Gene and protein expression of myosin heavy chain in Nellore cattle comparing growth or meat tenderness traits.

The objective was to investigate gene and protein expression of myosin heavy chain (MyHC) in Nellore cattle slaughtered at different weights (BW) or degrees of meat tenderness. Ninety animals with initial BW 370 ± 37 kg, 24 months of age, were slaughtered after 95 days on feed. We evaluated shear force (SF), myofibrillar fragmentation index, ribeye area, backfat thickness, marbling, color, and cooking losses. Subsequently, 24 animals were selected and divided into four contrasting groups, in which light (BW = 504.58 ± 32.36 kg) versus heavy animals (BW = 604.83 ± 42.97 kg) and animals with tender (SF = 3.88 ± 0.57 kg) versus tough meat (SF = 7.95 ± 1.04 kg) were compared. The MYH7, MYH2 and MYH1 genes were analyzed by real-time PCR. The MyHC isoforms (MyHC-I, MyHC-IIa, and MyHC-IIx) were quantified by SDS-PAGE electrophoresis. We found lower expression of MYH2 and MYH1 genes in heavy compared to light animals and a higher amount of MyHC-I isoform in the tough meat group compared to the tender meat group. Protein expression of MyHC-IIa was higher in the tender meat group. A negative correlation was found of this protein and SF (tenderness), suggesting MyHC-IIa as a biomarker of meat quality.

Exome analysis and functional classification of identified variants in racing Quarter Horses.

The main objectives of this study were to identify and functionally classify SNPs and indels by exome sequencing of animals of the racing line of Quarter Horses. Based on the individual genomic estimated breeding values (GEBVs) for maximum speed index (SImax) obtained for 349 animals, two groups of 20 extreme animals were formed. Of these individuals, 20 animals with high GEBVs for SImax and 19 with low GEBVs for SImax had their exons and 5' and 3' UTRs sequenced. Considering SNPs and indels, 105 182 variants were identified in the expressed regions of the Quarter Horse genome. Of these, 72 166 variants were already known and 33 016 are new variants and were deposited in a database. The analysis of the set of gene variants significantly related (Padjusted  < 0.05) to extreme animals in conjunction with the predicted impact of the changes and the physiological role of protein product pointed to two candidate genes potentially related to racing performance: SLC3A1 on ECA15 and CCN6 on ECA10.

Retraction Note to: L-glutamine supplementation induces insulin resistance in adipose tissue and improves insulin signalling in liver and muscle of rats with diet-induced obesity.

In light of forensic evidence indicating duplication and/or manipulation of western blot images the Editor-in-Chief is retracting the article cited above.

Fish oil prevents changes induced by a high-fat diet on metabolism and adipokine secretion in mice subcutaneous and visceral adipocytes.

KEY POINTS: Fish oil (FO), rich in omega-3 polyunsaturated fatty acids, has beneficial effects on changes induced by obesity and partially prevents associated comorbidities. The effects of FO on adipocytes from different adipose tissue depots in high-fat (HF) diet induced obese mice have not been uninvestigated. This is the first study to examine the effects of FO on changes in metabolism and adipokine production in adipocytes from s.c. (inguinal; ING) or visceral (retroperitoneal; RP) white adipose depots in a HF diet-induced obese mice. Unlike most studies performed previously, FO supplementation was initiated 4 weeks before the induction of obesity. HF diet caused marked changes in ING (glucose uptake and secretion of adiponectin, tumour necrosis factor-α and interleukin-6 in ING) and RP (lipolysis, de novo lipogenesis and secretion of pro-inflammatory cytokines) adipose depots. Previous and concomitant FO administration prevented the changes in ING and RP adipocytes induced by the HF diet. ABSTRACT: In the present study, we investigated the effect of fish oil (FO) on metabolism and adipokine production by adipocytes from s.c. (inguinal; ING) and visceral (retroperitoneal; RP) white adipose depots in high-fat (HF) diet-induced obese mice. Mice were divided into CO (control diet), CO+FO, HF and HF+FO groups. The HF group presented higher body weight, glucose intolerance, insulin resistance, higher plasma total and low-density lipoprotein cholesterol levels, and greater weights of ING and RP adipose depots accompanied by hypertrophy of the adipocytes. FO exerted anti-obesogenic effects associated with beneficial effects on dyslipidaemia and insulin resistance in mice fed a HF diet (HF+FO group). HF raised RP adipocyte lipolysis and the production of pro-inflammatory cytokines and reduced de novo synthesis of fatty acids, whereas, in ING adipocytes, it decreased glucose uptake and adiponectin secretion but did not change lipolysis. Therefore, the adipose depots play different roles in HF diet-induced insulin resistance according to their location in the body. Concerning cytokine secretion, adipocytes per se in addition to white adopise tissue infiltrated leukocytes have to be considered in the aetiology of the comorbidities associated with obesity. Evidence is presented showing that previous and concomitant administration of FO can prevent changes in metabolism and the secretion of hormones and cytokines in ING and RP adipocytes induced by HF.

