Annapurna Chalasani

Nrf2 impacts cellular bioenergetics by controlling substrate availability for mitochondrial respiration

Summary Transcription factor Nrf2 and its repressor Keap1 regulate a network of cytoprotective genes involving more than 1% of the genome, their best known targets being drug-metabolizing and antioxidant genes. Here we demonstrate a novel role for this pathway in directly regulating mitochondrial bioenergetics in murine neurons and embryonic fibroblasts. Loss of Nrf2 leads to mitochondrial depolarisation, decreased ATP levels and impaired respiration, whereas genetic activation of Nrf2 increases the mitochondrial membrane potential and ATP levels, the rate of respiration and the efficiency of oxidative phosphorylation. We further show that Nrf2-deficient cells have increased production of ATP in glycolysis, which is then used by the F1Fo-ATPase for maintenance of the mitochondrial membrane potential. While the levels and in vitro activities of the respiratory complexes are unaffected by Nrf2 deletion, their activities in isolated mitochondria and intact live cells are substantially impaired. In addition, the rate of regeneration of NADH after inhibition of respiration is much slower in Nrf2-knockout cells than in their wild-type counterparts. Taken together, these results show that Nrf2 directly regulates cellular energy metabolism through modulating the availability of substrates for mitochondrial respiration. Our findings highlight the importance of efficient energy metabolism in Nrf2-mediated cytoprotection.

Signal transducer and activator of transcription 2 deficiency is a novel disorder of mitochondrial fission

See Dasgupta et al. (doi:10.1093/awv237) for a scientific commentary on this article. Shahni et al. identify a novel mutation in STAT2, which encodes a component of the JAK-STAT cytokine signalling pathway, in three patients with severe neurological deterioration following viral infection. STAT2 is shown to regulate mitochondrial fission, suggesting a new avenue for treatment of mitochondrial diseases and possibly common neurodegenerative disorders.

Autosomal-recessive cerebellar ataxia caused by a novel ADCK3 mutation that elongates the protein: clinical, genetic and biochemical characterisation

Background The autosomal-recessive cerebellar ataxias (ARCA) are a clinically and genetically heterogeneous group of neurodegenerative disorders. The large number of ARCA genes leads to delay and difficulties obtaining an exact diagnosis in many patients and families. Ubiquinone (CoQ10) deficiency is one of the potentially treatable causes of ARCAs as some patients respond to CoQ10 supplementation. The AarF domain containing kinase 3 gene (ADCK3) is one of several genes associated with CoQ10 deficiency. ADCK3 encodes a mitochondrial protein which functions as an electron-transfer membrane protein complex in the mitochondrial respiratory chain (MRC). Methods We report two siblings from a consanguineous Pakistani family who presented with cerebellar ataxia and severe myoclonus from adolescence. Whole exome sequencing and biochemical assessment of fibroblasts were performed in the index patient. Results A novel homozygous frameshift mutation in ADCK3 (p.Ser616Leufs*114), was identified in both siblings. This frameshift mutation results in the loss of the stop codon, extending the coding protein by 81 amino acids. Significant CoQ10 deficiency and reduced MRC enzyme activities in the index patients fibroblasts suggested that the mutant protein may reduce the efficiency of mitochondrial electron transfer. CoQ10 supplementation was initiated following these genetic and biochemical analyses. She gained substantial improvement in myoclonic movements, ataxic gait and dysarthric speech after treatment. Conclusion This study highlights the importance of diagnosing ADCK3 mutations and the potential benefit of treatment for patients. The identification of this new mutation broadens the phenotypic spectrum associated with ADCK3 mutations and provides further understanding of their pathogenic mechanism.

