F.Miller 1 , O.L.Vinogradova 1,2

1 Institute for Biomedical Problems of Russian Academy of Sciences, Moscow, Russia;

2 Lomonosov Moscow State University, Moscow, Russia

Endurance exercise results in pronounced metabolic changes in skeletal muscle and activates AMP-dependent protein kinase (AMPK), Ca-calmodulin-dependent protein kinase and mitogen-activated pro- tein kinase p38. This leads to activation of peroxisome proliferatior- activated receptor gamma coactivator 1 alpha (PGC-1α) a master regu- lator of mitochondrial biogenesis. On the other hand, aerobic exercise is known not to increase the postexercise myofibrillar fractional syn- thesis rate probably because of negative regulation of mTORC1 path- way by AMPK. Moreover, it might be followed by muscle protein breakdown by activation of ubiquitin proteasome system. The aim of present study was to examine the possibility to eliminate the negative effects of endurance exercise by essential amino acids feeding during postexercise recovery. Nine amateur endurance trained males carried out test sessions: endurance exercise (70 min) and endurance exercise followed by branched-chain amino acids (0.2 g/kg of body weight) feeding. Biopsy samples from m.vastus lateralis were taken before, 40 min, 5 h and 21 h after termination of endurance exercise. Expression of metabolic (PGC-1a, TFMs) and catabolic (Myostatin, Atrogin-1, MuRF) genes were evaluated by real-time PCR. Expression of anabol- ic and catabolic signaling regulators (p70, FOXO1) as well as PGC-1 alpha in cytoplasmic and nuclear fraction were measured by Western blot.

Endurance exercise alone and combined with amino acids feeding was accompanied by significant accumulation of capillary blood lactate level. Expression of mitochondrial biogenesis genes was increased as well as activation of their upstream kinases. Expression of the exercise- induced catabolism markers was different in two groups. Thus admin- istration of amino acids may be used to optimize the effect of endurance exercise.

The work is supported by RFBR grant № 14-04-01807.

AMINO ACID NEUROTRANSMITTERS OF CNS AS SIGNALING MOLECULES AT THE VERTEBRATE NEUROMUSCULAR

JUNCTION: FACTS AND HYPOTHESES A.I. Malomouzh

Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. box 30, Kazan, 420111, Russia

In neurobiology for decades the ‘Dale’s principle’ dominated, ac- cording to which, one neuron synthesizes, stores, and releases a single transmitter liberated from all axon terminals. In this regard, vertebrate motoneuron for a long time was considered as a cell capable to release acetylcholine only. However, by the early 90’s, a large amount of exper- imental data was obtained, the analysis of which led to the formation of the modern theory of ‘co-transmission’. According to this theory, one or several types of synaptically active molecules, co-transmitters (coexisting transmitters) are released from the neuron together with basic mediator.

These co-transmitters are capable of exerting their own effects in the tar- get cell, regulating the release of primary neurotransmitter (presynaptic modulation) or modulating the physiological response in the postsynaptic cell (postsynaptic modulation). At present, it can be stated that the phe- nomenon of co-release of several neurotransmitters from the nerve end- ings is the rule rather than the exception for the entire nervous system, including peripheral part. Some signaling molecules that do not meet the definition of ‘co-transmitters’ are involved in the functioning of the syn- aptic apparatus too. They are released from either neuron, but inde- pendently of the primary neurotransmitter, or have a glial origin or they are released from the postsynaptic cell and, along with co-transmitters, exert their modulating and/or neurotrophic effects.

