Myelin basic protein in frozen and unfrozen bovine brain: a study of autolytic changes in situ

Effects of aging and alcohol on the biochemical composition of histologically normal human brain

Human brains were removed at autopsy and examined grossly and histologically for any abnormality or evidence of disease. Sixty-two brains appearing normal by these criteria were examined further. First, a detailed record of alcohol consumption was obtained. Second, frozen punches of gray and white matter were used to determine the compositional change associated with age and drinking patterns. Increased age was associated with an increase in the water content, particularly in the white matter, a decline in RNA content in gray matter, a decline in total protein in white matter, and a decline in both myelin and the myelin-like subfraction. The loss of myelin membrane in white matter corresponded to a similar increase in water content, although there was an additional loss of some nonmyelin protein. There was no significant shift in the density between the myelin and the myelin-like membranes, and the protein composition of myelin was not significantly altered by age. A history of heavy alcohol consumption was associated with a relative increase in total protein in white matter even though heavy drinking accelerated the age-related loss of myelin. Presumably, alcohol produced a lag in the rate at which nonmyelin proteins are lost or accelerated the accumulation of abnormal protein. Alcohol consumption did not influence the myelin composition or the ratio of myelin and myelin-like membranes. The interval between patient death and autopsy was shown to have little or no effect on the samples used in this study. These data show that normal aging, uncomplicated by other disease processes, can have a significant effect on the composition of brain tissue, particularly the white matter, and that heavy alcohol consumption accelerates degenerative change, even in tissue appearing normal by histology.

Autolytic changes of human white matter: an electron microscopic and electrophoretic study

The effect of autolysis on the electrophoretic pattern of the 3H-labeled membrane glycoproteins derived from human brain white matter (WM) was investigated and correlated with electron microscopic findings. Samples were taken from the WM of outer zones of routine surgical specimens sent for pathologist's examination. The WM samples were incubated at +4 and +25 degrees C for 6 and 24 hr and analyzed by electron microscopy and by galactose oxidase labeling with subsequent SDS-polyacrylamide gradient gel electrophoresis. The effect of freezing and thawing was also studied. In electron microscopic examination myelin was found to have degenerated after an incubation of 24 hr at +4 and +25 degrees C, and it was severely disrupted after 24 hr at +25 degrees C, when a periaxonal network-like change was observed. The major labeled membrane glycoprotein band with an estimated molecular weight (MW) of 138,000 was stable during the first 24 hr of incubations at both +4 and +25 degrees C. No marked changes were noticed in the electrophoretic pattern of all of the WM membrane proteins labeled by [3H]acetic anhydride technique. In frozen and thawed specimens there was an increase in the intensity of the band with a MW of 86,500 and a new band appeared at the MW region of 25,000. The present results suggest that despite the apparent stability of the major glycoprotein band during the first 24 hr of autolysis, there are ultrastructural abnormalities in the myelin sheath, which should be taken into consideration during interpretation of changes in pathologic conditions.

Myelin in the developing human cerebrum

In order to ascertain the true composition of human myelin at the earliest stages of development and to shed some light on the controversial results published to date, the lipid and protein composition of myelin from unfrozen cerebrum of very young infants was compared to the values obtained later in development and to those obtained by other investigators using frozen human brain. The effect of 3 different procedures of myelin isolation, as well as varying periods of storing the brain in frozen state, were tested on the final composition of myelin. All myelin preparations were of a very high degree of purity, and the lipid composition changed very little either with age or by varying the method or the time of storage of the brain. Protein composition, on the other hand, changed drastically after freezing the brain for increasing periods, and the percentage of myelin basic protein (MBP) decreased to one-third of its original value after about a year of brain storage. However, when myelin was isolated from unfrozen brain immediately after autopsy, very high values of MBP were obtained, even in newborn cerebral myelin, which was quite mature from a morphological as well as from a biochemical point of view. These data reveal that the developmental changes of human myelin are much more subtle than has previously been thought.

Regional studies of myelin proteins in human brain and spinal cord

The myelin specific proteins, myelin basic protein (MBP) and myelin proteolipid protein (PLP) were quantitated by radioimmunoassay (RIA) and the activity of the enzyme 2',3'-cyclic 3' phosphohydrolase (CNP) measured, in 27 regions of normal brain and spinal cord. Varying regional concentrations for each protein and regional variations for protein ratios were noted, supporting the concept of a varying chemical composition for myelin throughout the central nervous system (CNS). Variation was also noted among myelin subfractions from a single region. Regions with special sensitivity to the multiple sclerosis process had relatively lower proportions of CNP in several, but not all cases.

Isoelectric focusing of myelin membrane proteins

Human myelin was isolated from the white matter of autopsy brains. Myelin proteins were characterized by isoelectric focusing in ultrathin slab gels in a pH range from 3.5 to 10 after solubilization with urea and Nonidet P 40. The protein profile in the acidic region (pH below 6.2) revealed at least twelve faint bands which comprised only a few percent of the total myelin proteins. Most of the myelin proteins were focused in the neutral range (pH 6.2-7.8) which showed two sharper and three broader major bands, the total number of bands in this region being about twenty. The basic pH range (pH above 7.8) contained about 30% of the proteins, and revealed a very intense band near the cathode with seven to nine weaker bands below pH 9.0. When the myelin was partially delipidated prior to solubilization, an additional broad "band" was observed at the area pH 8.0-8.5.

