Protein synthesis in a cell-free system from rat brain sensitive to ACTH-like peptides

Phosphorylation changes following weakly reinforced learning and ACTH-induced memory consolidation for a weak learning experience

The formation of a protein synthesis-dependent long-term memory stage in day-old chicks trained on a passive discriminated avoidance task has been shown to occur only with an adequate level of reinforcement, and is preceded by a significant change in the phosphorylation state of the forebrain synaptosomal membrane protein GAP43 protein. In the present study, it is shown that weakly reinforced training did not lead to formation of a long-term memory stage or to any change in phosphate incorporation into forebrain P2M protein bands. However, administration of ACTH immediately posttraining led to both the formation of the long-term memory stage and a preceding significant increase in the phosphorylation of GAP43. These findings are consistent with the view that a reinforcement-dependent neurohormone-mediated change to the phosphorylation of this synaptosomal membrane protein may be implicated in the triggering of long-term memory consolidation.

ACTH-related peptides: receptors and signal transduction systems involved in their neurotrophic and neuroprotective actions

ACTH-related peptides are promising neurotrophic and neuroprotective agents, as demonstrated in many in vivo and in vitro studies. They accelerate nerve repair after injury, improving both sensor and motor function. Furthermore, ACTH-related peptides have neuroprotective properties against cisplatin- and taxol-induced neurotoxicity, they improve neuronal function in animals with neuropathy due to experimental diabetes, and they prevent degeneration of myelinated axons in rats suffering from experimental allergic neuritis, a model of peripheral demyelinating neuropathy. Studies in neuronal cultures have corroborated these clinical observations and serve to investigate the mechanism of action of the ACTH-related peptide effects. This paper reviews both in vitro and in vivo effects and emphasizes the mechanism of action. Recent data on melanotrophic receptors and signal transduction systems will be discussed in this context.

The influences of fragments and analogs of ACTH/MSH upon recovery from nervous system injury

Post-injury treatment with some fragments and analogs of the adrenocorticotropic hormone (ACTH) can influence recovery after nervous system injury. This review considers both the successful and unsuccessful attempts to facilitate neural and behavioral recovery from nervous system damage via post-injury administration of these compounds. To date no single unifying explanation for the mixed results observed in animals prepared with forebrain injuries has been achieved. Several possible explanations for the variety of observations reported and several potentially productive avenues for future research are suggested.

The effects of melanocortins and electrical fields on neuronal growth

The effects of the neuropeptide molecules, adrenocorticotrophic hormone or alpha-melanocyte stimulating hormone, on various parameters of in vitro nerve growth, have been studied in the presence and absence of a small applied electric field. Striking effects on rates of nerve growth occurred. Selected concentrations of either substance alone, produced a three- to fourfold increase in nerve growth rate; other concentrations were inhibitory. The applied electric field alone increased rates of growth threefold. Further augmented rates of growth were seen when either neuropeptide was present simultaneously with an applied field. Under these latter conditions, galvanotropic (cathodal) orientation persisted, while nerve branching was suppressed. Given the clinical interest in melanocortin-stimulated nerve regeneration, perhaps a combined electrical and neuropeptide approach would be warranted.

In vitro translation in a hamster brain cell-free system

We have developed a cell-free translation system derived from hamster brain tissue. The optimal incorporation conditions were 160 mM K+, 2 mM Mg2+ and microM spermine. The absence of this latter compound could be compensated only by doubling (to 4 mM) Mg2+ concentration. This system was inhibited by cycloheximide and emetine (elongation inhibitors) as well as NaF and aurintricarboxilic acid (ATA) (initiation inhibitors). The nature of the ATA inhibiting effect was studied by kinetic comparison with cycloheximide and polyribosome sedimentation pattern.

