Biology subjects

Wade-Martins, R.

Publications and source records attributed to Wade-Martins, R..

25 records · Page 2Linked to original sources

bioRxiv2020

L-type calcium channel contribution to striatal dopamine release is governed by calbindin-D28K, the dopamine transporter, D2-receptors, α2δ-subunits and sex differences

Ca2+ entry into nigrostriatal dopamine (DA) neurons and axons via L-type voltage-gated Ca2+ channels (LTCCs) contributes respectively to pacemaker activity and DA release, and has long been thought to contribute to vulnerability to degeneration in Parkinsons disease. LTCC function is greater in DA axons and neurons from substantia nigra pars compacta than from ventral tegmental area, but this is not explained by channel expression level. We tested the hypothesis that LTCC-control of DA release is governed rather by local mechanisms, focussing on candidate biological factors known to operate differently between types of DA neurons and/or be associated with their differing vulnerability to parkinsonism, including biological sex, -synuclein, DA transporters (DATs), and calbindin-D28k (Calb1). We detected evoked DA release ex vivo in mouse striatal slices using fast-scan cyclic voltammetry, and assessed LTCC support of DA release by detecting the inhibition of DA release by the LTCC inhibitors isradipine or CP8. Using genetic knockouts or pharmacological manipulations we identified that striatal LTCC support of DA release depended on multiple intersecting factors, in a regionally and sexually divergent manner. LTCC function was promoted by factors associated with Parkinsonian risk, including male sex, -synuclein, DAT, and a dorsolateral co-ordinate, but limited by factors associated with protection i.e. female sex, glucocerebrosidase activity, Calb1, and ventromedial co-ordinate. Together, these data show that LTCC function in DA axons, and isradipine effect, are locally governed and suggest they vary in a manner that in turn might impact on, or reflect, the cellular stress that leads to parkinsonian degeneration. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/186411v2_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@1ccc783org.highwire.dtl.DTLVardef@13e7296org.highwire.dtl.DTLVardef@d4e3d3org.highwire.dtl.DTLVardef@b9427b_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2020

A human single-cell atlas of the Substantia nigra reveals novel cell-specific pathways associated with the genetic risk of Parkinson's disease and neuropsychiatric disorders.

We describe a human single-nuclei transcriptomic atlas for the Substantia nigra (SN), generated by sequencing ~ 17,000 nuclei from matched cortical and SN samples. We show that the common genetic risk for Parkinsons disease (PD) is associated with dopaminergic neuron (DaN)-specific gene expression, including mitochondrial functioning, protein folding and ubiquitination pathways. We identify a distinct cell type association between PD risk and oligodendrocyte-specific gene expression. Unlike Alzheimers disease (AD), we find no association between PD risk and microglia or astrocytes, suggesting that neuroinflammation plays a less causal role in PD than AD. Beyond PD, we find associations between SN DaNs and GABAergic neuron gene expression patterns with multiple neuropsychiatric disorders. Nevertheless, we find that each neuropsychiatric disorder is associated with a distinct set of genes within that neuron type. This atlas guides our aetiological understanding by associating SN cell type expression profiles with specific disease risk.

neuroscience↗

bioRxiv2020

Inhibition of the SUV4-20 H1 histone methyltransferase increases frataxin expression in Friedreich's ataxia patient cells

The molecular mechanisms of reduced frataxin (FXN) expression in Friedreichs ataxia (FRDA) are linked to epigenetic modification of the FXN locus caused by the disease-associated GAA expansion. Here, we identify that SUV4-20 histone methyltransferases, specifically SUV4-20 H1, play an important role in the regulation of FXN expression and represent a novel therapeutic target. Using a human FXN-GAA-Luciferase repeat expansion genomic DNA reporter model of FRDA, we screened the Structural Genomics Consortium epigenetic probe collection. We found that pharmacological inhibition of the SUV4-20 methyltransferases by the tool compound A-196 increased the expression of FXN by approximately 1.5-fold in the reporter cell line and in several FRDA cell lines and patient-derived primary peripheral blood mononuclear cells. SUV4-20 inhibition was accompanied by a reduction in H4K20me2 and H4K20me3 and an increase in H4K20me1, but only modest (1.4-7.8%) perturbation in genome-wide expression was observed. Finally, based on the structural activity relationship and crystal structure of A-196, novel small molecule A-196 analogues were synthesized and shown to give a 20-fold increase in potency for increasing FXN expression. Overall, our results suggest that histone methylation is important in the regulation of FXN expression, and highlight SUV4-20 H1 as a potential novel therapeutic target for FRDA.

neuroscience↗

bioRxiv2019

Transgenic mice expressing human alpha-synuclein in noradrenergic neurons develop locus coeruleus pathology and non-motor features of Parkinson's disease

