Myelin Proteomics: Molecular Anatomy of an Insulating Sheath

Fast-transmitting vertebrate axons are electrically insulated with multiple layers of nonconductive plasma membrane of glial cell origin, termed myelin. The myelin membrane is dominated by lipids, and its protein composition has historically been viewed to be of very low complexity. In this review, we discuss an updated reference compendium of 342 proteins associated with central nervous system myelin that represents a valuable resource for analyzing myelin biogenesis and white matter homeostasis. Cataloging the myelin proteome has been made possible by technical advances in the separation and mass spectrometric detection of proteins, also referred to as proteomics. This led to the identification of a large number of novel myelin-associated proteins, many of which represent low abundant components involved in catalytic activities, the cytoskeleton, vesicular trafficking, or cell adhesion. By mass spectrometry-based quantification, proteolipid protein and myelin basic protein constitute 17% and 8% of total myelin protein, respectively, suggesting that their abundance was previously overestimated. As the biochemical profile of myelin-associated proteins is highly reproducible, differential proteome analyses can be applied to material isolated from patients or animal models of myelin-related diseases such as multiple sclerosis and leukodystrophies

Exogenous Ca2+-ATPase isoform effects on Ca2+ transients of embryonic chicken and neonatal rat cardiac myocytes

Sarco-endoplasmic reticulum Ca2+-ATPase from fast skeletal (SERCA1) or cardiac muscle (SERCA2a) was expressed in embryonic chicken and neonatal rat cardiac myocytes by adenovirus vectors, with c-myc tags on both constructs to compare expression and distinguish exogenous from endogenous SERCA2a in myocytes.Expression of the two isoforms was similar (approximately 3-fold higher than endogenous SERCA). However, SERCA1 activity was 2-fold greater than SERCA2a activity, due to intrinsic differences in turnover rates. Activation of both exogenous SERCA isoforms by Ca2+ was displaced to slightly lower [Ca2+], suggesting that the overexpressed isoforms were independent of phospholamban. In fact, phospholamban and calsequestrin expression were unchanged.Decay time constants of cytosolic Ca2+ transients from cells overexpressing SERCA1 were reduced by 30–40 % and half-widths by 10–15 % compared to controls. SERCA2a overexpression produced much less acceleration of transients in chick than in rat, and less acceleration than SERCA1 overexpression in either species. There was no significant change in resting [Ca2+], peak amplitudes, or in the amount of Ca2+ releasable by caffeine from overexpression of either SERCA isoform. However, the amplitudes of the transients increased with SERCA1 overexpression when pacing frequency limited refilling of the sarcoplasmic reticulum.It is concluded that total SERCA transport velocity has a primary effect on the decay phase of transients. Transport velocity is affected by SERCA isoform turnover rate, temperature, and/or SERCA copy number