Olig2-astrocytes express neutral amino acid transporter SLC7A10 (Asc-1) in the adult brain

Targeting harmful effects of non-excitatory amino acids as an alternative therapeutic strategy to reduce ischemic damage

The involvement of the excitatory amino acids glutamate and aspartate in cerebral ischemia and excitotoxicity is well-documented. Nevertheless, the role of non-excitatory amino acids in brain damage following a stroke or brain trauma remains largely understudied. The release of amino acids by necrotic cells in the ischemic core may contribute to the expansion of the penumbra. Our findings indicated that the reversible loss of field excitatory postsynaptic potentials caused by transient hypoxia became irreversible when exposed to a mixture of just four non-excitatory amino acids (L-alanine, glycine, L-glutamine, and L-serine) at their plasma concentrations. These amino acids induce swelling in the somas of neurons and astrocytes during hypoxia, along with permanent dendritic damage mediated by N-methyl-D-aspartate receptors. Blocking N-methyl-D-aspartate receptors prevented neuronal damage in the presence of these amino acids during hypoxia. It is likely that astroglial swelling caused by the accumulation of these amino acids via the alanine-serine-cysteine transporter 2 exchanger and system N transporters activates volume-regulated anion channels, leading to the release of excitotoxins and subsequent neuronal damage through N-methyl-D-aspartate receptor activation. Thus, previously unrecognized mechanisms involving non-excitatory amino acids may contribute to the progression and expansion of brain injury in neurological emergencies such as stroke and traumatic brain injury. Understanding these pathways could highlight new therapeutic targets to mitigate brain injury.

Coordinated regulation of cortical astrocyte maturation by OLIG1 and OLIG2 through BMP7 signaling modulation

Astrocyte maturation is crucial for brain function, yet the mechanisms regulating this process remain poorly understood. In this study, we identify the bHLH transcription factors Olig1 and Olig2 as essential coordinators of cortical astrocyte maturation. We demonstrate that Olig1 and Olig2 work synergistically to regulate cortical astrocyte maturation by modulating Bmp7 expression. Genetic ablation of both Olig1 and Olig2 results in defective astrocyte morphology, including reduced process complexity and an immature gene expression profile. Single-cell RNA sequencing reveals a shift towards a less mature astrocyte state, marked by elevated levels of HOPX and GFAP, resembling human astrocytes. Mechanistically, Olig1 and Olig2 bind directly to the Bmp7 enhancer, repressing its expression to promote astrocyte maturation. Overexpression of Bmp7 in vivo replicates the astrocyte defects seen in Olig1/2 double mutants, confirming the critical role of BMP7 signaling in this process. These findings provide insights into the transcriptional and signaling pathways regulating astrocyte development and highlight Olig1 and Olig2 as key regulators of cortical astrocyte maturation, with potential implications for understanding glial dysfunction in neurological diseases.

Single-cell chromatin accessibility landscape profiling reveals the diversity of epigenetic regulation in the rat nervous system

The mammalian nervous system controls complex functions through highly specialized and interacting structures. Single-cell sequencing can provide information on cell-type-specific chromatin structure and regulatory elements, revealing differences in chromatin organization between different cell types and their potential roles of these differences in brain function. Here, we generated a chromatin accessibility dataset through single-cell ATAC-seq of 174,593 high-quality nuclei from 16 adult rat brain regions. We identified cell subtypes of both neuronal and non-neuronal cells with highly specific distributions and characterized gene regulatory elements associated with cell type-specific regions. To further investigate the gene regulatory network involved in spinal cord regeneration, we integrated our scATAC-seq data with published single-nucleus RNA-seq data from the spinal cord, and we identified more detailed regeneration related elements by drawing GRNs centered on the transcription factor Jun in the OPC. We also performed similar integration analyses in the midbrain. Our findings provide a solid foundation for the comprehensive dissection of the molecular architecture of the mammalian nervous system.

A method for selective and efficient isolation of gray matter astrocytes from the spinal cord of adult mice

A growing body of evidence indicates intra- and inter-regional heterogeneity of astrocytes in the brain. However, because of a lack of an efficient method for isolating astrocytes from the spinal cord, little is known about how much spinal cord astrocytes are heterogeneous in adult mice. In this study, we developed a new method for isolating spinal astrocytes from adult mice using a cold-active protease from Bacillus licheniformis with an astrocyte cell surface antigen-2 (ACSA-2) antibody. Using fluorescence-activated cell sorting, isolated spinal ACSA-2+ cells were divided into two distinct populations, ACSA-2high and ACSA-2low. By analyzing the expression of cell-type marker genes, the ACSA-2high and ACSA-2low populations were identified as astrocytes and ependymal cells, respectively. Furthermore, ACSA-2high cells had mRNAs encoding genes that were abundantly expressed in the gray matter (GM) but not white matter astrocytes. By optimizing enzymatic isolation procedures, the yield of GM astrocytes also increased. Therefore, our newly established method enabled the selective and efficient isolation of GM astrocytes from the spinal cord of adult mice and may be useful for bulk- or single-cell RNA-sequencing under physiological and pathological conditions.

