Astrocyte heterogeneity within white matter tracts and a unique subpopulation of optic nerve head astrocytes

Mazumder, Arpan G.; Julé, Amélie M.; Cullen, Paul; Sun, Daniel

doi:10.1016/j.isci.2022.105568

Cited by 12 publications

(37 citation statements)

References 72 publications

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“…A limitation of this study was that WM astrocytes were not isolated from the spinal cord using our method. A similar difficulty was also reported in the optic nerve, which may be related to the dense myelination of these tissues [ 28 ]. Fluorescence-activated nuclei sorting [ 29 ] or Ribo Tag immunoprecipitation [ 30 ] may be used to overcome this limitation.…”

Section: Discussionsupporting

confidence: 65%

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

Iwasaki,

Kohro,

Tsuda

2024

Mol Brain

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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.

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Section: Discussionsupporting

confidence: 65%

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

Iwasaki,

Kohro,

Tsuda

2024

Mol Brain

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“…In part, this would be expected from the morphological differences in astrocytes of the two regions [25]. A recent report by Mazumder et al also investigated regional astrocyte gene expression in the mouse unmyelinated ONH (equivalent to UON in our studies) using the ribotag approach, which enriches for translated mRNAs [11]. While this and the present study had certain overlapping or complementary findings, there were also significant differences.…”

Section: Discussionmentioning

confidence: 46%

Regional Gene Expression in the Retina, Optic Nerve Head, and Optic Nerve of Mice with Experimental Glaucoma and Optic Nerve Crush

Keuthan

Schaub

Wei

et al. 2023

Preprint

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A major risk factor for glaucomatous optic neuropathy is the level of intraocular pressure (IOP), which can lead to retinal ganglion cell axon injury and cell death. The optic nerve has a rostral unmyelinated portion at the optic nerve head followed by a caudal myelinated region. The unmyelinated region is differentially susceptible to IOP–induced damage in rodent models and in human glaucoma. While several studies have analyzed gene expression changes in the mouse optic nerve following optic nerve injury, few were designed to consider the regional gene expression differences that exist between these distinct areas. We performed bulk RNA–sequencing on the retina and on separately micro–dissected unmyelinated and myelinated optic nerve regions from naïve C57BL/6 mice, mice after optic nerve crush, and mice with microbead–induced experimental glaucoma (total = 36). Gene expression patterns in the naïve unmyelinated optic nerve showed significant enrichment of the Wnt, Hippo, PI3K–Akt, and transforming growth factor β pathways, as well as extracellular matrix—receptor and cell membrane signaling pathways, compared to the myelinated optic nerve and retina. Gene expression changes induced by both injuries were more extensive in the myelinated optic nerve than the unmyelinated region, and greater after nerve crush than glaucoma. Changes three and fourteen days after injury largely subsided by six weeks. Gene markers of reactive astrocytes did not consistently differ between injury states. Overall, the transcriptomic phenotype of the mouse unmyelinated optic nerve was significantly different from immediately adjacent tissues, likely dominated by expression in astrocytes, whose junctional complexes are inherently important in responding to IOP elevation.

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“…Elevated levels of oxidative phosphorylation result in increased production of reactive oxygen species (ROS), a source of oxidative stress and potential contributor to glaucoma ( 12 , 120 ). Conversely, astrocytes provide antioxidant support in the central nervous system through glutathione production, the peroxiredoxin system, and other mechanisms, and our transcriptional results suggest that this is the case at the ONH as well, with high levels of glutathione transferase and peroxidase transcription implying that this population of astrocytes acts to ameliorate the effects of local production of ROS ( 90 , 121 , 122 ). Secondly, the enrichment of oxidative phosphorylation related genes was accompanied by indicators of lower levels of glycolysis, an alternative mechanism by which astrocytes generate energy in the brain ( 123 ).…”

