Supplementary Table S1: Major constituents of the extracellular matrix and associated components of the sarcolemma, cytoskeleton and
the contractile apparatus and their potential roles in the molecular pathogenesis of muscular dystrophy
Abbreviations: AChE, acetylcholinesterase; COL, collagen; ECM, extracellular matrix; FN, fibronectin; MMP, matrix metalloproteinase; DG,
dystroglycan; Dp, dystrophin protein; LAM, laminin; MAP, microtubule-associated protein; MARP, muscle ankyrin repeat protein; MBP,
myosin binding protein; MMP, matrix metalloproteinase; nAChR, nicotinic acetylcholine receptor, NMJ, neuromuscular junction; PRELP,
proline-arginine-rich end leucine-rich repeat protein; SG, sarcoglycan; SLRP, small leucine-rich repeat proteoglycan; TIMP, tissue inhibitor of
MMP; Tn, troponin, TM, tropomyosin
Protein constituents
Subcellular
Biological functions and potential pathophysiological role
localization
Collagen I, Collagen III and
Interstitial
Collagens represent the most abundant structural proteins in contractile tissues. The
Collagen V (plus other minor
ECM
fibrillar structure of the ECM has a critical function in muscle tissue stabilization, the
types of collagens that are mostly
maintenance of elasticity, the embedding of capillaries and nerves, and the mechanical
expressed during myogenesis:
transduction of force from contractile fibres to their anchoring tissue. COL I is the
COL XI, XII, XIV, XV and
primary collagen in the perimysium and tendon and its levels are increased in dystrophic
XVIII)
muscles.
Collagen VI
ECM
Major structural constituent forming microfibrils that provide structural support during
microfibrils
excitation-contraction-relaxation cycles; COL VI levels are increased during muscular
dystrophy-related fibrosis
Collagen IV (with minor
Basal lamina
Major non-fibrillar collagen isoform of the muscle basement membrane that directly
constituents COL VI, XV and
surrounds muscle fibres and interacts with the laminin-dystroglycan-dystrophin axis and
XVIII)
the fibronectin-integrin axis; COL IV is affected in muscular dystrophy-related fibrosis
Fibronectin
Basal lamina
Glycoprotein of the ECM that connects laminin and collagen networks; Serum FN levels
are significantly increased in Duchenne patients establishing FN as a potential biomarker
of dystrophinopathy
Dermatopontin
ECM
Small ECM protein that is involved in matrix assembly; drastically increased expression
in muscular dystrophy-related fibrosis
Asporin
ECM
SLRP-type proteoglycan that is mostly associated with cartilage matrix; increased
expression in muscular dystrophy-related fibrosis
Prolargin
Basal lamina
PRELP-type protein of the basement membrane; increased expression in muscular
dystrophy-related fibrosis
Biglycan
Basal lamina
Small SLRP-type proteoglycan molecule that interacts with the dystrophin complex via
-SG and -SG; increased expression in muscular dystrophy-related fibrosis
Decorin
ECM
Small SLRP-type molecule that presents the primary proteoglycan of tendon structure
and perimysium; increased expression in muscular dystrophy-related fibrosis
Mimecan
ECM
Small SLRP-type proteoglycan molecule, also known as osteoglycin; increased
expression in muscular dystrophy-related fibrosis
Syndecan
ECM
Heparan sulfate proteoglycan that is crucial for satellite cell maintenance and skeletal
muscle regeneration; transiently up-regulated during muscle differentiation
Perlecan
Basal lamina
Basement membrane-specific heparan sulfate proteoglycan; transiently up-regulated
during muscle differentiation and mislocated in glycosylation-deficient muscular
dystrophy
Fibromodulin
Interstitial
Small SLRP-type proteoglycan with a crucial role in collagen fibril formation;
ECM
fibromodulin-deficient tendon exhibits abnormal collagen fibrils
Lumican
ECM
SLRP-type proteoglycan; increased expression in muscular dystrophy-related fibrosis
Aggrecan
ECM
Chondroitin sulphate proteoglycan with large aggregates in cartilage; expression is
affected in some forms of congenital muscular dystrophy
Nidogen/Entactin
Basal lamina
Basement membrane glycoprotein that is transiently expressed during myogenesis;
drastically reduced in aged and dystrophic heart muscle
Periostin (Osteoblast-specific
ECM
factor OSF-2) and Osteopontin
Matricellular proteins, such as periostin and osteopontin, are non-architectural ECM
components that modulate cell-matrix interactions and have a regulatory role during
development and degeneration-regeneration cycles; drastic increase in dystrophinopathyrelated fibrosis
Matrix metalloproteinases (MMP-
ECM
Matrix metalloproteinases are involved in the degradation of ECM proteins and have a
1, MMP-2, MMP-9, MMP-10,
crucial role during collagen deposition and fibre regeneration; MMP-2, MMP-9 and
MMP-13)
MMP-10 are increased in muscular dystrophy; greatly elevated serum levels of MMP-9
following muscle disintegration suggest this enzyme as a potential biomarker of
dystrophinopathy.
