Membrane and extracellular matrix diseases

An overview on Membrane and extracellular matrix diseases; cystic fibrosis, achondroplasia, marfan syndrome, spherocytosis, ehlers-danlos syndrome

1. Membrane and extracellular matrix diseases Dr Joyce MWATONOKA Mmed PCH Januar y 2019

2. Cell membrane Membranes are complex structures composed of lipids, carbohydrates, and proteins The basic structure of all membranes is the lipid bilayer Proteins in membranes can be classified as receptors , transporters , ion channels , enzymes , and structural components

3. Cont…

4. Biomedical importance of membranes Separate one cell from another and thus permit cellular individuality Has selective permeabilities (provided mainly by channels and pumps for ions and substrates) and acts as a barrier Plasma membrane plays key roles in cell-cell interactions and in transmembrane signaling Membranes also form specialized compartments (organelles) within the cell

5. Cont… Function as integral elements in excitation-response coupling Provide sites of energy transduction , such as in photosynthesis and oxidative phosphorylation Normal cellular function depends on normal membranes. Specific deficiencies or alterations of certain membrane components lead to a variety of diseases

6. Membrane diseases Members of all of these classes are often glycosylated , so that mutations affecting this process may alter their function These disorders mainly reflect mutations in proteins of the plasma membrane, with one affecting lysosomal function (Inclusion-Cell (I-Cell) Disease/ Mucolipidosis Type II)

7. Cont… Membrane proteins can also be affected by conditions other than mutations such as formation of auto antibodies to acetylcholine receptor in skeletal muscles causes myasthenia gravis Ischemia can quickly affect the integrity of various ion channels in membranes. Abnormalities of membrane constituents other than proteins can also be harmful

8. Cont… Mutations in genes encoding proteins in other membranes can also have harmful consequences. Eg , mutations in genes encoding mitochondrial membrane proteins involved in oxidative phosphorylation can cause neurologic and other problems ( eg , Leber’s hereditary optic neuropathy; LHON – loss of central vision)

9. Some diseases of the membranes Cystic fibrosis Red cell membrane defects Achondroplasia Congenital long QT syndrome Wilson disease I-cell disease Leber’s hereditary optic neuropathy

10. Cystic fibrosis It is a recessive genetic disorder that involves multiple organ systems but chiefly results in chronic respiratory infections , pancreatic enzyme insufficiency , and associated complications End-stage lung disease is the principal cause of death Caused by mutation on chromosome 7 , encoding a protein of 1480 amino acids, named cystic fibrosis trans-membrane regulator (CFTR) which is a cyclic AMP-regulated Cl − channel

11. Cont… The commonest mutation (~70%) is deletion of three bases, resulting in loss of residue 508, a phenylalanine. Leading to defective protein maturation and early degradation However, more than 900 other mutations have been identified Incidence 1:3,400 in causians

12. Cont… These mutations affect CFTR in at least four ways: 1) Its amount is reduced 2) It may be susceptible to misfolding and retention within the ER or Golgi apparatus 3) Mutations in the nucleotide-binding domains may affect the ability of the Cl − channel to open, an event affected by ATP 4) The mutations may also reduce the rate of ion flow through a channel, generating less of a Cl − current

13. Pathophysiology Defective CFTR results in decreased secretion of chloride and increased reabsorption of sodium and water across epithelial cells Resulting in reduced epithelial lining fluid and decreased hydration of mucus making mucus that is stickier to bacteria, which promotes infection and inflammation Secretions in the respiratory tract, pancreas, GI tract, sweat glands, and other exocrine tissues have increased viscosity, which makes them difficult to clear

14. Cont…

15. Clinical features

16. Diagnosis of CF Requirements for dx include either positive genetic testing or positive sweat chloride test >60 mmol /L and 1 of the following: Typical COPD Documented exocrine pancreatic insufficiency Positive family history (usually an affected sibling)

17. Management No definitive treatment Maintaining lung function by controlling respiratory infection and clearing airways of mucus ( abx ,  mucolytics eg ; acetylcistein , expectorants eg;hypertonic saline, inhaled bronchodilators, chest physical therapy and postural drainage) Nutritional therapy ( ie , enzyme supplements, multivitamin) to maintain adequate growth Gene therapy to restore the activity of CFTR

