Lipopolysaccharide administration in vivo induces differential expression of cAMP-specific phosphodiesterase 4B mRNA splice variants in the mouse brain

Comparative study of the expression of cholinergic system components in the CNS of experimental autoimmune encephalomyelitis mice: Acute vs remitting phase

Acetylcholine (ACh) is involved in the modulation of the inflammatory response. ACh levels are regulated by its synthesizing enzyme, choline acetyltransferase (ChAT), and by its hydrolyzing enzymes, mainly acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A more comprehensive understanding of the cholinergic system in experimental autoimmune encephalomyelitis (EAE) disease progression could pave the path for the development of therapies to ameliorate multiple sclerosis (MS). In this work, we analyzed possible alterations of the CNS cholinergic system in the neuroinflammation process by using a MOG-induced EAE mice model. MOG- and vehicle-treated animals were studied at acute and remitting phases. We examined neuropathology and analyzed mRNA expression of ChAT, AChE and the α7 subunit of the nicotinic acetylcholine receptor (α7nAChR), as well as AChE and BuChE enzyme activities, in brain and spinal cord sections during disease progression. The mRNA expression and enzyme activities of these cholinergic markers were up- or down-regulated in many cholinergic areas and other brain areas of EAE mice in the acute and remitting phases of the disease. BuChE was present in a higher proportion of astroglia and microglia/macrophage cells in the EAE remitting group. The observed changes in cholinergic markers expression and cellular localization in the CNS during EAE disease progression suggests their potential involvement in the development of the neuroinflammatory process and may lay the ground to consider cholinergic system components as putative anti-inflammatory therapeutic targets for MS.

The Past, Present, and Future of Phosphodiesterase-4 Modulation for Age-Induced Memory Loss

The purpose of this chapter is to highlight the state of progress for phosphodiesterase-4 (PDE4) modulation as a potential therapeutic for psychiatric illness, and to draw attention to particular hurdles and obstacles that must be overcome in future studies to develop PDE4-mediated therapeutics. Pathological and non-pathological related memory loss will be the focus of the chapter; however, we will at times also touch upon other psychiatric illnesses like anxiety and depression. First, we will provide a brief background of PDE4, and the rationale for its extensive study in cognition. Second, we will explore fundamental differences in individual PDE4 subtypes, and then begin to address differences between pathological and non-pathological aging. Alterations of cAMP/PDE4 signaling that occur within normal vs. pathological aging, and the potential for PDE4 modulation to combat these alterations within each context will be described. Finally, we will finish the chapter with obstacles that have hindered the field, and future studies and alternative viewpoints that need to be addressed. Overall, we hope this chapter will demonstrate the incredible complexity of PDE4 signaling in the brain, and will be useful in forming a strategy to develop future PDE4-mediated therapeutics for psychiatric illnesses.

Phosphodiesterase 4b expression plays a major role in alcohol-induced neuro-inflammation

It is increasingly evident that alcohol-induced, gut-mediated peripheral endotoxemia plays a significant role in glial cell activation and neuro-inflammation. Using a mouse model of chronic alcohol feeding, we examined the causal role of endotoxin- and cytokine-responsive Pde4 subfamily b (Pde4b) expression in alcohol-induced neuro-inflammation. Both pharmacologic and genetic approaches were used to determine the regulatory role of Pde4b. In C57Bl/6 wild type (WT) alcohol fed (WT-AF) animals, alcohol significantly induced peripheral endotoxemia and Pde4b expression in brain tissue, accompanied by a decrease in cAMP levels. Further, along with Pde4b, there was a robust activation of astrocytes and microglia accompanied by significant increases in the inflammatory cytokines (Tnfα, Il-1β, Mcp-1 and Il-17) and the generalized inflammatory marker Cox-2. At the cellular level, alcohol and inflammatory mediators, particularly LPS, Tnfα and Hmgb1 significantly activated microglial cells (Iba-1 expression) and selectively induced Pde4b expression with a minimal to no change in Pde4a and d isoforms. In comparison, the alcohol-induced decrease in brain cAMP levels was completely inhibited in WT mice treated with the Pde4 specific pharmacologic inhibitor rolipram and in Pde4b-/- mice. Moreover, all the observed markers of alcohol-induced brain inflammation were markedly attenuated. Importantly, glial cell activation induced by systemic endotoxemia (LPS administration) was also markedly decreased in Pde4b-/- mice. Taken together, these findings strongly support the notion that Pde4b plays a critical role in coordinating alcohol-induced, peripheral endotoxemia mediated neuro-inflammation and could serve as a significant therapeutic target.

