Early postmortem degradation of actin muscle protein in Algerian Sahraoui dromedaries

The present study aimed to evaluate actin degradation during the early postmortem time in Longissimus Lumborum muscle according to Sahraoui dromedary's age. A sample of eight males, young (2 years old) and adult (8 years old) dromedaries, was used to investigate meat quality traits and actin proteolysis during the conversion of muscle to meat. Results demonstrated higher pH values in young compared to adult with a polyphasic pH drop profile. While, age did not affect drip loss (DL) and the values at 72 h postmortem varied from 5 to 9%. Western blot revealed that actin proteolysis occurred since 1 h postmortem and that it was affected by age and postmortem time. In particular, the 32 and 25 kDa actin fragments could be potential markers of ongoing meat tenderization.

Trends of polypharmacy among older adults with schizophrenia in Quebec, Canada between 2000 and 2017

Background

Schizophrenia is a severe psychiatric disorder associated with an increased risk of type 2 diabetes, dyslipidemia and obesity. As adults with schizophrenia age, they become at high risk for multimorbidity and polypharmacy. However, little is known about the trends in total medications use within this population. The objective of this study was to draw a portrait of polypharmacy among Quebec older adults with schizophrenia from 2000 to 2017.

Methods

This population-based cohort study used the data of the Quebec Integrated Chronic Disease Surveillance System of the National Institute of Public Health of Quebec to characterize recent trends and patterns of medications use, according to age and sex. We identified all Quebec residents over 65 years with an ICD-9 or ICD-10 diagnosis of schizophrenia. We calculated the total number of medications used by every individual in each year under study, and the age- and sex-standardized proportion of individuals with polypharmacy (10+ medications, 15+, and 20+). We further identified the clinical and socio-demographic factors associated with polypharmacy using Poisson regression models with robust variance estimation.

Results

From 2000 to 2017, the prevalence of total medications used increased across all age groups, with a median of 8 medications consumed in 2000-2001, which rose to 11 in 2016-2017. The age-standardized proportion of people exposed to different degrees of polypharmacy also increased over time: 5+: 76.6% to 89.3%; 10+ drugs: 36.9% to 62.2%; 15+: 13.3% to 34.4%; 20+: 3.9% to 14.4%. In the multivariate regression, the only clinically significant factor associated with polypharmacy was the high number of diseases (e.g., 5+: RR = 1.29; 95% IC:1.44-1.53).

Conclusions

This study shows a noticeable increase in polypharmacy exposure of older adults with schizophrenia, raising concerns about the growing risks for adverse effects and drug interactions with antipsychotic treatments.

Key messages

Polypharmacy has constantly grown in the last two decades. Further research is needed to better understand outcomes of polypharmacy among older individuals with schizophrenia.

Serine Protease Inhibitors as Good Predictors of Meat Tenderness: Which Are They and What Are Their Functions?

Since years, serine proteases and their inhibitors were an enigma to meat scientists. They were indeed considered to be extracellular and to play no role in postmortem muscle proteolysis. In the 1990's, we observed that protease inhibitors levels in muscles are a better predictor of meat tenderness than their target enzymes. From a practical point of view, we therefore choose to look for serine protease inhibitors rather than their target enzymes, i.e. serine proteases and the purpose of this report was to overview the findings obtained. Fractionation of a muscle crude extract by gel filtration revealed three major trypsin inhibitory fractions designed as F1 (Mr:50-70 kDa), F2 (Mr:40-60 kDa) and F3 (Mr:10-15kD) which were analyzed separately. Besides antithrombin III, an heparin dependent thrombin inhibitor, F1 and F2 comprised a large set of closely related trypsin inhibitors encoded by at least 8 genes bovSERPINA3-1 to A3-8 and able to inhibit also strongly initiator and effector caspases. They all belong to the serpin superfamily, known to form covalent complexes with their target enzymes, were located within muscle cells and found in all tissues and fluids examined irrespective of the animal species. Potential biological functions in living and postmortem muscle were proposed for all of them. In contrast to F1 and F2 which have been more extensively investigated only preliminary findings were provided for F3. Taken together, these results tend to ascertain the onset of apoptosis in postmortem muscle. However, the exact mechanisms driving the cell towards apoptosis and how apoptosis, an energy dependent process, can be completed postmortem remain still unclear.

Caspases and Thrombin Activity Regulation by Specific Serpin Inhibitors in Bovine Skeletal Muscle

In living cells, after activation, protein inhibitors constitute the last step of proteases activity regulation. This review intends to provide original information about a group of bovine muscle serine proteases inhibitors belonging to the Serpin superfamily and characterized at the gene and protein level. This report is the only one and the first to provide much information on this group of proteases inhibitors of the serpin type and their potential biological functions. Amongst the eight genes identified in bovine, three serpins were purified from the muscle tissue and characterized. These are two members of the bovSERPINA3 family, i.e., bovSERPINA3-1 and A3-3, and the last one is antithrombin III (AT-III or BovSERPINC1). BovSERPINA3 family comprises at least eight protein members encoded by different genes mapped on chromosome 7q23-q26 cluster. BovSERPINA3-1 and A3-3 were shown to locate within muscle cells and are cross-class inhibitors strongly active against trypsin as well as against human initiator and effector caspases 8 and 3. They constitute a key apoptosis control in mammals. They were thus expressed in proliferating and confluent myoblasts phases where cells must be alive but not in myotubes. Antithrombin III inhibits trypsin and, in a heparin dependent manner, thrombin. AT-III and its mRNA were expressed in muscle cells and in differentiating primary myoblasts in culture.

