ISG15 blocks cardiac glycolysis and ensures sufficient mitochondrial energy production during Coxsackievirus B3 infection

AIMS

Virus infection triggers inflammation and, may impose nutrient shortage to the heart. Supported by type I interferon (IFN) signalling, cardiomyocytes counteract infection by various effector processes, with the IFN-stimulated gene of 15 kDa (ISG15) system being intensively regulated and protein modification with ISG15 protecting mice Coxsackievirus B3 (CVB3) infection. The underlying molecular aspects how the ISG15 system affects the functional properties of respective protein substrates in the heart are unknown.

METHODS AND RESULTS

Based on the protective properties due to protein ISGylation, we set out a study investigating CVB3-infected mice in depth and found cardiac atrophy with lower cardiac output in ISG15-/- mice. By mass spectrometry, we identified the protein targets of the ISG15 conjugation machinery in heart tissue and explored how ISGylation affects their function. The cardiac ISGylome showed a strong enrichment of ISGylation substrates within glycolytic metabolic processes. Two control enzymes of the glycolytic pathway, hexokinase 2 (HK2) and phosphofructokinase muscle form (PFK1), were identified as bona fide ISGylation targets during infection. In an integrative approach complemented with enzymatic functional testing and structural modelling, we demonstrate that protein ISGylation obstructs the activity of HK2 and PFK1. Seahorse-based investigation of glycolysis in cardiomyocytes revealed that, by conjugating proteins, the ISG15 system prevents the infection-/IFN-induced up-regulation of glycolysis. We complemented our analysis with proteomics-based advanced computational modelling of cardiac energy metabolism. Our calculations revealed an ISG15-dependent preservation of the metabolic capacity in cardiac tissue during CVB3 infection. Functional profiling of mitochondrial respiration in cardiomyocytes and mouse heart tissue by Seahorse technology showed an enhanced oxidative activity in cells with a competent ISG15 system.

CONCLUSION

Our study demonstrates that ISG15 controls critical nodes in cardiac metabolism. ISG15 reduces the glucose demand, supports higher ATP production capacity in the heart, despite nutrient shortage in infection, and counteracts cardiac atrophy and dysfunction.

Validity and Diagnostic Accuracy of Early Written Expression Screeners in Kindergarten

Many students struggle with the basic skill of writing, yet schools lack technically adequate screening measures to identify students at risk in this area. Measures that allow for valid screening decisions that identify students in need of interventions to improve performance are greatly needed. The purpose of this study was to evaluate the validity and diagnostic accuracy of early writing screeners. Two early writing screening measures, Picture Word and Word Dictation, were administered to a diverse sample of 95 kindergarten students, almost half of whom were classified as English language learners and almost 70% identified ethnically as Hispanic. It was hypothesized that the early writing screening measures would demonstrate moderate to strong relationships with a standardized norm-referenced measure of written expression and adequate diagnostic accuracy for identifying kindergarten students at risk. Findings indicate that concurrent validity coefficients for both Picture Word and Word Dictation tasks ranged from .32 to .70 with the Written Expression cluster of the Woodcock–Johnson Tests of Achievement–IV and .26 to .61 with the Writing Samples and Sentence Writing Fluency subtests. Diagnostic accuracy results suggest these measures are a promising option for screening early writing skills. Implications for practice and directions for future research are discussed.

Lehrplanorientierte Inklusion hämophiler Kinder und Jugendlicher im Sportunterricht

Inclusive paedagogic thinking and acting is a modern and increasingly important topic in school sports. It will affect teachers as well as parents and students. The new international guidelines and national curricula enable new ways of inclusion especially for students with chronic illnesses like haemophilia. Special help from the sport teachers is of vital importance.

In our project “fit for life” where we advice children and young adults with haemophilia to find their appropriate sport, we developed a new approach for an optimised inclusion of children with haemophilia into sport lessons. The whole project is running in corporation with the German Sport Teachers Association/ Hessen. We analysed and rated the actual curricula of the different school years and looked at the specific needs, risks and necessary abilities for persons with haemophilia. By this means we gathered about 600 typical movements and/or exercises for school sports and developed individual advice and adapted exercise solutions for sport lessons.

Risk perception and psychological morbidity in men at elevated risk for prostate cancer

OBJECTIVE

As prostate-specific antigen (psa) makes prostate cancer (pca) screening more accessible, more men are being identified with conditions that indicate high risk for developing pca, such as elevated psa and high-grade intraepithelial neoplasia (hgpin). In the present study, we assessed psychological well-being and risk perception in individuals with those high-risk conditions.

