Changes in mRNA levels of the sarcoplasmic/endoplasmic-reticulum Ca(2+)-ATPase isoforms in the rat soleus muscle regenerating from notexin-induced necrosis

The Meeting of Micropeptides with Major Ca2+ Pumps in Inner Membranes-Consideration of a New Player, SERCA1b

Calcium is a major signalling bivalent cation within the cell. Compartmentalization is essential for regulation of calcium mediated processes. A number of players contribute to intracellular handling of calcium, among them are the sarco/endoplasmic reticulum calcium ATP-ases (SERCAs). These molecules function in the membrane of ER/SR pumping Ca²⁺ from cytoplasm into the lumen of the internal store. Removal of calcium from the cytoplasm is essential for signalling and for relaxation of skeletal muscle and heart. There are three genes and over a dozen isoforms of SERCA in mammals. These can be potentially influenced by small membrane peptides, also called regulins. The discovery of micropeptides has increased in recent years, mostly because of the small ORFs found in long RNAs, annotated formerly as noncoding (lncRNAs). Several excellent works have analysed the mechanism of interaction of micropeptides with each other and with the best known SERCA1a (fast muscle) and SERCA2a (heart, slow muscle) isoforms. However, the array of tissue and developmental expressions of these potential regulators raises the question of interaction with other SERCAs. For example, the most abundant calcium pump in neonatal and regenerating skeletal muscle, SERCA1b has never been looked at with scrutiny to determine whether it is influenced by micropeptides. Further details might be interesting on the interaction of these peptides with the less studied SERCA1b isoform.

Protective action of ultrasound-guided electrolysis technique on the muscle damage induced by notexin in rats

It is known that exercise can be one of the causes of muscular damage. In recent times, physiotherapists and medical professionals have been employing USGET techniques to stimulate muscle recovery to improve its performance after the injury. We pretend to analyse if the Ultrasound-guided electrolysis (USGET) technique could reduce muscle damage, inflammation, and pain in the present study. Female Wistar rats were assigned to one of three different groups: control (C), notexin (NOT) and notexin with USGET (electrolysis at 6mA) (NOT+USGET). We used the USGT technique, based on electrical stimulation with a continuous current of 4 pulses at an intensity of 6 mA for 5 seconds, conveyed to the muscle. The response was tested with motor function tests. In these tests, we could observe an increase in time and foot faults when crossing a beam in the NOT group compared to C group rats. On the other hand, a significant decrease in both variables was detected in the NOT+USGET compared to the NOT group. Muscle power was measured with a grip strength test, obtaining far better performances in NOT+USGET rats when compared to NOT rats. Moreover, the USGET technique prevented the increase of pro-inflammatory proteins IL-6 and chemokines CCL3 (Chemokine (C-C motif) ligand 3), CCL4 (Chemokine (C-C motif) ligand 4), and CCL5 (Chemokine (C-C motif) ligand 5) with their receptor CCR5 (C-C chemokine receptor type 5), induced by notexin in the quadriceps. At the same time, the study evidenced a decrease in both CCR8 (C-C chemokine receptor type 5,) and NF-ᴋB (nuclear factor- ᴋB) expressions after USGET treatment. On the other hand, we obtained evidence that demonstrated anti-inflammatory properties of the USGET technique, thus being the increase in IL-10 (Interleukin 10) and IL-13 (Interleukin 13) in the NOT+USGET group compared to the NOT group. Furthermore, when applying NSGET after damage, an increase in anti-inflammatory mediators and reduction of pro-inflammatory mediators, which, overall, promoted muscle regeneration, was observed. These results support the idea that the NSGET technique improves muscle recovery after toxic damages, which would justify its employment.

Syndecan-4 influences mammalian myoblast proliferation by modulating myostatin signalling and G1/S transition

Myostatin, a TGF‐β superfamily member, is a negative regulator of muscle growth. Here we describe how myostatin activity is regulated by syndecan‐4, a ubiquitous transmembrane heparan sulfate proteoglycan. During muscle regeneration the levels of both syndecan‐4 and promyostatin decline gradually after a sharp increase, concurrently with the release of mature myostatin. Promyostatin and syndecan‐4 co‐immunoprecipitate, and the interaction is heparinase‐sensitive. ShRNA‐mediated silencing of syndecan‐4 reduces C2C12 myoblast proliferation via blocking the progression from G1‐ to S‐phase of the cell cycle, which is accompanied by elevated levels of myostatin and p21(Waf1/Cip1), and decreases in cyclin E and cyclin D1 expression. Our results suggest that syndecan‐4 functions as a reservoir for promyostatin regulating the local bioavailability of mature myostatin.

The Effect of SERCA1b Silencing on the Differentiation and Calcium Homeostasis of C2C12 Skeletal Muscle Cells

The sarcoplasmic/endoplasmic reticulum Ca2+ATPases (SERCAs) are the main Ca2+ pumps which decrease the intracellular Ca2+ level by reaccumulating Ca2+ into the sarcoplasmic reticulum. The neonatal SERCA1b is the major Ca2+ pump in myotubes and young muscle fibers. To understand its role during skeletal muscle differentiation its synthesis has been interfered with specific shRNA sequence. Stably transfected clones showing significantly decreased SERCA1b expression (cloneC1) were selected for experiments. The expression of the regulatory proteins of skeletal muscle differentiation was examined either by Western-blot at the protein level for MyoD, STIM1, calsequestrin (CSQ), and calcineurin (CaN) or by RT-PCR for myostatin and MCIP1.4. Quantitative analysis revealed significant alterations in CSQ, STIM1, and CaN expression in cloneC1 as compared to control cells. To examine the functional consequences of the decreased expression of SERCA1b, repeated Ca2+-transients were evoked by applications of 120 mM KCl. The significantly higher [Ca2+]i measured at the 20th and 40th seconds after the beginning of KCl application (112±3 and 110±3 nM vs. 150±7 and 135±5 nM, in control and in cloneC1 cells, respectively) indicated a decreased Ca2+-uptake capability which was quantified by extracting the maximal pump rate (454±41 μM/s vs. 144±24 μM/s, in control and in cloneC1 cells). Furthermore, the rate of calcium release from the SR (610±60 vs. 377±64 μM/s) and the amount of calcium released (843±75 μM vs. 576±80 μM) were also significantly suppressed. These changes were also accompanied by a reduced activity of CaN in cells with decreased SERCA1b. In parallel, cloneC1 cells showed inhibited cell proliferation and decreased myotube nuclear numbers. Moreover, while cyclosporineA treatment suppressed the proliferation of parental cultures it had no effect on cloneC1 cells. SERCA1b is thus considered to play an essential role in the regulation of [Ca2+]i and its ab ovo gene silencing results in decreased skeletal muscle differentiation.

CaMKII content affects contractile, but not mitochondrial, characteristics in regenerating skeletal muscle

Background

The multi-meric calcium/calmodulin-dependent protein kinase II (CaMKII) is the main CaMK in skeletal muscle and its expression increases with endurance training. CaMK family members are implicated in contraction-induced regulation of calcium handling, fast myosin type IIA expression and mitochondrial biogenesis. The objective of this study was to investigate the role of an increased CaMKII content for the expression of the contractile and mitochondrial phenotype in vivo. Towards this end we attempted to co-express alpha- and beta-CaMKII isoforms in skeletal muscle and characterised the effect on the contractile and mitochondrial phenotype.

