Development and regeneration of motor systems under the influence of ACTH peptides

Cell Reprogramming and Differentiation Utilizing Messenger RNA for Regenerative Medicine

The COVID-19 pandemic generated interest in the medicinal applications of messenger RNA (mRNA). It is expected that mRNA will be applied, not only to vaccines, but also to regenerative medicine. The purity of mRNA is important for its medicinal applications. However, the current mRNA synthesis techniques exhibit problems, including the contamination of undesired 5'-uncapped mRNA and double-stranded RNA. Recently, our group developed a completely capped mRNA synthesis technology that contributes to the progress of mRNA research. The introduction of chemically modified nucleosides, such as N1-methylpseudouridine and 5-methylcytidine, has been reported by Karikó and Weissman, opening a path for the practical application of mRNA for vaccines and regenerative medicine. Yamanaka reported the production of induced pluripotent stem cells (iPSCs) by introducing four types of genes using a retrovirus vector. iPSCs are widely used for research on regenerative medicine and the preparation of disease models to screen new drug candidates. Among the Yamanaka factors, Klf4 and c-Myc are oncogenes, and there is a risk of tumor development if these are integrated into genomic DNA. Therefore, regenerative medicine using mRNA, which poses no risk of genome insertion, has attracted attention. In this review, the author summarizes techniques for synthesizing mRNA and its application in regenerative medicine.

Melanocortins and opioids modulate early postnatal growth in rats

This study was undertaken to investigate the effects of melanocortins and opioids on rat early postnatal body and organ growth. Among melanocortins tested desacetyl-alpha-melanocyte-stimulating hormone (alpha-MSH) at dosages of 0.3 and 3 micrograms/g/day was effective in stimulating neonatal growth with a weight gain of 7 and 5.6%, respectively, after 2 weeks of treatment. Likewise, a weight rise of 4.2 and 3% was obtained with 3 micrograms/g/day of both alpha-MSH and Nle4-D-Phe7 alpha-MSH. As far as opioids were concerned, while N-acetyl-beta-endorphin (beta-End) was ineffective, the activity of beta-End was dependent on dosage. Indeed, newborns treated with 0.03 microgram/g/day showed a slight, but significant, increase in weight, whereas a marked decrease in growth followed treatment with 0.3 and, mainly, 3 micrograms/g/day, with a final weight loss of 3.4 and 5.5%, respectively. All melanocortins exerted a positive action on muscular and brain trophism and, in addition, desacetyl-alpha-MSH also induced a rise of fat deposits. On the contrary, while the 0.03 microgram/g/day beta-End dose caused an increase in muscular and brain weight, the higher dosages of the opioid were detrimental, not only for muscle and brain, but also for both liver and spleen weight. A slight, although significant (P < 0.05), enhancement of serum dehydroepiandrosterone sulfate (DHEAS) level was found after the injection of 0.3 microgram/g desacetyl-alpha-MSH, whereas both the 0.3 and 3 micrograms/g doses of desacetyl-alpha-MSH and the 3 micrograms/g dose of alpha-MSH determined the rise of plasma androstenedione (P < 0.05). All tested melanocortins and opioids failed to modify the concentrations of corticosterone. Our results suggest that melanocortins and opioids can modulate early postnatal growth in rats either by direct or indirect mechanisms.

Specificity versus redundancy of melanocortins in nerve regeneration

The results of the present study demonstrate that administration of the ACTH-(4-9) analogue Org 2766 acutely enhances behavioral, morphological, and biochemical recovery after nigrostriatal destruction. Animals treated with Org 2766 (10 micrograms/kg every 24 hr) demonstrated an acceleration of denervation supersensitivity and a significantly decreased ipsilateral rotational response, as compared to their saline counterparts. Upon evaluation of the mesolimbic DA system using open field behavior, peptide-treated rats demonstrated a compensatory response in their rearing behavior. Furthermore, tyrosine hydroxylase immunocytochemical analysis indicated an enhanced staining in the Org 2766-treated groups. This evaluation was confirmed and quantified using specific high-affinity dopamine uptake. The brains of animals treated with Org 2766 maintained higher uptake levels, suggesting a greater fiber density than the saline-treated animals. Although recovery via reinnervation is very unlikely in this short period of time, improved recovery may be the result of a protective effect of Org 2766 after administration of 6-OHDA into the substantia nigra. Thus, it appears that Org 2766 provides the rapid effects in this system, by both accelerating some compensatory mechanisms necessary for functional recovery and promoting cell survival by providing neuronal protection. However, it does not appear that this protection is due to NMDA receptor manipulation. Org 2766 neither mimicked the NMDA antagonist MK-801 behaviorally nor biochemically in binding displacement studies. Interestingly, other studies have suggested that only the full ACTH molecule, and fragments larger than ACTH-(1-17), demonstrated binding activity at micromolar concentrations, whereas the shorter, noncorticotropic fragments were either less active or inactive (Table 2). As for ACTH-(4-10) immunoreactivity, it appears that this neurotrophic fragment of ACTH reappears in adults following injury to the nigrostriatal system. In addition, the systemically administered ACTH-(4-9) analogue, Org 2766, seems to be gaining access to the CNS, but is only effective in the injured system. Therefore, based on the immunocytochemical localization of the ACTH-(4-10) fragment in neonatal brains and in the injured adult rat CNS, the interesting possibility may be raised that endogenous ACTH peptides appear during both ontogeny and regeneration. These studies demonstrate once again that biological responses to the family of ACTH/MSH peptides depend on the specific peptide fragment administered, its dosage, and the timing of the administration. Consequently, since early intervention is of vital importance in CNS recovery processes, synergistic administration of ACTH fragments and other neurotrophic agents may offer a viable approach with which to combat degeneration in the CNS.