Genetic study of skin thickness and its association with postweaning growth in Nellore cattle: estimation of the genetic parameters.

The objective of the present study was to estimate genetic parameters for skin thickness (ST) and postweaning weight gain (PWG550) in Nellore cattle. Records were obtained from 152,392 Nellore animals born between 2001 and 2011. ST was measured in the posterior region of the animal's scapula with a millimeter caliper. The animals were assigned to different contemporary groups, formed on the basis of farm, year, sex, feeding regimen at weaning, date of weaning, feeding regimen at 450 days of age, and date of weighing at 450 days of age. The genetic parameters were estimated by Bayesian analysis using the GIBBS1F90 program. The mean ST and PWG550 observed were 7.71 ± 2.04 mm and 115.95 ± 36.17 kg, respectively. The posterior mean estimates of heritability (h2) were 0.12 ± 0.02 and 0.29 ± 0.02 for ST and PWG550, respectively. The posterior mean estimates of the phenotypic, genetic, and environmental correlations between the traits were 0.16 ± 0.0, 0.17 ± 0.02, and 0.17 ± 0.09, respectively. The traits ST and PWG550 showed sufficient additive genetic variance to be used as selection criteria in breeding programs. The low genetic correlation obtained indicates that genes favoring the expression of one trait may not influence the other. Consequently, a selection favoring ST would be less efficient in increasing PWG550.

Genetic parameters for earnings in Quarter Horse.

In this study, we estimated the heritability (h(2)) of earnings in the Quarter Horse in order to evaluate the inclusion of this trait in breeding programs. Records from 14,754 races of 2443 horses from 1978-2009 were provided by Sorocaba Hippodrome, São Paulo, Brazil. All ancestors of the registered horses were included in the pedigree file until the 4th generation. Log-transformed performance measures (LPM) were analyzed for animals aged 2, 3, and 4 years and during their entire career. The h(2) estimates were obtained using a multi-trait model and Gibbs sampling that included the effects of sex, year of race, and animal in all analyses. Five analyses were performed: 1 in which LPM was divided by the number of prizes, 1 in which LPM was divided by the number of race starts, and 3 analyses that included the number of prizes, number of race starts, and both (LPM_cNPS) as covariates. Analysis was performed with and without inclusion of the maternal effect. Models were compared based on the deviance information criterion and LPM_cNPS including maternal effects was found to be the best model. The h(2) estimates and standard deviation obtained using model LPM_cNPS were 0.19 ± 0.08, 0.21 ± 0.08, 0.22 ± 0.09, and 0.21 ± 0.07 for earnings at 2, 3, and 4 years of age and total career, respectively. Our analyses indicate that earnings are subject to selection and can be included in breeding programs to improve the racing performance of Quarter Horses.

Tolerability of glutamine supplementation in older adults: a double-blind placebo-controlled randomized clinical trial.

