Housekeeping proteins: How useful are they in skeletal muscle diabetes studies and muscle hypertrophy models?

Therapeutical Potential of T3 as Adjuvant Therapy in Male Alloxan-induced Diabetic Rats

Alloxan-induced diabetic rats present with hypothyroidism. When treated with triiodothyronine (T3), glycemia and proinflammatory cytokine expression are downregulated, improving insulin sensitivity. The effectiveness of associating T3 with insulin (replacement dose [6 U] and [3 U]) in controlling glycemia was investigated in this experimental model. Male Wistar rats were made diabetic by alloxan injection and sorted into groups treated or not with insulin (3 or 6 U) associated or not with T3 (1.5 µg 100 g-1 BW) for 28 days. Nondiabetic rats constituted the control group. Fasting glycemia, glucose decay rate, and thyrotropin (TSH) were measured in the blood/serum of all animals. Immunoblotting was used to assess total GLUT4 expression in skeletal muscles and epididymal white adipose tissue. Cytokine and nuclear factor-κB (NF-κB) expression were measured in these tissues and liver. Diabetic rats presented with increased fasting glycemia, inflammatory cytokines, and NF-κB expression, TSH levels, and insulin resistance. In diabetic rats treated with T3 and/or insulin, these parameters were decreased, whereas GLUT4 and anti-inflammatory cytokine expression were increased. T3 combined with 3-U insulin restored the parameters to values of the control group and was more effective at controlling glycemia than 6-U insulin. Thus, a combination of T3 and insulin might represent a promising strategy for diabetes management since it reduces the insulin requirement by half and improves glycemic control of diabetic rats, which could postpone insulin resistance that develops with chronic insulin administration. These findings open a perspective for using thyroid analogues that provide tissue-specific effects, which might result in a potentially more effective treatment of diabetes.

Belt electrode tetanus muscle stimulation reduces denervation-induced atrophy of rat multiple skeletal muscle groups

Belt electrode-skeletal muscle electrical stimulation (B-SES) involves the use of belt-shaped electrodes to contract multiple muscle groups simultaneously. Twitch contractions have been demonstrated to protect against denervation-induced muscle atrophy in rats, possibly through mitochondrial biosynthesis. This study examined whether inducing tetanus contractions with B-SES suppresses muscle atrophy and identified the underlying molecular mechanisms. We evaluated the effects of acute (60 Hz, 5 min) and chronic (60 Hz, 5 min, every alternate day for one week) B-SES on the tibialis anterior (TA) and gastrocnemius (GAS) muscles in Sprague-Dawley rats using belt electrodes attached to both ankle joints. After acute stimulation, a significant decrease in the glycogen content was observed in the left and right TA and GAS, suggesting that B-SES causes simultaneous contractions in multiple muscle groups. B-SES enhanced p70S6K phosphorylation, an indicator of the mechanistic target of rapamycin complex 1 activity. During chronic stimulations, rats were divided into control (CONT), denervation-induced atrophy (DEN), and DEN + electrically stimulated with B-SES (DEN + ES) groups. After seven days of treatment, the wet weight (n = 8-11 for each group) and muscle fiber cross-sectional area (CSA, n = 6 for each group) of the TA and GAS muscles were reduced in the DEN and DEN + ES groups compared with that in the CON group. The DEN + ES group showed significantly higher muscle weight and CSA than those in the DEN group. Although RNA-seq and pathway analysis suggested that mitochondrial biogenesis is a critical event in this phenomenon, mitochondrial content showed no difference. In contrast, ribosomal RNA 28S and 18S (n = 6) levels in the DEN + ES group were higher than those in the DEN group, even though RNA-seq showed that the ribosome biogenesis pathway was reduced by electrical stimulation. The mRNA levels of the muscle proteolytic molecules atrogin-1 and MuRF1 were significantly higher in DEN than those in CONT. However, they were more suppressed in DEN + ES than those in DEN. In conclusion, tetanic electrical stimulation of both ankles using belt electrodes effectively reduced denervation-induced atrophy in multiple muscle groups. Furthermore, ribosomal biosynthesis plays a vital role in this phenomenon.

Korean red ginseng suppresses mitochondrial apoptotic pathway in denervation-induced skeletal muscle atrophy

Background

Skeletal muscle denervation leads to motor neuron degeneration, which in turn reduces muscle fiber volumes. Recent studies have revealed that apoptosis plays a role in regulating denervation-associated pathologic muscle wasting. Korean red ginseng (KRG) has various biological activities and is currently widely consumed as a medicinal product worldwide. Among them, ginseng has protective effects against muscle atrophy in in vivo and in vitro. However, the effects of KRG on denervation-induced muscle damage have not been fully elucidated.

Methods

We induced skeletal muscle atrophy in mice by dissecting the sciatic nerves, administered KRG, and then analyzed the muscles. KRG was administered to the mice once daily for 3 weeks at 100 and 400 mg/kg/day doses after operation.

Results

KRG treatment significantly increased skeletal muscle weight and tibialis anterior (TA) muscle fiber volume in injured areas and reduced histological alterations in TA muscle. In addition, KRG treatment reduced denervation-induced apoptotic changes in TA muscle. KRG attenuated p53/Bax/cytochrome c/Caspase 3 signaling induced by nerve injury in a dose-dependent manner. Also, KRG decreases protein kinase B/mammalian target of rapamycin pathway, reducing restorative myogenesis.

Conclusion

Thus, KRG has potential protective role against denervation-induced muscle atrophy. The effect of KRG treatment was accompanied by reduced levels of mitochondria-associated apoptosis.

Melatonin Alleviates the Impairment of Muscle Bioenergetics and Protein Quality Control Systems in Leptin-Deficiency-Induced Obesity

Leptin is critically compromised in the major common forms of obesity. Skeletal muscle is the main effector tissue for energy modification that occurs as a result of the effect of endocrine axes, such as leptin signaling. Our study was carried out using skeletal muscle from a leptin-deficient animal model, in order to ascertain the importance of this hormone and to identify the major skeletal muscle mechanisms affected. We also examined the therapeutic role of melatonin against leptin-induced muscle wasting. Here, we report that leptin deficiency stimulates fatty acid β-oxidation, which results in mitochondrial uncoupling and the suppression of mitochondrial oxidative damage; however, it increases cytosolic oxidative damage. Thus, different nutrient-sensing pathways are disrupted, impairing proteostasis and promoting lipid anabolism, which induces myofiber degeneration and drives oxidative type I fiber conversion. Melatonin treatment plays a significant role in reducing cellular oxidative damage and regulating energy homeostasis and fuel utilization. Melatonin is able to improve both glucose and mitochondrial metabolism and partially restore proteostasis. Taken together, our study demonstrates melatonin to be a decisive mitochondrial function-fate regulator in skeletal muscle, with implications for resembling physiological energy requirements and targeting glycolytic type II fiber recovery.

Differential Cellular Interactome in Schizophrenia and Bipolar Disorder-Discriminatory Biomarker Role

Schizophrenia (SCH) and bipolar disorder (BD) are two of the most important psychiatric pathologies due to their high population incidence and disabling power, but they also present, mainly in their debut, high clinical similarities that make their discrimination difficult. In this work, the differential oxidative stress, present in both disorders, is shown as a concatenator of the systemic alterations-both plasma and erythrocyte, and even at the level of peripheral blood mononuclear cells (PBMC)-in which, for the first time, the different affectations that both disorders cause at the level of the cellular interactome were observed. A marked erythrocyte antioxidant imbalance only present in SCH generalizes to oxidative damage at the plasma level and shows a clear impact on cellular involvement. From the alteration of protein synthesis to the induction of death by apoptosis, including proteasomal damage, mitochondrial imbalance, and autophagic alteration, all the data show a greater cellular affectation in SCH than in BD, which could be linked to increased oxidative stress. Thus, patients with SCH in our study show increased endoplasmic reticulum (ER)stress that induces increased proteasomal activity and a multifactorial response to misfolded proteins (UPR), which, together with altered mitochondrial activity, generating free radicals and leading to insufficient energy production, is associated with defective autophagy and ultimately leads the cell to a high apoptotic predisposition. In BD, however, oxidative damage is much milder and without significant activation of survival mechanisms or inhibition of apoptosis. These clear differences identified at the molecular and cellular level between the two disorders, resulting from progressive afflictions in which oxidative stress can be both a cause and a consequence, significantly improve the understanding of both disorders to date and are essential for the development of targeted and preventive treatments.

Mechanisms of mechanical overload-induced skeletal muscle hypertrophy: current understanding and future directions

Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill trained. Much of the preclinical rodent and human resistance training research to date supports that involved mechanisms include enhanced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, an expansion in translational capacity through ribosome biogenesis, increased satellite cell abundance and myonuclear accretion, and postexercise elevations in muscle protein synthesis rates. However, several lines of past and emerging evidence suggest that additional mechanisms that feed into or are independent of these processes are also involved. This review first provides a historical account of how mechanistic research into skeletal muscle hypertrophy has progressed. A comprehensive list of mechanisms associated with skeletal muscle hypertrophy is then outlined, and areas of disagreement involving these mechanisms are presented. Finally, future research directions involving many of the discussed mechanisms are proposed.

