cAMP analogs promote survival and neurite outgrowth in cultures of rat sympathetic and sensory neurons independently of nerve growth factor.

Abstract

cAMP analogs promote survival and neurite outgrowth in cultures of rat sympathetic and sensory neurons independently of nerve growth factor (neurotrophic agents/neuronal regeneration/neuronal differentiaion/8-(4-chlorophenylthio)-cAMP/8-bromo-cAMP) RUSSELL E. RYDEL* AND LLOYD A. GREENEt Department of Pharmacology, New York University School of Medicine, 550 First Avenue, New York, NY 10016 Communicated by Rodolfo R. Llinas, September 8, 1987 (received for review May 8, 1987) ABSTRACT Nerve growth factor (NGF) is a neurotrophic agent for sympathetic and embryonic sensory neurons both in vivoi and in vitro. We report here that the membrane-permeant cAMP analogs, 8-(4-chlorophenylthio)-cAMP and 8-bromocAMP, can replace NGF in promoting long-term survival and neurite outgrowth in cultures of rat neonatal sympathetic and embryonic sensory neurons. N'-substituted analogs, including the more commonly used N6,02'-dibutyryl-cAMP, are less efficacious. Additivity and switching experiments indicate that the cAMP analogs affect the same neuronal population as that maintained by NGF. However, unlike NGF, the cAMP analogs do not evoke somatic hypertrophy. Moreover, studies with sympathetic neurons reveal that the neurotrophic actions of the cAMP analogs, but not of NGF, are blocked by the axial diastereoisomer of adenosine 3',5'-phosphorothioate, a competitive cAMP antagonist. Thus, the mechanism by which cAMP analogs promote neuronal survival and differentiation appears to involve activation of cAMP-dependent protein kinases, whereas, in contrast, the same effects of NGF neither require nor are mediated by such a pathway. Furthermore, the different efficacies observed with N6-and C8-substituted cAMP analogs suggest that this neurotrophic pathway may involve differential activation of the regulatory subunits of cAMP-dependent protein kinases. The presence of this parallel, cAMP-responsive, neurotrophic pathway in at least two types of NGF-responsive neurons may be developmentally important and has the potential to be exploited for the treatment of injuries or diseases affecting these and possibly other nerve cells.A wide variety of extracellular signals, both inside and outside the nervous system, produce many of their diverse responses by regulating the phosphorylation of specific proteins. In particular, protein phosphorylation has been implicated as a molecular mechanism by which extracellular signals regulate various intracellular functions in nervous tissue, including neuronal excitability, neurotransmitter biosynthesis and release, and also neuronal growth, differentiation, and morphology (reviewed in ref. 1). One mechanism by which many extracellular signals regulate protein phosphorylation involves the synthesis of cAMP and subsequent activation of its target enzymes, the cAMP-dependent protein kinases (reviewed in ref.2). In vertebrate nervous tissue, the regulatory subunits of cAMP-dependent protein kinases appear to be the major, if not the only, proteins that bind and are activated by cAMP (3, 4).One of the...

Trophic Support of Cultured Spiral Ganglion Neurons by Depolarization Exceeds and Is Additive with that by Neurotrophins or cAMP and Requires Elevation of [Ca2+]iwithin a Set Range

“…We show here that cpt-cAMP promoted SGN survival and neurite length comparable with that in neurotrophins, but cell somata and neurites appeared shrunken and thin, unlike their appearance in 30K or neurotrophins. Rydel and Greene (1988) found that NGF promoted sympathetic neuron somatic hypertrophy and neurite growth to a much greater degree than did cAMP analogs. However, in sympathetic neurons, cAMP analogs did not antagonize somatic or neuritic growth promoted by NGF nor antagonize growth in neurons plated on laminin, whereas SGNs maintained with cpt-cAMP have shrunken somata and thin neurites, even in the presence of laminin and neurotrophins.…”

“…Permeant cAMP analogs have been shown previously to promote sympathetic neuronal survival (Rydel and Greene, 1988). This may be relevant to support by afferent input in vivo, because neurotransmitters can stimulate adenylate cyclase activity.…”

“…Ca 2ϩ and cAMP function in intracellular pathways that are distinct from each other and from the pathway used by neurotrophin signal transduction. Trophic support of sympathetic or sensory neurons by NGF does not require cAMP signaling (Rydel and Greene, 1988), nor does trophic support of cerebellar granule cells by peptide growth factors of cAMP require increased [Ca 2ϩ ] i (Galli et al, 1995). Additivity among depolarization, peptide neurotrophic factor, and substratum in the trophic support of cultured ciliary ganglion neurons (Schmidt and Kater, 1993) appears to depend on the recruitment of different intracellular signals by laminin and depolarization (Schmidt and Kater, 1995).…”

Melanocortin receptors mediate α-MSH-induced stimulation of neurite outgrowth in neuro 2A cells

“…Daily injections with dibutyryl cAMP (dbcAMP) enhanced the recovery of sensorimotor function in rats after a sciatic nerve crush [28]. cAMP analogs promote neurite outgrowth in cultures of rat sympathetic and sensory neurons [31]. The stimulation of neurite outgrowth by forskolin and/or dbcAMP has been reported for several neuroblastoma cell lines [22,23,27].…”

Nedd2 Is Required for Apoptosis after Trophic Factor Withdrawal, But Not Superoxide Dismutase (SOD1) Downregulation, in Sympathetic Neurons and PC12 Cells

“…The initiating mechanisms of death seem to be distinct in each instance. Apoptosis triggered by NGF deprivation is blocked by cAMP analogs (Rydel and Greene, 1988;Rukenstein et al, 1991) and high concentrations of N-acetylcysteine (Ferrari et al, 1995), whereas these agents do not inhibit death induced by downregulation of SOD1 (Troy et al, 1996a,c). In contrast, the latter is blocked by vitamin E (Troy and Shelanski, 1994) and inhibitors of nitric oxide (NO) synthase (Troy et al, 1996a), which have no effect on apoptosis evoked by NGF withdrawal (Ferrari et al, 1995;Farinelli et al, 1996).…”