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1.  HIBCH mutations can cause Leigh-like disease with combined deficiency of multiple mitochondrial respiratory chain enzymes and pyruvate dehydrogenase 
Deficiency of 3-hydroxy-isobutyryl-CoA hydrolase (HIBCH) caused by HIBCH mutations is a rare cerebral organic aciduria caused by disturbance of valine catabolism. Multiple mitochondrial respiratory chain (RC) enzyme deficiencies can arise from a number of mechanisms, including defective maintenance or expression of mitochondrial DNA. Impaired biosynthesis of iron-sulphur clusters and lipoic acid can lead to pyruvate dehydrogenase complex (PDHc) deficiency in addition to multiple RC deficiencies, known as the multiple mitochondrial dysfunctions syndrome.
Two brothers born to distantly related Pakistani parents presenting in early infancy with a progressive neurodegenerative disorder, associated with basal ganglia changes on brain magnetic resonance imaging, were investigated for suspected Leigh-like mitochondrial disease. The index case had deficiencies of multiple RC enzymes and PDHc in skeletal muscle and fibroblasts respectively, but these were normal in his younger brother. The observation of persistently elevated hydroxy-C4-carnitine levels in the younger brother led to suspicion of HIBCH deficiency, which was investigated by biochemical assay in cultured skin fibroblasts and molecular genetic analysis.
Specific spectrophotometric enzyme assay revealed HIBCH activity to be below detectable limits in cultured skin fibroblasts from both brothers. Direct Sanger sequence analysis demonstrated a novel homozygous pathogenic missense mutation c.950G
HIBCH deficiency, a disorder of valine catabolism, is a novel cause of the multiple mitochondrial dysfunctions syndrome, and should be considered in the differential diagnosis of patients presenting with multiple RC deficiencies and/or pyruvate dehydrogenase deficiency.
PMCID: PMC4222069  PMID: 24299452
Mitochondrial disease; Multiple respiratory chain enzyme deficiencies; Pyruvate dehydrogenase deficiency; 3-hydroxy-isobutyryl-CoA hydrolase; HIBCH; Acylcarnitines; Multiple mitochondrial dysfunctions syndrome; Valine catabolism; Organic aciduria
•Mutations in the ROC, COR and Kinase domain of LRRK2 alter the autophagic response to starvation.•LC3-I/II ratio following starvation is altered by mutations, as well as p62 and WIPI2 positive puncta.•This occurs independently of any alteration in downstream targets of mTORC1.
LRRK2 is one of the most important genetic contributors to Parkinson’s disease (PD). Point mutations in this gene cause an autosomal dominant form of PD, but to date no cellular phenotype has been consistently linked with mutations in each of the functional domains (ROC, COR and Kinase) of the protein product of this gene. In this study, primary fibroblasts from individuals carrying pathogenic mutations in the three central domains of LRRK2 were assessed for alterations in the autophagy/lysosomal pathway using a combination of biochemical and cellular approaches. Mutations in all three domains resulted in alterations in markers for autophagy/lysosomal function compared to wild type cells. These data highlight the autophagy and lysosomal pathways as read outs for pathogenic LRRK2 function and as a marker for disease, and provide insight into the mechanisms linking LRRK2 function and mutations.
PMCID: PMC3858825  PMID: 24211199
LRRK2, leucine rich repeat kinase 2; ROC, ras of complex proteins; COR, C-terminal of ROC; PD, Parkinson’s disease; ICC, Immunocytochemistry; LRRK2; Parkinson’s disease; Autophagy; Lysosomes; Signaling pathways
Cell Reports  2013;3(6):1795-1805.
The molecular basis of cytochrome c oxidase (COX, complex IV) deficiency remains genetically undetermined in many cases. Homozygosity mapping and whole-exome sequencing were performed in a consanguineous pedigree with isolated COX deficiency linked to a Leigh syndrome neurological phenotype. Unexpectedly, affected individuals harbored homozygous splice donor site mutations in NDUFA4, a gene previously assigned to encode a mitochondrial respiratory chain complex I (NADH:ubiquinone oxidoreductase) subunit. Western blot analysis of denaturing gels and immunocytochemistry revealed undetectable steady-state NDUFA4 protein levels, indicating that the mutation causes a loss-of-function effect in the homozygous state. Analysis of one- and two-dimensional blue-native polyacrylamide gels confirmed an interaction between NDUFA4 and the COX enzyme complex in control muscle, whereas the COX enzyme complex without NDUFA4 was detectable with no abnormal subassemblies in patient muscle. These observations support recent work in cell lines suggesting that NDUFA4 is an additional COX subunit and demonstrate that NDUFA4 mutations cause human disease. Our findings support reassignment of the NDUFA4 protein to complex IV and suggest that patients with unexplained COX deficiency should be screened for NDUFA4 mutations.