In this double-blind placebo-controlled randomized investigation, we assessed the tolerability of glutamine in older adults recruited from three daycare centers. The relevance of studying glutamine supplementation in elderly patients lies in its potential to provide a well-tolerated intervention. Glutamine, a crucial amino acid, plays a vital role in various physiological processes, including immune function and protein synthesis. Understanding its impact on older adults is essential, given the potential implications for their health and well-being. Participants received a daily dose of 12.4 g of oral effervescent glutamine (EGln group) or maltodextrin (placebo group) for 60 days. Fifteen patients from each group completed the study. The mean ages were 77.0±9.1 and 79.0±6.9 years for the EGln and placebo groups, respectively. We evaluated body mass index, aminogram, hemogram, plasma levels of glucose, prealbumin, albumin, urea, creatinine, uric acid, C-reactive protein, vitamin D, calcium, sodium, potassium, and the plasma activities of aspartate aminotransferase and alanine aminotransferase. Notably, we quantified a broad array of inflammatory markers and growth factors providing a holistic understanding of the potential effects of glutamine supplementation. The results demonstrated that oral glutamine did not induce significant changes in any evaluated parameters, and no adverse effects were reported. This finding suggested that the dosage of glutamine used in this study was well-tolerated and safe. This information contributes to the broader understanding of glutamine supplementation, emphasizing its safety and supporting its potential as a viable intervention for maintaining health in aging individuals.

Changes in food intake, metabolic parameters and insulin resistance are induced by an isoenergetic, medium-chain fatty acid diet and are associated with modifications in insulin signalling in isolated rat pancreatic islets.

Long-chain fatty acids are capable of inducing alterations in the homoeostasis of glucose-stimulated insulin secretion (GSIS), but the effect of medium-chain fatty acids (MCFA) is poorly elucidated. In the present study, we fed a normoenergetic MCFA diet to male rats from the age of 1 month to the age of 4 months in order to analyse the effect of MCFA on body growth, insulin sensitivity and GSIS. The 45% MCFA substitution of whole fatty acids in the normoenergetic diet impaired whole body growth and resulted in increased body adiposity and hyperinsulinaemia, and reduced insulin-mediated glucose uptake in skeletal muscle. In addition, the isolated pancreatic islets from the MCFA-fed rats showed impaired GSIS and reduced protein kinase Ba (AKT1) protein expression and extracellular signal-related kinase isoforms 1 and 2 (ERK(1/2)) phosphorylation, which were accompanied by increased cellular death. Furthermore, there was a mildly increased cholinergic sensitivity to GSIS. We discuss these findings in further detail, and advocate that they might have a role in the mechanistic pathway leading to the compensatory hyperinsulinaemic status found in this animal model.

Linseed oil attenuates fatty liver disease in mice fed a high-carbohydrate diet.

The impact of linseed oil as a lipid source on liver disease induced by a high-carbohydrate diet (HCD) was evaluated. Adult male Swiss mice received an HCD containing carbohydrates (72.1%), proteins (14.2%), and lipids (4.0%). The Control HCD group (HCD-C) received an HCD containing lard (3.6%) and soybean oil (0.4%) as lipid sources. The L10 and L100 groups received an HCD with 10 and 100% linseed oil as lipid sources, respectively. A group of mice were euthanized before receiving the diets (day 0) and the remaining groups after 56 days of receiving the diets (HCD-C, L10, and L-100 groups). Morphological and histopathological analyses, as well as collagen deposition were evaluated. Perivenous hepatocytes (PVH) of the HCD-C group were larger (P<0.05) than periportal hepatocytes (PPH) in the median lobe (ML) and left lobe (LL). There was a greater (P<0.05) deposition of type I collagen in PPH (vs PVH) and in the ML (vs LL). The ML exhibited a higher proportion of apoptotic bodies, inflammatory infiltrate, and hepatocellular ballooning. All these alterations (hepatocyte size, deposition of type I collagen, apoptotic bodies, inflammatory infiltrate, and hepatocellular ballooning) induced by HCD were prevented or attenuated in L10 and L100 groups. Another indicator of the beneficial effects of linseed oil was the lower (P<0.05) number of binucleated hepatocytes (HCD-C vs L10 or L100 group). In general, the L100 group had greater effects than the L10 group. In conclusion, linseed oil impedes or reduces the liver injury progression induced by an HCD.

