Mitochondrial dynamics, elimination and biogenesis during post-ischemic recovery in ischemia-resistant and ischemia-vulnerable gerbil hippocampal regions

Transient ischemic attacks (TIA) result from a temporary blockage in blood circulation in the brain. As TIAs cause disabilities and often precede full-scale strokes, the effects of TIA are investigated to develop neuroprotective therapies. We analyzed changes in mitochondrial network dynamics, mitophagy and biogenesis in sections of gerbil hippocampus characterized by a different neuronal survival rate after 5-minute ischemia-reperfusion (I/R) insult. Our research revealed a significantly greater mtDNA/nDNA ratio in CA2-3, DG hippocampal regions (5.8 ± 1.4 vs 3.6 ± 0.8 in CA1) that corresponded to a neuronal resistance to I/R. During reperfusion, an increase of pro-fission (phospho-Ser616-Drp1/Drp1) and pro-fusion proteins (1.6 ± 0.5 and 1.4 ± 0.3 for Mfn2 and Opa1, respectively) was observed in CA2-3, DG. Selective autophagy markers, PINK1 and SQSTM1/p62, were elevated 24-96 h after I/R and accompanied by significant elevation of transcription factors proteins PGC-1α and Nrf1 (1.2 ± 0.4, 1.78 ± 0.6, respectively) and increased respiratory chain proteins (e.g., 1.5 ± 0.3 for complex IV at I/R 96 h). Contrastingly, decreased enzymatic activity of citrate synthase, reduced Hsp60 protein level and electron transport chain subunits (0.88 ± 0.03, 0.74 ± 0.1 and 0.71 ± 0.1 for complex IV at I/R 96 h, respectively) were observed in I/R-vulnerable CA1. The phospho-Ser616-Drp1/Drp1 was increased while Mfn2 and total Opa1 reduced to 0.88 ± 0.1 and 0.77 ± 0.17, respectively. General autophagy, measured as LC3-II/I ratio, was activated 3 h after reperfusion reaching 2.37 ± 0.9 of control. This study demonstrated that enhanced mitochondrial fusion, followed by late and selective mitophagy and mitochondrial biogenesis might together contribute to reduced susceptibility to TIA.

Validation of the Reference Genes for Expression Analysis in the Hippocampus after Transient Ischemia/Reperfusion Injury in Gerbil Brain

Transient brain ischemia in gerbils is a common model to study the mechanisms of neuronal changes in the hippocampus. In cornu ammonnis 2-3, dentate gyrus (CA2-3,DG) regions of the hippocampus, neurons are resistant to 5-min ischemia/reperfusion (I/R) insult, while cornu ammonnis 1 (CA1) is found to be I/R-vulnerable. The quantitative polymerase chain reaction (qRT-PCR) is widely used to study the expression of genes involved in these phenomena. It requires stable and reliable genes for normalization, which is crucial for comparable and reproducible analyses of expression changes of the genes of interest. The aim of this study was to determine the best housekeeping gene for the I/R gerbil model in two parts of the hippocampus in controls and at 3, 48, and 72 h after recanalization. We selected and tested six reference genes frequently used in central nervous system studies: Gapdh, Actb, 18S rRNA, Hprt1, Hmbs, Ywhaz, and additionally Bud23, using RefFinder, a comprehensive tool based on four commonly used algorithms: delta cycle threshold (Ct), BestKeeper, NormFinder, and geNorm, while Hprt1 and Hmbs were the most stable ones in CA2-3,DG. Hmbs was the most stable in the whole hippocampal formation. This indicates that the general use of Hmbs, especially in combination with Gapdh, a highly expressed reference gene, seems to be suitable for qRT-PCR normalization in all hippocampal regions in this model.

The Metabolic Changes between Monolayer (2D) and Three-Dimensional (3D) Culture Conditions in Human Mesenchymal Stem/Stromal Cells Derived from Adipose Tissue

INTRODUCTION

One of the key factors that may influence the therapeutic potential of mesenchymal stem/stromal cells (MSCs) is their metabolism. The switch between mitochondrial respiration and glycolysis can be affected by many factors, including the oxygen concentration and the spatial form of culture. This study compared the metabolic features of adipose-derived mesenchymal stem/stromal cells (ASCs) and dedifferentiated fat cells (DFATs) cultivated as monolayer or spheroid culture under 5% O₂ concentration (physiological normoxia) and their impact on MSCs therapeutic abilities.

RESULTS

We observed that the cells cultured as spheroids had a slightly lower viability and a reduced proliferation rate but a higher expression of the stemness-related transcriptional factors compared to the cells cultured in monolayer. The three-dimensional culture form increased mtDNA content, oxygen consumption rate (OCR) and extracellular acidification rate (ECAR), especially in DFATs-3D population. The DFATs spheroids also demonstrated increased levels of Complex V proteins and higher rates of ATP production. Moreover, increased reactive oxygen species and lower intracellular lactic acid levels were also found in 3D culture.

CONCLUSION

Our results may suggest that metabolic reconfiguration accompanies the transition from 2D to 3D culture and the processes of both mitochondrial respiration and glycolysis become more active. Intensified metabolism might be associated with the increased demand for energy, which is needed to maintain the expression of pluripotency genes and stemness state.

Disrupted Calcium Homeostasis in Duchenne Muscular Dystrophy: A Common Mechanism behind Diverse Consequences

Duchenne muscular dystrophy (DMD) leads to disability and death in young men. This disease is caused by mutations in the DMD gene encoding diverse isoforms of dystrophin. Loss of full-length dystrophins is both necessary and sufficient for causing degeneration and wasting of striated muscles, neuropsychological impairment, and bone deformities. Among this spectrum of defects, abnormalities of calcium homeostasis are the common dystrophic feature. Given the fundamental role of Ca2+ in all cells, this biochemical alteration might be underlying all the DMD abnormalities. However, its mechanism is not completely understood. While abnormally elevated resting cytosolic Ca2+ concentration is found in all dystrophic cells, the aberrant mechanisms leading to that outcome have cell-specific components. We probe the diverse aspects of calcium response in various affected tissues. In skeletal muscles, cardiomyocytes, and neurons, dystrophin appears to serve as a scaffold for proteins engaged in calcium homeostasis, while its interactions with actin cytoskeleton influence endoplasmic reticulum organisation and motility. However, in myoblasts, lymphocytes, endotheliocytes, and mesenchymal and myogenic cells, calcium abnormalities cannot be clearly attributed to the loss of interaction between dystrophin and the calcium toolbox proteins. Nevertheless, DMD gene mutations in these cells lead to significant defects and the calcium anomalies are a symptom of the early developmental phase of this pathology. As the impaired calcium homeostasis appears to underpin multiple DMD abnormalities, understanding this alteration may lead to the development of new therapies. In fact, it appears possible to mitigate the impact of the abnormal calcium homeostasis and the dystrophic phenotype in the total absence of dystrophin. This opens new treatment avenues for this incurable disease.