METHODS

A questionnaire consisting of a psychological symptom survey, a trait risk-aversion survey, and a cancer-specific risk perception survey was administered to 168 patients with early-stage localized pca and 69 patients at high risk for pca (n = 16 hgpin, n = 53 psa > 4 ng/mL). Analysis of variance was used to examine differences in psychological well-being and appraisal of risk between the groups.

RESULTS

Compared with the pca group, the high-risk group perceived their risk of dying from something other than pca to be significantly lower (p = 0.007). However, pca patients reported significantly more clinically important psychological symptoms.

CONCLUSIONS

The identification of prostate conditions that predict progression to cancer might not result in the psychological symptoms commonly experienced by pca patients, but does appear to be related to a distorted perception of the disease's mortal risk. Patients with pca experience reduced psychological well-being, but better understand the risks of pca recurrence and death. Education on the risks and outcomes of pca can help at-risk men to view health assessments with reduced worry.

[Curricula oriented inclusion of children and adolescents with haemophilia in school sports--a new approach within the project "fit for life"]

Inclusive paedagogic thinking and acting is a modern and increasingly important topic in school sports. It will affect teachers as well as parents and students. The new international guidelines and national curricula enable new ways of inclusion especially for students with chronic illnesses like haemophilia. Special help from the sport teachers is of vital importance. In our project "fit for life" where we advice children and young adults with haemophilia to find their appropriate sport, we developed a new approach for an optimised inclusion of children with haemophilia into sport lessons. The whole project is running in corporation with the German Sport Teachers Association/Hessen. We analysed and rated the actual curricula of the different school years and looked at the specific needs, risks and necessary abilities for persons with haemophilia. By this means we gathered about 600 typical movements and/or exercises for school sports and developed individual advice and adapted exercise solutions for sport lessons.

The allergen Bet v 1 in fractions of ambient air deviates from birch pollen counts

BACKGROUND

Proof is lacking that pollen count is representative for allergen exposure, also because allergens were found in nonpollen-bearing fractions of ambient air.

OBJECTIVE

We monitored simultaneously birch pollen and the major birch pollen allergen Bet v 1 in different size fractions of ambient air from 2004 till 2007 in Munich, Germany.

METHODS

Air was sampled with a ChemVol high-volume cascade impactor equipped with stages for particulate matter (PM)>10 microm, 10 microm>PM>2.5 microm, and 2.5 microm>PM>0.12 microm. Allergen was determined with a Bet v 1-specific ELISA. Pollen count was assessed with a Burkard pollen trap. We also measured the development of allergen in pollen during ripening.

RESULTS

About 93 +/- 3% of Bet v 1 was found in the PM > 10 microm fraction, the fraction containing birch pollen. We did not measure any Bet v 1 in 2.5 microm > PM > 0.12 microm. Either in Munich no allergen was in this fraction or the allergen was absorbed to diesel soot particles that also deposit in this fraction. Pollen released 115% more Bet v 1 in 2007 than in 2004. Also within 1 year, the release of allergen from the same amount of pollen varied more than 10-fold between different days. This difference was explained by a rapidly increasing expression of Bet v 1 in pollen in the week just before pollination. Depending on the day the pollen is released during ripening, its potency varies.

CONCLUSION

In general, pollen count and allergen in ambient air follow the same temporal trends. However, because a 10-fold difference can exist in allergen potency of birch pollen, symptoms might be difficult to correlate with pollen counts, but perhaps better with allergen exposure.

Stretch of mammalian nerve in vitro: effect on compound action potentials

Stretch of nerve has been reported to decrease the amplitude of the compound action potential (CAP) with a complete block appearing in approximately 30 minutes. But for the most part, those experiments were carried out in vivo, and it is generally accepted that the failure of responses was due to a closure of vessels supplying the nerve with a resulting ischemia and anoxia. These studies were undertaken to determine if stretch of nerve has effects that are independent of interference with its vascular supply. In the studies, lengths of rat sciatic and dog peroneal nerves were removed and placed in a chamber supplied with oxygen in which their CAPs were continuously elicited and recorded. This in vitro preparation obviated interference with the nerve's metabolism on stretching. We have previously shown that the form change termed 'beading,' appearing within 10 seconds and reversing as quickly on relaxation, can be elicited with tensions of only several grams. We wished to determine if stretch adequate to produce beading could alter CAPs with the same rapidity. Tensions below 2 g had little effect. On applying tensions of 10-100 g, levels well above those needed to bead the fibers, both increases and decreases of CAP amplitude were seen. The changes occurred within 10 seconds of stretch application, the time at which beading arises with stretch. Although the decreases of CAP amplitudes could be accounted for by beading, the degree of CAP change did not correspond to the amount of tension applied. We hypothesize that the constrictions in the beaded fibers increase axial resistivity and diminish local currents so as to block conduction. The lack of an increasing degree of decreased CAP amplitude with increases in tension is ascribed to the inhibition of elongation offered by the collagen fibrils present in nerve. Collagenase applied to nerves allowed a further increase in length, producing a 'hyperbeading,' showing much longer lengths of beading constrictions on stretch. This would further increase axial resistance and is taken to account for the greater decreases of CAP amplitudes seen following collagenase treatment. To account for those cases where increases of CAP amplitude were seen on stretch, we hypothesize that stretch can also cause an increase in the excitability of the nodes. The outcome of stretch in any given nerve would be the resultant of two opposing actions; beading of the internodes causes a decrease of local currents leading to block of CAPs, while an increased excitability of the nodes acts to augment the responses.