Results

Fast-twitch muscle m. gastrocnemius (GM) and slow-twitch muscle m. soleus (SOL) of the right leg of 3-month old rats were transfected via electro-transfer of injected expression plasmids for native α/β CaMKII. Effects were identified from the comparison to control-transfected muscles of the contralateral leg and non-transfected muscles. α/β CaMKII content in muscle fibres was 4-5-fold increased 7 days after transfection. The transfection rate was more pronounced in SOL than GM muscle (i.e. 12.6 vs. 3.5%). The overexpressed α/β CaMKII was functional as shown through increased threonine 287 phosphorylation of β-CaMKII after isometric exercise and down-regulated transcripts COXI, COXIV, SDHB after high-intensity exercise in situ. α/β CaMKII overexpression under normal cage activity accelerated excitation-contraction coupling and relaxation in SOL muscle in association with increased SERCA2, ANXV and fast myosin type IIA/X content but did not affect mitochondrial protein content. These effects were observed on a background of regenerating muscle fibres.

Conclusion

Elevated CaMKII content promotes a slow-to-fast type fibre shift in regenerating muscle but is not sufficient to stimulate mitochondrial biogenesis in the absence of an endurance stimulus.

The neonatal sarcoplasmic reticulum Ca2+-ATPase gives a clue to development and pathology in human muscles

The sarcoplasmic/endoplasmic reticulum calcium ATPase 1 (SERCA1) has two muscle specific splice isoforms; SERCA1a in fast-type adult and SERCA1b in neonatal and regenerating skeletal muscles. At the protein level the only difference between these two isoforms is that SERCA1a has C-terminal glycine while SERCA1b has an octapeptide tail instead. This makes the generation of a SERCA1a specific antibody not feasible. The switch between the two isoforms is a hallmark of differentiation so we describe here a method based on the signal ratios of the SERCA1b specific and pan SERCA1 antibodies to estimate the SERCA1b/SERCA1a dominance on immunoblot of human muscles. Using this method we showed that unlike in mouse and rat, SERCA1b was only expressed in pre-matured infant leg and arm muscles; it was replaced by SERCA1a in more matured neonatal muscles and was completely absent in human foetal and neonatal diaphragms. Interestingly, only SERCA1a and no SERCA1b were detected in muscles of 7-12 years old boys with Duchenne, a degenerative-regenerative muscular dystrophy. However, in adult patients with myotonic dystrophy type 2 (DM2), the SERCA1b dominated over SERCA1a. Thus the human SERCA1b has a different expression pattern from that of rodents and it is associated with DM2.

Extracellular deposition of matrilin-2 controls the timing of the myogenic program during muscle regeneration

Here, we identify a role for the matrilin-2 (Matn2) extracellular matrix protein in controlling the early stages of myogenic differentiation. We observed Matn2 deposition around proliferating, differentiating and fusing myoblasts in culture and during muscle regeneration in vivo. Silencing of Matn2 delayed the expression of the Cdk inhibitor p21 and of the myogenic genes Nfix, MyoD and Myog, explaining the retarded cell cycle exit and myoblast differentiation. Rescue of Matn2 expression restored differentiation and the expression of p21 and of the myogenic genes. TGF-β1 inhibited myogenic differentiation at least in part by repressing Matn2 expression, which inhibited the onset of a positive-feedback loop whereby Matn2 and Nfix activate the expression of one another and activate myoblast differentiation. In vivo, myoblast cell cycle arrest and muscle regeneration was delayed in Matn2(-/-) relative to wild-type mice. The expression levels of Trf3 and myogenic genes were robustly reduced in Matn2(-/-) fetal limbs and in differentiating primary myoblast cultures, establishing Matn2 as a key modulator of the regulatory cascade that initiates terminal myogenic differentiation. Our data thus identify Matn2 as a crucial component of a genetic switch that modulates the onset of tissue repair.

Transfection efficiency along the regenerating soleus muscle of the rat

We investigated the efficiency of a single plasmid transfection along the longitudinal axis of the regenerating soleus of young rats. This also reflected transfection efficiency along the fibers because the soleus is a nearly fusiform muscle in young animals. The complete regeneration was induced by notexin and the transfection was made by intramuscular injection of enhanced green fluorescent protein- or Discosoma red-coding plasmids after 4 days. One week after transfection the number of transfected fibers was higher at the place of injection (i.e., in the muscle belly) and lower or absent at the ends of the muscle. The inspection of longitudinal sections and neuromuscular endplates indicated that one of the reasons of uneven transfection might be the shortness of transfected myotubes and the other reason might be the limit of diffusion of transgenic proteins from the expressing nuclei. As a result, the efficiency of transfection in the whole regenerating muscle was much lower than it could be estimated from the most successfully transfected part.

Restricted Myogenic Potential of Mesenchymal Stromal Cells Isolated from Umbilical Cord

Nonhematopoietic cord blood cells and mesenchymal cells of umbilical cord Wharton's jelly have been shown to be able to differentiate into various cell types. Thus, as they are readily available and do not raise any ethical issues, these cells are considered to be a potential source of material that can be used in regenerative medicine. In our previous study, we tested the potential of whole mononucleated fraction of human umbilical cord blood cells and showed that they are able to participate in the regeneration of injured mouse skeletal muscle. In the current study, we focused at the umbilical cord mesenchymal stromal cells isolated from Wharton's jelly. We documented that limited fraction of these cells express markers of pluripotent and myogenic cells. Moreover, they are able to undergo myogenic differentiation in vitro, as proved by coculture with C2C12 myoblasts. They also colonize injured skeletal muscle and, with low frequency, participate in the formation of new muscle fibers. Pretreatment of Wharton's jelly mesenchymal stromal cells with SDF-1 has no impact on their incorporation into regenerating muscle fibers but significantly increased muscle mass. As a result, transplantation of mesenchymal stromal cells enhances the skeletal muscle regeneration.

Regulation of the alternative splicing of sarcoplasmic reticulum Ca²⁺-ATPase1 (SERCA1) by phorbol 12-myristate 13-acetate (PMA) via a PKC pathway

Myotonic dystrophy type 1 (DM1) is a multi-systemic disease with no established treatment to date. Small, cell-permeable molecules hold the potential to treat DM1. In this study, we investigated the association between protein kinase C (PKC) signaling and splicing of sarcoplasmic reticulum Ca(2+)-ATPase1 (SERCA1). Our aim was to clarify the mechanisms underlying the regulation of alternative splicing, in order to explore new therapeutic strategies for DM1. By assessing the splicing pattern of the endogenous SERCA1 gene in HEK293 cells, we found that treatment with phorbol 12-myristate 13-acetate (PMA) regulated SERCA1 splicing. Interestingly, treatment with PMA for 48 h normalized SERCA1 splicing, while treatment for 1.5h promoted aberrant splicing. These two responses showed dose dependency and were completely abolished by the PKC inhibitor Ro 31-8220. Furthermore, repression of PKCβII and PKCθ by RNAi mimicked prolonged PMA treatment. These results indicate that PKC signaling is involved in the splicing of SERCA1 and provide new evidence for a link between alternative splicing and PKC signaling.

