Lactate dehydrogenase expression at the onset of altered loading in rat soleus muscle

Integrative Metabolomics, Enzymatic Activity, and Gene Expression Analysis Provide Insights into the Metabolic Profile Differences between the Slow-Twitch Muscle and Fast-Twitch Muscle of Pseudocaranx dentex

The skeletal muscles of teleost fish encompass heterogeneous muscle types, termed slow-twitch muscle (SM) and fast-twitch muscle (FM), characterized by distinct morphological, anatomical, histological, biochemical, and physiological attributes, driving different swimming behaviors. Despite the central role of metabolism in regulating skeletal muscle types and functions, comprehensive metabolomics investigations focusing on the metabolic differences between these muscle types are lacking. To reveal the differences in metabolic characteristics between the SM and FM of teleost, we conducted an untargeted metabolomics analysis using Pseudocaranx dentex as a representative model and identified 411 differential metabolites (DFMs), of which 345 exhibited higher contents in SM and 66 in FM. KEGG enrichment analysis showed that these DFMs were enriched in the metabolic processes of lipids, amino acids, carbohydrates, purines, and vitamins, suggesting that there were significant differences between the SM and FM in multiple metabolic pathways, especially in the metabolism of energy substances. Furthermore, an integrative analysis of metabolite contents, enzymatic activity assays, and gene expression levels involved in ATP-PCr phosphate, anaerobic glycolysis, and aerobic oxidative energy systems was performed to explore the potential regulatory mechanisms of energy metabolism differences. The results unveiled a set of differential metabolites, enzymes, and genes between the SM and FM, providing compelling molecular evidence of the FM achieving a higher anaerobic energy supply capacity through the ATP-PCr phosphate and glycolysis energy systems, while the SM obtains greater energy supply capacity via aerobic oxidation. These findings significantly advance our understanding of the metabolic profiles and related regulatory mechanisms of skeletal muscles, thereby expanding the knowledge of metabolic physiology and ecological adaptation in teleost fish.

Comparison of Effects from Ultrasound Thawing, Vacuum Thawing and Microwave Thawing on the Quality Properties and Oxidation of Porcine Longissimus Lumborum

The effects of vacuum thawing (VT), ultrasound thawing (UT) and microwave thawing (MT) on the quality, protein and lipid oxidation, internal temperature distribution and microstructure of porcine longissimus lumborum were compared. The results showed that a significant decrease (p < 0.05) in quality compared with those of fresh meat (FM) occurred for all of the thawing samples, especially for the MT samples. Changes in quality of the VT and UT samples were less significant than those of the MT samples. The increases in carbonyl content and TBARS value indicated that proteins and lipids in the thawing samples were oxidized. The decreases in uniform degrees of internal temperature distributions of muscles from the thawing samples were analysed by infrared thermography. Scanning electron microscopy images showed that the myofibril arrangements of thawing samples were looser than those of the FM samples with compact and ordered structure, which was proven by the obvious increase in the myofibril gap value of the thawing samples.

Meat Color Stability of Ovine Muscles Is Related to Glycolytic Dehydrogenase Activities

The relationship between glycolytic dehydrogenase, including glyceraldehyde-3-phosphate dehydrogenase (GAPDH), lactic dehydrogenase (LDH), and meat color stability was studied in this study using ovine muscle. Three different ovine muscles, including M. longissimus lumborum (LL), M. semimembranosus (SM), and M. psoas major (PM), were obtained (n = 10, respectively), and then displayed for 7 days at 4 °C. The LL and SM muscle had higher surface redness, higher (P < 0.05) GAPDH activity, nicotinamide adenine dinucleotide (NADH) content, and lower (P < 0.05) LDH-B activity than PM muscles during display. The PM muscle had the worst color stability and lowest NADH content. These results suggest that variation in color stability of physiologically different muscles may be affected by glycolysis dehydrogenases. Comparatively, our data showed that GAPDH may play a more important role than LDH-B to maintain meat color stability.

Sensorial, structural and functional response of rats subjected to hind limb immobilization

AIMS

This study analyzed the sensorial, structural and functional response of rats subjected to paw immobilization.

MAIN METHODS

Animal pelvis, hip, knee and ankle were immobilized using waterproof tape during two weeks for assessment of sensorial response to thermal (hot plate test) and mechanical stimuli (Von Frey test), motor system structure (histology and radiography) and muscle function (soleus contractility).

KEY FINDINGS

Disuse animals became more responsive to thermal stimuli (49%), although less responsive to mechanical challenge (58%). Disuse animals showed local injuries such as reduction in muscle fiber diameter (16.7% in gastrocnemius, 5.7% in soleus), contractile activity (55% of the control maximal tonic contraction) and tibia cortical thickness (9.3%), besides increased nitrite:protein ratio, suggestive of protein degradation. Disuse also evoked systemic adaptations that include increase in serum lactate dehydrogenase (36.1%) and alkaline phosphatase (400%), but reduction in calcium (8.4%) and total serum protein (5.5%), especially albumin (34.2%).

