Comparison of the neuritogenic activity of cyclic nucleotides and skeletal muscle-conditioned medium on ciliary ganglia in vitro

Phosphodiesterases S-sulfhydration contributes to human skeletal muscle function

The increase in intracellular calcium is influenced by cyclic nucleotides (cAMP and cGMP) content, which rating is governed by phosphodiesterases (PDEs) activity.Despite it has been demonstrated a beneficial effect of PDEs inhibitors in different pathological conditions involving SKM, not much is known on the role exerted by cAMP-cGMP/PDEs axis in human SKM contractility. Here, we show that Ssulfhydration of PDEs modulates human SKM contractility in physiological and pathological conditions. Having previously demonstrated that, in the rare human syndrome Malignant Hyperthermia (MH), there is an overproduction of hydrogen sulfide (H 2S) within SKM contributing to hyper-contractility, here we have used MH negative diagnosed biopsies (MHN) as healthy SKM, and MH susceptible diagnosed biopsies (MHS) as a pathological model of SKM hypercontractility. The study has been performed on MHS and MHN human biopsies after diagnosis has been made and on primary SKM cells derived from both MHN and MHS biopsies. Our data demonstrate that in normal conditions PDEs are S-sulfhydrated in both quadriceps' biopsies and primary SKM cells. This post translational modification (PTM) negatively regulates PDEs activity with consequent increase of both cAMP and cGMP levels. In hypercontractile biopsies, due to an excessive H2S content, there is an enhanced Ssulfhydration of PDEs that further increases cyclic nucleotides levels contributing to SKM hyper-contractility. Thus, the identification of a new endogenous PTM modulating PDEs activity represents an advancement in SKM physiopathology understanding.

Influence of cAMP and protein kinase A on neurite length from spiral ganglion neurons

Regrowth of peripheral spiral ganglion neuron (SGN) fibers is a primary objective in efforts to improve cochlear implant outcomes and to potentially reinnervate regenerated hair cells. Cyclic adenosine monophosphate (cAMP) regulates neurite growth and guidance via activation of protein kinase A (PKA) and Exchange Protein directly Activated by Cylic AMP (Epac). Here we explored the effects of cAMP signaling on SGN neurite length in vitro. We find that the cAMP analog, cpt-cAMP, exerts a biphasic effect on neurite length; increasing length at lower concentrations and reducing length at higher concentrations. This biphasic response occurs in cultures plated on laminin, fibronectin, or tenascin C suggesting that it is not substrate dependent. cpt-cAMP also reduces SGN neurite branching. The Epac-specific agonist, 8-pCPT-2'-O-Me-cAMP, does not alter SGN neurite length. Constitutively active PKA isoforms strongly inhibit SGN neurite length similar to higher levels of cAMP. Chronic membrane depolarization activates PKA in SGNs and also inhibits SGN neurite length. However, inhibition of PKA fails to rescue neurite length in depolarized cultures implying that activation of PKA is not necessary for the inhibition of SGN neurite length by chronic depolarization. Expression of constitutively active phosphatidylinositol 3-kinase, but not c-Jun N-terminal kinase, isoforms partially rescues SGN neurite length in the presence of activated PKA. Taken together, these results suggest that activation of cAMP/PKA represents a potential strategy to enhance SGN fiber elongation following deafness; however such therapies will likely require careful titration so as to promote rather than inhibit nerve fiber regeneration.

Ganglioside potentiation of NGF-independent trophic agents on sensory ganglia

The ability of gangliosides to potentiate nerve growth factor (NGF)-independent trophic agents was determined by examining the capacity of an exogenous mixture of bovine brain gangliosides (BBG) and the monosialoganglioside GM1 to enhance the neuritogenic action of conditioned media (CM). CM were prepared with cultures of C6 glioma cells, neonatal rat astroglial cells, rat L6 myoblasts and chick embryonic skeletal muscle. Chick embryonic (9 day) dorsal root ganglia (DRG) were cultured on collagen-coated surfaces. The nutrient media with serum added or serum-free N1 medium were supplemented with 50% of one of the CM with or without BBG (150 micrograms/ml) or GM1 (150 micrograms/ml). The neuritogenic responses of DRG 48 h in vitro were evaluated microscopically on the basis of neurite length and number. The neurite promoting action of the factor(s) present in the various CM was potentiated by BBG or GM1 and resulted in increased neurite length and number.

Inhibition of conditioned media-mediated neuritogenesis of sensory ganglia by monoclonal antibodies to GM1 ganglioside

The monosialoganglioside GM1 can potentiate the neuritogenic activity of media conditioned by several cell types: neonatal glia, C6 glioma, embryonic chick heart or skeletal muscle and the rat myogenic line L6. To probe further the neuritogenic activity of conditioned media (CM), 5 mouse monoclonal antibodies (mAbs) against GM1, designated B6, C3, C4h2, D1 and D3 were incorporated individually into nutrient medium (NM) supplemented with CM prior to incubation with sensory ganglia. Nine-day embryonic chick dorsal root ganglia were explanted onto collagen-coated coverslips and incubated at 35 degrees C for 5 h in NM supplemented with 150 micrograms/ml GM1. After washing with NM, the explants were re-fed with NM + CM containing 20% mAb and cultured for an additional 43 h. The resultant neuritogenesis was evaluated microscopically by determining mean neurite number and length of randomly mixed cultures. The 5 antibodies differed in their capacities to inhibit CM-mediated neuritogenesis of these primed target cells. D1 and D3 were most effective in reducing neurite length and number produced by all sources of the CM, while C3 and C4h2 were intermediate in their inhibition of neurite initiation (number). The effect of B6 on neurite initiation and elongation was the least. The ability of these mAbs to inhibit neuritogenic activity of CM derived from both glial and myogenic tissue suggests that gangliosides play a basic role in neuronal development. The differing responses elicited by the individual mAbs may reflect a relationship between the structural complexity of the GM1 molecule and the neuritogenic mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Ganglioside potentiation of NGF-independent conditioned medium enhancement of neuritic outgrowth from spinal cord and ciliary ganglia explants

Culture medium conditioned (CM) by embryonic chick skeletal muscle or RN22 Schwannoma cells enhanced dramatically the neuritic development of chick embryonic spinal cord slices explanted onto a collagen substratum. The addition of a mixture of bovine brain gangliosides (BBG) or the monosialoganglioside GM1 to this medium potentiated the nerve growth factor (NGF)-independent CM-mediated neuritogenesis. A 3-4 fold increase in spinal cord outgrowth was due to increased neurite number, length and branching. The ability of the gangliosides to potentiate the positive neuritogenic action of CM was not limited solely to spinal cord cultures since similar results were obtained in parallel studies employing organized cultures of embryonic chick ciliary ganglia. These studies demonstrate the ability of gangliosides to enhance the trophic action of factor(s) present in CM. They suggest further that gangliosides may play a modulatory role in the development of the nervous system.

Cyclic nucleotide content of ciliary and dorsal root ganglia during embryonic development in the chick

The concentration of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) was measured in developing chick ciliary (CG) and dorsal root ganglia (DRG) as a function of embryonic age from day 8 through day 18 using radioimmunoassays. The concentration of cAMP and cGMP increased in both ganglia from day 8 through day 14. cAMP levels were nearly two-fold higher in DRG than in CG. Normalization of the data for ciliary ganglia to the number of cells per ganglion and calculation of their molar concentrations indicates a 48% increase in cGMP and a 3.2-fold increase in cAMP during the developmental process of natural neuronal cell death.