The sarcoglycan complex in Schwann cells and its role in myelin stability.
Sarcoglycans are originally identified in muscle for their involvement in limb-girdle muscular dystrophies. They form a multi-meric complex (alpha-, beta-, gamma-, delta-sarcoglycan) that associates with dystrophin, dystroglycan and other proteins to constitute the larger dystrophin-glycoprotein complex at the muscle membrane. Three sarcoglycan subunits (epsilon-, beta-, delta-sarcoglycan) were previously identified in Schwann cells and shown to associate with dystroglycan and a Schwann cell-specific dystrophin isoform (Dp116) at the outermost Schwann cell membrane. Currently, little is known about the exact composition and function of the sarcoglycan complex in the peripheral nervous system. In this study, we showed that the Schwann cell sarcoglycan complex consists of epsilon-, beta-, delta-sarcoglycan and the newly identified zeta-sarcoglycan subunit. The expression of sarcoglycans precedes the onset of myelination and is induced by neurons. In sarcoglycan-deficient BIO14.6 hamsters, loss of the Schwann cell sarcoglycan complex reduces the steady state levels of alpha-dystroglycan and Dp116. Ultrastructural analysis of sciatic nerves from the mutant animals revealed altered myelin sheaths and disorganized Schmidt-Lanterman incisures indicative of myelin instability. The disruption in myelin structure increased in severity with age. Nerve conduction studies also showed subtle electrophysiological abnormalities in the BIO14.6 hamsters consistent with reduced myelin stability. Together, these findings suggest an important role of sarcoglycans in the stability of peripheral nerve myelin.
Cai
Hong
H
Sigfried and Janet Weis Center for Research, M.C. 26-11, the Geisinger Clinic, 100 North Academy Avenue, Danville, PA 17822, USA.
Erdman
Robert A
RA
Zweier
Lynnsey
L
Chen
Jiwei
J
Shaw
John H
JH
Baylor
Kelly A
KA
Stecker
Mark M
MM
Carey
David J
DJ
Chan
Yiu-mo Michael
YM
D000375:Aging; D000818:Animals; D002478:Cells, Cultured; D018920:Coculture Techniques; D006224:Cricetinae; D003593:Cytoplasm / Q000648:ultrastructure; D004355:Drug Stability; D049030:Dystroglycans / Q000737:chemistry / Q000378:metabolism; D004594:Electrophysiology; D008297:Male; D008854:Microscopy, Electron; D009186:Myelin Sheath / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D009420:Nervous System / Q000503:physiopathology; D009431:Neural Conduction; D020033:Protein Isoforms / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D017207:Rats, Sprague-Dawley; D049031:Sarcoglycans / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D012583:Schwann Cells / Q000378:metabolism* / Q000648:ultrastructure; D012584:Sciatic Nerve / Q000648:ultrastructure; D013997:Time Factors
D020033:Protein Isoforms; D049031:Sarcoglycans; D049030:Dystroglycans