Brigitte Picard

Relationships between muscle characteristics and meat quality traits of young Charolais bulls

Charolais bull calves (106) were used to study the variability in meat quality attributes in relation to the variability in muscle characteristics in the Longissimus thoracis (LT) muscle. The variability in traits was adjusted either to constant age or constant weight at slaughter and thus originated only from differences between animals born, reared and fattened in the same location. The following meat quality attributes were measured: the strength of the myofibrillar resistance to a 20% compression strain measured on the raw meat 2, 7 and 21 days post mortem; and taste panel scores of tenderness (initial and overall), flavour and juiciness of steaks grilled to a 55°C core temperature 6 or 15 days post-mortem. The following muscle characteristics were measured 24 h after slaughter: pH, dry matter, protein, lipid, heme iron and collagen contents, collagen solubility, LDH and ICDH activity, the proportion of slow twitch myosin heavy chain, the mean muscle fibre area and the mean sarcomere length. One fourth to one third of the variability of 2 day mechanical strength and 15 day tenderness or flavour scores were related to the variability in muscle characteristics. Tenderness and strength measurements were predominantly related to the muscle fibre area, collagen characteristics and energetic metabolic activity. Dry matter content was the principal muscle characteristic related to flavour.

Recent advances in cattle functional genomics and their application to beef quality

The advent of high-throughput DNA sequencing techniques, array technology and protein analysis has increased the efficiency of research in bovine muscle physiology, with the ultimate objective of improving beef quality either by breeding or rearing factors. For genetic purposes, polymorphisms in some key genes have been reported for their association with beef quality traits. The sequencing of the bovine genome has dramatically increased the number of available gene polymorphisms. The association of these new polymorphisms with the variability in beef quality (e.g. tenderness, marbling) for different breeds in different rearing systems will be a very important issue. For rearing purposes, global gene expression profiling at the mRNA or protein level has already shown that previously unsuspected genes may be associated either with muscle development or growth, and may lead to the development of new molecular indicators of tenderness or marbling. Some of these genes are specifically regulated by genetic and nutritional factors or differ between different beef cuts. In recognition of the potential economic benefits of genomics, public institutions in association with the beef industry are developing livestock genomics projects around the world. From the scientific, technical and economical points of view, genomics is thus reshaping research on beef quality.

Skeletal muscle proteomics in livestock production

Proteomics allows studying large numbers of proteins, including their post-translational modifications. Proteomics has been, and still are, used in numerous studies on skeletal muscle. In this article, we focus on its use in the study of livestock muscle development and meat quality. Changes in protein profiles during myogenesis are described in cattle, pigs and fowl using comparative analyses across different ontogenetic stages. This approach allows a better understanding of the key stages of myogenesis and helps identifying processes that are similar or divergent between species. Genetic variability of muscle properties analysed by the study of hypertrophied cattle and sheep are discussed. Biological markers of meat quality, particularly tenderness in cattle, pigs and fowl are presented, including protein modifications during meat ageing in cattle, protein markers of PSE meat in turkeys and of post-mortem muscle metabolism in pigs. Finally, we discuss the interest of proteomics as a tool to understand better biochemical mechanisms underlying the effects of stress during the pre-slaughter period on meat quality traits. In conclusion, the study of proteomics in skeletal muscles allows generating large amounts of scientific knowledge that helps to improve our understanding of myogenesis and muscle growth and to control better meat quality.

Myostatin and the skeletal muscle atrophy and hypertrophy signaling pathways

Myostatin, a member of the transforming growth factor-β superfamily, is a potent negative regulator of skeletal muscle growth and is conserved in many species, from rodents to humans. Myostatin inactivation can induce skeletal muscle hypertrophy, while its overexpression or systemic administration causes muscle atrophy. As it represents a potential target for stimulating muscle growth and/or preventing muscle wasting, myostatin regulation and functions in the control of muscle mass have been extensively studied. A wealth of data strongly suggests that alterations in skeletal muscle mass are associated with dysregulation in myostatin expression. Moreover, myostatin plays a central role in integrating/mediating anabolic and catabolic responses. Myostatin negatively regulates the activity of the Akt pathway, which promotes protein synthesis, and increases the activity of the ubiquitin–proteasome system to induce atrophy. Several new studies have brought new information on how myostatin may affect both ribosomal biogenesis and translation efficiency of specific mRNA subclasses. In addition, although myostatin has been identified as a modulator of the major catabolic pathways, including the ubiquitin–proteasome and the autophagy–lysosome systems, the underlying mechanisms are only partially understood. The goal of this review is to highlight outstanding questions about myostatin-mediated regulation of the anabolic and catabolic signaling pathways in skeletal muscle. Particular emphasis has been placed on (1) the cross-regulation between myostatin, the growth-promoting pathways and the proteolytic systems; (2) how myostatin inhibition leads to muscle hypertrophy; and (3) the regulation of translation by myostatin.