Nerve regeneration through a two-ply biodegradable nerve guide in the rat and the influence of ACTH4-9 nerve growth factor

Biodegradable polyurethane-based (PU) nerve guides, instilled with or without ACTH4-9 analog (a melanocortin) were used for bridging an 8 mm gap in the rat sciatic nerve and were evaluated for function and histological appearance after 16 weeks of implantation. Autologous nerve grafts functioned as controls. The guides successfully enabled the sciatic nerve to regenerate across the 8 mm gap, thus effectively reestablishing the contact between the proximal and distal nerve ends. The mean conduction velocity, motor latency, and muscle action potentials of all the nerve guides did not differ significantly from the autografts. The histological quality of the regeneration in the nerve guides was significantly better than in the autografts; in the nerve guides, a well-defined nerve cable of normal architecture had regenerated without extensive endoneural scarring as seen in the autografts. ACTH4-9 instilled in the nerve guides showed a slight, but significant, increase in the number of myelinated axons. It is concluded that biodegradable PU nerve guides result in similar functional recovery when compared with autografts, but their histological quality is significantly better. ACTH4-9 showed only slight, but significant, improved nerve growth promoting activity. Therefore biodegradable PU nerve guides with ACTH4-9 would appear to be promising alternatives to autografts for bridging nerve defects.

Melanocortins and fast axonal transport in intact and regenerating sciatic nerve

The effect of ACTH/MSH peptides on fast axonal transport along intact or regenerating sciatic nerve was examined following injection of tritiated leucine into the rat lumbar spinal cord. The rate of fast axonal transport was not significantly changed by treatment with ACTH/MSH(4-10), the ACTH(4-9) analog ORG 2766, hypophysectomy, or adrenalectomy. Fast axonal transport was unchanged in regenerating nerves and in regenerating, ACTH(4-10)-treated nerves. However, treatment with ORG 2766 in dosages of either 1 or 10 micrograms/kg/day IP for seven days significantly reduced (62% and 64%, respectively) the crest height of the fast axonal transport curve of intact sciatic nerve. The results suggest that the reported peptide-induced enhancement of nerve regeneration is not due to changes in the rate of fast axonal transport.

Preparation of a cell-free extract from rat brain which can initiate protein synthesis in vitro

A cell-free protein synthesis system, derived from brains of 3 mo-old male Fischer-344 rats, has been characterized. The optimum conditions for amino acid incorporation in the system were 5 mM magnesium ion and 200 mM potassium ion. Incorporation depended on the addition of ATP, GTP, and an energy-generating system, and was sensitive to addition of the drugs aurintricarboxylic acid and sodium fluoride, inhibitors of initiation of protein synthesis. Both 40S and 80S initiation complexes were labeled in vitro, using [35S]methionine. Such labeling was sensitive to the protein synthesis inhibitors, aurintricarboxylic acid and sodium fluoride. The system, which can initiate protein synthesis, should be of use for examining mechanisms which underlie alterations in rat brain protein synthesis induced by various treatments.

The effect of ACTH4-9 analog (Org2766) on some cerebrospinal fluid parameters in patients with Alzheimer's disease

In a double-blind, placebo-controlled study, the central nervous system effects of an ACTH4-9 analog, Org2766 (40 mg/day), in Alzheimer's disease were assessed by measuring cerebrospinal fluid parameters during 6 months' treatment. Somatostatin-like immunoreactivity and cholinesterase activity, which are known to be reduced in cerebrospinal fluid of Alzheimer patients compared with controls, did not change during treatment. As a marker of noradrenergic and dopaminergic systems, we measured dopamine-beta-hydroxylase and homovanillic acid, but both levels were static. These results suggest that Org2766 did not interact with the transmitter systems, which are thought to be disturbed in Alzheimer's disease.

Regulation of deoxyglucose uptake by adrenocorticotropic hormone in cultured neurons

The influence of ACTH and some of its N-terminal related peptides was investigated on the uptake of (3H)-2-deoxy-D-glucose in pure cultures of neurons from chick embryo cerebral hemispheres. ACTH influences deoxyglucose uptake in a time and dose-dependent fashion. The stimulation of deoxyglucose uptake is observed after a delay of 6-8 h and requires active protein synthesis. ACTH does not affect deoxyglucose in non-neuronal cells (astroglial cells, hepatocytes, myoblasts, fibroblasts). The effect of various peptide hormones, neuropeptides and growth factors, active in the central nervous system or other tissues, has also been examined. None of these were able to stimulate deoxyglucose uptake, suggesting that the regulation of hexose uptake in neurons is specific for the ACTH-related peptides.

