrocytes of a NSE-APPsw transgenic mouse model of AD. Astrocyte-derived MT protected N2a neuroblastoma cells and primary cortical neurons against Aβ toxicity with concurrent reduction of reactive oxygen species levels. MT reversed Aβ-induced down-regulation of Bcl-2 and survival signaling in neuroblastoma cells. Moreover, MT inhibited Aβ-induced proinflammatory cytokine production from microglia. The neurotoxicity of Aβ-stimulated microglia was significantly attenuated by MT-I. The results indicate that MT released from reactive astrocytes may antagonize Aβ neurotoxicity by direct inhibition of Aβ neurotoxicity and indirect suppression of neurotoxic microglial activation. These findings broaden the understanding of neurotoxic mechanisms of Aβ and the crosstalk between Aβ and MT in AD.

Emerging roles of p53 in glial cell function in health and disease

Emerging evidence suggests that p53, a tumor suppressor protein primarily involved in cancer biology, coordinates a wide range of novel functions in the CNS including the mediation of pathways underlying neurodegenerative disease pathogenesis. Moreover, an evolving concept in cell and molecular neuroscience is that glial cells are far more fundamental to disease progression than previously thought, which may occur via a noncell-autonomous mechanism that is heavily dependent on p53 activities. As a crucial hub connecting many intracellular control pathways, including cell-cycle control and apoptosis, p53 is ideally placed to coordinate the cellular response to a range of stresses. Although neurodegenerative diseases each display a distinct and diverse molecular pathology, apoptosis is a widespread hallmark feature and the multimodal capacity of the p53 system to orchestrate apoptosis and glial cell behavior highlights p53 as a potential unifying target for therapeutic intervention in neurodegeneration.

Moderate dietary restriction reduces p53-mediated neurovascular damage and microglia activation after hypoxic ischemia in neonatal brain

BACKGROUND AND PURPOSE

Neurovascular damage, including neuronal apoptosis and blood-brain barrier (BBB) damage, and microglia activation account for the hypoxic-ischemia (HI) susceptibility in neonatal brain. The p53 upregulation is involved in apoptosis, endothelial cell damage, and microglia activation. We hypothesized that underweight induced by dietary restriction (DR) protects against HI in rat pups by attenuating p53-mediated neurovascular damage.

METHODS

Male rat pups were grouped as normal litter (NL) size (12 pups/dam), DR (18 pups/dam), and extreme DR (24 pups/dam) from postnatal day 1 and subjected to HI on postnatal day 7. Immunohistochemistry and immunoblotting were used to determine p53, phospho-murine double minute-2, caspases, BBB damage and microglia activation, and immunofluorescence to determine the cellular distribution of p53. Pharmacological approaches were used to regulate p53.

RESULTS

The NL, DR, and extreme DR pups had similar TUNEL-positive cells and caspases on postnatal day 7 and comparable learning performance at adulthood. After HI, the DR-HI, but not extreme DR-HI, pups had significantly lower p53, higher phospho-murine double minute-2, lower cleaved caspases, less BBB damage and microglia activation, and less brain volume loss than NL-HI pups. In NL-HI pups, p53 expression was located mainly in the neurons, endothelial cells, and microglia. The p53 blockage by pifithrin-α in NL-HI pups decreased apoptosis, BBB damage, and microglia activation, and was neuroprotective. In contrast, upregulating p53 by nutlin-3 in DR-HI pups increased apoptosis, BBB damage, and microglia activation, and worsened brain damage.

CONCLUSIONS

Moderate DR, but not extreme DR, reduces p53-mediated neurovascular damage after HI and confers long-term protection in neonatal brain.

Role of p53 in neurodegenerative diseases

BACKGROUND

p53 plays an important role in many areas of cellular physiology and biology, ranging from cellular development and differentiation to cell cycle arrest and apoptosis. Many of its functions are attributed to its role in assuring proper cellular division. However, since the establishment of its role in cell cycle arrest, damage repair, and apoptosis (thus also establishing its importance in cancer development), numerous reports have demonstrated additional functions of p53 in various cells. In particular, p53 appears to have important functions as it relates to neurodegeneration and synaptic plasticity.

OBJECTIVE

In this review, we will address p53 functions as it relates to various neurodegenerative diseases, mainly its implications in the development of HIV-associated neurocognitive disorders.

CONCLUSION

p53 plays a pivotal role in the development of neurodegenerative diseases through its interaction with cellular factors, viral factors, and/or small RNAs that have the ability to promote the development of these diseases. Hence, inhibition of p53 may present an ideal target to restore neuronal functions.

Positive allosteric modulation of metabotropic glutamate receptor 5 down-regulates fibrinogen-activated microglia providing neuronal protection

Microglial activation and blood brain barrier dysfunction are significant hallmarks in an array of neurodegenerative disorders. A leaky blood brain barrier potentially allows infiltration of blood-borne proteins into the CNS parenchyma, and previous studies have shown that the blood borne protein fibrinogen (FG) can activate microglia to produce a neurotoxic phenotype. Here we show that FG-mediated neurotoxicity and ERK1/2 phosphorylation in neuronal cultures is significantly attenuated by activation of metabotropic glutamate receptor 5 (mGluR5) but not mGluR2. Furthermore, FG-mediated microglial activation was down-regulated by direct mGluR5 activation on these cells but not by mGluR2, suggesting that targeting microglial mGluR5 provides neuronal protection against blood protein-triggered innate inflammatory responses.