The PDE4 cAMP-Specific Phosphodiesterases: Targets for Drugs with Antidepressant and Memory-Enhancing Action

The PDE4 cyclic nucleotide phosphodiesterases are essential regulators of cAMP abundance in the CNS through their ability to regulate PKA activity, the phosphorylation of CREB, and other important elements of signal transduction. In pre-clinical models and in early-stage clinical trials, PDE4 inhibitors have been shown to have antidepressant and memory-enhancing activity. However, the development of clinically-useful PDE4 inhibitors for CNS disorders has been limited by variable efficacy and significant side effects. Recent structural studies have greatly enhanced our understanding of the molecular configuration of PDE4 enzymes, especially the "long" PDE4 isoforms that are abundant in the CNS. The new structural data provide a rationale for the development of a new generation of PDE4 inhibitors that specifically act on long PDE4 isoforms. These next generation PDE4 inhibitors may also be capable of targeting the interactions of select long forms with their "partner" proteins, such as RACK1, β-arrestin, and DISC1. They would therefore have the ability to affect cAMP levels in specific cellular compartments and target localized cellular functions, such as synaptic plasticity. These new agents might also be able to target PDE4 populations in select regions of the CNS that are implicated in learning and memory, affect, and cognition. Potential therapeutic uses of these agents could include affective disorders, memory enhancement, and neurogenesis.

Reduced Contextual Discrimination following Alcohol Consumption or MDMA Administration in Mice

The recreational drugs, alcohol and 3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") have both been shown to cause immune activation in vivo, and they are linked to cognitive impairment and anxiety-like behaviors in rodents. The neuronal effects of these drugs in the hippocampal area, an area that has been a focus of studies aiming to explain the mechanisms underlying anxiety related-disorders, remains poorly understood. Therefore we investigated the specific inflammatory impact of alcohol and MDMA on this area of the brain and on a hippocampal-related behavioral task. We centered our study on two inflammatory factors linked to anxiety-related disorders, namely Interleukin-1β (IL-1β) and brain-derived neurotrophic factor (BDNF). We subjected drug-consuming mice to a battery of behavioral tests to evaluate general activity, anxiety-like and depressive-live behaviors. We then introduced them to a contextual fear discrimination task and immune-related effects were examined by immunohistochemical and biochemical studies. Our results suggest that there is a relationship between the induction of immune activated pathways by voluntary alcohol consumption and a high-dose MDMA. Furthermore, the ability of mice to perform a contextual fear discrimination task was impaired by drug consumption and we report long term inflammatory alterations in the hippocampus even several weeks after drug intake. This information will be helpful for discovering new selective drug targets, and to develop treatments and preventive approaches for patients with anxiety-related disorders.

Macrophage subsets and microglia in multiple sclerosis

Along with microglia and monocyte-derived macrophages, macrophages in the perivascular space, choroid plexus, and meninges are the principal effector cells in neuroinflammatory and neurodegenerative disorders. These phagocytes are highly heterogeneous cells displaying spatial- and temporal-dependent identities in the healthy, injured, and inflamed CNS. In the last decade, researchers have debated on whether phagocytes subtypes and phenotypes are pathogenic or protective in CNS pathologies. In the context of this dichotomy, we summarize and discuss the current knowledge on the spatiotemporal physiology of macrophage subsets and microglia in the healthy and diseased CNS, and elaborate on factors regulating their behavior. In addition, the impact of macrophages present in lymphoid organs on CNS pathologies is defined. The prime focus of this review is on multiple sclerosis (MS), which is characterized by inflammation, demyelination, neurodegeneration, and CNS repair, and in which microglia and macrophages have been extensively scrutinized. On one hand, microglia and macrophages promote neuroinflammatory and neurodegenerative events in MS by releasing inflammatory mediators and stimulating leukocyte activity and infiltration into the CNS. On the other hand, microglia and macrophages assist in CNS repair through the production of neurotrophic factors and clearance of inhibitory myelin debris. Finally, we define how microglia and macrophage physiology can be harnessed for new therapeutics aimed at suppressing neuroinflammatory and cytodegenerative events, as well as promoting CNS repair. We conclude that microglia and macrophages are highly dynamic cells displaying disease stage and location-specific fates in neurological disorders. Changing the physiology of divergent phagocyte subsets at particular disease stages holds promise for future therapeutics for CNS pathologies.

