Astrocyte development—More questions than answers

Solubilized β-Glucan Supplementation in C57BL/6J Mice Dams Augments Neurodevelopment and Cognition in the Offspring Driven by Gut Microbiome Remodeling

A maternal diet rich in dietary fiber, such as β-glucan, plays a crucial role in the offspring's acquisition of gut microbiota and the subsequent shaping of its microbiome profile and metabolome. This in turn has been shown to aid in neurodevelopmental processes, including early microglial maturation and immunomodulation via metabolites like short chain fatty acids (SCFAs). This study aimed to investigate the effects of oat β-glucan supplementation, solubilized by citric acid hydrolysis, from gestation to adulthood. Female C57BL/6J mice were orally supplemented with soluble oat β-glucan (ObG) or carboxymethyl cellulose (CMC) via drinking water at 200 mg/kg body weight during breeding while the control group received 50 mg/kg body weight of carboxymethyl cellulose. ObG supplementation increased butyrate production in the guts of both dams and 4-week-old pups, attributing to alterations in the gut microbiota profile. One-week-old pups from the ObG group showed increased neurodevelopmental markers similar to four-week-old pups that also exhibited alterations in serum markers of metabolism and anti-inflammatory cytokines. Notably, at 8 weeks, ObG-supplemented pups exhibited the highest levels of spatial memory and cognition compared to the control and CMC groups. These findings suggest a potential enhancement of neonatal neurodevelopment via shaping of early-life gut microbiome profile, and the subsequent increased later-life cognitive function.

Monomeric pilose antler peptide improves depression-like behavior in mice by inhibiting FGFR3 protein expression

ETHNOPHARMACOLOGICAL RELEVANCE

It has been found that pilose antler peptide has an antidepressant effect on depression. However, the exact molecular mechanism of its antidepressant effect is still unclear.

AIM OF THE STUDY

The study sought to determine the impact of monomeric pilose antler peptide (PAP; sequence LVLVEAELRE) on depression as well as investigate potential molecular mechanisms.

MATERIALS AND METHODS

Chronic unexpected mild stress (CUMS) was used to establish the model, and the effect of PAP on CUMS mice was detected by the behavioral test. The influence of PAP on neuronal cells and dendritic spine density was observed by immunofluorescence and Golgi staining. FGFR3 and the CaMKII-associated pathway were identified using quantitative real-time polymerase chain reaction, and Western blot analysis was utilized to measure their proteins and gene expression levels. Molecular docking and microscale thermophoresis were applied to detect the binding of PAP and FGFR3. Finally, the effect of FGFR3's overexpression on PAP treatment of depression was detected.

RESULTS

PAP alleviated the changes in depressive behavior induced by CUMS, promoted the growth of nerve cells, and the density of dendritic spines was increased to its original state. PAP therapy successfully downregulated the expression of FGFR3 and ERK1/2 while upregulating the expression of CREB, BDNF, and CaMKII.

CONCLUSION

Based on the current research, PAP has a therapeutic effect on depression brought on by CUMS by inhibiting FGFR3 expression and enhancing synaptic plasticity.

Astrocytes in the adult dentate gyrus-balance between adult and developmental tasks

Astrocytes, a major glial cell type in the brain, are indispensable for the integration, maintenance and survival of neurons during development and adulthood. Both life phases make specific demands on the molecular and physiological properties of astrocytes, and most research projects traditionally focus on either developmental or adult astrocyte functions. In most brain regions, the generation of brain cells and the establishment of neural circuits ends with postnatal development. However, few neurogenic niches exist in the adult brain in which new neurons and glial cells are produced lifelong, and the integration of new cells into functional circuits represent a very special form of plasticity. Consequently, in the neurogenic niche, the astrocytes must be equipped to execute both mature and developmental tasks in order to integrate newborn neurons into the circuit and yet maintain overall homeostasis without affecting the preexisting neurons. In this review, we focus on astrocytes of the hippocampal dentate gyrus (DG), and discuss specific features of the astrocytic compartment that may allow the execution of both tasks. Firstly, astrocytes of the adult DG are molecularly, morphologically and functionally diverse, and the distinct astrocytes subtypes are characterized by their localization to DG layers. This spatial separation may lead to a functional specification of astrocytes subtypes according to the neuronal structures they are embedded in, hence a division of labor. Secondly, the astrocytic compartment is not static, but steadily increasing in numbers due to lifelong astrogenesis. Interestingly, astrogenesis can adapt to environmental and behavioral stimuli, revealing an unexpected astrocyte dynamic that allows the niche to adopt to changing demands. The diversity and dynamic of astrocytes in the adult DG implicate a vital contribution to hippocampal plasticity and represent an interesting model to uncover mechanisms how astrocytes simultaneously fulfill developmental and adult tasks.