Comparison of satellite cell-derived myoblasts and C2C12 differentiation in two- and three-dimensional cultures: changes in adhesion protein expression

Changes in the expression of adhesion proteins involved in myoblast differentiation were investigated in monolayer (two-dimensional) and 3D (three-dimensional) cell cultures. The expression of integrin alpha3 subunit, integrin beta1 subunit, ADAM12 (a disintegrin and metalloproteinase 12), tetraspanins CD9 and CD81 and M-cadherin were examined in the murine myoblast cell line C2C12 and in a primary culture of rat satellite cells. Myoblasts in monolayer and 3D cultures showed significant differences in their morphology and cytoskeletal organization. All of the studied proteins participated in myoblast fusion in each culture examined, but differences in their levels of expression were observed. Satellite cell-derived myoblasts exhibited higher expression of adhesion protein mRNAs than C2C12 cells. Also, C2C12 cells from a 3D culture showed slightly higher expression of adhesion protein transcripts than the same cells cultured as a monolayer. Significantly, the levels of adhesion protein mRNAs were found to change in parallel in all cell culture types. Despite this finding, it is important that differences between satellite cell-derived myoblasts and cell line C2C12 grown in monolayer and 3D cultures are taken into account when studying processes of myoblast differentiation in vitro.

Myostatin up-regulation is associated with the skeletal muscle response to hypoxic stimuli

Myostatin and hypoxia signalling pathways are able to induce skeletal muscle atrophy, but whether a relationship between these two pathways exists is currently unknown. Here, we tested the hypothesis that a potential mechanism for hypoxia effect on skeletal muscle may be through regulation of myostatin. We reported an induction of myostatin expression in muscles of rats exposed to chronic hypoxia. Interestingly, we also demonstrated increased skeletal muscle myostatin protein expression in skeletal muscle of hypoxemic patients with severe chronic obstructive pulmonary disease (COPD). Parallel studies in human skeletal muscle cell cultures showed that induction of myostatin expression in myotubes treated with hypoxia-mimicking agent such as cobalt chloride (CoCl(2)) is associated with myotube atrophy. Furthermore, we demonstrated that inhibition of myostatin by means of genetic deletion of myostatin or treatment with blocking antimyostatin antibodies inhibits the CoCl(2)-induced atrophy in muscle cells. Finally, addition of recombinant myostatin restored the CoCl(2)-induced atrophy in myostatin deficient myotubes. These results strongly suggest that myostatin can play an essential role in the adaptation of skeletal muscle to hypoxic environment.

The effect of passive movement on denervated soleus highlights a differential nerve control on SERCA and MyHC isoforms

The sarco-endoplasmic reticulum Ca2+ ATP-ase (SERCA) and myosin heavy chain (MyHC) levels were measured in hindlimb-denervated and selectively denervated rat soleus muscles. Selective denervation allowed passive movement of the soleus, whereas hindlimb denervation rendered it to passivity. To minimize chronic effects, we followed the changes only for 2 weeks. Selective denervation resulted in less muscle atrophy, a faster slow-to-fast transition of MyHC isoforms, and less coordinated expressions of the slow vs fast isoforms of MyHC and SERCA. Generally, expression of the slow-twitch type SERCA2a was found to be less dependent, whereas the slow-twitch type MyHC1 was the most dependent on innervation. Our study shows that passive movement is able to ameliorate denervation-induced atrophy of the soleus and that it also accentuates the dyscoordination in the expression of the corresponding slow and fast isoforms of MyHC and SERCA.

Regeneration of reinnervated rat soleus muscle is accompanied by fiber transition toward a faster phenotype

The functional recovery of skeletal muscles after peripheral nerve transection and microsurgical repair is generally incomplete. Several reinnervation abnormalities have been described even after nerve reconstruction surgery. Less is known, however, about the regenerative capacity of reinnervated muscles. Previously, we detected remarkable morphological and motor endplate alterations after inducing muscle necrosis and subsequent regeneration in the reinnervated rat soleus muscle. In the present study, we comparatively analyzed the morphometric properties of different fiber populations, as well as the expression pattern of myosin heavy chain isoforms at both immunohistochemical and mRNA levels in reinnervated versus reinnervated-regenerated muscles. A dramatic slow-to-fast fiber type transition was found in reinnervated soleus, and a further change toward the fast phenotype was observed in reinnervated-regenerated muscles. These findings suggest that the (fast) pattern of reinnervation plays a dominant role in the specification of fiber phenotype during regeneration, which can contribute to the long-lasting functional impairment of the reinnervated muscle. Moreover, because the fast II fibers (and selectively, a certain population of the fast IIB fibers) showed better recovery than did the slow type I fibers, the faster phenotype of the reinnervated-regenerated muscle seems to be actively maintained by selective yet undefined cues.

Androgens negatively regulate myostatin expression in an androgen-dependent skeletal muscle

Myostatin is an important negative regulator of skeletal muscle growth, while androgens are strong positive effectors. In order to investigate the possible interaction between myostatin and androgen pathways, we followed myostatin expression in the androgen-dependent levator ani (LA) muscle of the rat as a function of androgen status. By testosterone deprivation (castration), we induced LA growth arrest in young male rats, whilst atrophy in adult ones, however, both processes could be reversed by testosterone supplementation. After castration, a significant up-regulation of active myostatin protein (and its propeptide) was found, whereas the subsequent testosterone treatment reduced myostatin protein levels to normal values in both young and adult rats. Similarly, a testosterone-induced suppression of myostatin mRNA levels was observed in castrated adult but not in young animals. Altogether, androgens seem to have strong negative impact on myostatin expression, which might be a key factor in the weight regulation of LA muscle.

Reduced Expression of the Sarcoplasmic Calcium Pump SERCA2 in Skeletal Muscle From Patients With Chronic Obstructive Pulmonary Disease and Low Body Weight

OBJECTIVE

To compare the concentrations and extent of nitration of sarcoplasmic-endoplasmic reticulum Ca(2+) adenosine triphosphatase 2 (SERCA2) in biopsies of the quadriceps femoris from patients with chronic obstructive pulmonary disease (COPD) who have normal or low body mass index (BMI).

PATIENTS AND METHODS

The patients were divided into 2 groups (n=7, each group), one containing individuals with normal BMI (> 21 kg/m(2)) and the other with low BMI (< 21 kg/m(2)). Forced spirometry and blood gas analysis were performed in both groups and percutaneous needle biopsies of the lateral portion of the quadriceps femoris muscle were performed. Western blots were used to assess the concentration of SERCA2 in the biopsy material. To determine whether or not the protein was tyrosine-nitrated, immunoprecipitation of SERCA2 was performed with an antinitrotyrosine antibody followed by Western blotting to determine the concentration of the tyrosine-nitrated protein.

RESULTS

Expression of SERCA2 was significantly lower in patients with low BMI (4.2 [0.5] vs 8.1 [1.2] integrated optical density units, P < .05). SERCA2 was also tyrosine-nitrated in the patients with low BMI. Finally, a significant negative correlation was observed between the concentration of SERCA2 and that of inducible nitric oxide synthase (determined in a previous study using the same biopsy material) in patients with COPD and low BMI (r=-0.89, P=.007), while such a correlation was not observed in patients with COPD and normal BMI (r=0.35, P=.43).

CONCLUSIONS

In patients with COPD, SERCA2 concentration is reduced and the protein is tyrosine-nitrated in skeletal muscle from patients with low BMI compared to those with normal BMI. These results indicate the presence of a previously unrecognized cellular alteration in skeletal muscle from patients with COPD and low muscle weight.

