Sarcospan-dependent Akt activation is required for utrophin expression and muscle regeneration

JL Marshall, J Holmberg, E Chou, AC Ocampo… - Journal of Cell …, 2012 - rupress.org
JL Marshall, J Holmberg, E Chou, AC Ocampo, J Oh, J Lee, AK Peter, PT Martin…
Journal of Cell Biology, 2012rupress.org
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 …
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.
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