SIGNIFICANCE

Two weeks of functional paw disuse leads to local and systemic harmful adaptive changes in sensorial and structural systems. This study brings new insights into nervous and motor system mechanism associated with therapeutic limb immobilization in muscle and skeletal pathological conditions.

Lactate dehydrogenase regulation in aged skeletal muscle: Regulation by anabolic steroids and functional overload

Aging alters the skeletal muscle response to overload-induced growth. The onset of functional overload is characterized by increased myoblast proliferation and an altered muscle metabolic profile. The onset of functional overload is associated with increased energy demands that are met through the interconversion of lactate and pyruvate via the activity of lactate dehydrogenase (LDH). Testosterone targets many of the processes activated at the onset of functional overload. However, the effect of aging on this metabolic plasticity at the onset of functional overload and how anabolic steroid administration modulates this response is not well understood. The purpose of this study was to determine if aging would alter overload-induced LDH activity and expression at the onset of functional overload and whether anabolic steroid administration would modulate this response. Five-month and 25-month male Fischer 344xF1 BRN were given nandrolone decanoate (ND) or sham injections for 14days and then the plantaris was functionally overloaded (OV) for 3days by synergist ablation. Aging reduced muscle LDH-A & LDH-B activity 70% (p<0.05). Aging also reduced LDH-A mRNA abundance, however there was no age effect on LDH-B mRNA abundance. In 5-month muscle, both ND and OV decreased LDH-A and LDH-B activity. However, there was no synergistic or additive effect. In 5-month muscle, ND and OV decreased LDH-A mRNA expression with no change in LDH-B expression. In 25-month muscle, ND and OV increased LDH-A and LDH-B activity. LDH-A mRNA expression was not altered by ND or OV in aged muscle. However, there was a main effect of OV to decrease LDH-B mRNA expression. There was also an age-induced LDH isoform shift. ND and OV treatment increased the "fast" LDH isoforms in aged muscle, whereas ND and OV increased the "slow" isoforms in young muscle. Our study provides evidence that aging alters aspects of skeletal muscle metabolic plasticity normally induced by overload and anabolic steroid administration.

Whey proteins are more efficient than casein in the recovery of muscle functional properties following a casting induced muscle atrophy

The purpose of this study was to investigate the effect of whey supplementation, as compared to the standard casein diet, on the recovery of muscle functional properties after a casting-induced immobilization period. After an initial (I0) evaluation of the contractile properties of the plantarflexors (isometric torque-frequency relationship, concentric power-velocity relationship and a fatigability test), the ankle of 20 male adult rats was immobilized by casting for 8 days. During this period, rats were fed a standard diet with 13% of casein (CAS). After cast removal, rats received either the same diet or a diet with 13% of whey proteins (WHEY). A control group (n = 10), non-immobilized but pair-fed to the two other experimental groups, was also studied and fed with the CAS diet. During the recovery period, contractile properties were evaluated 7 (R7), 21 (R21) and 42 days (R42) after cast removal. The immobilization procedure induced a homogeneous depression of average isometric force at R7 (CAS: − 19.0±8.2%; WHEY: − 21.7±8.4%; P<0.001) and concentric power (CAS: − 26.8±16.4%, P<0.001; WHEY: − 13.5±21.8%, P<0.05) as compared to I0. Conversely, no significant alteration of fatigability was observed. At R21, isometric force had fully recovered in WHEY, especially for frequencies above 50 Hz, whereas it was still significantly depressed in CAS, where complete recovery occurred only at R42. Similarly, recovery of concentric power was faster at R21 in the 500−700°/s range in the WHEY group. These results suggest that recovery kinetics varied between diets, the diet with the whey proteins promoting a faster recovery of isometric force and concentric power output as compared to the casein diet. These effects were more specifically observed at force level and movement velocities that are relevant for functional abilities, and thus natural locomotion.