Autophagy signaling in hypertrophied muscles of diabetic and control rats

Autophagy plays a vital role in cell homeostasis by eliminating nonfunctional components and promoting cell survival. Here, we examined the levels of autophagy signaling proteins after 7 days of overload hypertrophy in the extensor digitorum longus (EDL) and soleus muscles of control and diabetic rats. We compared control and 3-day streptozotocin-induced diabetic rats, an experimental model for type 1 diabetes mellitus (T1DM). EDL muscles showed increased levels of basal autophagy signaling proteins. The diabetic state did not affect the extent of overload-induced hypertrophy or the levels of autophagy signaling proteins (p-ULK1, Beclin-1, Atg5, Atg12-5, Atg7, Atg3, LC3-I and II, and p62) in either muscle. The p-ULK-1, Beclin-1, and p62 protein expression levels were higher in the EDL muscle than in the soleus before the hypertrophic stimulus. On the contrary, the soleus muscle exhibited increased autophagic signaling after overload-induced hypertrophy, with increases in Beclin-1, Atg5, Atg12-5, Atg7, Atg3, and LC3-I expression in the control and diabetic groups, in addition to p-ULK-1 in the control groups. After hypertrophy, Beclin-1 and Atg5 levels increased in the EDL muscle of both groups, while p-ULK1 and LC3-I increased in the control group. In conclusion, the baseline EDL muscle exhibited higher autophagy than the soleus muscle. Although TDM1 promotes skeletal muscle mass loss and strength reduction, it did not significantly alter the extent of overload-induced hypertrophy and autophagy signaling proteins in EDL and soleus muscles, with the two groups exhibiting different patterns of autophagy activation.

Role of the endoplasmic reticulum in the search for early biomarkers of meat quality

Defects in meat quality such as dark, firm and dry (DFD) beef have been related to high levels of oxidative stress that produce cellular alterations that may affect to the process of meat quality acquisition. Despite the important role of endoplasmic reticulum (ER) in the cellular response to oxidative stress, its function in the muscle-to-meat conversion process has not yet been studied. In this study, differences in muscular antioxidant defense and the unfolded protein response (UPR) of the ER in CONTROL (normal pH₂₄) and dark, firm, and dry (DFD, pH₂₄ ≥ 6.2) beef at 24 h post-mortem were analyzed to understand the changes in the muscle-to-meat conversion process related to meat quality defects. DFD meat showed poor quality, lower antioxidant activity (P < 0.05) and higher UPR activation (P < 0.05), which indicates higher oxidative stress what could partly explain the occurrence of meat quality defects. Therefore, the biomarkers of these cellular processes (IRE1α, ATF6α, and p-eIF2α) are putative biomarkers of meat quality.

Low-frequency electrical stimulation of bilateral hind legs by belt electrodes is effective for preventing denervation-induced atrophies in multiple skeletal muscle groups in rats

Belt electrode skeletal muscle electrical stimulation (B-SES) can simultaneously contract multiple muscle groups. Although the beneficial effects of B-SES in clinical situations have been elucidated, its molecular mechanism remains unknown. In this study, we developed a novel rodent B-SES ankle stimulation system to test whether low-frequency stimulation prevents denervation-induced muscle atrophy. Electrical stimulations (7‒8 Hz, 30 min) with ankle belt electrodes were applied to Sprague-Dawley rats daily for one week. All animals were assigned to the control (CONT), denervation-induced atrophy (DEN), and DEN + electrical stimulation (ES) groups. The tibialis anterior (TA) and gastrocnemius (GAS) muscles were used to examine the effect of ES treatment. After seven daily sessions of continuous stimulation, muscle wet weight (n = 8-11), and muscle fiber cross-sectional area (CSA, n = 4-6) of TA and GAS muscles were lower in DEN and DEN + ES than in CON. However, it was significantly higher in DEN than DEN + ES, showing that ES partially prevented muscle atrophy. PGC-1α, COX-IV, and citrate synthase activities (n = 6) were significantly higher in DEN + ES than in DEN. The mRNA levels of muscle proteolytic molecules, Atrogin-1 and Murf1, were significantly higher in DEN than in CONT, while B-SES significantly suppressed their expression (p < 0.05). In conclusion, low-frequency electrical stimulation of the bilateral ankles using belt electrodes (but not the pad electrodes) is effective in preventing denervation-induced atrophy in multiple muscles, which has not been observed with pad electrodes. Maintaining the mitochondrial quantity and enzyme activity by low-frequency electrical stimulation is key to suppressing muscle protein degradation.

Housekeeping Proteins in Meat Quality Research: Are They Reliable Markers for Internal Controls in Western Blot? A Mini Review

Advancements in technology and analytical methods enable researchers to explore the biochemical events that cause variation in meat quality. Among those, western blot techniques have been successfully used in identifying and quantifying the key proteins that have critical functions in the development of meat quality. Housekeeping proteins, like β-actin, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and tubulins are often used as internal controls in western blots to normalize the abundance of the protein of interest. However, there are increasing concerns about using housekeeping proteins for western blot normalization, as these proteins do not demonstrate any loading differences above the relatively small total protein loading amounts of 10μg. In addition, the interaction between these housekeeping proteins and programmed cell death processes highlights the concerns about using the housekeeping protein as the internal control in meat quality research. Moreover, recent proteomic research has indicated that the abundance of some housekeeping proteins, like β-actin, GAPDH, and tubulin, can be altered by preslaughter stress, dietary supplementation, sex, slaughter method, genotype, breed, aging period, muscle type, and muscle portion. Furthermore, these housekeeping proteins could have differential expression in meat with differing color stability, tenderness, and water holding capacity. Therefore, this review aims to examine the realities of using housekeeping proteins as the loading control in meat quality research and introduce some alternative methods that can be used for western blot normalization.

Endoplasmic Reticulum Stress and Autophagy Markers in Soleus Muscle Disuse-Induced Atrophy of Rats Treated with Fish Oil

Endoplasmic reticulum stress (ERS) and autophagy pathways are implicated in disuse muscle atrophy. The effects of high eicosapentaenoic (EPA) or high docosahexaenoic (DHA) fish oils on soleus muscle ERS and autophagy markers were investigated in a rat hindlimb suspension (HS) atrophy model. Adult Wistar male rats received daily by gavage supplementation (0.3 mL per 100 g b.w.) of mineral oil or high EPA or high DHA fish oils (FOs) for two weeks. Afterward, the rats were subjected to HS and the respective treatments concomitantly for an additional two-week period. After four weeks, we evaluated ERS and autophagy markers in the soleus muscle. Results were analyzed using two-way analysis of variance (ANOVA) and Bonferroni post hoc test. Gastrocnemius muscle ω-6/ω-3 fatty acids (FAs) ratio was decreased by both FOs indicating the tissue incorporation of omega-3 fatty acids. HS altered (p < 0.05) the protein content (decreasing total p38 and BiP and increasing p-JNK2/total JNK2 ratio, and caspase 3) and gene expressions (decreasing BiP and increasing IRE1 and PERK) of ERS and autophagy (decreasing Beclin and increasing LC3 and ATG14) markers in soleus. Both FOs attenuated (p < 0.05) the increase in PERK and ATG14 expressions induced by HS. Thus, both FOs could potentially attenuate ERS and autophagy in skeletal muscles undergoing atrophy.

Cardiomyocyte-specific Txnip C247S mutation improves left ventricular functional reserve in streptozotocin-induced diabetic mice

Underlying molecular mechanisms for the development of diabetic cardiomyopathy remain to be determined. Long-term exposure to hyperglycemia causes oxidative stress, which leads to cardiomyocyte dysfunction. Previous studies established the importance of thioredoxin-interacting protein (Txnip) in cellular redox homeostasis and glucose metabolism. Txnip is a highly glucose-responsive molecule that interacts with the catalytic center of reduced thioredoxin and inhibits the antioxidant function of thioredoxin. Here, we show that the molecular interaction between Txnip and thioredoxin plays a pivotal role in the regulation of redox balance in the diabetic myocardium. High glucose increased Txnip expression, decreased thioredoxin activities, and caused oxidative stress in cells. The Txnip-thioredoxin complex was detected in cells with overexpressing wild-type Txnip but not Txnip cysteine 247 to serine (C247S) mutant that disrupts the intermolecular disulfide bridge. Then, diabetes was induced in cardiomyocyte-specific Txnip C247S knock-in mice and their littermate control animals by injections of streptozotocin (STZ). Prolonged hyperglycemia upregulated myocardial Txnip expression in both genotypes. The absence of Txnip's inhibition of thioredoxin in Txnip C247S mutant hearts promoted mitochondrial antioxidative capacities in cardiomyocytes, thereby protecting the heart from oxidative damage by diabetes. Stress hemodynamic analysis uncovered that Txnip C247S knock-in hearts have a greater left ventricular contractile reserve than wild-type hearts under STZ-induced diabetic conditions. These results provide novel evidence that Txnip serves as a regulator of hyperglycemia-induced cardiomyocyte toxicities through direct inhibition of thioredoxin and identify the single cysteine residue in Txnip as a therapeutic target for diabetic injuries.NEW & NORTEWORTHY Thioredoxin-interacting protein (Txnip) has been of great interest as a molecular mechanism to mediate diabetic organ damage. Here, we provide novel evidence that a single mutation of Txnip confers a defense mechanism against myocardial oxidative stress in streptozotocin-induced diabetic mice. The results demonstrate the importance of Txnip as a cysteine-containing redox protein that regulates antioxidant thioredoxin via disulfide bond-switching mechanism and identify the cysteine in Txnip as a therapeutic target for diabetic cardiomyopathy.

