Cuprizone demyelination induces a unique inflammatory response in the subventricular zone.

BackgroundCuprizone leads to demyelination of the corpus callosum (CC) and activates progenitor cells in the adjacent subventricular zone (SVZ), a stem cell niche which contributes to remyelination. The healthy SVZ contains semi-activated microglia and constitutively expresses the pro-inflammatory molecule galectin-3 (Gal-3) suggesting the niche uniquely regulates inflammation. MethodsWe studied the inflammatory response to cuprizone in the SVZ and CC in Gal-3 knockout mice using immunohistochemistry and with the in vitro neurosphere assay. ResultsCuprizone caused loss of myelin basic protein (MBP) immunofluorescence in the CC suggesting demyelination. Cuprizone increased the density of CD45+/Iba1+ microglial cells and also increased Gal-3 expression in the CC. Surprisingly, the number of Gal-3+ and CD45+ cells decreased in the SVZ after cuprizone, suggesting inflammation was selectively reduced therein. Inflammation can regulate SVZ proliferation and indeed the number of phosphohistone H3+ (PHi3+) cells decreased in the SVZ but increased in the CC in both genotypes after cuprizone treatment. BrdU+ SVZ cell numbers also decreased in the SVZ after cuprizone, and this effect was significantly greater at 3 weeks in Gal-3 −/− mice compared to WT, suggesting Gal-3 normally limits SVZ cell emigration following cuprizone treatment. ConclusionsThis study reveals a uniquely regulated inflammatory response in the SVZ and shows that Gal-3 participates in remyelination in the cuprizone model. This contrasts with more severe models of demyelination which induce SVZ inflammation and suggests the extent of demyelination affects the SVZ neurogenic response.</p

Galectin‐3 diminishes Wnt signaling in the postnatal subventricular zone

Postnatal subventricular zone (pSVZ) stem and progenitor cell proliferation is regulated by several developmental signaling pathways such as Wnt/β‐catenin. However, the molecular regulation of Wnt function in the pSVZ is poorly understood. We previously showed that Wnt signaling is upregulated in an SVZ gliomagenesis in vivo model. As well, the pro‐inflammatory molecule Galectin‐3 (Gal‐3) increases Wnt signaling in cancer cells and is expressed in the SVZ. Therefore, we asked if Gal‐3 has a similar function on Wnt signaling in the pSVZ. We interrogated Wnt signaling using a signaling reporter as well as immunohistochemistry and showed that Wnt signaling predominates upstream in the pSVZ lineage but is downregulated in migrating neuroblasts. Biochemical analysis of SVZ cells, in vivo and in neurosphere stem/progenitor cells, showed that Gal‐3 physically interacts with multiple forms of β‐catenin, which is a major downstream regulator of Wnt signaling. Functional analyses demonstrated, in vitro and in vivo, that Gal‐3 knockdown increases Wnt signaling and conversely that Gal‐3 OE inhibits Wnt/β‐catenin signaling in the pSVZ. This latter result suggested that Gal‐3, which is consistently increased in brain injury, may decrease pSVZ proliferation. We showed that Gal‐3 OE decreased proliferation without altering cell cycle re‐entry and that it increased p27Kip1, a molecule which induces cell cycle exit. Our data uncover a novel regulator of Wnt signaling in the SVZ, Gal‐3, which does so in a manner opposite to cancer

Blocked angiogenesis in Galectin-3 null mice does not alter cellular and behavioral recovery after middle cerebral artery occlusion stroke.

Angiogenesis is thought to decrease stroke size and improve behavioral outcomes and therefore several clinical trials are seeking to augment it. Galectin-3 (Gal-3) expression increases after middle cerebral artery occlusion (MCAO) and has been proposed to limit damage 3days after stroke. We carried out mild MCAO that damages the striatum but spares the cerebral cortex and SVZ. Gal-3 gene deletion prevented vascular endothelial growth factor (VEGF) upregulation after MCAO. This inhibited post-MCAO increases in endothelial proliferation and angiogenesis in the striatum allowing us to uniquely address the function of angiogenesis in this model of stroke. Apoptosis and infarct size were unchanged in Gal-3(-/-) mice 7 and 14 days after MCAO, suggesting that angiogenesis does not affect lesion size. Microglial and astrocyte activation/proliferation after MCAO was similar in wild type and Gal-3(-/-) mice. In addition, openfield activity, motor hemiparesis, proprioception, reflex, tremors and grooming behaviors were essentially identical between WT and Gal-3(-/-) mice at 1, 3, 7, 10 and 14 days after MCAO, suggesting that penumbral angiogenesis has limited impact on behavioral recovery. In addition to angiogenesis, increased adult subventricular zone (SVZ) neurogenesis is thought to provide neuroprotection after stroke in animal models. SVZ neurogenesis and migration to lesion were overall unaffected by the loss of Gal-3, suggesting no compensation for the lack of angiogenesis in Gal-3(-/-) mice. Because angiogenesis and neurogenesis are usually coordinately regulated, identifying their individual effects on stroke has hitherto been difficult. These results show that Gal-3 is necessary for angiogenesis in stroke in a VEGF-dependant manner, but suggest that angiogenesis may be dispensable for post-stroke endogenous repair, therefore drawing into question the clinical utility of augmenting angiogenesis