Melanotropins as growth factors

Peptides that regulate the growth of tissues, whether in a positive or negative manner, are termed growth factors. The melanocortins, neurotrophic sequences that correspond to peptide fragments contained within ACTH-(1-13), beneficially affect neural growth during development and regeneration. Analogues of ACTH-(4-9) (Org 2766) and ACTH-(4-10) (BIM 22015) are capable of sustaining neurite outgrowth from cultured dorsal root ganglion and spinal cord cells in the absence of nerve growth factor. The development of sexually dimorphic behavior in both male and female rats is influenced by perinatal administration of ACTH. This change appears to be correlated with changes in the growth and metabolism of developing serotonergic and dopaminergic systems in the hypothalamic nuclei associated with male and female sexual behavior. Similar melanotropic influences are found in the developing neuromuscular system. Neuromuscular development is accelerated by perinatal administration of melanocortins, provoking both nerve and muscle to attain early maturation. However, the responding tissue varies pivotally with age: early in gestation, embryonic muscle is acutely sensitive to peptide exposure; but once innervation has occurred, only the developing nerve reacts to melanocortin treatment. Melanocortins have little if any effect on the normal, adult neuromuscular system. Following peripheral nerve injury or pathology, melanotropins once again become effective growth factors, accelerating and enhancing nerve regeneration and muscle reinnervation. Electrophysiological, morphological, biochemical, and functional tests all indicate that ACTH-(4-10), Org 2766, BIM 22015, and alpha-MSH improve various facets of nerve regeneration, the degree to which the specific parameter is improved being dependent on the peptide fragment, its dosage, and pattern of administration. BIM 22015, while less effective as a neurotrophic factor, has potent myotrophic effects that the other peptides lack. Org 2766 may provide some protective action to the injured CNS as demonstrated by tests of cognitive function following brain lesions, although evaluation of recovery is sometimes enigmatic. Recovery from destruction of the nigrostriatal system is more easily measured through tests of motor function and open field behavior, both of which support a protective role for Org 2766. Compensatory mechanisms, including the presence of increased tyrosine hydroxylase and greater density of dopaminergic fibers, may be involved. Melanocortins are effective growth factors in sciatic nerve regeneration in neonatal rats. Both alpha-MSH and ACTH-(4-10) favor the formation of morphologically normal end plates despite the trauma following nerve crush at postnatal day 2.(ABSTRACT TRUNCATED AT 400 WORDS)

A decade of changing perceptions about neuropeptides

The last decade has seen rapid growth in research with neuropeptides. During this time, we have been actively developing several concepts including the highly controversial one that peptides can cross the blood-brain barrier in intact form. One of the endogenous brain peptides used as a prototype for that concept, Tyr-MIF-1, also was used for the concept of the existence of endogenous antiopiate neuropeptides. As has been true for most novel developments in science, these concepts, as well as some older ones, were met with a great deal of skepticism when first suggested. Eventually, however, amnesia concerning the difficulties initially encountered with the introduction of new concepts occurs, with their subsequent "rediscovery" made easier.