Small intestine remodeling in male Goto-Kakizaki rats

BACKGROUND

Obesity is associated with the development of insulin resistance (IR) and type-2 diabetes mellitus (T2DM); however, not all patients with T2DM are obese. The Goto-Kakizaki (GK) rat is an experimental model of spontaneous and non-obese T2DM. There is evidence that the intestine contributes to IR development in GK animals. This information prompted us to investigate small intestine remodeling in this animal model.

METHODS

Four-month-old male Wistar (control) and GK rats were utilized for the present study. After removing the small intestine, the duodenum, proximal jejunum, and distal ileum were separated. We then measured villi and muscular and mucosa layer histomorphometry, goblet cells abundance, total myenteric and submucosal neuron populations, and inflammatory marker expression in the small intestinal segments and intestinal transit of both groups of animals.

KEY RESULTS

We found that the GK rats exhibited decreased intestinal area (p < 0.0001), decreased crypt depth in the duodenum (p = 0.01) and ileum (p < 0.0001), increased crypt depth in the jejunum (p < 0.0001), longer villi in the jejunum and ileum (p < 0.0001), thicker villi in the duodenum (p < 0.01) and ileum (p < 0.0001), thicker muscular layers in the duodenum, jejunum, and ileum (p < 0.0001), increased IL-1β concentrations in the duodenum and jejunum (p < 0.05), and increased concentrations of NF-κB p65 in the duodenum (p < 0.01), jejunum and ileum (p < 0.05). We observed high IL-1β reactivity in the muscle layer, myenteric neurons, and glial cells of the experimental group. GK rats also exhibited a significant reduction in submucosal neuron density in the jejunum and ileum, ganglionic hypertrophy in all intestinal segments studied (p < 0.0001), and a slower intestinal transit (about 25%) compared to controls.

CONCLUSIONS

The development of IR and T2DM in GK rats is associated with small intestine remodeling that includes marked alterations in small intestine morphology, local inflammation, and reduced intestinal transit.

Hmox1 (Heme Oxygenase-1) Protects Against Ischemia-Mediated Injury via Stabilization of HIF-1α (Hypoxia-Inducible Factor-1α)

OBJECTIVE

Hmox1 (heme oxygenase-1) is a stress-induced enzyme that catalyzes the degradation of heme to carbon monoxide, iron, and biliverdin. Induction of Hmox1 and its products protect against cardiovascular disease, including ischemic injury. Hmox1 is also a downstream target of the transcription factor HIF-1α (hypoxia-inducible factor-1α), a key regulator of the body's response to hypoxia. However, the mechanisms by which Hmox1 confers protection against ischemia-mediated injury remain to be fully understood. Approach and Results: Hmox1 deficient (Hmox1-/-) mice had impaired blood flow recovery with severe tissue necrosis and autoamputation following unilateral hindlimb ischemia. Autoamputation preceded the return of blood flow, and bone marrow transfer from littermate wild-type mice failed to prevent tissue injury and autoamputation. In wild-type mice, ischemia-induced expression of Hmox1 in skeletal muscle occurred before stabilization of HIF-1α. Moreover, HIF-1α stabilization and glucose utilization were impaired in Hmox1-/- mice compared with wild-type mice. Experiments exposing dermal fibroblasts to hypoxia (1% O2) recapitulated these key findings. Metabolomics analyses indicated a failure of Hmox1-/- mice to adapt cellular energy reprogramming in response to ischemia. Prolyl-4-hydroxylase inhibition stabilized HIF-1α in Hmox1-/- fibroblasts and ischemic skeletal muscle, decreased tissue necrosis and autoamputation, and restored cellular metabolism to that of wild-type mice. Mechanistic studies showed that carbon monoxide stabilized HIF-1α in Hmox1-/- fibroblasts in response to hypoxia.

CONCLUSIONS

Our findings suggest that Hmox1 acts both downstream and upstream of HIF-1α, and that stabilization of HIF-1α contributes to Hmox1's protection against ischemic injury independent of neovascularization.

Mitochondrial Reversible Changes Determine Diastolic Function Adaptations During Myocardial (Reverse) Remodeling

BACKGROUND

Often, pressure overload-induced myocardial remodeling does not undergo complete reverse remodeling after decreasing afterload. Recently, mitochondrial abnormalities and oxidative stress have been successively implicated in the pathogenesis of several chronic pressure overload cardiac diseases. Therefore, we aim to clarify the myocardial energetic dysregulation in (reverse) remodeling, mainly focusing on the mitochondria.

METHODS

Thirty-five Wistar Han male rats randomly underwent sham or ascending (supravalvular) aortic banding procedure. Echocardiography revealed that banding induced concentric hypertrophy and diastolic dysfunction (early diastolic transmitral flow velocity to peak early-diastolic annular velocity ratio, E/E': sham, 13.6±2.1, banding, 18.5±4.1, P=0.014) accompanied by increased oxidative stress (dihydroethidium fluorescence: sham, 1.6×10⁸±6.1×10⁷, banding, 2.6×10⁸±4.5×10⁷, P<0.001) and augmented mitochondrial function. After 8 to 9 weeks, half of the banding animals underwent overload relief by an aortic debanding surgery (n=10).

RESULTS

Two weeks later, hypertrophy decreased with the decline of oxidative stress (dihydroethidium fluorescence: banding, 2.6×10⁸±4.5×10⁷, debanding, 1.96×10⁸±6.8×10⁷, P<0.001) and diastolic dysfunction improved simultaneously (E/E': banding, 18.5±4.1, debanding, 15.1±1.8, P=0.029). The reduction of energetic demands imposed by overload relief allowed the mitochondria to reduce its activity and myocardial levels of phosphocreatine, phosphocreatine/ATP, and ATP/ADP to normalize in debanding towards sham values (phosphocreatine: sham, 38.4±7.4, debanding, 35.6±8.7, P=0.71; phosphocreatine/ATP: sham, 1.22±0.23 debanding, 1.11±0.24, P=0.59; ATP/ADP: sham, 6.2±0.9, debanding, 5.6±1.6, P=0.66). Despite the decreased mitochondrial area, complex III and V expression increased in debanding compared with sham or banding. Autophagy and mitophagy-related markers increased in banding and remained higher in debanding rats.

CONCLUSIONS

During compensatory and maladaptive hypertrophy, mitochondria become more active. However, as the disease progresses, the myocardial energetic demands increase and the myocardium becomes energy deficient. During reverse remodeling, the concomitant attenuation of cardiac hypertrophy and oxidative stress allowed myocardial energetics, left ventricle hypertrophy, and diastolic dysfunction to recover. Autophagy and mitophagy are probably involved in the myocardial adaptation to overload and to unload. We conclude that these mitochondrial reversible changes underlie diastolic function adaptations during myocardial (reverse) remodeling.

Moving human muscle physiology research forward: an evaluation of fiber type-specific protein research methodologies

Human skeletal muscle is a heterogeneous tissue composed of multiple fiber types that express unique contractile and metabolic properties. While analysis of mixed fiber samples predominates and holds value, increasing attention has been directed toward studying proteins segregated by fiber type, a methodological distinction termed “fiber type-specific.” Fiber type-specific protein studies have the advantage of uncovering key molecular effects that are often missed in mixed fiber homogenate studies but also require greater time and resource-intensive methods, particularly when applied to human muscle. This review summarizes and compares current methods used for fiber type-specific protein analysis, highlighting their advantages and disadvantages for human muscle studies, in addition to recent advances in these techniques. These methods can be grouped into three categories based on the initial processing of the tissue: 1) muscle-specific fiber homogenates, 2) cross sections of fiber bundles, and 3) isolated single fibers, with various subtechniques for performing fiber type identification and protein quantification. The relative implementation for each unique methodological approach is analyzed from 83 fiber type-specific studies of proteins in live human muscle found in the literature to date. These studies have investigated several proteins involved in a wide range of cellular functions that are important to muscle tissue. The second half of this review summarizes key findings from this ensemble of fiber type-specific human protein studies. We highlight examples of where this analytical approach has helped to improve understanding of important physiological topics such as insulin sensitivity, muscle hypertrophy, muscle fatigue, and adaptation to different exercise programs.