Brain glucose hypometabolism and hippocampal inflammation in Goto-Kakizaki rats.

Brain glucose hypometabolism and neuroinflammation are early pathogenic manifestations in neurological disorders. Neuroinflammation may also disrupt leptin signaling, an adipokine that centrally regulates appetite and energy balance by acting on the hypothalamus and exerting neuroprotection in the hippocampus. The Goto-Kakizaki (GK) rat is a non-obese type 2 diabetes mellitus (T2DM) animal model used to investigate diabetes-associated molecular mechanisms without obesity jeopardizing effects. Wistar and GK rats received the maintenance adult rodent diet. Also, an additional control group of Wistar rats received a high-fat and high-sugar diet (HFHS) provided by free consumption of condensed milk. All diets and water were provided ad libitum for eight weeks. Brain glucose uptake was evaluated by 2-deoxy-2-[fluorine-18] fluoro-D-glucose under basal (saline administration) or stimulated (CL316,243, a selective ß3-AR agonist) conditions. The animals were fasted for 10-12 h, anesthetized, and euthanized. The brain was quickly dissected, and the hippocampal area was sectioned and stored at -80°C in different tubes for protein and RNA analyses on the same animal. GK rats exhibited attenuated brain glucose uptake compared to Wistar animals and the HFHS group under basal conditions. Also, the hippocampus of GK rats displayed upregulated leptin receptor, IL-1ß, and IL-6 gene expression and IL-1ß and the subunit of the transcription factor NF-κB (p-p65) protein expression. No significant alterations were detected in the hippocampus of HFHS rats. Our data indicated that a genetic predisposition to T2DM has significant brain deteriorating features, including brain glucose hypometabolism, neuroinflammation, and leptin signaling disruption in the hippocampal area.

Effect of N-acetylcysteine on markers of skeletal muscle injury after fatiguing contractile activity.

The effects of N-Acetylcysteine (NAC), an unspecific antioxidant, on fatiguing contractile activity-induced injury were investigated. Twenty-four male Wistar rats were randomly assigned to two groups. The placebo group (N=12) received one injection of phosphate buffer (PBS) 1 h prior to contractile activity induced by electrical stimulation. The NAC group (NAC; N=12) received electrical stimulation for the same time period and NAC (500 mg/kg, i.p.) dissolved in PBS 1 h prior to electrical stimulation. The contralateral hindlimb was used as a control, except in the analysis of plasma enzyme activities, when a control group (rats placebo group not electrically stimulated and not treated) was included. The following parameters were measured: tetanic force, muscle fatigue, plasma activities of creatine kinase (CK) and lactate dehydrogenase (LDH), changes in muscle vascular permeability using Evans blue dye (EBD), muscle content of reactive oxygen species (ROS) and thiobarbituric acid-reactive substances (TBARS) and myeloperoxidase (MPO) activity. Muscle fatigue was delayed and tetanic force was preserved in NAC-treated rats. NAC treatment decreased plasma CK and LDH activities. The content of muscle-derived ROS, TBARS, EBD and MPO activity in both gastrocnemius and soleus muscles were also decreased by NAC pre-treatment. Thus, NAC has a protective effect against injury induced by fatiguing contractile activity in skeletal muscle.

A short review on the features of the non-obese diabetic Goto-Kakizaki rat intestine.

The Goto-Kakizaki (GK) rat is a non-obese experimental model of type 2 diabetes mellitus (T2DM) that allows researchers to monitor diabetes-induced changes without jeopardizing the effects of obesity. This rat strain exhibits notable gastrointestinal features associated with T2DM, such as marked alterations in intestinal morphology, reduced intestinal motility, slow transit, and modified microbiota compared to Wistar rats. The primary treatments for diabetic patients include administration of hypoglycemic agents and insulin, and lifestyle changes. Emerging procedures, including alternative therapies, metabolic surgeries, and modulation of the intestinal microbiota composition, have been shown to improve the diabetic state of GK rats. This review describes the morpho-physiological diabetic-associated features of the gastrointestinal tract (GIT) of GK rats. We also describe promising strategies, e.g., metabolic surgery and modulation of gut microbiota composition, used to target the GIT of this animal model to improve the diabetic state.

