In this project, novel factors causing severe neurological and multiorgan disorders of childhood are characterized in vivo and in vitro, focusing on new disease pathomechanisms. The field of inherited disorders of the nervous system has undergone a major revolution in recent decades. As a result, many genetic defects are known to be responsible for neurological diseases, but frequently not much is known about the resulting protein product and the pathophysiological basis of the disease. Our project constitutes a powerful approach to elucidate novel genetic causes, metabolic consequences, pathomechanisms and treatment options in human neurometabolic diseases by monitoring cellular responses at functional, translational and protein levels. The research objectives will be pursued in the following three lines: 1) novel proteins related to early human development, cell division and differentiation, and cell energy metabolism, 2) the role of cellular signalling pathways in the pathogenesis of severe neurological and multiorgan diseases, and 3) mechanisms of mitochondria-targeted drug toxicity. The ultimate goal of the research work is focused on prevention and improved diagnostics of diseases related to brain development and degeneration, aiming to influence prenatal diagnostics, genetic counselling, treatment options and long-term prognosis, which will have a valuable impact on an individual’s quality of life.
By using exome sequencing we have identified several novel candidate genes without known function associated with severe early-onset multiorgan diseases in children, strongly reflecting unique features of the Finnish population.
Most recently, in collaboration with Dr. Eamonn Sheridan (University of Leeds, Leeds, UK) we have demonstrated for the first time that mutations in a striatal-enriched phosphodiesterase PDE10A cause a hyperkinetic movement disorder in humans. In collaboration with Prof Nicholas Brandon (Neuroscience Research Unit, Pfizer Research and Development, Cambridge, MA, USA) a Y107C knock-in mouse model was generated and this mouse model shows decreased Pde10a, displays motor abnormalities, an impaired capacity to inactivate cyclic-AMP and a blunted pharmacological response to PDE10A inhibitors. The manuscript titled “Biallelic Mutations in PDE10A Lead to Loss of Striatal PDE10A and a Hyperkinetic Movement Disorder with Onset in Infancy” was published in American Journal of Human Genetics in 2016 (Dr. Hinttala shares the first authorship, and Dr. Uusimaa shares the last authorship). These scientific breakthrough observations highlight the critical role of PDE10A in motor control and may have significant implications for ongoing therapeutic trials.
As the focus of the project is on dysfunction of cellular energy metabolism, we also aim to find novel genetic causes and pathomechanisms related to mitochondrial disorders and develop disease diagnostics. Mitochondrial diseases are among the most common inherited neurometabolic diseases. Mitochondria are the power plants of the eukaryotic cell, being essential for survival. They support aerobic respiration by providing ATP for intracellular metabolic pathways. In addition, several other metabolic pathways are present in mitochondria, including the Krebs cycle, β-oxidation, and lipid synthesis. Given its fundamental role in the human body, defects of mitochondrial function can be highly deleterious. The clinical spectrum of mitochondrial diseases is very diverse and, most often, tissues with high energy demand are affected. Age at onset is very variable and first symptoms may become at any age. Pediatric patients with mitochondrial diseases often present with severe multiorgan diseases, encephalomyopathies or isolated myopathies, intractable seizures and various neurological symptoms, liver, kidney or endocrinological manifestations, or cardiorespiratory failure. Treatment of mitochondrial diseases is mainly supportive.
Mitochondria-targeted drug toxicity is a major problem for the pharmaceutical and healthcare sectors. This is of particular concern as regards anti-epileptic drugs (AEDs), because epilepsy can lead to mitochondrial impairment and mitochondrial dysfunction can cause epilepsy. A number of AEDs, including sodium valproate (VPA) are linked to mitochondrial toxicity and cause foetal anticonvulsant syndrome. Approximately one third of people with epilepsy do not achieve control of seizures with antiepileptic drugs, demonstrating the urgent need for new safe and effective treatments. The risk of VPA-induced hepatotoxicity is increased in patients with mitochondrial diseases and especially in patients with polymerase gamma (POLG1) mutations. We have studied valproate-induced liver failure associated with POLG1 mutations (Hynynen et al. manuscript in preparation) and the prognosis for these patients after liver transplantation. We showed that POLG1 mutation status and age at presentation of valproate-induced liver failure can affect prognosis. Our results highlight the importance of analysing the POLG1 gene in cases of suspected mitochondrial disease before the introduction of valproate therapy, and treatment with valproic acid should be avoided in these patients (Hynynen et al. 2014).
