Sarcospan-dependent Akt activation is required for utrophin expression and muscle regeneration.
Utrophin is normally confined to the neuromuscular junction (NMJ) in adult muscle and partially compensates for the loss of dystrophin in mdx mice. We show that Akt signaling and utrophin levels were diminished in sarcospan (SSPN)-deficient muscle. By creating several transgenic and knockout mice, we demonstrate that SSPN regulates Akt signaling to control utrophin expression. SSPN determined α-dystroglycan (α-DG) glycosylation by affecting levels of the NMJ-specific glycosyltransferase Galgt2. After cardiotoxin (CTX) injury, regenerating myofibers express utrophin and Galgt2-modified α-DG around the sarcolemma. SSPN-null mice displayed delayed differentiation after CTX injury caused by loss of utrophin and Akt signaling. Treatment of SSPN-null mice with viral Akt increased utrophin and restored muscle repair after injury, revealing an important role for the SSPN-Akt-utrophin signaling axis in regeneration. SSPN improved cell surface expression of utrophin by increasing transportation of utrophin and DG from endoplasmic reticulum/Golgi membranes. Our experiments reveal functions of utrophin in regeneration and new pathways that regulate utrophin expression at the cell surface.
Department of Integrative Biology and Physiology and 2 Molecular Biology Institute, University of California-Los Angeles, Los Angeles, CA 90095, USA.
Jamie L
JL
Marshall
Johan
J
Holmberg
Eric
E
Chou
Amber C
AC
Ocampo
Jennifer
J
Oh
Joy
J
Lee
Angela K
AK
Peter
Paul T
PT
Martin
Rachelle H
RH
Crosbie-Watson
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion; D004195:Disease Models, Animal; D049030:Dystroglycans / Q000378:metabolism; D004789:Enzyme Activation; D006031:Glycosylation; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012038:Regeneration; D015398:Signal Transduction; D049411:Utrophin / Q000378:metabolism*
D002352:Carrier Proteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; C491632:Sspn protein, mouse; D049411:Utrophin; D049030:Dystroglycans; D051057:Proto-Oncogene Proteins c-akt