and -Sarcoglycans are Decreased in the Detrusor
Smooth Muscle Cells of the Partially Obstructed Rabbit Bladder
Wenjie Wei, Pamela S. Howard, Steven A. Zderic and Edward J. Macarak*
From the Department of Anatomy and Cell Biology, University of Pennsylvania and Division of Pediatric Urology, Children’s Hospital
of Philadelphia (SAZ), Philadelphia, Pennsylvania
Purpose: We evaluated and quantified the levels of sarcoglycans present in the detrusor muscle layer of rabbits with partial
bladder outlet obstruction.
Materials and Methods: Rabbits underwent surgery, as previously described, to partially obstruct the urethra. One, 3, 7
and 14 days after obstruction the detrusor muscle layer was dissected free of the remaining bladder tissue and extracted with
detergent to isolate the transmembrane components of the dystroglycan-glycoprotein complex. Several components of the
dystroglycan-glycoprotein complex were characterized and quantified by sodium dodecyl sulfate-polyacrylamide gel electro-
phoresis and Western blotting.
Results: Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis several bands were noted on gels with a
molecular weight (43 and 35 kDa, respectively) corresponding to and -sarcoglycan. As obstruction progressed longitudi-
nally, the levels of and -sarcoglycan showed progressive decrease at the protein level with -sarcoglycan levels recovering
at later time points. Bladders with a functional physiology that showed more advanced symptoms of dysfunction had a greater
decrease in and -sarcoglycan protein.
Conclusions: The levels of and -sarcoglycan progressively change with obstruction with greater changes occurring in the
levels of -sarcoglycan. It is likely that alterations in the dystroglycan-glycoprotein complex are responsible for some of the
changes in muscle physiology that occur as a consequence of obstruction.
Key Words: bladder; rabbits; sarcoglycan; bladder neck obstruction; muscle, smooth
S
arcoglycans are transmembrane components of the
DGC, which links the cytoskeleton to the extracellular
matrix in adult muscle fibers and transfers muscle
contractile force across the sarcolemma. In addition to SGs,
DGC components include DG as well as syntrophins, dys-
trobrevin and sarcospan. The SG transmembrane subunit of
the DGC consists of components in skeletal and cardiac
muscle, including , , , , and -SG.
1–3
Since it was first
discovered in rabbit skeletal muscle in 1994 by Yoshida
et al,
4
the SG complex has also been found in smooth muscle
cells of the lung, blood vessels and gastroenteric tract. How-
ever, in smooth muscle the component is replaced by .
Numerous sarcoglycanopathies have been recognized since
1994, when a selective defect of the SG complex in severe
childhood autosomal recessive muscular dystrophy was dis-
covered.
5
All SG molecules are glycosylated with molecular
weights in the range of 35 to 50 kDa, as estimated by sodium
dodecyl sulfate-polyacrylamide gel electrophoresis.
The extracellular and intracellular domains of -SG (43
kDa) comprise 229 and 63 amino acids, respectively, sepa-
rated by a membrane spanning domain composed of 26
amino acids. -DG and -SG directly bind to each other,
presumably at their extracellular domains. Native glycosy-
lated -SG has a molecular size of 35 kDa. The extracellular
and intracellular domains of -SG comprise 231 and 35
amino acids, respectively, separated by a membrane span-
ning domain composed of 25 amino acids.
Although there is a great deal known about DGC in
skeletal muscle, relatively little is known regarding the
function of this complex in smooth muscle. In skeletal mus-
cle it has been shown that at 1 end of the molecule -DG
binds to dystrophin, while at its other end it binds to -DG.
In turn -DG is linked to the -chain of laminin, which is a
major component of the basement membrane surrounding
smooth muscle cells.
6,7
Thus, DGC is believed to be stabi-
lized by SGs, which are integral transmembrane proteins
that bind to -DG instead of to dystrophin directly.
8
Since
actin binds to dystrophin inside the cell and DGC binds to
laminin outside the cell, this complex provides a direct me-
chanical link between the contractile machinery, cytoskele-
ton and matrix.
The functional significance of dystrophin and DGs has
been well documented.
6,7,9,10
Their importance in certain
muscle pathologies was broadly recognized when it was
shown that a selective defect of the SG complex is caused by
an autosomal recessive mutation. This defect results in ab-
sence of the SG complex as well as weakened binding of
dystrophin to -DG and -DG to -DG.
5,11–14
Thus, based on
these studies we assume that SGs have important roles in
Submitted for publication August 8, 2007.
Study received approval from the institutional animal care and
use committees of Children’s Hospital of Philadelphia and Univer-
sity of Pennsylvania.
Supported by National Institutes of Health Grants DK052620 and
DK48215.
* Correspondence: School of Dental Medicine, University of Pennsyl-
vania, 240 South 40th St., Philadelphia, Pennsylvania 19104 (tele-
phone: 215 898-8993; FAX: 215 898-1687; e-mail: macarak@biochem.
dental.upenn.edu).
0022-5347/08/1795-2052/0 Vol. 179, 2052-2056, May 2008
THE JOURNAL OF UROLOGY
®
Printed in U.S.A.
Copyright © 2008 by AMERICAN UROLOGICAL ASSOCIATION DOI:10.1016/j.juro.2008.01.006
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