Tissue inhibitors of matrix
ECM
metalloproteinases TIMPs
The class of endogenous tissue inhibitors of metalloproteinases are crucial regulatory
factors in the development, adaptation and degradation of the ECM; and are associated
with the migration and differentiation of satellite cells in dystrophic and regenerating
fibres
Laminin-211 (Merosin)
Basal lamina
The large laminin 211 complex plays a key role in the structural integrity of the
muscle basement membrane and interacts with the dystroglycan-dystrophin axis and the
fibronectin-integrin axis; Laminin expression is apparently not majorly affected in
dystrophic skeletal muscles, but this basement membrane protein appears to be reduced
in Dp427-deficient cardiac fibres
Spectrin
Membrane
Core cytoskeletal anchoring protein that interacts with many essential muscle proteins,
cytoskeleton
including the Na+/K+-ATPase, Na+-channels, ankyrin, desmin and -actinin; spectrin
appears to be unaltered in most dystrophic muscles, but is slightly increased in the
severely dystrophic diaphragm muscle
Ankyrin
Integrin (71)
Membrane
Sarcolemma-associated ankyrin molecules provide interactions between the spectrin-
cytoskeleton
and actin-containing membrane cytoskeleton and a variety of integral membrane proteins
Sarcolemma
Crucial integral anchor protein of the skeletal muscle surface that provides transsarcolemmal linkage between the cytoskeletal network of contractile fibres and
extracellular laminin complexes; increases in components of the integrin-laminin axis
have therapeutic potential to treat dystrophinopathies
Paxillin and the integrin-
Cytoskeleton
The multi-domain scaffolding protein paxillin interacts directly with integrins and forms
associated cytoskeleton-cell-
a cytoskeleton-cell-matrix adhesion complex with many other potential binding partners,
matrix adhesion complex
such as talin, zyxin, tensin, vinculin, dysbindin and myospryn
Dystrophin (full-length Dp427
Sub-
Major cytoskeletal protein that provides linkage between dystroglycans and the
isoform)
sarcolemmal
subsarcolemmal network of cortical actin; primary genetic abnormalities in dystrophin
membrane
gene cause dystrophinopathies
cytoskeleton
-Dystroglycan (-DG), LARGE
Extracellular
Cell surface-associated receptor for the basal lamina protein laminin that requires
glycan
receptor
LARGE (like-acetylglucosaminyltransferase)-dependent glycosylation for binding to
laminin; -DG is greatly reduced in Dp427-deficient muscle tissue
-Dystroglycan (-DG)
Sarcolemma
Integral glycoprotein with direct linkage to dystrophin; -DG is the central
plasmalemma-spanning protein of the dystrophin complex and greatly reduced in
Dp427-deficient muscle tissues
Sarcoglycan (-SGs)
Sarcolemma
Integral proteins with an indirect linkage to dystrophin; all components of the SG subcomplex are greatly reduced in Dp427-deficient muscle tissue
Sarcospan
Sarcolemma
Tetraspan-like low-molecular-mass protein component of the supramolecular dystrophin
complex; greatly reduced in Dp427-deficient muscle tissue
Syntrophins
Membrane
Family of dystrophin-associated proteins whereby α-syntrophin interacts closely with
cytoskeleton
nNOS within the dystrophin complex; syntrophins are greatly reduced in Dp427deficient muscle tissues
Dystrobrevins
Membrane
Dystrophin-associated proteins that also interact with dysbindin and syncoilin; greatly
Syncoilin
Utrophin
Agrin
cytoskeleton
reduced in Dp427-deficient muscle tissue
Intermediate
Syncoilin is associated with α-dystrobrevin and represents a muscle-specific component
filament
of the intermediate filament
NMJ-specific
Full-length utrophin isoform Up395 forms a complex at the NMJ with a variety of
homologue of
proteins, such as agrin, AChE, Na+-channel, nAChR, the muscle-specific kinase MuSK,
dystrophin
Lrp4, rapsyn, neuregulin and nNOS
Basal lamina
Large proteoglycan that closely associates with the dystrophin/utrophin-complex via -
of NMJ
DG and has a crucial role in the development of the NMJ via agrin-induced clustering of
the nAChR complex; agrin levels are decreased in dystrophin-deficient basement
membranes in the central nervous system
Dysferlin
Sarcolemma
Ca+-regulatory protein with a crucial role in the repair mechanisms of the muscle
plasmalemma via promoting the swift resealing of surface membranes following
disruption by mechanical stress; close interaction with caveolin-3
Cortical Actin
Membrane
Cortical actin binds directly to the full-length dystrophin isoform Dp427 and thereby
cytoskeleton
forms a critical stabilising linkage between the membrane cytoskeleton and the
sarcolemma
Vinculin
Cytoskeleton
Membrane cytoskeletal protein involved in force-transducing costamere structures with a
complementary distribution to dystrophin; the vinculin-talin-integrin complex appears to
partly compensate dystrophin deficiency in muscular dystrophy
Desmin
Intermediate
Major intermediate filament protein that provides structural integrity to muscle fibres;
filament
