Defects in the cytochromebc 1 complex in mitochondrial diseases

The clinical and biochemical findings of 14 patients with an isolated defect of thebc ₁ complex have been summarized. The heterogeneity of this group of disorders reflects the severity and tissue specific expression of the defect and the complexity of this multisubunit protein with components that are coded on both nuclear and mitochondrial DNA. The data on several patients with a combined defect of cytochrome oxidase and thebc ₁ complex or with multiple respiratory chain defects have also been presented and discussed in relation to our knowledge of the biosynthesis and assembly of the respiratory chain complexes. The severity of the defectin vivo is illustrated in one patient with isolated complex III deficiency by measurement of O₂ consumption and CO₂ production following exercise, or by³¹P-NMR. The latter also provides a means by which response to therapy can be followed.     

“Gearing” up for dynamin-catalyzed membrane fission

Endocytic dynamins self-assemble into helical scaffolds and utilize energy from GTP hydrolysis to constrict and sever tubular membranous necks of budded endocytic intermediates. They bind the membrane using a pleckstrin-homology domain (PHD). The PHD is characterized by four unstructured loops, two of which partially insert into the membrane. Recent studies reveal that loop insertion lowers the bending rigidity of the membrane and that mutations in these two loops produce separable and opposite effects on the efficiency of dynamin-catalyzed membrane fission. Here, we review the current understanding of dynamin-catalyzed membrane fission and attempt to reconcile contrasting notions that have emerged from biochemical and cellular studies evaluating the role of the PHD in this process. We propose that two membrane-inserting loops act as “gears” that define the catalytic efficiency of the dynamin helical scaffold in membrane fission.     

Rewiring of Glutamine Metabolism Is a Bioenergetic Adaptation of Human Cells with Mitochondrial DNA Mutations

1. Download high-res image (150KB)
2. Download full-size image

     

Chemical,biochemical, preclinical and clinical studies of Ganoderma lucidum polysaccharide as an approved drug for treating myopathy and other diseases in China

Ganoderma lucidum is an edible medicinal mushroom known as “Lingzhi” in China and “Reishi or Manetake” in Japan. It is a highly prized vitality‐enhancing herb for more than 2000 years. G. lucidum polysaccharide (GLPS) has been identified as one of the major bioactive components and developed into a drug named “Ji 731 Injection” in China since 1973. The large‐scale production of the drug began in 1985 and approved by the Chinese FDA as “Polysaccharidum of G. lucidum Karst Injection” (Ling Bao Duo Tang Zhu She Ye) in 2000, which is applied intramuscularly. After more than forty years of clinical use, its efficacy, safety and long‐term tolerability have been recognized by neurologists. It is one of a few non‐hormonal drugs used for treating refractory myopathy. It is also used for combination therapy, which reduces the amount of glucocorticoid required for myopathy patient who is in remission. In addition, it reduces adverse reactions and improves the quality of life for cancer patients during chemotherapy. We found 81 qualified chemical, biochemical, preclinical and clinical studies of GLPS both in English and in Chinese spanning from 1973 to 2017 by searching CNKI (China National Knowledge Infrastructure), Wanfang database and PubMed. The molecular mechanisms underlying GLPS's antioxidant, anti‐tumour, immune‐modulatory, hypoglycaemic, hypolipidaemic and other activities are discussed. Both preclinical and clinical studies are either deliberated or indexed in the current article. We aimed at providing a molecular picture as well as a clinical basis to comprehend GLPS as one of few polysaccharide‐based modern medicines with complicated chemical and pharmacological properties that prevent it from entering the world's market.     

Functional Diagnostics in Mitochondrial Diseases

Mitochondrial diseases (MD) with respiratory chain defects are caused by genetic mutations that determine an impairment of the electron transport chain functioning. Diagnosis often requires a complex approach with measurements of serum lactate, magnetic resonance spectroscopy (MRS), muscle histology and ultrastructure, enzymology, genetic analysis, and exercise testing. The ubiquitous distribution of the mitochondria in the human body explains the multiple organ involvement. Exercise intolerance is a common symptom of MD, due to increased dependence of skeletal muscle on anaerobic metabolism, with an excess lactate generation, phosphocreatine depletion, enhanced free radical production, reduced oxygen extraction and electron flux through the respiratory chain. MD treatment has included antioxidants (vitamin E, alpha lipoic acid), coenzyme Q10, riboflavin, creatine monohydrate, dichloroacetate and exercise training. Exercise is a particularly important tool in diagnosis as well as in the management of these diseases.     

