Project description:Recessive mutations in EXOSC3, encoding a subunit of the human RNA exosome complex, cause Pontocerebellar hypoplasia type 1b (PCH1B). We report a boy with severe muscular hypotonia, psychomotor retardation, progressive microcephaly, and cerebellar atrophy. Biochemical abnormalities comprised mitochondrial Complex I and PDHc deficiency. Whole exome sequencing uncovered a known EXOSC3-mutation p.(D132A) as the underlying cause. In patient fibroblasts, >50% of the EXOSC3 protein was trapped in the cytosol. mtDNA-copy numbers in muscle were reduced to 40%, but mutations in the mtDNA and nuclear mitochondrial genes were excluded. RNA-seq of patient muscle showed highly increased mRNA-copy numbers, especially for genes encoding structural subunits of OXPHOS-complexes I, III, and IV, possibly due to reduced degradation by a dysfunctional exosome complex. This is the first case of mitochondrial dysfunction associated with an EXOSC3 mutation, which expands the phenotypic spectrum of PCH1B. We discuss the links between exosome and mitochondrial dysfunction.
Project description:Pontocerebellar Hypoplasia Type 10 (PCH10) is a childhood neurodegenerative disease caused by bi-allelic p.R140H variants in CLP1, a multifunctional RNA kinase, by unknown pathophysiological mechanisms. Here, we combine novel patient data with mutation-specific in vivo and in vitro models to define motor neuron dysfunction as a penetrant, prominent feature of PCH10 and uncover a previously unrecognized mRNA misprocessing signature in motor neurons that likely contributes to pathology.
Project description:Pontocerebellar Hypoplasia Type 10 (PCH10) is a childhood neurodegenerative disease caused by bi-allelic p.R140H variants in CLP1, a multifunctional RNA kinase, by unknown pathophysiological mechanisms. Here, we combine novel patient data with mutation-specific in vivo and in vitro models to define motor neuron dysfunction as a penetrant, prominent feature of PCH10 and uncover a previously unrecognized mRNA misprocessing signature in motor neurons that likely contributes to pathology.
Project description:Pontocerebellar Hypoplasia Type 10 (PCH10) is a childhood neurodegenerative disease caused by bi-allelic p.R140H variants in CLP1, a multifunctional RNA kinase, by unknown pathophysiological mechanisms. Here, we combine novel patient data with mutation-specific in vivo and in vitro models to define motor neuron dysfunction as a penetrant, prominent feature of PCH10 and uncover a previously unrecognized mRNA misprocessing signature in motor neurons that likely contributes to pathology.
Project description:Kynureninase is a member of a large family of catalytically diverse but structurally homologous pyridoxal 5'-phosphate (PLP) dependent enzymes known as the aspartate aminotransferase superfamily or alpha-family. The Homo sapiens and other eukaryotic constitutive kynureninases preferentially catalyze the hydrolytic cleavage of 3-hydroxy-l-kynurenine to produce 3-hydroxyanthranilate and l-alanine, while l-kynurenine is the substrate of many prokaryotic inducible kynureninases. The human enzyme was cloned with an N-terminal hexahistidine tag, expressed, and purified from a bacterial expression system using Ni metal ion affinity chromatography. Kinetic characterization of the recombinant enzyme reveals classic Michaelis-Menten behavior, with a Km of 28.3 +/- 1.9 microM and a specific activity of 1.75 micromol min-1 mg-1 for 3-hydroxy-dl-kynurenine. Crystals of recombinant kynureninase that diffracted to 2.0 A were obtained, and the atomic structure of the PLP-bound holoenzyme was determined by molecular replacement using the Pseudomonas fluorescens kynureninase structure (PDB entry 1qz9) as the phasing model. A structural superposition with the P. fluorescens kynureninase revealed that these two structures resemble the "open" and "closed" conformations of aspartate aminotransferase. The comparison illustrates the dynamic nature of these proteins' small domains and reveals a role for Arg-434 similar to its role in other AAT alpha-family members. Docking of 3-hydroxy-l-kynurenine into the human kynureninase active site suggests that Asn-333 and His-102 are involved in substrate binding and molecular discrimination between inducible and constitutive kynureninase substrates.
Project description:Purine biosynthesis and metabolism, conserved in all living organisms, is essential for cellular energy homeostasis and nucleic acids synthesis. The de novo synthesis of purine precursors is under tight negative feedback regulation mediated by adenine and guanine nucleotides. We describe a new early-onset distinct neurodegenerative condition resulting from mutations in the adenosine monophosphate deaminase 2 gene (AMPD2). Patients have characteristic brain imaging features of pontocerebellar hypoplasia (PCH), due to loss of brainstem and cerebellar parenchyma. We found that AMPD2 plays an evolutionary conserved role in the maintenance of cellular guanine nucleotide pools by regulating the feedback inhibition of adenosine derivatives on de novo purine synthesis. AMPD2 deficiency results in defective GTP-dependent initiation of protein translation, which can be rescued by administration of purine precursors. These data suggest AMPD2-related PCH as a new potentially treatable early-onset neurodegenerative disease. An 18 chip study, that compares iPSC derived neural progenitor cells from two individuals: a patient with pontocerebellar hypoplasia and an unaffected parent. Samples are run as either non-treated, treated with Adenosine, or treated with Adenosine and AICAr. Three replicates are included for every individuals in every treatment condition.
Project description:Extracellular vesicles (EVs) enable cell-to-cell communication in the nervous system essential for development and adult function. Endosomal Sorting Complex Required for Transport (ESCRT) complex proteins regulate EV formation and release. Recent work shows loss of function (LOF) mutations in, CHMP1A, which encodes one ESCRT-III member, cause autosomal recessive microcephaly with pontocerebellar hypoplasia in humans (Mochida et al., 2012). Here we show CHMP1A is required for maintenance of progenitors in human cerebral organoids and that mouse Chmp1a is required for progenitor proliferation in cortex and cerebellum and specifically for sonic hedgehog (SHH) mediated proliferation through SHH secretion. CHMP1A mutation reduces intraluminal vesicle (ILV) formation in multivesicular bodies (MVBs), and EV release. SHH protein is present on a subset of EVs marked by a unique set of proteins we call ART-EVs. CHMP1A’s requirement in formation of ART-EVs and other EVs provides a model to elucidate EV functions in multiple brain processes.