Modulation of phosphorylation of a 30-kD polyribosomal protein (pp30) by ACTH and spermine: comparison with modulation of brain protein synthesis

Gel electrophoretic separation of proteins phosphorylated in a postmitochondrial supernatant fraction of brain in the presence of spermine or adrenocorticotropin (ACTH) indicated modulation in only one region (30 kD) of the gel. The 30-kD (pp30) protein together with enzyme activity catalyzing its phosphorylation and sensitivity of the phosphorylation to spermine and ACTH were retained in a free polyribosomal fraction of this extract. ACTH(11-24) inhibited phosphorylation at all the spermine or Mg2+ concentrations tested. Structure-activity studies revealed that the inhibitory activity within ACTH(1-24) resides in the sequences ACTH(11-24), (5-18, 17Lys, 18Lys)-NH2, (15-24), (7-16)-NH2, and (1-16)-NH2 and can also be found in certain polylysine fragments. Phosphorylation under conditions suitable for measuring protein synthesis revealed only one phosphoprotein (pp30), sensitive to both ACTH(15-24) and spermine. The possibility of a relationship between modulation of pp30 phosphorylation and modulation of brain cell-free protein synthesis is discussed in relation to the effects of ACTH, spermine, and Mg2+.

Cyclic nucleotide- and calcium-independent phosphorylation of proteins in rat brain polyribosome: effects of ACTH, spermine, and hemin

The incorporation of [gamma-32P]ATP into proteins of rat brain polyribosomes was studied in vitro. The effects of cyclic nucleotides, calcium, hemin, ACTH, GTP, and spermine were examined. The incorporation of phosphate into proteins increased with time and phosphatase activity was very low; thus, the extent of phosphorylation was predominantly a reflection of protein kinase activity. Phosphorylation of proteins was not sensitive to Ca2+ in the presence or absence of either calmodulin or phosphatidylserine. Phosphorylation was also unaffected by cyclic nucleotides in the absence of exogenous enzymes. However, addition of a cAMP-dependent protein kinase together with cAMP resulted in a stimulation of the incorporation of phosphate into 4 phosphoproteins (pp70, pp58, pp43, and pp32); phosphorylation of pp32 was completely dependent on the addition of the kinase. ACTH (1-24), (11-24), and spermine inhibited the endogenous phosphorylation of one protein band (pp30). The phosphorylation of this 30 kD band was also selectively increased by hemin (5 microM). Higher concentrations of hemin exerted an inhibitory effect on the majority of the phosphoproteins. Protein phosphatase activity was not influenced by ACTH or spermine. The specific inhibition of pp30 phosphorylation by ACTH or spermine is most probably explained by an interaction with a cyclic nucleotide- and Ca2+ -independent protein kinase.

Modulation of protein synthesis in a cell-free system derived from rat brain by corticotropin (ACTH), magnesium, and spermine

Modulation of protein synthesis by fragments of the ACTH molecule has been studied in a cell-free system obtained from subcortical brain tissue of rats. Both the activity of the protein-synthesizing system and its sensitivity to ACTH-like peptides appeared to be highly dependent on the Mg2+ and spermine concentrations. At optimal Mg2+ concentrations (4 mM) the peptide sequences ACTH(1-24) and (11-24) were both inhibitory, the latter being the more active. The inhibitory effect was reduced or abolished at higher (suboptimal) concMg2+ concentrations. Spermine, like ACTH, inhibited protein synthesis at the optimal Mg2+ concentration. However, at lower Mg2+ concentrations spermine had a stimulatory effect and maximal activity was obtained at 0.75-1.0 mM Mg2+. In the presence of spermine (60 microM) and Mg2+ (0.75 mM), a half-maximal inhibition of protein synthesis was obtained with a peptide concentration of 5 microM. A structure-activity study showed that the peptides ACTH(7-16)-NH2, (11-24), (5-18, 17Lys 18Lys)-NH2 and (15-24) were active in inhibiting protein synthesis, whereas the fragments ACTH(1-16)-NH2 and (17-24) were inactive. The results are discussed in terms of an interaction between ACTH, Mg2+, and spermine, and intracellular processes involved in protein synthesis.

