RRM1 variants cause a mitochondrial DNA maintenance disorder via impaired de novo nucleotide synthesis

Genetic diseases; Mitochondria; Molecular pathologyEnfermedades genéticas; Mitocondrias; Patología molecularMalalties genètiques; Mitocondris; Patologia molecularMitochondrial DNA (mtDNA) depletion/deletions syndromes (MDDS) encompass a clinically and etiologically heterogenous group of mitochondrial disorders caused by impaired mtDNA maintenance. Among the most frequent causes of MDDS are defects in nucleoside/nucleotide metabolism, which is critical for synthesis and homeostasis of the deoxynucleoside triphosphate (dNTP) substrates of mtDNA replication. A central enzyme for generating dNTPs is ribonucleotide reductase, a critical mediator of de novo nucleotide synthesis composed of catalytic RRM1 subunits in complex with RRM2 or p53R2. Here, we report 5 probands from 4 families who presented with ptosis and ophthalmoplegia as well as other clinical manifestations and multiple mtDNA deletions in muscle. We identified 3 RRM1 loss-of-function variants, including a dominant catalytic site variant (NP_001024.1: p.N427K) and 2 homozygous recessive variants at p.R381, which has evolutionarily conserved interactions with the specificity site. Atomistic molecular dynamics simulations indicate mechanisms by which RRM1 variants affect protein structure. Cultured primary skin fibroblasts of probands manifested mtDNA depletion under cycling conditions, indicating impaired de novo nucleotide synthesis. Fibroblasts also exhibited aberrant nucleoside diphosphate and dNTP pools and mtDNA ribonucleotide incorporation. Our data reveal that primary RRM1 deficiency and, by extension, impaired de novo nucleotide synthesis are causes of MDDS.This work was supported by Department of Defense Focused Program Award W81XWH2010807 (to MH), NIH research grant P01 HD32062 (to MH), and NIH grant 35 GM139453 (to JF). MH is supported by the Arturo Estopinan TK2 Research Fund, Nicholas Nunno Foundation, JDM Fund for Mitochondrial Research, Shuman Mitochondrial Disease Fund, the Marriott Mitochondrial Disease Clinic Research Fund from the J. Willard and Alice S. Marriott Foundation, and NIH grant U54 NS078059. Work in Newcastle upon Tyne was supported by the Wellcome Centre for Mitochondrial Research (203105/Z/16/Z), Medical Research Council International Centre for Genomic Medicine in Neuromuscular Disease (MR/S005021/1), UK NIHR Biomedical Research Centre in Age and Age Related Diseases award to the Newcastle upon Tyne Hospitals NHS Foundation, the Lily Foundation, and the UK National Health Service Highly Specialised Service for Rare Mitochondrial Disorders. RWT receives financial support from the Pathological Society. EWS was funded by a Medical Research Council PhD studentship. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant ACI-1548562. JBGC is supported by grant BIO210070 from XSEDE. The authors thank the patients and their families for collaborating in this study and Saba Tadesse for technical support of mitochondrial respiratory chain enzyme activities. We also thank the Genome Technology Center at the Radboud University Medical Center and BGI Copenhagen for WES technical support

An NF-κB - EphrinA5-Dependent Communication between NG2+ Interstitial Cells and Myoblasts Promotes Muscle Growth in Neonates

SummarySkeletal muscle growth immediately following birth is critical for proper body posture and locomotion. However, compared with embryogenesis and adulthood, the processes regulating the maturation of neonatal muscles is considerably less clear. Studies in the 1960s predicted that neonatal muscle growth results from nuclear accretion of myoblasts preferentially at the tips of myofibers. Remarkably, little information has been added since then to resolve how myoblasts migrate to the ends of fibers. Here, we provide insight into this process by revealing a unique NF-κB-dependent communication between NG2+ interstitial cells and myoblasts. NF-κB in NG2+ cells promotes myoblast migration to the tips of myofibers through cell-cell contact. This occurs through expression of ephrinA5 from NG2+ cells, which we further deduce is an NF-κB target gene. Together, these results suggest that NF-κB plays an important role in the development of newborn muscles to ensure proper myoblast migration for fiber growth

Extensive arterial and venous thrombo-embolism with chemotherapy for testicular cancer: a case report

Germ cell tumours tend to affect young adults and with advanced treatments achieve more than 90% cure rates. Over the years cisplatin has significantly improved the relapse free survival in these patients, hence forming an essential component of chemotherapy regimes. But, the thrombo-embolic complications suffered with cisplatin significantly affect the quality of life in these young patients

Nf-κb Inhibition Rescues Cardiac Function By Remodeling Calcium Genes In A Duchenne Muscular Dystrophy Model

Duchenne muscular dystrophy (DMD) is a neuromuscular disorder causing progressive muscle degeneration. Although cardiomyopathy is a leading mortality cause in DMD patients, the mechanisms underlying heart failure are not well understood. Previously, we showed that NF-κB exacerbates DMD skeletal muscle pathology by promoting inflammation and impairing new muscle growth. Here, we show that NF-κB is activated in murine dystrophic (mdx) hearts, and that cardiomyocyte ablation of NF-κB rescues cardiac function. This physiological improvement is associated with a signature of upregulated calcium genes, coinciding with global enrichment of permissive H3K27 acetylation chromatin marks and depletion of the transcriptional repressors CCCTC-binding factor, SIN3 transcription regulator family member A, and histone deacetylase 1. In this respect, in DMD hearts, NF-κB acts differently from its established role as a transcriptional activator, instead promoting global changes in the chromatin landscape to regulate calcium genes and cardiac function