Biomechanics of stretch-induced beading

To account for the beading of myelinated fibers, and axons of unmyelinated nerve fibers as well of neurites of cultured dorsal root ganglia caused by mild stretching, a model is presented. In this model, membrane tension and hydrostatic pressure are the basic factors responsible for axonal constriction, which causes the movement of axonal fluid from the constricted regions into the adjoining axon, there giving rise to the beading expansions. Beading ranges from a mild undulation, with the smallest degree of stretch, to more globular expansions and narrow intervening constrictions as stretch is increased: the degree of constriction is physically limited by the compaction of the cytoskeleton within the axons. The model is a general one, encompassing the possibility that the membrane skeleton, composed mainly of spectrin and actin associated with the inner face of the axolemma, could be involved in bringing about the constrictions and beading.

The origin and nature of beading: a reversible transformation of the shape of nerve fibers

Nerve fibers which appear beaded (varicose, spindle-shaped, etc.) are often considered the result of pathology, or a preparation artifact. However, beading can be promptly elicited in fresh normal nerve by a mild stretch and revealed by fast-freezing and freeze-substitution, or by aldehyde fixating at a temperature near 0 degree C (cold-fixation). The key change in beading are the constrictions, wherein the axon is much reduced in diameter. Axoplasmic fluid and soluble components are shifted from the constrictions into the expansions leaving behind compacted microtubules and neurofilaments. Labeled cytoskeletal proteins carried down by slow axonal transport are seen to move with the soluble components and not to have been incorporated into and remain with, the cytoskeletal organelles on beading the fibers. Lipids and other components of the myelin sheath are also shifted from the constrictions into the expansions, with preservation of its fine structure and thickness. Additionally, myelin intrusions into the axons are produced and a localized bulging into the axon termed "leafing". The beading constrictions do not arise from the myelin sheath: beading occurs in the axons of unmyelinated fibers. It does not depend on the axonal cytoskeleton: exposure of nerves in vitro to beta, beta'-iminodipropionitrile (IDPN) disaggregates the cytoskeletal organelles and even augments beading. The hypothesis advanced was that the beading constrictions are due to the membrane skeleton; the subaxolemmal network comprised of spectrin/fodrin, actin, ankyrin, integrins and other transmembrane proteins. The mechanism can be activated directly by neurotoxins, metabolic changes, and by an interruption of axoplasmic transport producing Wallerian degeneration.

Origin of beading constrictions at the axolemma: presence in unmyelinated axons and after beta,beta'-iminodipropionitrile degradation of the cytoskeleton

Myelinated nerve fibres become beaded when nerves are subjected to a mild stretch; the beading is seen as varicosities, a series of alternating constrictions and enlargements, when using freeze-substitution or cold-fixation to hold this labile form change in place during fixation. One possibility for how this form change comes about is that the myelin sheath or its Schwann cell initiates beading. We now report, however, that a similar beading is seen in the axons of unmyelinated fibres. In electron micrographs, longitudinal sections of axons show the series of constrictions and expansions typical of beading. In cross-sections, axons with unusually small diameter, corresponding to the constrictions, are seen to contain closely packed microtubules and neurofilaments while neighbouring swollen axons with widely dispersed microtubules correspond to the beading expansions. Another possibility for the form change is that the cytoskeleton is responsible for beading. We discovered that direct exposure of nerves to beta, beta'-iminodipropionitrile in vitro for 1-6 h causes both axonal microtubules and neurofilaments to become degraded and replaced by an amorphous residue. Nevertheless, beta,beta'-iminodipropionitrile-treated nerves show constrictions in myelinated fibres when stretched. An even greater degree of beading with narrower and longer constrictions appears in some fibres, with the expanded regions having oblate ends giving the appearance of a string of sausages. In cross-sections taken through the constrictions, a greater than usual reduction of axonal area was seen, this was due to the loss of cytoskeletal organelles which would act to limit the degree of constriction. With longer exposure to beta, beta'-iminodipropinitrile more fibres show complete degeneration of the cytoskeleton and form ovoids typical of Wallerian degeneration. Unmyelinated axons of beta, beta'-iminodipropionitrile-treated nerves which showed degeneration of their cytoskeleton with its replacement by amorphous material still demonstrated beading. As neither the myelin sheath nor the intact cytoskeleton within the axon is necessary for beading, by exclusion, we consider beading constrictions to be initiated at the level of the axolemma. In our hypothesis the membrane skeleton is responsible; namely, the spectrin, actin and other molecular species lining the inside of the axolemma and binding to transmembrane proteins. The membrane skeleton may be activated by stretch via transmembrane proteins (e.g. beta 1-integrins). The membrane skeleton mechanism may also be directly engaged in the production of Wallerian degeneration or be induced by neurotoxic agents.