Investigations during the last two decades indicate a role for glu- tamate (which is the most abundant excitatory neurotransmitter in the CNS) as a signalling molecule at the neuromuscular junction of verte- brates. So, it has been established that glutamate is present in the cyto- plasm of motoneurons, is associated with synaptic vesicles and can be released from motor nerve ending. Furthermore, glutamate receptors and glutamate transporters have been found at the neuromuscular junction directly. It appeared that this amino acid is able to influence the processes of acetylcholine release from motor neuron, and modulatory mechanisms of glutamate action in mammalian and amphibian neuromuscular junc- tions are different. Moreover, in the latter it varies apparently during on- togeny. It was shown that in the early stages of establishing and maturing

of amphibian neuromuscular junction glutamate facilitates quantal acetyl- choline release, whereas in adult animals, the amino acid inhibits the quantal secretion of primary neurotransmitter, and this effect is more pro- nounced at higher frequencies of nerve stimulation. At the same time, at the mammalian neuromuscular junctions any effects of glutamate on quantal acetylcholine release have not been established yet. However, the inhibitory action of this amino acid on the non-quantal acetylcholine re- lease was revealed. Since a majority of data indicates that tonic neuro- transmitter release is one of the neurotrophic control factors then gluta- mate can be considered as a regulator of neurotrophic influence. Due to the fact that glutamate receptors activation (both at amphibian and mam- malian endplates) may be accompanied by the elevation of nitric oxide (NO) synthesis, and the contribution of NO-mediated signaling in metab- olism and contraction of muscle fibers was revealed, glutamate might be assumed to participate in a wide range of physiological functions.

Gamma-aminobutyric acid (GABA), in contrast to glutamate, is the major inhibitory neurotransmitter in the synapses of CNS and plays a key role in the development, maturation and functioning of brain modulating neuronal activity. Research conducted in the 70’s to the present day, demonstrated that GABAergic signaling is not restricted to the CNS, and this amino acid can play the role of signaling molecule at peripheral syn- apses too. Functional GABA receptors have been detected on sympathet- ic and sensory neurons, on unmyelinated axons in vagal and sympathetic nerve trunks, on myelin-producing Schwann cells and on embryonic skeletal muscle cells. Furthermore, it was shown that GABA reduces the release of acetylcholine from the preganglionic fibers in the rat cervical ganglion and in the bullfrog sympathetic ganglion. At the same time, at the neuromuscular synapse no effects of GABA on the parameters of the quantal acetylcholine release and muscle contraction have been shown.

However, recently we have shown that metabotropic GABAB receptors are localized (apparently presynaptically) at mature rat neuromuscular synapse and that their activation leads to a decrease in the intensity of non-quantal acetylcholine release.

Thus, currently the neuromuscular synapse must be regarded as a ra- ther complex and highly plastic morphological and functional structure with a number of multiple-intercellular signaling pathways which can in- volve directly amino acids, previously considered only as CNS mediators.

Supported by grant of RFBR (№ 14-04-01788) and Program of the President of the Russian Federation (Science School no. 5584.2014.4).

INVOLVEMENT OF PHOSPHATIDYLINOSITOL 4,5-BISPHOSPATE-BINDING PROTEINS IN THE CONTROL

OF CONTRACTILE OSCILLATIONS IN PHYSARUM POLYCEPHALUM PLASMODIUM N.B. Matveeva, S.I. Beylina, A.A. Klyueva, V.A. Teplov Institute of Theoretical and Experimental Biophysics, Russian Academy

of Sciences, Pushchino, Moscow region, 142290, Russia

Phosphatidylinositol 4,5-bisphospate (PIP2) is responsible for a wide range of membrane-related phenomena as a source of three second messengers: inositol 1,4,5-trisphosphate (IP3), diacylglycerol (DAG), and phosphatidylinositol 3,4,5-trisphosphate (PIP3). It is also a site of binding of phosphatidylinositol-3phosphatase (PTEN) and PH-domains of pro- teins controlling the cell contractile apparatus. As a substrate of phospho- lipase C (PLC), PIP2 is a key regulator of the intracellular Ca²⁺ concentra- tion and is responsible for calcium fluctuations and waves. The concen- tration of free PIP2 in the membrane is important for these processes. The release of this phospholipid from membrane clusters formed by PIP2- binding proteins causes the phosphorylation of their regulatory domains by protein kinase C (PKC) or interaction with Ca²⁺/calmodulin (Ca²⁺/CaM) [1]. Because the activation of PKC is provided by the prod- ucts of PIP2 hydrolysis DAG and IP3, which releases Ca²⁺ from internal stories, PIP2-binding proteins form in the membrane pools of PIP2, mobi- lized during the activation of the IP3 receptor (IP3R), which appears to be capable to maintain, through PKC and Ca²⁺/CaM, the membrane concen- tration of free PIP2 and thereby its activity.

