Rapid induction of REDD1 expression by endurance exercise in rat skeletal muscle

An acute bout of exercise induces repression of protein synthesis in skeletal muscle due in part to reduced signaling through the mammalian target of rapamycin complex 1 (mTORC1). Previous studies have shown that upregulated expression of regulated in DNA damage and development (REDD) 1 and 2 is an important mechanism in the regulation of mTORC1 activity in response to a variety of stresses. This study investigated whether induction of REDD1/2 expression occurs in rat skeletal muscle in response to a burst of endurance exercise. In addition, we determined if ingestion of glucose or branched chain amino acids (BCAA) before exercise changes the expression of REDD1/2 in muscle. Rats ran on a motor-driven treadmill at a speed of 28 m min⁻¹ for 90 min, and then the gastrocnemius muscle was removed and analyzed for phosphorylation of the eukaryotic initiation factor (eIF) 4E binding protein 1 (4E-BP1) and expression of REDD1/2. Exercise repressed the mTORC1-signaling pathway regardless of the ingestion of nutrients before the exercise, as shown by dephosphorylation of 4E-BP1. In addition, exercise induced the expression of REDD1 mRNA (∼8-fold) and protein (∼3-fold). Exercise-induced expression of REDD1 was not affected by the ingestion of glucose or BCAA. Expression of REDD2 mRNA was not altered by either exercise or nutrients. These findings indicated that enhanced expression of REDD1 may be an important mechanism that could partially explain the downregulation of mTORC1 signaling, and subsequent inhibition of protein synthesis in skeletal muscle during exercise.     

Single bout of running exercise changes LC3-II expression in rat cardiac muscle

Macroautophagy (autophagy) is an intracellular catalytic process. We examined the effect of running exercise, which stimulates cardiac work physiologically, on the expression of microtubule-associated protein 1 light chain 3 (LC3)-II, an indicator of autophagy, as well as some autophagy-related proteins in rat cardiac muscle. The left ventricles were taken from rats immediately (0 h), and at 0.5 h, 1 h or 3 h after a single bout of running exercise on a treadmill for 30 min and also from rats in a rest condition. In these samples, we evaluated the level of LC3-II and p62, and the phosphorylation level of mammalian target of rapamycin (mTOR), Akt and AMP-activated protein kinase alpha (AMPKα) by Western blotting. The exercise produced a biphasic change in LC3-II, with an initial decrease observed immediately after the exercise and a subsequent increase 1 h thereafter. LC3-II then returned to the rest level at 3 h after the exercise. A negative correlation was found between the LC3-II expression and mTOR phosphorylation, which plays a role in inhibiting autophagy. The exercise increased phosphorylation of AMPKα, which stimulates autophagy via suppression of mTOR phosphorylation, immediately after exercise. The level of p62 and phosphorylated Akt was not altered significantly by the exercise. These results suggest for the first time that a single bout of running exercise induces a biphasic change in autophagy in the cardiac muscle. The exercise-induced change in autophagy might be partially mediated by mTOR in the cardiac muscle.     

Binding of glyceraldehyde-3-phosphate dehydrogenase to the cis-acting element of structure-anchored repression in ccn2 mRNA

Studies increasingly indicate that inflammation induced by β-amyloid (Aβ) contributes to the progression of Alzheimer’s disease (AD). How to inhibit the enhanced production of proinflammatory cytokines stimulated by Aβ is an important research subject for the treatment of AD. In this study, we investigated the inhibitory effect and the molecular mechanism of the lipoxin A₄ (LXA₄) on the production of interleukin-1β (IL-1β) and tumor necrosis factorα (TNFα) induced by β-amyloid in the cortex and hippocampus of mice, and in Aβ-stimulated BV2 cells, a mouse microglial cell line. LXA₄ down-regulated the protein expression of IL-1β and TNFα, attenuated the gene expressions of IL-1β and TNFα, inhibited the degradation of IκBα, inhibited translocation of NF-κB p65 subunit into the nucleus induced by β-amyloid in the cortex and hippocampus of mice, and in Aβ-stimulated BV2 cells, and the inhibitory effects were dose dependently elevated. Our findings suggest that LXA₄ inhibits the production of IL-1β and TNFα induced by β-amyloid in the cortex and hippocampus of mice, and in BV2 microglial cells via the NF-κB signal pathway.     

Intermedilysin induces EGR-1 expression through calcineurin/NFAT pathway in human cholangiocellular carcinoma cells

RNF8 is a nuclear protein having an N-terminal forkhead-associated (FHA) domain and a C-terminal RING-finger (RF) domain. Depletion of RNF8 caused cell growth inhibition and cell cycle arrest at not only S but also G2/M phases. In addition, cell death was frequently observed in RNF8-depleted cells. Analyses of time-lapse microscopy revealed that the cells died in mitosis and interphase. To elucidate the RNF8 function in M phase, the Plk1 content in RNF8-depleted cells was examined. The amount of RNF8 decreased time-dependently, whereas Plk1 reciprocally increased by transfection of RNF8 siRNA. Protein contents of RNF8 and Plk1 among various cell lines were also compared. RNF8 in normal cell lines was much higher than that in many cancer cell lines. Conversely, Plk1 in normal cell lines was lower than in cancer cell lines. These results suggest that RNF8 is downregulated in many cancer cells and inversely correlated with Plk1.     