Dynamic Changes in Neuroglial Reaction and Tissue Repair after Photothrombotic Stroke in Neonatal Mouse

Perinatal and neonatal ischemic stroke is a significant cause of cognitive and behavioral impairments. Further research is needed to support models of neonatal ischemic stroke and advance our understanding of the mechanisms of infarction formation following such strokes. We used two different levels of photothrombotic stroke (PTS) models to assess stroke outcomes in neonatal mice. We measured brain damage, dynamic changes in glial cells, and neuronal expression at various time points within two weeks following ischemic injury. Our results from 2,3,5-Triphenyltetrazolium chloride (TTC) staining and immunofluorescence staining showed that in the severe group, a dense border of astrocytes and microglia was observed within 3 days post infarct. This ultimately resulted in the formation of a permanent cortical cavity, accompanied by neuronal loss in the surrounding tissues. In the mild group, a relatively sparse arrangement of glial borders was observed 7 days post infarct. This was accompanied by intact cortical tissue and the restoration of viability in the brain tissue beyond the glial boundary. Additionally, neonatal ischemic injury leads to the altered expression of key molecules such as Aldh1L1 and Olig2 in immature astrocytes. In conclusion, we demonstrated the dynamic changes in glial cells and neuronal expression following different degrees of ischemic injury in a mouse model of PTS. These findings provide new insights for studying the cellular and molecular mechanisms underlying neuroprotection and neural regeneration after neonatal ischemic injury.

Reactive Gliosis in Neonatal Disorders: Friend or Foe for Neuroregeneration?

A developing nervous system is particularly vulnerable to the influence of pathophysiological clues and injuries in the perinatal period. Astrocytes are among the first cells that react to insults against the nervous tissue, the presence of pathogens, misbalance of local tissue homeostasis, and a lack of oxygen and trophic support. Under this background, it remains uncertain if induced astrocyte activation, recognized as astrogliosis, is a friend or foe for progressing neonatal neurodevelopment. Likewise, the state of astrocyte reactivity is considered one of the key factors discriminating between either the initiation of endogenous reparative mechanisms compensating for aberrations in the structures and functions of nervous tissue or the triggering of neurodegeneration. The responses of activated cells are modulated by neighboring neural cells, which exhibit broad immunomodulatory and pro-regenerative properties by secreting a plethora of active compounds (including interleukins and chemokines, neurotrophins, reactive oxygen species, nitric oxide synthase and complement components), which are engaged in cell crosstalk in a paracrine manner. As the developing nervous system is extremely sensitive to the influence of signaling molecules, even subtle changes in the composition or concentration of the cellular secretome can have significant effects on the developing neonatal brain. Thus, modulating the activity of other types of cells and their interactions with overreactive astrocytes might be a promising strategy for controlling neonatal astrogliosis.

Astrocyte Development in the Rodent

Astrocytes have gained increasing recognition as key elements of a broad array of nervous system functions. These include essential roles in synapse formation and elimination, synaptic modulation, maintenance of the blood-brain barrier, energetic support, and neural repair after injury or disease of the nervous system. Nevertheless, our understanding of mechanisms underlying astrocyte development and maturation remains far behind that of neurons and oligodendrocytes. Early efforts to understand astrocyte development focused primarily on their specification from embryonic progenitors and the molecular mechanisms driving the switch from neuron to glial production. Considerably, less is known about postnatal stages of astrocyte development, the period during which they are predominantly generated and mature. Notably, this period is coincident with synapse formation and the emergence of nascent neural circuits. Thus, a greater understanding of astrocyte development is likely to shed new light on the formation and maturation of synapses and circuits. Here, we highlight key foundational principles of embryonic and postnatal astrocyte development, focusing largely on what is known from rodent studies.

Developmental origin and local signals cooperate to determine septal astrocyte identity

Astrocyte specification during development is influenced by both intrinsic and extrinsic factors, but the precise contribution of each remains poorly understood. Here we show that septal astrocytes from Nkx2.1 and Zic4 expressing progenitor zones are allocated into non-overlapping domains of the medial (MS) and lateral septal nuclei (LS) respectively. Astrocytes in these areas exhibit distinctive molecular and morphological features tailored to the unique cellular and synaptic circuit environment of each nucleus. Using single-nucleus (sn) RNA sequencing, we trace the developmental trajectories of cells in the septum and find that neurons and astrocytes undergo region and developmental stage-specific local cell-cell interactions. We show that expression of the classic morphogens Sonic hedgehog (Shh) and Fibroblast growth factors (Fgfs) by MS and LS neurons respectively, functions to promote the molecular specification of local astrocytes in each region. Finally, using heterotopic cell transplantation, we show that both morphological and molecular specifications of septal astrocytes are highly dependent on the local microenvironment, regardless of developmental origins. Our data highlights the complex interplay between intrinsic and extrinsic factors shaping astrocyte identities and illustrates the importance of the local environment in determining astrocyte functional specialization.