The goal of the work was to elucidate the mechanism of the regula- tion of the membrane concentration of free PIP2 in the Physarum polycephalum plasmodium, a giant ameboid cell, which exhibits regulari- ties of motile behavior common with those of tissue cells. The plasmodi- um generates auto-oscillations of the intracellular Ca²⁺ concentration, the contractile activity, and the membrane potential and responds to receptor stimulation by attractants with an increase in their frequency. In tensiometric experiments, which are difficult to realize on tissue cells, contractile oscillations were monitored by changes of the longitudinal force generated by isolated plasmodial strands about 5 mm in length and 0.4 mm in diameter under isometric conditions at temperature 22⁰C.

The presence of feedbacks regulating the activity of IP3R, which plays a crucial role in the plasmodial oscillator [2], suggests the possibil-

ity of oscillatory changes in the level of PIP2 and its participation in the regulation of the cytoskeleton dynamics not only through Ca²⁺ but also through phospholipids. It was shown using neomycin as a substrate inhib- itor of PLC and the aminosteroid U73122, an effective blocker of recep- tor-induced PLC activation without inhibition of the enzyme per se, that the activation of PLC is a necessary condition for the generation of autooscillations and the motile response of plasmodium to signal mole- cules secreted by the cell itself [3, 4]. U73122 changed the period of autooscillations but did not abolish autooscillations.

As opposed to U73122, neomycin led to the termination of autooscillations; however, their damping might continue for hours. The response to the inhibitor depended not only on the physiological state of the plasmodium and the concentrations used but also on the pH of medium.

For example, at рН 4.6, an optimal value for the plasmodium cultivation, neomycin at concentrations of 0.1-1 mM at first induced a transient rise in the isometric force, which was accompanied by an increase in the period and amplitude of its oscillations, but the strand stiffness did not change [3].

The duration of the oscillatory regime, which was retained in the presence of neomycin, corresponded to the conception about the development of its effect in membranes of living cells. Neomycin, as a substrate inhibitor of PLC, reduced its activity by gradually binding PIP2, which was released during oscillations. The process was accompanied by the appearance of hyaloplasm-filled membrane blebs typical of PIP2-blocking agents [5].

These blebs resulted from the local detachment of the membrane from cy- toskeleton, which was accompanied by a decrease in the magnitude of the force, as well as the amplitude and period of its oscillations. These changes in the cell stress and consequently in the intracellular pressure determine, according to our mathematical model, the conditions of excitation of the plasmodial oscillator and its parameters [6]. On the retention of the cortex, an increase in the pressure may result from the enhancement of depolymerization of cytoplasmic actin during the PIP2 blockade by neomy- cin [7]. This confirms that PIP2 is the major target of the inhibitor and a regulator of the state of the Physarum cytoskeleton.

The probability of the formation of a complex of neomycin with PIP2 and its competition with PLC for free PIP2 should substantially depend on the dynamics of the association–dissociation of PIP2-binding proteins during the contractile cycle and on the possibility of the phosphoinositide resynthesis, which evidently determines the duration of decay of oscilla- tions. The efficiency of neomycin abruptly increased with increasing pH of

medium, which is probably due to a strong pH dependence of the mem- brane potential of plasmodium, which increased from -50 mV at рН 5 to - 120 mV at рН 7 [8]. The gradient of the membrane potential is surely im- portant for the penetration of neomycin to the target in the cytoplasmic leaflet of the plasma membrane, primary PIP2 location in eukaryotic cells..

