Astrocytes in a dish:Using pluripotent stem cells to model neurodegenerative and neurodevelopmental disorders

Neuroscience and Neurobiology have historically been neuron biased, yet up to 40% of the cells in the brain are astrocytes. These cells are heterogeneous and regionally diverse but universally essential for brain homeostasis. Astrocytes regulate synaptic transmission as part of the tripartite synapse, provide metabolic and neurotrophic support, recycle neurotransmitters, modulate blood flow and brain blood barrier permeability and are implicated in the mechanisms of neurodegeneration. Using pluripotent stem cells (PSC), it is now possible to study regionalised human astrocytes in a dish and to model their contribution to neurodevelopmental and neurodegenerative disorders. The evidence challenging the traditional neuron-centric view of degeneration within the CNS is reviewed here, with focus on recent findings and disease phenotypes from human PSC-derived astrocytes. In addition we compare current protocols for the generation of regionalised astrocytes and how these can be further refined by our growing knowledge of neurodevelopment. We conclude by proposing a functional and phenotypical characterisation of PSC-derived astrocytic cultures that is critical for reproducible and robust disease modelling

Hyperexcitability in young iPSC-derived C9ORF72 mutant motor neurons is associated with increased intracellular calcium release

S.B. was supported by a Motor Neuron Disease Association studentship (WadeMartins/Oct13/867-792) and D.A.B was supported by the Monument Trust Discovery Award (J-1403) from Parkinson’s UK. The work was supported by the Medical Research Council Dementias Platform UK Stem Cell Network (Grant MR/M024962/1 to RW-M).A large hexanucleotide repeat expansion in the C9ORF72 gene is the most prevalent cause of amyotrophic lateral sclerosis (ALS). To better understand neuronal dysfunction during ALS progression, we studied motor neuron (MN) cultures derived from iPSC lines generated from C9ORF72 (C9) expansion carriers and unaffected controls. C9 and control MN cultures showed comparable mRNA levels for MN markers SMI-32, HB9 and ISL1 and similar MN yields (> 50% TUJ1/SMI-32 double-positive MNs). Using whole-cell patch clamp we showed that C9-MNs have normal membrane capacitance, resistance and resting potential. However, immature (day 40) C9-MNs exhibited a hyperexcitable phenotype concurrent with increased release of calcium (Ca2+) from internal stores, but with no changes to NaV and KV currents. Interestingly, this was a transient phenotype. By day 47, maturing C9-MNs demonstrated normal electrophysiological activity, displaying only subtle alterations on mitochondrial Ca2+ release. Together, these findings suggest the potential importance of a developmental component to C9ORF72-related ALS.Publisher PDFPeer reviewe

Efficient and Scalable Generation of Human Ventral Midbrain Astrocytes from Human-Induced Pluripotent Stem Cells

In Parkinson's disease, progressive dysfunction and degeneration of dopamine neurons in the ventral midbrain cause life-changing symptoms. Neuronal degeneration has diverse causes in Parkinson's, including non-cell autonomous mechanisms mediated by astrocytes. Throughout the CNS, astrocytes are essential for neuronal survival and function, as they maintain metabolic homeostasis in the neural environment. Astrocytes interact with the immune cells of the CNS, microglia, to modulate neuroinflammation, which is observed from the earliest stages of Parkinson's, and has a direct impact on the progression of its pathology. In diseases with a chronic neuroinflammatory element, including Parkinson's, astrocytes acquire a neurotoxic phenotype, and thus enhance neurodegeneration. Consequently, astrocytes are a potential therapeutic target to slow or halt disease, but this will require a deeper understanding of their properties and roles in Parkinson's. Accurate models of human ventral midbrain astrocytes for in vitro study are therefore urgently required. We have developed a protocol to generate high purity cultures of ventral midbrain-specific astrocytes (vmAstros) from hiPSCs that can be used for Parkinson's research. vmAstros can be routinely produced from multiple hiPSC lines, and express specific astrocytic and ventral midbrain markers. This protocol is scalable, and thus suitable for high-throughput applications, including for drug screening. Crucially, the hiPSC derived-vmAstros demonstrate immunomodulatory characteristics typical of their in vivo counterparts, enabling mechanistic studies of neuroinflammatory signaling in Parkinson's