Alterations of seizure-induced c-fos immunolabelling and gene expression in the rat cerebral cortex following dexamethasone treatment

We examined the effects of dexamethasone on the expression of the inducible transcription factor c-fos in 4-aminopyridine (4-AP) seizures. Induction of c-fos mRNA due to 4-AP-elicited convulsion was detected by means of the polymerase chain reaction (PCR) in samples from the neocortex. Adult male rats were pretreated with different doses of dexamethasone (0.5, 1, 3, 5mg/kg body weight); 1h later 5mg/kg 4-AP was injected intraperitoneally. Controls received the solvent of dexamethasone. Pretreatment with dexamethasone provided significant symptomatic protection against 4-AP-induced convulsions. Immunohistochemistry was used to evaluate the presence of the c-fos protein. The number of Fos-immunoreactive nuclei per section area was measured in the neocortex and hippocampus. Pretreatment with dexamethasone resulted in a dose-dependent, significant decrease of seizure-induced Fos-protein immunoreactivity in the neocortex, in the hilum of the dentate fascia, as well as in regions CA1-3 of the hippocampus, compared to control animals. Brains processed for mRNA isolation and PCR, displayed a significant increase of c-fos mRNA following the 4-AP treatment, while pretreatment with dexamethasone did not prevent or decrease this boosted c-fos mRNA expression. We conclude that seizure-induced c-fos expression and intracellular Fos-protein localization are mediated by transmitter and receptor systems, and dexamethasone significantly decreases Fos immunoreactivity, probably by regulating the intracellular traffic of the protein. We also conclude that dexamethasone does not interfere with the genomic regulation of c-fos mRNA synthesis.

The expression of the neonatal sarcoplasmic reticulum Ca2+ pump (SERCA1b) hints to a role in muscle growth and development

The neonatal isoform of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 1 (SERCA1b) is a Ca2+ pump with a well-known developmentally regulated transcript level but an undefined protein expression and function. Specific antibodies were generated to show that SERCA1b is exclusively expressed in myoblasts and myotubes of cultured and regenerating muscle. However, the SERCA1b protein was not detectable in normal adult fast and slow muscles. Studies of the in vitro differentiating myogenic cell lines C2C12 and sol8 showed that SERCA1b is the main SERCA1 protein isoform induced during differentiation and that it is found in the myotubes. Remarkably in BC3H1 cells, which show incomplete differentiation and are reluctant to form myotubes, express the SERCA1b mRNA but not the corresponding protein. SERCA1b protein was also absent from stretched or denervated adult soleus, in spite of the fact that its mRNA level was upregulated. SERCA1b accounts for nearly the total of SERCA1 expression in the diaphragm of newborn mice, which suggests that the insufficient function and development of the diaphragm in the SERCA1 null mutant mice may be due to the lack of SERCA1b. Our studies point to an important regulation of SERCA1b expression at the protein level and hints to a role in the growth of the developing muscle.

The effects of the phenylalanine 256 to valine mutation on the sensitivity of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) Ca2+ pump isoforms 1, 2, and 3 to thapsigargin and other inhibitors

Three isoforms of the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase (SERCA) are known to exist in mammalian cells. This study investigated the effects of thapsigargin and a variety of commonly used hydrophobic inhibitors on these SERCA isoforms (i.e. SERCA1b, SERCA2b, and SERCA3a), which were transiently expressed in COS-7 cells. In addition, the study assessed whether the introduction of the phenylalanine to valine mutation at position 256 (F256V), known to reduce the potency of thapsigargin inhibition in avian SERCA1, affects the other SERCA isoforms in a similar manner and whether this mutation also affects the inhibition by other inhibitors. This study has shown that the sensitivity to thapsigargin is different for the SERCA isoforms (apparent K(i) values being 0.21, 1.3, and 12 nm for SERCA1b, SERCA2b, and SERCA3a, respectively). The reduction in thapsigargin sensitivity caused by the F256V mutation was also different for the three isoforms, with SERCA2b only being modestly affected by this mutation. Although some of the other inhibitors investigated (i.e. cyclopiazonic acid and curcumin) showed some differences in their sensitivity toward the SERCA isoforms, most were little affected by the F256V mutation, indicating that they inhibit the Ca(2+)-ATPase by binding to sites on SERCA distinct from that of thapsigargin.

Glucose-induced mixed [Ca2+]c oscillations in mouse beta-cells are controlled by the membrane potential and the SERCA3 Ca2+-ATPase of the endoplasmic reticulum

Stimulatory concentrations of glucose induce two patterns of cytosolic Ca2+ concentration ([Ca2+]c) oscillations in mouse islets: simple or mixed. In the mixed pattern, rapid oscillations are superimposed on slow ones. In the present study, we examined the role of the membrane potential in the mixed pattern and the impact of this pattern on insulin release. Simultaneous measurement of [Ca2+]c and insulin release from single islets revealed that mixed [Ca2+]c oscillations triggered synchronous oscillations of insulin secretion. Simultaneous recordings of membrane potential in a single beta-cell within an islet and of [Ca2+]c in the whole islet demonstrated that the mixed pattern resulted from compound bursting (i.e., clusters of membrane potential oscillations separated by prolonged silent intervals) that was synchronized in most beta-cells of the islet. Each slow [Ca2+]c increase during mixed oscillations was due to a progressive summation of rapid oscillations. Digital image analysis confirmed the good synchrony between subregions of an islet. By contrast, islets from sarco(endo)plasmic reticulum Ca2+-ATPase isoform 3 (SERCA3)-knockout mice did not display typical mixed [Ca2+]c oscillations in response to glucose. This results from a lack of progressive summation of rapid oscillations and from altered spontaneous electrical activity, i.e., lack of compound bursting, and membrane potential oscillations characterized by lower-frequency but larger-depolarization phases than observed in SERCA3+/+ beta-cells. We conclude that glucose-induced mixed [Ca2+]c oscillations result from compound bursting in all beta-cells of the islet. Disruption of SERCA3 abolishes mixed [Ca2+]c oscillations and augments beta-cell depolarization. This latter observation indicates that the endoplasmic reticulum participates in the control of the beta-cell membrane potential during glucose stimulation.

Transient upregulation of connexin43 gap junctions and synchronized cell cycle control precede myoblast fusion in regenerating skeletal muscle in vivo

The spatio-temporal expression of gap junction connexins (Cx) was investigated and correlated with the progression of cell cycle control in regenerating soleus muscle of Wistar rats. Notexin caused a selective myonecrosis followed by the complete recapitulation of muscle differentiation in vivo, including the activation, commitment, proliferation, differentiation and fusion of myogenic cells. In regenerating skeletal muscle, only Cx43 protein, out of Cx-s 26, -32, -37, -40, -43 and -45, was detected in desmin positive cells. Early expression of Cx43 in the proliferating single myogenic progenitors was followed by a progressive upregulation in interacting myoblasts until syncytial fusion, and then by a rapid decline in multinucleate myotubes. The significant upregulation of Cx43 gap junctions in aligned myoblasts preceding fusion was accompanied by the widespread nuclear expression of cyclin-dependent kinase inhibitors p21(waf1/Cip1) and p27(kip1) and the complete loss of Ki67 protein. The synchronized exit of myoblasts from the cell cycle following extensive gap junction formation suggests a role for Cx43 channels in the regulation of cell cycle control. The potential of Cx43 channels to stimulate p21(waf1/Cip1) and p27(kip1) is known. In the muscle, proving the involvement of Cx43 in either a direct or a bystander cell cycle regulation requires functional investigations.