Preoperative myocardial expression of E3 ubiquitin ligases in aortic stenosis patients undergoing valve replacement and their association to postoperative hypertrophy

Currently, aortic valve replacement is the only treatment capable of relieving left ventricle pressure overload in patients with severe aortic stenosis. It aims to improve cardiac function and revert hypertrophy, by triggering myocardial reverse remodeling. Despite immediately relieving afterload, reverse remodeling turns out to be extremely variable. Among other factors, the extent of reverse remodeling may depend on how well ubiquitin-proteasome system tackle hypertrophy. Therefore, we assessed tagged ubiquitin and ubiquitin ligases in the left ventricle collected from patients undergoing valve replacement and tested their association to the degree of reverse remodeling. Patients were classified according to the regression of left ventricle mass (ΔLVM) and assigned to complete (ΔLVM≥15%) or incomplete (ΔLVM≤5%) reverse remodeling groups. No direct inter-group differences were observed. Nevertheless, correlation analysis supports a fundamental role of the ubiquitin-proteasome system during reverse remodeling. Indeed, total protein ubiquitination was associated to hypertrophic indexes such as interventricular septal thickness (r = 0.55, p = 0.03) and posterior wall thickness (r = 0.65, p = 0.009). No significant correlations were observed for Muscle Ring Finger 3. Surprisingly, though, higher levels of atrogin-1 were associated to postoperative interventricular septal thickness (r = 0.71, p = 0.005). In turn, Muscle Ring Finger 1 correlated negatively with this postoperative hypertrophy marker (r = -0.68, p = 0.005), suggesting a cardioprotective role during reverse remodeling. No significant correlations were found with left ventricle mass regression, although a trend for a negative association between the ligase Murine Double Minute 2 and mass regression (r = -0.44, p = 0.10) was found. Animal studies will be necessary to understand whether this ligase is protective or detrimental. Herein, we show, for the first time, an association between the preoperative myocardial levels of ubiquitin ligases and postoperative hypertrophy, highlighting the therapeutic potential of targeting ubiquitin ligases in incomplete reverse remodeling.

Supplementation with Fermented Rice Bran Attenuates Muscle Atrophy in a Diabetic Rat Model

Fermented rice bran (FRB), a prospective supplement, has been proven to ameliorate certain medical conditions. However, its nutraceutical effect on muscle atrophy has never been investigated. The present study aimed to evaluate the effect of FRB on muscle atrophy in a streptozotocin (STZ)-induced diabetic rat model. Three groups of Sprague-Dawley rats, namely the control, STZ, and FRB groups, were treated as follows. The diabetic groups (STZ and FRB) were injected intraperitoneally with STZ (40 mg/kg BW), whereas the control group was injected with the vehicle. The STZ and control groups were fed the AIN93M diet, and the FRB group was fed 10% of FRB based on the AIN93M diet. The diabetic groups had reduced muscle size compared to the control group; however, these changes were alleviated in the FRB group. Moreover, the FRB group had a significantly lower expression of FBXO32/Atrogin-1 and TRIM63/MuRF1 (p < 0.05) due to blocked NF-κB activation. In conclusion, the anti-inflammatory effect of FRB may be beneficial for ameliorating muscle atrophy in diabetic conditions.

Reaching task performance is associated to neuromuscular junction adaptations in rats with induced diabetes mellitus

Upper limb performance is affected by diabetes mellitus (DM). Neuromuscular junction (NMJ) is a key structure to understand the relationship between performance and morphology in DM. The aim of the study was to analyze NMJ plasticity due to DM in an animal model and its relationship with the function of forelimbs in rats. Twelve Wistar rats were divided into control (C) and DM groups. Animals were trained to perform a grasping task, following procedures of habituation, shaping, and reaching task. DM was induced using streptozotocin. Forelimb neuromuscular performance for dexterity was evaluated one day before DM induction and five weeks following induction. After that, biceps, triceps, and finger flexors and extensors were removed. Connective tissue and muscle fiber cross-sectional area (CSA) were measured. NMJ was assessed by its morphometric characteristics (area, perimeter, and maximum diameter), using ImageJ software. Motor performance analyses were made using single pellet retrieval task performance test. Student’s t-test was used for comparisons between groups. A significant decrease in all NMJ morphometric parameters was observed in the DM group compared with the C group. Results showed that DM generated NMJ retraction in muscles involved in a reaching task. These alterations are related to signs of muscular atrophy and to poor reaching task performance. In conclusion, induced DM caused NMJ retraction and muscular atrophy in muscles involved in reaching task performance. Induced DM caused significantly lower motor performance, especially in the final moments of evaluation, when DM compromised the tropism of the muscular tissue.

Nox4 - RyR1 - Nox2: Regulators of micro-domain signaling in skeletal muscle

The ability for skeletal muscle to perform optimally can be affected by the regulation of Ca²⁺ within the triadic junctional space at rest. Reactive oxygen species impact muscle performance due to changes in oxidative stress, damage and redox regulation of signaling cascades. The interplay between ROS and Ca²⁺ signaling at the triad of skeletal muscle is therefore important to understand as it can impact the performance of healthy and diseased muscle. Here, we aimed to examine how changes in Ca²⁺ and redox signaling within the junctional space micro-domain of the mouse skeletal muscle fibre alters the homeostasis of these complexes. The dystrophic mdx mouse model displays increased RyR1 Ca²⁺ leak and increased NAD(P)H Oxidase 2 ROS. These alterations make the mdx mouse an ideal model for understanding how ROS and Ca²⁺ handling impact each other. We hypothesised that elevated t-tubular Nox2 ROS increases RyR1 Ca²⁺ leak contributing to an increase in cytoplasmic Ca²⁺, which could then initiate protein degradation and impaired cellular functions such as autophagy and ER stress. We found that inhibiting Nox2 ROS did not decrease RyR1 Ca²⁺ leak observed in dystrophin-deficient skeletal muscle. Intriguingly, another NAD(P)H isoform, Nox4, is upregulated in mice unable to produce Nox2 ROS and when inhibited reduced RyR1 Ca²⁺ leak. Our findings support a model in which Nox4 ROS induces RyR1 Ca²⁺ leak and the increased junctional space [Ca²⁺] exacerbates Nox2 ROS; with the cumulative effect of disruption of downstream cellular processes that would ultimately contribute to reduced muscle or cellular performance.

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Nox2 ROS does not influence RyR1 Ca²⁺ leak in skeletal muscle.

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Lack of Nox2 ROS increases Nox4 expression.

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Nox4 ROS induces RyR1 Ca²⁺ leak via S-nitrosylation.

The insulin resistance is reversed by exogenous 3,5,3'triiodothyronine in type 2 diabetic Goto-Kakizaki rats by an inflammatory-independent pathway

PURPOSE

Diabetes mellitus (DM) has a multifactorial etiology that imparts a particular challenge to effective pharmacotherapy. Thyroid hormone actions have demonstrated beneficial effects in diabetic as well as obese rats. In both conditions, inflammation status plays a crucial role in the development of insulin resistance. Taking this into consideration, the present study aimed to demonstrate another possible pathway of thyroid hormone action on insulin sensitivity in a spontaneous type 2 diabetic rat model: the Goto-Kakizaki (GK) rats. GK animals present all typical hallmarks of type 2 DM (T2DM), except the usual peripheric inflammatory condition, observed in the other T2DM animal models.

METHODS

GK rats were treated or not with 3,5,3'triiodothyronine (T3). Insulin sensitivity, glucose tolerance, and proteins related to glucose uptake and utilization were evaluated in the skeletal muscle, white adipose tissue, and liver.

RESULTS

GK rats T3-treated presented enhanced insulin sensitivity, increased GLUT-4 content in the white adipose tissue and skeletal muscle, and increased hexokinase and citrate synthase content in skeletal muscle. Both non-treated and T3-treated GK rats did not present alterations in cytokine content in white adipose tissue, skeletal muscle, liver, and serum.

CONCLUSIONS

These results indicate that T3 improves insulin sensitivity in diabetic rats by a novel inflammatory-independent mechanism.

MicroRNA miR-222 mediates pioglitazone beneficial effects on skeletal muscle of diet-induced obese mice

Pioglitazone belongs to the class of drugs thiazolidinediones (TZDs) and is an oral hypoglycemic drug, used in the treatment of type 2 diabetes, which improves insulin sensitivity in target tissues. Adipose tissue is the main target of pioglitazone, a PPARg and PPARa agonist; however, studies also point to skeletal muscle as a target. Non-PPAR targets of TZDs have been described, thus we aimed to study the direct effects of pioglitazone on skeletal muscle and the possible role of microRNAs as targets of this drug. Pioglitazone treatment of obese mice increased insulin-mediated glucose transport as a result of increased fatty acid oxidation and mitochondrial activity. PPARg blockage by treatment with GW9662 nullified pioglitazone's effect on systemic and muscle insulin sensitivity and citrate synthase activity of obese mice. After eight weeks of high-fat diet, miR-221-3p expression in soleus muscle was similar among the groups and miR-23b-3p and miR-222-3p were up-regulated in obese mice compared to the control group, and treatment with pioglitazone was able to reverse this condition. In vitro studies in C2C12 cells suggest that inhibition of miR-222-3p protects C2C12 cells from insulin resistance and increased non-mitochondrial respiration induced by palmitate. Together, these data demonstrate a role of pioglitazone in the downregulation of microRNAs that is not dependent on PPARg. Moreover, miR-222 may be a novel PPARg-independent mechanism through which pioglitazone improves insulin sensitivity in skeletal muscle.