The beaded form of myelinated nerve fibers

When the nerves are lightly stretched and fixed by freeze-substitution, their fibers show the form-change termed "beading" which consists of a series of undulating constrictions and swellings in the internodes. This form change has not ordinarily been seen in chemically fixed nerves, or when it has, it has been ascribed to a pathological change or an artifact. We now report that beading is also retained in normal nerves when, following a light maintained stretch, they are fixed with aldehydes at a temperature close to 0 degrees C. The degree of beading in single fibers teased from the aldehyde fixed nerves was graded and found to be maximal at 0 degrees C, falling off with increased temperature until, at temperatures above 16 degrees C, most fibers showed no beading or a very mild beading. The fibers of nerves cold-fixed at 0 degrees C displayed the characteristics as freeze-substituted fibers, but with a somewhat smaller number of maximally beaded fibers and an 18% reduction in microtubule numbers in the axons. Desheathing or slitting the sheaths of the nerves before cold-fixation increased the probability of retaining beading. Exposure of stretched nerves to the aldehyde fixative at room temperatures for times as short as 3-5 min before they were cold-fixed showed a diminished degree of beading, indicating that aldehydes can have a deleterious effect on the beading mechanism which we hypothesize to be present in the fiber. This action is distinct from the general cross-linking action of aldehydes.

The relation of the beading of myelinated nerve fibers to the bands of Fontana

The bands of Fontana, appearing as spirals or irregular light and dark strips crossing the surface of unstretched nerves, are due to the wavy disposition of nerve fibers within the epineural-perineural sheaths. A mean tension of 2.7 +/- 0.23 (S.E.M.) g applied to segments of rat tibial nerves straightens the fibers and unbands the nerves causing them to lengthen by 9.35 +/- 0.89%. The nerves cold-fixed in situ at that point showed the myelinated fibers to be beaded. On relaxation the nerves rebanded and the fibers were no longer beaded. The tension at which unbanding occurred was better determined when the epineural-perineural sheaths were slit longitudinally. Under these conditions, unbanding occurred at a mean tension of 0.59 +/- 0.08 g and the nerves lengthened by 8.56 +/- 0.58%. The lengthening was not statistically different from that seen in sheathed nerves. In preparations with the epineural-perineural sheaths removed, banding was lost with tensions of 0.20 +/- 0.03 g and the nerves lengthened by 12.1 +/- 1.04%. The tensions needed were significantly lower than that for the sheathed and slit-sheath nerve groups. When cold-fixed, when banding was lost, the fibers were seen to be beaded. Banding of the desheathed nerves returned on relaxation of the nerves. However, after tensions of 8 g they showed plasticity in which the ends of the nerves needed to be pushed together to initiate rebanding in comparison to sheathed or sheath-slit nerves which rebanded spontaneously following relaxation after even higher tensions of 40 g. At the highest tensions the nerves remained extended and could not be forcibly rebanded.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of alcohol feeding on synthesis and secretion of apolipoproteins by regenerating rat sciatic nerve

The amounts of apolipoprotein (apo) E and A1 released into the culture medium were examined in the regenerating nerves distal to a crush site following chronic alcohol feeding. Cultured minced segments of regenerating nerves taken from rats fed an alcohol-containing liquid diet for 5 weeks released only 50% of apoE but nearly 200% of apoA1 when compared with rats pair-fed with a control diet. The extent of decrease in medium apoE corresponded to the decrease of apoE mRNA in the nerve. Thus, chronic alcohol ingestion affects apoE synthesis of regenerating nerves by changing its mRNA level. On the other hand, apoA1 mRNA remained undetectable in regenerating and intact nerves whether the rats were fed alcohol or not. Furthermore, the amount of apoA1 released by the regenerating nerve into the culture medium was not significantly larger than that present in the nerve tissue prior to incubation. Therefore, it is most likely that apoA1 released by the injured nerve originated from the bloodstream and the increase in apoA1 content seen in the crushed nerve of alcohol-fed rats is due to an enhanced permeability of the nerve-blood barrier. Since the burst of apolipoproteins in the injured nerve is likely to play a role in nerve regeneration, the perturbation of apolipoprotein contents in regenerating nerves by chronic alcohol consumption may contribute to the pathogenesis of alcoholic neuropathy.