Graphical Abstract
•Mutations in NDUFA4, assigned to encode a complex I subunit, cause human COX deficiency•Confirmed interaction between NDUFA4 and the COX holoenzyme in control muscle•The COX holoenzyme without NDUFA4 is detectable with no abnormal subassemblies in patient muscle•NDUFA4 is essential for complex IV activity, but is not required for assembly of the COX holoenzyme
Isolated cytochrome c oxidase (COX) deficiency is a frequent finding in human mitochondrial disease. Mutations in nuclear-encoded structural subunits are extremely rare, and, in many cases, the molecular basis remains undetermined. Recent evidence in cell lines has suggested that NDUFA4, previously assigned to encode a complex I subunit, actually encodes a structural component of COX. Hanna and colleagues now demonstrate that NDUFA4 mutations cause human COX deficiency, thus confirming NDUFA4 as a COX subunit that is essential for the enzyme’s activity.
PMCID: PMC3701321  PMID: 23746447
PLoS ONE  2012;7(8):e43099.
Our understanding of the molecular mechanisms of many neurological disorders has been greatly enhanced by the discovery of mutations in genes linked to familial forms of these diseases. These have facilitated the generation of cell and animal models that can be used to understand the underlying molecular pathology. Recently, there has been a surge of interest in the use of patient-derived cells, due to the development of induced pluripotent stem cells and their subsequent differentiation into neurons and glia. Access to patient cell lines carrying the relevant mutations is a limiting factor for many centres wishing to pursue this research. We have therefore generated an open-access collection of fibroblast lines from patients carrying mutations linked to neurological disease. These cell lines have been deposited in the National Institute for Neurological Disorders and Stroke (NINDS) Repository at the Coriell Institute for Medical Research and can be requested by any research group for use in in vitro disease modelling. There are currently 71 mutation-defined cell lines available for request from a wide range of neurological disorders and this collection will be continually expanded. This represents a significant resource that will advance the use of patient cells as disease models by the scientific community.
PMCID: PMC3428297  PMID: 22952635
Nature Communications  2011;2:440-.
A major barrier to research on Parkinson's disease is inaccessibility of diseased tissue for study. One solution is to derive induced pluripotent stem cells from patients and differentiate them into neurons affected by disease. Triplication of SNCA, encoding α-synuclein, causes a fully penetrant, aggressive form of Parkinson's disease with dementia. α-Synuclein dysfunction is the critical pathogenic event in Parkinson's disease, multiple system atrophy and dementia with Lewy bodies. Here we produce multiple induced pluripotent stem cell lines from an SNCA triplication patient and an unaffected first-degree relative. When these cells are differentiated into midbrain dopaminergic neurons, those from the patient produce double the amount of α-synuclein protein as neurons from the unaffected relative, precisely recapitulating the cause of Parkinson's disease in these individuals. This model represents a new experimental system to identify compounds that reduce levels of α-synuclein, and to investigate the mechanistic basis of neurodegeneration caused by α-synuclein dysfunction.
Pluripotent stem cells can be generated from the somatic cells of humans and are a useful model to study disease. Here, pluripotent stem cells are made from a patient with familial Parkinson's disease, and the resulting neurons exhibit elevated levels of α-synuclein, recapitulating the molecular features of the patient's disease.
PMCID: PMC3265381  PMID: 21863007
Human Molecular Genetics  2010;19(24):4861-4870.
Mitochondrial dysfunction and perturbed degradation of proteins have been implicated in Parkinson's disease (PD) pathogenesis. Mutations in the Parkin and PINK1 genes are a cause of familial PD. PINK1 is a putative kinase associated with mitochondria, and loss of PINK1 expression leads to mitochondrial dysfunction, which increases with time. Parkin is suggested to be downstream of PINK1 and also mediates the removal of damaged mitochondria by macroautophagy (mitophagy). We investigated whether mitochondrial dysfunction in dopaminergic SH-SY5Y cells following decreased PINK1 expression by RNAi may in part be due to the inhibition of mitophagy. Reduced flux through the macroautophagy pathway was found to be coincident with the inhibition of ATP synthesis following 12 days of PINK1 silencing. Overexpression of parkin in these cells restored both autophagic flux and ATP synthesis. Overexpression and RNAi studies also indicated that PINK1 and parkin were required for mitophagy following CCCP-induced mitochondrial damage. The ubiquitination of several mitochondrial proteins, including mitofusin 1 and mitofusin 2, were detected within 3 h of CCCP treatment. These post-translational modifications were reduced following the silencing of parkin or PINK1. The ubiquitination of mitochondrial proteins appears to identify mitochondria for degradation and facilitate mitophagy. PINK1 and parkin are thus required for the removal of damaged mitochondria in dopaminergic cells, and inhibition of this pathway may lead to the accumulation of defective mitochondria which may contribute to PD pathogenesis.
PMCID: PMC3583518  PMID: 20871098
PLoS ONE  2011;6(7):e22489.