Coenzyme Q10 Levels Are Decreased in the Cerebellum of Multiple-System Atrophy Patients

Background The objective of this study was to evaluate whether the levels of coenzyme Q10 (CoQ10) in brain tissue of multiple system atrophy (MSA) patients differ from those in elderly controls and in patients with other neurodegenerative diseases. Methods Flash frozen brain tissue of a series of 20 pathologically confirmed MSA patients [9 olivopontocerebellar atrophy (OPCA) type, 6 striatonigral degeneration (SND) type, and 5 mixed type] was used for this study. Elderly controls (n = 37) as well as idiopathic Parkinsons disease (n = 7), dementia with Lewy bodies (n = 20), corticobasal degeneration (n = 15) and cerebellar ataxia (n = 18) patients were used as comparison groups. CoQ10 was measured in cerebellar and frontal cortex tissue by high performance liquid chromatography. Results We detected a statistically significant decrease (by 3–5%) in the level of CoQ10 in the cerebellum of MSA cases (P = 0.001), specifically in OPCA (P = 0.001) and mixed cases (P = 0.005), when compared to controls as well as to other neurodegenerative diseases [dementia with Lewy bodies (P<0.001), idiopathic Parkinsons disease (P<0.001), corticobasal degeneration (P<0.001), and cerebellar ataxia (P = 0.001)]. Conclusion Our results suggest that a perturbation in the CoQ10 biosynthetic pathway is associated with the pathogenesis of MSA but the mechanism behind this finding remains to be elucidated.

Absence of Intracellular Ion Channels TPC1 and TPC2 Leads to Mature-Onset Obesity in Male Mice, Due to Impaired Lipid Availability for Thermogenesis in Brown Adipose Tissue

Intracellular calcium-permeable channels have been implicated in thermogenic function of murine brown and brite/beige adipocytes, respectively transient receptor potential melastin-8 and transient receptor potential vanilloid-4. Because the endo-lysosomal two-pore channels (TPCs) have also been ascribed with metabolic functionality, we studied the effect of simultaneously knocking out TPC1 and TPC2 on body composition and energy balance in male mice fed a chow diet. Compared with wild-type mice, TPC1 and TPC2 double knockout (Tpcn1/2(-/-)) animals had a higher respiratory quotient and became obese between 6 and 9 months of age. Although food intake was unaltered, interscapular brown adipose tissue (BAT) maximal temperature and lean-mass adjusted oxygen consumption were lower in Tpcn1/2(-/-) than in wild type mice. Phosphorylated hormone-sensitive lipase expression, lipid density and expression of β-adrenergic receptors were also lower in Tpcn1/2(-/-) BAT, whereas mitochondrial respiratory chain function and uncoupling protein-1 expression remained intact. We conclude that Tpcn1/2(-/-) mice show mature-onset obesity due to reduced lipid availability and use, and a defect in β-adrenergic receptor signaling, leading to impaired thermogenic activity, in BAT.

Coenzyme Q10 in the Treatment of Mitochondrial Disease

Currently, there is a paucity of available treatment strategies for oxidative phosphorylation disorders. Coenzyme Q10 (CoQ10) and related synthetic quinones are the only agents to date that have pr...

P50 Genetic dysfunction of MT-ATP6 can cause axonal Charcot-Marie-Tooth disease

Tooth disease Robert D.S. Pitceathly, MRCP, Sinead M. Murphy, MRCP, Ellen Cottenie, MSc, Annapurna Chalasani, PhD, Mary G. Sweeney, BSc, Cathy Woodward, BSc, Ese E. Mudanohwo, BSc, Iain Hargreaves, PhD, Simon Heales, PhD, John Land, PhD, Janice L. Holton, PhD, Henry Houlden, PhD, Julian Blake, MRCP, Michael Champion, FRCPCH, Frances Flinter, PhD, Stephanie Robb, FRCPCH, Rupert Page, FRCP, Michael Rose, FRCP, Jacqueline Palace, FRCP, Carol Crowe, MD, Cheryl Longman, FRCP, Michael P. Lunn, FRCP, Shamima Rahman, PhD, Mary M. Reilly, FRCP, Michael G. Hanna, FRCP