No abstract

Klotho mutant (kl/kl) mice, a type of short-lived mouse models, display several aging-related phenotypes. To investigate whether the atrophy of skeletal muscles is induced in these mice via activation of the ubiquitin-proteasomal pathway and/or the autophagic-lysosomal pathway through an alteration of insulin/IGF-I signaling, we analyzed the activity of the two pathways for protein degradation and components of the insulin/IGF signaling pathway in their skeletal muscles. The masseter, tongue, and gastrocnemius muscles in kl/kl showed marked reductions in muscle weight and in myofiber diameter compared with +/+. The autophagic-lysosomal pathway in kl/kl was activated in the masseter and tongue, but not in the gastrocnemius, compared with that in +/+, whereas the ubiquitin-proteasomal pathway in these three muscles of kl/kl was not altered. No marked difference in the phosphorylation levels of insulin/IGF-I signaling components, such as insulin/IGF-I receptor, Akt, and FoxO in three muscles studied were found between kl/kl and +/+, but the phosphorylation levels of signaling component at the downstream of mTOR such as 4E-BP1 and p70 S6K were suppressed in the masseter and tongue of kl/kl compared with +/+. Deficiency of essential amino acids is reported to activate the autophagy-lysosomal pathway through the down-regulation of mTOR, not through IGF-Akt-FoxO. The masseter and tongue seem to be more actively moved than limb muscles in kl/kl, because they are essential for survival activities such as mastication, swallowing, and respiration. Thus, the deficiency of amino acid by the active movement of the masseter and tongue seems to stimulate the autophagic-lysosomal pathway via the down-regulation of mTOR signalling pathway.

Summary. The inhibition of apoptosis by glycyrrhizin (GL) in hepatic injury induced by injection of lipopolysaccharide (LPS)/D-galactosamine (D-GalN

Reactive oxygen species (ROS) are believed to be involved in radiation-induced xerostomia, and the application of antioxidants may be a promising method for treating patients suffering from salivary gland dysfunction. In this study, we examined the ability of the antioxidant superoxide dismutase (SOD) to restore radiation-induced salivary gland dysfunction using a mouse model of radiation-induced salivary gland hypofunction and ultraviolet B (UVB)-irradiated human salivary gland cells. We administered lecithinized SOD (PC-SOD) prior to and after irradiation and measured the amount of saliva secreted. To confirm ROS generation, flow cytometry was performed using an oxidant-sensitive fluorescent dye, dihydroethidium, and CM-H(2)DCFDA. While no significant decrease in saliva secretion was observed after irradiation in the mice that were treated with PC-SOD, a significant reduction in saliva secretion was noted in the irradiated mice that were not treated with PC-SOD. Furthermore, flow cytometry clearly revealed that PC-SOD eliminated superoxide (O(2)(-)) induced by UVB radiation. These results suggested that PC-SOD may protect against exocrine gland dysfunction induced by radiation, presumably by rapidly converting O(2)(-) to hydrogen peroxide. We believe that our results may advance the potential application of antioxidants for the prevention of ROS-induced xerostomia.

Little is known about the effects of obesity on skeletal muscle consisting of approximately 80% type I (slow) fibers, such as that in the soleus muscle, although type I fibers have an enhanced capacity for mitochondrial respiration and fatty acid oxidation. We investigated the effects of obesity on the soleus muscle in the rat. Rats were fed a high-fat diet (protein:fat:-carbohydrate ¼ 20:57:23; 508 kcal/100 g) or a control diet (protein:fat:carbohydrate ¼ 20:10:70; 366 kcal/100 g) for 10 weeks. We analyzed the accumulation of intramyocellular triacylglycerol (IMTG), fiber type composition, and the biogenesis and function of the mitochondria in the soleus muscle of the rat during 10 weeks of feeding, using histochemical and realtime polymerase chain reaction analyses. Obesity increased body weight and markedly elevated IMTG levels in type I, but not in type II, fibers of the soleus muscle throughout the feeding period. Obesity also inhibited the biogenesis and function in the mitochondria and altered the fiber type composition in the soleus muscle. The suppression of biogenesis and function in the mitochondria, and the alteration in the fiber type composition may be attributable to the marked IMTG accumulation in the soleus muscle of the rat. Anat Rec, 294:1904Rec, 294: -1912Rec, 294: , 2011. V V C 2011 Wiley-Liss, Inc.