Degeneration of locus coeruleus (LC) neurons and dysregulation of noradrenergic signaling are ubiquitous features of Parkinsons disease (PD). The LC is among the first brain regions affected by -synuclein (asyn) pathology, yet how asyn affects these neurons remains unclear. LC-derived norepinephrine (NE) can stimulate neuroprotective mechanisms and modulate immune cells, while dysregulation of NE neurotransmission may exacerbate disease progression, particularly non-motor symptoms, and contribute to the chronic neuroinflammation associated with PD pathology. Although transgenic mice overexpressing asyn have previously been developed, transgene expression is usually driven by pan-neuronal promoters and thus has not been selectively targeted to LC neurons. Here we report a novel transgenic mouse expressing human wild-type asyn under control of the noradrenergic-specific dopamine {beta}-hydroxylase promoter. These mice developed oligomeric and conformation-specific asyn in LC neurons, alterations in hippocampal and LC microglial abundance, upregulated GFAP expression, degeneration of LC fibers, decreased striatal dopamine (DA) metabolism, and age-dependent behaviors reminiscent of non-motor symptoms of PD that were rescued by adrenergic receptor antagonists. These mice provide novel insights into how asyn pathology affects LC neurons and how central noradrenergic dysfunction may contribute to early PD pathophysiology. Significance statement-synuclein (asyn) pathology and loss of neurons in the locus coeruleus (LC) are two of the most ubiquitous neuropathologic features of Parkinsons disease (PD). Dysregulated NE neurotransmission is associated with the non-motor symptoms of PD including sleep disturbances, emotional changes such as anxiety and depression, and cognitive decline. Importantly, loss of central NE may contribute to the chronic inflammation in, and progression of, PD. We have generated a novel transgenic mouse expressing human asyn in LC neurons to investigate how increased asyn expression affects the function of the central noradrenergic transmission and associated behaviors. We report cytotoxic effects of oligomeric and conformation-specific asyn, astrogliosis, LC fiber degeneration, disruptions in striatal dopamine metabolism, and age-dependent alterations in non-motor behaviors without inclusions.

neuroscience↗

bioRxiv2019

LRRK2 is recruited to phagosomes and co-recruits Rab8 and Rab10 in human pluripotent stem cell-derived macrophages

The Parkinsons disease-associated gene, LRRK2, is also associated with immune disorders and infectious disease, and is expressed in immune subsets. Here, we characterise a platform for interrogating the expression and function of endogenous LRRK2 in authentic human phagocytes, using human induced Pluripotent Stem Cell-derived macrophages and microglia. Endogenous LRRK2 is expressed and upregulated by interferon-{gamma} in these cells, including a 187kD cleavage product. Using LRRK2 knockout and G2019S isogenic repair lines, we find that LRRK2 is not involved in initial phagocytic uptake of bioparticles, but is recruited to LAMP1(+)/Rab9(+) maturing phagosomes, and LRRK2 kinase inhibition enhances its residency at the phagosome. Importantly, LRRK2 is required for Rab8a and Rab10 recruitment to phagosomes, implying that LRRK2 operates at the intersection between phagosome maturation and recycling pathways in these professional phagocytes.

immunology↗

bioRxiv2019

Astrocytic striatal GABA transporter activity governs dopamine release and shows maladaptive downregulation in early parkinsonism

Striatal dopamine (DA) is critical for action and learning. Recent data show DA release is under tonic inhibition by striatal GABA. Ambient striatal GABA tone on striatal projection neurons can be governed by plasma membrane GABA uptake transporters (GATs) on astrocytes. However, whether striatal GATs and astrocytes determine DA output are unknown. We reveal that DA release in mouse dorsolateral striatum, but not nucleus accumbens core, is governed by GAT-1 and GAT-3. These GATs are partly localized to astrocytes, and are enriched in dorsolateral striatum compared to accumbens core. In a mouse model of early parkinsonism, GATs were downregulated and tonic GABAergic inhibition of DA release augmented, with corresponding attenuation of GABA co-release from dopaminergic axons. These data define previously unappreciated and important roles for GATs and astrocytes in determining DA release in striatum, and reveal a maladaptive plasticity in early parkinsonism that impairs DA output in vulnerable striatal regions. HighlightsO_LIGABA transporters set the level of GABA inhibition of DA output in dorsal striatum C_LIO_LIAstrocytes facilitate DA release levels by limiting tonic GABA inhibition C_LIO_LITonic inhibition of DA release is augmented in a mouse model of early parkinsonism C_LIO_LIDA and GABA co-release are reduced in a mouse model of early parkinsonism C_LI

neuroscience↗

bioRxiv2018

The making of a Lewy body: the role of alpha-synuclein post-fibrillization modifications in regulating the formation and the maturation of pathological inclusions.

Although converging evidence point to alpha-synuclein (a-syn) aggregation and Lewy body (LB) formation as central events in Parkinson's disease (PD), the molecular mechanisms that regulate these processes and their role in disease pathogenesis remain poorly understood. Herein, we applied an integrative biochemical, structural and imaging approach to elucidate the sequence, molecular and cellular mechanisms that regulate LB formation in primary neurons. Our results establish that post-fibrillization C-terminal truncation mediated by calpains 1 and 2 and potentially other enzymes, plays critical roles in regulating a-syn seeding, fibrillization and orchestrates many of the events associated with LB formation and maturation. These findings combined with the abundance of a-syn truncated species in LBs and pathological a-syn aggregates have significant implications for ongoing efforts to develop therapeutic strategies based on targeting the C-terminus of a-syn or proteolytic processing of this region.

neuroscience↗