Strenuous swimming raises blood non-enzymatic antioxidant capacity in rats.

The non-enzymatic antioxidant system protects blood components from oxidative damage and/or injury. Herein, plasma non-enzymatic antioxidant capacity after acute strenuous swimming exercise (Exe) and exercise until exhaustion (Exh) was measured in rats. The experiments were carried out in never exposed (Nex) and pre-exposed (Pex) groups. The Nex group did not undergo any previous training before the acute strenuous swimming test and the Pex group was submitted to daily swimming for 10 min in the first week and 15 min per day in the second week before testing. Plasma glucose, lactate, and pyruvate were measured and plasma total protein sulfhydryl groups (thiol), trolox equivalent antioxidant capacity (TEAC), ferric reducing ability of plasma (FRAP), and total radical-trapping antioxidant parameter (TRAP) levels were evaluated. There were marked increases in plasma lactate concentrations (Nex-Control 1.31±0.20 vs NexExe 4.16±0.39 vs NexExh 7.19±0.67) and in thiol (Nex-Control 271.9±5.6 vs NexExh 314.7±5.7), TEAC (Nex-Control 786.4±60.2 vs NexExh 1027.7±58.2), FRAP (Nex-Control 309.2±17.7 vs NexExh 413.4±24.3), and TRAP (Nex-Control 0.50±0.15 vs NexExh 2.6±0.32) levels after acute swimming and/or exhaustion. Also, there were increased plasma lactate concentrations (Pex-Control 1.39±0.15 vs PexExe 5.22±0.91 vs PexExh 10.07±0.49), thiol (Pex-Control 252.9±8.2 vs PexExh 284.6±6.7), FRAP (Pex-Control 296.5±15.4 vs PexExh 445.7±45.6), and TRAP (Pex-Control 1.8±0.1 vs PexExh 4.6±0.2) levels after acute swimming and/or exhaustion. Lactate showed the highest percent of elevation in the Nex and Pex groups. In conclusion, plasma lactate may contribute to plasma antioxidant defenses, and the TRAP assay is the most sensitive assay for assessing plasma non-antioxidant capacity after strenuous exercise.

Reviewing physical exercise in non-obese diabetic Goto-Kakizaki rats.

There is a high incidence of non-obese type 2 diabetes mellitus (non-obese-T2DM) cases, particularly in Asian countries, for which the pathogenesis remains mainly unclear. Interestingly, Goto-Kakizaki (GK) rats spontaneously develop insulin resistance (IR) and non-obese-T2DM, making them a lean diabetes model. Physical exercise is a non-pharmacological therapeutic approach to reduce adipose tissue mass, improving peripheral IR, glycemic control, and quality of life in obese animals or humans with T2DM. In this narrative review, we selected and analyzed the published literature on the effects of physical exercise on the metabolic features associated with non-obese-T2DM. Only randomized controlled trials with regular physical exercise training, freely executed physical activity, or skeletal muscle stimulation protocols in GK rats published after 2008 were included. The results indicated that exercise reduces plasma insulin levels, increases skeletal muscle glycogen content, improves exercise tolerance, protects renal and myocardial function, and enhances blood oxygen flow in GK rats.

Poor prognosis indicators of type-2 diabetic COVID-19 patients.