Removal kinetic of Escherichia coli and enterococci in a laboratory pilot scale wastewater maturation pond

During the last 15 years several authors studied the disinfection in waste stabilisation pond (WSP) and several empirical models were developed. There are huge differences between the models describing this process and there is really a need to improve the design of ponds for better disinfection. This paper addresses the Escherichia coli and enterococci disinfection in a laboratory pilot scale maturation pond (1.5 l) with light intensity (0, 12 and 25 W/m(2)) under controlled pH, temperature and dissolved oxygen (DO) conditions. The aim of this study is to improve modelling for a better design of disinfection in maturation ponds (MP) and to identify the key parameters influencing the process. It was found that kinetic coefficients K values for E. coli and enterococci are closely dependent on physicochemical parameters. K values increase with increasing pH, I, T and DO. E. coli disinfection depends closely on the pH and the DO and increases strongly when the pH is above 8.5. The enterococci disinfection depends essentially on DO. Two equations are suggested to calculate the kinetic coefficient K related to the environmental average state variables.

Mutagenesis of the bovSERPINA3-3 demonstrates the requirement of aspartate-371 for intermolecular interaction and formation of dimers

The family of serpins is known to fold into a metastable state that is required for the proteinase inhibition mechanism. One of the consequences of this conformational flexibility is the tendency of some mutated serpins to form polymers, which occur through the insertion of the reactive center loop of one serpin molecule into the A-sheet of another. This "A-sheet polymerization" has remained an attractive explanation for the molecular mechanism of serpinopathies. Polymerization of serpins can also take place in vitro under certain conditions (e.g., pH or temperature). Surprisingly, on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, bovSERPINA3-3 extracted from skeletal muscle or expressed in Escherichia coli was mainly observed as a homodimer. Here, in this report, by site-directed mutagenesis of recombinant bovSERPINA3-3, with substitution D371A, we demonstrate the importance of D371 for the intermolecular linkage observed in denaturing and reducing conditions. This residue influences the electrophoretic and conformational properties of bovSERPINA3-3. By structural modeling of mature bovSERPINA3-3, we propose a new "non-A-sheet swap" model of serpin homodimer in which D371 is involved at the molecular interface.

Removal improvement of bacteria (Escherichia coli and enterococci) in maturation ponds using baffles

Korba wastewater treatment plant is a conventional activated sludge followed by three maturation ponds (MP1, MP2, MP3) in series acting as a tertiary treatment. The first study of wastewater treatment plants showed that the effluent concentration of Escherichia coli and enterococci at the outlet of the (MP3) varies between 10(3) and 10(4)CFU/100 ml. After the hydrodynamic study conducted by Rhodamine WT which showed short-circuiting in the MP1, two baffles were introduced in the first maturation pond (MP1) to improve the hydrodynamic and the sanitary performances. The second hydraulic study showed that the dispersion number 'd' was reduced from 1.45 to 0.43 by this engineering intervention and the Peclet number was raised from 0.69 to 2.32. The hydraulic retention time was increased by 14 h. Because of well-designed baffles, the removal efficiency of E. coli and enterococci was raised between 0.2 and 0.7 log units for the first maturation pond.

Comparative analysis of existing disinfection models

For a long time Marais's model has been the main tool for disinfection prediction in waste stabilization ponds (WSPs), although various authors have developed other disinfection models. Some ten other empirical models have been listed over the past fifteen years. Unfortunately, their predictions of disinfection in a given pond are very different. The existing models are too empirical to give reliable predictions: often their explanatory variables were chosen arbitrarily. In this work, we try to demonstrate that if influent variables have daily variations, the use of their average values in simulations may overestimate the disinfection effect. New methods are thus needed to provide better fittings of the models. Better knowledge of the mechanisms involved is needed to improve disinfection models.

Inhibition of human initiator caspase 8 and effector caspase 3 by cross-class inhibitory bovSERPINA3-1 and A3-3

Serpins are a superfamily of structurally conserved proteins. Inhibitory serpins use a suicide substrate-like mechanism. Some are able to inhibit cysteine proteases in cross-class inhibition. Here, we demonstrate for the first time the strong inhibition of initiator and effector caspases 3 and 8 by two purified bovine SERPINA3s. SERPINA 3-1 (uniprotkb:Q9TTE1) binds tighly to human CASP3 (uniprotkb:P42574) and CASP8 (uniprotkb:Q14790) with k(ass) of 4.2x10(5) and 1.4x10(6) M(-1)s(-1), respectively. A wholly similar inhibition of human CASP3 and CASP8 by SERPINA3-3 (uniprotkb:Q3ZEJ6) was also observed with k(ass) of 1.5x10(5) and 2.7x10(6) M(-1)s(-1), respectively and form SDS-stable complexes with both caspases. By site-directed mutagenesis of bovSERPINA3-3, we identified Asp(371) as the potential P1 residue for caspases. The ability of other members of this family to inhibit trypsin and caspases was analysed and discussed.