Peptide Dendrimers with Non-Symmetric Bola Structure Exert Long Term Effect on Glioblastoma and Neuroblastoma Cell Lines

BACKGROUND

Glioblastoma (GBM) is the most common malignant tumor of the central nervous system (CNS). Neuroblastoma (NB) is one of the most common cancers of childhood derived from the neural crest cells. The survival rate for patients with GBM and high-risk NB is poor; therefore, novel therapeutic approaches are needed. Increasing evidence suggests a dual role of redox-active compounds in both tumorigenesis and cancer treatment. Therefore, in this study, polyfunctional peptide-based dendrimeric molecules of the bola structure carrying residues with antiproliferative potential on one side and the antioxidant residues on the other side were designed.

METHODS

We synthesized non-symmetric bola dendrimers and assessed their radical scavenging potency as well as redox capability. The influence of dendrimers on viability of rat primary cerebellar neurons (CGC) and normal human astrocytes (NHA) was determined by propidium iodide staining and cell counting. Cytotoxicity against human GBM cell lines, T98G and LN229, and NB cell line SH-SY5Y was assessed by cell counting and colony forming assay.

RESULTS

Testing of CGC and NHA viability allowed to establish a range of optimal dendrimers structure and concentration for further evaluation of their impact on two human GBM and one human NB cell lines. According to ABTS, DPPH, FRAP, and CUPRAC antioxidant tests, the most toxic for normal cells were dendrimers with high charge and an excess of antioxidant residues (Trp and PABA) on both sides of the bola structure. At 5 μM concentration, most of the tested dendrimers neither reduced rat CGC viability below 50-40%, nor harmed human neurons (NHA). The same dose of compounds 16 or 22, after 30 min treatment decreased the number of SH-SY5Y and LN229 cells, but did not affect the number of T98G cells 48 h post treatment. However, either compound significantly reduced the number of colonies formed by SH-SY5Y, LN229, and T98G cells measured 14 days after treatment.

CONCLUSIONS

Peptide dendrimers with non-symmetric bola structure are excellent scaffolds for design of molecules with pro/antioxidant functionality. Design of molecules with an excess of positive charges and antioxidant residues rendered molecules with high neurotoxicity. Single, 30 min exposition of the GBM and NB cell lines to the selected bola dendrimers significantly suppressed their clonogenic potential.

Molecular Antioxidant Properties and In Vitro Cell Toxicity of the p-Aminobenzoic Acid (PABA) Functionalized Peptide Dendrimers

BACKGROUND

Exposure to ozone level and ultraviolet (UV) radiation is one of the major concerns in the context of public health. Numerous studies confirmed that abundant free radicals initiate undesired processes, e.g. carcinogenesis, cells degeneration, etc. Therefore, the design of redox-active molecules with novel structures, containing radical quenchers molecules with novel structures, and understanding their chemistry and biology, might be one of the prospective solutions. Methods: We designed a group of peptide dendrimers carrying multiple copies of p-aminobenzoic acid (PABA) and evaluated their molecular antioxidant properties in 1,1'-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) tests. Cytotoxicity against human melanoma and fibroblast cells as well as against primary cerebral granule cells (CGC) alone and challenged by neurotoxic sodium glutamate and production of reactive oxygen species (ROS) in presence of dendrimers were measured. Results: PABA-terminated dendrimers express enhanced radical and radical cation scavenging properties in relation to PABA alone. In cellular tests, the dendrimers at 100 M fully suppress and between 20⁻100 M reduce proliferation of the human melanoma cell line. In concentration 20 M dendrimers generate small amount of the reactive oxygen species (<25%) but even in their presence human fibroblast and mouse cerebellar granule cells remain intact Moreover, dendrimers at 0.2⁻20 µM concentration (except one) increased the percentage of viable fibroblasts and CGC cells treated with 100 M glutamate. Conclusions: Designed PABA-functionalized peptide dendrimers might be a potential source of new antioxidants with cationic and neutral radicals scavenging potency and/or new compounds with marked selectivity against human melanoma cell or glutamate-stressed CGC neurons. The scavenging level of dendrimers depends strongly on the chemical structure of dendrimer and the presence of other groups that may be prompted into radical form. The present studies found different biological properties for dendrimers constructed from the same chemical fragments but the differing structure of the dendrimer tree provides once again evidence that the structure of dendrimer can have a significant impact on drug⁻target interactions.

Cortical Synaptic Transmission and Plasticity in Acute Liver Failure Are Decreased by Presynaptic Events

Neurological symptoms of acute liver failure (ALF) reflect decreased excitatory transmission, but the status of ALF-affected excitatory synapse has not been characterized in detail. We studied the effects of ALF in mouse on synaptic transmission and plasticity ex vivo and its relation to distribution of (i) synaptic vesicles (sv) and (ii) functional synaptic proteins within the synapse. ALF-competent neurological and biochemical changes were induced in mice with azoxymethane (AOM). Electrophysiological characteristics (long-term potentiation, whole-cell recording) as well as synapse ultrastructure were evaluated in the cerebral cortex. Also, sv were quantified in the presynaptic zone by electron microscopy. Finally, presynaptic proteins in the membrane-enriched (P2) and cytosolic (S2) fractions of cortical homogenates were quantitated by Western blot. Slices derived from symptomatic AOM mice presented a set of electrophysiological correlates of impaired transmitter release including decreased field potentials (FPs), increased paired-pulse facilitation (PPF), and decreased frequency of spontaneous and miniature excitatory postsynaptic currents (sEPSCs/mEPSCs) accompanied by reduction of the spontaneous transmitter release-driving protein, vti1A. Additionally, an increased number of sv per synapse and a decrease of P2 content and/or P2/S2 ratio for sv-associated proteins, i.e. synaptophysin, synaptotagmin, and Munc18–1, were found, in spite of decreased content of the sv-docking protein, syntaxin-1. Slices from AOM-treated asymptomatic mice showed impaired long-term potentiation (LTP) and increased PPF but no changes in transmitter release or presynaptic protein composition. Our findings demonstrate that a decrease of synaptic transmission in symptomatic ALF is associated with inefficient recruitment of sv proteins and/or impaired sv trafficking to transmitter release sites.