A systematic approach to quantitative Western blot analysis

Attaining true quantitative data from WB requires that all the players involved in the procedure are quality controlled including the user. Appropriate protein extraction method, electrophoresis, and transfer of proteins, immunodetection of blotted protein by antibodies, and the ultimate step of imaging and analyzing the data is nothing short of a symphony. Like with any other technology in life-sciences research, Western blotting can produce erroneous and irreproducible data. We provide a systematic approach to generate quantitative data from Western blot experiments that incorporates critical validation steps to identify and minimize sources of error and variability throughout the Western blot process.

Short-term creatine supplementation changes protein metabolism signaling in hindlimb suspension

The effect of a short-term creatine supplementation on hindlimb suspension (HS)-induced muscle atrophy was investigated. Creatine monohydrate (5 g/kg b.w. per day) or placebo, divided in 2 daily doses, was given by oral gavage for 5 days. Rats were maintained in HS with dietary supplementation concomitantly for 5 days. Body weight, soleus and EDL muscle masses, and cross-sectional areas (CSA) of the muscle fibers were measured. Signaling pathways associated with skeletal muscle mass regulation (FST, MSTN, FAK, IGF-1, MGF, Akt, mTOR, atrogin-1, and MuRF1 expressions, and Akt, S6, GSK3B, and 4EBP1 proteins) were evaluated in the muscles. Soleus muscle exhibited more atrophy than the EDL muscle due to HS. Creatine supplementation attenuated the decrease of wet weight and increased p-4EBP1 protein in the EDL muscle of HS rats. Also, creatine increased mTOR and atrogin-1 expressions in the same muscle and condition. In the absence of HS, creatine supplementation increased FAK and decreased MGF expressions in the EDL muscle. Creatine attenuated the increase in FST expression due to HS in the soleus muscle. MuRF1 expression increased in the soleus muscle due to creatine supplementation in HS animals whereas atrogin-1 expression increased still further in this group compared with untreated HS rats. In conclusion, short-term creatine supplementation changed protein metabolism signaling in soleus and EDL muscles. However, creatine supplementation only slightly attenuated the mass loss of both muscles and did not prevent the CSA reduction and muscle strength decrease induced by HS for 5 days.

ER stress activation in the intestinal mucosa but not in mesenteric adipose tissue is associated with inflammation in Crohn's disease patients

Chronic/abnormal activation of endoplasmic reticulum (ER) stress is linked to the exacerbation of the inflammatory process and has been recently linked to Crohn’s disease (CD) pathophysiology. We investigated the intestinal mucosa and the mesenteric adipose tissue (MAT) collected from CD patients with active disease (CD group) and from non-IBD patients (CTR group) to study ER stress activation and to address tissue-specific modulation in CD. The intestinal mucosa of CD patients showed an upregulation in the expression of ER stress related genes, including ATF3, DNAJC3, STC2, DDIT3, CALR, HSPA5 and HSP90B1. Results showed that EIF2AK3 gene was upregulated, along with increased protein expression of p-eIF2α and p-eIF2α/eIF2α ratio. Additionally, ERN1 gene expression was upregulated, along with an increased spliced/activated form sXBP1 protein. Despite the upregulation of ATF6 gene expression in the intestinal mucosa of CD patients, no differences were found in ATF6 protein expression. Lastly, the analysis of MAT revealed unchanged levels of ER stress markers along with no differences in the activation of UPR. However, chaperone gene expression was modulated in the MAT of CD patients. To conclude, our results address tissue-specific differences in UPR activation in CD and point the ER stress as an important pro-inflammatory mechanism in CD, specifically in the intestinal mucosa.

NAD+ precursor increases aerobic performance in mice

PURPOSE

Nicotinamide riboside (NR) acts as a potent NAD⁺ precursor and improves mitochondrial oxidative capacity and mitochondrial biogenesis in several organisms. However, the effects of NR supplementation on aerobic performance remain unclear. Here, we evaluated the effects of NR supplementation on the muscle metabolism and aerobic capacity of sedentary and trained mice.

METHODS

Male C57BL/6 J mice were supplemented with NR (400 mg/Kg/day) over 5 and 10 weeks. The training protocol consisted of 5 weeks of treadmill aerobic exercise, for 60 min a day, 5 days a week. Bioinformatic and physiological assays were combined with biochemical and molecular assays to evaluate the experimental groups.

RESULTS

NR supplementation by itself did not change the aerobic performance, even though 5 weeks of NR supplementation increased NAD⁺ levels in the skeletal muscle. However, combining NR supplementation and aerobic training increased the aerobic performance compared to the trained group. This was accompanied by an increased protein content of NMNAT3, the rate-limiting enzyme for NAD + biosynthesis and mitochondrial proteins, including MTCO1 and ATP5a. Interestingly, the transcriptomic analysis using a large panel of isogenic strains of BXD mice confirmed that the Nmnat3 gene in the skeletal muscle is correlated with several mitochondrial markers and with different phenotypes related to physical exercise. Finally, NR supplementation during aerobic training markedly increased the amount of type I fibers in the skeletal muscle.

CONCLUSION

Taken together, our results indicate that NR may be an interesting strategy to improve mitochondrial metabolism and aerobic capacity.

Comprehensive Profiles of mRNAs and miRNAs Reveal Molecular Characteristics of Multiple Organ Physiologies and Development in Pigs

The pig (Sus scrofa) is not only an important livestock animal but also widely used as a biomedical model. However, the understanding of the molecular characteristics of organs and of the developmental skeletal muscle of the pig is severely limited. Here, we performed a comprehensive transcriptome profiling of mRNAs and miRNAs across nine tissues and three skeletal muscle developmental stages in the Guizhou miniature pig. The reproductive organs (ovary and testis) had greater transcriptome complexity and activity than other tissues, and the highest transcriptome similarity was between skeletal muscle and heart (R = 0.79). We identified 1,819 mRNAs and 96 miRNAs to be tissue-specific in nine organs. Testis had the largest number of tissue-specific mRNAs (992) and miRNAs (40). Only 15 genes and two miRNAs were specifically expressed in skeletal muscle and fat, respectively. During postnatal skeletal muscle development, the mRNAs associated with focal adhesion, Notch signaling, protein digestion, and absorption pathways were up-regulated from D0 to D30 and then down-regulated from D30 and D240, while genes with opposing expression patterns were significantly enriched in the oxidative phosphorylation and proteasome pathways. The miRNAs mainly regulated genes associated with insulin, Wnt, fatty acid biosynthesis, Notch, MAPK, TGF-beta, insulin secretion, ECM-receptor interaction, focal adhesion, and calcium signaling pathways. We also identified 37 new miRNA-mRNA interaction pairs involved in skeletal muscle development. Overall, our data not only provide a rich resource for understanding pig organ physiology and development but also aid the study of the molecular functions of mRNA and miRNA in mammals.

Adiponectin is required for pioglitazone-induced improvements in hepatic steatosis in mice fed a high-fat diet

Pioglitazone has been used for the treatment of nonalcoholic fatty liver disease (NAFLD) related to diabetes. The role of adiponectin in pioglitazone-induced improvements in NAFLD was studied by using wild-type (adipoWT) and adiponectin knockout (adipoKO) mice. High-fat diet fed mice were insulin resistant, glucose intolerant and had increased hepatic lipid accumulation as evidenced by increased NAFLD activity score. Despite pioglitazone has improved insulin resistance in both genotypes, hepatic steatosis was only improved in adipoWT obese mice. Amelioration of NAFLD in adipoWT mice promoted by pioglitazone was associated with up-regulation of Pparg, Fgf21 and down-regulation of Pepck liver expression. On the other hand, resistance to pioglitazone treatment in adipoKO mice was associated with increased expression of miR-192 and Hsl, which was not followed by increased fatty acid oxidation. In conclusion, our data provides evidence that increased adiponectin production by pioglitazone is necessary for its beneficial action on NAFLD.

Adaptations to high-intensity interval training in skeletal muscle require NADPH oxidase 2

OBJECTIVE

Reactive oxygen species (ROS) have been proposed as signaling molecules mediating exercise training adaptation, but the ROS source has remained unclear. This study aimed to investigate if increased NADPH oxidase (NOX)2-dependent activity during exercise is required for long-term high-intensity interval training (HIIT) in skeletal muscle using a mouse model lacking functional NOX2 complex due to absent p47phox (Ncf1) subunit expression (ncf1* mutation).

