Mitochondria account for essential cellular pathways, from ATP production to nucleotide metabolism, and their deficits lead to neurological disorders and contribute to the onset of age-related... Show moreMitochondria account for essential cellular pathways, from ATP production to nucleotide metabolism, and their deficits lead to neurological disorders and contribute to the onset of age-related diseases. Direct neuronal reprogramming aims at replacing neurons lost in such conditions, but very little is known about the impact of mitochondrial dysfunction on the direct reprogramming of human cells. Here, we explore the effects of mitochondrial dysfunction on the neuronal reprogramming of induced pluripotent stem cell (iPSC)-derived astrocytes carrying mutations in the NDUFS4 gene, important for Complex I and associated with Leigh syndrome. This led to the identification of the unfolded protein response as a major hurdle in the direct neuronal conversion of not only astrocytes and fibroblasts from patients but also control human astrocytes and fibroblasts. Its transient inhibition potently improves reprogramming by influencing the mitochondria-endoplasmic-reticulum-stress-mediated pathways. Taken together, disease modeling using patient cells unraveled novel general hurdles and ways to overcome these in human astrocyte-to-neuron reprogramming. Show less
Pilotto, F.; Douthwaite, C.; Diab, R.; Ye, X.Q.; Qassab, Z. al; Tietje, C.; ... ; Saxena, S. 2023
Toxic proteinaceous deposits and alterations in excitability and activity levels characterize vulnerable neuronal populations in neurodegenerative diseases. Using in vivo two-photon imaging in... Show moreToxic proteinaceous deposits and alterations in excitability and activity levels characterize vulnerable neuronal populations in neurodegenerative diseases. Using in vivo two-photon imaging in behaving spino-cerebellar ataxia type 1 (Sca1) mice, wherein Purkinje neurons (PNs) degenerate, we identify an inhibitory cir-cuit element (molecular layer interneurons [MLINs]) that becomes prematurely hyperexcitable, compro-mising sensorimotor signals in the cerebellum at early stages. Mutant MLINs express abnormally elevated parvalbumin, harbor high excitatory-to-inhibitory synaptic density, and display more numerous synaptic connections on PNs, indicating an excitation/inhibition imbalance. Chemogenetic inhibition of hyperexcit-able MLINs normalizes parvalbumin expression and restores calcium signaling in Sca1 PNs. Chronic inhibi-tion of mutant MLINs delayed PN degeneration, reduced pathology, and ameliorated motor deficits in Sca1 mice. Conserved proteomic signature of Sca1 MLINs, shared with human SCA1 interneurons, involved the higher expression of FRRS1L, implicated in AMPA receptor trafficking. We thus propose that circuit-level def-icits upstream of PNs are one of the main disease triggers in SCA1. Show less
We examined the role of repeat expansions in the pathogenesis of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) by analyzing whole-genome sequence data from 2,442 FTD/ALS... Show moreWe examined the role of repeat expansions in the pathogenesis of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) by analyzing whole-genome sequence data from 2,442 FTD/ALS patients, 2,599 Lewy body dementia (LBD) patients, and 3,158 neurologically healthy subjects. Pathogenic expansions (range, 40-64 CAG repeats) in the huntingtin (HTT) gene were found in three (0.12%) patients diagnosed with pure FTD/ALS syndromes but were not present in the LBD or healthy cohorts. We replicated our findings in an independent collection of 3,674 FTD/ALS patients. Postmortem evaluations of two patients revealed the classical TDP-43 pathology of FTD/ALS, as well as huntingtin-positive, ubiquitin-positive aggregates in the frontal cortex. The neostriatal atrophy that pathologically defines Huntington's disease was absent in both cases. Our findings reveal an etiological relationship between HTT repeat expansions and FTD/ALS syndromes and indicate that genetic screening of FTD/ALS patients for HTT repeat expansions should be considered.Keywords: amyotrophic lateral sclerosis; frontotemporal dementia; huntingtin; repeat expansions; whole-genome sequencing.Published by Elsevier Inc. Show less