Meat quality and composition of three muscles from French cull cows and young bulls

The quality of grilled steaks was assessed by experienced panellists in longissimus thoracis (LT), semitendinosus (St) and triceps brachii (TB) muscles of Aubrac, Charolais, Limousin and Salers breeds raised in two production systems: 15-, 19- and 24-month-old bulls and 4-, 6- and 8-year-old cull cows. Scores for sensory ‘initial tenderness’, ‘overall tenderness’, ‘juiciness’, ‘residue after mastication’ and ‘flavour intensity’ for all 497 meats were pooled to derive three eating quality classes. Meats from the bulls and cows and from the four breeds were evenly distributed among the three eating quality classes. The highest quality class, representing one third of all the meats, contained 45% of the LT, 35% of the TB and 21% of the St muscles and one third of the meats from the 8-year-old cull cows. The meats in this class tended to have finer fibres, a greater proportion of slow oxidative fibres, slower post-mortem glycolysis, lower connective tissue and higher fat contents than those in the lower classes. Lipid content accounted for proportionately 0·56 of the variation in flavour intensity and pH at 3 h post mortem, 0·52 of the variation in tenderness due to muscle and slaughter age. Considering both young bulls and cull cows together, tenderness was highest in the meats from 15-month-old bulls and low in the meats from the intermediate age groups, and flavour and juiciness was highest in the meats from the oldest animals from each production system.

Opportunities for predicting and manipulating beef quality.

Meat quality is a complex concept and can be defined as the characteristics of meat which satisfy consumers and citizens. The quality concept can be divided into intrinsic quality traits (which are the characteristics of the product itself) and extrinsic quality traits (which are more or less associated to the product for instance the price, a major determinant of purchase, or any brand or quality label). Quality can also be generic for the mass market or specific for niche markets. The relative importance of the different quality traits varies with human culture and time with a general trend of an increasing contribution of healthiness, safety and extrinsic quality traits. This review underlines the need for the development of methods to interpret and aggregate measures under specific rules to be defined in order to produce an overall assessment of beef quality. Such methods can be inferred for example from genomic results or data related to muscle biochemistry to better predict tenderness or flavor. A more global assurance quality scheme (the Meat Standards Australia System) based on the aggregation of sensory quality traits has been developed in Australia to ensure palatability to consumers. We speculated that the combination of indices related to sensory and nutritional quality, social and environmental considerations (carbon footprint, animal welfare, biodiversity of pasture, rural development, etc.) and economic efficiency (incomes of farmers and of others players along the supply chain, etc.) will provide objective assessment of the overall quality of beef (i.e. incorporating an all encompassing approach) not only for the mass market but also to support official quality labels of niche markets which are so far mainly associated with the geographical origins of the products.

Classification of bovine muscle fibres by different histochemical techniques

The classification of bovine muscle fibres is of particular interest for the food industry because meat tenderness depends in part on the proportion of the different types of fibres. It is, therefore, important to define reliable methods for classifying fibre types. There are several classification systems. One is based on contractile type alone, as revealed by myofibrillar ATPase activity or with antibodies against myosin heavy chain. Others take both contractile and metabolic types into account. In this study, the classifications of fibres obtained by these three systems were compared on the semitendinosus and longissimus thoracis muscles of 35 Charolais bulls. Only the use of antibodies allowed the identification of a proportion of hybrid fibres containing two isoforms of fast myosin heavy chain (2a and 2b). In addition, the combination of metabolic types showed that the metabolism of these hybrid fibres differed according to the muscle.

