Stichting ParkinsonFonds, Dorpmans-Wigmans Stichting, Erasmus Medical Center, ZonMw-Memorabel programme, EU Joint Programme Neurodegenerative Disease Research (JPND), Parkinson's UK, Avtal om Läkarutbildning och Forskning (ALF) and Parkinsonfonden (Sweden), Lijf and Leven foundation, and cross-border grant of Alzheimer Netherlands-Ligue Européene Contre la Maladie d'Alzheimer (LECMA).

Sphingolipidoses are severe, mostly infantile lysosomal storage disorders (LSDs) caused by defective glycosphingolipid degradation. Two of these sphingolipidoses, Tay Sachs and Sandhoff diseases, are caused by β‐Hexosaminidase (HEXB) enzyme deficiency, resulting in ganglioside (GM2) accumulation and neuronal loss. The precise sequence of cellular events preceding, and leading to, neuropathology remains unclear, but likely involves inflammation and lysosomal accumulation of GM2 in multiple cell types. We aimed to determine the consequences of Hexb activity loss for different brain cell types using zebrafish. Hexb deficient zebrafish (hexb−/−) showed lysosomal abnormalities already early in development both in radial glia, which are the neuronal and glial progenitors, and in microglia. Additionally, at 5 days postfertilization, hexb−/− zebrafish showed reduced locomotor activity. Although specific oligosaccharides accumulate in the adult brain, hexb−/−) zebrafish are viable and apparently resistant to Hexb deficiency. In all, we identified cellular consequences of loss of Hexb enzyme activity during embryonic brain development, showing early effects on glia, which possibly underlie the behavioral aberrations. Hereby, we identified clues into the contribution of non‐neuronal lysosomal abnormalities in LSDs affecting the brain and provide a tool to further study what underlies the relative resistance to Hexb deficiency in vivo.

Loss-of-function variants in the low-density lipoprotein receptor-related protein 10 (LRP10) gene have been associated with autosomal-dominant Parkinson’s disease (PD), PD dementia, and dementia with Lewy bodies (DLB). Moreover, LRP10 variants have been found in individuals diagnosed with progressive supranuclear palsy and amyotrophic lateral sclerosis. Despite this genetic evidence, little is known about the expression and function of LRP10 protein in the human brain under physiological or pathological conditions. To better understand how LRP10 variants lead to neurodegeneration, we first performed an in-depth characterisation of LRP10 expression in post-mortem brains and human-induced pluripotent stem cell (iPSC)-derived astrocytes and neurons from control subjects. In adult human brain, LRP10 is mainly expressed in astrocytes and neurovasculature but undetectable in neurons. Similarly, LRP10 is highly expressed in iPSC-derived astrocytes but cannot be observed in iPSC-derived neurons. In astrocytes, LRP10 is present at trans-Golgi network, plasma membrane, retromer, and early endosomes. Interestingly, LRP10 also partially co-localises and interacts with sortilin-related receptor 1 (SORL1). Furthermore, although LRP10 expression and localisation in the substantia nigra of most idiopathic PD and DLB patients and LRP10 variant carriers diagnosed with PD or DLB appeared unchanged compared to control subjects, significantly enlarged LRP10-positive vesicles were detected in a patient carrying the LRP10 p.Arg235Cys variant. Last, LRP10 was detected in Lewy bodies (LB) at late maturation stages in brains from idiopathic PD and DLB patients and in LRP10 variant carriers. In conclusion, high LRP10 expression in non-neuronal cells and undetectable levels in neurons of control subjects indicate that LRP10-mediated pathogenicity is initiated via cell non-autonomous mechanisms, potentially involving the interaction of LRP10 with SORL1 in vesicle trafficking pathways. Together with the specific pattern of LRP10 incorporation into mature LBs, these data support an important mechanistic role for disturbed vesicle trafficking and loss of LRP10 function in neurodegenerative diseases.

Recent studies using animal models have generated profound insight into the functions of various subsets of innate lymphoid cells (ILCs). The group 2 ILC subset (ILC2) has been implicated in tissue homeostasis, defense responses against parasites, tissue repair, and immunopathology associated with type-2 immunity. In addition, progress has also been made in translating these findings from animal studies into a context of human immunity. Importantly, recent observations strongly support a role for ILC2s in several diseases of the human respiratory system. However, many aspects of human ILC2 biology are still unclear, including how these cells develop and which signals control their activity. As a result, the exact role played by ILCs in human health and disease remains poorly understood. Here, we summarize our current understanding of human ILC2 biology and focus on their potential involvement in various human respiratory disorders.

