Polyamines affect growth of cultured rat cerebellar neurons in different sera

Utilization of Aminoguanidine Prevents Cytotoxic Effects of Semen

Studies of human semen in cell or tissue culture are hampered by the high cytotoxic activity of this body fluid. The components responsible for the cell damaging activity of semen are amine oxidases, which convert abundant polyamines, such as spermine or spermidine in seminal plasma into toxic intermediates. Amine oxidases are naturally present at low concentrations in seminal plasma and at high concentrations in fetal calf serum, a commonly used cell culture supplement. Here, we show that, in the presence of fetal calf serum, seminal plasma, as well as the polyamines spermine and spermidine, are highly cytotoxic to immortalized cells, primary blood mononuclear cells, and vaginal tissue. Thus, experiments investigating the effect of polyamines and seminal plasma on cellular functions should be performed with great caution, considering the confounding cytotoxic effects. The addition of the amine oxidase inhibitor aminoguanidine to fetal calf serum and/or the utilization of serum-free medium greatly reduced this serum-induced cytotoxicity of polyamines and seminal plasma in cell lines, primary cells, and tissues and, thus, should be implemented in all future studies analyzing the role of polyamines and semen on cellular functions.

α-synuclein aggregation and its modulation

Parkinson's disease (PD) is a neurological disorder marked by the presence of cytoplasmic inclusions, Lewy bodies (LBs) and Lewy neurites (LNs) as well as the degeneration of dopamine producing neurons in the substantia nigra region of the brain. The LBs and LNs in PD are mainly composed of aggregated form of a presynaptic protein, α-synuclein (α-Syn). However, the mechanisms of α-Syn aggregation and actual aggregated species responsible for the degeneration of dopaminergic neurons have not yet been resolved. Despite the fact that α-Syn aggregation in LBs and LNs is crucial and mutations of α-Syn are associated with early onset PD, it is really a challenging task to establish a correlation between α-Syn aggregation rate and PD pathogenesis. Regardless of strong genetic contribution, PD is mostly sporadic and familial forms of the disease represent only a minor part (<10%) of all cases. The complexity in PD further increases due to the involvement of several cellular factors in the pathogenesis of the disease as well as the environmental factors associated with the risk of developing PD. Therefore, effect of these factors on α-Syn aggregation pathway and how these factors modulate the properties of wild type (WT) as well as mutated α-Syn should be collectively taken into account. The present review specifically provides an overview of recent research on α-Syn aggregation pathways and its modulation by several cellular factors potentially relevant to PD pathogenesis. We also briefly discuss about effect of environmental risk factors on α-Syn aggregation.

Spermine binding to Parkinson's protein alpha-synuclein and its disease-related A30P and A53T mutants

Aggregation of alpha-synuclein (alpha-syn), a protein implicated in Parkinson's disease (PD), is believed to progress through formation of a partially folded intermediate. Using nanoelectrospray ionization (nano-ESI) mass spectrometry combined with ion mobility measurements we found evidence for a highly compact partially folded family of structures for alpha-syn and its disease-related A53T mutant with net charges of -6, -7, and -8. For the other early onset PD mutant, A30P, this highly compact population was only evident when the protein had a net charge of -6. When bound to spermine near physiologic pH, all three proteins underwent a charge reduction from the favored solution charge state of -10 to a net charge of -6. This charge reduction is accompanied by a dramatic size reduction of about a factor of 2 (cross section of 2600 A2 (-10 charge state) down to 1430 A2 (-6 charge state)). We conclude that spermine increases the aggregation rate of alpha-syn by inducing a collapsed conformation, which then proceeds to form aggregates.

Astroglia growth retardation and increased microglia proliferation by lithium and ornithine decarboxylase inhibitor in rat cerebellar cultures: Cytotoxicity by combined lithium and polyamine inhibition

