Improved Tetanic Force and Mitochondrial Calcium Homeostasis by Astaxanthin Treatment in Mouse Skeletal Muscle

Loss of adenosine A3 receptors accelerates skeletal muscle regeneration in mice following cardiotoxin-induced injury

Skeletal muscle regeneration is a complex process orchestrated by multiple interacting steps. An increasing number of reports indicate that inflammatory responses play a central role in linking initial muscle injury responses to timely muscle regeneration following injury. The nucleoside adenosine has been known for a long time as an endogenously produced anti-inflammatory molecule that is generated in high amounts during tissue injury. It mediates its physiological effects via four types of adenosine receptors. From these, adenosine A3 receptors (A3Rs) are not expressed by the skeletal muscle but are present on the surface of various inflammatory cells. In the present paper, the effect of the loss of A3Rs was investigated on the regeneration of the tibialis anterior (TA) muscle in mice following cardiotoxin-induced injury. Here we report that regeneration of the skeletal muscle from A3R-/- mice is characterized by a stronger initial inflammatory response resulting in a larger number of transmigrating inflammatory cells to the injury site, faster clearance of cell debris, enhanced proliferation and faster differentiation of the satellite cells (the muscle stem cells), and increased fusion of the generated myoblasts. This leads to accelerated skeletal muscle tissue repair and the formation of larger myofibers. Though the infiltrating immune cells expressed A3Rs and showed an increased inflammatory profile in the injured A3R-/- muscles, bone marrow transplantation experiments revealed that the increased response of the tissue-resident cells to tissue injury is responsible for the observed phenomenon. Altogether our data indicate that A3Rs are negative regulators of injury-related regenerative inflammation and consequently also that of the muscle fiber growth in the TA muscle. Thus, inhibiting A3Rs might have a therapeutic value during skeletal muscle regeneration following injury.

Astaxanthin delays brain aging in senescence-accelerated mouse prone 10: inducing autophagy as a potential mechanism

Brain aging is a complex biological process often associated with a decline in cognitive functions and motility. Astaxanthin (AST) is a strong antioxidant capable of crossing the blood-brain barrier. The effect of AST on brain aging and its physiological and molecular mechanism are still unclear. The study aimed to investigate whether AST from AstaReal A1010 improved brain aging by inducing autophagy in SAMP10 mice. Different concentrations of AstaReal A1010 were intragastrically administered to 6-month-old SAMP10 mice for 3 months. The results demonstrated that AST delayed age-related cognitive decline, motor ability and neurodegeneration, upregulated the expression levels of autophagy-related genes beclin-1 and LC3 in the brain. It may induce autophagy by regulating IGF-1/Akt/mTOR and IGF-1/Akt/FoxO3a signaling. Treatment with autophagy inhibitor 3-methyladenine (3MA) partly reversed the anti-aging effect of AST. In conclusion, our findings suggest that AST may induce autophagy by regulating IGF-1/Akt/mTOR and IGF-1/Akt/FoxO3a signaling, thereby delaying age-related neurodegeneration and cognitive decline in SAMP10 mice.

Genetic Manipulation of CB1 Cannabinoid Receptors Reveals a Role in Maintaining Proper Skeletal Muscle Morphology and Function in Mice

The endocannabinoid system (ECS) refers to a widespread signaling system and its alteration is implicated in a growing number of human diseases. Cannabinoid receptors (CBRs) are highly expressed in the central nervous system and many peripheral tissues. Evidence suggests that CB1Rs are expressed in human and murine skeletal muscle mainly in the cell membrane, but a subpopulation is present also in the mitochondria. However, very little is known about the latter population. To date, the connection between the function of CB1Rs and the regulation of intracellular Ca²⁺ signaling has not been investigated yet. Tamoxifen-inducible skeletal muscle-specific conditional CB1 knock-down (skmCB1-KD, hereafter referred to as Cre^+/-) mice were used in this study for functional and morphological analysis. After confirming CB1R down-regulation on the mRNA and protein level, we performed in vitro muscle force measurements and found that peak twitch, tetanus, and fatigue were decreased significantly in Cre^+/- mice. Resting intracellular calcium concentration, voltage dependence of the calcium transients as well as the activity dependent mitochondrial calcium uptake were essentially unaltered by Cnr1 gene manipulation. Nevertheless, we found striking differences in the ultrastructural architecture of the mitochondrial network of muscle tissue from the Cre^+/- mice. Our results suggest a role of CB1Rs in maintaining physiological muscle function and morphology. Targeting ECS could be a potential tool in certain diseases, including muscular dystrophies where increased endocannabinoid levels have already been described.