Cardiac ankyrin repeat protein is a marker of skeletal muscle pathological remodelling

In an attempt to identify potential therapeutic targets for the correction of muscle wasting, the gene expression of several pivotal proteins involved in protein metabolism was investigated in experimental atrophy induced by transient or definitive denervation, as well as in four animal models of muscular dystrophies (deficient for calpain 3, dysferlin, alpha-sarcoglycan and dystrophin, respectively). The results showed that: (a) the components of the ubiquitin-proteasome pathway are upregulated during the very early phases of atrophy but do not greatly increase in the muscular dystrophy models; (b) forkhead box protein O1 mRNA expression is augmented in the muscles of a limb girdle muscular dystrophy 2A murine model; and (c) the expression of cardiac ankyrin repeat protein (CARP), a regulator of transcription factors, appears to be persistently upregulated in every condition, suggesting that CARP could be a hub protein participating in common pathological molecular pathway(s). Interestingly, the mRNA level of a cell cycle inhibitor known to be upregulated by CARP in other tissues, p21(WAF1/CIP1), is consistently increased whenever CARP is upregulated. CARP overexpression in muscle fibres fails to affect their calibre, indicating that CARP per se cannot initiate atrophy. However, a switch towards fast-twitch fibres is observed, suggesting that CARP plays a role in skeletal muscle plasticity. The observation that p21(WAF1/CIP1) is upregulated, put in perspective with the effects of CARP on the fibre type, fits well with the idea that the mechanisms at stake might be required to oppose muscle remodelling in skeletal muscle.

An original SERPINA3 gene cluster: elucidation of genomic organization and gene expression in the Bos taurus 21q24 region

Background

The superfamily of serine proteinase inhibitors (serpins) is involved in numerous fundamental biological processes as inflammation, blood coagulation and apoptosis. Our interest is focused on the SERPINA3 sub-family. The major human plasma protease inhibitor, α1-antichymotrypsin, encoded by the SERPINA3 gene, is homologous to genes organized in clusters in several mammalian species. However, although there is a similar genic organization with a high degree of sequence conservation, the reactive-centre-loop domains, which are responsible for the protease specificity, show significant divergences.

Results

We provide additional information by analyzing the situation of SERPINA3 in the bovine genome. A cluster of eight genes and one pseudogene sharing a high degree of identity and the same structural organization was characterized. Bovine SERPINA3 genes were localized by radiation hybrid mapping on 21q24 and only spanned over 235 Kilobases. For all these genes, we propose a new nomenclature from SERPINA3-1 to SERPINA3-8. They share approximately 70% of identity with the human SERPINA3 homologue. In the cluster, we described an original sub-group of six members with an unexpected high degree of conservation for the reactive-centre-loop domain, suggesting a similar peptidase inhibitory pattern. Preliminary expression analyses of these bovSERPINA3s showed different tissue-specific patterns and diverse states of glycosylation and phosphorylation. Finally, in the context of phylogenetic analyses, we improved our knowledge on mammalian SERPINAs evolution.

Conclusion

Our experimental results update data of the bovine genome sequencing, substantially increase the bovSERPINA3 sub-family and enrich the phylogenetic tree of serpins. We provide new opportunities for future investigations to approach the biological functions of this unusual subset of serine proteinase inhibitors.

Proteomic identification of actin-derived oligopeptides in dry-cured ham

An intense proteolysis of muscle proteins, mainly due to the action of endogenous proteolytic enzymes, has been reported to occur during the processing of dry-cured ham. This gives rise to an important generation of free amino acids and peptides of small size that contribute directly or indirectly to flavor characteristics of the final product. The nature and properties of the free amino acids generated during postmortem proteolysis have been well established. However, little is known about the identity of peptides generated during the processing of dry-cured ham. In the present paper, we describe the isolation (by ethanol precipitation followed by size exclusion and reverse phase chromatographies) and identification (by matrix-assisted laser desorption/ionization time-of-flight MS and collision-induced dissociation MS/MS) in a Spanish dry-cured ham of the following four oligopeptides: (A) TKQEYDEAGPSIVHR, (B) ITKQEYDEAGPSIVHRK, (C) DSGDGVTHNVPIYE, and (D) DSGDGVTHNVPIYEG. This is the first time that these peptide fragments have been reported in dry-cured ham at the end of processing. Sequence homology analysis revealed that the four peptides originated from muscle actin, indicating an extensive hydrolysis of this protein during dry-curing. Some of the cleavage sites corresponding to these fragments in actin were reproduced by other authors through the incubation of this myofibrillar protein in the presence of cathepsin D (EC 3.4.23.5), thus supporting a relevant action of this enzyme during the processing of dry-cured ham.

Purification of the skeletal muscle protein Endopin 1B and characterization of the genes encoding Endopin 1A and 1B isoforms

In the present work, a new endopin-like serpin designed mEndopin 1B was purified from bovine muscle. Biochemical characterizations (amino acid sequencing and Maldi-Tof mass spectrometry peptide mapping) demonstrated that the purified protein is different from the previously described Endopin 1, renamed mEndopin 1A. The genes and cDNA of both endopins were characterized. The cDNA sequence of mEndopin 1B encodes a predicted protein of 411 amino-acids with a molecular mass of 43808Da. The mEndopin 1B gene comprised four coding exons and an additional 5' untranslated exon. The reactive site sequence of mEndopin 1B is somewhat different from that of mEndopin 1A. Nevertheless, both serpins have a similar peptidase inhibitory pattern against examined proteases (elastase, trypsin, plasmin and chymotrypsin). The high expression of both mEndopin 1A and 1B in bovine serum and tissues and their high efficiency to inhibit elastase (k(ass) approximately 10(6)-10(7) M(-1) s(-1)) suggested that these serpins might play a major role in inflammatory processes.

