Turnover of myelin proteins in mouse brain in vivo

Abstract

The incorporation of tyrosine into proteins was measured after the subcutaneous implantation of a pellet of [14C]tyrosine in mice. This method keeps the specific radioactivity of free tyrosine fairly constant and makes it possible to follow incorporation up to a 10-day period. At the end of 10 days most of the protein-bound tyrosine was replaced (i.e. most protein turned over) in lung, liver, heart, kidney and spleen; about half was replaced in brain, one-quarter in muscle. The rate of protein turnover in myelin was approx. 40% of that of whole brain proteins; at 10 days one-fifth of the myelin proteins were replaced. All protein components of myelin measured were in a dynamic state; incorporation decreased in the following order, Wolfgram greater than DM-20 greater than basic greater than proteolipid proteins. The incorporation of tyrosine into each protein fraction was greater in the 0-5-day than in the 5-10-day period, indicating heterogeneity of metabolic rates. The results show that after myelination at least a portion of each protein component of myelin is undergoing significant metabolic turnover. In the adult, myelin components are not stable, but turnover is heterogeneous, and each protein may be compartmentalized. Turnover can be influenced by a variety of factors.

Study of the expression of myelin proteolipid protein (lipophilin) using a cloned complementary DNA

“…This may reflect either a differential reduction in the transcription rate or in the stability of the messages for the two proteins. Interestingly, this difference in mRNA levels correlates well with reports that MBP turns over more rapidly than PLP (31,32).…”

A Mammalian Protein Homologous to Fructosamine-3-Kinase Is a Ketosamine-3-Kinase Acting on Psicosamines and Ribulosamines but not on Fructosamines

“…Such enzymes are expected to play an important role in tissues that contain proteins with long (half-)lives. This is certainly the case of erythrocytes and lenses (29), but it is also true for brain, where myelin proteins have a half-life much longer than 10 days (30). Interestingly, the knockout of another protein-repair enzyme, isoaspartylmethyl-transferase (31), resulted in intractable seizures, leading to death of the mice after a few weeks.…”

Simvastatin regulates oligodendroglial process dynamics and survival

“…Within the central nervous system (CNS), myelin is produced by oligodendrocytes (OLGs) and continues to undergo a natural turnover throughout life (Lajtha et al, 1977). Myelin and OLGs are the apparent targets of the immunemediated injury that underlies the development of multiple sclerosis (MS) (Pouly et al, 2000).…”