Two Blood Monocytic Biomarkers (CCL15 and p21) Combined with the Mini-Mental State Examination Discriminate Alzheimer's Disease Patients from Healthy Subjects

Background

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. In AD, monocytes migrate across the blood-brain barrier and differentiate into microglia, are linked to inflammatory responses and display age-dependent decreases in telomere lengths.

Methods

Six monocyte-specific chemokines and the (telomere-associated) tumor suppressor proteins p53 and p21 were determined by multiplex immunoassay in plasma and monocyte extracts of patients with AD or mild cognitive impairment, and levels were compared between patients and controls (without cognitive impairment).

Results

CCL15 (macrophage inflammatory protein-1δ), CXCL9 (monokine-induced by interferon-γ) and p21 levels were decreased in monocytes of AD patients compared with controls.

Conclusion

The combination of monocytic CCL15 and p21 together with the Mini-Mental State Examination enables to differentiate AD patients from controls with high specificity and sensitivity.

Interleukin 4 induces the apoptosis of mouse microglial cells by a caspase-dependent mechanism

Microglial cells are resident macrophages in the central nervous system (CNS) and become activated in many pathological conditions. Activation of microglial cells results in reactive microgliosis, manifested by an increase in cell number in the affected CNS regions. The control of microgliosis may be important to prevent pathological damage to the brain. The type 2 cytokine IL-4 has been reported to be protective in brain inflammation. However, its effect on microglial cell survival was not well understood. In this study, we report a dual effect of IL-4 on the survival of mouse microglial cells. In a 6h short term culture, IL-4 reduced the death of microglial cells induced by staurosporine. In contrast, in long term treatment (more than 48h), IL-4 increased the apoptotic death of both primary mouse microglial cells and a microglial cell line N9. Mechanistic studies revealed that, in microglial cells, IL-4 increased the levels of cleaved caspase 3 and PARP, which is down-stream of activated caspase 3. In addition, IL-4 down regulated the autophagy and the antiapoptotic protein Bcl-xL in microglial cells. On the other hand, the pre-incubation of microglial cells with IL-4 for 24h, attenuated the cell death induced by the neurotoxic peptide amyloid beta 1-42 (Aβ42). Our observations demonstrate a novel function of IL-4 in regulating the survival of microglial cells, which may have important significance in reduction of undesired inflammatory responses in the CNS.

Transcription factor p53 influences microglial activation phenotype

Several neurodegenerative diseases are influenced by the innate immune response in the central nervous system (CNS). Microglia have proinflammatory and subsequently neurotoxic actions as well as anti-inflammatory functions that promote recovery and repair. Very little is known about the transcriptional control of these specific microglial behaviors. We have previously shown that in HIV-associated neurocognitive disorders (HAND), the transcription factor p53 accumulates in microglia and that microglial p53 expression is required for the in vitro neurotoxicity of the HIV coat glycoprotein gp120. These findings suggested a novel function for p53 in regulating microglial activation. Here, we report that in the absence of p53, microglia demonstrate a blunted response to interferon-γ, failing to increase expression of genes associated with classical macrophage activation or secrete proinflammatory cytokines. Microarray analysis of global gene expression profiles revealed increased expression of genes associated with anti-inflammatory functions, phagocytosis, and tissue repair in p53 knockout (p53(-/-)) microglia compared with those cultured from strain matched p53 expressing (p53(+/+)) mice. We further observed that p53(-/-) microglia demonstrate increased phagocytic activity in vitro and expression of markers for alternative macrophage activation both in vitro and in vivo. In HAND brain tissue, the alternative activation marker CD163 was expressed in a separate subset of microglia than those demonstrating p53 accumulation. These data suggest that p53 influences microglial behavior, supporting the adoption of a proinflammatory phenotype, while p53 deficiency promotes phagocytosis and gene expression associated with alternative activation and anti-inflammatory functions.

Chromogranin peptides in brain diseases

Synaptic disturbances may play a key role in the pathophysiology of neuropsychiatric diseases. In this article, we review immunohistological findings of chromogranin peptides in neurodegenerative and neurodevelopmental disorders, with particular emphasis on Alzheimer's disease, the disorder chromogranins have been studied most extensively. Data was collected from existing and new experimental data and medline research. This review focuses on synaptic changes elicited by chromogranin peptides immunoreactivity in Alzheimer's disease, as well in schizophrenia and amyotrophic lateral sclerosis (ALS). An imbalanced availability of chromogranin peptides may be responsible for impaired neurotransmission and a reduced functioning of dense core vesicles. Since chromogranin A was postulated as a potent proinflammatory agent, we focused on chromogranin A in neuroinflammation in Alzheimer's disease and ALS. Further understanding of role and function of chromogranin peptides in neuropathological conditions is still required.