The Effect of a Novel c.820C>T (Arg274Trp) Mutation in the Mitofusin 2 Gene on Fibroblast Metabolism and Clinical Manifestation in a Patient

Charcot-Marie-Tooth disease type 2A (CMT2A) is an autosomal dominant axonal peripheral neuropathy caused by mutations in the mitofusin 2 gene (MFN2). Mitofusin 2 is a GTPase protein present in the outer mitochondrial membrane and responsible for regulation of mitochondrial network architecture via the fusion of mitochondria. As that fusion process is known to be strongly dependent on the GTPase activity of mitofusin 2, it is postulated that the MFN2 mutation within the GTPase domain may lead to impaired GTPase activity, and in turn to mitochondrial dysfunction. The work described here has therefore sought to verify the effects of MFN2 mutation within its GTPase domain on mitochondrial and endoplasmic reticulum morphology, as well as the mtDNA content in a cultured primary fibroblast obtained from a CMT2A patient harboring a de novo Arg274Trp mutation. In fact, all the parameters studied were affected significantly by the presence of the mutant MFN2 protein. However, using the stable model for mitofusin 2 obtained by us, we were next able to determine that the Arg274Trp mutation does not impact directly upon GTP binding. Such results were also confirmed for GTP-hydrolysis activity of MFN2 protein in patient fibroblast. We therefore suggest that the biological malfunctions observable with the disease are not consequences of impaired GTPase activity, but rather reflect an impaired contribution of the GTPase domain to other MFN2 activities involving that region, for example protein-protein interactions.

[Mitofusin 2 and mitochondrial dynamics in norm and pathology]

Results of an intensive research performed during last 25 years have revealed that an understanding of biochemical and molecular principles of oxidative phosphorylation has not finished the streak of ground-breaking discoveries of newly identified mitochondrial functions in numerous cellular processes. Among other things it has been shown that mitochondria undergo reversible fission and fusion processes, and may form a complex network which functionally and structurally interacts with the endoplasmic reticulum membranes and probably also other organelles. An organization of mitochondrial network is closely controlled and is of high importance for numerous intracellular processes to occur properly. In this review, mitofusin 2 - one of a few proteins involved in a maintenance of an appropriate mitochondrial architecture, and in the consequence in the regulation of mitochondrial metabolism and calcium signalling, the controlling of the mitochondrial DNA level, and the regulation of cell proliferation and differentiation is the focus. Mutations within mitofusin 2-encoding gene are a cause of Charcot-Marie-Tooh 2A - type neuropathies while an affected expression of this protein seems to be related to neoplasia, type 2 diabetes, or vascular hyperplasia. Numerous experimental data confirm pleiotropic effects of mitofisin 2 in animal cells.

Mitofusin 2 Deficiency Affects Energy Metabolism and Mitochondrial Biogenesis in MEF Cells

Mitofusin 2 (Mfn2), mitochondrial outer membrane protein which is involved in rearrangement of these organelles, was first described in pathology of hypertension and diabetes, and more recently much attention is paid to its functions in Charcot-Marie-Tooth type 2A neuropathy (CMT2A). Here, cellular energy metabolism was investigated in mouse embryonic fibroblasts (MEF) differing in the presence of the Mfn2 gene; control (MEFwt) and with Mfn2 gene depleted MEFMfn2-/-. These two cell lines were compared in terms of various parameters characterizing mitochondrial bioenergetics. Here, we have shown that relative rate of proliferation of MEFMfn2-/- cells versus control fibroblasts depend on serum supplementation of the growth media. Moreover, MEFMfn2-/- cells exhibited significantly increased respiration rate in comparison to MEFwt, regardless of serum supplementation of the medium. This effect was correlated with increased level of mitochondrial markers (TOM20 and NAO) as well as mitochondrial transcription factor A (TFAM) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) protein levels and unchanged total ATP content. Interestingly, mitochondrial DNA content in MEFMfn2-/- cells was not reduced. Fundamentally, these results are in contrast to a commonly accepted belief that mitofusin 2 deficiency inevitably results in debilitation of mitochondrial energy metabolism. However, we suggest a balance between negative metabolic consequences of mitofusin 2 deficiency and adaptive processes exemplified by increased level of PGC-1α and TFAM transcription factor which prevent an excessive depletion of mtDNA and severe impairment of cell metabolism.

[Mitofusin 2 as a crucial peripheral nervous system protein and a common regulator of cell metabolism]

Some of the metabolic disorders are manifested by a predominantly expressed symptoms from the single organ, however, they display discrete symptoms from other tissues. Charcot Marie Tooth disease (CMT) divided into demyelinating (CMT1) and axonal (CMT2) subtypes is characterized by a slowly progressive wasting of distal muscles. CMT2A form diagnosis requires identification of mutation in a gene coding for mitofusin 2 (MFN2). Mitofusin 2 is a protein of an outer mitochondrial membrane encoded in the nuclear genome and characterized by numerous biochemical functions. Mfn2 is involved mainly in the fusion of mitochondria and the cooperation between endoplasmic reticulum and mitochondria. It seems probably that Mfn2 possesses also some regulatory functions and takes part in a regulation of respiratory chain activity, transcription of several proteins and in intracellular signals transduction. Mfn2-linked pathology is also observed in diabetes and heart diseases. Here, we aim to show that mitofusin 2 is a protein crucial not only for peripheral nerve disorders but is a one of the common regulator of cell metabolism.

Identification of a voltage-gated potassium channel in gerbil hippocampal mitochondria

Transient cerebral ischemia is known to induce endogenous mechanisms that can prevent or delay neuronal injury, such as the activation of mitochondrial potassium channels. However, the molecular mechanism of this effect remains unclear. In this study, the single-channel activity was measured using the patch-clamp technique of the mitoplasts isolated from gerbil hippocampus. In 70% of all patches, a potassium-selective current with the properties of a voltage-gated Kv-type potassium channel was recorded with mean conductance 109+/-6pS in a symmetrical solution. The channel was blocked at negative voltages and irreversibly by margatoxin, a specific Kv1.3 channel inhibitor. The ATP/Mg(2+) complex and Ca(2+) ions had no effect on channel activity. Additionally, agitoxin-2, a potent inhibitor of voltage-gated potassium channels, had no effect on mitochondrial channel activity. This observation suggests that in contrast to surface membrane channels, the mitochondrial voltage-gated potassium channel could have a different molecular structure with no affinity to agitoxin-2. Western blots of gerbil hippocampal mitochondria and immunohistochemistry on gerbil brain sections confirmed the expression of the Kv1.3 protein in mitochondria. Our findings indicate that gerbil brain mitochondria contain a voltage-gated potassium channel that can influence the function of mitochondria in physiological and pathological conditions and that has properties similar to the surface membrane Kv1.3 channel.

Pharmacology of mitochondrial potassium channels: dark side of the field

Mitochondrial potassium channels play an important role in cytoprotection. Potassium channels in the inner mitochondrial membrane are modulated by inhibitors and activators (potassium channel openers) previously described for plasma membrane potassium channels. The majority of mitochondrial potassium channel modulators exhibit a broad spectrum of off-target effects. These include uncoupling properties, inhibition of the respiratory chain and effects on cellular calcium homeostasis. Therefore, the rational application of channel inhibitors or activators is crucial to understanding the cellular consequences of mitochondrial channel inhibition or activation. Moreover, understanding their side-effects should facilitate the design of a specific mitochondrial channel opener with cytoprotective properties. In this review, we discuss the complex interactions of potassium channel inhibitors and activators with cellular structures.