Point mutations in LRRK2 cause autosomal dominant Parkinson's disease. Despite extensive efforts to determine the mechanism of cell death in patients with LRRK2 mutations, the aetiology of LRRK2 PD is not well understood. To examine possible alterations in gene expression linked to the presence of LRRK2 mutations, we carried out a case versus control analysis of global gene expression in three systems: fibroblasts isolated from LRRK2 mutation carriers and healthy, non-mutation carrying controls; brain tissue from G2019S mutation carriers and controls; and HEK293 inducible LRRK2 wild type and mutant cell lines. No significant alteration in gene expression was found in these systems following correction for multiple testing. These data suggest that any alterations in basal gene expression in fibroblasts or cell lines containing mutations in LRRK2 are likely to be quantitatively small. This work suggests that LRRK2 is unlikely to play a direct role in modulation of gene expression, although it remains possible that this protein can influence mRNA expression under pathogenic cicumstances.
PMCID: PMC3142158  PMID: 21799870
Inherited metabolic diseases (IMDs) comprise a diverse group of generally progressive genetic metabolic disorders of variable clinical presentations and severity. We have undertaken a study using microarray gene expression profiling of cultured fibroblasts to investigate 68 patients with a broad range of suspected metabolic disorders, including defects of lysosomal, mitochondrial, peroxisomal, fatty acid, carbohydrate, amino acid, molybdenum cofactor, and purine and pyrimidine metabolism. We aimed to define gene expression signatures characteristic of defective metabolic pathways.
Total mRNA extracted from cultured fibroblast cell lines was hybridized to Affymetrix U133 Plus 2.0 arrays. Expression data was analyzed for the presence of a gene expression signature characteristic of an inherited metabolic disorder and for genes expressing significantly decreased levels of mRNA.
No characteristic signatures were found. However, in 16% of cases, disease-associated nonsense and frameshift mutations generating premature termination codons resulted in significantly decreased mRNA expression of the defective gene. The microarray assay detected these changes with high sensitivity and specificity.
In patients with a suspected familial metabolic disorder where initial screening tests have proven uninformative, microarray gene expression profiling may contribute significantly to the identification of the genetic defect, shortcutting the diagnostic cascade.
PMCID: PMC3009951  PMID: 21122112
Colorectal cancer is the third most-common cancer and the second most-common cause of cancer related death in UK. Although chemotherapy plays significant role in the treatment of colorectal cancer, morbidity and mortality due to drug resistance and cancer metastasis are yet to be eliminated. Recently, doxycycline has been reported to have cytotoxic and anti-proliferating properties in various cancer cells. In this study, whether doxycycline was apoptosis threshold lowering agent in colorectal cancer cells by targeting mitochondria was answered.
This study showed dose-dependent cytotoxic effects of cisplatin, oxaliplatin and doxycycline in HT29 colorectal cancer cells. Doxycycline showed inhibition of cytochrome-c-oxidase activity in these cells over a time-period. The pre-treatment of doxycycline reported statistically significant increased cytotoxicity of cisplatin and oxaliplatin compared to cisplatin and oxaliplatin alone. The caspase studies revealed significantly less expression and activity of caspase 3 in HT29 cells pre-treated with doxycycline compared to the cells treated with cisplatin and oxaliplatin alone.
It was concluded that doxycycline lowered the apoptotic threshold in HT 29 cells by targeting mitochondria. This also raised possible caspase-independent mechanisms of apoptosis in HT29 cells when pre-treated with doxycycline however this needs further research work.
PMCID: PMC2940783  PMID: 20819205
PLoS ONE  2009;4(3):e4756.
Mitochondrial dysfunction has been implicated in the pathogenesis of Parkinson's disease (PD). Impairment of the mitochondrial electron transport chain (ETC) and an increased frequency in deletions of mitochondrial DNA (mtDNA), which encodes some of the subunits of the ETC, have been reported in the substantia nigra of PD brains. The identification of mutations in the PINK1 gene, which cause an autosomal recessive form of PD, has supported mitochondrial involvement in PD. The PINK1 protein is a serine/threonine kinase localized in mitochondria and the cytosol. Its precise function is unknown, but it is involved in neuroprotection against a variety of stress signalling pathways.
Methodology/Principal Findings
In this report we have investigated the effect of silencing PINK1 expression in human dopaminergic SH-SY5Y cells by siRNA on mtDNA synthesis and ETC function. Loss of PINK1 expression resulted in a decrease in mtDNA levels and mtDNA synthesis. We also report a concomitant loss of mitochondrial membrane potential and decreased mitochondrial ATP synthesis, with the activity of complex IV of the ETC most affected. This mitochondrial dysfunction resulted in increased markers of oxidative stress under basal conditions and increased cell death following treatment with the free radical generator paraquat.
This report highlights a novel function of PINK1 in mitochondrial biogenesis and a role in maintaining mitochondrial ETC activity. Dysfunction of both has been implicated in sporadic forms of PD suggesting that these may be key pathways in the development of the disease.
PMCID: PMC2649444  PMID: 19270741

Results 1-12 (12)