The Memory Orchestra: Contribution of Astrocytes

Phosphodiesterase 8 (PDE8): Distribution and Cellular Expression and Association with Alzheimer's Disease

Phosphodiesterase 8 (PDE8), as a member of PDE superfamily, specifically promotes the hydrolysis and degradation of intracellular cyclic adenosine monophosphate (cAMP), which may be associated with pathogenesis of Alzheimer's disease (AD). However, little is currently known about potential role in the central nervous system (CNS). Here we investigated the distribution and expression of PDE8 in brain of mouse, which we believe can provide evidence for studying the role of PDE8 in CNS and the relationship between PDE8 and AD. Here, C57BL/6J mice were used to observe the distribution patterns of two subtypes of PDE8, PDE8A and PDE8B, in different sexes in vivo by western blot (WB). Meanwhile, C57BL/6J mice were also used to demonstrate the distribution pattern of PDE8 in selected brain regions and localization in neural cells by WB and multiplex immunofluorescence staining. Furthermore, the triple transgenic (3×Tg-AD) mice and wild type (WT) mice of different ages were used to investigate the changes of PDE8 expression in the hippocampus and cerebral cortex during the progression of AD. PDE8 was found to be widely expressed in multiple tissues and organs including heart, kidney, stomach, brain, and liver, spleen, intestines, and uterus, with differences in expression levels between the two subtypes of PDE8A and PDE8B, as well as two sexes. Meanwhile, PDE8 was widely distributed in the brain, especially in areas closely related to cognitive function such as cerebellum, striatum, amygdala, cerebral cortex, and hippocampus, without differences between sexes. Furthermore, PDE8A was found to be expressed in neuronal cells, microglia and astrocytes, while PDE8B is only expressed in neuronal cells and microglia. PDE8A expression in the hippocampus of both female and male 3×Tg-AD mice was gradually increased with ages and PDE8B expression was upregulated only in cerebral cortex of female 3×Tg-AD mice with ages. However, the expression of PDE8A and PDE8B was apparently increased in both cerebral cortex and hippocampus in both female and male 10-month-old 3×Tg-AD mice compared WT mice. These results suggest that PDE8 may be associated with the progression of AD and is a potential target for its prevention and treatment in the future.

Mechanisms by Which SARS-CoV-2 Invades and Damages the Central Nervous System: Apart from the Immune Response and Inflammatory Storm, What Else Do We Know?

Initially reported as pneumonia of unknown origin, COVID-19 is increasingly being recognized for its impact on the nervous system, despite nervous system invasions being extremely rare. As a result, numerous studies have been conducted to elucidate the mechanisms of nervous system damage and propose appropriate coping strategies. This review summarizes the mechanisms by which SARS-CoV-2 invades and damages the central nervous system, with a specific focus on aspects apart from the immune response and inflammatory storm. The latest research findings on these mechanisms are presented, providing new insights for further in-depth research.

Dietary fatty acid composition drives neuroinflammation and impaired behavior in obesity

Nutrient composition in obesogenic diets may influence the severity of disorders associated with obesity such as insulin-resistance and chronic inflammation. Here we hypothesized that obesogenic diets rich in fat and varying in fatty acid composition, particularly in omega 6 (ω6) to omega 3 (ω3) ratio, have various effects on energy metabolism, neuroinflammation and behavior. Mice were fed either a control diet or a high fat diet (HFD) containing either low (LO), medium (ME) or high (HI) ω6/ω3 ratio. Mice from the HFD-LO group consumed less calories and exhibited less body weight gain compared to other HFD groups. Both HFD-ME and HFD-HI impaired glucose metabolism while HFD-LO partly prevented insulin intolerance and was associated with normal leptin levels despite higher subcutaneous and perigonadal adiposity. Only HFD-HI increased anxiety and impaired spatial memory, together with increased inflammation in the hypothalamus and hippocampus. Our results show that impaired glucose metabolism and neuroinflammation are uncoupled, and support that diets with a high ω6/ω3 ratio are associated with neuroinflammation and the behavioral deterioration coupled with the consumption of diets rich in fat.