Astaxanthin improves preserved semen quality at 17°C by enhancing sperm antioxidant and motility properties

Porcine sperm is rich in polyunsaturated fatty acids; therefore, it is highly susceptible to oxidative damage during storage. Inhibition of oxidative stress during preservation is essential for maintaining sperm motility. Astaxanthin is a potent antioxidant used in the cosmetic and pharmaceutical industries. This study aimed to explore the effect of supplementing astaxanthin as an extender of porcine semen preservation dilutions at 17°C. Various concentrations of astaxanthin were added to diluted porcine semen at 17°C. We performed computer-assisted semen analysis, evaluation of plasma membrane integrity and acrosome integrity, and measurement of total antioxidant activity, malondialdehyde (MDA) content, reactive oxygen species levels, superoxide dismutase (SOD) activity, catalase (CAT) activity, glutathione peroxidase (GSH-PX) activity and sperm motility parameters. Compared with the control group, the addition of 0.25 μg/ml astaxanthin group significantly improved sperm motility parameters stored on the fifth day; these were increased levels of sperm SOD, GSH-PX and CAT (p < .05), increased sperm adenosine trisphosphate and lactate dehydrogenase levels and decreased sperm MDA levels (p < .05). These findings suggest that adding 0.25 μg/ml of astaxanthin improves the quality of porcine semen stored at 17°C. Our findings provide theoretical support for developing new protective agents critical for preserving pig semen at 17°C.

Astaxanthin Exerts Anabolic Effects via Pleiotropic Modulation of the Excitable Tissue

Astaxanthin is a lipid-soluble carotenoid influencing lipid metabolism, body weight, and insulin sensitivity. We provide a systematic analysis of acute and chronic effects of astaxanthin on different organs. Changes by chronic astaxanthin feeding were analyzed on general metabolism, expression of regulatory proteins in the skeletal muscle, as well as changes of excitation and synaptic activity in the hypothalamic arcuate nucleus of mice. Acute responses were also tested on canine cardiac muscle and different neuronal populations of the hypothalamic arcuate nucleus in mice. Dietary astaxanthin significantly increased food intake. It also increased protein levels affecting glucose metabolism and fatty acid biosynthesis in skeletal muscle. Inhibitory inputs innervating neurons of the arcuate nucleus regulating metabolism and food intake were strengthened by both acute and chronic astaxanthin treatment. Astaxanthin moderately shortened cardiac action potentials, depressed their plateau potential, and reduced the maximal rate of depolarization. Based on its complex actions on metabolism and food intake, our data support the previous findings that astaxanthin is suitable for supplementing the diet of patients with disturbances in energy homeostasis.

Astaxanthin as a Novel Mitochondrial Regulator: A New Aspect of Carotenoids, beyond Antioxidants

Astaxanthin is a member of the carotenoid family that is found abundantly in marine organisms, and has been gaining attention in recent years due to its varied biological/physiological activities. It has been reported that astaxanthin functions both as a pigment, and as an antioxidant with superior free radical quenching capacity. We recently reported that astaxanthin modulated mitochondrial functions by a novel mechanism independent of its antioxidant function. In this paper, we review astaxanthin’s well-known antioxidant activity, and expand on astaxanthin’s lesser-known molecular targets, and its role in mitochondrial energy metabolism.

Impaired Skeletal Muscle Development and Regeneration in Transglutaminase 2 Knockout Mice

Skeletal muscle regeneration is triggered by local inflammation and is accompanied by phagocytosis of dead cells at the injury site. Efferocytosis regulates the inflammatory program in macrophages by initiating the conversion of their inflammatory phenotype into the healing one. While pro-inflammatory cytokines induce satellite cell proliferation and differentiation into myoblasts, growth factors, such as GDF3, released by healing macrophages drive myoblast fusion and myotube growth. Therefore, improper efferocytosis may lead to impaired muscle regeneration. Transglutaminase 2 (TG2) is a versatile enzyme participating in efferocytosis. Here, we show that TG2 ablation did not alter the skeletal muscle weights or sizes but led to the generation of small size myofibers and to decreased grip force in TG2 null mice. Following cardiotoxin-induced injury, the size of regenerating fibers was smaller, and the myoblast fusion was delayed in the tibialis anterior muscle of TG2 null mice. Loss of TG2 did not affect the efferocytic capacity of muscle macrophages but delayed their conversion to Ly6C-CD206+, GDF3 expressing cells. Finally, TG2 promoted myoblast fusion in differentiating C2C12 myoblasts. These results indicate that TG2 expressed by both macrophages and myoblasts contributes to proper myoblast fusion, and its ablation leads to impaired muscle development and regeneration in mice.