Focused Ultrasound Stimulation as a Neuromodulatory Tool for Parkinson’s Disease::A Scoping Review

Non-invasive focused ultrasound stimulation (FUS) is a non-ionising neuromodulatory technique that employs acoustic energy to acutely and reversibly modulate brain activity of deep-brain structures. It is currently being investigated as a potential novel treatment for Parkinson’s disease (PD). This scoping review was carried out to map available evidence pertaining to the provision of FUS as a PD neuromodulatory tool. In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extension for Scoping Reviews, a search was applied to Ovid MEDLINE, Embase, Web of Science and Cochrane Central Register of Controlled Trials on 13 January 2022, with no limits applied. In total, 11 studies were included: 8 were from China and 1 each from Belgium, South Korea and Taiwan. All 11 studies were preclinical (6 in vivo, 2 in vitro, 2 mix of in vivo and in vitro and 1 in silico). The preclinical evidence indicates that FUS is safe and has beneficial neuromodulatory effects on motor behaviour in PD. FUS appears to have a therapeutic role in influencing the disease processes of PD, and therefore holds great promise as an attractive and powerful neuromodulatory tool for PD. Though these initial studies are encouraging, further study to understand the underlying cellular and molecular mechanisms is required before FUS can be routinely used in PD

The miRNA transcriptome of cerebrospinal fluid in preterm infants reveals the signaling pathways that promote reactive gliosis following cerebral hemorrhage

IntroductionGerminal Matrix-Intraventricular Haemorrhage (GM-IVH) is one of the most common neurological complications in preterm infants, which can lead to accumulation of cerebrospinal fluid (CSF) and is a major cause of severe neurodevelopmental impairment in preterm infants. However, the pathophysiological mechanisms triggered by GM-IVH are poorly understood. Analyzing the CSF that accumulates following IVH may allow the molecular signaling and intracellular communication that contributes to pathogenesis to be elucidated. Growing evidence suggests that miRs, due to their key role in gene expression, have a significant utility as new therapeutics and biomarkers.MethodsThe levels of 2,083 microRNAs (miRs) in 15 CSF samples from 10 infants with IVH were measured using miRNA whole transcriptome sequencing. Gene ontology (GO) and miR family analysis were used to uncover dysregulated signalling which were then validated in vitro in human foetal neural progenitor cells treated with IVH-CSF.ResultsFive hundred eighty-seven miRs were differentially expressed in the CSF extracted at least 2 months after injury, compared to CSF extracted within the first month of injury. GO uncovered key pathways targeted by differentially expressed miRs including the MAPK cascade and the JAK/STAT pathway. Astrogliosis is known to occur in preterm infants, and we hypothesized that this could be due to abnormal CSF-miR signaling resulting in dysregulation of the JAK/STAT pathway – a key controller of astrocyte differentiation. We then confirmed that treatment with IVH-CSF promotes astrocyte differentiation from human fetal NPCs and that this effect could be prevented by JAK/STAT inhibition. Taken together, our results provide novel insights into the CSF/NPCs crosstalk following perinatal brain injury and reveal novel targets to improve neurodevelopmental outcomes in preterm infants

Abnormal scaffold attachment factor 1 expression and localisation in spinocerebellar ataxias and huntington’s chorea

