Clinical Cell Biology Organelles in Health and Disease

Transcription

1 Department of Ophthalmology University of Kiel, University Medical Center Director: Prof. Dr. Johann Roider Clinical Cell Biology Organelles in Health and Disease Prof. Dr. Alexa Klettner

2 Clinical cell biology - Cell organelles Learning goal: Basic anatomy, function and diseases of the different organelles (nucleus, peroxisomes, mitochondria, lysosomes) Topic 1: Nucleus - structure (nuclear envelope, lamina, pores) - organization (chromatin, chromosomes) - function (RNA synthesis, ribosome biogenesis, DNA replication) Topic 2: Peroxisomes - structure (membrane, enzymes) - biogenesis (division, budding, protein import) - function (fatty acid ß-oxidation, lipogenesis, reactive oxygen species metabolism) Topic 3: Mitochondria - structure (membranes, cristae, genome, heteroplasmy) - biogenesis (fission/fusion) - function (oxidative phosphorylation, apoptosis) Topic 4: Lyosomes - structure (membrane, hydrolases, ph) - biogenesis (interaction with endosomes and autophagosomes) - function (degradation, phagocytosis, autophagy )

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4 Nucleus: Anatomy - surrounded by two membranes - outer membrane continuous with Endoplasmic reticulum (ER) - perinuclear space = lumen of the rough ER - envelope contains pores

5 Nucleus

6 Nucleus: Function - messenger RNA synthesis and processing - ribosome subunit biogenesis - DNA replication

7 Copyright protected Nucleus

8 Nucleus Lamins - nuclear lamina is composed of nuclear lamins (A, B and C). - lamin A and C are coded in LMNA gene - intermediate filament proteins in the nucleus - form associated filamentous structures - underlie the nuclear envelope - interact with neighboring proteins

9 Nucleus Lamins: Functions - provide nuclear stability - connect the nucleus to the cytoskeleton - modulate chromatin organization and gene expression

10 Nucleus Lamins: Functions/Mutation - decrease nuclear stability - increase nuclear fragility - disturb mechanotransduction signaling - muscle-specific defects in many laminopathies - altered lamin expression reported in many cancers

11 Nucleus - Laminopathies - >500 mutations in LMNA - 4 major disease groups - striated muscle disease - lipodystrophies - peripheral neuropathies - accelerated aging

12 Nucleus - Laminopathies

13 Nucleus - Hutchinson-Gilford Progeria Syndrome Children with HGPS appear normal at birth but fail to thrive shortly thereafter and die in their early teens from myocardial infractions or stroke. Clinical symptoms include - alopecia (hair loss) - beaked nose - sclerodermatous skin - dwarfism - lipodystrophy - osteoporosis - progressive arteriosclerotic disease

14 Nucleus - Hutchinson-Gilford Progeria Syndrome - caused by de novo mutation in LMNA gene C>T, p.g608g in exon 11 of LMNA - mutation activates a cryptic splice site - resulting in a truncated form of prelamin A (progerin) - prelamin A mrna contains an internal deletion of 150 base pairs - Progerin lacks 50 amino acids near its C terminus - remains farnesylated, - stays tightly associated with the inner nuclear membrane Leads to - lobulation of the nuclear envelope - thickening of the nuclear lamina - loss of peripheral heterochromatin - stiffer nuclei

15 Nucleus - Hutchinson-Gilford Progeria Syndrome Structural hypothesis: lamin mutations increase nuclear fragility resulting in cell death and progressive failure in tissues exposed to repetitive mechanical stress. Gene regulation hypothesis: lamin mutations interfere with tissue-specific genes Stem cell hypothesis: lamin mutations impair stem cell function.

16 Nucleus - Hutchinson-Gilford Progeria Syndrome

17 Peroxisomes

18 Peroxisomes Functions Quelle

19 Peroxisomes Biogenesis

20 Peroxisomes Peroxins (PEX) Regulators of peroxisome biogenesis Pex3, Pex16, and Pex19 are critical for assembly of peroxisomal membrane and import of peroxisomal membrane proteins - Pex19 is a soluble chaperone, imports receptor for newly synthesized peroxisomal membrane proteins - Pex3 functions as a docking receptor for Pex19 - Pex16 acts as a docking site for recruitment of Pex3 Peroxisomal targeting sequences (PTSs) allowing proteins to be shuttled into peroxisomes - Pex5 is an import receptor for PTS1-containing peroxisomal matrix proteins - Pex7 in an import receptor for PTS2-containing peroxisomal matrix proteins

21 Peroxisomes Disease Impairment of one or more peroxisomal functions result in peroxisomal disorders - peroxisome biogenesis disorder - single peroxisomal (enzyme-)protein deficiency - single peroxisomal substrate transport deficiencies.