Monocarboxylate transporter expression at the onset of skeletal muscle regeneration

The onset of skeletal muscle regeneration is characterized by proliferating myoblasts. Proliferating myoblasts have an increased energy demand and lactate exchange across the sarcolemma can be used to address this increased demand. Monocarboxylate transporters (MCTs) are involved in lactate transport across the sarcolemma and are known to be affected by various physiological stimuli. However, MCT expression at the onset of skeletal muscle regeneration has not been determined. The purpose of this study was to determine if skeletal muscle regeneration altered MCT expression in regenerating tibialis anterior (TA) muscle. Male C57/BL6 mice were randomly assigned to either a control (uninjured) or bupivacaine (injured) group. Three days post injection, the TA was extracted for determination of protein and gene expression. A 21% decrease in muscle mass to tibia length (2.4 ± 0.1 mg/mm vs. 1.9 ± 0.2 mg/mm, P < 0.02) was observed. IGF-1 and MyoD gene expression increased 5.0-fold (P < 0.05) and 3.5-fold (P < 0.05), respectively, 3 days post bupivacaine injection. MCT-1 protein was decreased 32% (P < 0.03); however, MCT-1 gene expression was not altered. There was no difference in MCT4 protein or gene expression. Lactate dehydrogenase (LDH)-A protein expression increased 71% (P < 0.0004). Protein levels of LDH-B and mitochondrial enzyme cytochrome C oxidase subunit decreased 3 days post bupivacaine injection. CD147 and PKC-θ protein increased 64% (P < 0.03) and 79% (P < 0.02), respectively. MCT1 but not MCT4 expression is altered at the onset of skeletal muscle regeneration possibly in an attempt to regulate lactate uptake and use by skeletal muscle cells.

Nutritional strategies to attenuate muscle disuse atrophy

Situations such as recovery from injury or illness require otherwise healthy humans to undergo periods of disuse, which lead to considerable losses of skeletal muscle mass and, subsequently, numerous negative health consequences. It has been established that prolonged disuse (>10 days) leads to a decline in basal and postprandial rates of muscle protein synthesis, without an apparent change in muscle protein breakdown. It also seems, however, that an early and transient (1-5 days) increase in basal muscle protein breakdown may also contribute to disuse atrophy. A period of disuse reduces energy requirements and appetite. Consequently, food intake generally declines, resulting in an inadequate dietary protein consumption to allow proper muscle mass maintenance. Evidence suggests that maintaining protein intake during a period of disuse attenuates disuse atrophy. Furthermore, supplementation with dietary protein and/or essential amino acids can be applied to further aid in muscle mass preservation during disuse. Such strategies are of particular relevance to the older patient at risk of developing sarcopenia. More work is required to elucidate the impact of disuse on basal and postprandial rates of muscle protein synthesis and breakdown. Such information will provide novel targets for nutritional interventions to further attenuate muscle disuse atrophy and, as such, support healthy aging.

Skeletal muscle mass recovery from atrophy in IL-6 knockout mice

AIM

Skeletal muscle interleukin-6 (IL-6) expression is induced by continuous contraction, overload-induced hypertrophy and during muscle regeneration. The loss of IL-6 can alter skeletal muscle's growth and extracellular matrix remodelling response to overload-induced hypertrophy. Insulin-like growth factor-1 (IGF-1) gene expression and related signalling through Akt/mTOR is a critical regulator of muscle mass. The significance of IL-6 expression during the recovery from muscle atrophy is unclear. This study's purpose was to determine the effect of IL-6 loss on mouse gastrocnemius (GAS) muscle mass during recovery from hindlimb suspension (HS)-induced atrophy.

METHODS

Female C57BL/6 [wild type (WT)] and IL-6 knockout (IL-6 KO) mice at 10 weeks of age were assigned to control, HS or HS followed by normal cage ambulation groups.

RESULTS

GAS muscle atrophy was induced by 10 days of HS. HS induced a 20% loss of GAS mass in both WT and IL-6 KO mice. HS+7 days of recovery restored WT GAS mass to cage-control values. GAS mass from IL-6 KO mice did not return to cage-control values until HS+14 days of recovery. Both IGF-1 mRNA expression and Akt/mTOR signalling were increased in WT muscle after 1 day of recovery. In IL-6 KO muscle, IGF-1 mRNA expression was decreased and Akt/mTOR signalling was not induced after 1 day of recovery. MyoD and myogenin mRNA expression were both induced in WT muscle after 1 day of recovery, but not in IL-6 KO muscle.

CONCLUSION

  Muscle IL-6 expression appears important for the initial growth response during the recovery from disuse.

Overload-induced skeletal muscle extracellular matrix remodelling and myofibre growth in mice lacking IL-6

AIM

Overloading healthy skeletal muscle produces myofibre hypertrophy and extracellular matrix remodelling, and these processes are thought to be interdependent for producing muscle growth. Inflammatory cytokine interleukin-6 (IL-6) gene expression is induced in overloaded skeletal muscle, and the loss of this IL-6 induction can attenuate the hypertrophic response to overload (OV). Although the OV induction of IL-6 in skeletal muscle may be an important regulator of inflammatory processes and satellite cell proliferation, less is known about its role in the regulation of extracellular matrix remodelling. The purpose of the current study was to examine if OV-induced extracellular matrix remodelling, muscle growth, and associated gene expression were altered in mice that lack IL-6, when compared with wild-type mice.