Lithium, the most prevalent treatment for manic-depressive illness, might have a neuroprotective effect after brain injury. In culture, lithium can exert neurotoxic effects associated with reduction in polyamine synthesis but neuroprotective effects as cultured neurons mature. Cumulative evidence suggests that lithium may exert some of its effects on neurons indirectly, by initially acting on glial cells. We used rat cerebellar cultures to ascertain the effects of lithium on ornithine decarboxylase (ODC) activity, the enzyme catalyzing the first step in polyamine synthesis, and to compare effects of lithium with those of the ODC inhibitor alpha-difluoromethylornithine (DFMO) on neuron survival and glial growth. Switching cultures from high (25 mM) to low (5 mM) KCl concentrations served as the traumatic neuronal insult. The results indicate the following. 1) Whereas high depolarizing KCl concentration enhances neuron survival, it inhibits astroglial growth. 2) Lithium (LiCl; 1-5 mM) enhances neuronal survival but inhibits astroglial growth. 3) Lithium treatment leads to reduced ODC activity. 4) DFMO enhances neuron survival but inhibits astroglial growth. 5) Lithium and DFMO lead to transformation of astroglia from epithelioid (flat) to process-bearing morphology and to increased numbers of microglia. 6) Combined lithium plus DFMO treatment is cytolethal to both neurons and glia in culture. In conclusion, lithium treatment results in growth retardation and altered cell morphology of cultured astroglia and increased microglia proliferation, and these effects may be associated with inhibition of polyamine synthesis. This implies that direct effects on astrocytes and microglia may contribute to the effects of lithium on neurons.

Modified single-stranded oligonucleotides inhibit aggregate formation and toxicity induced by expanded polyglutamine

Huntington's disease (HD) is caused by an increase in the length of the poly(Q) tract in the huntingtin (Htt) protein, which changes its solubility and induces aggregation. Aggregation occurs in two general phases, nucleation and elongation, and agents designed to block either phase are being considered as potential therapeutics. We demonstrate that inclusion formation can be retarded by introducing modified, single-stranded oligonucleotides into a model neuronal cell line. This cell-based assay is used in conjunction with a standardized biochemical assay to identify molecules that can disrupt the process of aggregate formation. Active oligonucleotides include a 6-mer containing a single phosphorothioate linkage on each terminus, a 53-mer and a 9-mer containing three phosphorothioate linkages at each end, and a 25-mer consisting of all modified RNA residues. The disruption process directed by the active oligonucleotides appears to be independent of sequence specificity and complementarity. In contrast, the activity is more dependent on the type of chemical modifications contained within the oligonucleotide. Some oligonucleotides that demonstrated inhibition activity were also found to extend the life span of PC12 cells after the toxic Htt aggregation process was induced. Our data provide the first evidence that short synthetic oligonucleotides inhibit a fundamental pathological pathway of HD and may provide the basis for a novel therapeutic approach.

Substrate specificity of the bovine serum amine oxidase and in situ characterisation of aminoaldehydes by NMR spectroscopy

The oxidation of spermidine or homospermidine with bovine serum amine oxidase (BSAO) was monitored in situ, using proton nuclear magnetic resonance spectroscopy in water with 10% D(2)O. NMR assignments were performed by spin decoupling and COSY spectra or by comparison with data from synthetic aminoaldehydes. The results represent the first in situ characterisation of the highly reactive aminoaldehydes and showed oxidation at the N(1) amino group of spermidine and homospermidine. Comparison of homospermidine with a variety of substrates revealed that among straight chain di- and polyamines both an aminopropyl group and two primary amino groups separated by seven (norspermidine) or eight (spermidine) carbon atoms were required for optimal substrate ability. However, highest activity was seen with the substrate N-(4-aminobutyl)hexahydropyrimidine, showing that the substrate channel of BSAO has a dual substrate preference, with moderately bulky substituents at the distal end of a diamine contributing equally well as an alkyl amino group. Cytotoxic investigations of a variety of substrates for BSAO, confirmed previous results, that cytotoxicity is primarily linked to polyamines encompassing the aminopropyl moiety. No acrolein was observed at any time during the oxidation showing that it reacts very fast with available amino groups forming a variety of derivatives.

Cellular polyamines promote the aggregation of alpha-synuclein

The cellular polyamines putrescine, spermidine, and spermine accelerate the aggregation and fibrillization of alpha-synuclein, the major protein component of Lewy bodies associated with Parkinson's disease. Circular dichroism and fluorometric thioflavin T kinetic studies showed a transition of alpha-synuclein from unaggregated to highly aggregated states, characterized by lag and transition phases. In the presence of polyamines, both the lag and transition times were significantly shorter. All three polyamines accelerated the aggregation and fibrillization of alpha-synuclein to a degree that increased with the total charge, length, and concentration of the polyamine. Electron and scanning force microscopy of the reaction products after the lag phase revealed the presence of aggregated particles (protofibrils) and small fibrils. At the end of the transition phase, alpha-synuclein formed long fibrils in all cases, although some morphological variations were apparent. In the presence of polyamines, fibrils formed large networks leading ultimately to condensed aggregates. In the absence of polyamines, fibrils were mostly isolated. We conclude that the polyamines at physiological concentrations can modulate the propensity of alpha-synuclein to form fibrils and may hence play a role in the formation of cytosolic alpha-synuclein aggregates.