22 Peroxisomes Zellweger Spectrum diseases (biogenesis disorder) Mutation in PEX genes -> Peroxisomes either absent or empty (ghosts) - Zellweger syndrome - neonatal adrenoleukodystrophy - infantile refsum disease - (rhizomelic chondrodysplasia punctate)

23 Peroxisomes Zellweger Spectrum diseases

24 Peroxisomes Zellweger Syndrome Infants usually do not survive their first year due to respiratory compromise, gastrointestinal bleeding, and liver failure. Symptoms: - malfunction of the cortex (neuronal migration defects) - severe degeneration of the white matter involving both hemispheres of cerebrum and cerebellum - craniofacial dysmorphism - hypotonia - seizures - failure to thrive - hepatomegaly - psychomotor retardation - sensory deafness - absent reflexes - visual loss with retinopathy and extinguished electroretinograms

25 Peroxisomes Zellweger Syndrome The brain pathology in peroxisomal disorders can be grouped into three major classes i) abnormalities in neuronal migration or differentiation ii) defects in the formation or maintenance of central white matter iii) post-developmental neuronal degeneration.

26 Peroxisomes Zellweger Spectrum disease Severe neurological deficits: Peroxisomes - generate building blocks for the synthesis of myelin - exert the last step in the biosynthesis of docosahexaenoic acid, DHA, (important for the nervous system) - degrade toxic compounds that can either interfere with proper brain formation or damage brain structures. - degrade D-amino acids such as D-aspartate and D-serine, which modulate synaptic signaling by altering the efficiency of synaptic transmission.

27 Mitochondria

28 Mitochondria: Genome - circular mitochondrial genome (mtdna) - consists of only 16,569 base pairs - is present in multiple copies in all cells - MtDNA encodes only 37 gene products - 13 poly-peptides that are structural OXPHOS subunits plus - 22 transfer RNAs (trna) and two ribosomal RNAs (rrna) required for their synthesis. (The remaining mitochondrial proteins are nuclear encoded, synthesized in the cytosol and importated into the mitochondria. )

29 Mitochondria: Heteroplasmy - A mixture of wild-type and mutated mtdna within one cell. At a cellular level, the percentage level of heteroplasmy determines whether there is a biochemical defect affecting oxidative phosphorylation and ATP synthesis

30 Mitochondria: Apoptosis

31 Copyright protected Mitochondria: oxidative Phosphorylation (OXPHOS)

32 Mitochondria: oxidative Phosphorylation (OXPHOS)

33 Mitochondria - Disease - genetic human disorders leading to a primary defect in mitochondria oxidative phosphorylation (OXPHOS)

34 Mitochondria - Disease - marked variation in clinical features in patients, involving several different organs and leading to multisystem presentations - mitochondrial disease affect mostly muscle and neuronal tissue

35 Mitochondria OXPHOS diseases

36 Mitochondria OXPHOS diseases

37 Mitochondria Leigh Syndrome - progressive neurodegenerative disorder - most patients present between 3 and 12 month of age (adult onset is possible) - disease course: rapid deterioration of cognitive and motor function - death mostly due to respiratory failure - high genetic heterogeneity (>75 mutations found)

38 Mitochondria Leigh Syndrome Criteria for diagnosis: - clinical evidence of brainstem and/or basal ganglia dysfunction - intellectual and motor developmental delay - abnormal energy metabolism indicated by - a severe defect in oxidative phosphorylation or pyruvate dehydrogenase activity or - a molecular diagnosis in a gene related to mitochondria energy generation or - elevated serum or CSF lactate

39 Mitochondria Leigh Syndrome

40 Mitochondria Leigh Syndrome Complex I and IV mutations the most common causes for Leigh syndrom

41 Lysosomes - Filled with more than 60 different hydrolases (lipases, proteases, glycosidases) for catabolic degradation - Monitor intracellular energy and nutrient status - Enters cycles of fusion and fission with late endosomes and autophagosomes for digestion of substrates - Abnormal accumulation of lysosomal material causes >50 rare, inherited metabolic disorders (lysosomal storage disorders, LSD) - Most LSDs are caused by mutations in hydrolases

42 Lysosomes - Function

43 Lysosomes - Lysosomal storage disease

44 Lysosomes - Lysosomal storage disease

45 Lysosomes - Lysosomal storage disease

46 Lysosomes - Gaucher - Autosomal recessive LSD - caused by a genetic deficient activity of the lysosomal enzyme glucocerebrosidase (GBA1 gene) - accumulation of glucocerebroside in lysosomes of tissue macrophages primarily in the liver, bone marrow and spleen - Symptoms involve hepatosplenomegaly, thrombocytopenia, skeletal deformations and bone fractures - three types

47 Lysosomes - Gaucher 95% of all cases

48 Lysosomes - Gaucher - Potential Pathological pathway: Macrophage activation

49 Lysosomes - Gaucher - Treatment option - Enzyme replacement therapy (ERT) - Substrate reduction therapy (SRT) - Pharmacological chaperones

50 Fatty acids/cholesterol: Metabolism Atherosclerosis Learning goals: 1) Types of lipids (classes, structure, ), Function of lipids (give examples), 2) Synthesis of lipids (fatty acids), degradation of lipids (beta oxidation, ketogenisis) 3) Function, Synthesis and elemination of steroids (e.g. cholesterol) 4) Lipid transport (lipoproteins) and storage, glycolipid storage disorders