Molecular forms of acetylcholinesterase in the rat extensor digitorum longus and soleus muscles regenerating from notexin-induced necrosis

The activity of acetylcholinesterase molecular forms were examined after separation on sucrose gradients during notexin-induced necrosis and the following regeneration in rat extensor digitorum longus (EDL) and soleus (SOL) muscles. All forms dropped rapidly in both muscles in the first few days after single notexin injection. After a delay small globular forms (G1+G2) started to regenerate from day 7 and larger forms (G4 and A12) from day 10 in EDL. The A8 form which cannot be detected in normal EDL was present between day 7 and day 28. In SOL the recovery of AChE forms begun already on day 3. The small globular forms displayed a more rapid increase between day 3 and day 7 then the other forms. In SOL we observed a temporary overshooting peak at day 7 in the activity of all molecular forms. Both muscles recovered their normal AChE pattern by that time when muscle fibres regained their normal diameter (day 28). Most of the events of regeneration of AChE forms resembled those of normal myogenesis.

Expression of SERCA2a is not regulated by calcineurin or upon mechanical unloading in skeletal muscle regeneration

This study investigates to what extent the expression of the slow myosin heavy chain (MyHCI) isoform and the slow type sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) isoform are co-regulated in fibers of regenerating skeletal soleus muscle. Both overexpression of cain, a calcineurin inhibitor, or partial tenotomy prevented the expression of MyHCI but left SERCA2a expression unaffected in fibers of regenerating soleus muscles. These data complement those from different experimental models and clearly show that the expression of MyHCI and SERCA2a--the major proteins mediating, respectively, the slow type of contraction and relaxation--are not coregulated in regenerating soleus muscle.

The calcineurin activity and MCIP1.4 mRNA levels are increased by innervation in regenerating soleus muscle

The level of active subunit of calcineurin and the calcineurin (Cn) enzyme activity are increased in innervated but not in denervated slow type regenerating skeletal soleus muscle. These nerve-dependent increases were not accompanied by similar increases in the mRNA levels. The changes in the mRNA level of the modulatory calcineurin interacting protein, MCIP1.4, reflected the calcineurin activity and did not increase in denervated regenerating muscles compared to the innervated regenerating controls. The increases in Cn activity and in MCIP1.4 mRNA levels occurred before the switch from fast to slow-type myosin heavy chain isoforms, a phenomenon similarly known to be dependent on innervation. This highlights the role of mediators, acting between the nerve and calcineurin, in the formation of slow fiber identity.

Myotoxic phospholipases A2 and the regeneration of skeletal muscles

The review explains why the myotoxic phospholipases A2 and cardiotoxins are such important tools in the study of the regeneration and maturation of mammalian skeletal muscle. The role of satellite cells as precursors of cell-based regeneration is discussed and recent controversies on the origin of myogenic cells involved in the regeneration of mature skeletal muscle are addressed. This is followed by discussions of sarcomere reconstruction, myosin and sarcoplasmic reticulum ATPase expression, the electrophysiological properties of regenerating muscle, and the reconstruction of the neuromuscular junction. The emphasis throughout is on the plastic changes of major structural and functional proteins that occur during regeneration, and on other influences that determine the final outcome of regenerative activity such as innervation, thyroid status, mechanical work and the functional integrity of the microcirculation. The review closes with a discussion of some of the factors--such as active regeneration--that influence the success of gene-based therapies applied to inherited muscle disease.

Expression of SERCA2a is independent of innervation in regenerating soleus muscle

The speed of contraction of a skeletal muscle largely depends on the myosin heavy chain isoforms (MyHC), whereas the relaxation is initiated and maintained by the sarcoplasmic reticulum Ca2+-ATPases (SERCA). The expression of the slow muscle-type myosin heavy chain I (MyHCI) is entirely dependent on innervation, but, as we show here, innervation is not required for the expression of the slow-type sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) in regenerating soleus muscles of the rat, although it can play a modulator role. Remarkably, the SERCA2a level is even higher in denervated than in innervated regenerating soleus muscles on day 7 when innervation is expected to resume. Later, the level of SERCA2a protein declines in denervated regenerated muscles but it remains expressed, whereas the corresponding mRNA level is still increasing. SERCA1 (i.e., the fast muscle-type isoform) expression shows only minor changes in denervated regenerating soleus muscles compared with innervated regenerating controls. When the soleus nerve was transected instead of the sciatic nerve, SERCA2a and MyHCI expressions were found to be even more uncoupled because the MyHCI nearly completely disappeared, whereas the SERCA2a mRNA and protein levels decreased much less. The transfection of regenerating muscles with constitutively active mutants of the Ras oncogene, known to mimic the effect of innervation on the expression of MyHCI, did not affect SERCA2a expression. These results demonstrate that the regulation of SERCA2a expression is clearly distinct from that of the slow myosin in the regenerating soleus muscle and that SERCA2a expression is modulated by neuronal activity but is not entirely dependent on it.

Non-competitive NMDA receptor antagonists moderate seizure-induced c-fos expression in the rat cerebral cortex

We examined the effects of non-competitive NMDA glutamate receptor antagonists on seizures elicited by 4-aminopyridine (4-AP), and in particular, on the expression of the transcription factor c-fos induced by these seizures. Induction of c-fos mRNA due to 4-AP-elicited seizures was ascertained by reverse transcription polymerase chain reaction in samples of the neocortex. Adult rats were pretreated with the NMDA receptor antagonists amantadine (40 mg/kg), ketamine (3mg/kg), dizocilpine (MK-801; 1mg/kg) or dextrometorphan (40 mg/kg); 4-AP (5mg/kg) was then injected i.p. Controls were treated with either antagonist only or with 4-AP only. Pretreatment with the antagonists (with the exception of amantadine) increased the latency of behavioural seizures, but not all of the antagonists caused symptomatic seizure protection. In the brains which were processed for Fos immunohistochemistry, quantitative evaluation of immunostained cells was performed in the neocortex and hippocampus. Treatment with either antagonist did not induce by itself c-fos expression, with the exception of amantadine, which caused slight Fos induction in the neocortex. Pretreatment with all the antagonists resulted in decrease of seizure-induced Fos immunoreactivity with respect to non-pretreated animals. Decrease of immunostained cells was significant in the neocortex, in the granule cell layer and hilus of the dentate gyrus, in hippocampal areas CA1 and CA2. MK-801, ketamine and dextrometorphan decreased significantly Fos immunoreactivity also in area CA3. The decrease of Fos immunostaining was not directly correlated with a suppression of behavioural seizures. The results support an important role of NMDA receptors in c-fos gene induction in acute 4-AP seizures.

Sarcolipin overexpression in rat slow twitch muscle inhibits sarcoplasmic reticulum Ca2+ uptake and impairs contractile function

Sarcolipin (SLN) is an inhibitor of sarco(endo)plasmic reticulum Ca(2+)-ATPases (SERCAs) in vitro, but its function in vivo has not been defined. NF-SLN cDNA (SLN tagged N-terminally with a FLAG epitope) was introduced into rat soleus muscle in one hindlimb by plasmid injection and electrotransfer. Western blotting showed expression and co-immunoprecipitation showed physical interaction between NF-SLN and SERCA2a. Contractile properties and SERCA2a function were assessed and compared with vector-injected contralateral soleus muscles. NF-SLN reduced both peak twitch force (P(t)) (123.9 +/- 12.5 versus 69.8 +/- 8.9 millinewtons) and tetanic force (P(o)) (562.3 +/- 51.0 versus 300.7 +/- 56.9 millinewtons) and reduced both twitch and tetanic rates of contraction (+dF/dt) and relaxation (-dF/dt) significantly. Repetitive stimulation (750-ms trains at 50 Hz once every 2 s for 3 min) showed that NF-SLN increased susceptibility to fatigue. These changes in contractile function were observed in the absence of endogenous phospholamban, and NF-SLN had no effect on either SERCA2a or SERCA1a expression levels. NF-SLN also decreased maximal Ca(2+) transport activity at pCa 5 by 31% with no significant change in apparent Ca(2+) affinity (6.36 +/- 0.07 versus 6.39 +/- 0.08 pCa units). These results show that NF-SLN expression impairs muscle contractile function by inhibiting SERCA function and diminishing sarcoplasmic reticulum Ca(2+) stores.