METHODS

HIIT was investigated after an acute bout of exercise and after a chronic intervention (3x/week for 6 weeks) in wild-type (WT) vs. NOX2 activity-deficient (ncf1*) mice. NOX2 activation during HIIT was measured using an electroporated genetically-encoded biosensor. Immunoblotting and single-fiber microscopy was performed to measure classical exercise-training responsive endpoints in skeletal muscle.

RESULTS

A single bout of HIIT increased NOX2 activity measured as p47-roGFP oxidation immediately after exercise but not 1 h or 4 h after exercise. After a 6-week HIIT regimen, improvements in maximal running capacity and some muscle training-markers responded less to HIIT in the ncf1* mice compared to WT, including superoxide dismutase 2, catalase, hexokinase II, pyruvate dehydrogenase and protein markers of mitochondrial oxidative phosphorylation complexes. Strikingly, HIIT-training increased mitochondrial network area and decreased fragmentation in WT mice only.

CONCLUSION

This study suggests that HIIT exercise increases NOX2 activity in skeletal muscle and shows that NOX2 activity is required for specific skeletal muscle adaptations to HIIT relating to antioxidant defense, glucose metabolism, and mitochondria.

Overweight in the Elderly Induces a Switch in Energy Metabolism that Undermines Muscle Integrity

Aging is characterized by a progressive loss of skeletal muscle mass and function (sarcopenia). Obesity exacerbates age-related decline and lead to frailty. Skeletal muscle fat infiltration increases with aging and seems to be crucial for the progression of sarcopenia. Additionally, skeletal muscle plasticity modulates metabolic adaptation to different pathophysiological situations. Thus, cellular bioenergetics and mitochondrial profile were studied in the skeletal muscle of overweight aged people without reaching obesity to prevent this extreme situation. Overweight aged muscle lacked ATP production, as indicated by defects in the phosphagen system, glycolysis and especially mostly by oxidative phosphorylation metabolic pathway. Overweight subjects exhibited an inhibition of mitophagy that was linked to an increase in mitochondrial biogenesis that underlies the accumulation of dysfunctional mitochondria and encourages the onset of sarcopenia. As a strategy to maintain cellular homeostasis, overweight subjects experienced a metabolic switch from oxidative to lactic acid fermentation metabolism, which allows continued ATP production under mitochondrial dysfunction, but without reaching physiological aged basal levels. This ATP depletion induced early signs of impaired contractile function and a decline in skeletal muscle structural integrity, evidenced by lower levels of filamin C. Our findings reveal the main effector pathways at an early stage of obesity and highlight the importance of mitochondrial metabolism in overweight and obese individuals. Exploiting mitochondrial profiles for therapeutic purposes in humans is an ambitious strategy for treating muscle impairment diseases.

Exercise-induced AMPK activation and IL-6 muscle production are disturbed in adiponectin knockout mice

BACKGROUND

Adiponectin exhibits anti-inflammatory actions and is mainly expressed in adipose tissue. However, recent studies have shown that adiponectin can also be secreted by skeletal muscle fibers with autocrine and paracrine effects.

OBJECTIVES

To analyze the role of adiponectin in the metabolic and inflammatory response of skeletal muscle after acute exhaustive aerobic exercise.

METHODS

C57BL/6 (WT) and adiponectin knockout (AdKO) mice underwent four days of treadmill running adaptation and at the fifth day, they performed an incremental maximum test to determine the maximum speed (Vmax). Acute exercise consisted of one hour at 60% Vmax. Mice were euthanatized 2 and 24 h after acute exercise session.

RESULTS

Serum and gastrocnemius adiponectin increased after 2-hours of acute exercise. NEFA concentrations were lower in non-exercise AdKO, and decreased 2-hours after exercise only in WT. No differences were found in muscle triacylglycerol content; however, glycogen content was higher in AdKO in non-exercise (p-value = 0.005). WT showed an increase in AMP-activated protein kinase (AMPK) phosphorylation 2-hours after exercise and its level went back to normal after 24-hours. Otherwise, exercise was not able to modify AMPK in the same way as in AdKO. WT showed an increase in the phosphorylation of ACC (Ser79) 2-hours after exercise and return to normal after 24-hours of exercise (p-value < 0.05), kinects that was not observed in AdKO mice. IL-10 and IL-6 concentration was completely different among genotypes. In WT, these cytokines were increased at 2 (p-value < 0.01) and 24 h (p-value < 0.001) after exercise when compared with AdKO. NF-κBp65 protein and gene expression were not different between genotypes.

CONCLUSION

Adiponectin influences muscle metabolism, mainly by the decrease in exercise-induced AMPK phosphorylation, inflammatory profile and IL-6 in the muscle.

Beneficial effects of thyroid hormone on adipose inflammation and insulin sensitivity of obese Wistar rats

Thyroid hormones play an important role in glucose metabolism and there is evidence of increased prevalence of thyroid dysfunction in obese and diabetic patients. This study aimed at evaluating the thyroid function and the effects of the triiodothyronine (T3) treatment on glycemia control, insulin sensitivity and subclinical inflammation in cafeteria‐diet‐induced obesity in rats. Obesity was induced in male Wistar rats by offering a cafeteria diet and a subset of the obese rats was treated with T3 (1.5 μg per 100 g of body weight) for a 28‐day period. The pituitary‐thyroid axis was evaluated by molecular and biochemical parameters. Cytokine content was measured in the serum as well as in the mesenteric and epididymal white adipose tissue. Obese rats exhibited impairment of glycemia control, increased content of inflammatory cytokines in mesenteric white adipose tissue, decreased serum thyrotropin (TSH) concentration and increased sodium/iodide symporter (NIS) and TSH receptor (TSHR) protein content in thyroid gland. T3 treatment improved insulin sensitivity, glucose tolerance, and reduced inflammatory cytokine content in mesenteric white adipose tissue. In the thyroid gland NIS, TSHR, and thyroperoxidase (TPO) content were reduced while thyroglobulin (TG) content was increased by T3. The thyrotrophic response to negative feedback exerted by T3 was preserved in obese rats. The present data reinforce the beneficial effects of T3 treatment of obese rats on the improvement of insulin sensitivity and on the negative modulation of inflammatory cytokine expression in adipose tissue. Moreover, we have evidenced that the pituitary‐thyroid axis is affected in obese rats, as illustrated by the impaired TSH secretion.

Hypoxia impairs adaptation of skeletal muscle protein turnover- and AMPK signaling during fasting-induced muscle atrophy

BACKGROUND

Hypoxemia in humans may occur during high altitude mountaineering and in patients suffering from ventilatory insufficiencies such as cardiovascular- or respiratory disease including Chronic Obstructive Pulmonary Disease (COPD). In these conditions, hypoxemia has been correlated to reduced appetite and decreased food intake. Since hypoxemia and reduced food intake intersect in various physiological and pathological conditions and both induce loss of muscle mass, we investigated whether hypoxia aggravates fasting-induced skeletal muscle atrophy and evaluated underlying protein turnover signaling.

METHODS

Mice were kept under hypoxic (8% oxygen) or normoxic conditions (21% oxygen), or were pair-fed to the hypoxia group for 12 days. Following an additional 24 hours of fasting, muscle weight and protein turnover signaling were assessed in the gastrocnemius muscle by RT-qPCR and Western blotting.

RESULTS

Loss of gastrocnemius muscle mass in response to fasting in the hypoxic group was increased compared to the normoxic group, but not to the pair-fed normoxic control group. Conversely, the fasting-induced increase in poly-ubiquitin conjugation, and expression of the ubiquitin 26S-proteasome E3 ligases, autophagy-lysosomal degradation-related mRNA transcripts and proteins, and markers of the integrated stress response (ISR), were attenuated in the hypoxia group compared to the pair-fed group. Mammalian target of rapamycin complex 1 (mTORC1) downstream signaling was reduced by fasting under normoxic conditions, but sustained under hypoxic conditions. Activation of AMP-activated protein kinase (AMPK) / tuberous sclerosis complex 2 (TSC2) signaling by fasting was absent, in line with retained mTORC1 activity under hypoxic conditions. Similarly, hypoxia suppressed AMPK-mediated glucocorticoid receptor (GR) signaling following fasting, which corresponded with blunted proteolytic signaling responses.

CONCLUSIONS

Hypoxia aggravates fasting-induced muscle wasting, and suppresses AMPK and ISR activation. Altered AMPK-mediated regulation of mTORC1 and GR may underlie aberrant protein turnover signaling and affect muscle atrophy responses in hypoxic skeletal muscle.