METHODS

Male C57/BL6 (WT) and C57/BL6 x IL-6(-/-) (IL-6(-/-)) mice (10 weeks of age) were assigned to either a sham control or synergist ablation OV treatments for 3, 21 or 56 days.

RESULT

Plantaris muscle mass increased 59% in WT and 116% in IL-6(-/-) mice after 21 day OV. Myofibre CSA was also increased by 21 day OV in both WT and IL-6(-/-) mice. OV induced a twofold greater increase in the volume of non-contractile tissue in IL-6(-/-) muscle compared to WT. OV also induced a significantly greater accumulation of hydroxyproline and procollagen-1 mRNA in IL-6(-/-) muscle, when compared with WT muscle after 21 day OV. Transforming growth factor-beta and insulin-like growth factor-1 mRNA expression were also induced to a greater extent in IL-6(-/-) muscle when compared with WT muscle after 21 day OV. There was no effect of IL-6 loss on the induction of myogenin, and cyclin D1 mRNA expression after 3 day OV. However, MyoD mRNA expression in 3 day OV IL-6(-/-) muscle was attenuated when compared with WT OV mice.

CONCLUSION

IL-6 appears to be necessary for the normal regulation of extracellular matrix remodelling during OV-induced growth.

Identification of mono-ubiquitinated LDH-A in skeletal muscle cells exposed to oxidative stress

We previously reported that oxidative stress is associated with unloading-mediated ubiquitination of muscle proteins. To further elucidate the involvement of oxidative stress in ubiquitination, we examined the ubiquitination profile in rat myoblastic L6 cells after treatment with hydrogen peroxide. Hydrogen peroxide induced many ubiquitinated proteins with low molecular masses (less than 60 kDa) as well as high molecular masses (more than 160 kDa). Among them, a 42-kDa-ubiquitinated protein was abundantly accumulated and immediately disappeared after the treatment. Microsequencing revealed that the 42-kDa-protein was identical to the mono-ubiquitinated form of rat lactate dehydrogenase A (LDH-A), and we confirmed that hydrogen peroxide induced the mono-ubiquitination of LDH-A in COS7 cells overexpressing LDH-A and ubiquitin. Under unloading conditions, such as tail-suspension and spaceflight, mono-ubiquitinated LDH was accumulated in gastrocnemius muscle. Interestingly, E-64-d plus pepstatin, lysosomal protease inhibitors, further accumulated mono-ubiquitinated LDH-A in the cells after treatment with hydrogen peroxide, while they did not affect the amount of poly-ubiquitinated LDH. In contrast, epoxomicin, a potent proteasome inhibitor, did not change the amount of mono-ubiquitinated LDH-A in L6 cells treated with hydrogen peroxide, although it significantly increased the amount of poly-ubiquitinated LDH. Our results suggest that oxidative stress induces not only poly-ubiquitination but also mono-ubiquitination of LDH-A, which may be involved in its lysosomal degradation during unloading.

Length-tension relationships are altered in regenerating muscles of the rat after bupivacaine injection

Intramuscular injection of bupivacaine causes complete degeneration of fibers in extensor digitorum longus (EDL) muscles of rats, followed by complete regeneration within 60 days. Previous studies have shown that regenerated EDL muscles are protected from contraction-induced injury 60 days after bupivacaine injection. It is possible that these regenerated muscles have altered length-tension relations because of fiber remodeling. We tested the hypothesis that length-tension relations are different in bupivacaine-injected and noninjected control muscles. EDL and soleus muscles of the right hindlimb of deeply anesthetized rats were injected with bupivacaine and then allowed to recover for 7, 14, 21, or 60 days (7D, 14D, 21D, 60D), and isometric contractile properties were assessed. Muscles of the contralateral limb were not injected and served as control. EDL muscles recovered from bupivacaine injection more rapidly than soleus muscles, with mass restored to control levels at 21D, and isometric tetanic force (Po) restored to control at 60D. In contrast, mass and Po of injected soleus muscles was not restored to control even at 60D. In 7D EDL muscles, length-tension curves were shifted leftward compared with control, but in 21D and 60D EDL muscles length-tension curves were right shifted significantly (treatment × muscle length: P < 0.001). Although no clear shift in the position of the length-tension curve was observed in regenerating soleus muscles, force production was enhanced on the descending limb of the curve in 60D soleus muscles (treatment × relative muscle length: P < 0.01). The rightward shift in the length-tension curve of EDL muscles 60 days after bupivacaine injection is likely to contribute to the mechanism for their previously observed protection from contraction-induced injury.