Pathomechanisms caused by dysfunction of as yet uncharacterized proteins will be studied in further detail as the underlying causes of neurodegenerative and multiorgan manifestations. Novel physiological consequences and functional interactions of these gene products are revealed in human neuronal models as well as in transgenic mice, and fruit fly and zebrafish models. These studies will lead to a broader understanding of the factors behind early human development, cell energy metabolism, cellular signalling pathways, neurodegeneration and tissue fibrosis.
Mitochondrial blossoms. Electron micrograph showing altered mitochondrial structure in patient fibroblasts stained with osmium tetroxide.
Carrozzo R, Verrigni D, Rasmussen M, de Coo R, Amartino H, Bianchi M, Buhas D, Mesli S, Naess K, Born AP, Woldseth B, Prontera P, Batbayli M, Ravn K, Joensen F, Cordelli DM, Santorelli FM, Tulinius M, Darin N, Duno M, Jouvencel P, Burlina A, Stangoni G, Bertini E, Redonnet-Vernhet I, Wibrand F, Dionisi-Vici C, Uusimaa J, Vieira P, Osorio AN, McFarland R, Taylor RW, Holme E, Ostergaard E. Succinate-CoA ligase deficiency due to mutations in SUCLA2 and SUCLG1: phenotype and genotype correlations in 71 patients. J Inherit Metab Dis 39:243-52, 2016.
Diggle CP, Sukoff Rizzo SJ, Popiolek M, Hinttala R, Schülke JP, et al (incl Uusimaa J). Biallelic Mutations in PDE10A Lead to Loss of Striatal PDE10A and a Hyperkinetic Movement Disorder with Onset in Infancy. Am J Hum Genet 98:735-43, 2016.
Lehtonen JM, Forsström S, Bottani E, Viscomi C, Baris OR, et al (incl Uusimaa J). FGF21 is a biomarker for mitochondrial translation and mtDNA maintenance disorders. Neurology 87:2290-2299, 2016.
Widgren P, Hurme A, Falck A, Keski-Filppula R, Remes AM, Moilanen J, Majamaa K, Kervinen M, Uusimaa J. Genetic aetiology of ophthalmological manifestations in children - a focus on mitochondrial disease-related symptoms. Acta Ophthalmol 94:83-91, 2016.
Hinttala R, Sasarman F, Nishimura T, Antonicka H, Brunel-Guitton C, Schwartzentruber J, Fahiminiya S, Majewski J, Faubert D, Ostergaard E, Smeitink JA, Shoubridge EA. An N-terminal formyl methionine on COX 1 is required for the assembly of cytochrome c oxidase. Hum Mol Genet. 24:4103-13, 2015.
Komulainen T, Hautakangas MR, Hinttala R, Pakanen S, Vähäsarja V, Lehenkari P, Olsen P, Vieira P, Saarenpää-Heikkilä O, Palmio J, Tuominen H, Kinnunen P, Majamaa K, Rantala H, Uusimaa J. Mitochondrial DNA Depletion and Deletions in Paediatric Patients with Neuromuscular Diseases: Novel Phenotypes. JIMD Rep. 23:91-100, 2015.
Komulainen T, Lodge T, Hinttala R, Bolszak M, Pietilä M, Koivunen P, Hakkola J, Poulton J, Morten KJ, Uusimaa J. Sodium valproate induces mitochondrial respiration dysfunction in HepG2 in vitro cell model. Toxicology. 331:47-56, 2015.
Hynynen J, Komulainen T, Tukiainen E, Nordin A, Arola J, Kälviäinen R, Jutila L, Röyttä M, Hinttala R, Majamaa K, Mäkisalo H, Uusimaa J. Acute liver failure after valproate exposure in patients with POLG1 mutations and the prognosis after liver transplantation. Liver Transpl. 20:1402-12, 2014.
Sofou K, De Coo IF, Isohanni P, Ostergaard E, Naess K, De Meirleir L, Tzoulis C, Uusimaa J, De Angst IB, Lönnqvist T, Pihko H, Mankinen K, Bindoff LA, Tulinius M, Darin N. A multicenter study on Leigh syndrome: disease course and predictors of survival. Orphanet J Rare Dis. 9:52, 2014.