Section: Optic Nerve Head Astrocytesmentioning

confidence: 66%

“…Our recent transcriptional study of astrocytes under physiological conditions in the normo-tensive mouse optic nerve highlights a number of key differences between those of the ONH and the myelinated optic nerve proper, bolstering the idea that this a distinct population ( 90 ). Unsurprisingly, given the role of ONH astrocytes in remodeling the extracellular matrix during glaucoma, under physiological conditions we found that pathways related to ECM maintenance were highly enriched in this population relative to those of the myelinated optic nerve and corpus callosum ( 13 ).…”

Section: Optic Nerve Head Astrocytesmentioning

confidence: 68%

“…The astrocytes of the optic nerve, in particular, have historically been considered as a homogeneous population, although the specialized anatomy of the optic nerve head and its role as a key site of early glaucomatous damage later gave rise to a specific interest in the functions of astrocytes there. Recent functional studies have highlighted specialized roles for these astrocytes that may be unique, and a transcriptional study of astrocytes in the optic nerve published by our group highlights that these astrocytes may be best understood as a distinct population from those of the myelinated optic nerve ( 55 , 89 , 90 ). Intriguingly, other recent work suggests that these populations are nevertheless extensively networked across anatomically large distances by gap junctions, facilitating coordination of non-cell autonomous support functions at a previously unappreciated scale ( 57 ).…”

Section: Zones Of the Retinal Ganglion Cell Axon And Attendant White ...mentioning

confidence: 99%

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Astrocytes of the eye and optic nerve: heterogeneous populations with unique functions mediate axonal resilience and vulnerability to glaucoma

Cullen

Sun

2023

Front. Ophthalmol.

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The role of glia, particularly astrocytes, in mediating the central nervous system’s response to injury and neurodegenerative disease is an increasingly well studied topic. These cells perform myriad support functions under physiological conditions but undergo behavioral changes – collectively referred to as ‘reactivity’ – in response to the disruption of neuronal homeostasis from insults, including glaucoma. However, much remains unknown about how reactivity alters disease progression – both beneficially and detrimentally – and whether these changes can be therapeutically modulated to improve outcomes. Historically, the heterogeneity of astrocyte behavior has been insufficiently addressed under both physiological and pathological conditions, resulting in a fragmented and often contradictory understanding of their contributions to health and disease. Thanks to increased focus in recent years, we now know this heterogeneity encompasses both intrinsic variation in physiological function and insult-specific changes that vary between pathologies. Although previous studies demonstrate astrocytic alterations in glaucoma, both in human disease and animal models, generally these findings do not conclusively link astrocytes to causative roles in neuroprotection or degeneration, rather than a subsequent response. Efforts to bolster our understanding by drawing on knowledge of brain astrocytes has been constrained by the primacy in the literature of findings from peri-synaptic ‘gray matter’ astrocytes, whereas much early degeneration in glaucoma occurs in axonal regions populated by fibrous ‘white matter’ astrocytes. However, by focusing on findings from astrocytes of the anterior visual pathway – those of the retina, unmyelinated optic nerve head, and myelinated optic nerve regions – we aim to highlight aspects of their behavior that may contribute to axonal vulnerability and glaucoma progression, including roles in mitochondrial turnover and energy provisioning. Furthermore, we posit that astrocytes of the retina, optic nerve head and myelinated optic nerve, although sharing developmental origins and linked by a network of gap junctions, may be best understood as distinct populations residing in markedly different niches with accompanying functional specializations. A closer investigation of their behavioral repertoires may elucidate not only their role in glaucoma, but also mechanisms to induce protective behaviors that can impede the progressive axonal damage and retinal ganglion cell death that drive vision loss in this devastating condition.

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Astrocyte heterogeneity within white matter tracts and a unique subpopulation of optic nerve head astrocytes

Cited by 12 publications

References 72 publications

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

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

Regional Gene Expression in the Retina, Optic Nerve Head, and Optic Nerve of Mice with Experimental Glaucoma and Optic Nerve Crush

Astrocytes of the eye and optic nerve: heterogeneous populations with unique functions mediate axonal resilience and vulnerability to glaucoma

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