SAFB1 is a DNA and RNA binding protein that is highly expressed in the cerebellum and hippocampus and is involved in the processing of coding and non‐coding RNAs, splicing and dendritic function. We analyzed SAFB1 expression in the post‐mortem brain tissue of spinocerebellar ataxia (SCA), Huntington’s disease (HD), Multiple sclerosis (MS), Parkinson’s disease patients and controls. In SCA cases, the expression of SAFB1 in the nucleus was increased and there was abnormal and extensive expression in the cytoplasm where it co‐localized with the markers of Purkinje cell injury. Significantly, no SAFB1 expression was found in the cerebellar neurons of the dentate nucleus in control or MS patients; however, in SCA patients, SAFB1 expression was increased significantly in both the nucleus and cytoplasm of dentate neurons. In HD, we found that SAFB1 expression was increased in the nucleus and cytoplasm of striatal neurons; however, there was no SAFB1 staining in the striatal neurons of controls. In PD substantia nigra, we did not see any changes in neuronal SAFB1 expression. iCLIP analysis found that SAFB1 crosslink sites within ATXN1 RNA were adjacent to the start and within the glutamine repeat sequence. Further investigation found increased binding of SAFB1 to pathogenic ATXN1‐85Q mRNA. These novel data strongly suggest SAFB1 contributes to the etiology of SCA and Huntington’s chorea and that it may be a pathological marker of polyglutamine repeat expansion diseases

Distinct regulation of hippocampal neuroplasticity and ciliary genes by corticosteroid receptors

Glucocorticoid hormones (GCs) are of critical importance for maintaining brain health, but their involvement in mental disorders is poorly understood. Here the authors show how GCs act through hippocampal mineralocorticoid and glucocorticoid receptors to impact the gene regulatory programs underpinning neuronal plasticity, ciliogenesis and behavioral adaptation

Loss of MicroRNA-7 Regulation Leads to α-Synuclein Accumulation and Dopaminergic Neuronal Loss In Vivo

Abnormal alpha-synuclein (α-synuclein) expression and aggregation is a key characteristic of Parkinson's disease (PD). However, the exact mechanism(s) linking α-synuclein to the other central feature of PD, dopaminergic neuron loss, remains unclear. Therefore, improved cell and in vivo models are needed to investigate the role of α-synuclein in dopaminergic neuron loss. MicroRNA-7 (miR-7) regulates α-synuclein expression by binding to the 3' UTR of the Synuclein Alpha Non A4 Component of Amyloid Precursor (SNCA) gene and inhibiting its translation. We show that miR-7 is decreased in the substantia nigra of patients with PD and, therefore, may play an essential role in the regulation of α-synuclein expression. Furthermore, we have found that lentiviral-mediated expression of miR-7 complementary binding sites to stably induce a loss of miR-7 function results in an increase in α-synuclein expression in vitro and in vivo. We have also shown that depletion of miR-7 using a miR-decoy produces a loss of nigral dopaminergic neurons accompanied by a reduction of striatal dopamine content. These data suggest that miR-7 has an important role in the regulation of α-synuclein and dopamine physiology and may provide a new paradigm to study the pathology of PD

Nanoparticle-induced neuronal toxicity across placental barriers is mediated by autophagy and dependent on astrocytes

The potential for maternal nanoparticle (NP) exposures to cause developmental toxicity in the fetus without the direct passage of NPs has previously been shown, but the mechanism remained elusive. We now demonstrate that exposure of cobalt and chromium NPs to BeWo cell barriers, an in vitro model of the human placenta, triggers impairment of the autophagic flux and release of interleukin-6. This contributes to the altered differentiation of human neural progenitor cells and DNA damage in the derived neurons and astrocytes. Crucially, neuronal DNA damage is mediated by astrocytes. Inhibiting the autophagic degradation in the BeWo barrier by overexpression of the dominant-negative human ATG4BC74A significantly reduces the levels of DNA damage in astrocytes. In vivo, indirect NP toxicity in mice results in neurodevelopmental abnormalities with reactive astrogliosis and increased DNA damage in the fetal hippocampus. Our results demonstrate the potential importance of autophagy to elicit NP toxicity and the risk of indirect developmental neurotoxicity after maternal NP exposure