Myelin intrusions in beaded nerve fibers

Small intrusions form in the internodes in or near the constrictions of beaded fibers prepared by fast-freezing and freeze-substituting mildly stretched nerves in the cat and rat. They appear as inwardly directed folds of the inner lamellae of the myelin sheath, or regularly formed spheres composed of lamellae with major dense and interperiod lines like those of the myelin sheath. A splitting of the lamellae and separation of the major dense lines may occur with an accumulation of Schwann cell cytoplasm between them, the result of an influx of cytoplasmic fluid from nearby constrictions. Longitudinally oriented microtubules have been observed in the intrusions, in the adaxonal Schwann cell cytoplasm, and in the innermost lamellae of the myelin sheath. The paranodes contain a number of larger intrusions in the form of spurs and globules along with shelve-like folds of the myelin sheath oriented in the longitudinal direction. Axoplasmic fluid driven from the constrictions during beading can enter the paranodes to smooth out their folds leaving the globular and spur-shaped myelin intrusions in isolation. Their wall thickness, measured from the central opening to the surface of the intrusion, is the same as that of the myelin sheath or, in some cases, double, the result of the folding of a spur-like intrusion upon itself. Intrusions unconnected to the sheath are seen in unbeaded fibers with regular, compact lamellae surrounded by axolemma. Others lack a covering axolemma and consist of variably disorganized and irregularly shaped lamellae suggesting that they are undergoing fragmentation and dissolution within the axon. The hypothesis is advanced that the intrusions in the internodes arise from an excess of lipid and other myelin components when the diameter of the sheath is reduced in the beading constrictions. In the paranodes, excess myelin components moved into these regions form the shelf-like folds which may fuse to form intrusions. These, separated from the myelin sheath, undergo fragmentation and dissolution and are carried by retrograde transport to the cell bodies where their constituent components can be reutilized.

Slow transport of freely movable cytoskeletal components shown by beading partition of nerve fibers in the cat

To account for the transport in nerve fibers of tubulin and neurofilament proteins in slow component a, the Structural Hypothesis holds that these proteins are assembled into microtubules and neurofilaments in the cell bodies and the cytoskeletal organelles then moved down in the fibers as part of an interconnected matrix at a uniform rate of about 1 mm/day. The Unitary Hypothesis, on the other hand, considers these proteins to be carried down within the fibers as soluble components or as freely movable small polymers or subunits turning over locally in the stationary cytoskeleton. To differentiate between the two hypotheses, cat L7 dorsal roots were taken at times from 7 to 25 days after their L7 dorsal root ganglia were injected with [3H]leucine to assess the labeling of the cytoskeleton by the use of beading and autoradiography. Beading was induced by a mild stretch and after fast-freezing and freeze-substitution of the roots for histological preparation, the beads were seen in the fibers as a series of expanded regions alternating with constrictions. In the constrictions the cytoskeleton was compacted into an area as small as 5% that of the normal axon, with the axoplasmic fluid and displaceable (freely movable) components squeezed from the constrictions into the adjoining expansions. Roots taken after 7 and 14 days, times consistent with slow component a downflow, were assessed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and their content of tubulin and neurofilament proteins shown to constitute 40-50% of all the labeled proteins present. In autoradiographs of dorsal roots taken at those times, numerous grains due to radioactivity were located over the non-constricted regions of the fibers. Few or no grains were present over the constrictions after 7 days. The findings are in accord with the labeled tubulins and neurofilament proteins being present in soluble form in the fibers and expressed from the constrictions into the expansions of the beaded fibers. In contrast, a number of fibers in roots taken at 14-20 days after injection showed somewhat higher grain densities over the constrictions, and more so after 25 days, indicating uptake of labeled subunits into the cytoskeletal organelles at later times. The results are consistent with the downflow of tubulin and neurofilament proteins as soluble components which drop off in the axon to turn over locally in their respective cytoskeletal organelles.

