Reactive oxygen species (ROS) mediate the effects of leucine on translation regulation and type I collagen production in hepatic stellate cells

Antifibrogenic and apoptotic effects of Ocoxin in cultured rat hepatic stellate cells

Ocoxin is a nutritional supplement that has been shown to exert antioxidant and immunomodulatory responses in patients with chronic hepatitis C. The present work aimed to determine the effects of Ocoxin on activated hepatic stellate cells (HSC), the cell type mainly responsible for collagen deposition in the fibrotic liver. Ocoxin was found to reduce the survival of a cell line of immortalized non-tumoral rat HSC in a dose-response fashion and to diminish collagen type I levels. This latter effect was observed even at doses not affecting cell survival, pointing to an antifibrogenic action for the supplement. The decrease in viability exerted by Ocoxin on HSC correlated with an increase in histone-associated fragments in the cytoplasm and with increased activity of caspase-3, indicating the induction of apoptosis. To determine the molecular mechanisms mediating Ocoxin-induced apoptosis, the activation of members of the MAPK family was analyzed. Incubation of HSC with Ocoxin caused a transient and dramatic enhancement on ERK, JNK, and p38 MAPK phosphorylation levels. Using specific inhibitors for these enzymes, p38 MAPK was identified as a key mediator of the apoptotic effect of Ocoxin on HSC.

IgE Downregulates PTEN through MicroRNA-21-5p and Stimulates Airway Smooth Muscle Cell Remodeling

The patho-mechanism leading to airway wall remodeling in allergic asthma is not well understood and remodeling is resistant to therapies. This study assessed the effect of immunoglobulin E (IgE) in the absence of allergens on human primary airway smooth muscle cell (ASMC) remodeling in vitro. ASMCs were obtained from five allergic asthma patients and five controls. Proliferation was determined by direct cell counts, mitochondrial activity by expression of cytochrome c, protein expression by immunoblotting and immuno-fluorescence, cell migration by microscopy imaging, and collagen deposition by cell based ELISA and RNA expression by real time PCR. Non-immune IgE activated two signaling pathways: (i) signal transducer and activator of transcription 3 (STAT3)→miR-21-5p→downregulating phosphatase and tensin homolog (PTEN) expression, and (ii) phosphatidylinositol 3-kinases (PI3K)→protein kinase B (Akt)→mammalian target of rapamycin (mTOR)→ribosomal protein S6 kinase beta-1 (p70s6k)→peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC1-α)→peroxisome proliferator-activated receptor-γ (PPAR-γ)→cyclooxygenase-2 (COX-2)→mitochondrial activity, proliferation, migration, and extracellular matrix deposition. Reduced PTEN expression correlated with enhanced PI3K signaling, which upregulated ASMC remodeling. The inhibition of microRNA-21-5p increased PTEN and reduced mTOR signaling and remodeling. Mimics of microRNA-21-5p had opposing effects. IgE induced ASMC remodeling was significantly reduced by inhibition of mTOR or STAT3. In conclusion, non-immune IgE alone is sufficient for stimulated ASMC remodeling by upregulating microRNA-21-5p. Our findings suggest that the suppression of micoRNA-21-5p may present a therapeutic target to reduce airway wall remodeling.

Decreased autophagy was implicated in the decreased apoptosis during decidualization in early pregnant mice

Folate deficiency is a major risk factor of birth defects. Mechanistic studies on folate deficiency resulting in birth defects have mainly focused on fetal development. There have been few studies on folate deficiency from the point of view of the mother's uterus. In our previous study, we demonstrated that folate deficiency inhibits apoptosis of decidual cells, thereby restraining decidualization of the endometrium and impairing pregnancy. In this study, we further investigated the potential mechanism by which folate deficiency decreases endometrial apoptosis during decidualization. To investigate whether endometrium autophagy was inhibited under folate deficiency during decidualization, we performed real-time PCR for endometrial LC3 and P62 on day 6 (D6) to D8 of pregnancy in mice, and both were significantly changed compared to non-folate-deficient mice. Western blots showed that LC3-II and P62 were also changed in folate-deficient mice. Compared with control mice, a few punctuate LC3-II structures were detected in the folate deficiency group by immunofluorescence. Transmission electron micrographs of decidual cells on D8 showed that there were no evident autophagosomes in the folate deficiency group. In addition, apoptosis-related protein analysis by western blotting, TUNEL staining and flow cytometry showed that decreased endometrial apoptosis on D8 of pregnancy under folate deficiency was reversed after treatment with rapamycin, an autophagy inducer. ROS measurement showed that the endometrium ROS level was reduced by folate deficiency and that rapamycin reversed this effect on day 8 of pregnancy. All the results suggest that inhibiting endometrial autophagy may be implicated in the decreased endometrial apoptosis under folate deficiency during decidualization.