Uusimaa J, Evans J, Smith C, Butterworth A, Craig K, Ashley N, Liao C, Carver J, Diot A, Macleod L, Hargreaves I, Al-Hussaini A, Faqeih E, Asery A, Al Balwi M, Eyaid W, Al-Sunaid A, Kelly D, van Mourik I, Ball S, Jarvis J, Mulay A, Hadzic N, Samyn M, Baker A, Rahman S, Stewart H, Morris AA, Seller A, Fratter C, Taylor RW, Poulton J. Clinical, biochemical, cellular and molecular characterization of mitochondrial DNA depletion syndrome due to novel mutations in the MPV17 gene. Eur J Hum Genet. 22:184-91, 2014.
Uusimaa J, Gowda V, McShane A, Smith C, Evans J, Shrier A, Narasimhan M, O'Rourke A, Rajabally Y, Hedderly T, Cowan F, Fratter C, Poulton J. Prospective study of POLG mutations presenting in children with intractable epilepsy: prevalence and clinical features. Epilepsia. 54:1002-11, 2013.
Uusimaa J, Jungbluth H, Fratter C, Crisponi G, Feng L, Zeviani M, Hughes I, Treacy EP, Birks J, Brown GK, Sewry CA, McDermott M, Muntoni F, Poulton J. Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease. J Med Genet. 48:660-8, 2011.
Komulainen T, Hinttala R, Kärppä M, Pajunen L, Finnilä S, Tuominen H, Rantala H, Hassinen I, Majamaa K, Uusimaa J. POLG1 p.R722H mutation associated with multiple mtDNA deletions and a neurological phenotype. BMC Neurol. 10:29, 2010.
O'Toole JF, Liu Y, Davis EE, Westlake CJ, Attanasio M, Otto EA, (incl. Nuutinen M, Kärppä M, Ignatius J, Uusimaa J, Pakanen S, Jaakkola E, Tuominen H, Hassinen I), Nurnberg P, Jackson PK, Khanna H, Katsanis N, Hildebrandt F. Individuals with mutations in XPNPEP3, which encodes a mitochondrial protein, develop a nephronophthisis-like nephropathy. J Clin Invest. 120:791-802, 2010.
Bolszak M, Anttonen AK, Komulainen T, Hinttala R, Pakanen S, Sormunen R, Herva R, Lehesjoki AE, Majamaa K, Rantala H, Uusimaa J. Digenic mutations in severe myoclonic epilepsy of infancy. Epilepsy Res. 85:300-4, 2009.
Uusimaa J, Hinttala R, Rantala H, Päivärinta M, Herva R, Röyttä M, Soini H, Moilanen JS, Remes AM, Hassinen IE, Majamaa K. Homozygous W748S mutation in the POLG1 gene in patients with juvenile-onset Alpers syndrome and status epilepticus. Epilepsia. 49:1038-45, 2008.
Uusimaa J, Moilanen JS, Vainionpää L, Tapanainen P, Lindholm P, Nuutinen M, Löppönen T, Mäki-Torkko E, Rantala H, Majamaa K. Prevalence, segregation, and phenotype of the mitochondrial DNA 3243A>G mutation in children. Ann Neurol. 62:278-87, 2007.
Ugalde C, Hinttala R, Timal S, Smeets R, Rodenburg RJ, Uusimaa J, van Heuvel LP, Nijtmans LG, Majamaa K, Smeitink JA. Mutated ND2 impairs mitochondrial complex I assembly and leads to Leigh syndrome. Mol Genet Metab. 90:10-4, 2007.
Hinttala R, Smeets R, Moilanen JS, Ugalde C, Uusimaa J, Smeitink JA, Majamaa K. Analysis of mitochondrial DNA sequences in patients with isolated or combined oxidative phosphorylation system deficiency. J Med Genet. 43:881-6, 2006.
Collaboration with the University of Oxford, UK (Prof Joanna Poulton, Dr. Karl Morten), McGill University, Canada (Prof Eric Shoubridge, Prof Jacek Majewski), and University of Geneva (Dr. Subashika Govindan, PhD).