Astrocytes and Memory: Implications for the Treatment of Memory-related Disorders

Memory refers to the imprint accumulated in the brain by life experiences and represents the basis for humans to engage in advanced psychological activities such as thinking and imagination. Previously, research activities focused on memory have always targeted neurons. However, in addition to neurons, astrocytes are also involved in the encoding, consolidation, and extinction of memory. In particular, astrocytes are known to affect the recruitment and function of neurons at the level of local synapses and brain networks. Moreover, the involvement of astrocytes in memory and memory-related disorders, especially in Alzheimer's disease (AD) and post-traumatic stress disorder (PTSD), has been investigated extensively. In this review, we describe the unique contributions of astrocytes to synaptic plasticity and neuronal networks and discuss the role of astrocytes in different types of memory processing. In addition, we also explore the roles of astrocytes in the pathogenesis of memory-related disorders, such as AD, brain aging, PTSD and addiction, thus suggesting that targeting astrocytes may represent a potential strategy to treat memory-related neurological diseases. In conclusion, this review emphasizes that thinking from the perspective of astrocytes will provide new ideas for the diagnosis and therapy of memory-related neurological disorders.

Astrocytes: new evidence, new models, new roles

Astrocytes have been in the limelight of active research for about 3 decades now. Over this period, ideas about their function and role in the nervous system have evolved from simple assistance in energy supply and homeostasis maintenance to a complex informational and metabolic hub that integrates data on local neuronal activity, sensory and arousal context, and orchestrates many crucial processes in the brain. Rapid progress in experimental techniques and data analysis produces a growing body of data, which can be used as a foundation for formulation of new hypotheses, building new refined mathematical models, and ultimately should lead to a new level of understanding of the contribution of astrocytes to the cognitive tasks performed by the brain. Here, we highlight recent progress in astrocyte research, which we believe expands our understanding of how low-level signaling at a cellular level builds up to processes at the level of the whole brain and animal behavior. We start our review with revisiting data on the role of noradrenaline-mediated astrocytic signaling in locomotion, arousal, sensory integration, memory, and sleep. We then briefly review astrocyte contribution to the regulation of cerebral blood flow regulation, which is followed by a discussion of biophysical mechanisms underlying astrocyte effects on different brain processes. The experimental section is closed by an overview of recent experimental techniques available for modulation and visualization of astrocyte dynamics. We then evaluate how the new data can be potentially incorporated into the new mathematical models or where and how it already has been done. Finally, we discuss an interesting prospect that astrocytes may be key players in important processes such as the switching between sleep and wakefulness and the removal of toxic metabolites from the brain milieu.

The role and potential therapeutic targets of astrocytes in central nervous system demyelinating diseases

Astrocytes play vital roles in the central nervous system, contributing significantly to both its normal functioning and pathological conditions. While their involvement in various diseases is increasingly recognized, their exact role in demyelinating lesions remains uncertain. Astrocytes have the potential to influence demyelination positively or negatively. They can produce and release inflammatory molecules that modulate the activation and movement of other immune cells. Moreover, they can aid in the clearance of myelin debris through phagocytosis and facilitate the recruitment and differentiation of oligodendrocyte precursor cells, thereby promoting axonal remyelination. However, excessive or prolonged astrocyte phagocytosis can exacerbate demyelination and lead to neurological impairments. This review provides an overview of the involvement of astrocytes in various demyelinating diseases, emphasizing the underlying mechanisms that contribute to demyelination. Additionally, we discuss the interactions between oligodendrocytes, oligodendrocyte precursor cells and astrocytes as therapeutic options to support myelin regeneration. Furthermore, we explore the role of astrocytes in repairing synaptic dysfunction, which is also a crucial pathological process in these disorders.