Bovine muscle 20S proteasome: I. Simple purification procedure and enzymatic characterization in relation with postmortem conditions

Over the last decade, several sets of evidence support a possible contribution of the 20S proteasome to the meat tenderizing process. This assumption was emphasized by recent investigations demonstrating that the 20S proteasome was active in the absence of activators and exhibited endo- and exoproteolytic activities, a status often strongly debated before. In the present work, we developed a new rapid and simple purification procedure for muscle 20S proteasome and revisited the physicochemical properties of this complex in relation with the postmortem muscle environmental conditions, i.e. temperature, pH, osmolarity, etc. From a crude extract obtained from freshly excised muscle tissue, reasonable amounts of highly pure proteasome were prepared within a maximum of 4 days using only three chromatography steps. This purified proteasome was used to investigate the effect of pH, temperature, ionic strength and sodium dodecyl sulphate (SDS) on the major hydrolytic activities of this complex, i.e. trypsin-like (TL), chymotrypsin-like (CL) and peptidylglutamyl peptide hydrolase (PGPH) activities. Taken together, the data obtained suggest that the 20S proteasome constitutes a high hydrolytic potential in postmortem muscle conditions. To attest this finding, the 20S proteasome was further quantified by ELISA in at death and postmortem muscles including Longissimus, Rectus abdominis, Diaphragma pedialis and Tensor fascia latae bovine muscles. The primary conclusion was that time course changes in proteasome concentrations were not dependent on the kinetics of the pH fall. Secondly, the proteasome concentration in conditioned meat was in good agreement with previously reported proteolytic activity. Furthermore, the decrease in the muscle proteasome concentration can be considered as slow and this is particularly true in type 1 muscles for which the decrease in the amount of this complex did not exceed 7% during the first three days postmortem. This would suggest that the 20S proteasome was relatively stable during meat conditioning, a feature supporting a potential role in the meat tenderizing process.

Characterization of the bovine PRKAG3 gene: structure, polymorphism, and alternative transcripts

The bovine PRKAG3 gene encodes the AMPK gamma3 subunit, one isoform of the regulatory gamma subunit of the AMP-activated protein kinase (AMPK). The AMPK plays a major role in the regulation of energy metabolism and mutations affecting the genes encoding the gamma subunits have been shown to influence AMPK activity. The gamma3 subunit is involved in the regulation of AMPK activity in skeletal muscle and strongly influences glycogen metabolism. Glycogen content in muscle is correlated to meat quality in livestock because it influences postmortem maturation process and ultimate pH. Naturally occurring mutations in the porcine PRKAG3 gene highly affect meat quality by influencing glycogen content before slaughter. We present the characterization of the bovine PRKAG3 gene and a polymorphism analysis in three cattle breeds. Thirty-two SNPs were identified among which 13 are in the coding region, one is in the 3' UTR, and 18 are in the introns. Five of them change an amino acid in the PRKAG3 protein sequence. Allelic frequencies were determined in the three breeds considered, and mutant alleles affecting the coding sequence are found at a very low frequency. Alternative splicing sites were identified at two positions of the gene, introducing heterogeneity in the population of proteins translated from the gene.

Calpain 1-titin interactions concentrate calpain 1 in the Z-band edges and in the N2-line region within the skeletal myofibril

Calpain 1, a ubiquitous calcium-dependent intracellular protease, was recently found in a tight association with myofibrils in skeletal muscle tissue [Delgado EF, Geesink GH, Marchello JA, Goll DE & Koohmaraie M (2001) J Anim Sci79, 2097-2107). Our immunofluorescence and immunoelectron microscopy investigations restrain the protease location at the periphery of the Z-band and at the midpoint of the I-band. Furthermore, calpain 1 is found to localize in myofibril fractures, described as proteolysis sites, in postmortem bovine skeletal red muscles, near the calcium deposits located at the N1 and N2 level. This in situ localization of calpain 1 is substantiated by binding assays with two titin regions covering the I-band region: a native fragment of 150 kDa (identified by mass spectrometry) that includes the N-terminal Z8-I5 region and the N1-line region of titin, and an 800 kDa fragment external to the N1 line that bears the PEVK/N2 region. These two titin fragments are shown to tightly bind calpain 1 in the presence of CaCl(2) and E64, a calpain inhibitor. In the absence of E64, they are cleaved by calpain 1. We conclude that titin affords binding sites to calpain 1, which concentrates the protease in the regions restrained by the Z-band edge and the N1-line as well as at the N2-line level, two sarcomeric regions where early postmortem proteolysis is detected.