The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signaling pathways and functions, including the regulation of crucial proteins for neurodegeneration, such as alpha-synuclein, tau, and LRRK2. Here, we report the identification of variants in the PTPA/PPP2R4 gene, encoding a major PP2A activator, in two families with early-onset parkinsonism and intellectual disability. We carried out clinical studies and genetic analyses, including genome-wide linkage analysis, whole-exome sequencing, and Sanger sequencing of candidate variants. We next performed functional studies on the disease-associated variants in cultured cells and knock-down of ptpa in Drosophila melanogaster. We first identified a homozygous PTPA variant, c.893T > G (p.Met298Arg), in patients from a South African family with early-onset parkinsonism and intellectual disability. Screening of a large series of additional families yielded a second homozygous variant, c.512C > A (p.Ala171Asp), in a Libyan family with a similar phenotype. Both variants co-segregate with disease in the respective families. The affected subjects display juvenile-onset parkinsonism and intellectual disability. The motor symptoms were responsive to treatment with levodopa and deep brain stimulation of the subthalamic nucleus. In overexpression studies, both the PTPA p.Ala171Asp and p.Met298Arg variants were associated with decreased PTPA RNA stability and decreased PTPA protein levels; the p.Ala171Asp variant additionally displayed decreased PTPA protein stability. Crucially, expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. PTPA ortholog knock-down in Drosophila neurons induced a significant impairment of locomotion in the climbing test. This defect was age-dependent and fully reversed by L-DOPA treatment. We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability. Our findings might also provide new insights for understanding the role of the PP2A complex in the pathogenesis of more common forms of neurodegeneration.

Astrocytes are the most populous cell type of the human central nervous system and are essential for physiological brain function. Increasing evidence suggests multiple roles for astrocytes in Parkinson's disease (PD), nudging a shift in the research focus, which historically pivoted around the ventral midbrain dopaminergic neurons (vmDANs). Studying human astrocytes and other cell types in vivo remains technically and ethically challenging. However, in vitro reprogrammed human stem cell-based models provide a promising alternative. Here, we describe a novel protocol for astrocyte differentiation from human stem cell-derived vmDANs-generating progenitors. This protocol simulates the regionalization, gliogenic switch, radial migration, and final differentiation that occur in the developing human brain. We have characterized the morphological, molecular, and functional features of these ventral midbrain astrocytes with a broad palette of techniques. In addition, we have developed a new pipeline for calcium imaging data analysis called deCLUTTER2+(deconvolution of Ca2+fluorescent patterns) that can be used to discover spontaneous or cue-dependent patterns of Ca2+transients. Altogether, our protocol enables the characterization of the functional properties of human ventral midbrain astrocytes under physiological conditions and in PD.

Astrocytes are the most populous cell type of the human central nervous system and are essential for physiological brain function. Increasing evidence suggests multiple roles for astrocytes in Parkinson's disease (PD), nudging a shift in the research focus, which historically pivoted around the ventral midbrain dopaminergic neurons (vmDANs). Studying human astrocytes and other cell types in vivo remains challenging. However, in vitro reprogrammed human stem cell-based models provide a promising alternative. Here, we describe a novel protocol for astrocyte differentiation from human stem cell-derived vmDANs-generating progenitors. This protocol simulates the regionalization, gliogenic switch, radial migration, and final differentiation that occur in the developing human brain. We have characterized the morphological, molecular, and functional features of these ventral midbrain patterned astrocytes with a broad palette of techniques, and identifiesd novel candidate midbrain-astrocyte specific markers. In addition, we have developed a new pipeline for calcium imaging data analysis called deCLUTTER2+ (deconvolution of Ca2+ fluorescent patterns) that can be used to discover spontaneous or cue-dependent patterns of Ca2+ transients. Altogether, our protocol enables the characterization of the functional properties of human ventral midbrain patterned astrocytes under physiological conditions and in disease.