Primate-specific response of astrocytes to stroke limits peripheral macrophage infiltration

Abstract

Reactive astrocytes play critical roles after brain injuries but their precise function in stroke is not well defined. Here, we utilized single nuclei transcriptomics to characterize astrocytes after ischemic stroke in nonhuman primate (NHP) marmoset monkey primary visual cortex. We identified 19 putative subtypes of astrocytes from injured and uninjured brain hemispheres and observed nearly complete segregation between stroke and control astrocyte clusters. We then screened for genes that might be limiting stroke recovery and discovered that one neurite-outgrowth inhibitory protein, NogoA, previously associated with oligodendrocytes but not astrocytes, was expressed in numerous reactive astrocyte subtypes. NogoA upregulation on reactive astrocytes was confirmed in vivo for NHP and human, but not observed to the same extent in rodent. Further in vivo and in vitro studies determined that NogoA mediated an anti-inflammatory response which limits deeper infiltration of peripheral macrophages from the lesion during the subacute post-stroke period. Specifically, these findings are relevant to the development of NogoA-targeting therapies shortly after ischemic stroke. Our findings have uncovered the complexity and species specificity of astrocyte responses, which need to be considered more when investigating novel therapeutics for brain injury.

Diversity of Reactive Astrogliosis in CNS Pathology: Heterogeneity or Plasticity?

“…Interestingly, these subsets were noted to express a mixture of "A1" and "A2" genes (Boghdadi et al, 2020a), further highlighting the limited utility of applying binary categorization to what is most likely a nuanced spectrum of activation states. Interestingly, certain astrocyte subsets in the peri-infarct region expressed Nogo-A (Boghdadi et al, 2020a), well-known as a robust neurite outgrowth inhibitor (Chen et al, 2000;GrandPre et al, 2000;Kim et al, 2004;Schwab, 2004). Astrocyte diversity in models of ischemic stroke most likely represents predominant contribution of plasticity in response to the changing post-injury environment superimposed upon a background of heterogeneity, manifested in the post-natal brain as regionally specific astrocyte subsets with variable responses FIGURE 3 | Pre-clinical models of ischemic stroke, CNS demyelination, and traumatic injury used to look at astrocyte diversity.…”

“…Reactive astrogliosis is observed in virtually all neurological conditions, including epilepsy ( Steinhäuser et al, 2015 ), neoplastic disease ( Priego et al, 2018 ; Heiland et al, 2019 ), demyelination ( Woodruff and Franklin, 1999 ; Williams et al, 2007 ; Tassoni et al, 2019 ; Rawji et al, 2020 ), traumatic injury ( Faulkner et al, 2004 ; Filous and Silver, 2016 ; Boghdadi et al, 2020a ), neurodegeneration ( Vargas et al, 2008 ; Ben Haim et al, 2015 ), and ischemic stroke ( Zhao and Rempe, 2010 ; Zamanian et al, 2012 ; Rakers et al, 2019 ), as well as microbial CNS infections ( Drögemüller et al, 2008 ; Soung and Klein, 2018 ; Geyer et al, 2019 ) and neurotoxin exposure ( O’Callaghan et al, 2014 ; Wheeler et al, 2019 ). Reactive astrogliosis enables astrocytes to serve key roles in CNS pathological states, including metabolic support of vulnerable neurons, regulation of BBB permeability, remodeling of extracellular matrix (ECM), mobilizing progenitors, as well as immunomodulation, synaptic remodeling, and neurite outgrowth ( Woodruff et al, 2004 ; Sofroniew and Vinters, 2010a ; Anderson et al, 2014 ; Pekny and Pekna, 2014 ; Escartin et al, 2019 , 2021 ).…”

“…Transcriptomic studies have revealed astrocyte diversity in models of ischemic stroke ( Zamanian et al, 2012 ; Rakers et al, 2019 ; Boghdadi et al, 2020a ). For example, ischemic insult induces differential expression of a host of genes in diverse subsets of astrocytes, including genes involved in neuroinflammation, apoptosis, and transepithelial migration of leukocytes ( Zamanian et al, 2012 ) as well as cell division and migration ( Rakers et al, 2019 ).…”

Improved post-stroke spontaneous recovery by astrocytic extracellular vesicles

“…Astrocytes and astrocytic gliosis are known to impede the recovery of injured tissue by blocking axonal sprouting through the production of structural astrocytic proteins such as glial fibrillary acidic protein (GFAP) and vimentin 18 , as well as neurite-inhibiting signaling molecules such as Nogo-A 19 . Nonetheless, astrocytes have multiple essential support functions, whose loss can precipitate or contribute to neurodegeneration 20 .…”

“…The copyright holder for this preprint (which this version posted April 20, 2021. ; https://doi.org/10.1101/2021.04. 19.440321 doi: bioRxiv preprint astrocytes obtained from P2 newborn rats. The isolation method employed in this study, which involves differential centrifugation, produces a homogeneous EV population with a size consistent with exosomes, as analyzed by transmission electron microscopy (Figure 1a) and nanoparticle tracking analysis (Figure 1c, and d).…”