Pathogenic TNNI1 variants disrupt sarcomere contractility resulting in hypo- and hypercontractile muscle disease

Topic:

Other

Poster Number: T373

Author(s):

Sandra Donkervoort, MS, CGC, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Martijn van de Locht, Department of Physiology, Amsterdam UMC (location VUmc), Dario Ronchi, Dino Ferrari Center, Department of Pathophysiology and Transplantation, University of Milan, Janine Reunert, Department of General Pediatrics, University of Münster, Catriona McLean, Department of Anatomical Pathology, Alfred Hospital, Maha Zaki, Clinical Genetics Department, Human Genetics and Genome Research Institute, National Research Centre, Rotem Orbach, MD, NINDS/DIR/CNP/NGB/NNDCS, Josine de Winter, PhD, Amsterdam UMC, Stefan Conijn, Department of Physiology, Amsterdam UMC (location VUmc), Daan Hoomoedt, Department of Physiology, Amsterdam UMC (location VUmc), Osorio Lopes Abath Neto, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Francesca Magri, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Neurology Unit, Angela Viaene, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Reghan Foley, MD, National Institutes of Health, Svetlana Gorokhova, MD, PhD, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Véronique Bolduc, PhD, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Ying Hu, MS, National Institutes of Health, Nicole Acquaye, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Laura Napoli, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Neuromuscular and Rare Disease Unit, Julien Park, University Hospital Münster, Department of General Pediatrics, Kalyan Immadisetty, Department of Cell and Molecular Physiology, Loyola University, Lee Miles, School of Biological Sciences, Monash University, Mona Essawi, Medical Molecular Genetics Department, Human Genetics and Genome Research Institute, Salar McModie, Department of Neurology, Alfred Health, Leonardo Ferreira, Department of Physiology, Amsterdam UMC (location VUmc), Simona Zanotti, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Neuromuscular and Rare Disease Unit, Sarah Neuhaus, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Livija Medne, Division of Human Genetics, Children's Hospital of Philadelphia,, Nagham ElBagoury, Medical Molecular Genetics Department, Human Genetics and Genome Research Institute, Kory Johnson, Bioinformatics Core, NINDS, NIH, Yong Zhang, Bioinformatics Core, NINDS, NIH, Nigel Laing, PhD, Neurogenetics Unit, Department of Diagnostic Genomics, PathWest Laboratory Medicine, Mark Davis, Neurogenetics Unit, Department of Diagnostic Genomics, PathWest Laboratory Medicine, Robert Bryson-Richardson, School of Biological Sciences, Monash University, Darren Hwee, Research and Development, Cytokinetics Inc., James Hartman, Research and Development, Cytokinetics Inc., Fady Malik, Research and Development, Cytokinetics Inc., Peter Kekenes-Huskey, Department of Cell and Molecular Physiology, Loyola University, Giacomo Pietro Comi, MD, PRESIDIO OSP MAGG POLICLINICO - PAD MONTEGGIA CLINICA NEUROLOGIA, Wessam Sharaf-Eldin, Medical Molecular Genetics Department, Human Genetics and Genome Research Institute, Thorsten Marquardt, Department of General Pediatrics, University of Münster, Gianina Ravenscroft, Centre for Medical Research University of Western Australia, Carsten Bonnemann, MD, PhD, National Institutes of Health, Coen Ottenheijm, Department of Physiology, Amsterdam UMC (location VUmc)

Troponin I (TnI) regulates thin filament activation and muscle contraction. Two isoforms, TnI-fast (TNNI2) and TnI-slow (TNNI1), are predominantly expressed in fast- and slow-twitch myofibers respectively. TNNI2 variants are a rare cause of arthrogryposis, while TNNI1 variants have not been conclusively established to cause skeletal myopathy. We identified both recessive loss-of-function TNNI1 variants, as well as dominant gain-of-function TNNI1 variants as a cause of muscle disease, each with distinct physiological consequences and disease mechanisms. For the loss-of-function scenario, we report three families with biallelic TNNI1 variants (F1: p.R14H/c.190-9G>A, F2 and F3: homozygous p.R14C), manifesting with early onset progressive muscle weakness and rod formation on muscle histology. For the gain-of-function scenario, we report two families with a dominantly acting heterozygous TNNI1 variant (F4: p.R174Q, F5: p.K176del), manifesting with muscle cramping, myalgias, and rod formation in F5. In zebrafish, TnI proteins with either of the missense variants (p.R14H; p.R174Q) incorporate into thin filaments. Molecular dynamics simulations suggest that the loss-of-function p.R14H variant decouples TnI from TnC, which was supported by functional studies showing a reduced force response of sarcomeres to submaximal [Ca2+] in patient’s myofibers. This contractile deficit was reversed by a novel slow skeletal muscle troponin activator. In contrast, patient’s myofibers with the gain-of-function p.R174Q variant showed an increased force to submaximal [Ca2+], which was reversed by the small-molecule drug mavacamten. Our findings demonstrate that TNNI1 variants cause muscle disease with variant-specific pathomechanisms, manifesting as either a hypo- or a hypercontractile phenotype, suggesting rational therapeutic strategies for each mechanism.