Resveratrol treatment reduces the appearance of tubular aggregates and improves the resistance to fatigue in aging mice skeletal muscles

Resveratrol (RES) is a polyphenolic compound found in grapes, peanuts, and in some berries. RES has been reported to exhibit antioxidant, anti-inflammatory, anti-proliferative properties, and to target mitochondrial-related pathways in mammalian cells and animal models. Therefore, RES is currently advised as supplement in the diet of elderly individuals. Although it is hypothesized that some of RES beneficial actions likely arise from its action on the skeletal muscle, the investigation of RES effects on this tissue remains still elusive. This study reports the effects of a 0,04% RES-supplemented diet for six months, on the skeletal muscle properties of C57/BL6 aging mice. The analysis of the morphology, protein expression, and functional-mechanical properties of selected skeletal muscles in treated compared to control mice, revealed that treated animals presented less tubular aggregates and a better resistance to fatigue in an ex-vivo contraction test, suggesting RES as a good candidate to reduce age-related alterations in muscle.

Molecular signatures and functional analysis of beige adipocytes induced from in vivo intra-abdominal adipocytes

Beige adipocytes can be induced from white adipocytes and precursors upon stimulation by cold temperatures and act like brown adipocytes to increase energy expenditure. Most in vivo studies examining the mechanisms for the induction of beige adipocytes have focused on subcutaneous white adipose tissue (sWAT; benign fat) in the mouse. How intra-abdominal WAT (aWAT; malignant fat) develops into beige adipocytes remains obscure, largely because there is a lack of a good animal model for the induction of beige adipocytes from aWAT. To better understand the development of beige adipocytes from mammalian WATs, especially aWAT, we induced beige adipocytes from bat aWAT and mouse sWAT by exposure to cold temperatures and analyzed their molecular signatures. RNA sequencing followed by whole genome-wide expression analysis shows that beige adipocytes induced from bat aWAT, rather than sWAT, have molecular signatures resembling those of mouse sWAT-induced beige adipocytes and exhibit dynamic profiles similar to those of classical brown adipocytes. In addition, we identified molecular markers that were highly enriched in beige adipocytes and conserved between bat aWAT and mouse sWAT, a set that included the genes Uqcrc1 and Letm1. Furthermore, knockdown of Uqcrc1 and Letm1 expression shows that they are required not only for beige adipocyte differentiation but also for preadipocyte maturation. This study presents a new model for research into the induction of beige adipocytes from aWAT in vivo, which, when combined with models where beige adipocytes are induced from sWAT, provides insight into therapeutic approaches for combating obesity-related diseases in humans.

Ileal pouch of ulcerative colitis and familial adenomatous polyposis patients exhibit modulation of autophagy markers

Total retocolectomy with ileal pouch-anal anastomosis (IPAA) is the surgery of choice for patients with ulcerative colitis (UC) that are refractory to clinical treatment. Pouchitis is one of the most common complications after this procedure. Defects in autophagy have been reported in inflammatory bowel diseases. However, there are no studies on the IP. Therefore, we studied markers for autophagy in the IP mucosa of UC and FAP patients comparing them to controls with a normal distal ileum. Sixteen patients with IP in "J" shape, asymptomatic and with endoscopically normal IP were evaluated. The control group consisted of eight patients with normal colonoscopy. There was a significant decrease in the transcriptional levels of ATG5, MAP1LC3A and BAX in the FAP group. There was also a decrease in the protein level of Beclin-1 in the UC and FAP compared to the control group. Although the LC3II levels by immunoblot were higher in the UC group, LC3/p62 co-localization were lower in the immunofluorescence analysis in the UC and FAP compared to the control group. Corroborating these results, there was an increase of p62 by immunoblot in the UC group. These findings indicated a modulation of macroautophagy markers in the IP, which may explain the mucosa inflammation predisposition.

Tubulin or Not Tubulin: Heading Toward Total Protein Staining as Loading Control in Western Blots

Western blotting is an analytical method widely used for detecting and (semi-)quantifying specific proteins in given samples. Western blots are continuously applied and developed by the protein community. This review article focuses on a significant, but not yet well-established, improvement concerning the internal loading control as a prerequisite to accurately quantifying Western blots. Currently, housekeeping proteins (HKPs) like actin, tubulin, or GAPDH are often used to check for equal loading or to compensate potential loading differences. However, this loading control has multiple drawbacks. Staining of the total protein on the blotting membrane has emerged as a better loading control. Total protein staining (TPS) represents the actual loading amount more accurately than HKPs due to minor technical and biological variation. Further, the broad dynamic range of TPS solves the issue of HKPs that commonly fail to show loading differences above small loading amounts of 0.5-10 μg. Although these and further significant advantages have been demonstrated over the past 10 years, only a small percentage of laboratories take advantage of it. The objective of this review article is to collect and compare information about TPS options and to invite users to reconsider their applied loading control. Nine benefits of TPS are discussed and seven different variants are critically evaluated by comparing technical details. Consequently, this review article offers an orientation in selecting the appropriate staining type. I conclude that TPS should be the preferred loading control in future Western blot approaches.

Protein arginine methyltransferase expression and activity during myogenesis

Despite the emerging importance of protein arginine methyltransferases (PRMTs) in regulating skeletal muscle plasticity, PRMT biology during muscle development is complex and not completely understood. Therefore, our purpose was to investigate PRMT1, -4, and -5 expression and function in skeletal muscle cells during the phenotypic remodeling elicited by myogenesis. C₂C₁₂ muscle cell maturation, assessed during the myoblast (MB) stage, and during days 1, 3, 5, and 7 of differentiation, was employed as an in vitro model of myogenesis. We observed PRMT-specific patterns of expression and activity during myogenesis. PRMT4 and -5 gene expression was unchanged, while PRMT1 mRNA and protein content were significantly induced. Cellular monomethylarginines (MMAs) and symmetric dimethylarginines (SDMAs), indicative of global and type II PRMT activities, respectively, remained steady during development, while type I PRMT activity indicator asymmetric dimethylarginines (ADMAs) increased through myogenesis. Histone 4 arginine 3 (H4R3) and H3R17 contents were elevated coincident with the myonuclear accumulation of PRMT1 and -4. Collectively, this suggests that PRMTs are methyl donors throughout myogenesis and demonstrate specificity for their protein targets. Cells were then treated with TC-E 5003 (TC-E), a selective inhibitor of PRMT1 in order to specifically examine the enzymes role during myogenic differentiation. TC-E treated cells exhibited decrements in muscle differentiation, which were consistent with attenuated mitochondrial biogenesis and respiratory function. In summary, the present study increases our understanding of PRMT1, -4, and -5 biology during the plasticity of skeletal muscle development. Our results provide evidence for a role of PRMT1, via a mitochondrially mediated mechanism, in driving the muscle differentiation program.

Hypertrophy Stimulation at the Onset of Type I Diabetes Maintains the Soleus but Not the EDL Muscle Mass in Wistar Rats

Diabetes mellitus induces a reduction in skeletal muscle mass and strength. Strength training is prescribed as part of treatment since it improves glycemic control and promotes increase of skeletal muscle mass. The mechanisms involved in overload-induced muscle hypertrophy elicited at the establishment of the type I diabetic state was investigated in Wistar rats. The purpose was to examine whether the overload-induced hypertrophy can counteract the hypotrophy associated to the diabetic state. The experiments were performed in oxidative (soleus) or glycolytic (EDL) muscles. PI3K/Akt/mTOR protein synthesis pathway was evaluated 7 days after overload-induced hypertrophy of soleus and of EDL muscles. The mRNA expression of genes associated with different signaling pathways that control muscle hypertrophy was also evaluated: mechanotransduction (FAK), Wnt/β-catenin, myostatin, and follistatin. The soleus and EDL muscles when submitted to overload had similar hypertrophic responses in control and diabetic animals. The increase of absolute and specific twitch and tetanic forces had the same magnitude as muscle hypertrophic response. Hypertrophy of the EDL muscle from diabetic animals mostly involved mechanical loading-stimulated PI3K/Akt/mTOR pathway besides the reduced activation of AMP-activated protein kinase (AMPK) and decrease of myostatin expression. Hypertrophy was more pronounced in the soleus muscle of diabetic animals due to a more potent activation of rpS6 and increased mRNA expression of insulin-like growth factor-1 (IGF-1), mechano-growth factor (MGF) and follistatin, and decrease of myostatin, MuRF-1 and atrogin-1 contents. The signaling changes enabled the soleus muscle mass and force of the diabetic rats to reach the values of the control group.