Changes in the expression of insulin-like growth factor 1 variants in the postnatal brain development and in neonatal hypoxia-ischaemia

Insulin-like growth factor-1 (IGF-1) is a multifunctional peptide of which numerous isoforms exist. The predominant form, IGF-1Ea is involved in physiological processes while IGF-1Ec (mechano-growth factor, MGF) is expressed in response to a different set of stimuli. We have identified specific changes in the expression patterns of these IGF-1 variants in brain development in normal rats and following neonatal hypoxia-ischaemia (HI). Both IGF-1Ea and IGF-1Ec are expressed during normal postnatal brain development, albeit with highly specific temporal distributions. In contrast, HI produced increased and prolonged expression of the IGF-1Ec isoform only. Importantly, hypoxia alone stimulated the expression of IGF-1Ec as well. Thus, IGF-1Ec may play a role in HI pathology. Neonatal hypoxia-ischaemia occurs in approximately 1:4000-1:10,000 newborns and causes neurological deficits in approximately 75% of those affected. Unfortunately, no specific treatment is available. IGF-1 is known to have neuroprotective activity and its IGF-1Ec variant appears to be an endogenous protective factor in hypoxia-ischaemia. Therefore, IGF-1Ec could potentially be developed into a therapeutic modality for the attenuation or prevention of neuronal damage in this and related disorders.

Association of protein kinase C delta and phospholipid scramblase 3 in hippocampal mitochondria correlates with neuronal vulnerability to brain ischemia

Recent findings support the idea that mitochondrial integrity plays an important role in the propagation of excitotoxic ischemic signal and PKC is implicated in the regulation of mitochondrial membranes properties. One of the targets of PKC delta is phospholipid scramblase 3 (PLSCR3), an enzyme responsible for cardiolipin translocation from the inner to outer mitochondrial membrane. To get an insight into in vivo mechanism by which PKC delta mediates ischemia/reperfusion injury of hippocampal neurons, we examined the effects of transient brain ischemia in gerbil on association of PKC delta with mitochondria isolated from ischemia-vulnerable (CA1) and ischemia-resistant regions, and interactions between PKC delta and PLSCR3. Postischemic, biphasic and brain region-specific translocation of PKC delta to mitochondria was observed. First peak was at 30-60 min of reperfusion and the second was observed after 72-96 h following ischemia. PKC delta was translocated to mitochondria only in CA1 region. The PLSCR3 mRNA and protein was detected in brain by RT-PCR and sequence analysis, Western blotting and immunocytochemistry in electron microscopy (EM). Co-immunoprecipitation and double-labeled immuno-EM showed association of PKC delta and PLSCR3 in postischemic CA1 mitochondria. Additionally, the amount of tBid associated with mitochondria was elevated 96 h following ischemia. Our data suggest that in the postischemic brain PKC delta co-localizes with PLSCR3 in mitochondria and this event might influence the mitochondrial membranes architecture and delayed neurons degeneration.

Kalirin-7, a protein enriched in postsynaptic density, is involved in ischemic signal transduction

Regulators of mitogen activated protein kinases (MAPK) and c-Jun N-terminal/stress-activated kinase (JNK) include Rho-like small GTP-binding proteins and their regulators. SynGAP and kalirin-7 are postsynaptic density-enriched proteins identified through their interaction with Rho GTPases and PSD-95 scaffold protein. We examined immunoreactivity of SynGAP, kalirin-7, and PSD-95, phosphorylation of MAPK and JNK in control and postischemic hippocampus in gerbil model of transient forebrain ischemia. In normal brain higher amount of kalirin-7 but a lower amount of P-JNK was found in ischemia-resistant hippocampal area: CA2-3, DG than in ischemia-vulnerable CA1. After 5 min ischemia and 1 h reperfusion a decrease of P-ERK and increase of P-JNK were uniformly observed in the hippocampal parts. By contrast, the amount of kalirin-7 in CA2-3, DG reached 56% (P < 0.001) of control while was doubled in CA1. Oppositely, the immunoreactivity of SynGAP was increased in CA2-3, DG and reduced in CA1. Our data indicate that SynGAP and kalirin-7 take part in the regulation of ischemic signal transduction but the mechanism does not seem directly connected with the activation of MAPK and JNK.

[Protein kinases in mitochondria]

Mitochondria, besides playing a central role in energy metabolism within the cell, are involved in a cohort of other processes like cellular differentiation and apoptosis. Investigations during recent few years have shown that protein kinases, including PKA, PKB/Akt, PKC, Raf-1, p38 MAPK, JNK, ERK1/2, Src, Fyn and Csk, may directly interact with mitochondrial proteins. Their role mainly concentrates at phosphorylation of pro- and anti-apoptotic proteins (Bad, Bax, Bcl-2, Bcl-xL), phosphorylation/modification of electron transport chain proteins (complex I, COIV), MPTP forming proteins VDAC and ANT, proteins of mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) and phospholipid scramblase 3 (PLSCR3). Many experimental data showed the presence of protein kinases in the outer and inner mitochondrial membranes as well as in the mitochondrial matrix during in vitro cell stimulations, in neurodegenerative diseases and in in vivo ischaemia heart preconditioning. These data show that translocation of protein kinases to mitochondria plays an important role especially during ischaemia/reperfusion in brain and heart.

Neuroprotective effects of short peptides derived from the Insulin-like growth factor 1

Insulin-like growth factor I (IGF-1) is a peptide synthesized in response to growth hormone stimulation. While most of the circulating IGF-1 comes from the liver, it can also be produced in other tissues and both its expression and processing undergo tissue-specific regulation. The predominant form, IGF-1Ea is a circulating factor while two others, IGF-1Eb and IGF-1Ec (MGF), are mostly expressed in different tissues or in response to various stimuli and show some preferences with respect to the signal transduction pathways they activate. In skeletal muscle specific forms of IGF-1 play a role in development and growth and in addition to these physiological roles IGF-1 functions in the damaged muscle. IGF-1 is also important for the developing and adult brain and can reduce neuronal death caused by different types of injuries. Like many other peptide hormones IGF-1 originates from a precursor pro-hormone that undergoes extensive post-translational modifications. Processing liberates the mature peptide, which acts via the specific IGF-1 receptor but additional short peptides can arise from both N- and C-termini of various IGF-1 isoforms. These derivatives function as autonomous biologically active peptides and extremely potent neuroprotective agents. Their biological effects are independent of the activation of the IGF-1 receptor. Unfortunately, little is known about their mechanism(s) of action. Likewise, the existence of the endogenous production and wider biological effects of these short peptides are uncertain. However, considering the difference in the modes of action it might be possible to dissociate the unwanted and potentially dangerous mitogenic activity of the full-length IGF-1 exerted via its receptor from the neuroprotective effects of short derivatives mediated through different pathways. Such small molecules show good penetration through the blood brain barrier, can be inexpensively manufactured and modified to increase their stability. Therefore, they are good candidates for development into a neuroprotective therapeutic modality.