18. Postural drainage

19. Postural drainage

20. Red cell membrane defect Hereditary spherocytosis Hereditary elliptocytosis Hereditary stomatocytosis Pyropoikilocytosis . In each abnormalities of the red cell membrane result in hemolysis

21. Hereditary spherocytosis (HS) HS is an AD familial hemolytic disorder associated with a variety of mutations that lead to defects in RBC membrane proteins It is the most common inherited abnormality of the red blood cell membranes The morphologic hallmark of HS is the microspherocyte , which is caused by loss of RBC membrane surface area and has abnormal osmotic fragility in vitro Incidence 1:5000

22.  Abnormalities in RBC membrane proteins in HS Spectrin deficiency alone Combined spectrin and ankyrin deficiency Band 3 deficiency Protein 4.2 defects Spectrin ; a cytoskeletal protein Ankyrin ; linker proteins between the spectrin-actin based cytoskeleton and integral membrane proteins

23. Cont… Spectrin is made up of alpha-beta dimers Mutations of alpha - spectrin are associated with recessive forms of HS, whereas mutations of beta - spectrin occur in autosomal dominant forms of HS Translocation of xsome 8 or deletion of the short arm of xsome 8, where ankyrin gene is located 75-80% of patients with autosomal dominant HS have combined spectrin and ankyrin deficiency

24. Cont… Clinical features Signs of anemia Jaundice Splenomegally Diagnosis Family hx Peripheral blood smear; Spherocytes and reticulocytes FBC; - Mild to moderate anemia - Reticulocytosis -Increased mean corpuscular hemoglobin concentration (MCHC) Hyperbilirubinemia

25. Management Splenectomy is the standard treatment for patients with clinically severe HS Improves RBCs survival

26. Achondroplasia Is an AD genetic disorder caused by mutations in the gene encoding the fibroblast growth factor receptor 3 (FGFR3), making the resulting protein overactive FGFR3 is a negative regulator of bone growth Achondroplasia is the most common form of short-limb dwarfism and is characterized by disproportionate shortness of limbs and relative macrocephaly

27. Cont… 97% of achondroplasia is caused by a single point mutation in the gene encoding FGFR3, in which a glycine is substituted with an arginine residue at position 380 of the FGFR3 a.a sequence Upon ligand binding, the mutation decreases the elimination of the receptor/ ligand complex resulting in prolonged intracellular signaling Over-activity of FGFR3 inhibits chondrocyte proliferation and restricts long bone length

28. Cont… Failure of a echondrial bone ossification (long bones) Intramembranous ossification; normal Thus, achondroplastic dwarfs with normal trunk size, but small arms and legs Macrocephaly with prominent forehead and flattened nasal bridge Kyphosis

29. Management Currently no prevention or treatment Somatotropin (recombinant human growth hormone); augment height, but does not substantially affect the height of an individual with achondroplasia

30. Cont…

31. THE EXTRACELLULAR MATRIX Most mammalian cells are located in tissues where they are surrounded by a complex extracellular matrix (ECM) often referred to as “connective tissue” The ECM contains three major classes of biomolecules :

32. Cont… 1 )The structural proteins ; a) Collagen ; major component, 25% of proteins. All collagen types have a triple helical structure. Provides an extracellular framework. At least 28 distinct types of collagen made up of 30 distinct polypeptide chains (each encoded by a separate gene) have been identified in human tissues Collagen form long rodlike fibers assembled by lateral association of these triple helical units into fibrils

33. Cont…

34. Cont… Collagen biosynthesis is complex, involving at least eight enzyme-catalyzed posttranslational steps b) Elastin ; a major protein component of tissues that require elasticity such as arteries, lungs, bladder, skin and elastic ligaments and cartilage. Allows tissues in the body to resume their shape after stretching or contracting

35. Cont… c) Fibrillin ; large glycoprotein secreted by fibroblast. Found commonly in zonular fibers of the lens, periostium , arterial walls. Major structural component of microfibrils (fine fiber-like strands which provide a scaffold for the deposition of elastin in the ECM) Fibrillin 1 ; major component of microfibril Fibrillin 2 ; have a role in early elastogenesis Fibrillin 3 ; mainly located in the brain Fibrillin 4 ; structure is similar to fibrillin 2

36. Cont… 2 ) Certain specialized proteins such as fibronectin , and laminin (adhesive glycoproteins to attach cells to matrix) 3 ) Proteoglycans ( mucoproteins ); protein-polysaccharide complexes. Combine with collagen to form cartilage

