Grooming and growing with microglia

Neurobiology and Therapeutic Potential of Cyclooxygenase-2 (COX-2) Inhibitors for Inflammation in Neuropsychiatric Disorders

Neuropsychiatric disorders, such as depression, bipolar disorder, schizophrenia, obsessive-compulsive disorder, and neurodevelopmental disorders such as autism spectrum disorder, are associated with significant illness burden. Accumulating evidence supports an association between these disorders and inflammation. Consequently, anti-inflammatory agents, such as the cyclooxygenase-2 inhibitors, represent a novel avenue to prevent and treat neuropsychiatric illness. In this paper, we first review the role of inflammation in psychiatric pathophysiology including inflammatory cytokines' influence on neurotransmitters, the hypothalamic-pituitary-adrenal axis, and microglial mechanisms. We then discuss how cyclooxygenase-2-inhibitors influence these pathways with potential therapeutic benefit, with a focus on celecoxib, due to its superior safety profile. A search was conducted in PubMed, Embase, and PsychINFO databases, in addition to Clinicaltrials.gov and the Stanley Medical Research Institute trial registries. The results were presented as a narrative review. Currently available outcomes for randomized controlled trials up to November 2017 are also discussed. The evidence reviewed here suggests cyclooxygenase-2 inhibitors, and in particular celecoxib, may indeed assist in treating the symptoms of neuropsychiatric disorders; however, further studies are required to assess appropriate illness stage-related indication.

HIV Tat protein: Is Tat-C much trickier than Tat-B?

Out of various subtypes of human immunodeficiency virus type 1 (HIV-1), subtype B and C cause most of the infections worldwide. Clade specific differences have been reported in differences in clinical picture of HIV pathogenesis. Transcription of the HIV-1 genome is regulated by the interaction of HIV Tat protein to the trans-activation response (TAR) element. The differential binding of clade B and C Tat proteins to TAR and differences in activation of NF-κB cascade leading to differential transactivation capacity and cytokine expression has been examined in this study. More stable Tat-TAR complex formation by Tat-C revealed by EMSA and higher TNF-α expression shown by Tat-C compared to Tat-B leads to higher NF-κB activation, which may be plausible cause for higher transactivation by Tat-C as obtained by FACS analysis. This comparative study would be helpful in understanding the basic mechanism of clade specific Tat protein differences and their functional relationships.

Pharmacological, experimental therapeutic, and transcranial magnetic stimulation treatments for compulsivity and impulsivity

Obsessive-compulsive disorder (OCD) has been recently drawn apart from anxiety disorder by the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) and clustered together with related disorders (eg, hoarding, hair pulling disorder, skin picking), which with it seems to share clinical and neurophysiological similarities. Recent literature has mainly explored brain circuitries (eg, orbitofrontal cortex, striatum), molecular pathways, and genes (eg, Hoxb8, Slitrk5, Sapap3) that represent the new target of the treatments; they also lead the development of new probes and compounds. In the therapeutic field, monotherapy with cognitive behavioral therapy (CBT) or selective serotonin reuptake inhibitors (SSRIs) is recommendable, but combination or augmentation with a dopaminergic or glutamatergic agent is often adopted. A promising therapy for OCD is represented by repetitive transcranial magnetic stimulation (rTMS), which is suitable to treat compulsivity and impulsivity depending on the protocol of stimulation and the brain circuitries targeted.

Neuropathogenesis: rogue glia cause mayhem in the brain

Glia, including astrocytes, microglia and oligodendrocytes, are important components that maintain the architecture of the brain and in many ways contribute to the proper functioning of neurons. Glial cells vastly outnumber neurons in the brain and independently control several crucial brain functions. Impaired glial cells are the cause of several diseases, and pharmacological targeting to repair damaged glia will enable functional recovery in patients suffering from devastating neurological disorders. The interaction between glial cells and some patrolling immune cells in the brain comprise the brain-specific immune system that protects the brain from extraneous agents and repairs injured tissue. While this system can cope with minor insults and infections, when faced with significant challenges such as AIDS dementia, multiple sclerosis, Huntington’s disease, Parkinson’s disease, etc., an effective and balanced immune response that facilitates repair and protection is found wanting. Several debilitating neurological disorders are often associated with dysfunctional glial cells that have limited ability to repair the injured brain and even promote brain damage. In this discussion, specific signaling pathways in glia that are affected in AIDS dementia and periventricular white matter injury will be highlighted.

Neuroinflammation and psychiatric illness

Multiple lines of evidence support the pathogenic role of neuroinflammation in psychiatric illness. While systemic autoimmune diseases are well-documented causes of neuropsychiatric disorders, synaptic autoimmune encephalitides with psychotic symptoms often go under-recognized. Parallel to the link between psychiatric symptoms and autoimmunity in autoimmune diseases, neuroimmunological abnormalities occur in classical psychiatric disorders (for example, major depressive, bipolar, schizophrenia, and obsessive-compulsive disorders). Investigations into the pathophysiology of these conditions traditionally stressed dysregulation of the glutamatergic and monoaminergic systems, but the mechanisms causing these neurotransmitter abnormalities remained elusive. We review the link between autoimmunity and neuropsychiatric disorders, and the human and experimental evidence supporting the pathogenic role of neuroinflammation in selected classical psychiatric disorders. Understanding how psychosocial, genetic, immunological and neurotransmitter systems interact can reveal pathogenic clues and help target new preventive and symptomatic therapies.