Cytochrome c binds to inositol (1,4,5) trisphosphate and ryanodine receptors in vivo after transient brain ischemia in gerbils

Previously we have shown that the biphasic efflux of mitochondrial protein cytochrome c to cytoplasm is one of the important events of the delayed postichemic neuronal death. We concluded that early and transient appearance of cytochrome c in cytoplasm of cells recovering after ischemia was decisive for initiation of the pathological signaling cascade leading to neuronal death, but the precise mechanism remained unknown. In vitro cytochrome c was identified as a messenger that coordinates mitochondrial-endoplasmatic reticulum interactions that drive apoptosis. Here we show that in vivo cytochrome c interacts with inositol (1,4,5) trisphosphate receptor type 1 in gerbil hippocampus subjected to transient brain ischemia and short reperfusion. Moreover, cytochrome c binds also to ryanodine receptor type 2, the role of which in postischemic neuronal death is suggested. The complexes could be coimmunoprecipitated by antibodies against any of the two proteins. Our data verified that the mechanism observed in vitro applies to the pathological in vivo situation.

A strong neuroprotective effect of the autonomous C‐terminal peptide of IGF‐1 Ec (MGF) in brain ischemia

The ischemic stroke is the third leading cause of death in developed countries. The C-terminal peptide of mechano-growth factor (MGF), an alternatively spliced variant of insulin-like growth factor 1 (IGF-1), was found to function independently from the rest of the molecule and showed a neuroprotective effect in vivo and in vitro. In vivo, in a gerbil model of transient brain ischemia, treatment with the synthetic MGF C-terminal peptide provided very significant protection to the vulnerable neurons. In the same model, ischemia evoked increased expression of endogenous MGF in the ischemia-resistant hippocampal neurons, suggesting that the endogenous MGF might have an important neuroprotective function. In an in vitro organotypic hippocampal culture model of neurodegeneration, the synthetic peptide was as potent as the full-length IGF-1 while its effect lasted significantly longer than that of recombinant IGF-1. While two peptides showed an additive effect, the neuroprotective action of the C-terminal MGF was independent from the IGF-1 receptor, indicating a new mode of action for this molecule. Although MGF is known for its regenerative capability in skeletal muscle, our findings demonstrate for the first time a neuroprotective role against ischemia for this specific IGF-1 isoform. Therefore, the C-terminal MGF peptide has a potential to be developed into a therapeutic modality for the prevention of neuronal damage.

The role of protein kinase C and cyclic AMP in the ammonia-induced shift of the taurine uptake/efflux balance towards efflux in C6 cells

A previous study showed that treatment of C6 glioma cells with 10 mM ammonium chloride monia") for 24 h decreases taurine uptake and evokes sodium-dependent taurine efflux, indicating reversal of the taurine transporter (TauT)-mediated transport as an underlying mechanism. Consistent with the involvement of TauT we now show that the ammonia-induced changes in Tau uptake and efflux are inhibited by the protein kinase C (PKC) activator phorbol 12,13-dibutyrate (PDBu). Ammonia treatment of C6 cells resulted in increased intracellular accumulation of cAMP. Incubation of the cells with dibutyryl cAMP (dbcAMP) mimicked the effects of ammonia on both taurine uptake and efflux. The effects of dbcAMP on taurine uptake and efflux were additive to the effects of ammonia. Collectively, the results suggest that the effects of ammonia on taurine uptake and efflux may be partly mediated by cAMP. Consistent with this mechanism, the adenyl cyclase inhibitor, miconazole reduced the stimulation of efflux by ammonia.

Transient cerebral ischemia induces delayed proapoptotic Bad translocation to mitochondria in CA1 sector of hippocampus

Delayed ischemic brain damage is associated with mitochondrial dysfunction, but the underlying mechanisms are not known in detail. Recent data suggest that the process is associated with multidirectional changes in the activities of various proteins located in mitochondria. Of these, the stress-activated kinase JNK is delay-activated postischemia. We induced 5 min cerebral ischemia in gerbils followed by 3, 24, 48, 72 and 96 h of reperfusion. Here we show the postischemic translocation of proapoptotic protein Bad to mitochondria. Immunoelectron microscopic examination revealed the co-appearance of Bad and Bcl-2 proteins in postischemic mitochondria in ischemia-vulnerable CA1 sector of hippocampus as opposed to the ischemia-resistant DG region. Mitochondrial increase of Bad protein is coincident with a transient decrease of the active, phosphorylated form of prosurvival kinase, Raf-1, under conditions of long reperfusion. The above demonstrated sequence of events is likely to play a role in delayed postischemic nerve cell death.

Neuroprotection by cyclosporin A following transient brain ischemia correlates with the inhibition of the early efflux of cytochrome C to cytoplasm

The efflux of mitochondrial protein cytochrome C to cytoplasm is one of the key events of mitochondrial dysfunction observed in post-ischemic pathology. We investigated the effect of intra-carotid infusion of 5-10 mg/kg of cyclosporin A (CsA) on the neuronal survival in CA1 sector of hippocampus and on the subcellular localization of cytochrome C in the model of 5 min gerbil brain ischemia. To discriminate between the immunosuppressive and the mitochondria protecting component of CsA action, we compared the effect of CsA with one other immunosuppressant FK506. Almost 75% of neurons in ischemia-affected brain area were saved after CsA but not after FK506 treatment. This protective effect was only observed when the drug was infused immediately upon reperfusion. Early CsA treatment was able to block an initial phase of cytochrome C release, occurring transiently at 30 min post-ischemia, an effect never observed after FK506 administration. We assessed the neuroprotective potency of CsA vs. FK506 in rat cortical primary culture treated with compounds that mimic destructive signals induced by brain ischemia. In all cases, neuronal death and cytochrome C release were evidently suppressed by CsA applied not later than 30 min after the initial insult. Thus, early treatment with CsA in vitro and after bolus intra-carotid injection in vivo can save neurons by inhibition of cytochrome C efflux to cytoplasm.