Cytoskeletal organelles and myelin structure of beaded nerve fibers

Freshly removed cat peripheral nerves and lumbar spinal cord roots were prepared by freeze-substitution to study the form changes, cytoskeletal alterations and myelin structure in beaded nerve fibers. Fibers of unstretched nerves so prepared were close to cylindrical. When lightly stretched with tensions of 2-10 g before being rapidly frozen, beading appeared as a series of constrictions between the more normally expanded regions of the internodes with the paranodal regions spared. Beading also was seen in the fibers of sciatic and radial nerves fast-frozen in situ with the limbs placed in full extension to cause stretching. The cross-sectional area of the axon in the constrictions of beaded fibers was reduced by as much as 95%. The compaction of the microtubules and neurofilaments in the constructions was accounted for by the movement of axoplasmic fluid from the constrictions axially into the nearby regions where the axon and fiber diameters are close to normal. The electron-lucid area approximately 5 nm thick around the microtubules appeared to hinder their close approach in the constrictions although some microtubules touch. The neurofilaments are generally separated at a mean distance of 8-10 nm and approach to a mean distance of 4 nm in the constrictions. Neither the beading nor the reversal of beading, which occurs on relaxation from stretch, was blocked by periods of anoxia lasting several hours. Deletion of calcium from the incubating medium initiated some small amount of beading and additionally greatly augmented the beading on stretch. Beading also was present in some of the myelinated fibers of the dorsal columns of the spinal cord where stretch would not be present. These findings suggest that beading is due to a contractile process in the axon initiated by stretch and by other changed states of the fiber. Concomitantly with the contraction of the axon in the beading constrictions, the myelin sheath in that region was greatly reduced in circumference, to as much as 1/3 to 1/5 of normal. The decrease of the sheath diameter was not accompanied by a change in its thickness or in its lamellar fine structure. A repeat distance of the dense lines of 14 nm was measured in both the constricted and nonconstricted regions. To account for these findings lipid, and most likely other components of the myelin lamellar membranes, must move longitudinally from the constrictions in the plane of the lamellar membranes, and do this within 5-10 s.(ABSTRACT TRUNCATED AT 400 WORDS)

Depression of fast axonal transport produced by tullidora

The fast axoplasmic transport of labeled proteins was studied in cats showing hindlimb paralysis 4-7 weeks after a single oral dose of tullidora (Karwinskia humboldtiana) toxins. The isotope (3H-leucine) was injected into the spinal ganglion and the contralateral spinal cord of the seventh lumbar segment in order to study transport in sensory and motor fibers. The axoplasmic transport in motor fibers of the sciatic nerve was clearly altered in tullidora-treated cats. The majority of these animals showed a gradual decline of radioactivity from the cord to the periphery instead of the clear-cut wave front always seen in normal cats. An apparent wave was seen in three treated cats but the wave peak was behind the normal position and the slope of the wave front was reduced. While the rate of transport indicated by the farthest extent of the foot of the slope was not in all cases significantly changed, the results all indicated a hindered transport by the reduced slope front in the distal segments of the motor axons. In contrast, the axoplasmic transport appeared normal in the sensory fibers of all but one tullidora-treated cat. Light and electron microscopy of medial gastrocnemius and sural (cutaneous) nerves revealed axonal constrictions and axolemal irregularities associated with organelle retention after tullidora treatment. Also, some mitochondria appeared swollen. These changes were more frequent and intense in the motor nerve fibers than in the cutaneous nerve fibers.

Localization of calcium in nerve fibers

Using the desheathed nerve preparation, a pyroantimonate precipitation method was used to examine the distribution of electron-dense particles seen in various organelles of the nerve fibers following exposure of nerve to various levels of Ca2+ in vitro. The presence of Ca2+ in the electron-dense particles was indicated by their extraction with EGTA and by the use of energy-dispersive X-ray microanalysis. In normal Ringer or in a Ca2+ -free medium, electron-dense particles were seen associated with the outer membrane of the mitochondria, with the smooth endoplasmic reticulum (SER), along the axolemma and yet others scattered throughout the axoplasm. When nerves were incubated in media containing higher than normal concentrations of 20-60 mM Ca2+, an increase in the number of such electron-dense particles was seen in the axoplasm and within the mitochondrial matrix. Nerves loaded with a high concentration of 60mM Ca2+ could be depleted of these particles after transfer to a Ca2+ -free or low Ca2+ Ringer medium. The sequestration of Ca2+ in axonal organelles is discussed with respect to Ca2+-regulatory mechanisms in the axon needed to maintain a low level of Ca2+ which is optimal for the support of axoplasmic transport.

Dependence of batrachotoxin block of axoplasmic transport on sodium

Batrachotoxin (BTX) in the low concentration range of 19-190 nM blocks axoplasmic transport in the desheathed cat peroneal nerve in vitro. When the level of Na+ in the incubation medium was reduced to 10 mM, the blocking effect of BTX was much diminished, and in an Na+-free medium BTX had no effect on transport at all. The blocking action of BTX with Na+ present was inhibited by increasing the concentration of Ca2+ in the experimental medium. Relatively small increases were effective with a maximum protection seen when the Ca2+ concentrations were 7-10 mM. The results support the view that an increase in axonal Na+ is inhibitory to the transport mechanism. The results are discussed on the basis of the recently developed transport filament model of axoplasmic transport which takes into account an obligatory role for Ca2+ in transport and its axonal regulation. The possible relation of intraaxonal Na+ concentration to the Ca2+ level is also discussed.