Effect of microheterogeneity on the structure and function of the myelin basic protein

The basic protein is a major component of central nerve myelin containing species with varying amounts of phosphorylation and deamidation in situ. Components of basic protein were separated on the basis of net charge. Differences in ionic interactions of components of basic protein in a two-phase partition system with beef brain phosphatidyl serine were small, but there was a tendency for less charged components to require less lipid to achieve the same degree of solubilization into the chloroform phase. Spectroscopic properties of the components were identical using the following techniques: far ultraviolet circular dichroism, difference ultraviolet spectroscopy, fluorescent determination of tyrosine pK values and fluorescence energy transfer. At alkaline pH transfer from Trp to Tyr O- was 25% efficient which indicates that the closest accepting tyrosine is approx. 10 A away (the closest fluorescent tyrosine is over 20 A away). In 6 M guanidinium chloride this transfer was abolished while difference spectra indicated that the aromatic amino acids became more exposed in this solvent. These results show that the basic protein has definite secondary structure but that is not affected by the post-translation modifications.

Studies of human myelin proteins during old age

The electrophoretic protein patterns of myelin isolated from frontal and callosal white matter were studied in adult man up to the age of 90 years. The proportions of the four major myelin proteins remained virtually unchanged as did the total protein content of white matter and of purified myelin. The total mass of purified myelin that could be recovered from white matter gradually decreased with age, suggesting an age-related loss of myelin sheath and probably neurons as well, without detectable alterations of the regular protein composition of myelin. In most cases basic protein of myelin was preceded by one or two minor protein components on electrophoresis. One of them is tentatively identified as "prebasic" protein similar to the one previously observed in other species, because of its close electrophoretic apposition to the main basic protein. The second component was found less frequently and was thought to arise from specific types of proteolysis of myelin proteins. Prolonged time intervals between death and autopsy had little, if any, effect on the proportions of basic protein and proteolipid protein. Similar results were obtained when bovine brain was incubated under conditions designed to simulate post-mortem autolysis. It was there fore concluded that meaningful data on proteins of human central myelin may be obtained even though an autopsy was not performed within a few hours of death.

Immunocytochemical method to identify myelin basic protein in oligodendroglia and myelin sheaths of the human nervous system

To study the distribution of basic protein (BP) and other myelin constituents immunocytochemically in human nervous tissue, we modified the unlabeled antibody enzyme (peroxidase-antiperoxidase) method. The technique is described here. Because the availability of unfixed tissue from human central nervous system is limited, we tested the method on blocks that had been fixed in formalin and embedded in paraffin, fixed and stored in 4% formalin, or frozen at autopsy and stored. We obtained the best results with paraffin blocks. BP antiserum stained oligodendroglia and myelin sheaths in the developing human nervous system. In the adult, myelin sheaths were well stained. Also, abnormalities associated with myelin breakdown could be identified in multiple sclerosis lesions. The results suggest that this method will be useful in studying the cellular distribution of myelin components in human demyelinating diseases.

Myelin protein composition in the rat spinal cord in culture and in vivo: a developmental comparison

Biochemical characterization of the development of myelin in vitro was extended to an analysis of myelin protein composition in cultures of explanted foetal rat spinal cord. Myelin fractions were isolated from pooled explants after 12-30 days in vitro and, for comparison, from the spinal cords of rats of equivalent developmental ages. Electron microscopic examination of the culture myelin fractions revealed the presence of multilamellar myelin fragments and some single membranes. All fractions were analyzed using a micro-polyacrylamide gel electrophoresis technique. Qualitatively similar protein profiles were observed for myelin isolated from either cultures or from spinal cords. Fractions from cultures contained a greater proportion of high molecular weight proteins than those from spinal cords, although with respect to the 'major' myelin proteins, a quantitatively similar developmental pattern was observed both in vivo and in vitro.

Turnover of myelin proteins in mouse brain in vivo

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.

Changes in CNS myelin proteins and glycoproteins after in situ autolysis

The effects of postmortem autolysis in situ on myelin proteins and glycoproteins were studied in 25- and 125-day-old mouse brain and in adult bovine brainstem. In bovine myelin a loss of the major myelin glycoprotein was the only difference observed when the tissue was left at 19 degrees C for 24 hours compared to immediately frozen material. In the autolysed mouse brain, the myelin major glycoprotein was the most affected component with a 55% decrease. Both myelin basic protein components were degraded with a 35% loss. The other myelin proteins did not change under the conditions used for this study. There was also no change in the specific activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase, a myelin-associated enzyme. Using the double labelling technique with [3H]fucose and [3 5S] sulfate as precursors injected intracranially, a shift of the major myelin glycoprotein labelled with radioactive sulfate towards a smaller apparent molecular size was observed as a result of the autolysis whereas the electrophoretic mobility of the fucose labelled major peak was unaffected.