Structure of a novel class II phospholipase D: catalytic cleft is modified by a disulphide bridge

Phospholipases D (PLDs) are principally responsible for the local and systemic effects of Loxosceles envenomation including dermonecrosis and hemolysis. Despite their clinical relevance in loxoscelism, to date, only the SMase I from Loxosceles laeta, a class I member, has been structurally characterized. The crystal structure of a class II member from Loxosceles intermedia venom has been determined at 1.7 Å resolution. Structural comparison to the class I member showed that the presence of an additional disulphide bridge which links the catalytic loop to the flexible loop significantly changes the volume and shape of the catalytic cleft. An examination of the crystal structures of PLD homologues in the presence of low molecular weight compounds at their active sites suggests the existence of a ligand-dependent rotamer conformation of the highly conserved residue Trp230 (equivalent to Trp192 in the glycerophosphodiester phosphodiesterase from Thermus thermophofilus, PDB code: 1VD6) indicating its role in substrate binding in both enzymes. Sequence and structural analyses suggest that the reduced sphingomyelinase activity observed in some class IIb PLDs is probably due to point mutations which lead to a different substrate preference.     

SOD1 (copper/zinc superoxide dismutase) deficiency drives amyloid β protein oligomerization and memory loss in mouse model of Alzheimer disease

Oxidative stress is closely linked to the pathogenesis of neurodegeneration. Soluble amyloid β (Aβ) oligomers cause cognitive impairment and synaptic dysfunction in Alzheimer disease (AD). However, the relationship between oligomers, oxidative stress, and their localization during disease progression is uncertain. Our previous study demonstrated that mice deficient in cytoplasmic copper/zinc superoxide dismutase (CuZn-SOD, SOD1) have features of drusen formation, a hallmark of age-related macular degeneration (Imamura, Y., Noda, S., Hashizume, K., Shinoda, K., Yamaguchi, M., Uchiyama, S., Shimizu, T., Mizushima, Y., Shirasawa, T., and Tsubota, K. (2006) Proc. Natl. Acad. Sci. U.S.A. 103, 11282-11287). Amyloid assembly has been implicated as a common mechanism of plaque and drusen formation. Here, we show that Sod1 deficiency in an amyloid precursor protein-overexpressing mouse model (AD mouse, Tg2576) accelerated Aβ oligomerization and memory impairment as compared with control AD mouse and that these phenomena were basically mediated by oxidative damage. The increased plaque and neuronal inflammation were accompanied by the generation of N(ε)-carboxymethyl lysine in advanced glycation end products, a rapid marker of oxidative damage, induced by Sod1 gene-dependent reduction. The Sod1 deletion also caused Tau phosphorylation and the lower levels of synaptophysin. Furthermore, the levels of SOD1 were significantly decreased in human AD patients rather than non-AD age-matched individuals, but mitochondrial SOD (Mn-SOD, SOD2) and extracellular SOD (CuZn-SOD, SOD3) were not. These findings suggest that cytoplasmic superoxide radical plays a critical role in the pathogenesis of AD. Activation of Sod1 may be a therapeutic strategy for the inhibition of AD progression.     

Cadaverine covalently linked to the peptidoglycan serves as the correct constituent for the anchoring mechanism between the outer membrane and peptidoglycan in Selenomonas ruminantium

In Selenomonas ruminantium, a strictly anaerobic and gram-negative bacterium, cadaverine covalently linked to the peptidoglycan is required for the interaction between the peptidoglycan and the S-layer homologous (SLH) domain of the major outer membrane protein Mep45. Here, using a series of diamines with a general structure of NH(3)(+)(CH(2))(n)NH(3)(+) (n = 3 to 6), we found that cadaverine (n = 5) specifically serves as the most efficient constituent of the peptidoglycan in acquiring the high resistance of the cell to external damage agents and is required for effective interaction between the SLH domain of Mep45 and the peptidoglycan, facilitating the correct anchoring of the outer membrane to the peptidoglycan.     

Secreted phospholipase A2 revisited

Phospholipase A(2) (PLA(2)) catalyses the hydrolysis of the sn-2 position of glycerophospholipids to yield fatty acids and lysophospholipids. So far, more than 30 enzymes that possess PLA(2) or related activity have been identified in mammals. About one third of these enzymes belong to the secreted PLA(2) (sPLA(2)) family, which comprises low molecular weight, Ca(2+) requiring, secreted enzymes with a His/Asp catalytic dyad. Individual sPLA(2)s display distinct localizations and enzymatic properties, suggesting their specialized biological roles. However, in contrast to intracellular PLA(2)s, whose roles in signal transduction and membrane homoeostasis have been well documented, the biological roles of sPLA(2)s in vivo have remained obscure until recently. Over the past decade, information fuelled by studies employing knockout and transgenic mice as well as specific inhibitors, in combination with lipidomics, has clarified when and where the different sPLA(2) isoforms are expressed, which isoforms are involved in what types of pathophysiology, and how they exhibit their specific functions. In this review, we highlight recent advances in PLA(2) research, focusing mainly on the physiological functions of sPLA(2)s and their modes of action on 'extracellular' phospholipid targets versus lipid mediator production.