Glutamine uptake and expression of mRNA's of glutamine transporting proteins in mouse cerebellar and cerebral cortical astrocytes and neurons

The relative roles of the three sodium-dependent transport systems: A, ASC and N in the uptake of [3H]Gln, and the compatibility of the uptake characteristics with the expression of mRNAs coding for the Gln transporting molecules, were examined in primary cultures of astrocytes and neurons derived from mouse cerebellum, a glutaminergic system-enriched structure, and in cerebral cortex. Gln uptake activity (Vmax) was higher in cerebellar astrocytes or neurons than in their cerebral cortical counterparts. The N-methylamino-isobutyric acid (MeAiB)- and pH-sensitive, system A-mediated component of the uptake, and the uptake of [14C]MeAiB itself, was much more active in neurons than in astrocytes derived from either region. Also, the expression of mRNA for GlnT (SAT1), a system A isoform specific for Gln, was only expressed in neurons derived from both structures, while an alanine (Ala)-preferring system A transporter, SAT2, was expressed in neurons and astrocytes from either region. System ASC-mediated Gln uptake and expression of ASCT2 mRNA were in both structures more pronounced in astrocytes than in neurons, consistent with the postulated role of ASCT2 in the efflux of de novo synthesized Gln from astrocytes. System N-mediated (threonine+MeAiB-inhibitable) Gln uptake showed comparable activities in all four types of cells, which is compatible with the ubiquitous expression of NAT2 mRNA-a mouse brain-specific N-system isoform.

Glutamine transport in C6 glioma cells shows ASCT2 system characteristics

Previous studies from this laboratory have shown that glutamine (Gln) uptake in a rat astrocytoma-derived C6 cell line shows characteristics similar with the uptake of a model ASC system substrate, threonine, whose pH-dependence and partial tolerance of Li(+) substitution for Na(+) resemble the ASCT2 variant of the system. In support of the previous findings, RT-PCR analysis revealed that C6 cells strongly express ASCT2 mRNA, but not at all GlnT mRNA or NAT2 mRNA, the A and N system variants specifically engaged in Gln transport in normal CNS. Other features of Gln transport in C6 cells indicating the involvement of ASCT2 system included its resistance to ouabain and stimulation of Gln efflux from the cells in the presence of excess Gln or cysteine (Cys), demonstrating that the system operates in the exchange mode. Replacement of NaCl in the incubation medium with isoosmotic sucrose did neither significantly affect the kinetics, nor any other major characteristics of Gln or Thr transport, including its pH-dependence, inhibition by ASCT system substrates or resistance to the model system A substrate-N-methylamino-isobutyric acid (MeAiB).

Human cord blood-derived cells attain neuronal and glial features in vitro

Neural stem cells are clonogenic, self-renewing cells with the potential to differentiate into brain-specific cell lines. Our study demonstrates that a neural-stem-cell-like subpopulation can be selected and expanded in vitro by the use of human umbilical cord blood cells, which are a relatively easily available starting material. Through a combination of antigen-driven magnetic cell sorting and subfractionation according to cell surface adhesive properties, we have isolated a clonogenic fraction devoid of hematopoietic or angiogenetic properties but with relatively high self-renewal potency. The resulting clones express nestin, a neurofilament protein that is one of the most specific markers of multipotent neural stem cells. In the presence of selected growth factors or in the rat brain co-culture system, the progeny of these cells can be oriented towards the three main neural phenotypes: neurons,astroglia and oligodendroglia. The cells show high commitment (about 30% and 40% of the population) to neuronal and astrocytic fate, respectively. Interestingly, upon differentiation, the neural-type precursor cells of cord blood origin also give rise to a relatively high proportion of oligodendrocytes — 11% of the total population of differentiating cells.

Glutamine transport in C6 glioma cells: substrate specificity and modulation in a glutamine deprived culture medium

A previous study has shown that glutamine (Gln) uptake in C6 cells grown in a standard medium containing 2 mM Gln, is predominantly mediated by a sodium-dependent system that is inhibited by ASC system substrates alanine (Ala), serine (Ser), cysteine (Cys) and threonine (Thr), shows pH sensitivity and partial tolerance to substitution of Na+ by Li+, features compatible with system ASCT2 that is strongly expressed in cultured astrocytes. The uptake was not inhibited by the model system A substrate alpha-(methylamino)isobutyric acid (MeAiB), and glycine (Gly) or proline (Pro), indicating that the substrate-regulated system A as defined by routine criteria is relatively inactive in these cells (Dolinska et al., 2000). In this study we compared the uptake of radiolabeled Gln and a model ASC substrate -Thr in cells grown to the same density in Gln-containing and Gln-deprived media. Cells grown in the absence of Gln showed a reduced activity of system ASC-mediated Gln uptake, and the system lost tolerance for Li+ and became somewhat more resistant to lowering pH of the medium. In contrast to cultured astrocytes deprived of Gln, the overall Gln uptake activity in C6 cells adapted to grow in a medium without Gln was lower than in cells grown in a Gln containing medium, and the uptake by system A remained inactive. C6 cells cultured both in the presence and absence of Gln expressed ASCT2 mRNA, indicating that system ASCT2-mediated Gln uptake is modulated at a posttranscriptional level. In contrast to Gln uptake, Thr uptake was more active in cells cultured in the absence of Gln and showed neither pH dependence nor lithium tolerance in either medium, which is typical of an uptake mediated by the widespread ASCT1 isoform of system ASC. In C6 cells grown in the presence or absence of Gln alike, approximately 20% of the sodium-dependent Gln uptake was resistant to MeAiB+Thr, indicating contribution of system N. The N system-mediated uptake in C6 cells grown in the absence, but not in the presence of Gln was not inhibited by glutamate (Glu) that conforms to the characteristics of the glial N system variant, SN1.

Interrelations between nuclear-factor kappa B activation, glial response and neuronal apoptosis in gerbil hippocampus after ischemia

Spatial and temporal relations between transcriptional factor NF kappa B activation and glia reaction in gerbil hippocampus after transient cerebral ischemia has been studied. Activation of protein binding to NF kappa B consensus oligonucleotide was determined by electrophoretic mobility gel shift assay (EMSA) in homogenates from dorsal (DP- an equivalent of CA1 sector) and abdominal (AbP- containing CA2-4 and gyrus dentatus) parts of hippocampus. A significant activation of NF kappa B binding was observed exclusively in DP as early as 3 h after ischemia and at this time that response preceded any other morphological signs of postischemic tissue injury. This early enhancement of NF kappa B binding was followed by microglia activation visualized in CA1 pyramidal region at 24 h of recovery by histochemical staining with lectin from Ricinus communis (RCA-120). Simultaneously, only a moderate increase of immunostaining against glial fibrillary acidic protein (GFAP) was observed homogeneously in all parts of hippocampus. This uniform pattern of astrogliosis was preserved until postischemic day 3-4, when apoptotic DNA fragmentation in CA1 pyramidal neurons had been clearly documented by TUNEL staining. At this period however, continuous elevation of NF kappa B binding in DP corresponded with similar response manifested also in AbP of the hippocampus. These results evidence a preferential NF kappa B involvement in an early microglia activation in the apoptogenic CA1 sector, although its role in a later astrocytic response to ischemia could not be neglected too.