Polyamines prevent apoptotic cell death in cultured cerebellar granule neurons

Polyamines play critical roles during the development of brain neurons. In the present study we examined the effects of polyamines on neuronal apoptotic death. Rat cerebellar granule neurons were cultured in the presence of a depolarizing concentration of KCl (25 mM) in the medium. Apoptotic neuronal death was induced by changing the medium to that containing 5.6 mM KCl without serum. Spermine as well as spermidine and putrescine prevented cell death in a concentration-dependent manner with the order of potency being spermine > spermidine > putrescine. The effect of spermine was partially blocked by several NMDA-type glutamate receptor antagonists including (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801). MK-801-sensitive neuroprotection by spermine depended on cell density. Activation of CPP32 (caspase-3/Yama/apopain)-like proteolytic activity, a key mediator of apoptosis, precedes neuronal death, and polyamines prevented an increase in this activity. These results demonstrate that polyamines protect neurons from apoptotic cell death through both NMDA receptor-dependent and -independent mechanisms, acting upstream from the activation of CPP32-like protease(s).

Agmatine treatment is neuroprotective in rodent brain injury models

Agmatine is a naturally occurring guanidino compound, found in bacteria and plants, with several proposed nervous system-related functions suggestive of beneficial effects in central nervous system injury. Here evidence is presented that agmatine can exert potent neuroprotection in both in vitro and in vivo rodent models of neurotoxic and ischemic brain injuries. The cumulative evidence lead us to suggest that agmatine, a relatively nontoxic compound, be tried for potential therapeutic use after neurotrauma and in neurodegenerative disorders.

Chemotaxis and accumulation of nerve growth factor by microglia and macrophages

Astrocytes and microglia play a critical role in the reaction of the central nervous system (CNS) to trauma. Although both astrocytes and microglia can produce it, accumulation of immunoreactive nerve growth factor (the prototype neurotrophin important for the survival of several classes of neurons) was observed selectively in cultured microglia and macrophages, rather than in astrocytes. Furthermore, microglia were found to display chemotaxis toward a localized source of nerve growth factor and, as demonstrated by autoradiography, take up extracellular nerve growth factor. These findings suggest that microglia, the brain's own macrophages, participate in the regulation of nerve growth factor availability in a site-specific manner. This novel function may assume a general importance both in the CNS and the peripheral nervous system at critical times after trauma when this neurotrophin is needed for nerve cell survival.

Lithium exerts a time-dependent and tissue-selective attenuation of the dexamethasone-induced polyamine response in rat brain and liver

It has previously been shown that chronic, but not acute, lithium treatment indirectly prevents the dexamethasone-induced increase in brain polyamine-metabolizing enzymes. In the present study we determined the effects of lithium treatment on changes in cellular polyamines, 6 h after dexamethasone challenge (3 mg/kg intraperitoneally). The findings demonstrate that chronic lithium (daily intraperitoneal 2.5 mmol/kg injections for 2 weeks) treatment completely prevents the accumulation of putrescine, in parallel to its prevention of the dexamethasone-induced increase in ornithine decarboxylase activity. A partial attenuation of this polyamine response was also observed in the liver. Only minor and inconsistent changes were observed in the concentrations of the polyamines, spermidine and spermine. Acute lithium treatment (a single injection at times ranging from 1 to 24 h prior to dexamethasone challenge) did not attenuate the dexamethasone-induced increases in brain putrescine concentration nor in ornithine decarboxylase activity. It is suggested that prevention of the stress-induced polyamine response in the brain may be an important mechanism through which prophylactic lithium may exert its beneficial effect in manic-depressive illness.

Depletion of polyamines prevents the neurotrophic activity of the GABA-agonist THIP in cultured rat cerebellar granule cells

Effects of polyamine depletion by alpha-difluoromethylornithine (DFMO) were studied on the GABA-agonist mediated enhancement of the morphological development of cultured rat cerebellar granule cells. An increase in the number of neurite extending cells and in the cytoplasmic density of organelles relevant for protein synthesis was observed upon culturing in the presence of 4,5,6,7-tetrahydro-isoxazole[5,4-c]pyridin-3-ol (THIP) for 4 days. The intracellular concentrations of putrescine, spermidine, and spermine in these cultures were similar to the concentrations of the polyamines observed in cultures grown in a plain culture medium for 1, 2, 3 or 4 days, respectively. Upon culturing in the simultaneous presence of THIP and DFMO, the concentrations of putrescine and spermadine were reduced to less than 20% of the levels in the controls. This depletion was associated with a severely impaired morphological development of the granule cell cultures. Thus, the number of neurite extending cells was reduced to 50% of the number in the control cultures upon culturing in the presence of DFMO alone or in combination with THIP. Moreover, the THIP mediated increase in the cytoplasmic density of rough endoplasmic reticulum, Golgi apparatus and different types of vesicles was prevented by the exposure to DFMO.