Molecular profiles of Quadriceps muscle in myostatin-null mice reveal PI3K and apoptotic pathways as myostatin targets

BackgroundMyostatin (MSTN), a member of the TGF-β superfamily, has been identified as a negative regulator of skeletal muscle mass. Inactivating mutations in the MSTN gene are responsible for the development of a hypermuscular phenotype. In this study, we performed transcriptomic and proteomic analyses to detect altered expression/abundance of genes and proteins. These differentially expressed genes and proteins may represent new molecular targets of MSTN and could be involved in the regulation of skeletal muscle mass.ResultsTranscriptomic analysis of the Quadriceps muscles of 5-week-old MSTN-null mice (n = 4) and their controls (n = 4) was carried out using microarray (human and murine oligonucleotide sequences) of 6,473 genes expressed in muscle. Proteomic profiles were analysed using two-dimensional gel electrophoresis coupled with mass spectrometry. Comparison of the transcriptomic profiles revealed 192 up- and 245 down- regulated genes. Genes involved in the PI3K pathway, insulin/IGF pathway, carbohydrate metabolism and apoptosis regulation were up-regulated. Genes belonging to canonical Wnt, calcium signalling pathways and cytokine-receptor cytokine interaction were down-regulated. Comparison of the protein profiles revealed 20 up- and 18 down-regulated proteins spots. Knockout of the MSTN gene was associated with up-regulation of proteins involved in glycolytic shift of the muscles and down-regulation of proteins involved in oxidative energy metabolism. In addition, an increased abundance of survival/anti-apoptotic factors were observed.ConclusionAll together, these results showed a differential expression of genes and proteins related to the muscle energy metabolism and cell survival/anti-apoptotic pathway (e.g. DJ-1, PINK1, 14-3-3ε protein, TCTP/GSK-3β). They revealed the PI3K and apoptotic pathways as MSTN targets and are in favour of a role of MSTN as a modulator of cell survival in vivo.

Functional analysis of beef tenderness.

Meat tenderness represents a complex assembly of different cellular pathways. As a consequence, genomics studies have revealed many different proteins considered as tenderness markers. So it is difficult to have an overview of tenderness in terms of cellular pathways. In this work cellular pathways of tenderness were analyzed, an interactome of 330 proteins was designed, and explanations of tenderization processes were proposed.

Ontogenesis of muscle and adipose tissues and their interactions in ruminants and other species

The lean-to-fat ratio, that is, the relative masses of muscle and adipose tissue, is a criterion for the yield and quality of bovine carcasses and meat. This review describes the interactions between muscle and adipose tissue (AT) that may regulate the dynamic balance between the number and size of muscle v. adipose cells. Muscle and adipose tissue in cattle grow by an increase in the number of cells (hyperplasia), mainly during foetal life. The total number of muscle fibres is set by the end of the second trimester of gestation. By contrast, the number of adipocytes is never set. Number of adipocytes increases mainly before birth until 1 year of age, depending on the anatomical location of the adipose tissue. Hyperplasia concerns brown pre-adipocytes during foetal life and white pre-adipocytes from a few weeks after birth. A decrease in the number of secondary myofibres and an increase in adiposity in lambs born from mothers severely underfed during early pregnancy suggest a balance in the commitment of a common progenitor into the myogenic or adipogenic lineages, or a reciprocal regulation of the commitment of two distinct progenitors. The developmental origin of white adipocytes is a subject of debate. Molecular and histological data suggested a possible transdifferentiation of brown into white adipocytes, but this hypothesis has now been challenged by the characterization of distinct precursor cells for brown and white adipocytes in mice. Increased nutrient storage in fully differentiated muscle fibres and adipocytes, resulting in cell enlargement (hypertrophy), is thought to be the main mechanism, whereby muscle and fat masses increase in growing cattle. Competition or prioritization between adipose and muscle cells for the uptake and metabolism of nutrients is suggested, besides the successive waves of growth of muscle v. adipose tissue, by the inhibited or delayed adipose tissue growth in bovine genotypes exhibiting strong muscular development. This competition or prioritization occurs through cellular signalling pathways and the secretion of proteins by adipose tissue (adipokines) and muscle (myokines), putatively regulating their hypertrophy in a reciprocal manner. Further work on the mechanisms underlying cross-talk between brown or white adipocytes and muscle fibres will help to achieve better understanding as a prerequisite to improving the control of body growth and composition in cattle.