Delayed induction of apoptosis by ammonia in C6 glioma cells

Ammonia is a neurotoxin whose administration in large doses causes coma and death of the exposed animals, but whether and in what degree these whole body effects are related to the death of CNS cells is not known. Since the downstream effects of ammonia in cultured CNS cells appear to be partly mediated by overactivation of several putative signalling mechanisms characteristic for the apoptotic program, we speculated that ammonia neurotoxicity may be apoptogenic. In this study, C6 glioma cells grown in 2% serum were exposed to 5 mM or 10 mM NH(4)Cl (ammonia) for 96 h and tested for the appearance of apoptosis by (a) Hoechst staining, (b) TUNEL reaction and (c) DNA ladder, at different times of exposure. In cultures exposed to either 5 mM or 10 mM ammonia, about 10% of the cells were found to enter apoptosis at 48 h of exposure, and the number of apoptotic cells rose to 30% at 72 h, and to 50% at 96 h of exposure, respectively. The first transduction signal purportedly involved in apoptosis, activation of PKCalphabeta, was transient and appeared already after 3-6 h of treatment. Coincident with pronounced manifestation of apoptosis (at 72 h and even more at 96 h of exposure) was an increased transfer of the transcription factor NFkappaB from cytoplasmto nucleus as revealed by EMSA assay. The number of cells affected by ammonia-induced apoptosis was markedly reduced by incubation with a NOS inhibitor, L-NAME at 100 microM concentration. The results indicate that ammonia-induced apoptosis is a result of a complex interplay of at least three signalling molecules: NO, PKC and the transcription factor NFkappaB, with NFkappaB being possibly involved in the induction of iNOS and generation of toxic levels of NO in the cells.

Dual response of calpain to rat brain postdecapitative ischemia

Calpains, Ca(2+)-dependent neutral proteinases (microM and mM Ca(2+)-sensitive), and their endogenous inhibitor calpastatin were examined in rat brain. Specific activity of m-calpain exceeded almost 10 times that of mu-calpain, and the both isoforms of calpain together with calpastatin were mainly located in the soluble fraction of homogenate. Acute postdecapitative ischemia of 15 min duration resulted in a gradual, time-dependent decrease of total mu-calpain activity (to 60% of control values) and in the moderate elevation of calpastatin activity (by 28%). The decrease of total mu-calpain activity coincided with its remarkable increase (above 300% of control values) in particulate fraction. In the case of m-calpain, the only observed effect of ischemia was its redistribution and, as a consequence, the elevation of activity in particulate fraction. The accumulation of breakdown products, resulting from calpain-catalyzed proteolysis of fodrin (as revealed by Western blotting) indicated activation of calpain under ischemia. The findings suggest that this rapid activation involves partial enzyme translocation toward membranes, and is followed (at least in acute phase) by mu-calpain downregulation and increased calpastatin activity.

Phosphorylation of protein kinase C substrate proteins in rat hippocampal slices--effect of calpain inhibition

Incubation of the acutely dissected rat hippocampal slices in calcium-containing media resulted in spontaneous activation-translocation of classical PKC isoforms and their subsequent (especially gamma-type) proteolytic degradation. These changes were blocked by calpain inhibitor MDL 28 170 in 100 microM concentration. Rat hippocampal slices were metabolically prelabelled with 32Pi and stimulated with NMDA/glycine, depolarization or phorbol dibutyrate (PDBu) treatment. The basal phosphorylation of specific PKC substrates (MARCKS, neuromodulin and neurogranin) was significantly reduced in non-stimulated slices by MDL pretreatment. In contrast, only the slices where calpain activity was inhibited responded to further NMDA or phorbol dibutyrate stimulation by a substantial increase of PKC-dependent protein phosphorylation. It is concluded that the PKC phosphorylation system is severely affected by non-specific activation and a subsequent, calpain-dependent proteolysis in the acutely prepared hippocampal slices. Calpain inhibition by 100 microM MDL partially prevented these changes and increased stimulus-dependent phosphorylation of PKC-specific protein substrates.

Enhancement of 3[H]D-aspartate release during ischemia like conditions in rat hippocampal slices: source of excitatory amino acids

Ischemic neuronal injury is supposed to be caused in part by the extracellular accumulation of excitatory amino acids (EAA). Neurotransmitter and metabolic EAA can be released from synaptic vesicles and cytoplasm of neurones and glial cells. In this study the release of the glutamate analogue [3H]D-aspartate ([3H]D-ASP), loaded into 500 microns slices of rat hippocampus, was investigated. The efflux of the label was measured during anoxic-aglycemic ("ischemic") and normoxic K+ depolarization. To identify the pools from which [3H]D-ASP is released we have estimated its calcium dependence and the effects of inhibitors of: (1) Na(+)-dependent transporter of amino acids (100 microM L-trans-pyrrolidine-2,4-dicarboxylic acid/L-trans-PDC/), (2) sodium channel (1 microM tetrodotoxin TTX), and (3) anion channel (1 mM furosemide). [3H]D-ASP released upon normoxic depolarization was 40% inhibited by TTX, nearly 40% by L-trans-PDC and over 50% by furosemide. The "ischemic" release was in 40% calcium dependent, completely TTX independent and in approximately 50% blocked by furosemide treatment. Our data suggest that EAA accumulated in the synaptic cleft during ischemia are mainly released from the cytosolic compartment by mechanisms which are connected with the ischemic increase of extracellular potassium concentration.

Changes of Ca2+/calmodulin-dependent protein kinase-II after transient ischemia in gerbil hippocampus

Transient cerebral ischemia induces, besides delayed neurodegeneration in selected brain structures, a number of early responses which may mediate ischemic injury/repair processes. Here we report that 5 min exposure to cerebral ischemia in gerbils induces a rapid inhibition and subsequent translocation of Ca2+/calmodulin-dependent protein kinase II (CaMKII). These changes were partially reversible during a 24 h post-ischemic recovery. Concomitantly the total amount of the enzyme protein, as revealed by Western blotting (alpha-subunit specific), remained stable. This is consistent with our previous hypothesis, that the mechanism of ischemic CaMKII down-regulation involves a reversible posttranslational modification-(auto)phosphorylation, rather than the degradation of enzyme protein. The effectiveness of known modulators of post-ischemic outcome in counteracting CaMKII inhibition was tested. Three of these drugs, namely dizocilpine (MK-801), N-nitro-L-arginine methyl ester (L-NAME) and ginkgolide (BN52021), all significantly attenuated the enzyme response to ischemia, whereas an obvious diversity in the time-course of their actions implicates different mechanisms involved.