Assessing the Potential of Nutraceuticals as Geroprotectors on Muscle Performance and Cognition in Aging Mice

Aging and frailty are associated with a decline in muscle force generation, which is a direct consequence of reduced muscle quantity and quality. Among the leading contributors to aging is the generation of reactive oxygen species, the byproducts of terminal oxidation. Their negative effects can be moderated via antioxidant supplementation. Krill oil and astaxanthin (AX) are nutraceuticals with a variety of health promoting, geroprotective, anti-inflammatory, anti-diabetic and anti-fatigue effects. In this work, we examined the functional effects of these two nutraceutical agents supplemented via pelleted chow in aging mice by examining in vivo and in vitro skeletal muscle function, along with aspects of intracellular and mitochondrial calcium homeostasis, as well as cognition and spatial memory. AX diet regimen limited weight gain compared to the control group; however, this phenomenon was not accompanied by muscle tissue mass decline. On the other hand, both AX and krill oil supplementation increased force production without altering calcium homeostasis during excitation-contraction coupling mechanism or mitochondrial calcium uptake processes. We also provide evidence of improved spatial memory and learning ability in aging mice because of krill oil supplementation. Taken together, our data favors the application of antioxidant nutraceuticals as geroprotectors to improve cognition and healthy aging by virtue of improved skeletal muscle force production.

The Role of Orai1 in Regulating Sarcoplasmic Calcium Release, Mitochondrial Morphology and Function in Myostatin Deficient Skeletal Muscle

In mice a naturally occurring 12-bp deletion in the myostatin gene is considered responsible for the compact phenotype (Mstn^{Cmpt–dl1Abc}, Cmpt) labeled by a tremendous increase in body weight along with signs of muscle weakness, easier fatigability, decreased Orai1 expression and store operated calcium entry (SOCE). Here, on the one hand, Cmpt fibers were reconstructed with venus-Orai1 but this failed to restore SOCE. On the other hand, the endogenous Orai1 was silenced in fibers from wild type C57Bl6 mice which resulted in ∼70% of Orai1 being silenced in whole muscle homogenates as confirmed by Western blot, accompanied by an inhibitory effect on the voltage dependence of SR calcium release that manifested in a slight shift toward more positive potential values. This maneuver completely hampered SOCE. Our observations are consistent with the idea that Orai1 channels are present in distinct pools responsible for either a rapid refilling of the SR terminal cisternae connected to each voltage-activated calcium transient, or a slow SOCE associated with an overall depletion of calcium in the SR lumen. Furthermore, when Cmpt cells were loaded with the mitochondrial membrane potential sensitive dye TMRE, fiber segments with depolarized mitochondria were identified covering on average 26.5 ± 1.5% of the fiber area. These defective areas were located around the neuromuscular junction and displayed significantly smaller calcium transients. The ultrastructural analysis of the Cmpt fibers revealed changes in the mitochondrial morphology. In addition, the mitochondrial calcium uptake during repetitive stimulation was higher in the Cmpt fibers. Our results favor the idea that reduced function and/or expression of SOCE partners (in this study Orai1) and mitochondrial defects could play an important role in muscle weakness and degeneration associated with certain pathologies, perhaps including loss of function of the neuromuscular junction and aging.

β-Cryptoxanthin Improves p62 Accumulation and Muscle Atrophy in the Soleus Muscle of Senescence-Accelerated Mouse-Prone 1 Mice

We investigated the effects of β-cryptoxanthin on skeletal muscle atrophy in senescence-accelerated mouse-prone 1 (SAMP1) mice. For 15 weeks, SAMP1 mice were intragastrically administered vehicle or β-cryptoxanthin. At 35 weeks of age, the skeletal muscle mass in SAMP1 mice was reduced compared with that in control senescence-accelerated mouse-resistant 1 (SAMR1) mice. β-cryptoxanthin increased muscle mass with an increase in the size of muscle fibers in the soleus muscle of SAMP1 mice. The expressions of autophagy-related factors such as beclin-1, p62, LC3-I, and LC3-II were increased in the soleus muscle of SAMP1 mice; however, β-cryptoxanthin administration inhibited this increase. Unlike in SAMR1 mice, p62 was punctately distributed throughout the cytosol in the soleus muscle fibers of SAMP1 mice; however, β-cryptoxanthin inhibited this punctate distribution. The cross-sectional area of p62-positive fiber was smaller than that of p62-negative fiber, and the ratio of p62-positive fibers to p62-negative fibers was increased in SAMP1 mice. β-cryptoxanthin decreased this ratio in SAMP1 mice. Furthermore, β-cryptoxanthin decreased the autophagy-related factor expression in murine C2C12 myotube. The autophagy inhibitor bafilomycin A1, but not the proteasome inhibitor MG132, inhibited the β-cryptoxanthin-induced decrease in p62 and LC3-II expressions. These results indicate that β-cryptoxanthin inhibits the p62 accumulation in fibers and improves muscle atrophy in the soleus muscle of SAMP1 mice.