Antisense inhibition of myoD expression in regenerating rat soleus muscle is followed by an increase in the mRNA levels of myoD, myf-5 and myogenin and by a retarded regeneration

It has been reported that muscles of myoD-/- mice present a lower potential to regenerate, but there are no reports on the effect of acute interference with myoD expression limited in space and time to only a particular regenerating muscle. Here we relied on antisense inhibition of this factor. Four different oligos were tested. The suppression of regeneration indices (the expression of desmin, the formation of myotubes and the initiation of endplates) was the most pronounced, with the oligomer targeting a region encompassing the translation start site of myoD. A mixed backbone phosphorothioate-phosphate diester oligo (200 microl at 20 microM) was still detectable in the muscles 1 h after its administration and reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the level of the targeted 5' end of the myoD mRNA was selectively decreased. The level of myoD protein was also lowered. Four hours after the antisense treatment, when the oligos were no longer detectable, the myoD mRNA level was restored and 24 h later it exceeded controls together with that of myf-5 and myogenin. After 4 weeks, the antisense-treated soleus muscles were similar to the control-treated and the untreated regenerated soleus with respect to fiber types and motor endplates, however, they contained smaller fibers which reflected the asynchronity of regeneration. This shows that successfully targeted simple antisense oligonucleotides can be used as selective tools for inhibition of individual factors in studying the process of muscle regeneration.

Regenerating soleus and extensor digitorum longus muscles of the rat show elevated levels of TNF-alpha and its receptors, TNFR-60 and TNFR-80

We measured the mRNA and protein levels of tumor necrosis factor-alpha (TNF-alpha) and the transcript levels of its receptors (TNFR-60 and TNFR-80) in the rat soleus (slow twitch) and extensor digitorum longus (EDL; fast twitch) muscles regenerating from notexin-induced necrosis. On the first day after administration of the toxin, when most fibers were necrotic and invaded by inflammatory cells/macrophages, dramatic increases of transcript and protein levels of TNF-alpha and of the mRNA levels of its receptors were observed. The transcript levels of TNF-alpha and TNFR-60, but not of TNFR-80, showed a second but smaller increase at the time when newly formed muscle fibers became reinnervated. In situ hybridization showed that on day 1, during the phase of extensive necrosis, the transcript of TNF-alpha was abundantly present and on day 4 of regeneration it was most often seen in areas devoid of desmin. The mRNA level of TNF-alpha was not detectable in BC(3)H1- and C2C12-cultured myoblasts and it was low in freeze-injured muscle, corresponding to the relatively mild degree of inflammation elicited by freezing. Therefore, our results are most consistent with the view that inflammatory cells/macrophages are the main source of TNF-alpha.

Myostatin levels in regenerating rat muscles and in myogenic cell cultures

Myostatin is a newly described member of the TGF-beta superfamily acting as a secreted negative regulator of skeletal muscle mass in several species, but whose mode of action remains largely unknown. In the present work, we followed the myostatin mRNA and protein levels in rat soleus and extensor digitorum longus (EDL) muscles regenerating in vivo from notexin-induced necrosis, and the myostatin transcript levels in two different in vitro myogenic differentiation models: i.e. in mouse BC3H1 and C2Cl2 cultured cells. The in vivo regenerating rat skeletal muscles showed a characteristic time-dependent expression of myostatin mRNA. After notexin injection, the transcript levels dropped below the detection limit on day 1 in soleus and close to the detection limit on day 3 in EDL, then increased to a maximum on day 7 in soleus and after 28 days finally reached the control values in both types of muscles. In contrast, the myostatin protein levels increased dramatically on the first days of regeneration in both muscles, i.e. at the time when its transcript level was low. Later on the myostatin protein level gradually declined to normal in soleus while in EDL it stayed high some days longer and decreased to normal on days 21-28. In vitro proliferating myoblasts produced low level of myostatin mRNA, which increased upon induction of differentiation suggesting that functional innervation is no prerequisite for myostatin expression. Myostatin production in vitro seems not to be dependent on myocyte fusion either, since it is observed in differentiated BC3H1 cells, which are defective in myofiber formation.

Regulation of ventricular fibrillation by heme oxygenase in ischemic/reperfused hearts

We have assessed the relationship between reperfusion-induced ventricular fibrillation (VF) and heme oxygenase (HO) mRNA expression using northern blotting, reverse transcription-polymerase chain reaction (RT-PCR), and enzyme activity in isolated working ischemic/reperfused rat hearts. Isolated hearts were subjected to 30 min of global ischemia followed by 120 min of reperfusion. Upon reperfusion with VF, cardiac function was registered (n = 6 in each group), and HO mRNAs and enzyme activities were measured at the end of reperfusion in hearts that showed VF or did not develop VF. The expression of HO-1 mRNA (about fourfold) was observed in ischemic/reperfused nonfibrillated myocardium in comparison with the nonischemic control hearts. In those hearts when VF was developed, the expression of HO-1 mRNA was not observed in comparison with the nonischemic control myocardium. The results measured by RT-PCR and enzyme analysis support the data obtained by northern blotting. In additional studies, we decided to approach the question from a different angle. Thus, the purpose of our work was also to study the role of HO expression and enzyme activity in electrically fibrillated hearts without the ischemic/reperfused protocol. To simulate the period of 10 min of reperfusion-induced VF, hearts were electrically fibrillated, then defibrillated, and perfused for an additional 110 min, and HO-1 mRNA expression and enzyme activities were determined. Thus, electrically induced VF resulted in about 60%, 60%, and 70% reduction in HO-1 mRNA expression, RT-PCR signal intensity, and enzyme activity, respectively, compared with the nonfibrillated ischemic/reperfused group. In conclusion, our data provide evidence that the development of reperfusion-induced VF inhibits HO-1 mRNA expression and enzyme activity in both electrically fibrillated myocardium and ischemic/reperfused fibrillated hearts. The results clearly show that HO-1 mRNA expression and enzyme activity were increased in ischemic/reperfused nonfibrillated myocardium, suggesting that interventions that are able to increase HO-1 mRNA expression and enzyme activity may prevent the development of VF.

Effects of oxidative stress on the expression of antioxidative defense enzymes in spontaneously hypertensive rat hearts

Little is known concerning the effect of oxidative stress on the expression of antioxidative enzymes in the decompensated cardiac hypertrophy of spontaneously hypertensive rats (SHR), considered as a model of dilative cardiomyopathy in man. Superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) were characterized in isolated perfused hearts of 18 month old SHR and the age-matched normotensive control Wistar-Kyoto (WKY) rats, before and after 30 min infusion of 25 microM H(2)O(2). After infusion of H(2)O(2), aortic flow decreased in WKY from 26.2 +/- 2.2 to 16.0 +/- 0.8 ml/min (p <.05) but not in SHR (18.2 +/- 1.9 vs. 20.7 +/- 2.2 ml/min). This protection was related to the higher myocardial activities of GPx, MnSOD and CuZnSOD in SHR, compared with those of the WKY group. Although total SOD activity in the SHR fell after H(2)O(2) exposure (to 1.81 +/- 0.13 from 3.56 +/- 0.49 U/mg of protein), catalase activity increased (to 2.46 +/- 0.34 from 1.56 +/- 0.29 k min(-1)mg(-1)protein), compared with the pre-infusion period (p <.05 in each case). In additional studies, hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. The results obtained in ischemic/reperfused hearts show the same changes in enzyme activities measured as it was observed in H(2)O(2) perfused hearts, indicating that oxidative stress is independent of the way it was induced. The higher catalase activity derived from elevated mRNA synthesis. The antioxidative system in dilative cardiomyopathic hearts of SHR is induced, probably due to episodes of oxidative stress, during the process of decompensation. This conditioning of the antioxidative potential may help overcome acute stress situations caused by reactive oxygen species in the failing myocardium.