The neomycin concentration at рН 7, which causes the arrest of au- to-oscillations on strands similar to the effect of 2-APB, an inhibitor of the IP3 receptor [2], decreased from 3–5 mM at рН 4.6 (which was ob- served only on microplasmodia [3]) to 100 μM (fig. 1а). The response of period at the initial stage of the restoration was by ~25% shorter than in the control and then increased due to the elongation of the contraction of plasmodium to the inhibitor was two-phasic: after the termination of auto-

Fig. 1. Comparative effects of neomycin at concentrations of 0.1 mM (a) and 5 mM (b) and under the combined action of neomycin with the PKC inhibitor UCN-01 at concentrations of 1 µМ (a) and 5 µМ (c) on the re- gime of isometric force auto-oscillations of protoplasmic strands (expla- nations in text).

oscillations for 10–30 min, they gradually resumed; the oscillation phase.

As it was shown on preparations of cardiocyte sarcolemmes, the binding of PIP2 by neomycin stimulates the activity of phosphatidylinositol 5- kinase, which catalyzes the synthesis of PIP2. The significant increase in PIP2 concentration was also induced by the expression in PC12B cells of the protein MARCKS but not its mutant form devoid of the effector do- main binding to PIP2. Probably the restoration of autooscillations in plasmodium is also related to the stimulation of PIP2 resynthesis, alt- hough this question undoubtedly requires further studies with the use of the inhibitors of 4- and 5-inositolkinases. In favor of the activation of re- synthesis of PIP2 upon its binding by neomycin is the acceleration of the restoration of autooscillations with increasing initial frequency at higher concentrations of the inhibitor. At a neomycin concentration of 5 mM, the oscillations resumed within 10 min (fig. 1b) and were accompanied by a more intensive formation of protoplasm-filled blebs than at pН 4.6, which prevented the increase in ectoplasm tension.

To determine whether PIP2-binding proteins similar to MARKS are involved in the regulation of the concentration of free PIP2 in the mem- brane of plasmodium, we examined the effect of the PKC inhibitors staurosporine, UCN-01 (7-hydroxystaurosporine), and Ro-31-8220 sepa- rately and in combination of these inhibitors with the Ca²⁺/CaM inhibitor calmidazolium (1 μM) and with neomycin on the mode of autooscilla- tions of the contractile activity. The main criterion for the assessment of the effect of PKC inhibitors was the duration of the termination of autooscillations induced by neomycin in comparison with the effect of their combined action in parallel experiments.

The inhibitors of PKC in combination with calmidazolium induced a slow decay of autooscillations. They also induced a twofold increase in the duration of the termination of autooscillations in response to neomy- cin added in their presence. It should be noted that the addition of calmidazolium (1 μM) diminished the effect of the PKC inhibitors. This is probably related to its influence on other targets, which led to an in- crease in the intracellular calcium concentration. The most pronounced neomycin-like effect was induced by UCN-01, a selective inhibitor for conventional and novel PKC isotypes. At a concentration of 5 μM, UCN- 01 increased the period and amplitude of autooscillations and enhanced the effect of neomycin added in its presence, which manifested itself as an increase in the duration of the absence of autooscillations (30–40 min) (fig. 1c). When used upon the restoration of autooscillations in the pres-

ence of neomycin, all PKC inhibitors accelerated the increase in the peri- od of restored autooscillations due to the elongation of the contraction phase, which coincides in time with the increase in the concentration of free calcium in the cytoplasm [8]. The results count in favor of the as- sumption that the plasmodial membrane contains MARCKS-like proteins and PKC-controlled pools of PIP2; however, further studies are needed to confirm this assumption.

References

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2. Matveeva N.B., Teplov V.A., Beylina S.I. // Biochemistry (Moscow) Suppl. Ser. A: Membrane and Cell Biology. 2010. 4: 70–76.

3. Matveeva N.B., Beylina S.I., Teplov V.A. // Biol. Membrany. 2006. 23:

306-315. (in Russian).