Polyamines in rat brain extracellular space after ischemia

This article reports measurements of extracellular polyamines in rat brain. Microdialysis probes were implanted in the striatum and microperfusion samples were collected before, during, and after transient (20 min) global ischemia. Polyamine levels in microperfusates were measured by reverse-phase high-performance liquid chromatography after precolumn derivatization. No significant changes in extracellular polyamines were detected for up to 3 h following ischemia. We conclude that extracellular levels of polyamines (1) are comparable to the low levels in other extracellular compartments, and (2) do not change during the initial period of reperfusion, the period most critical for neuron survival after ischemia.

Effect of the substrate on neurofilament phosphorylation in mixed cultures of rat embryo spinal cord and dorsal root ganglia

The effect of the substrate on neurofilament phosphorylation was studied in primary cultures of spinal cord and dorsal root ganglia dissociated from 15-day-old rat embryos. On polylysine and Primaria substrates, spinal cord neurons formed aggregates connected by bundles of neurites. (Primaria dishes have a modified plastic surface with a net positive charge). On both polylysine and Primaria substrates, spinal cord neurons were stained with neurofilament monoclonal antibodies reacting with phosphorylated epitopes appearing early in rat embryo development, i.e. soon after neurofilament expression. Conversely, immunoreactivity with antibodies recognizing late phosphorylation events was only observed on Primaria substrates. As reported by many investigators, fibronectin and laminin were excellent substrates for dorsal root ganglia neurons in culture. However, on both laminin and fibronectin substrates immunoreactivity with antibodies recognizing late phosphorylation events, was only observed on Primaria substrates. As reported by many investigators, fibronectin and laminin were excellent substrates for dorsal root ganglia neurons in culture. However, on both laminin and fibronectin substrates immunoreactivity with antibodies recognizing late phosphorylation events, only occurred after several days in culture, at a time when non-neuronal cells (mainly astrocytes) had formed a confluent monolayer.

Dibutyryl cyclic AMP-induced changes in neuron-astroglia interactions and fibronectin immunocytochemistry in dissociated rat cerebellar cultures

In mixed primary embryonic CNS cultures flat astroglia grow exclusively underneath the initially formed neuronal network. This invasive under-growth results in neuronal detachment and degeneration. The present study sought to find out whether or not morphological differentiation of astroglia, from flat to process-bearing cells, could alter astroglial-neuronal growth relationships in rat cerebellar cultures. Morphological differentiation of astroglia was induced by treatment with dibutyryl cyclic AMP. The results demonstrate that in contrast to flat astroglia, large stellate astroglia can grow over the neurite bundles, and that in these dibutyryl cyclic AMP-treated cultures neurons can persist. Immunocytochemical studies show that the extracellular matrix protein fibronectin is present in these cultures and appears to be associated with flat astroglia rather than with stellate astroglia. The study indicates that in the presence of dibutyryl cyclic AMP transformed stellate astroglia interact differently with neurons and with the growth substratum as compared with flat astroglia.

Effects of glycosaminoglycans and proteinase inhibitors on astroglia-induced detachment of cultured rat cerebellar neurons

Neurons in mixed primary embryonic CNS cultures degenerate secondary to their detachment from the substratum. The present study demonstrates that in primary cultures of postnatal cerebellum, detachment of neurons can be prevented by antiproliferative drugs which inhibit the growth of astroglia. Several types of proteinase inhibitors did not affect the process of detachment. However, among several types of glycosaminoglycans, heparan sulfate and to a lesser degree heparin, could reversibly inhibit neuron detachment without causing morphological changes of astroglia. The enzymes heparitinase and heparinase caused neuron detachment but only within the first 24-48 hr after plating and not in older cultures. We conclude: (1) cerebellar interneurons in culture are not dependent on astroglia for their survival; (2) astroglia are most probably responsible for neuron detachment via a membrane associated activity and (3) heparan sulfate-like glycosaminoglycans are important in neuron-substratum attachment.