Meningeal and choroid plexus cells--novel drug targets for CNS disorders

The meninges and choroid plexus perform many functions in the developing and adult human central nervous system (CNS) and are composed of a number of different cell types. In this article I focus on meningeal and choroid plexus cells as targets for the development of drugs to treat a range of traumatic, ischemic and chronic brain disorders. Meningeal cells are involved in cortical development (and their dysfunction may be involved in cortical dysplasia), fibrotic scar formation after traumatic brain injuries (TBI), brain inflammation following infections, and neurodegenerative disorders such as Multiple Sclerosis (MS) and Alzheimer's disease (AD) and other brain disorders. The choroid plexus regulates the composition of the cerebrospinal fluid (CSF) as well as brain entry of inflammatory cells under basal conditions and after injuries. The meninges and choroid plexus also link peripheral inflammation (occurring in the metabolic syndrome and after infections) to CNS inflammation which may contribute to the development and progression of a range of CNS neurological and psychiatric disorders. They respond to cytokines generated systemically and secrete cytokines and chemokines that have powerful effects on the brain. The meninges may also provide a stem cell niche in the adult brain which could be harnessed for brain repair. Targeting meningeal and choroid plexus cells with therapeutic agents may provide novel therapies for a range of human brain disorders.

Critical role for PDE4 subfamilies in the development of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis exhibiting neuroinflammation, axonal damage and demyelination, further characterized by T- and B-cell responses to myelin oligodendrocyte glycoprotein. Pharmacological manipulation of phosphodiesterases (PDEs) provokes profound anti-inflammatory responses through modulation of cAMP levels. The PDE4B subfamily has been related to the inflammatory immune response in mice and PDE4 inhibition produces amelioration of the clinical signs and delayed onset in the EAE model. Analyses of the expression of the mRNA coding for PDE4B splice variants revealed an upregulation of PDE4B2 in the brainstem and spinal cord of EAE mice which correlated with forkhead box P3 (FoxP3) and transforming growth factor beta (TGF-β) mRNAs expression in a score-dependent manner. The increase observed for the PDE4B protein was mainly found in antigen-presenting cells (APCs) such as dendritic cells and microglia/macrophages, in areas with high cellular infiltration. Unexpectedly, PDE4B(-/-) mice showed an earlier onset of the disease compared to wildtype mice. The results point to a possible role of the PDE4B enzyme and in particular the PDE4B2 splice variant during EAE pathogenesis, probably by modulating cAMP levels in APCs, consequently influencing the cytokine environment important for T-cell differentiation.

Comparison of cAMP-specific phosphodiesterase mRNAs distribution in mouse and rat brain

There are eleven families of phosphodiesterases that regulate cellular levels of cyclic nucleotides by degradation of cAMP or cGMP. Knowledge of the expression sites of different PDE genes in brain is of special importance for studies on development of specific inhibitors considering that, for example, PDE4 inhibitor treatments exhibit profound anti-inflammatory effects. To address possible species differences we examined the expression of mRNAs coding for the cAMP specific PDE4 and PDE7 families since inhibitors have been used in clinic for schizophrenia, mood disorders, cognition and inflammatory diseases treatment. We have compared the expression of these PDEs in mouse brain by in situ hybridization histochemistry in comparison with rat brain and found that their neuroanatomical distribution differs in a few areas.

Sex-related differences of cAMP-specific PDE4B3 mRNA in oligodendrocytes following systemic inflammation

Sex-related differences have been observed in the incidence and severity of several neurological diseases and in sepsis in humans. Cyclic adenosine monophosphate (cAMP) has been shown to play an important role in modulating the inflammatory environment during neuroinflammation and importantly in protecting myelin from excitotoxic cell death. Considering the sexual dimorphism in the functional properties of oligodendrocytes and the importance of a systemic inflammation in the progression of multiple sclerosis, we focused on identifying possible sex-related differences in the alterations previously reported for the two phosphodiesterase4B (PDE4B) splice-variants (PDE4B2 and PDE4B3) mRNA expression during innate neuroinflammation. PDE4A, PDE4B, and PDE4D are present in oligodendrocytes and we have previously reported that PDE4B3 mRNA is readily expressed in both oligodendrocytes and neurons. In this study, we analyzed the influence of an intraperitoneal lipopolysaccharide injection on the distribution pattern and expression levels of the PDE4B mRNA splicing variants in both male and female mice brains. Clear differences were observed in PDE4B2 and PDE4B3 mRNA expression levels in males compared with females in a time-dependent manner. Furthermore, we observed that the clear downregulation of PDE4B3 mRNA was reflected in a lower percentage of oligodendrocytes positive for this transcript which correlated with a decrease in inducible cAMP early repressor expression in female corpus callosum.