Localization of 2',3'-cyclic nucleotide-3'-phosphohydrolase within the vertebrate retina

Ca2+-dependent permeability transition regulation in rat brain mitochondria by 2',3'-cyclic nucleotides and 2',3'-cyclic nucleotide 3'-phosphodiesterase

Recent evidence indicates that 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), a marker enzyme of myelin and oligodendrocytes, is also present in neural and nonneural mitochondria. However, its role in mitochondria is still completely unclear. We found CNP in rat brain mitochondria and studied the effects of CNP substrates, 2',3'-cyclic nucleotides, on functional parameters of rat brain mitochondria. 2',3'-cAMP and 2',3'-cNADP stimulated Ca(2+) overload-induced Ca(2+) release from mitochondrial matrix. This Ca(2+) release under threshold Ca(2+) load correlated with membrane potential dissipation and mitochondrial swelling. The effects of 2',3'-cyclic nucleotides were suppressed by cyclosporin A, a potent inhibitor of permeability transition (PT). PT development is a key stage in initiation of apoptotic mitochondria-induced cell death. 2',3'-cAMP effects were observed on the functions of rat brain mitochondria only when PT was developed. This demonstrates involvement of 2',3'-cAMP in PT regulation in rat brain mitochondria. We also discovered that, under PT development, the specific enzymatic activity of CNP was reduced. Thus we hypothesize that suppression of CNP activity under threshold Ca(2+) load leads to elevation of 2',3'-cAMP levels that, in turn, promote PT development in rat brain mitochondria. Similar effects of 2',3'-cyclic nucleotides were observed in rat liver mitochondria. Involvement of CNP in PT regulation was confirmed in experiments using mitochondria from CNP-knockdown oligodendrocytes (OLN93 cells). CNP reduction in these mitochondria correlated with lowering the threshold for Ca(2+) overload-induced Ca(2+) release. Thus our results reveal a new function for CNP and 2',3'-cAMP in mitochondria, being a regulator/promotor of mitochondrial PT.

Expression of a catalytically inactive transmembrane protein tyrosine phosphatase epsilon (tm-PTP epsilon) delays optic nerve myelination

Reversible tyrosine phosphorylation is integral to the process of oligodendrocyte differentiation. To interfere with the subset of the phosphorylation cycle overseen by protein tyrosine phosphatase epsilon (PTP epsilon) in oligodendrocytes, we applied a substrate-trapping approach in the development of transgenic mice overexpressing a catalytically inactive, transmembrane PTP epsilon-hemaglutinin (tm-PTP epsilon-HA) from the dual promoter element of the gene encoding the myelin protein 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP). Transgene expression peaked during the active myelinating period, at 2-3 weeks postnatal. Two tyrosine phosphoproteins, alpha-enolase and beta-actin, were phosphorylated to a greater degree in transgenic mice. Despite a high degree of tm-PTP epsilon-HA expression, myelin was grossly normal in nearly all axonal tracts. Phenotypic abnormalities were limited to optic nerve, where a decrease in the degree of myelination was reflected by reduced levels of myelin proteins on postnatal day 21 (PND21), as well as a decrease in the density of differentiated oligodendrocytes. The optic chiasm was reduced in thickness in transgenic mice; optic nerves similarly exhibited a reduction in transverse width. Further analyses of the optic pathway demonstrated that transgenic protein was unexpectedly present in retinal ganglion cells, whose axons are the targets of myelination by optic nerve oligodendrocytes. On PND28, transgenic protein declined dramatically in both oligodendrocytes and retinal ganglion cells contributing to the recovery of optic nerve myelination. Thus, delayed myelination arises only when tm-PTP epsilon-HA is simultaneously expressed in myelin-forming glia and their neuronal targets. While tm-PTP epsilon related signaling pathways may figure in axon-glial interactions, interfering with tm-PTP epsilon activity does not perceptibly affect the development or myelinating capacity of most oligodendrocytes.

Secreted peptides as regulators of neuron-glia and glia-glia interactions in the developing nervous system

Secreted peptides of the nervous system help to regulate neuron-glia and glia-glia interactions during development. These regulatory factors, referred to as glia-promoting factors (GPFs), act on specific classes of glia and include oligodendroglia-stimulating peptides, interleukin-1 (IL-1), colony-stimulating factors (CSF), and fibroblast growth factor (FGF). The maturity of secretory and target cells determines, in part, the ability of a factor to influence glial proliferation, activation, or differentiation. During neural development, GPFs help to control such fundamentally important events as cell movement, neurite outgrowth, and myelination.

CNPase activity in the vertebrate retina, retinal pigmented epithelium, and choroid

The activity of the enzyme 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase, E.C.3.1.4.37) has been studied in the retina of three vertebrate species. Activity was highest in the goldfish, followed by Xenopus laevis and Rana pipiens. Also, high activity levels were found in goldfish retinal pigment epithelium and choroid, but not in the other two species. When added to in vitro culture systems, 2',3'-cyclic nucleotides were found to have no effect on goldfish cone retinomotor movement, but caused a marked inhibition of Rana pipiens rod outer segment disc membrane shedding. It is suggested that CNPase may play a role in cellular processes requiring membrane structural reorganization.

The distribution of 2':3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in the CNS of normal (+/+) and shiverer (Shi/Shi) mice

Immunohistochemical techniques were utilized to localize the putative myelin enzyme 2':3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in the central nervous system (CNS) of normal (+/+) and Shiverer (Shi/Shi) mice (Mus musculus). CNP appeared to be only associated with myelinated nerve fibers in the CNS (corpus callosum, subcortical white matter, caudate nucleus, cerebellum and medulla oblongata) of +/+ mice. However, little or no immunostaining was observed in the same regions of the CNS of Shi/Shi mice, although these mice have normal levels of a CNS CNP activity. Unexpectedly, oligodendrocytes (cell periphery) were not stained for CNP in either +/+ or Shi/Shi mice, although erythrocytes were immunostained.

An immunochemical investigation of 2':3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in bovine cerebrum and human oligodendroglioma

Bovine cerebrum, including the corpus callosum, and a human oligodendroglioma were investigated by an immunohistochemical technique to determine the distribution of 2':3'-cyclic nucleotide 3'-phosphodiesterase (CNP). Also, three human oligodendrogliomas (ODG) were characterized by an immunoblot procedure to identify a protein(s) with cross-reacting determinants to CNP and assayed for CNP activity. CNP was localized to oligodendrocytes in the corpus callosum and subcortical white matter and gray matter. Also, nerve fibers appeared to be stained. Further, cells of the human oligodendroglioma were immunostained which were similar in morphology to those cells stained in the bovine cerebrum; however, fewer than 5% of the oligodendroglioma cells were immunostained. Immunoblotting revealed two separate and distinct bands for the three oligodendrogliomas, showing cross-reactivity to bovine CNP antisera at about 53,000 and 46,000 daltons. Specific CNP activity of the three human oligodendrogliomas ranged from 0.4 to 1.6 mumole of 2':3'-cAMP hydrolyzed/min/mg protein.