Held, R.G.; Liu, C.L.; Ma, K.P.; Ramsey, A.M.; Tarr, T.B.; Nola, G. de; ... ; Kaeser, P.S. 2020
Presynaptic Ca(v)2 channels are essential for Ca2+-triggered exocytosis. In addition, there are two competing models for their roles in synapse structure. First, Ca2+ channels or Ca2+ entry may... Show morePresynaptic Ca(v)2 channels are essential for Ca2+-triggered exocytosis. In addition, there are two competing models for their roles in synapse structure. First, Ca2+ channels or Ca2+ entry may control synapse assembly. Second, active zone proteins may scaffold Ca(v)2s to presynaptic release sites, and synapse structure is Ca(v)2 independent. Here, we ablated all three Ca(v)2s using conditional knockout in cultured hippocampal neurons or at the calyx of Held, which abolished evoked exocytosis. Compellingly, synapse and active zone structure, vesicle docking, and transsynaptic nano-organization were unimpaired. Similarly, long-term blockade of action potentials and Ca2+ entry did not disrupt active zone assembly. Although Ca(v)2 knockout impaired the localization of beta subunits, alpha 2 delta-1 localized normally. Rescue with Ca(v)2 restored exocytosis, and Ca(v)2 active zone targeting depended on the intracellular C-terminus. We conclude that synapse assembly is independent of Ca(v)2s or Ca2+ entry through them. Instead, active zone proteins recruit and anchor Ca(v)2s via Ca(v)2 C-termini. Show less
Early career researchers (ECRs) are faced with a range of competing pressures in academia, making self-management key to building a successful career. The Organization for Human Brain Mapping... Show moreEarly career researchers (ECRs) are faced with a range of competing pressures in academia, making self-management key to building a successful career. The Organization for Human Brain Mapping undertook a group effort to gather helpful advice for ECRs in self-management. Show less
The midline glia are specialized, nonneuronal cells at the midline of the Drosophila central nervous system (CNS). During development, the midline glia provide guidance cues for extending axons. At... Show moreThe midline glia are specialized, nonneuronal cells at the midline of the Drosophila central nervous system (CNS). During development, the midline glia provide guidance cues for extending axons. At the same time, they migrate and help separate the two axon commissures. They then wrap around and ensheath the commissural axons. In many segments, a few of the glia do not enwrap the axons, and these cells die. The wrapper gene encodes a novel member of the immunoglobulin (Ig) superfamily. Wrapper protein is expressed specifically on the surface of midline glia. In wrapper mutant embryos, the midline glia express their normal guidance cues and migrate normally. However, they do not ensheath the commissural axons, and as a result, the glia die. In the absence of Wrapper, the two axon commissures are not properly separated. Show less
Postsynaptic sensitivity to glutamate was genetically manipulated at the Drosophila neuromuscular junction (NMJ) to test whether postsynaptic activity can regulate presynaptic function during... Show morePostsynaptic sensitivity to glutamate was genetically manipulated at the Drosophila neuromuscular junction (NMJ) to test whether postsynaptic activity can regulate presynaptic function during development. We cloned the gene encoding a second muscle-specific glutamate receptor, DGluRIIB, which is closely related to the previously identified DGluRIIA and located adjacent to it in the genome. Mutations that eliminate DGluRIIA (but not DGluRIIB) or transgenic constructs that increase DGluRIIA expression were generated. When DGluRIIA is missing, the response of the muscle to a single vesicle of transmitter is substantially de- creased. However, the responseof the muscle to nerve stimulation is normal because quantal content is significantly increased. Thus, a decrease in postsynaptic receptors leads to an increase in presynaptic transmitter release, indicating that postsynaptic activity controls a retrograde signal that regulates presynaptic function. Show less