Diabetes is associated with a worse prognosis and a high risk of morbidity and mortality in COVID-19 patients. We aimed to evaluate the main factors involved in the poor prognosis in diabetic patients. A total of 984 patients diagnosed with COVID-19 admitted to the hospital were included in this study. Patients were first divided into type-2 diabetic (DM+) and non-diabetic (DM-) groups. The participants were analyzed based on the National Early Warning Score (NEWS) and on the Quick-Sequential Organ Failure Assessment (qSOFA) to find the best prognostic risk score for our study. The DM+ and DM- groups were divided into non-severe and severe groups. Comparative and correlative analyses were used to identify the physiological parameters that could be employed for creating a potential risk indicator for DM+ COVID-19 patients. We found a poorer prognosis for the DM+ COVID-19 patients with a higher ICU admission rate, mechanical ventilation rate, vasopressor use, dialysis, and longer treatment times compared with the DM- group. DM+ COVID-19 patients had increased plasma glucose, lactate, age, urea, NEWS, and D-dimer levels, herein referred to as the GLAUND set, and worse prognosis and outcomes when compared with infected DM- patients. The NEWS score was a better indicator for assessing COVID-19 severity in diabetic patients than the q-SOFA score. In conclusion, diabetic COVID-19 patients should be assessed with the NEWS score and GLAUND set for determining their prognosis COVID-19 prognosis.

Serum amyloid A induces reactive oxygen species (ROS) production and proliferation of fibroblast.

Serum amyloid A (SAA) levels are elevated highly in acute phase response and elevated slightly and persistently in chronic diseases such as rheumatoid arthritis and diabetes. Given that fibroblasts exert profound effects on progression of inflammatory chronic diseases, the aim of this study was to investigate the response of fibroblasts to SAA. A dose-dependent increase in O(2) (-) levels was observed by treatment of fibroblasts with SAA (r = 0·99 and P ≤ 0·001). In addition, the expression of p47-phox was up-regulated by SAA (P < 0·001) and diphenyliodonium (DPI), a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, reduced the release of O(2) (-) by 50%. Also, SAA raised fibroblast proliferation (P < 0·001) and this effect was completely abolished by the addition of anti-oxidants (P < 0·001). These findings support the notion that, in chronic inflammatory sites, SAA activated fibroblast proliferation and ROS production.

Effect of medium/ω-6 long chain triglyceride-based emulsion on leucocyte death and inflammatory gene expression.

Lipid emulsion (LE) containing medium/ω-6 long chain triglyceride-based emulsion (MCT/ω-6 LCT LE) has been recommended in the place of ω-6 LCT-based emulsion to prevent impairment of immune function. The impact of MCT/ω-6 LCT LE on lymphocyte and neutrophil death and expression of genes related to inflammation was investigated. Seven volunteers were recruited and infusion of MCT/ω-6 LCT LE was performed for 6 h. Four volunteers received saline and no change was found. Blood samples were collected before, immediately afterwards and 18 h after LE infusion. Lymphocytes and neutrophils were studied immediately after isolation and after 24 and 48 h in culture. The following determinations were carried out: plasma-free fatty acids, triacylglycerol and cholesterol concentrations, plasma fatty acid composition, neutral lipid accumulation in lymphocytes and neutrophils, signs of lymphocyte and neutrophil death and lymphocyte expression of genes related to inflammation. MCT/ω-6 LCT LE induced lymphocyte and neutrophil death. The mechanism for MCT/ω-6 LCT LE-dependent induction of leucocyte death may involve changes in neutral lipid content and modulation of expression of genes related to cell death, proteolysis, cell signalling, inflammatory response, oxidative stress and transcription.

PPARγ expression is increased in systemic lupus erythematosus patients and represses CD40/CD40L signaling pathway.