Calcium and the mechanism of axoplasmic transport

Using desheathed cat peroneal nerves in in vitro studies, Ca2+ was recently shown to be required to maintain axoplasmic transport. Calmodulin was also shown to be present in nerve and to participate in transport. These findings open up new possibilities for a better understanding of the underlying mechanism of transport. In the transport filament model, the materials transported are bound to a common carrier, the transport filaments, which are moved along the microtubules by means of an interaction with the side arms of the microtubules. This is an energy-requiring process that depends on a supply of ATP, which is utilized by the Ca2+,Mg2+-ATPase associated with the side arms of the microtubules. The Ca2+,Mg2+-ATPase is activated by calmodulin at the low micromolar levels of free Ca2+ present in the axon. The level is kept low by calcium-regulatory mechanisms that include mitochondria, endoplasmic reticulum, and calcium-binding proteins. Nerves exposed to higher-than-normal concentrations of Ca2+ in the medium show an increased number of particles in these organelles as expected of their Ca2+-regulatory role. The nature of the calmodulin-Ca,Mg-ATPase complex associated with the side arms is discussed on the basis of the transport model. Also discussed is slow transport, which is explained on the basis of the model as a differential binding affinity to the transport filaments.

Patterns of slow transport in sensory nerves

An examination of the pattern of outflow of radioactivity in sciatic nerves was made at times from 1 to 82 days in the rat and up to 132 days in the cat after injecting the L5 and L7 dorsal root ganglia, respectively, with 3H-leucine. Slow waves moving at a rate of 1-2 mm/day were looked for on the basis of their reported presence in the motor fibers of the rat. A consistent pattern of slow waves was not seen in the cat or rat sensory fibers of the sciatic nerves nor was evidence of a slow wave found in the cat dorsal columns. Irregularities in the pattern of outflow which at times appeared as "waves" did so in an irregular fashion, a pattern inconsistent with a steady progression of slow waves in the fibers. The decrease of radioactivity appearing first near the ganglia helps create the impression of a wave along with irregular decreases in the overall levels of radio-activity with time. The results were explained on the basis of the unitary hypothesis. The labeled components are considered to be moved down the fiber by the fast transport mechanism, those components dropping off locally in the fibers early on, constituting the slow wave. As those components turn over locally in the various organelles of fiber and are further redistributed, they may at times give rise to what appears as waves.

External detection of axoplasmic transport using 32P-ATP as precursor

Axoplasmic transport was studied by employing a new external detection method, comparing it to the scintillation method. 32P-ATP was used as the precursor, and the pattern obtained was one typical of slow transport. The patterns recorded from nerves with the external detector system were seen to be closely similar to those found in the same nerves with the usual scintillation method, the external detector systems having the advantage of allowing studies to be made of changes in the pattern of transport in the same nerve over a period of days.

Calmodulin in mammalian nerve

Calmodulin, a calcium-dependent regulatory protein has been isolated from mammalian nerve. The protein has similarities to the calcium-binding protein earlier shown to be transported at a fast rate in the nerve fibers. The implication is that calmodulin, which has been shown to be involved in various key cellular processes, may have a relation to axoplasmic transport.

Block of axoplasmic transport in vitro by vinca alkaloids

The three potent antimitotic vinca alkaloids: vincristine (VCR), vinblastine (VLB), and vindesine (VDS) were compared for their effect in blocking axoplasmic transport in vitro using a desheathed preparation of the peroneal branch of cat sciatic nerve. A range of vinca alkaloid concentrations from 1-100 microM was examined. The relative order of potency in blocking axoplasmic transport was VCR greater than VLB greater than VDS at a concentration of 25 microM. At the higher concentrations block occurred so rapidly that a statistically significant difference between these agents could not be obtained. The relation of vinca block to the transport mechanism is discussed.