Muscle endopin 1, a muscle intracellular serpin which strongly inhibits elastase: purification, characterization, cellular localization and tissue distribution

In the present work, an endopin-like elastase inhibitor was purified for the first time from bovine muscle. A three-step chromatography procedure was developed including successively SP-Sepharose, Q-Sepharose and EMD-DEAE 650. This procedure provides about 300 microg of highly pure inhibitor from 500 g of bovine diaphragm muscle. The N-terminal sequence of the muscle elastase inhibitor, together with the sequence of a trypsin-generated peptide, showed 100% similarity with the cDNA deduced sequence of chromaffin cell endopin 1. Hence, the muscle inhibitor was designated muscle endopin 1 (mEndopin 1). mEndopin 1 had a molecular mass of 70 kDa, as assessed by both gel filtration and SDS/PAGE. According to the association rates determined, mEndopin 1 is a potent inhibitor of elastase (kass=2.41x10(7) M(-1).s(-1)) and trypsin (kass=3.92x10(6) M(-1).s(-1)), whereas plasmin (kass=1.78x10(3) M(-1).s(-1)) and chymotrypsin (kass=1.0x10(2) M(-1).s(-1)) were only moderately inhibited. By contrast, no inhibition was detected against several other selected serine proteinases, as well as against cysteine proteinases of the papain family. The cellular location of mEndopin in muscle tissue and its tissue distribution were investigated using a highly specific rabbit antiserum. The results obtained demonstrate an intracellular location and a wide distribution in bovine tissues.

Purification of bovine cathepsin B: proteomic characterization of the different forms and production of specific antibodies

Cathepsin B (EC 3.4.22.1) has been highly purified (14,225 fold) from bovine kidney by a rapid procedure that included the preparation of an enriched lysosomal extract, a selective fractionation with ammonium sulphate, size-exclusion chromatography, two cation-exchange chromatographies, and anion-exchange chromatography on diethylaminoethyl-Sephacel. After the last purification step, two hydrolytic peaks against Z-Phe-Arg-AMC were separated from each other, a minor peak corresponding to the cathepsin B single-chain form and a major one representing the double-chain form of cathepsin B. The single-chain form showed a molecular mass of 31 kDa on sodium dodecyl sulphate - polyacrylamide gel electrphoresis (PAGE) under reducing conditions, whereas the heavy chain of the double-chain form appeared as a doublet with molecular masses of 23.4 and 25 kDa, respectively. The identity of the different cathepsin B isoforms and the quality of the final enzyme preparation were confirmed by using two types of antibodies, one against a synthetic peptide sequence and one against purified cathepsin B. The proteomic study confirmed the identity of the different SDS-PAGE protein bands as cathepsin B isoforms and allowed the comparison and study of some structural differences between them at the level of their primary structures.

The calpain 1-alpha-actinin interaction. Resting complex between the calcium-dependent protease and its target in cytoskeleton

Calpain 1 behaviour toward cytoskeletal targets was investigated using two alpha-actinin isoforms from smooth and skeletal muscles. These two isoforms which are, respectively, sensitive and resistant to calpain cleavage, interact with the protease when using in vitro binding assays. The stability of the complexes in EGTA [Kd(-Ca2+) = 0.5 +/- 0.1 microM] was improved in the presence of 1 mm calcium ions [Kd(+Ca2+) = 0.05 +/- 0.01 microM]. Location of the binding structures shows that the C-terminal domain of alpha-actinin and each calpain subunit, 28 and 80 kDa, participates in the interaction. In particular, the autolysed calpain form (76/18) affords a similar binding compared to the 80/28 intact enzyme, with an identified binding site in the catalytic subunit, located in the C-terminal region of the chain (domain III-IV). The in vivo colocalization of calpain 1 and alpha-actinin was shown to be likely in the presence of calcium, when permeabilized muscle fibres were supplemented by exogenous calpain 1 and the presence of calpain 1 in Z-line cores was shown by gold-labelled antibodies. The demonstration of such a colocalization was brought by coimmunoprecipitation experiments of calpain 1 and alpha-actinin from C2.7 myogenic cells. We propose that calpain 1 interacts in a resting state with cytoskeletal targets, and that this binding is strengthened in pathological conditions, such as ischaemia and dystrophies, associated with high calcium concentrations.

Myofibrillar tightly bound calcium in skeletal muscle fibers: a possible role of this cation in titin strands aggregation

In muscle cells, part of the calcium is tightly bound to the N1- and N2-line of the sarcomere but its physiological significance was unknown. In the present work we reported the ability of a recombinant titin fragment spanning titin domains Z9 to I1 to tightly bind calcium ions with a K(d) of 0.049+/-0.004 nM. We further showed that calcium induced a spontaneous aggregation of the titin fragment and that the major aggregate is a tetramer. The implication of these findings on the organization of the six titin strands that emanate from the end of the thick filament within the I-band is discussed.

Calpain 3 is expressed in astrocytes of rat and Microcebus brain

The calcium-dependent protease calpain is involved in numerous functions, including the control of cell survival, plasticity and motility. Whereas the isoforms calpain 1 and 2 have been described as ubiquitously expressed enzymes, calpain 3 has been called "muscle-specific", although trace amounts of calpain 3 mRNA have been detected by Northern blot in brain homogenates. In this study, we validated antibodies raised either against the peptides that were specific for a given isoform or the peptides present in all the three isoforms. We then used the anti-calpain 3 antibodies together with antibodies directed against cell-type-specific proteins to determine by double- and triple-labelling immunocytochemistry if the protease is expressed in specific cell populations of rat as well as lesser mouse lemur (Microcebus murinus) brain. Calpain 3 was almost exclusively found in cells displaying astrocyte morphology. These cells, most of which co-expressed glial fibrillary acidic protein, were particularly numerous close to the striatal subventricular zone (where numerous neurones forming the rostral migratory stream (RMS) towards the olfactory bulbs are generated) and the RMS itself. Other immunoreactive cells were found close to the pial surface of the forebrain, in the corpus callosum and in the dentate gyrus. Calpain 3 may be involved in astrocyte plasticity and/or motility.