Anti-inflammatory Effects of Umbilical Cord Mesenchymal Stem Cell and Autologous Conditioned Serum on Oligodendrocyte, Astrocyte, and Microglial Specific Gene in Cuprizone Animal Model

BACKGROUND

Inflammation, myelin loss, astrocytosis, and microgliosis are pathological signs of the autoimmune and demyelinating disease known as multiple sclerosis (MS). Axonal and neuronal degenerations have basic molecular pathways. The remyelination process can be influenced by the secretome of mesenchymal stem cells due to their capacity for immunomodulation, differentiation, and neuroprotection. Microglial cells are divided into two subgroups: M1 and M2 phenotypes. A crucial component of the microglial function is the colony stimulating factor 1 receptor (CSF1R). We aimed to evaluate the immunomodulating effects of secretome and conditioned serum on the microglial phenotypes and improvement of demyelination in a cuprizone model of MS.

METHODS

The study used 48 male C57BL/6 mice, which were randomly distributed into 6 subgroups (n = 8), i.e., control, cuprizone, MSC (confluency 40% and 80%) secretome group, and blood derived conditioned serum (autologous and humanized). The animals were fed with 0.2% cuprizone diet for 12 weeks. Supplements were injected into the lateral tail vein using a 27-gauge needle every 3 days 500 μl per injection.

RESULTS

At 14 days after transplantation, animals from each group were sacrificed and analyzed by Real time PCR. The results showed that the administration of MSC secretome can efficiently reduce expression of pro-inflammatory cytokines (IL-1, IL6 and TNF-α) in the corpus callosum; also, conditioned serum downregulated IL-1. Moreover, the oligodendrocyte-specific gene was upregulated by secretome and conditioned serum treatment. Also, the expression of microglial- specific gene was reduced after treatment.

CONCLUSION

These findings demonstrated that the secretome isolated from MSCs used as a therapy decreased and increased the M1 and M2 levels, respectively, to control neuroinflammation in CPZ mice. In conclusion, the current study showed the viability of devising a method to prepare suitable MSCs and secreted factor to cure neurodegenerative diseases, as well as the capability of regulating MSC secretome patterns by manipulating the cell density.

Amino acid transporter Asc-1 (SLC7A10) expression is altered in basal ganglia in experimental Parkinsonism and L-dopa-induced dyskinesia model mice

In Parkinson's disease (PD), a decrease in dopamine levels in the striatum causes abnormal circuit activity in the basal ganglia, resulting in increased output via the substantia nigra pars reticulata (SNr). A characteristic feature of glutamatergic synaptic transmission in the basal ganglia circuitry under conditions of dopamine depletion is enhanced synaptic activity of NMDA receptors. However, the cause of this NMDA receptor hyperactivity is not fully understood. We focused on Asc-1 (SLC7A10), an alanine-serine-cysteine transporter, as one of the factors that regulate NMDA receptor activity by modulating D-serine and glycine concentration in synaptic clefts. We generated PD model mice by injection of 6-hydroxydopamine into the unilateral medial forebrain bundle and analyzed the expression level of Asc-1 mRNA in the nuclei of basal ganglia (the external segment of the globus pallidus (GPe), subthalamic nucleus (STN), and SNr) compared to control mice. Each nucleus was dissected using laser microdissection, and RNA was extracted and quantified by quantitative PCR. Asc-1 mRNA expression was significantly higher in the GPe and lower in the SNr under the PD state than that in control naïve mice. The STN showed no change in Asc-1 mRNA expression. We further modeled L-dopa-induced dyskinesia by administering L-dopa continuously for 14 days to the PD model mice and found that Asc-1 mRNA expression in the GPe and SNr became close to that of control mice, regardless of the presence of abnormal involuntary movements. The present study revealed that Asc-1 mRNA expression is differentially regulated in the basal ganglionic nuclei in response to striatal dopamine concentration (depleted or replenished) and suggests that Asc-1 can be a therapeutic target for the amelioration of motor symptoms of PD.

Astrocytes in Chronic Pain: Cellular and Molecular Mechanisms

Chronic pain is challenging to treat due to the limited therapeutic options and adverse side-effects of therapies. Astrocytes are the most abundant glial cells in the central nervous system and play important roles in different pathological conditions, including chronic pain. Astrocytes regulate nociceptive synaptic transmission and network function via neuron–glia and glia–glia interactions to exaggerate pain signals under chronic pain conditions. It is also becoming clear that astrocytes play active roles in brain regions important for the emotional and memory-related aspects of chronic pain. Therefore, this review presents our current understanding of the roles of astrocytes in chronic pain, how they regulate nociceptive responses, and their cellular and molecular mechanisms of action.

Astrocyte development in the cerebral cortex: Complexity of their origin, genesis, and maturation

In the mammalian brain, astrocytes form a heterogeneous population at the morphological, molecular, functional, intra-, and inter-region levels. In the past, a few types of astrocytes have been first described based on their morphology and, thereafter, according to limited key molecular markers. With the advent of bulk and single-cell transcriptomics, the diversity of astrocytes is now progressively deciphered and its extent better appreciated. However, the origin of this diversity remains unresolved, even though many recent studies unraveled the specificities of astroglial development at both population and individual cell levels, particularly in the cerebral cortex. Despite the lack of specific markers for each astrocyte subtype, a better understanding of the cellular and molecular events underlying cortical astrocyte diversity is nevertheless within our reach thanks to the development of intersectional lineage tracing, microdissection, spatial mapping, and single-cell transcriptomic tools. Here we present a brief overview describing recent findings on the genesis and maturation of astrocytes and their key regulators during cerebral cortex development. All these studies have considerably advanced our knowledge of cortical astrogliogenesis, which relies on a more complex mode of development than their neuronal counterparts, that undeniably impact astrocyte diversity in the cerebral cortex.