Roles of glial cells in schizophrenia: possible targets for therapeutic approaches

Glial cells consisting of oligodendrocytes, astrocytes, microglia, and NG2 positive cells are major cell populations in the central nervous system, number-wise. They function as effectors and modulators of neurodevelopment through a wide variety of neuron-glial cell interactions in brain development and functions. Glial cells can be affected by both genetic and environmental factors, leading to their dysfunctions in supporting neuronal development and functions. These in turn can affect neuronal cells, causing alterations at the circuitry level that manifest as behavioral characteristics associated with schizophrenia in late teens-early twenties. Glial cells are also involved in neuroinflammatory processes, which sometimes have deleterious effects on the normal brain development. If the glial involvement plays significant roles in schizophrenia, the processes involving glial cells can become possible therapeutic targets for schizophrenia. A number of known antipsychotics are shown to have beneficial effects on glial cells, but other drugs targeting glial cell functions may also have therapeutic effects on schizophrenia. The latter can be taken into consideration for future drug development for schizophrenia.

HIV-1 Tat C-mediated regulation of tumor necrosis factor receptor-associated factor-3 by microRNA 32 in human microglia

BACKGROUND

HIV-1 Tat protein is known to be associated with neuroinflammation, a condition that develops in almost half of patients infected with HIV-1. HIV-1 Tat can alter glial neuroprotective functions, leading to neurotoxicity within the CNS. HIV-1 Tat is known to be secreted from productively infected cells and can affect neighboring uninfected cells by modulating cellular gene expression in a bystander fashion.

METHODS

We were interested to study whether exogenous exposure to HIV-1 Tat-C protein perturbs the microRNA (miRNA) expression profile of human microglial cells, leading to altered protein expression. We used protein expression and purification, miRNA overexpression, miRNA knockdown, transfection, site-directed mutagenesis, real-time PCR, luciferase assay and western blotting techniques to perform our study.

RESULTS

HIV-1 Tat-C treatment of human microglial cells resulted in a dose-dependent increase in miR-32 expression. We found that tumor necrosis factor-receptor-associated factor 3 TRAF3) is a direct target for miR-32, and overexpression of miR-32 in CHME3 cells decreased TRAF3 both at the mRNA and the protein level. Recovery of TRAF3 protein expression after transfection of anti-miR-32 and the results of the luciferase reporter assay provided direct evidence of TRAF3 regulation by miR-32. We found that the regulation of interferon regulatory factor 3 (IRF3) and IRF7 is controlled by cellular levels of TRAF3 protein in microglial cells, as after overexpression of miR-32 and application of anti-miR-32, expression levels of IRF3 and IRF7 were inversely regulated by expression levels of TRAF3. Thus, our results suggest a novel miRNA mediated mechanism for regulation of TRAF3 in human microglial cells exposed to HIV-1 Tat C protein. These results may help to elucidate the detrimental neuroinflammatory consequences of HIV-1 Tat C protein in bystander fashion.

CONCLUSION

HIV-1 Tat protein can modulate TRAF3 expression through miRNA mediated pathway and can change the downstream expression of IRF3 and IRF7. This study demonstrates a novel mechanism of HIV-1 Tat C protein-mediated perturbation of miRNA, resulting in dysregulation of cellular TRAF3.

Neuropathogenesis of Noonan syndrome is mediated by inflammatory microglia

Microglia are resident hematopoietic cells that play important roles in the damaged or degenerating adult nervous system. Microglia are involved in neuropathogenesis of various diseases. Microglia are also essential for neuroprotection and comprise an essential component of the neural stem cell niche. The activation of microglia is an important phenomenon associated with several neurological disorders that arise from infections to developmental abnormalities and behavioral pathologies. Noonan syndrome (NS) is associated with mutations in the PTPN11 gene and also accounts for mental retardation in children. Interestingly, in mouse models of NS, mutations in the PTPN11 gene resulted in dysregulation of neural progenitors. The present study describes the activation of microglia in the NS mouse model, which results in an inflammatory phenotype with expression of IL-1b and defective phagocytosis. To test whether microglia from NS mice are important for neural precursor maintenance or self-renewal, embryonic neural precursors from the cortex of WT mice were cultured. Microglia from NS and WT mice were then added to cortical precursor cells which showed that microglia from NS mice inhibited astrogenesis. Together, these results demonstrate that microglia can dysregulate neural precursor development in NS, and suggest that alterations in microglial number as a consequence of genetic or pathological events may perturb neural development by directly affecting embryonic neural precursors.

Science Signaling Podcast: 9 November 2010

A nonvesicular, nonsynaptic form of communication between axons and neighboring cells may play a role under normal conditions and in disease.