ACTH/MSH(4-10) peptide increases postnatal metabolic activity of EDL muscle following early prenatal administration

ACTH/MSH(4-10) (10 micrograms/kg/b.i.d.; IP), administered to pregnant Sprague-Dawley rats during gestational days (GD) 3 to 12, significantly increased the metabolic activity of extensor digitorum longus (EDL) muscle at postnatal day 14. ACTH/MSH peptide, administered from day of birth to postnatal day 13, had no effect on EDL muscle metabolic activity using the 2,3,5-triphenyltetrazolium chloride indicator. By postnatal day 30, no differences were seen between the early prenatally treated group and saline controls. These results confirm our previous electrophysiological studies that showed that early prenatal ACTH/MSH(4-10) administration accelerates EDL muscle maturation.

Prenatal ontogenesis of pro-opiomelanocortin in the mouse central nervous system and pituitary gland: an in situ hybridization and immunocytochemical study

Pro-opiomelanocortin (POMC) mRNA detected by in situ hybridization and POMC/ACTH (adrenocorticotropin)-containing neurons detected by immunocytochemistry were first observed in the presumptive arcuate nucleus of embryonic mouse brain on gestational day 10.5 (E10.5). Immunostained fibers were also evident on E10.5 in the lateral and dorsal diencephalon. In these areas, a dense network of processes developed by E11.5 and extended into the mesencephalon. Fibers were detected in the myelencephalon at this stage and a day later (E12.5) in the spinal cord. Adult-like patterns of POMC/ACTH fibers were established in the diencephalon, mesencephalon, metencephalon and the myelencephalon between E13.5 and E15.5. POMC-expressing cells in the anterior and intermediate lobes of the pituitary gland appeared on E12.5 and E14.5, respectively. The early expression of POMC and the rapid establishment of dense fiber tracts in the brain is consistent with a role for POMC-derived peptides in the development of the central nervous system.

ACTH modulation of nerve development and regeneration

(1) The availability of short amino acid sequences of the naturally occurring ACTH 1-39 molecule has made it possible to separate the corticotropic characteristics of the parent molecule from its neurotrophic effects. Potent neurotrophic fragments are ACTH 4-10, an analog of ACTH 4-9 (Org 2766), and alpha-MSH (ACTH 1-13), peptide fragments that do not evoke corticosteroid secretion, yet clearly affect both the development and regeneration of peripheral nerve. (2) Early postnatal administration of either ACTH 4-10 or Org 2766 accelerates the neuromuscular development of the immature rat, increasing the contractile strength of the EDL muscle and inducing more rapid muscle contractions. Grasping strength and motor activity are increased; these are all changes indicative of more rapid neuromuscular maturation. Prenatal peptide treatment elicits a more complex pattern of response since administration early in gestation (GD 3-12) accelerates neuromuscular development whereas later administration (GD 13-21) decelerates maturation. (3) ACTH peptides have a similar accelerating effect on the morphology of the developing neuromuscular junction. At two weeks of age, nerve arborization is conspicuously increased by postnatal administration of either ACTH 4-10 or Org 2766, as is nerve terminal branching within the endplate itself. However, this is preceded by an initial depression of nerve branching in the 7-day-old rat pup. We conclude that while the developing neuromuscular system is sensitive to ACTH peptides, this susceptibility is age-related. The crucial role of these peptides may be limited to very brief, defined periods during which the peptides may interact with trophic or growth-associated substances, each of which may have its own decisive, circumscribed time frame of influence. (4) Perinatal administration of ACTH peptides affects CNS development. One measurable indication of this is an acceleration of eye opening. Early exposure to ACTH peptides has long-lasting effects on behavior, apparent when these animals are tested as adults. Increased spontaneous motor activity, heightened states of arousal and agitation, and changes in social behavior have been reported. Certain avoidance responses and tests of visual discrimination in male rats are improved by neonatal treatment with alpha-MSH. Overall motor activity is increased and the normal period of hyperactivity is initiated earlier. Male sexual behavior is decreased and sexually dimorphic behaviors in males are eliminated. alpha-MSH may alter the development of its own dopaminergic feedback circuitry while ACTH affects serotonin levels in the preoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of growth hormone treatment on the regeneration of rat sciatic nerve

The effect of human growth hormone (hGH) on regeneration of neuronal tissue have been studied in rats. A crush lesion was made on the sciatic nerve at the thigh level in intact or hypophysectomized rats. The hGH was administered systemically via subcutaneously implanted miniosmotic pumps. Regeneration was evaluated by the 'pinch-test' after 3, 4 and 6 days. Regeneration was significantly (P less than 0.05) impaired in hypophysectomized rats, but restored to normal after treatment with hGH (200 mIU/day). In intact rats treatment with 400 mIU/day hGH significantly (P less than 0.05) stimulated regeneration, whereas no effect was observed at 200 mIU/day. Immunoreactive insulin-like growth factor 1 (IGF-1) decreased in hypophysectomized rats, but rose again after hGH treatment. However, no consistent correlation between circulating IGF-1 and the rate of regeneration was found. Our results show that hGH can increase the rate of regeneration in peripheral nerves after injury. This can be due either to direct effects of hGH or to indirect effects via locally produced growth factors (e.g. somatomedins).