Development and evaluation of a sandwich ELISA for quantification of the 20S proteasome in human plasma

Because quantification of the 20S proteasome by functional activity measurements is difficult and inaccurate, we have developed an indirect sandwich enzyme-linked immunosorbent assays (ELISA) for quantification of the 20S proteasome in human plasma. This sandwich ELISA uses a combination of a monoclonal antibody (mcp 20) recognizing the C2-beta subunit of human 20S proteasome (Mr approximately 30,000) and a polyclonal rabbit anti-20S antibody which labels different subunits of the complex. The detection limit of the assay was established as 10 ng/ml (n=10, mean of zero standard+2 S.D.) and the recovery rate ranged from 96% to 104%. The within-run and between-run coefficients of variation (CV) ranges were 2.8-3.3 and 3.0-3.4, respectively. Using serial dilutions of plasma to which various amounts of purified 20S proteasome were added, a linear dose-response was observed between 102 and 2050 ng/ml with a slope of 1.004 and a coefficient of determination r(2) of 0.99. In a preliminary experiment performed on a limited number of patients, the present assay was used to quantify the 20S proteasome in plasma from healthy subjects (n=11) and from a limited number of patients with various diseases (two patients with each of the following diagnoses: acute myeloid leukaemia, chronic myeloproliferative syndromes, Hodgkin's disease and solid tumors). The average concentration of 20S proteasome in plasma from normal subjects was found to be 2319+/-237 ng/ml (n=11). With reference to this normal range, the plasma proteasome concentration was found to be increased in most of these pathological state and as high as 1200% when solid tumors had been detected. For patients with Hodgkin's disease, the changes were more variable whereas in patients with chronic lymphocytic leukaemia, the proteasome concentration was raised during the acute phase of disease and decreased during therapy. We suggest that this robust, accurate and highly reproducible assay could be used to quantify proteasome in human plasma and investigate its value as a biological marker for various malignant and nonmalignant diseases.

Plasma proteasome level is a potential marker in patients with solid tumors and hemopoietic malignancies

BACKGROUND

Proteasomes are nonlysosomal proteolytic structures that have been implicated in cell growth and differentiation. Abnormal expression levels of proteasomes have been described in tumor cells, and proteasomes can be detected and measured in plasma. The objective of this study was to characterize differences in proteasome levels between normal, healthy donors and patients with neoplastic disease and to correlate the findings with clinical status and other biologic markers of disease spread.

METHODS

Plasma proteasome levels were measured using a sandwich enzyme-linked immunosorbent assay in normal donors (n = 73 donors) and in patients with solid tumors (n = 20 patients), acute leukemia (n = 35 patients), myeloproliferative (n = 37 patients) and myelodysplastic (n = 19 patients) syndromes, chronic lymphocytic leukemia (n = 44 patients), non-Hodgkin lymphoma (n =104 patients), Hodgkin disease (n = 14 patients), other lymphoid disorders (n = 17 patients), and multiple myeloma (n = 27 patients).

RESULTS

In the normal donors, the plasma proteasome concentration was 2356 ng/mL +/- 127 ng/mL. Patients with solid tumors exhibited a significantly higher value (7589 ng/mL +/- 2124 ng/mL), similar to the patients with myeloproliferative (4099 ng/mL +/- 498 ng/mL) and myelodysplastic (2922 ng/mL +/- 322 ng/mL) syndromes. Patients with lymphoproliferative disorders, in contrast, had significantly lower values than normal donors (1751 ng/mL +/- 107 ng/mL), except those in aggressive phase of the disease. This low level persisted in patients who were in complete remission. Proteasome levels decreased during the initial phase of treatment. Although there was a significant correlation with serum lactic dehydrogenase levels, frequent discrepancies were noted. There was no correlation with C-reactive protein or beta2-microglobulin levels, even in the group of patients with multiple myeloma.

CONCLUSIONS

The plasma proteasome level is a potential new tool for the monitoring of patients with neoplastic disease. It is not correlated solely with cell lysis and may be involved in the pathophysiology of disease progression.

The calpain system and skeletal muscle growth

The first protein of a group of proteins now identified as belonging to the calpain system was purified in 1976. The calpain system presently is known to be constituted of three well-characterized proteins; several lesser studied proteins that have been isolated from invertebrates; and 10 mRNAs, two each in Drosophila and C. elegans and six in vertebrates, that encode proteins, which, based on sequence homology, belong to the calpain family. The three well-characterized proteins in the calpain family include two Ca2+-dependent proteolytic enzymes, µ-calpain and m-calpain, and a protein, calpastatin, that has no known activity other than to inhibit the two calpains. A substantial amount of experimental evidence accumulated during the past 25 yr has shown that the calpain system has an important role both in rate of skeletal muscle growth and in rate and extent of postmortem tenderization. Calpastatin seems to be the variable component of the calpain system, and skeletal muscle calpastatin activity is highly related to rate of muscle protein turnover and rate of postmortem tenderization. The current paradigm is that high calpastatin activity: 1) decreases rate of muscle protein turnover and hence is associated with an increased rate of skeletal muscle growth; and 2) decreases calpain activity in postmortem muscle and hence is associated with a lower rate of postmortem tenderization. This article summarizes some of the known properties of the calpain system and discusses the potential importance of the calpain system to animal science. Key words: Calpain, calpastatin, postmortem tenderization, skeletal muscle growth