37. Cont… The ECM is involved in many normal and pathologic processes eg , it plays important roles in development, in inflammatory states, and in the spread of cancer cells Several diseases ( eg , osteogenesis imperfecta and a number of types of the Ehlers- Danlos syndrome) are due to genetic disturbances of the synthesis of collagen

38. Ehlers- Danlos syndrome Comprises a group of inherited disorders whose principal clinical features are Hyper-extensibility of the skin Abnormal tissue fragility Increased joint mobility The clinical picture is variable, reflecting underlying extensive genetic heterogeneity

39. Cont… At least 10 types have been recognized, most but not all of which reflect a variety of lesions in the synthesis of collagen Type I ; Classic EDS (COL5A1/2 gene mutation) Type IV is the most serious because of its tendency for spontaneous rupture of arteries or the bowel, reflecting abnormalities in type III collagen (mutations in the  COL3A1  gene) Patients with type VI , due to a deficiency of lysyl hydroxylase , exhibit marked joint hypermobility and a tendency to ocular rupture

40. Types of EDS

41. Cont…

42. Management ; No cure Physical therapy; to strengthen the muscles and stabilize joints Braces to prevent joint dislocation

43. Osteogenesis imperfecta Brittle-bone disease/ Blue-sclera syndrome Incidence 1:20,000 A hereditary disease (AD) caused in 80% of cases by a mutation of 1 or 2 genes (COL1A1 gene on chromosome 17 encodes the pro-alpha 1  chain, and COL1A2 gene on chromosome 2 encodes the pro-alpha 2 chain) Pathologic changes are seen in all tissues of which type 1 collagen is an important constituent ( eg , bone, ligament, dentin, and sclera)

44. Cont… In OI due to quantitative defects of type 1 collagen, the mutations result in the production of a premature stop codon or a microsense frame shift, which leads to production of reduced amounts of structurally normal collagen Qualitative defects, substitution of a larger amino acid ( eg , cysteine or alanine ) for glycine results in abnormal helix formation, but these chains can combine with normal chains to produce type 1 collagen which is functionally impaired because of the mutant chain

45. Cont…

46. Cont…

47. Management No cure Supportive; surgery if it is likely to improve function eg ; intramedullary rod placement, correction of scoliosis Orthotics Bisphosphonates ( eg , pamidronate ) inhibit osteoclast -mediated bone resorption on the endosteal surface of bone. As a result unopposed osteoblastic new bone formation on the periosteal surface, increase in cortical thickness

48. Marfan syndrome Disorder caused by mutations in the FBN1 gene that encodes fibrillin , a glycoprotein of the fibrous connective tissue Inherited as an AD trait; incidence 1:98,000 Most cases are caused by missense mutations in the gene (on chromosome 15) for fibrillin 1 Fibrillin is found in the zonular fibers of the lens, in the periosteum , and associated with elastin fibers in the aorta (and elsewhere)

49. Pathophysiology in Marfan Syndrome

50. Clinical features It affects the eyes eg , causing dislocation of the lens ( ectopia lentis ), cataracts, retinal detachment The skeletal system ; most patients are tall and exhibit long digits ( arachnodactyly ), thoracolumbar scoliosis, pectus deformities, and hyperextensibility of the joints The cardiovascular system ( eg , causing weakness of the aortic media, leading to aortic dilatation and dissection)

51. Cont…

52. Diagnostic criteria for Marfan Syndrome

53. Management B-blockers reduces rate of aortic dilatation CCB??? As prophylaxis against aortic aneurism progression (limited evidence) Surgical interventions (Prophylactic aortic root surgery) Life expectancy depends on severity of cardiovascular involvement

54. Scurvy Scurvy affects the structure of collagen. However, it is due to a deficiency of ascorbic acid (vitamin C) and is not a genetic disease Its major signs are bleeding gums, subcutaneous hemorrhages, and poor wound healing These signs reflect defective synthesis of collagen due to reduced activity of the enzymes prolyl and lysyl hydroxylases , both of which require ascorbic acid as a cofactor and are involved in posttranslational modifications which give collagen molecules rigidity

55. Other diseases of ECM Epidemolysis bullos (mutation in keratin gene) Cutis laxas ( elastolysis ) Alport syndrome Williams syndrome

56. Thank you for your attention!!!