Modulation of signal transduction in rat synaptoneurosomes by platelet activating factor

The potential involvement of platelet activating factor (PAF, 1-O-alkyl 2-O-acetyl-sn-glycero-3-phosphocholine) in aggravation of ischemic brain injury has been recently postulated. Reported evidences in support of this thesis include increases of brain PAF concentration during ischemia and the neuroprotective effect exerted by PAF antagonists. In this article, we demonstrate that several PAF-mediated biochemical responses in synaptoneurosomes in vitro resemble these observed previously in ischemic brain and are widely acknowledged as the potentially causal factors in this pathology. In synaptoneurosomes prepared from rat hippocampus, 10 nM PAF caused an observable elevation of intracellular calcium as measured by fluorescence Fura-2A probe. A similar elevation of synaptoneurosomal [Ca2+]i was evoked by 1 mM glutamate treatment. As an effect of calcium entry after PAF application, a translocation of protein kinase C (PKC) toward plasma membranes was demonstrated by 3H-labeled phorbol-binding method. It was followed by an increase of 50 kDa proteolytic fragment of the enzyme (PKM) recognized on Western blots with anti-PKC antibody. Incubation of synaptoneurosomes in the presence of calcium chelators abolished these effects of PAF and significantly decreased the content of PKC in the membranes. Furthermore, PAF treatment markedly attenuated the receptor- and postreceptor-activated cAMP accumulation in synaptoneurosomes. The decrease of cAMP level seems to be secondary to the PAF-induced calcium entry with subsequent activation of cAMP-specific phosphodiesterase, since it was completely blocked by IBMX, a potent inhibitor of this enzyme. Our observations indicate that PAF in a concentration found in ischemic brain can elevate [Ca2+]i and potentiate calcium-dependent intracellular signalling in synaptoneurosomes in vitro, including PKC translocation/activation and proteolysis, followed by IBMX-sensitive inhibition of cAMP production. The relative contribution of these events to ischemic brain injury is currently under extensive investigation.

Modulation of ischemic signal by antagonists of N-methyl-D-aspartate, nitric oxide synthase, and platelet-activating factor in gerbil hippocampus

Cerebral ischemia in the gerbil results in early hippocampal changes, which include transient activation and/or translocation of protein kinase C (PKC), increased enzymatic activity of ornithine decarboxylase (ODC), and elevated DNA binding ability of activator protein-1 (AP1). The time-course of all three of these postischemic responses was found to be almost parallel, peaking at 3 hr after the ischemic insult. The effectiveness of known modulators of postischemic morphological outcome (MK-801, L-NAME, and gingkolides BN 52020 and BN 52021) in counteracting the induction of PKC, ODC, and AP1 formation was tested. These drugs were administrated as followed: MK-801 (a noncompetitive inhibitor of NMDA channel), 0.8 mg/kg i.p., 30 min before ischemia, and 5 min after the insult; L-NAME (competitive inhibitor of NO synthase), 10 mg/kg i.p., 30 min before ischemia, and 5 mg/kg, 5 min after ischemia; BN52020 and BN52021 (inhibitors of platelet-activating factor: PAF receptors) were administered as a suspension in 5% ethanol in water by oral route, 10 mg/kg for 3 days before ischemia. Three of these drugs, MK-801, L-NAME, and BN52021, significantly reduced ischemia-elevated activity of PKC and ODC, whereas AP1 formation was only partially attenuated. Our observations implicate the existence of different mechanism(s) for postischemic PKC and ODC activation, which in turn is engaged in AP1 induction.

Protein kinase C as an early and sensitive marker of ischemia-induced progressive neuronal damage in gerbil hippocampus

In the model of transient brain ischemia of 6-min duration in gerbils we have estimated: 1. The concentration of brain gangliosides: A significant decrease to about 70% of control was observed selectively in the hippocampus at 3 and 7 d after ischemia. 2. The activity of Na+,K(+)-ATPase: The enzyme activity was not affected in either hippocampus nor in cerebral cortex. 3. The malonaldehyde (MDA) concentration: The levels of MDA had increased at 30 min after ischemia up to 123 and 129% of control in hippocampus and cerebral cortex, respectively. 4. Immunoreactivity of protein kinase C detected by Western blotting: In hippocampus the early translocation toward membranes was followed by a decrease in total enzyme content at 6, 24, 72, and 96 h of postischemic recovery. Also, a sharp increase of 50 kDa isoform (PKM) was noticed immediately and at the early recovery times. The behavior of these biochemical markers of ischemic brain injury in the hippocampus after the short (6 min) insult was contrasted with their reaction in the cerebral cortex as well as after prolongation of the ischemia to 15 min. These results taken together indicate that an early increase in PKC translocation followed by a decrease is the most symptomatic for selective, delayed, postischemic hippocampal injury, resulting from short duration (6 min) ischemia of the gerbil brain.

Regulation of mitochondrial resting state respiration: slip, leak, heterogeneity?

The contribution of molecular slippage of proton pumps, of proton leak and of coupling heterogeneity of mitochondrial population to the well-known non-linear interrelationship between resting state respiration and the protonmotive force is discussed in view of the following experimental findings. (1) After blocking mitochondrial respiration with cyanide, the rate of dissipation of the membrane potential is non-linearly dependent on the actual membrane potential, similarly to the resting state respiration in mitochondria titrated with small amounts of an inhibitor. In contrast, delta pH dissipates proportionally to its actual value. (2) The rate of electron flow from succinate to ferricyanide depends upon the protonmotive force, similarly to the flow from succinate to oxygen. This strongly suggests that the H+/e- stoichiometry in complexes III and IV of the respiratory chain is constant. (3) Mitochondria 'in situ', in permeabilized Ehrlich ascites cells, exhibit the same non-linear flux/force relationship as isolated mitochondria. These results strongly suggest that the non-ohmic characteristics of the inner mitochondrial membrane, with respect to protons driven by the membrane potential but not by the concentration gradient, is the main factor responsible for the nonlinear flux/force relationship in resting state mitochondria.

Resting state respiration of mitochondria: reappraisal of the role of passive ion fluxes

Rat liver mitochondria respiring under resting state conditions in the presence of oligomycin were rapidly blocked with cyanide and the dissipation of the membrane potential, measured with a tetraphenylphosphonium-sensitive electrode, was followed over time. The plot of the rate of membrane potential dissipation versus the actual value of the membrane potential was nonlinear and identical to the plot of resting state respiration (titrated with small amounts of a respiratory inhibitor) versus the membrane potential. The relationship between the respiratory chain activity and the proton-motive force in mitochondria oxidizing succinate with either oxygen or ferricyanide as electron acceptors was also found to be identical. These results are interpreted as an indication that the passive permeability of the inner mitochondrial membrane toward ions is far more significant in maintaining resting state respiration than is the molecular slippage of the pumps in the respiratory chain. These results also confirm the non-ohmic characteristics of the inner mitochondrial membrane.