Systemic lupus erythematosus (SLE) is a heterogeneous disease involving several immune cell types and pro-inflammatory signals, including the one triggered by binding of CD40L to the receptor CD40. Peroxisome-proliferator activated receptor gamma (PPARγ) is a transcription factor with anti-inflammatory properties. Here we investigated whether CD40 and PPARγ could exert opposite effects in the immune response and the possible implications for SLE. Increased PPARγ mRNA levels were detected by real-time PCR in patients with active SLE, compared to patients with inactive SLE PPARγ/GAPDH mRNA = 2.21 ± 0.49 vs. 0.57 ± 0.14, respectively (p < 0.05) or patients with infectious diseases and healthy subjects (p < 0.05). This finding was independent of the corticosteroid therapy. We further explored these observations in human THP1 and in SLE patient-derived macrophages, where activation of CD40 by CD40L promoted augmented PPARγ gene transcription compared to non-stimulated cells (PPARγ/GAPDH mRNA = 1.14 ± 0.38 vs. 0.14 ± 0.01, respectively; p < 0.05). This phenomenon occurred specifically upon CD40 activation, since lipopolysaccharide treatment did not induce a similar response. In addition, increased activity of PPARγ was also detected after CD40 activation, since higher PPARγ-dependent transcription of CD36 transcription was observed. Furthermore, CD40L-stimulated transcription of CD80 gene was elevated in cells treated with PPARγ-specific small interfering RNA (small interfering RNA, siRNA) compared to cells treated with CD40L alone (CD80/GAPDH mRNA = 0.11 ± 0.04 vs. 0.05 ± 0.02, respectively; p < 0.05), suggesting a regulatory role for PPARγ on the CD40/CD40L pathway. Altogether, our findings outline a novel mechanism through which PPARγ regulates the inflammatory signal initiated by activation of CD40, with important implications for the understanding of immunological mechanisms underlying SLE and the development of new treatment strategies.

Application of proteomic to investigate the different degrees of meat tenderness in Nellore breed.

This study describes the association between meat tenderness and abundance of soluble muscle proteins in Nellore bulls (Bos indicus) using a proteomic approach. We evaluated shear force (SF) of Longissimus thoracis muscle 24 h after slaughter and selected three experimental groups of animals with moderately tender (TE; SF = 3.9 ± 0.7 kg), moderately tough (TO; SF = 5.6 ± 0.7 kg) and very tough meat (TO+; SF = 7.9 ± 1.4 kg). Proteome was investigated by two-dimensional electrophoresis (2D-PAGE) in combination with electrospray ionization-tandem mass spectrometry (ESI-MS/MS). The metabolic proteins triosephosphate isomerase (TPI1) and phosphoglucomutase 1 (PGM1), the structural protein profilin 1 (PFN1), and cytosol aminopeptidase (LAP3) were up-regulated (P < 0.05) in the TE meat group when compared to the TO and TO+ groups. Actin structural proteins (ACTA1, ACTB, and ACTG1), the oxidative stress protein peroxiredoxin (PRDX6, PRDX2, PRDX1, and PARK7), heat shock protein isoforms, and co-chaperones (CDC37 and STIP1) were up-regulated (P < 0.05) in the TO and TO+ meat groups. In addition, we also identified proteins PFN1, LAP3, PRDX1, PRDX2, HSPD1, and ARHGDIA to be associated with beef tenderness. The results reported herein demonstrated that meat tenderness in Nellore cattle depends on the modulation and expression of a set of proteins involved in different biological pathways. SIGNIFICANCE: The manuscript entitled "Application of proteomic to investigate the different degrees of meat tenderness in Nellore breed" describes a classical proteomics work using two-dimensional gel electrophoresis (2D-PAGE), followed by mass spectrometry coupled to electrospray ionization ion trap (ESI-MS/MS) in order to understand the biochemical engineering involved in the process of meat tenderness. We evaluated shear force (SF) of Longissimus thoracis muscle samples of Nellore cattle (n = 90) and select three experimental groups of animals with moderately tender (TE; SF = 3.9 ± 0.7), moderately tough (TO; SF = 5.6 ± 0.7) and very tough meat (TO+; SF = 7.9 ± 1.4). The proteomic approach allowed observing that meat tenderness is influenced by structural proteins (ACTA1, ACTG1, ACTB, MYL1 and PFN1), co-chaperones (CDC37 and STIP1), heat shock proteins (HSP90AA1, HSP90AB1, HSPD1, HSPA1L, HSPA1A and HSPB1), regulatory protein (ARHGDIA), metabolic proteins (TPI1 and PGM1) and oxidative stress proteins (PRDX1, PRDX2, PRDX6, PARK7). Our results suggest that meat tenderness in Nellore depends on the modulation and expression of a set of proteins involved in different biological pathways.