Galectin-3 modulates postnatal subventricular zone gliogenesis

Postnatal subventricular zone (SVZ) neural stem cells generate forebrain glia, namely astrocytes and oligodendrocytes. The cues necessary for this process are unclear, despite this phase of brain development being pivotal in forebrain gliogenesis. Galectin-3 (Gal-3) is increased in multiple brain pathologies and thereby regulates astrocyte proliferation and inflammation in injury. To study the function of Gal-3 in inflammation and gliogenesis, we carried out functional studies in mouse. We overexpressed Gal-3 with electroporation and using immunohistochemistry surprisingly found no inflammation in the healthy postnatal SVZ. This allowed investigation of inflammation-independent effects of Gal-3 on gliogenesis. Loss of Gal-3 function via knockdown or conditional knockout reduced gliogenesis, whereas Gal-3 overexpression increased it. Gal-3 overexpression also increased the percentage of striatal astrocytes generated by the SVZ but decreased the percentage of oligodendrocytes. These novel findings were further elaborated with multiple analyses demonstrating that Gal-3 binds to the bone morphogenetic protein receptor one alpha (BMPR1α) and increases bone morphogenetic protein (BMP) signaling. Conditional knockout of BMPR1α abolished the effect of Gal-3 overexpression on gliogenesis. Gain-of-function of Gal-3 is relevant in pathological conditions involving the human forebrain, which is particularly vulnerable to hypoxia/ischemia during perinatal gliogenesis. Hypoxic/ischemic injury induces astrogliosis, inflammation and cell death. We show that Gal-3 immunoreactivity was increased in the perinatal human SVZ and striatum after hypoxia/ischemia. Our findings thus show a novel inflammation-independent function for Gal-3; it is necessary for gliogenesis and when increased in expression can induce astrogenesis via BMP signaling

COVID-19 and possible links with Parkinson\u2019s disease and parkinsonism: from bench to bedside

This Viewpoint discusses insights from basic science and clinical perspectives on coronavirus disease 2019 (COVID-19)/severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection in the brain, with a particular focus on Parkinson\u2019s disease. Major points include that neuropathology studies have not answered the central issue of whether the virus enters central nervous system neurons, astrocytes or microglia, and the brain vascular cell types that express virus have not yet been identified. Currently, there is no clear evidence for human neuronal or astrocyte expression of angiotensin-converting enzyme 2 (ACE2), the major receptor for viral entry, but ACE2 expression may be activated by inflammation, and a comparison of healthy and infected brains is important. In contrast to the 1918 influenza pandemic and avian flu, reports of encephalopathy in COVID-19 have been slow to emerge, and there are so far no documented reports of parkinsonism apart from a single case report. We recommend consensus guidelines for the clinical treatment of Parkinson\u2019s patients with COVID-19. While a role for the virus in causing or exacerbating Parkinson\u2019s disease appears unlikely at this time, aggravation of specific motor and non-motor symptoms has been reported, and it will be important to monitor subjects after recovery, particularly for those with persisting hyposmia

Expression of Idh1R132H in the murine subventricular zone stem cell niche recapitulates early gliomagenesis

Isocitrate dehydrogenase 1 mutations drive human gliomagenesis, probably through neomorphic enzyme activity that produces D-2-hydroxyglutarate. To model this disease, we conditionally expressed Idh1^R132H in the subventricular zone (SVZ) of the adult mouse brain. The mice developed hydrocephalus and grossly dilated lateral ventricles, with accumulation of 2-hydroxyglutarate and reduced -ketoglutarate. Stem and transit amplifying/progenitor cell populations were expanded, and proliferation increased. Cells expressing SVZ markers infiltrated surrounding brain regions. SVZ cells also gave rise to proliferative subventricular nodules. DNA methylation was globally increased, while hydroxymethylation was decreased. Mutant SVZ cells over-expressed Wnt, cell cycle and stem cell genes, and shared an expression signature with human gliomas. Idh1^R132H mutation in the major adult neurogenic stem cell niche causes a phenotype resembling gliomagenesis