Characterization of Two Human Skeletal Calsequestrin Mutants Implicated in Malignant Hyperthermia and Vacuolar Aggregate Myopathy

Calsequestrin 1 is the principal Ca²⁺ storage protein of the sarcoplasmic reticulum of skeletal muscle. Its inheritable D244G mutation causes a myopathy with vacuolar aggregates, whereas its M87T “variant” is weakly associated with malignant hyperthermia. We characterized the consequences of these mutations with studies of the human proteins in vitro. Equilibrium dialysis and turbidity measurements showed that D244G and, to a lesser extent, M87T partially lose Ca²⁺ binding exhibited by wild type calsequestrin 1 at high Ca²⁺ concentrations. D244G aggregates abruptly and abnormally, a property that fully explains the protein inclusions that characterize its phenotype. D244G crystallized in low Ca²⁺ concentrations lacks two Ca²⁺ ions normally present in wild type that weakens the hydrophobic core of Domain II. D244G crystallized in high Ca²⁺ concentrations regains its missing ions and Domain II order but shows a novel dimeric interaction. The M87T mutation causes a major shift of the α-helix bearing the mutated residue, significantly weakening the back-to-back interface essential for tetramerization. D244G exhibited the more severe structural and biophysical property changes, which matches the different pathophysiological impacts of these mutations.     

组织蛋白酶D的功能多样性

组织蛋白酶D（cathepsin D,CTSD）是真核细胞溶酶体中天冬氨酸蛋白酶家族的主要成员,具有非常独特的合成和转运方式.CTSD由粗面内质网合成,通过多种蛋白质水解途径最终抵达细胞内的小泡结构（溶酶体、核内体、吞噬体）,从而发挥其生物学功能.早期认为,CTSD在溶酶体中只参与蛋白质的水解作用.近年研究发现,CTSD在多种生理（细胞增殖、细胞凋亡、细胞衰老和组织内稳态）和病理（阿尔茨海默病、动脉粥样硬化、先天性肌肉萎缩和癌症）条件中均发挥重要作用,并因其生物学功能的多样性而受到广泛关注.本文将着重对CTSD的生物合成与激活、生物学功能及临床应用进行综述,以期为疾病的诊断与治疗、药物的研发与筛选提供前沿的理论依据,为人类健康带来新的希望.     

Clinicopathological‐genetic features of congenital myasthenic syndrome from a Chinese neuromuscular centre

Congenital myasthenic syndrome (CMS) encompasses a heterogeneous group of inherited disorders affecting nerve transmission across the neuromuscular junction. The aim of this study was to characterize the clinical, physiological, pathohistological and genetic features of nine unrelated Chinese patients with CMS from a single neuromuscular centre. A total of nine patients aged from neonates to 34 years were enrolled who exhibited initial symptoms. Physical examinations revealed that all patients exhibited muscle weakness. Muscle biopsies demonstrated multiple myopathological changes, including increased fibre size variation, myofibrillar network disarray, necrosis, myofiber grouping, regeneration, fibre atrophy and angular fibres. Genetic testing revealed six different mutated genes, including AGRN (2/9), CHRNE (1/9), GFPT1 (1/9), GMPPB (1/9), PLEC (3/9) and SCN4A (1/9). In addition, patients exhibited differential responses to pharmacological treatment. Prompt utilization of genetic testing will identify novel variants and expand our understanding of the phenotype of this rare syndrome. Our findings contribute to the clinical, pathohistological and genetic spectrum of congenital myasthenic syndrome in China.     

Biochemical and ultrastructural features of human fibroblasts cultured from a new variant of type 3 lipid storage myopathy

A new variant of multisystemic lipid storage myopathy (type 3) has been identified. Human cultured fibroblasts present a major triacylglycerol storage whereas other neutral lipids and phospholipids are in the normal range. When feeding the cells in the presence of radiolabelled oleic acid we observed an accumulation of radiolabelled triacylglycerols demonstrating the endogenous biosynthesis of the stored triacylglycerols. After a 72-hr chase period, no degradation of radiolabelled triacylglycerols was observed. Histochemical examination of multisystemic lipid storage myopathy skin fibroblasts showed a massive accumulation of neutral lipids (stained by the fluorescent probe Nile Red) in cells grown in medium supplemented with 10% fetal calf serum. These cytoplasmic vacuoles were not obviously membrane-surrounded as shown by electron microscopy.