Regeneration and protein synthesis in the spinal cord: the influence of ACTH-like peptides on cell-free protein synthesis

To measure protein synthesis at the level of the cell bodies of motoneurons of the sciatic nerve, anterior horns were punched out of the spinal cord using microdissection techniques and a cell-free system was prepared. Injections of ACTH1-16 and ACTH4-10 were shown to enhance protein synthesis in the cell-free system, 1.5 h after treatment. Neither crush lesion of the sciatic nerve nor systemic treatment with ACTH4-10 produced clear changes in overall protein synthesis. Thus, the increase in overall protein synthesis by acute treatment with ACTH-like peptides cannot explain the previously reported stimulation of axonal regeneration after nerve crush.

Influence of adrenocorticotropic hormone on the growth of isolated neurons in culture

The present study reports the influence of adrenocorticotropic hormone (ACTH) on the development of cultured neurons from chick embryo cerebral hemispheres. Cultures were initiated in serum-supplemented medium and then transferred to serum-free hormonally-defined medium containing various concentrations of ACTH1--24. The effects of ACTH on the light microscopic features, metabolic activity and permeation properties were examined. The results demonstrate that ACTH exerts a trophic action on the neurons.

Ultrastructural study of effect of ACTH4-10 on nerve regeneration; axons become larger in number and smaller in diameter

Electron-microscopic analysis of the regenerating sciatic nerve in the rat showed that ACTH4-10 treatment stimulated the number of regenerating myelinated and unmyelinated fibers to a similar degree. Fourteen days following a crush lesion of the sciatic nerve, 23% more regenerating fibers were present in the ACTH4-10-treated group of animals. The increase in number of regenerating fibers was accompanied by a comparable decrease in axon diameter. The ACTH4-10 treatment did not change the number of lamellae in the myelin sheath.

Stimulation by ACTH4-10 of nerve fiber regeneration following sciatic nerve crush

The number of newly formed myelinated nerve fibers was counted in the sciatic and tibial nerves in the rat following sciatic nerve crush. Beginning at days 8 and 14 in the sciatic and tibial nerve, respectively, the number of new myelinated fibers increased steadily and eventually exceeded the original number by 40 and 30%, respectively. This overshoot in nerve fibers was accompanied by the presence of clusters of fibers. Both the overshoot and the clusters disappeared at later stages and returned gradually to normal values within 3 months. Chronic administration of ACTH4-10 to the animals resulted in higher numbers of new myelinated nerve fibers throughout the process of regeneration. This stimulation was most pronounced (a three-fold increase) during the initial stages of regeneration. A higher number of myelinated nerve fibers was also observed in ACTH-treated rats 60 and 96 days after sciatic nerve crush. No changes in diameter of the fibers could be observed. The results are discussed in terms of a stimulation of the number of outgrowing nerve fibers caused by the peptide treatment.

Effects of corticotrophin (ACTH) on recovery of sensorimotor function in the rat: structure-activity study

The recovery of sensorimotor function in rats was studied using a foot-flick response test after crushing the sciatic nerve. Every other day, the animals received a subcutaneous injection of ACTH1-24 or vehicle, immediately after the 'foot-flick' test. Rats treated with ACTH1-24 showed a faster recovery of sensorimotor function as compared to vehicle-treated rats. This beneficial effect was dose-dependent. In contrast, no effect on toe-spreading could be detected. To investigate what part of the peptide molecule would contain the active site and to exclude steroid mediation, smaller sequences of ACTH1-24 devoid of corticotrophic activity were tested. Treatment with ACTH1-16NH2, ACTH4-10 or [Met(O2)4,D-Lys8,Phe9]ACTH4-9 (Org. 2766) mimicked the effect of ACTH1-24, whereas treatment with ACTH11-24 did not effect the return of sensorimotor function. The stimulatory effects of corticotrophin1-24 and congeners on recovery of sensorimotor function are discussed in terms of a direct effect of these peptides on nervous tissue, probably through enhanced brain and spinal cord protein synthesis.