pathological changes of desmin are majorly involved in desminopathies; desmin appears
to be up-regulated in dystrophinopathis
Plectin
Cytoskeleton
As a cytoskeletal cross-linker protein, plectin provides the linkage between
microtubules, actin microfilaments and intermediate filaments; plectin is involved in the
myofibrillar aggregate disease plectinopathy
Filamin (Filamin 2, Filamin C)
Cytoskeleton
Filamin is involved in actin reorganization and cellular signalling, it also interacts with
SGs
Tubulin
Microtubules
--tubulins are the main components of microtubules, in addition to associated MAP
proteins, and form important filamentous intracellular structures; muscular dystrophy is
characterized by a disorganized and denser microtubular network
-actinin
Nebulin
Contractile
Actin-binding protein with a crucial function in the attachment between the contractile
apparatus
actin filament and the Z-disc in skeletal muscle fibres
Contractile
The large nebulin molecule can be considered an auxiliary filamentous structure of the
apparatus
sarcomere that is associated with the thin actin-containing filament and stretches the Iband from the Z-disk to part of the A-band towards the border of the H-zone
Titin
Contractile
Gigantic string-like structural element of the actomyosin apparatus that functions as an
apparatus
auxiliary filament and spans half of a sarcomere unit from the Z-disk to the M-line
complex in muscle fibres; titin is partially degraded in dystrophic fibres and N- and Cterminal fragments are released form leaky fibres. Titin fragments are detectable in urine
samples from Duchenne patients
Muscle ankyrin repeat protein
Titin filament
The molecular spring domain of the string-like titin filament interacts with the MARP
MARP
of contractile
complexes; MARP is believed to act as a signal transducer and a mechanical stress
Myosin heavy chains
apparatus
sensor of the sarcomeric unit
Contractile
The main motor molecule of the thick filament is one of the most abundant protein
apparatus
species in the A-band region of the contractile apparatus whereby its head structures
mediate the molecular cross-bridge/swinging lever-arm coupling between myosin
filaments and actin molecules; myosin heavy chain isoforms are differentially affected in
muscular dystrophy
Myosin light chains
Contractile
The regulatory and essential sub-types of myosin light chains are positioned within the
apparatus
A-band region of the contractile apparatus and mediate the coordinated movement of
differentially phosphorylated myosin cross-bridges away from thick filament structures
and are involved in the fine tuning of myosin motor function by providing structural
stability to the lever arm domain of the myosin head; myosin light chain isoforms are
differentially affected in muscular dystrophy
Myosin binding protein
Contractile
The MBP class of muscle proteins is located in the overlapping region between thick and
apparatus
thin filaments and is involved in thick myosin filament alignment; fast isoform MBP-C
is greatly reduced in motor neuron disease and dystrophinopathies
Actin
Contractile
The main motor molecule of the thin filament is positioned in the I-band and overlapping
apparatus
A-band region of the contractile apparatus functioning as the essential counterpart of
myosin heads during cross-bridge cycles and swinging myosin lever-arm mechanisms;
actin isoforms are differentially affected in muscular dystrophy
Troponin
Contractile
The troponin complex (TnT, TnI, TnC) is associated with the thin filament and is
apparatus
involved in the binding to actin and resulting inhibition of actomyosin ATPase activity,
the linking of the troponin complex to the inhibitory tropomyosin complexes and the
calcium sensing that is critical for the regulation of actomyosin coupling; troponin
isoforms are differentially affected in muscular dystrophy
Tropomyosin
Contractile
The TM class of regulatory muscle proteins is located to the thin actin filament and has
apparatus
an inhibitory role in the regulation of actomyosin interactions; tropomyosin isoforms are
differentially affected in muscular dystrophy
M-line complex (myomesin,
Contractile
The M-line complex at the centre of the sarcomere contains myomesin, a stabilizing
obscurin)
apparatus
cross-linker of myosin that provides a linkage of the thick filaments in the M-line region
and obscurin that provides a connection with the titin filament thereby providing a
mechanical link of the M-line complex within the sarcomere
B-Crystallin and associated Z-
Contractile
Abundant molecular chaperone that is located in close proximity to the Z-disc complex
disc complex (telethonin,
apparatus
containing telethonin, myozenin, desmin, myotilin, -actinin, -actin, plectin, synemin
myozenin, -actinin)
and filamin; variety of small heat shock proteins exhibit drastically elevated levels in
dystrophinopathy, as well as in other neuromuscular disorders including myofibrillar
aggregation diseases and sarcopenia of old age