Muscular dystrophies, clinical features Muscular dystrophies WHAT HAPPENS WHEN YOU HAVE NO MUSCLES
•Genetic disorders •Heterogeneous •Primarily affect the musculature •Tend to affect the connection between the sarcomeric structure and the basement membrane, surrounding the muscle cells
Increased endomysial connective tissue Variable fiber size Centrally located nuclei Infiltration Hypercontracted muscle fibers
Transmembrane receptors in skeletal muscle Dystrophin deficiency/Duchenne muscular dystrophy Which genes are involved??
• Mutations in more than 100 genes are likely to result BASEMENT MEMBRANE • The most common form of muscular dystrophy in human. in myopathies •~40 genes have so far been identified • About 1 in 3000 boys is affected by the disease. MUSCULAR DYSTROPHIES:
2J LAMININ-α2 CMD (dy/dy; dy) • Mutations are inherited or occur spontaneously due to the large size of the gene. •Transmembrane proteins α-SARCOGLYCANSARCOGLYCANα ARMD, LGMD2D α-DYSTROGLYCAN α DYSTROGLYCAN •Extracellular matrix proteins α β SARCOGLYCANβ ARMD, LGMD2E •Membrane-associated proteins α • The phenotype ranges from mild to severe. ββ-DYSTROGLYCANDYSTROGLYCAN α -SARCOGLYCANγ SARCOGLYCANγ ARMD, LGMD2C •Cytoplasmic proteases β β •Cytoplasmic proteins associated with sarcomeres γ Mild form (Becker muscular dystrophy) small in frame deletions •Protein modifying enzymes C the function of the protein is partially maintained. •Nuclear membrane proteins DYSTROPHIN DMD, BMD (mdx) Severe form (Duchenne muscular dystrophy) complete absence N of the protein. Death post-puberty.
ACTIN FILAMENT • The corresponding mouse model mdx, lacking dystrophin, develops histologically a muscular dystrophy but has a modified according to : Campbell, 1995; Worton, 1995 normal life span
1 Integrins The Integrin Super-Family
primary myogenesis secondary myogenesis adult
myoblasts MTJ MTJ
α5 α5 α6 α6 α7 β1D αv α7 α7 αv β 1A α4 β1D αv α4 α3 NMJ
α7β1 INTEGRIN
- specific laminin receptor
- two extracellular (X1, X2) two intracellular splice variants (A, B)
- associates with β1D in skeletal and cardiac muscle
- mainly expressed in skeletal and cardiac muscle but also found in smooth muscle, neurons, melanocytes
- deficiency of the α7 subunit leads to a muscular dystrophy in human and mice Tendon Tendon
myofilaments myofilaments
sarcolemma basement membrane
2 Transmembrane receptors in skeletal muscle Myotendinous junctions phenotype in integrin α7 null mice
BASEMENT MEMBRANE
WT MUSCULAR DYSTROPHIES:
2J LAMININ-α2 CMD (dy/dy; dy)
α-SARCOGLYCANSARCOGLYCANα ARMD, LGMD2D MUSCULAR α-DYSTROGLYCAN DYSTROPHIES: α DYSTROGLYCAN α β SARCOGLYCANβ ARMD, LGMD2E A7-/- α MD INTEGRIN α7β1 ββ-DYSTROGLYCANDYSTROGLYCAN α -SARCOGLYCANγ SARCOGLYCANγ ARMD, LGMD2C β β γ C
DYSTROPHIN DMD, BMD (mdx) N Tendon Tendon
ACTIN FILAMENT
myofilaments modified according to : Campbell, 1995; Worton, 1995
Mdx phenotype A7-/- phenotype Transmembrane receptors in skeletal muscle
BASEMENT MEMBRANE Integrin α7-/- mice
A7-/- MTJ stability A7-/-
α-DYSTROGLYCAN α DYSTROGLYCAN α x α INTEGRIN α7β1 ββ-DYSTROGLYCANDYSTROGLYCAN α β β WT γ WT C mdx mice N (dystrophin-deficient) WT A7-/- lateral ACTIN FILAMENT stability mdx mdx modified according to : Campbell, 1995; Worton, 1995
3 WT α7-/- mdx mdx/α7-/- Integrin α7/mdx double-mutant mice gain less weight than controls Tibialis anterior 14 A7+/+; mdx, female, n=1 A7+/-; mdx; female, n=1 A7+/-; mdx; male, n=4 A7-/-; mdx; female, n=1 12 Flexor hallicus 10 longus
8
Extensor 6 digitorum (g) weight Longus 4 (EDL)
2
Peroneus 0 0 5 10 15 20 25 age (days)
The number of fibers with The number of muscle fibers is reduced centrally located nuclei is low
WTmdx mdx/α7-/- WT mdx mdx/α7-/-
P10
P20 Central nucleiCentral (%) Number of muscle fibers
EDLPlantaris EDL Plantaris EDLPlantaris EDL Plantaris P10 P20 EDL Plantaris P10 P20
4 Satellite cell activation and function Satellite cell activation and renewal is Apoptosisisnotprominent impaired in integrin α7/mdx double-mutant mice
TUNEL + Lm α2 TUNEL + MHCdev H&E
DGC-/-
DKO
mdx
adapted from Hawke and Garry, 2001 adapted from Hawke and Garry, 2001
Satellite cell activation and renewal is impaired in integrin α7/mdx double-mutant mice WT α7-/- mdx mdx/α7-/- The laminin α2 chain is unaltered in double-mutant mice
Dystrophin WT α7-/- mdx mdx/α7-/- DGC-/-/α7-/-
Integrin α7 Laminin α2
Utrophin Laminin α4
α-Dystroglycan
adapted from Hawke and Garry, 2001
5 Transmembrane receptors in integrin α7/mdx Transmembrane receptors in skeletal muscle double-mutant mice
The phenotype of Integrin α7/mdx double-mutant mice closely resembles BASEMENT MEMBRANE BASEMENT MEMBRANE Duchenne muscular dystrophy
α α DYSTROGLYCAN α DYSTROGLYCAN α α Could integrin α7 be a therapeutic target for DMD? α α INTEGRIN α7β1 ββ-DYSTROGLYCANDYSTROGLYCAN α α β β β β γ γ C C
N N UTROPHIN ACTIN FILAMENT
ACTIN FILAMENT
modified according to : Campbell, 1995; Worton, 1995
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