Vimentin-GFAP transition in primary dissociated cultures of rat embryo spinal cord

Primary dissociated cultures derived from 15-day-old rat embryo spinal cord with or without dorsal root ganglia (DRG) were grown on polylysine, Primaria and laminin substrates. On polylysine and Primaria substrates, spinal cord neurons formed aggregates connected by bundles of neurites in a distinctive pattern similar to that observed in cultures derived from embryonal rat brain and neonatal rat cerebellum. After 2 days in culture, the number of cells stained with GFAP antibodies progressively increased within the vimentin-positive monolayer surrounding the neuronal aggregates. These astrocytes had the typical appearance of astrocytes in primary dissociated cultures derived from late fetal or early neonatal murine brain, i.e. large flat or stellate cells with thick processes staining equally well with GFAP and vimentin antibodies. Astrocytes found within the neuronal aggregates in 4-5 day cultures were markedly different, i.e. small stellate cells with slender processes forming a delicate mesh throughout the aggregate. These GFAP-positive cells stained only weakly with vimentin antibodies. Spinal cord neurons formed aggregates on laminin substrates but failed to extend neurites and rapidly degenerated. The large flat cells in the surrounding monolayer gradually invaded the aggregates. These cells stained with both GFAP and vimentin antibodies. DRG neurons developed equally well on Primaria and laminin substrates, extending their neurites on the vimentin-positive flat cells forming the monolayer regardless of their reactivity with GFAP antibodies.

Astroglia-induced detachment of central neurons but astroglia-dependent growth of peripheral neurons in rat embryonic spinal cord primary cultures

In mixed primary cultures, intrinsic neurons from embryonic mammalian brains degenerate secondary to their detachment from the substratum and this is caused by the under-growing co-cultured astroglia. In the present study we sought to find out whether or not peripheral neurons, sensory and motor neurons which reside and/or only project outside the CNS respectively, interact with astroglia similarly as their central counterparts do. Mixed primary cultures prepared from dissociated embryonic rat spinal cord and dorsal root ganglia were examined by phase and immunofluorescence microscopy after labeling with antibodies to neurofilaments (neuronal markers) and to glial fibrillary acidic protein and vimentin (astroglia markers). Acetylcholinesterase staining served as a marker for motor neurons. In this system astroglia grew exclusively under intrinsic neurons of the spinal cord and with time (about 8 days) all these neurons detached and disappeared. In contrast, astroglia were intimately associated with perikarya of peripheral neurons, sometimes growing over them. Furthermore, the neuritic processes of these neurons were attached to the undergrowing astroglia. Central neurons could be rescued by treatment of cultures with the antimitotic drug cytosine arabinoside which led to the elimination of astroglia. However, this treatment resulted in death of all peripheral neurons. We conclude: (1) survival of intrinsic CNS neurons in culture is independent of astroglia; (2) astroglia are responsible for the detachment of these neurons from their growth substratum; (3) survival of peripheral sensory and motoneurons is dependent on co-cultured astroglia and (4) the differences in neuron-astroglia interactions between central and peripheral neurons are membrane-associated and probably independent of soluble factors.

Detachment of cultured neurons from substratum by astrocytic membrane-associated activity. Implications for CNS regeneration?

In primary cultures of dissociated cells from 6-day-old rat cerebellum, astrocytes proliferated and grew under the initially formed network of neurons. The growing astrocytes invaded the culture growth surface, while the neurons detached from the substratum and died. By 8 days after plating a confluent layer of astrocytes has taken over the entire growth surface area and neurons have disappeared. Membrane fractions prepared from astrocytes of 8-day-old cultures, have led to detachment of growing neurons. After 2 days in the presence of membrane fractions, about 70% of the neurons disappeared and many of the remaining ones had detached or retracted processes. The results indicate that the well-known phenomenon of disappearance of neurons from mixed primary CNS cultures, is probably caused by a membrane-associated activity of the proliferating astrocytes which can disturb neuron-substratum attachments. Our in vitro study implies that astrocytes may have a membrane-associated activity which is expressed under certain conditions and can disturb the contacts of growing or regenerating axons with their growth substrata.

Cytotoxic effects of monodansylcadaverine and methylamine in primary cultures of rat cerebellar neurons

The effects of dansylcadaverine and methylamine, competitive inhibitors of transglutaminase, were examined in primary cultures of dissociated rat cerebellar neurons. Addition of the drugs at plating time resulted 24 hr later in irreversible cytotoxic effects evidenced by failure of aggregation and neurite formation. Cytotoxicity was dose-dependent with methylamine being more potent (IC50 = 20 microM) than dansylcadaverine (IC50 = 30 microM). The cytotoxic effects were less potent when drugs were added 24 hr after plating, the time when neurons had already begun to extend neurites. Drugs were effective in the various sera and heat-inactivated sera tested. We concluded that low doses of methylamine and dansylcadaverine have potent toxic effects on primary neuronal cultures.