The requirement for calcium ions and the effect of other ions on axoplasmic transport in mammalian nerve

1. Until recently it was believed that axoplasmic transport in vitro was not affected by Ca2+, transport being normal in Ca2+-free medium. This was found due to the presence of the relatively impermeable perineurial sheath around the nerve trunks. Using a desheathed cat peroneal nerve preparation, axoplasmic transport was shown to require an adequate level of Ca2+ in the external medium. In a buffered Ca2+-free medium, transport began to decline within 30 min and a complete block occurred in 2 . 6 hr. A concentration of 5 mM-Ca2+ added to a buffered isotonic sucrose of NaCl solution was able to maintain transport. With lower concentrations of Ca2+ of 1 . 5-3 . 0 mM, those usually present in the extracellular fluid or in a Ringer medium, some impairment of transport was seen but the addition of 4 mM-K+ restored the normal pattern of axoplasmic transport. With Ca2+ concentrations below 0 . 75 mM, however, 4 mM-K+ was unable to sustain transport. 2. Potassium by itself at a concentration of 4 mM when added to a buffered isotonic sucrose of NaCl medium was unable to prolong the time of transport block beyond that seen in buffered isotonic NaCl or sucrose solutions. In concentrations of K+ up to 25 mM, 1 . 5-5 mM-Ca2+ was required for normal transport. With moderately higher concentrations of K+ in the range of 50-100 mM, normal appearing transport was seen with or without Ca2+. This was seen whether or not Na+ was present in the medium. At higher levels of K+, 120-150 mM, decreased transport was seen, with or without the addition of either 15 mM-Na+ or Ca2+ in concentrations of 1 . 5-3 . 0 mM. 3. While Mg2+ could not substitute completely for Ca2+ in maintaining transport, it was able to prolong the time before block occurred. An extra 30-60 min of downflow was seen when 5 mM-Mg2+ was added to a buffered isotonic NaCl medium. Magnesium also acts synergistically with Ca2+. Concentration of Ca2+ as low as 0 . 25 mM was, with the addition of 1 . 5 mM-Mg2+, able to maintain transport. 4. The results are interpreted in the light of studies of the mechanism of Ca2+ regulation known to occur in giant nerve fibres and other clls controlling the level of free Ca2+. The relationship of Ca2+ to the mechanism considered to underlie axoplasmic transport in nerve fibres is also discussed.

Uptake of Vinca alkaloids into mammalian nerve and its subcellular components

Three Vinca alkaloids, vinblastine (VLB), vincristine (VCR), and vindesine (VDS), were recently found to affect axoplasmic transport to different degrees, with VCR the most potent. The uptake of these three species by desheathed cat sciatic nerves in vitro was determined by using tritium-labeled derivatives. In a sucrose medium, the uptake of VCR was found to be three to four times greater than that of VLB and VDS, which is in accord with the neurotoxicity of VCR. Uptake of VCR was dependent on Ca2+ concentration in the medium. Removal of Ca2+ from the incubation medium reduced the uptake of VCR, without having much effect on VLB or VDS uptake. The uptake of all three Vinca agents into nerve in a saline medium was about 50% of that in a sucrose medium, and elimination of Ca2+ from the saline incubation medium did not result in any significant change in uptake. High Ca2+ concentrations (100 mM) in the incubation medium, which cause a block of axoplasmic transport, did not change the total uptake of the Vinca alkaloids to any significant degree. The amount of labeled alkaloid found in the soluble fraction was, however, decreased by 50%. There was an increase in the amount present in the particulate fraction, caused, most likely, by an aggregation of vinca-binding components. The amount of VCR associated with tubulin-containing components isolated by gel filtration of the soluble fraction increased twofold when the nerves were exposed to a high-Ca2+ medium, as might be expected of a microtubule disassembly. Exposure of the nerve to low temperatures (0 degrees-4 degrees C) for 90 min did not show any effect on the total uptake of Vinca alkaloids.

Routing of transported materials in the dorsal root and nerve fiber branches of the dorsal root ganglion

After injection of the L7 dorsal root ganglion with 3H-leucine, fast axoplasmic transport carries some 3--5 x more labeled materials down the sensory fibers branches entering the sciatic nerve as compared to the dorsal root fiber branches of the neurons. Freeze-substitution preparations taken from the two sides of the lumbar seventh dorsal root ganglia of cats and monkeys showed little difference in the histograms of nerve fiber diameters of the sensory nerve fiber branch of these neurons as compared to the dorsal root fiber branches. A similar density of microtubules and of neurofilaments in the dorsal root and sensory nerve fiber branches over a wide range of fiber diameters was found in electron micrograph preparations. In the absence of an anatomical difference in the fibers to account for the asymmetrical outflow, a functional explanation based on the transport filament model was advanced.

Increased cyclic GMP in the end-plate region of denervated frog muscle

Denervated frog sartorius muscles showed an approximately 2--3 fold increase of cyclic GMP in their end-plate rich regions which did not appear up to 5 weeks after denervation in the normally end-plate-free pelvic region. No increase in cyclic AMP was seen in these preparations. The results suggest that the increase of cyclic GMP is related to processes specific to the region in which end plates are normally present.