ACTH peptides stimulate motor nerve sprouting in development

Maturational changes at the neuromuscular junction (nmj) of rat neonates were studied using scanning electron microscopy and light microscopy that permitted quantification of muscle fiber diameter, length of nerve terminal branching, end-plate area, and perimeter. Administration of ACTH 4-10 (10 micrograms/kg s.c. daily from day of birth) stimulated nerve terminal branching, an effect most evident in 14-day-old pups. The trisubstituted derivative of ACTH 4-9 (Org 2766) when administered at 0.01 microgram/kg/daily, had a more potent effect, increasing end-plate perimeter and nerve terminal branching on the first postnatal week and markedly increasing only nerve terminal branching at 14 days of age. This is a dose-responsive action since 10 micrograms/kg/daily severely inhibits nerve sprouting. By 21 days, there were no differences between peptide- and saline-treated neonates. Peptide-induced sprouting was elicited only in the first 2 weeks of postnatal life. This time course corresponds with the critical period for nmj maturation and ceases when polyneuronal innervation of muscle fibers also terminates. It is suggested that ACTH peptides may exert a physiological role on nerve sprouting during development.

Neonatal neuromuscular parameters vary in susceptibility to postnatal ACTH/MSH 4-10 administration

Neonatal Sprague-Dawley rats administered the fragment of adrenocorticotropic hormone ACTH/MSH 4-10 (10 micrograms/kg/daily, SC) postnatally, show marked differences in the plasticity of the functional and morphological parameters of their neuromuscular system. Initial contraction durations of the immature fast muscle, extensor digitorum longus (EDL), are shorter than saline-treated controls indicating accelerated development. Qualitative studies of the developing EDL neuromuscular junctions as viewed by the scanning electron microscope and quantitative analysis permitted by light microscopy confirms that ACTH/MSH 4-10 affects the maturation of the endplate region. Motor behavior of rat pups demonstrates an age-related difference in the susceptibility to this peptide fragment; one week old neonates showing no response to ACTH/MSH 4-10, two week old pups showing an increase in motor activity. The results indicate that while the developing neuromuscular system is sensitive to the input of ACTH/MSH peptide treatment, this susceptibility is age-related.

Mammalian neuromuscular development accelerated with early but slowed with late gestational administration of ACTH peptide

The neuropeptide ACTH 4-10, a nonsteroidogenic fragment of adrenocorticotropic hormone, has two distinct and opposite effects on developing nerve and muscle. Muscle is positively influenced by ACTH during the first part of gestation (G days 3-12) before innervation occurs. Subsequent effects on innervation are largely depressive and exerted only during G13-21. Treatment during G3-12 increases twitch amplitude, rise time and speed of contraction of directly and indirectly stimulated extensor digitorum longus (EDL) muscle of two wk old rats. Treatment during G13-21 slows contractions of indirectly stimulated EDL, whereas treatment throughout gestation (G3-G21) shows little effect. Thus, ACTH first accelerates muscle development then modulates this development through neuronal depression.

ACTH 4-9 analog (Org 2766) improves qualitative and quantitative aspects of motor nerve regeneration

ACTH 1-39 and many of its fragments enhance regeneration of rat peripheral nerve and improve motor unit reorganization. The analog of ACTH 4-9 (Org 2766), with longer-lasting activity and greater biological potency for many parameters, was evaluated for its restorative powers on neuromuscular function following denervation. Org 2766 (10 micrograms/kg/48 hr IP) was administered to rats starting 3 hr after crush denervation of the extensor digitorum longus (EDL) muscle. Contractile strength, motor unit performance under low, optimum and high frequency stimulation, and number and size distribution of motor units of the EDL stimulated through the regenerating peroneal nerve were compared to saline-treated controls. Muscles of parallel animal groups were stimulated directly in vitro. Contractile strength and motor unit performance during high frequency stimulation were significantly improved by Org 2766 treatment at both 7 and 11 days after crush denervation. Org 2766 improves motor unit reformation both qualitatively (more small motor units that are highly resistant to fatigue) and quantitatively (stronger motor units). This peptide does not affect muscle contractile components. Prolonged treatment (21 days) with Org 2766 has a negative effect on motor unit performance, indicating that it exerts its favorable effects early in regeneration and exposure to this peptide should be limited to this period.