Corticosteroids decrease mRNA levels of SERCA pumps, whereas they increase sarcolipin mRNA in the rat diaphragm

1. In order to explore the potential role of the sarcoplasmic-endoplasmic reticulum Ca2+-ATPase (SERCA)-type pumps and of their modulators phospholamban (PLB) and sarcolipin (SLN) in the functional alterations of the diaphragm induced by corticosteroid treatment, expression of SERCA, PLB and SLN was assessed by RT-PCR in the diaphragm of rats treated daily for 5 days either with triamcinolone (80 mg kg-1, n = 8) or with saline (control; 0.6 ml, n = 8). 2. Triamcinolone treatment reduced the normalised overall amount of all SERCA mRNA in diaphragm by 70 % compared to controls (P < 0.05). This reduction was accounted for by a relatively larger decrease in the SERCA1 mRNA (-69 %, P < 0.05) whilst the decrease in SERCA2 mRNA (-49 %, P = 0.09) did not reach statistical significance. As a result the relative proportion of SERCA2 mRNA was increased from 43 +/- 7 % in control diaphragm to 52 +/- 4 % after triamcinolone treatment (P < 0.05). 3. Only the adult isoform of SERCA1 (i.e. SERCA1a) mRNA was found in the diaphragm of the 15-week-old control rats. Furthermore, triamcinolone treatment resulted in reduced levels of SERCA2a (-40 %, P < 0.05) and increased levels of SLN mRNA (+100 %, P < 0.05), while the decrease in PLB mRNA (-31 %, P = 0.277) did not reach statistical significance. SERCA1b, SERCA2b and SERCA3 mRNA levels fell below the detection limit in the diaphragm of both control and triamcinolone-treated rats. 4. Compared to control diaphragm, control rat heart showed a relatively high PLB/(SERCA1 + SERCA2) mRNA ratio of 7.88 while this ratio amounted only to 0.16 in control extensor digitorum longus (EDL) muscle. Remarkably, the SLN/(SERCA1 + SERCA2) mRNA ratio in normal cardiac muscle (0.96) was nearly the same as in diaphragm, but in EDL it amounted to only 0.05 that in diaphragm. This indicates the very low expression of SLN in rat EDL. 5. These data reveal that considerable alterations in SERCA mRNA levels accompany the functional changes seen in diaphragm after corticosteroid treatment. The relatively larger decrease in SERCA1 mRNA is in agreement with the selective type II fibre atrophy previously observed in the diaphragm of triamcinolone-treated rats, but the magnitude of SERCA alterations is more pronounced than expected on the basis of the structural changes in the diaphragm. The increase in SLN mRNA levels may represent a compensatory mechanism.

Calcium handling proteins in isolated spinal motoneurons

Amyotrophic lateral sclerosis is characterized by motoneuron degeneration, in which glutamate-induced cell death is thought to play a pathogenic role. This excitotoxic process is mediated by cytosolic Ca2+ overload. The glutamatergic ionotropic channel molecules, which constitute a major route of Ca2+ entry, were present on cultured spinal motoneurons. Using ratio RT-PCR, the relative presence in isolated motoneurons of the GluR subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor was evaluated. GluR1 and GluR2 mRNAs were present abundantly, while GluR3 and GluR4 mRNAs were much less abundant. The relative amount of mRNAs encoding the different protein isoforms responsible for Ca2+ uptake into the internal stores and for controlled release of Ca2+ from these stores was also determined. For the sarco/endoplasmic reticulum Ca2+ ATPases (SERCAs), only the SERCA2b class 4 splice variant was found. The inositol 1,4,5-trisphosphate receptor (IP3R) mRNAs were mainly transcribed from the IP3RI and IP3RII genes. Heterogeneity was also observed for the ryanodine receptors (RyR) as the RyR1, RyR2 and RyR3 mRNAs were present.

Heme oxygenase and cardiac function in ischemic/reperfused rat hearts

We investigated whether the expression of heme oxygenase (HO) isozymes was related to the occurrence of ventricular fibrillation (VF) induced by ischemia/reperfusion in nondiabetic and diabetic myocardium. To study the role of HO-1 and HO-2 mRNA expression in VF, isolated hearts obtained from nondiabetic and 8-week diabetic rats were subjected to 30 min of ischemia followed by 2 h of reperfusion. Expression of HO-1 and HO-2 mRNA was studied in fibrillated and nonfibrillated myocardium using Northern blotting and reverse transcription polymerase chain reaction (RT-PCR). The effect of zinc protoporphyrin IX (Zn-PPIX), a potent inhibitor of HO activity, on HO activity was also studied in ischemic/reperfused hearts. Upon reperfusion, an expression of HO-1 was observed in nonfibrillated myocardium. HO-1 mRNA expression was significantly reduced in hearts showed VF. Zn-PPIX (5 microM) treatment reduced HO activity from its control values of 398+/-27 (in nondiabetics) and 370+/-20 pmol bilirubin/h (in diabetics) to 69+/-14 (in nondiabetics, p<.05) and 60+/-11 pmol bilirubin/h (in diabetics, p<.05), respectively, and all hearts, upon reperfusion, showed VF in both nondiabetic and diabetic subjects. HO-2 expression was unchanged in nonfibrillated and fibrillated myocardium. Postischemic function showed no correlation with the expression of these genes. Our data show that the mechanism(s) of ischemia/reperfusion-induced VF involves the downregulation of HO-1 mRNA and a reduction in HO activity. Furthermore, the mechanism(s) of VF at molecular level involving HO isozymes does not show a significant difference between nondiabetics and diabetics.

Prolonged passive stretch of rat soleus muscle provokes an increase in the mRNA levels of the muscle regulatory factors distributed along the entire length of the fibers

The mRNA levels of the adult and the neonatal sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases (SERCA1a and SERCA1b, respectively) and those of the muscle regulatory factors (MRFs: myoD, myf-5, myogenin, MRF4) have been assessed by RT PCR in rat soleus muscles immobilized for 3 days in an extended position (passive stretch). The transcript level of the fast type SERCA1a Ca(2+)-transport ATPase decreased to half of its normal value, whereas that of neonatal SERCA1b isoform increased 5-fold above control in stretched muscles. Immunostaining of muscle cross sections showed that the fraction of fibers expressing the SERCA1a protein was decreased evenly along the length of the stretched muscles indicating that a transformation occurred of fast fibers to slow ones. The mRNA levels of MRFs were elevated 3- to 6-fold above the normal level and were distributed evenly along the length of the stretched muscles. However in the controls these transcripts were more abundant at both ends of the muscle. The stretch increased the level of myoD and immunocytochemistry showed the expression of myoD protein in a number of nuclei of the stretched muscles whereas it was practically undetectable by this method in the control muscles. Western blotting did not indicate a significant stretch-induced increase in the level of the myogenin protein, in spite of the fact that immunocytochemistry tended to show more myogenin-positive nuclei in stretched muscles as compared to the controls. These data indicate that after 3 days of passive stretch the central and the terminal parts of the soleus muscle adapt similarly by increasing the levels of the MRFs, by decreasing the overall levels of the fast SERCA1-type of ATPase and by partially re-establishing a neonatal mode of alternative SERCA1 transcript splicing resulting in an increased SERCA1b/1a ratio.