Distinctiveness in virological features and pathogenic potentials of subgenotypes D1, D2, D3 and D5 of Hepatitis B virus

Distinct clinical features of HBV infection have been associated with different viral genotype/subgenotype. HBV Genotype-D comprised of 10 subgenotypes, D1–D10, whose clinical implications still remain elusive. We investigated for the first-time, the virologic characteristics and cytopathic effects of four non-recombinant D-subgenotypes, D1/D2/D3/D5. Expressions of viral/host genes were evaluated in Huh7 cells transfected with full-length, linear-monomers of HBV/D-subgenotypes or pGL3-Basic vector carrying subgenotype-specific HBx. Intracellular HBV-DNA and pregenomic-RNA levels were high in D1/D2 than D3/D5. Expressions of PreC-mRNA and HBx were highest for D2 and D1 respectively, whereas PreS2/S-transcript was significantly reduced in D5. Increased apoptotic cell death and marked upregulation in caspase-3/Bax/TNF-R1/FasR/TRAIL-R1/ROS/MCP-1/IP-10/MIP-1β expression were noticed specifically in D2- and also in D3-transfected cells, while D5 resulted in over-expression of ER-stress-markers. D-subgenotype-transfected Huh7 cells were co-cultured with PBMC of healthy-donors or LX-2 cells and significant increase in pro-inflammatory cytokines in PBMC and fibrogenic-markers in LX-2 were noticed in presence of D2/D3. Further, Huh7 cells transfected with D1, in particular and also D5, displayed remarkable induction of EMT-markers and high proliferative/migratory abilities. Collectively, our results demonstrated that D2/D3 were more associated with hepatic apoptosis/inflammation/fibrosis and D1/D5 with increased risk of hepatocarcinogenesis and emphasize the need for determining HBV-subgenotype in clinical practice.

Oxidative stress at low levels can induce clustered DNA lesions leading to NHEJ mediated mutations

DNA damage and mutations induced by oxidative stress are associated with various different human pathologies including cancer. The facts that most human tumors are characterized by large genome rearrangements and glutathione depletion in mice results in deletions in DNA suggest that reactive oxygen species (ROS) may cause gene and chromosome mutations through DNA double strand breaks (DSBs). However, the generation of DSBs at low levels of ROS is still controversial. In the present study, we show that H₂O₂ at biologically-relevant levels causes a marked increase in oxidative clustered DNA lesions (OCDLs) with a significant elevation of replication-independent DSBs. Although it is frequently reported that OCDLs are fingerprint of high-energy IR, our results indicate for the first time that H₂O₂, even at low levels, can also cause OCDLs leading to DSBs specifically in G1 cells. Furthermore, a reverse genetic approach revealed a significant contribution of the non-homologous end joining (NHEJ) pathway in H₂O₂-induced DNA repair & mutagenesis. This genomic instability induced by low levels of ROS may be involved in spontaneous mutagenesis and the etiology of a wide variety of human diseases like chronic inflammation-related disorders, carcinogenesis, neuro-degeneration and aging.

Impact of Thermal Stress on Kidney-Specific Gene Expression in Farmed Regional and Imported Rainbow Trout