Modulation of brain polyphosphoinositide metabolism by ACTH and beta-endorphin: structure-activity studies

This study describes effects of ACTH1-24 and beta-endorphin on brain polyphosphoinositide metabolism in vitro. The interconversion of these polyanionic phospholipids was studied by incubation of a lysed synaptosomal fraction with [gamma-32P]ATP. Of the membrane phospholipids only PA, DPI and TPI became labeled. The reference peptide ACTH1-24 stimulated the formation of TPI and inhibited the production of PA. For effects on TPI formation both the sequences ACTH5-7 and ACTH10-16 were needed. Effects on PA formation required the sequences ACTH7-10 and ACTH10-16. The basic amino acids in ACTH10-16 seemed to be of crucial importance for the peptide effects. A stimulatory effect on DPI was visible when ACTH was shortened from the N-terminus, and the essential information was in ACTH7-10. beta-endorphin inhibited PA formation and this effect was abolished by C-terminal shortening to gamma-endorphin. Other fragments of the C-terminus of beta-LPH, including the enkephalins, were ineffective. It is concluded that the structure-activity relationship on TPI/PA formation correlates with a similar relationship obtained on excessive grooming behavior in vivo. A possible correlation between the effects on polyPI metabolism and opiate-like effects, and effects on extinction of active avoidance behavior in vivo is discussed.

Biphasic modulation by ACTH-like peptides of protein synthesis in a cell-free system from rat brain

Brain protein synthesis in a cell-free system was stimulated by 10(-8) M-ACTH1-24. This stimulatory effect was completely inhibited by aurintricarboxylic acid (ATA), an inhibitor of reinitiation of new peptide chains. The N-terminal peptide sequence 4-10 exerted a biphasic modulation of cell-free protein synthesis, i.e., a stimulation at low concentrations (10(-8) and 10(-10) M) and an inhibition at a high concentration (10(-4) M). The D-isomer, ACTH4-10-7-D-phe, also showed a biphasic modulation that, however, was in a direction opposite to that shown by ACTH4-10-7-L-phe at 10(-8) M and 10(-4) M.

Pineal protein synthesis highly sensitive to ACTH-like neuropeptides

Pineal protein synthesis was studied in vitro over a period of 6-8 h after dissection. The level of protein synthetic activity of the pineal gland was greatly dependent on the time of dissection showing a maximum at midnight and a minimum at 10.00 h, 2 h after onset of light. Low concentrations of ACTH1-24 (down to 10(-11) M) could stimulate protein synthesis in vitro. The sensitivity to hormonal stimulation showed a circadian variation similar to that observed in the basal protein synthetic activity. Furthermore, overall synthetic activity appeared to be under neural influence. These neural and hormonal influences seemed to be mediated by beta-receptor stimulation and cyclic AMP. Structure-activity studies of the ACTH-effect on pineal protein synthesis gave results similar to those previously observed for excessive grooming behaviour, synaptic plasma membrane phosphorylation, adenylcyclase-activity and cell-free protein synthesis in brain. It was concluded, that overall pineal protein synthesis is both under neural and hormonal control. The action of ACTH on protein synthesis rate might be mediated by a calcium-dependent release of norepinephrine followed postsynaptically by beta-receptor activation, cAMP production, and stimulation of translation.

GTP-sensitive phosphorylation of proteins in a postmitochondrial supernatant from rat brainstem affected by ACTH1-24

The effect of ACTH1-24 and cyclic nucleotides on the endogenous phosphorylation of proteins from a postmitochondrial supernatant from rat brainstem was investigated in the presence and absence of GTP. Phosphorylation and its modulation by these compounds were studied in vitro by incorporation of labeled phosphate from [gamma-32P]ATP added to the incubation mixture. Phosphoproteins were subsequently analyzed by autoradiography after one- and two-dimensional separation. Eight ACTH-sensitive phosphoproteins of molecular weights 75 (IEP 4.0), 67, 64, 50 (IEP 4.7), 47 (IEP 4.8), 38, 34, and 24K were found. The effects of ACTH on phosphorylation were mainly inhibitory, and the affected protein bands did not coincide with the phosphoproteins sensitive to cyclic AMP and cyclic GMP. Phosphorylation of those phosphoprotein bands and its ACTH sensitivity appeared to be highly sensitive to GTP. It is suggested that the activity of protein kinases involved in hormone-sensitive phosphorylation in a postmitochondrial rat brainstem fraction is regulated by GTP-dependent mechanisms.