Ca2+-ATPases and their expression in the mammary gland of pregnant and lactating rats

The transcellular Ca2+ fluxes required for milk production must be rigorously regulated to maintain the low cytosolic Ca2+ concentrations critical to cell function. Ca2+-ATPases play a critical role in the maintenance of this cellular Ca2+ homeostasis. Using RT-PCR and sequencing, we identified six Ca2+ pumps in lactating mammary tissue. Three plasma membrane Ca2+-ATPases (PMCAs) were found (PMCA1b, PMCA2b, and PMCA4b). Two sarco (endo)plasmic reticulum Ca2+-ATPases (SERCAs) were identified (SERCA2 and SERCA3), and the rat homologue to the yeast Golgi Ca2+-ATPase RS-10 was also found. The pattern of mRNA expression of each of these pumps was examined in rat mammary tissue from the 7th day of pregnancy to the 21st day of lactation. Northern blots revealed increased mRNA expression for all Ca2+ pumps by the 14th day of lactation, and transcripts continued to increase through the 18th day of lactation. PMCA1b, PMCA4b, SERCA2, and SERCA3 showed the lowest levels of expression. RS-10 transcripts were more abundant than SERCA2, SERCA3, PMCA1b, and PMCA4b. RS-10 was the only pump to increase in expression before parturition. PMCA2b was the most abundant transcript found in lactating mammary tissue. At peak lactation, expression of PMCA2b approached that of actin. The high expression, high affinity for Ca2+, and high activity at low calmodulin concentrations exhibited by PMCA2b suggest that it is uniquely suited for maintenance of Ca2+ homeostasis in the lactating mammary gland. The pattern of expression and abundance of RS-10 suggest that it is a candidate for the Golgi Ca2+-ATPase shown to be important in maintaining the Golgi Ca2+ concentration required for casein synthesis and micelle formation.

mRNA levels of myogenic regulatory factors in rat slow and fast muscles regenerating from notexin-induced necrosis

The transcript levels of the myogenic regulatory factors (myoD, myf5, myogenin and MRF4) were measured by RT PCR in rat soleus (slow) and EDL (fast) muscles which were regenerating from notexin-induced necrosis. Some muscle fibers in the EDL were more resistant to the toxin, therefore the necrosis and the dominance of myoblasts were delayed for two days in EDL compared to soleus. In spite of this shift in time-course of necrosis, both types of muscle presented roughly similar, although variable, changes in the expression pattern of MRF mRNA levels. For both muscles, the myoD mRNA was upregulated on the first day after administration of the toxin, whereas concomitantly myf-5 mRNA disappeared but showed a substantial increase in later stages of regeneration. In contrast, the mRNA levels of the late MRFs myogenin and MRF4 decreased on day one only in the soleus, then increased on day three in both types of muscle. Meanwhile in EDL the level of MRF4 mRNA remained relatively normal. Four weeks after administration of the toxin the mRNA levels for each of the MRFs returned to nearly control levels. This shows that in spite of the different time course of the necrosis and regeneration, also documented by the microscopical morphology and the skeletal actin mRNA levels of the muscles, the level of MRF transcripts changed according to a quite predictable pattern; the upregulation corresponded to myoblast activation and the downregulation to the reinnervation.

Expression of the sarco/endoplasmic reticulum Ca(2+)-transport ATPase protein isoforms during regeneration from notexin-induced necrosis of rat soleus muscle

Expression levels of fast-twitch (SERCA1), slow-twitch (SERCA2a) and "housekeeping" (SERCA2b) isoforms of the sarcoplasmic reticulum Ca(2+)-transport ATPase were monitored during regeneration of rat soleus muscles following necrosis induced by the toxin notexin at the tissue level by Western blot analysis and at the cellular level by immunocytochemical analysis. Due to necrosis, levels of muscle-specific SERCA1 and SERCA2a isoforms dropped to low levels on the third day after injection of the toxin. Subsequently, during regeneration both isoforms recovered but with a different time course. Expression of the fast type SERCA1 increased first. This type showed its most pronounced increase between day 3 and 10. Expression of the slow type SERCA2a was biphasic. After an increase to approximately one third of the control value on days 5-10, it showed its main increase up to the control level between day 10 and 21. Expression levels of the house-keeping SERCA2b isoform remained relatively constant throughout the 4 weeks of regeneration. Between day 10 and 28, when new innervation is established, SERCA2a expression spread gradually over almost all fibers whereas the number of SERCA1-expressing fibers decreased and only a limited number of fibers co-expressed SERCA1 and SERCA2a. At 4 weeks of regeneration, expression of the fast isoform was found only in 12% of the fibers, whereas the slow form was found in 98% of the fibers. In the contralateral untreated soleus muscles, 26% SERCA1-positive and 81% SERCA2a-positive fibers were observed. Immunocytochemical analysis showed that SERCA1 and SERCA2a were co-expressed with fast and slow myosin isoforms in fibers of normal muscles but in regenerated muscle only slow myosin and slow SERCA isoforms correlated. The results show that during regeneration levels of fast and slow SERCA proteins change in a similar way as their mRNAs do. However, in regenerated soleus, unlike in normal muscle, expression of slow SERCA is coregulated only with the slow myosin isoform. This finding is in agreement with the fact that the number of slow type fibers is increased in regenerated soleus.

Expression of sarcoplasmic/endoplasmic reticulum Ca2+ ATPases in the rat extensor digitorum longus (EDL) muscle regenerating from notexin-induced necrosis

The level of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) mRNAs and proteins have been assessed by RT-PCR, immunoblotting and immunocytochemistry in the rat extensor digitorum longus (EDL) muscles during regeneration from notexin-induced necrosis. As a result of the necrosis, SERCA1 and SERCA2 declined on days 1 and 3 after administration of the toxin. Thereupon the mRNA of the fast isoform SERCA1 rapidly increased between days 5 and 10 to the normal level. The mRNA level of the "housekeeping" SERCA2b isoform increased markedly during the actual necrosis at days 1 and 5, probably due to invading cells. Then the mRNA level of the neonatal SERCA1b splice variant increased first, and exceeded the level of the adult SERCA1a transcript on day 5. At later stages of regeneration the neonatal form was gradually replaced by the adult SERCA1a form, thus recapitulating similar changes known to occur during normal ontogenesis. Along with SERCA1, the levels of the slow isoform (SERCA2a) mRNA and protein increased on day 5, but the SERCA2a mRNA levels never rose above 10% of SERCA1 and after 10 days gradually declined again. In the normal and regenerated muscles, SERCA1 was expressed in 97% of the fibres which accounted for the population of fast-twitch fibres (type IIa, type IIb and probably type IIx/d). SERCA2a was present in 6% of the fibres of normal muscle (mostly in the slow-twitch type I fibres). At the end of regeneration the number of fibres expressing SERCA2a was twice as high and were found in small groups, unlike in normal EDL, but about 50% of these clustered fibres also expressed SERCA1.