Balanced Diet-Fed Fat-1 Transgenic Mice Exhibit Lower Hindlimb Suspension-Induced Soleus Muscle Atrophy

The consequences of two-week hindlimb suspension (HS) on skeletal muscle atrophy were investigated in balanced diet-fed Fat-1 transgenic and C57BL/6 wild-type mice. Body composition and gastrocnemius fatty acid composition were measured. Skeletal muscle force, cross-sectional area (CSA), and signaling pathways associated with protein synthesis (protein kinase B, Akt; ribosomal protein S6, S6, eukaryotic translation initiation factor 4E-binding protein 1, 4EBP1; glycogen synthase kinase3-beta, GSK3-beta; and extracellular-signal-regulated kinases 1/2, ERK 1/2) and protein degradation (atrophy gene-1/muscle atrophy F-box, atrogin-1/MAFbx and muscle RING finger 1, MuRF1) were evaluated in the soleus muscle. HS decreased soleus muscle wet and dry weights (by 43% and 26%, respectively), muscle isotonic and tetanic force (by 29% and 18%, respectively), CSA of the soleus muscle (by 36%), and soleus muscle fibers (by 45%). Fat-1 transgenic mice had a decrease in the ω-6/ω-3 polyunsaturated fatty acids (PUFAs) ratio as compared with C57BL/6 wild-type mice (56%, p < 0.001). Fat-1 mice had lower soleus muscle dry mass loss (by 10%) and preserved absolute isotonic force (by 17%) and CSA of the soleus muscle (by 28%) after HS as compared with C57BL/6 wild-type mice. p-GSK3B/GSK3B ratio was increased (by 70%) and MuRF-1 content decreased (by 50%) in the soleus muscle of Fat-1 mice after HS. Balanced diet-fed Fat-1 mice are able to preserve in part the soleus muscle mass, absolute isotonic force and CSA of the soleus muscle in a disuse condition.

Overweight in elderly people induces impaired autophagy in skeletal muscle

Sarcopenia is the gradual loss of skeletal muscle mass, strength and quality associated with aging. Changes in body composition, especially in skeletal muscle and fat mass are crucial steps in the development of chronic diseases. We studied the effect of overweight on skeletal muscle tissue in elderly people without reaching obesity to prevent this extreme situation. Overweight induces a progressive protein breakdown reflected as a progressive withdrawal of anabolism against the promoted catabolic state leading to muscle wasting. Protein turnover is regulated by a network of signaling pathways. Muscle damage derived from overweight displayed by oxidative and endoplasmic reticulum (ER) stress induces inflammation and insulin resistance and forces the muscle to increase requirements from autophagy mechanisms. Our findings showed that failure of autophagy in the elderly deprives it to deal with the cell damage caused by overweight. This insufficiently efficient autophagy leads to an accumulation of p62 and NBR1, which are robust markers of protein aggregations. This impaired autophagy affects myogenesis activity. Depletion of myogenic regulatory factors (MRFs) without links to variations in myostatin levels in overweight patients suggest a possible reduction of satellite cells in muscle tissue, which contributes to declined muscle quality. This discovery has important implications that improve the understanding of aged-related atrophy caused by overweight and demonstrates how impaired autophagy is one of the main responsible mechanisms that aggravate muscle wasting. Therefore, autophagy could be an interesting target for therapeutic interventions in humans against muscle impairment diseases.

The Kv1.3 channel blocker Vm24 enhances muscle glucose transporter 4 mobilization but does not reduce body-weight gain in diet-induced obese male rats

AIMS

Voltage-gated potassium channels 1.3 (Kv1.3) can be targeted to reduce diet-induced obesity and insulin resistance in mice. Since species-specific differences in Kv1.3 expression and pharmacology have been observed, we tested the effect of Vm24, a high-affinity specific blocker of Kv1.3 channels from Vaejovis mexicanus smithi, on body weight (BW), glucose tolerance and insulin resistance in diet-induced obese rats.

MATERIALS AND METHODS

Young adult male Wistar rats were switched to a high-fat/high-fructose (HFF) diet. Eighteen days later animals were divided in two groups: vehicle and Vm24 group. Subcutaneous injections were applied every other day until sacrifice 2months later. An additional cohort was maintained on standard chow.

KEY FINDINGS

The HFF diet promoted obesity. Treatment with Vm24 did not alter various metabolic parameters such as food intake, BW gain, visceral white adipose tissue mass, adipocyte diameter, serum glucose, leptin and thyroid hormone concentrations, brown adipose tissue mass or uncoupling protein-1 expression, and insulin tolerance. Vm24 did reduce basal and glucose-stimulated serum insulin concentrations, serum C-peptide concentration, increased QUICKI, and tended to lower HOMA-IR. Vm24 treatment did not change the activation of insulin receptor substrate-1, but enhanced protein-kinase B activation and membrane glucose-transporter 4 (GLUT4) protein levels in skeletal muscle.

SIGNIFICANCE

In conclusion, in male rats, long-term blockade of Kv1.3 channels with Vm24 does not reduce weight gain and visceral adiposity induced by HFF diet; instead, it reduces serum insulin concentration, and enhances GLUT4 mobilization in skeletal muscle.

Transcriptional and Molecular Pathways Activated in Mesenteric Adipose Tissue and Intestinal Mucosa of Crohn's Disease Patients

Crohn's disease (CD) is a chronic inflammatory disorder, characterized by cytokine imbalance and transcription signaling pathways activation. In addition, the increase of mesenteric adipose tissue (MAT) near the affected intestinal area is a hallmark of CD. Therefore, we evaluated the transcription signaling pathways and cytokines expression in intestinal mucosa and MAT of active CD patients. Ten patients with ileocecal CD and eight with noninflammatory diseases were studied. The biopsies of intestinal mucosa and MAT were snap-frozen and protein expression was determined by immunoblotting. RNA levels were measured by qPCR. The pIkB/IkB ratio and TNFα level were significantly higher in intestinal mucosa of CD when compared to controls. However, STAT1 expression was similar between intestinal mucosa of CD and controls. Considering the MAT, the pIkB/IkB ratio was significantly lower and the anti-inflammatory cytokine IL10 was significantly higher in CD when compared to controls. Finally, the protein content of pSTAT1 was higher in MAT of CD compared to controls. These findings reinforce the predominance of the proinflammatory NF-kB pathway in CD intestinal mucosa. For the first time, we showed the activation of STAT1 pathway in MAT of CD patients, which may help to understand the physiopathology of this immune mediated disease.

Identification of reference genes and miRNAs for qRT-PCR in human esophageal squamous cell carcinoma

It is important to select an appropriate reference gene and miRNA when using quantitative real-time polymerase chain reaction (qRT-PCR) to analyze gene and miRNA expression. However, many commonly used reference genes and miRNAs are not stably expressed and therefore not suitable for normalization or quantification of qRT-PCR data. This study aims to identify appropriate reference genes and miRNAs for use in human esophageal squamous carcinoma qRT-PCR analysis. Using data provided by The Cancer Genome Atlas, we identified DDX5, LAPTM4A, P4HB, RHOA, miR-28-5p, miR-34a-5p, and miR-186-5p as candidate reference genes and miRNAs. We used qRT-PCR to verify the expression levels of these candidates and another seven commonly used reference genes and miRNAs. A set of 50 paired human normal esophageal tissues and squamous cell carcinoma samples were used in the analysis. We then used geNorm and NormFinder to analyze the results. DDX5, LAPTM4A, RHOA, ACTB, RNU48, miR-28-5p, miR-34a-5p, and miR-186-5p were stably expressed, indicating they are suitable for used as references in qRT-PCR analysis of esophageal squamous cell carcinoma. However, expression levels of 18s rRNA, GAPDH, P4HB, 5s rRNA, U6, and RNU6B varied greatly between esophageal normal and squamous cell carcinoma samples, indicating that they are not suitable for use as references in the qRT-PCR analysis of esophageal squamous cell carcinoma.

Effects of high EPA and high DHA fish oils on changes in signaling associated with protein metabolism induced by hindlimb suspension in rats

The effects of either eicosapentaenoic (EPA)- or docosahexaenoic (DHA)-rich fish oils on hindlimb suspension (HS)-induced muscle disuse atrophy were compared. Daily oral supplementations (0.3 mL/100 g b.w.) with mineral oil (MO) or high EPA or high DHA fish oils were performed in adult rats. After 2 weeks, the animals were subjected to HS for further 2 weeks. The treatments were maintained alongside HS At the end of 4 weeks, we evaluated: body weight gain, muscle mass and fat depots, composition of fatty acids, cross-sectional areas (CSA) of the soleus muscle and soleus muscle fibers, activities of cathepsin L and 26S proteasome, and content of carbonylated proteins in the soleus muscle. Signaling pathway activities associated with protein synthesis (Akt, p70S6K, S6, 4EBP1, and GSK3-beta) and protein degradation (atrogin-1/MAFbx, and MuRF1) were evaluated. HS decreased muscle mass, CSA of soleus muscle and soleus muscle fibers, and altered signaling associated with protein synthesis (decreased) and protein degradation (increased). The treatment with either fish oil decreased the ratio of omega-6/omega-3 fatty acids and changed protein synthesis-associated signaling. EPA-rich fish oil attenuated the changes induced by HS on 26S proteasome activity, CSA of soleus muscle fibers, and levels of p-Akt, total p70S6K, p-p70S6K/total p70S6K, p-4EBP1, p-GSK3-beta, p-ERK2, and total ERK 1/2 proteins. DHA-rich fish oil attenuated the changes induced by HS on p-4EBP1 and total ERK1 levels. The effects of EPA-rich fish oil on protein synthesis signaling were more pronounced. Both EPA- and DHA-rich fish oils did not impact skeletal muscle mass loss induced by non-inflammatory HS.