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6. Teplov V.A. // Protoplasma (Suppl.1). Cell Dynamics 1. 1988: 81-88.

7. De Corte V., Gettemans J., Vandekerckhove J. // FEBS Lett. 1997. 401:

191-196.

8. Kuroda R. et al. // Protoplasma (Suppl.1). Cell Dynamics 1. 1988: 72-80.

STRUCTURAL AND FUNCTIONAL EFFECTS OF TWO STABILIZING SUBSTITUTIONS, D137L AND G126R, IN THE MIDDLE PART OF α-TROPOMYOSIN MOLECULE

Alexander M. Matyushenko¹,Natalia V. Artemova¹, Daniil V. Shchepkin², Galina V. Kopylova², Sergey Y. Bershitsky², Andrey K. Tsaturyan^3,4, Nikolai N. Sluchanko¹,Dmitrii I. Levitsky^1,5

1 Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia

2 Institute of Immunology and Physiology, Russian Academy of Sciences, Yekaterinburg, Russia

3 Institute of Mechanics, Moscow State University, Moscow, Russia

4 Blagonravov Institute of Machines Science, Russian Academy of Sciences, Moscow, Russia

5 Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia

Tropomyosin (Tm) is an α-helical coiled-coil protein that binds along the length of actin filament and plays an essential role in the regula- tion of muscle contraction. There are two highly conserved non-canonical residues in the middle part of the Tm molecule, Asp137 and Gly126, which are thought to impart conformational instability (flexibility) to this

region of Tm which is considered crucial for its regulatory functions. It was shown previously that replacement of these residues by canonical ones (Leu substitution for Asp137 and Arg substitution for Gly126) re- sults in stabilization of the coiled-coil in the middle of Tm and affects its regulatory function [1, 2]. We extended these studies employing various methods and approaches (such as CD, limited proteolysis by trypsin, ATPase measurements, in vitro motility assay, etc.) to compare structural and functional features of recombinant human striated muscle α-Tm mu- tants carrying stabilizing substitutions D137L and G126R. Moreover, we for the first time analyzed the properties of Tm carrying both these substi- tutions within the same molecule. The results show that both substitutions similarly stabilize the Tm coiled-coil structure, and their combined action leads to further significant stabilization of the Tm molecule. This stabili- zation has no appreciable influence on the actin affinity for Tm, but it makes the Tm-actin complexes more stable as was shown by measuring the temperature dependences of thermal dissociation of these complexes monitored with light scattering. The stabilizing substitutions in the mid- dle part of Tm increase the ATPase activity of the myosin heads upon their interaction with actin filaments containing Tm and enhances maxi- mal sliding velocity of regulated actin filaments containing Tm and tro- ponin in the in vitro motility assay at high Ca²⁺ concentrations; moreover, this stabilization increases Са²⁺-sensitivity of the actin-myosin interaction underlying this sliding. We propose a possible explanation for the physio- logical effects of these substitutions in the middle part of Tm, according to which their effects on the Ca²⁺-regulated actin-myosin interaction can be accounted for not only by decreased flexibility of actin-bound Tm, but also by the influence of these substitutions on the interactions between the middle part of Tm and certain sites of the myosin head [3, 4].

This work was supported by RFBR (grants 12-04-00411, 13-04- 40099-K, 13-04-40099-H, 13-04-40100-H, 13-04-40101-H), the Program of Ural Branch RAS (project 12-P-4-1007), and the Program “Molecular and Cell Biology” of the Russian Academy of Sciences.

References

1. Sumida J.P., Wu E., and Lehrer S.S. (2008) “Conserved Asp-137 imparts flexibility to tropomyosin and affects function”. J. Biol. Chem. 283, 6728–6734.

2. Nevzorov I.A., Nikolaeva O.P, Kainov Y.A., Redwood C.S., and Levitsky D.I. (2011) “Conserved noncanonical residue Gly-126 confers instability to the middle part of the tropomyosin molecule”. J. Biol. Chem. 286, 15766–15772.