Purification and characterization of a new potential in vivo inhibitor of cathepsin L from bovine skeletal muscle

Four papain-inhibiting peaks, labeled F-I, F-II, F-III, and F-IV, were fractionated from a crude bovine muscle extract by gel filtration chromatography on Sephadex G100, and the F-III fraction was analyzed. From F-III, a cysteine proteinase inhibitor was purified by two successive anionic exchange chromatography steps on Q-Sepharose and Mono-Q columns. This inhibitor has a molecular weight of about 30 kDa. Regarding its specificity toward different proteinases, the purified 30 kDa inhibitor was inactive against serine (trypsin and chymotrypsin) and aspartyl (pepsin) families. In contrast, cathepsin L, H, B, and papain, four enzymes of the cysteine class were strongly inhibited suggesting that this inhibitor was specific to the cysteine proteinase group. However, no inhibitory activity was shown against calpains. Kinetic parameters, including inhibition constants (Ki), rate constant for association (kass) and time required for almost complete inhibition of proteinase in vivo were determined. The values are consistent with a possible physiological function for this inhibitor protein in controlling in vivo cathepsin L activity.

pH is regulated differently by glucose in skeletal muscle from fed and starved rats: a study using 31P-NMR spectroscopy

The aim of this study was to determine whether exogenous glucose metabolism influences the pH in superfused EDL muscle from growing rats fed or starved for 48 h (body weight 55 and 45 g, respectively). Energy state and intracellular pH of muscle were repeatedly monitored by 31P-nuclear magnetic resonance spectroscopy (31P-NMRS); glycogen and other energy metabolites were assayed enzymatically in muscle extracts at the end of the experiment. In EDL muscles from starved rats superfused with glucose for 4 h, intracellular pH was elevated (7-7.3), lactate concentration low, glycogen repletion very intense and citrate synthase activity high. We conclude that glucose was routed mainly toward both oxidative phosphorylation and glycogen synthesis in EDL muscles after food deprivation of rats. In contrast, the major pathway in muscles from fed rats may be glycolysis because the glycogen pool remained constant throughout the experiment. The additional and minor pH component (in the range of 6.5 to 6.8) seen in muscles from fed rats, even in the presence of exogenous glucose, might be due to impaired glucose utilization because this component appears also in muscles from starved rats superfused without glucose or with a nonmetabolizable analog of glucose. Consequently, direct pH measurement by 31P-NMR may be considered to be a precise criterion for evaluation of differences in metabolic potentialities of muscle studied ex vivo in relation to the nutritional state of rats.

Fish muscle cytoskeleton integrity is not dependent on intact thin filaments

Striated muscle cytoskeleton was studied by ultrastructure and electrophoresis. Treatment of sea bass white muscle myofibrils and glycerinated fibres with calpain caused disruption of costameres, intermediate filaments, and Z-line, without altering sarcomeres. V8 protease also caused loss of costameres and Z-line, and disrupted sarcomeres without affecting the intermediate filaments. Recombinant lipase caused loss of Z-lines and also sarcolemma detachment, without changing sarcomeres or intermediate filaments. DNase-1 removed thin filaments and partially removed Z-lines while leaving intact the sarcolemma attachments and intermediate filaments. Calpain, V8 protease, lipase and DNase-1 treatments induced extensive loss of alpha-actinin from the Z-line, which could be related to titin cleavage (calpain, V8), phosphoinositide hydrolysis (lipase), and actin depolymerisation (DNase-1). These results show that the cytoskeletal components are independent of intact thin filaments.

Tissue distribution and characterization of a 30-kDa cysteine proteinase inhibitor from bovine skeletal muscle

Gel chromatography on a Sephadex G100 column of a crude extract obtained from bovine diaphragma muscle separated four fractions (F-I, F-II, F-III and F-IV) in the range of 12-70 kDa that were active against either papain, trypsin or both. From the F-III fraction, a cysteine proteinase inhibitor was purified by two successive anionic exchange chromatographies on Q-Sepharose and Mono Q columns. The pooled active fraction had a Mw of approximately 30 kDa, and isoelectrofocusing revealed one band with a pI of 6.7. The papain-inhibiting activity was unaffected by dithiothreital or 2-mercaptoethanol treatment, and only one band was obtained after SDS-poly acrylamide gel electrophoresis under both reducing and non-reducing conditions. These results suggest that the 30-kDa muscle cysteine proteinase inhibitor did not contain disulphide bonds essential for activity and the protein was a monomer. This proteinase inhibitor is stable between 40 and 80 degrees C and pH 5-12. Furthermore, the 30-kDa inhibitor is stable to papain proteolysis. The tissue distribution of this inhibitor was investigated using double immunodiffusion and Western blot techniques that provided evidence for its presence in bovine heart, spleen, liver and lung and its absence in bovine plasma.

Proteolytic activity of proteasome on myofibrillar structures

The physiologic function of proteasome remains unclear. Evidence suggests a role in degradation of ubiquitin-protein conjugates, MHC antigen presentation, and some specificity of substrate within certain cell types. To explore further the properties of proteasome we have examined its effect on a well defined structure, the myofibril. We find that despite its large size (20S) proteasome is able to degrade myofibrils and intact, permeabilized muscle fibrils. The proteins degraded showed some specificity because actin, myosin and desmin were degraded faster than alpha-actinin, troponin T and tropomyosin. Changes in ultrastructure were slow and included a general loss of structure with Z and I bands effected before the M band and costameres.

