Mutations in valosin-containing protein (VCP) decrease ADP/ATP translocation across the mitochondrial membrane and impair energy metabolism in human neurons

Mutations in the gene encoding valosin-containing protein (VCP) lead to multisystem proteinopathies including frontotemporal dementia. We have previously shown that patient-derived VCP mutant fibroblasts exhibit lower mitochondrial membrane potential, uncoupled respiration, and reduced ATP levels. This study addresses the underlying basis for mitochondrial uncoupling using VCP knockdown neuroblastoma cell lines, induced pluripotent stem cells (iPSCs), and iPSC-derived cortical neurons from patients with pathogenic mutations in VCP. Using fluorescent live cell imaging and respiration analysis we demonstrate a VCP mutation/knockdown-induced dysregulation in the adenine nucleotide translocase, which results in a slower rate of ADP or ATP translocation across the mitochondrial membranes. This deregulation can explain the mitochondrial uncoupling and lower ATP levels in VCP mutation-bearing neurons via reduced ADP availability for ATP synthesis. This study provides evidence for a role of adenine nucleotide translocase in the mechanism underlying altered mitochondrial function in VCP-related degeneration, and this new insight may inform efforts to better understand and manage neurodegenerative disease and other proteinopathies

Alpha-Synuclein Oligomers Interact with Metal Ions to Induce Oxidative Stress and Neuronal Death in Parkinson's Disease

Protein aggregation and oxidative stress are both key pathogenic processes in Parkinson's disease, although the mechanism by which misfolded proteins induce oxidative stress and neuronal death remains unknown. In this study, we describe how aggregation of alpha-synuclein (α-S) from its monomeric form to its soluble oligomeric state results in aberrant free radical production and neuronal toxicity

Protein kinase C signalling during miracidium to mother sporocyst development in the helminth parasite, Schistosoma mansoni

For schistosomes, development of the miracidium to mother sporocyst within a compatible molluscan host requires considerable physiological and morphological changes by the parasite. The molecular mechanisms controlling such development have not been explored extensively. To begin to elucidate the importance of kinase-mediated signal transduction to this process, the phosphorylation (activation) of protein kinase C (PKC) in larval stages of Schistosoma mansoni undergoing in vitro transformation was explored. Mining of the S. mansoni genomic database revealed two S. mansoni PKC proteins with high homology to human PKCbeta and containing the conserved autophosphorylation (activation) site represented by serine 660 of human PKCbeta(II). Western blotting with anti-phosphospecific antibodies directed to this site demonstrated that miracidia freshly-hatched from eggs possessed PKC (78kDa) which was phosphorylated (activated) when miracidia were exposed to phorbol ester, and dephosphorylated (inhibited) following exposure to the PKC inhibitor GF109203X. Miracidia treated with the phospholipase C (PLC) inhibitor U73122 also displayed decreased PKC phosphorylation. S. mansoni PKC was phosphorylated during the initial 24h development of miracidia into mother sporocysts; after 31h and 48h development, phosphorylation was reduced by 72% and 86%, respectively. Confocal microscopy of miracidia revealed phosphorylated PKC associated with the neural mass, excretory vesicle, tegument, ciliated plates, terebratorium and germinal cells; in larvae undergoing transformation for 31h, phosphorylated PKC was only occasionally detected, being present in regions likely corresponding to the ridge cyton. Inhibition of PKC in miracidia by GF109230X resulted in accelerated transformation, particularly to the postmiracidium stage; ciliated plates were also shed from developing larvae more rapidly. These results highlight the dynamic nature of PKC signalling during S. mansoni postembryonic development and support a role for active PKC in restricting transformation of S. mansoni miracidia into mother sporocysts

Hypoxia signaling controls postnatal changes in cardiac mitochondrial morphology and function

AbstractFetal cardiomyocyte adaptation to low levels of oxygen in utero is incompletely understood, and is of interest as hypoxia tolerance is lost after birth, leading to vulnerability of adult cardiomyocytes. It is known that cardiac mitochondrial morphology, number and function change significantly following birth, although the underlying molecular mechanisms and physiological stimuli are undefined.Here we show that the decrease in cardiomyocyte HIF-signaling in cardiomyocytes immediately after birth acts as a physiological switch driving mitochondrial fusion and increased postnatal mitochondrial biogenesis. We also investigated mechanisms of ATP generation in embryonic cardiac mitochondria. We found that embryonic cardiac cardiomyocytes rely on both glycolysis and the tricarboxylic acid cycle to generate ATP, and that the balance between these two metabolic pathways in the heart is controlled around birth by the reduction in HIF signaling. We therefore propose that the increase in ambient oxygen encountered by the neonate at birth acts as a key physiological stimulus to cardiac mitochondrial adaptation

Molecular pharmacology in a simple model system: Implicating MAP kinase and phosphoinositide signalling in bipolar disorder

Understanding the mechanisms of drug action has been the primary focus for pharmacological researchers, traditionally using rodent models. However, non-sentient model systems are now increasingly being used as an alternative approach to better understand drug action or targets. One of these model systems, the social amoeba Dictyostelium, enables the rapid ablation or over-expression of genes, and the subsequent use of isogenic cell culture for the analysis of cell signalling pathways in pharmacological research. The model also supports an increasingly important ethical view of research, involving the reduction, replacement and refinement of animals in biomedical research. This review outlines the use of Dictyostelium in understanding the pharmacological action of two commonly used bipolar disorder treatments (valproic acid and lithium). Both of these compounds regulate mitogen activated protein (MAP) kinase and inositol phospholipid-based signalling by unknown means. Analysis of the molecular pathways targeted by these drugs in Dictyostelium and translation of discoveries to animal systems has helped to further understand the molecular mechanisms of these bipolar disorder treatments

A Missense Mutation in KCTD17 Causes Autosomal Dominant Myoclonus-Dystonia

Myoclonus-dystonia (M-D) is a rare movement disorder characterized by a combination of non-epileptic myoclonic jerks and dystonia. SGCE mutations represent a major cause for familial M-D being responsible for 30%–50% of cases. After excluding SGCE mutations, we identified through a combination of linkage analysis and whole-exome sequencing KCTD17 c.434 G>A p.(Arg145His) as the only segregating variant in a dominant British pedigree with seven subjects affected by M-D. A subsequent screening in a cohort of M-D cases without mutations in SGCE revealed the same KCTD17 variant in a German family. The clinical presentation of the KCTD17-mutated cases was distinct from the phenotype usually observed in M-D due to SGCE mutations. All cases initially presented with mild myoclonus affecting the upper limbs. Dystonia showed a progressive course, with increasing severity of symptoms and spreading from the cranio-cervical region to other sites. KCTD17 is abundantly expressed in all brain regions with the highest expression in the putamen. Weighted gene co-expression network analysis, based on mRNA expression profile of brain samples from neuropathologically healthy individuals, showed that KCTD17 is part of a putamen gene network, which is significantly enriched for dystonia genes. Functional annotation of the network showed an over-representation of genes involved in post-synaptic dopaminergic transmission. Functional studies in mutation bearing fibroblasts demonstrated abnormalities in endoplasmic reticulum-dependent calcium signaling. In conclusion, we demonstrate that the KCTD17 c.434 G>A p.(Arg145His) mutation causes autosomal dominant M-D. Further functional studies are warranted to further characterize the nature of KCTD17 contribution to the molecular pathogenesis of M-D