Cerebral proteinases in the growing rat

Postnatal changes of cathepsin D activity in rat liver and brain

Total and specific activity of cathepsin D (EC. 3.4.23.5) were measured in rat liver and brain from 1 to 98 days of age. The activity of cathepsin D in the liver of adult and newborn rats was the same while in the rat brain it was higher in adult than in newborn rats. In the liver maximum specific activity of cathepsin D occurred on the 10th postnatal day and minimum on the fourth day of age. In the brain maximum specific activity of the enzyme occurred on the 14th postnatal day. Total activity of cathepsin D increased after birth in rat liver and brain. These results are discussed in relation to the functional role of cathepsin D in the rat liver and the brain.

Cathepsin D and 2',3'-cyclic nucleotide 3'-phosphohydrolase in developing human foetal brain

Three peaks of proteinases were observed with hemoglobin, bovine serum albumin and casein as substrates at the pH of 3.5, 6.5 and 8.5, in prenatal human cerebral cortex. Cathepsin D (EC 3.4.23.5) was the most prominent, with hemoglobin as the preferred substrate. The enzyme was partially purified by Concanavalin A - Sepharose affinity chromatography and the nature of the active site was assessed with proteinase inhibitors. Inhibitor studies showed that similar to pepstatin A, benzethonium chloride was also strongly inhibitory to the enzyme. The distribution of cathepsin D, a neuronal marker, and 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37), a oligodendroglial marker in foetal brain regions with increasing gestation revealed that neurogenesis and gliogenesis occur concomitantly from earlier periods of gestation. Glial marker acquisition was particularly high in medulla and in spinal cord between 20 and 25 weeks of gestation.

Ontogenesis of neuropeptide degrading enzymes in the mouse brain

The ontogenesis of neuropeptide degrading enzymes was studied in the mouse brain, from the 10th gestational day up to adulthood. Two activities were followed: the pyroglutamate aminopeptidase and the post-proline cleaving enzyme, using either TRH or specific fluorgenic peptides as substrates. In the hypothalamus as well as in cerebral hemispheres, the specific activities of both enzymes was highest on the 13th fetal day and decline thereafter until the 20-22nd post-natal day, with a plateau around birth. In contrast, a classical peptidase, the leucyl-arylamidase increased only in fetal life, and reached the adult level before birth.

Protein degradation rates in regions of the central nervous system in vivo during development

The rate of protein degradation was estimated in several regions of rat brain at various ages by subtracting the rate of accumulation of protein from the rate of synthesis. The rate of degradation in cerebral hemisphere, which was 1.3%/h at 2 days of age, declined steadily with age, approaching the synthesis rate is about 30 days of age (0.8%/h). Degradation rates in the pons medulla, mid-brain and spinal cord were of a similar order to that in the cerebral hemisphere. The cerebellum had an exceptionally high rate of degradation in young rats, 1.9%/h at 2 days of age, which complemented its high rates of synthesis and accumulation. The degradation rate in the young was 2-2.5 times the rate in older rats and was approx. 65% of the synthesis rate during the more active phase of growth. The rapid accumulation of protein in the nervous system during the first week post partum was accompanied by high rates of breakdown, and was the result of a relatively small difference between that high rate of degradation and an even higher synthesis rate.

Enzymic hydrolysis of myelin basic protein and other proteins in central nervous system and lymphoid tissues from normal and demyelinating rats

Proteolytic activity of central-nervous-system tissue of the normal rat was examined over the pH range 2-9 with casein, haemoglobin and myelin basic protein as substrates. With casein as a substrate, brain and spinal cord homogenates showed very similar activity profiles with increasing pH, with the main peaks of proteolytic activity at pH 3-4 and 5-6. When haemoglobin was used, one broad main peak of activity from pH 3 to 5 was demonstrated. There was no optimum pH, however, for proteolytic activity with myelin basic protein as a substrate, and considerable hydrolysis were observed from pH 3.5 up to pH8. Proteolytic activity at the various pH values was compared by using homogenates of spinal cords from rats with acute experimental allergic encephalomyelitis and those from rats injected with Freund's adjuvant alone. The profiles of activity were similar with peaks at pH 3.5 and 5.5 with casein as a substrate, but the specific activity was significantly higher at most pH values in the spinal-cord homogenates from rats with experimental allergic encephalomyelitis. Similarly the spinal-cord homogenates from these latter rats contained much more proteolytic activity toward myelin basic protein throughout the pH range than was present in the control spinal cords. Homogenates from lymph nodes of rats with experimental allergic encephalomyelitis and from those of the controls contained two to three times as much proteolytic activity as that of the central-nervous-system tissue and had a different proteolytic activity profile form that of the central-nervous system, with higher activity at the neutral than at acid pH. The results are discussed with regard to the probability that inflammatory cells such as lymphocytes may be the cause of the increased proteolytic activity in the central nervous system of animals with experimental allergic encephalomyelitis, and that enzymes from these cells possess the capability of digesting myelin basic protein.

Changes in proteolytic enzymes and proteins during maturation of the brain

(1) Changes during development in the levels of proteinases and peptidases were measured in brain homogenates. At all ages di- and tripeptidase levels were 7-15-fold higher than proteinase activity. (2) Cathepsin A and D and neutral proteinase activity first decreased (during the 5 days before birth) and then increased (primarily during the first 10 days after birth) in development. The total enzyme content per unit weight of brain did not change greatly after 10 days, although specific activity fell owing to an increase in protein in older animals. (3) The developmental pattern of activities or peptidases measured with Leu-Gly and Leu-Gly-Gly and of arylamidases measured with Arg- and Arg-Arg-beta-naphthylamides was similar to that of proteinases. Total and specific activities increased rapidly after birth; then total activity did not change and specific activity decreased. (4) The proteinase content of tissue fractions (nuclear and lysosomal-mitochondrial) similarly reached a maximal peak in the rapid growth phase of the brain. (5) The decrease of hydrolytic activity after 10 days of age seems to parallel a decrease in the rates of protein breakdown in vivo, showing parallel behavior with decreasing protein turnover. In contrast, during the first 10 days of life protein turnover and calculated rate of protein breakdown in vivo decrease while the level of hydrolytic enzymes increases.