Purification and characterisation of a polymorphic low M(r) bovine muscle cysteine proteinase inhibitor: structural identity with fatty-acid-binding proteins

Three low molecular mass cysteine proteinase inhibitors were purified from a bovine skeletal muscle crude extract using a three-step procedure. The crude extract was first subjected to gel filtration on a Sephadex G100 column which separated five active fractions (F-I to F-V). Three papain inhibitors, P1, P2 and P3, were fractionated from the F-V fraction by chromatofocalisation on a poly buffer exchanger column. Purification was completed by chromatography on a Mono Q column. After SDS-PAGE, the three inhibitors showed only one band with an M(r) of 14,300. P1, P2 and P3 appeared to be highly resistant to temperature (40-90 degrees C), pH (3-10), reducing agents (5-50 mM) and to be specific for cysteine proteinases since no activity was detected against either serine or aspartyl proteinases. Although to a varying extent, P1, P2 and P3 inhibited papain, cathepsin B and cathepsin L. Analysis of the peptide mixtures of these inhibitors by RP-HPLC after hydrolysis with CNBr or aspartly endoproteinase N together with their amino acid composition revealed that P1, P2 and P3 cysteine proteinase inhibitors are isoforms of the same protein. As their N-terminal ends were blocked, partial sequence of some of these peptides was determined. Computer search in protein identification resources did not reveal any homology of these sequences with proteinase inhibitors of known primary structure. In contrast, they matched well with different parts of the total sequence of a fatty acid binding protein isolated from bovine heart. This homology was supported by the ability of these inhibitors to bind long chain fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteolytic and physicochemical mechanisms involved in meat texture development

Development in meat texture is a complex process originating very likely from a softening of the structural elements, especially myofibrils. This process probably involves two sets of mechanisms: 1) an enzymatic mechanism involving at least two of the three proteolytic systems so far identified and present in this tissue, namely lysosomal (cathepsins) and calcium dependent (calpains) proteinases; 2) a physicochemical mechanism based on the important post mortem rise in muscle osmotic pressure which could be twice as high as in live animals. Despite the large progress in muscle enzymology, the nature of the proteinases responsible for the post mortem proteolysis associated with the development in meat texture is still not clearly established. In the present review, data obtained from two different approaches attempting to answer this question were analysed. The first one was based on the identification of a set of structural and biochemical changes associated with meat texture development and to examine which proteolytic system or proteinase would be able to reproduce them when incubated with either myofibrils or muscle fibres as substrate. The second tentatively relates the rate and the extent of the changes in meat texture to the proteolytic equipment of the tissue. The first approach led to the conclusion that changes in muscle proteins and structure can be only explained by considering a synergistic action of both lysosomal and calcium-dependent proteinases. From the second, it was concluded that the process of meat texture development did not depend on the proteinase levels but was related to their initial potential efficiency assessed by measurement of the enzyme/inhibitor ratio. With respect to the physicochemical mechanisms, the post mortem rise in muscle osmotic pressure was shown to be responsible for some biochemical changes occurring in myofibrils. This was further substantiated by the fact that the greatest osmotic pressure values were observed in muscles exhibiting highest tenderising rate. On the other hand we provide evidence suggesting that the substrate, namely myofibrils, might constitute an important limiting step of the efficiency of both types of mechanism. Taken together, the findings presented emphasize that improvement of our knowledge in this field will greatly depend on the development of basic research on these different topics notably: 1) the mechanisms by which proteinases activities are regulated in living and post mortem muscles; and 2) the myofibrillar structure, especially in slow-twitch or type I muscles.

The role of ultimate pH in proteolysis and calpain/calpastatin activity in bovine muscle

Of a total of three Friesian cows, two of which had been treated with adrenalin before slaughter, Mm longissimus (LO), supraspinatus (SS), triceps brachii (TB) and rectus abdominis (RA) were sampled at different times post mortem (pm). pH, calpain/calpastatin activities and degradation of myofibrillar proteins, as evidenced by SDS-PAGE, were assessed. Contraction characteristics were measured by determining myofibrillar ATPase activities. Adrenalin treatment resulted in a high ultimate pH (6.48 +/- 0.40) and a faster decline pm of calpain I activity. The effect was similar in all four investigated muscles (72.4 +/- 5.4% decline at 24 h pm). The decline in calpain I activity in the control muscles was muscle-dependent and ranged from 22.8-74.3% at 24 h pm. Differences in ultimate pH did not lead to distinct rates of breakdown of proteins with molecular weights lower than that of myosin heavy chain. Calpastatin levels were muscle-dependent and correlated with myofibrillar ATPase activity (r = -0.99). In a second experiment Mm rectus abdominis (RA) and psoas major (PM) of adrenalin-treated (n = 6) and control (n = 6) Friesian-Holstein calves were sampled at 1 and 29 h pm for assessment of calpain activities. At seven days pm the M longissimus (LO) was sampled for tenderness evaluation. pH values were measured at 30 min, 4 h and 29 h pm. Adrenalin treatment resulted in a higher ultimate pH in the three muscles. Higher ultimate pH resulted in lower calpain activities in the RA at 29 h pm (P less than or equal to 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)