Malnutrition increases insoluble-to-soluble tubulin ratio and in vitro incorporation of 32ATP in rat cerebral cortex.

Wistar rats were fed a normal protein (25% casein) or an isoenergetic low protein (8% casein) diet from the day of birth to weaning on day 21. Litters were killed at weaning and cerebral cortex was removed. Tubulin was prepared by centrifugation at 100,000 g, 4 degrees C, as described by Shelansky et al. [Proc. Natn. Acad. Sci. U.S.A. 70, 765-768 (1973)]. Cold-insoluble tubulin was recovered in the pellet (P1) fraction and cold-soluble tubulin in the supernatant (S1) fraction. Alpha and beta tubulin were quantified by electrophoretic and immunological methods in both fractions. Our results indicated that malnutrition enhanced the ratio of cold-insoluble-tubulin-to-cold-soluble-tubulin. Furthermore malnutrition induced an increased in vitro incorporation of 32P into both soluble and insoluble tubulins. Although tubulin phosphorylation has been related to tubulin stability properties, we cannot unequivocally ascribe the increased insoluble/soluble tubulin ratio with malnutrition to increased in vitro incorporation of 32P.

Effect of phenylalanine and alpha-methylphenylalanine on in vitro incorporation of 32P into cytoskeletal cerebral proteins.

We studied the effects of L-phenylalanine and alpha-methylphenylalanine on 32P in vitro incorporation into cytoskeletal proteins from cerebral cortex of 17-day-old rats. Slices of cerebral cortex were incubated in the absence or presence of increasing concentrations of L-phenylalanine, alpha-methylphenylalanine or L-phenylalanine plus alpha-methylphenylalanine for 1 h. The cytoskeletal fraction obtained from slices was incubated in the presence of the same drugs and the 32P in vitro incorporation into cytoskeletal proteins was measured. Addition of alpha-methylphenylalanine did not change 32P in vitro incorporation into the cytoskeletal proteins, but phenylalanine decreased the in vitro phosphorylation of beta tubulin. Furthermore, addition of L-phenylalanine plus alpha-methylphenylalanine decreased the in vitro phosphorylation of both 160 kDa neurofilaments and alpha-tubulin.

Developmentally regulated in vitro phosphorylation of cytoskeletal proteins of the cerebral cortex of normal and malnourished rats.

In this investigation we studied developmentally regulated endogenous protein kinase activity in cytoskeletal proteins in the cerebral cortex of rats and the effect of early malnutrition imposed on dams on the pattern of 32P incorporation into the cytoskeleton of pups. Our results indicated that in vitro incorporation was maximum in 7-day-old pups for both normal and malnourished groups, decreasing with development, and reaching minimum values in adult animals. However, 32P incorporation into NF-M and tubulin was significantly lower in 7-day-old malnourished pups than in normal pups.

Malnutrition induces an increase in intermediate filament protein content of rat cerebral cortex.

Wistar rats were fed a normal protein (25% casein) or an isoenergetic low protein (8% casein) diet from the day of giving birth until pups were weaned. Some litters were killed at weaning; others (both normal and malnourished animals) received the 25% protein diet until d 90 when they were killed. Intermediate filament (IF) preparations were obtained by extraction of the cerebral cortex with a high salt PBS solution containing 1% Triton X-100. The pellet contained the bulk of the cytoskeleton proteins from tissue, identified as the 150- and 68-kDa subunits of neurofilaments (NF-M and NF-L, respectively), the 66-kDa associated protein, the 57-kDa intermediate filament-like protein, and the 50-kDa glial fibrillary acidic protein. Intermediate filament-enriched fractions from control and malnourished rats at both d 21 and 90 were scanned following two-dimensional gel electrophoresis to determine the effects of postnatal malnutrition on the intermediate filament protein content. The results indicated that postnatal malnutrition imposed during the brain growth spurt period did not alter the expression of IF proteins of the cerebral cortex in 21-d-old rats, but increased the expression of NF-L and NF-M proteins in adult rats.

Cytoskeletal-associated protein kinase and phosphatase activities from cerebral cortex of young rats.

We describe the phosphorylation system associated with the Triton-insoluble cytoskeletal fraction that phosphorylates in vitro the 150 kDa neurofilament subunit (NF-M) and alpha and beta tubulin from cerebral cortex of rats. The protein kinase activities were determined in the presence of 20 microM cyclic AMP (cAMP), 1 mM calcium and 1 microM calmodulin (Ca2+/calmodulin) or 1 mM calcium, 0.2 mM phosphatidylserine and 0.5 microM phorbol 12,13-dibutyrate (Ca2+/PS/PDBu). Phosphorylation of these cytoskeletal proteins increased approximately 35% and 65% in the presence of cAMP and Ca2+/calmodulin, respectively, but was unaffected in the presence of Ca2+/PS/PDBu. Basal phosphorylation of these proteins studied increased approximately 35% and 72% in the presence of 0.5 microM okadaic acid and 0.01 microM microcystin-LR, respectively, suggesting the presence of phosphatase type 1. Results suggest that at least two protein kinases and one protein phosphatase are associated with the Triton-insoluble cytoskeletal fraction from cerebral cortex of rats.

Effects of brain ischemia on intermediate filaments of rat hippocampus.

Neurofilaments subunits (NF-H, NF-M, NF-L) and glial fibrillary acidic protein (GFAP) were investigated in the hippocampus of rats after distinct periods of reperfusion (1 to 15 days) following 20 min of transient global forebrain ischemia in the rat. In vitro [14Ca]leucine incorporation was not altered until 48 h after the ischemic insult, however concentration of intermediate filament subunits significantly decreased in this period. Three days after the insult, leucine incorporation significantly increased while the concentration NF-H, NF-M, and NF-L were still diminished after 15 days of reperfusion. In vitro incorporation of 32P into NF-M and NF-L suffered immediately after ischemia, but returned to control values after two days of reperfusion. GFAP levels decreased immediately after ischemia but quickly recovered and significantly peaked from 7 to 10 days after the insult. These results suggest that transient ischemia followed by reperfusion causes proteolysis of intermediate filaments in the hippocampus, and the proteolysis could be facilitated by diminished phosphorylation levels of NF-M and NF-L.