Seasonal water temperatures can be stressful for fish in aquaculture and can therefore negatively influence their welfare. Although the kidney is the crucial organ associated with the primary stress response, knowledge about the stress-modulated kidney transcriptome in salmonids is limited. In the present study, we used a comparative microarray approach to characterize the general gene expression profiles of rainbow trout trunk kidney after a 2-week acclimation to mild heat (23 °C) and cold stress (8 °C). Hypothesizing that local adaptation influences stress performance, we aimed to identify differences in the temperature-induced gene expression in the regional trout strain BORN, in addition to a common imported strain. Moderate temperature challenge provoked typical stress response clusters, including heat-shock proteins or cold-inducible factors, in addition to altered energy metabolism in trout kidney. Mild cold, in particular, enhanced renal protein degradation processes, as well as mRNA and protein synthesis, while it also triggered fatty acid biosynthesis. Mild heat led to cytoskeleton-stabilizing processes and might have facilitated cell damage and infection. Furthermore, both breeding lines used different strategies for energy provision, cellular defense, and cell death/survival pathways. As a main finding, the genes involved in energy provision showed generally higher transcript levels at both temperatures in BORN trout compared to imported trout, indicating adjusted metabolic rates under local environmental conditions. Altogether, this study provides a general overview of stress-induced transcriptional patterns in rainbow trout trunk kidney, in addition to identifying genes and networks that contribute to the robustness of the BORN strain. Our analyses suggest SERPINH1 and CIRBP as general marker genes for heat stress and cold stress in trout, respectively.

Oxidation pathways underlying the pro-oxidant effects of apigenin

Apigenin, a natural flavone, is emerging as a promising compound for the treatment of several diseases. One of the hallmarks of apigenin is the generation of intracellular reactive oxygen species (ROS), as judged by the oxidation of reduced dichlorofluorescein derivatives seen in many cell types. This study aimed to reveal some mechanisms by which apigenin can be oxidized and how apigenin-derived radicals affect the oxidation of 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein (H(2)DCF), a probe usually employed to detect intracellular ROS. Apigenin induced a rapid oxidation of H(2)DCF in two different immortalized cell lines derived from rat and human hepatic stellate cells. However, apigenin did not generate ROS in these cells, as judged by dihydroethidium oxidation and extracellular hydrogen peroxide production. In cell-free experiments we found that oxidation of apigenin leads to the generation of a phenoxyl radical, which directly oxidizes H(2)DCF with catalytic amounts of hydrogen peroxide. The net balance of the reaction was the oxidation of the probe by molecular oxygen due to redox cycling of apigenin. This flavonoid was also able to deplete NADH and glutathione by a similar mechanism. Interestingly, H(2)DCF oxidation was significantly accelerated by apigenin in the presence of horseradish peroxidase and xanthine oxidase, but not with other enzymes showing peroxidase-like activity, such as cytochrome c or catalase. We conclude that in cells treated with apigenin oxidation of reduced dichlorofluorescein derivatives does not measure intracellular ROS and that pro- and antioxidant effects of flavonoids deduced from these experiments are inconclusive and must be confirmed by other techniques.

Extracellular matrix and liver disease

SIGNIFICANCE

The extracellular matrix (ECM) is a dynamic microenvironment that undergoes continuous remodeling, particularly during injury and wound healing. Chronic liver injury of many different etiologies such as viral hepatitis, alcohol abuse, drug-induced liver injury, obesity and insulin resistance, metabolic disorders, and autoimmune disease is characterized by excessive deposition of ECM proteins in response to persistent liver damage.

CRITICAL ISSUES

This review describes the main collagenous and noncollagenous components from the ECM that play a significant role in pathological matrix deposition during liver disease. We define how increased myofibroblasts (MF) from different origins are at the forefront of liver fibrosis and how liver cell-specific regulation of the complex scarring process occurs.

RECENT ADVANCES

Particular attention is paid to the role of cytokines, growth factors, reactive oxygen species, and newly identified matricellular proteins in the regulation of fibrillar type I collagen, a field to which our laboratory has significantly contributed over the years. We compile data from recent literature on the potential mechanisms driving fibrosis resolution such as MF' apoptosis, senescence, and reversal to quiescence.

FUTURE DIRECTIONS

We conclude with a brief description of how epigenetics, an evolving field, can regulate the behavior of MF and of how new "omics" tools may advance our understanding of the mechanisms by which the fibrogenic response to liver injury occurs.

Tetramethylpyrazine inhibits angiotensin II-induced activation of hepatic stellate cells associated with interference of platelet-derived growth factor β receptor pathways

Liver fibrosis represents a frequent event following chronic insult to trigger wound healing responses in the liver. Activation of hepatic stellate cells (HSCs) is a pivotal event during liver fibrogenesis. Compelling evidence indicates that the renin-angiotensin system (RAS) takes part in the pathogenesis of liver fibrosis. Angiotensin II (Ang II), the primary effector peptide of the RAS, has been demonstrated to be a potent pro-fibrogenic molecule for HSC activation. In this study we investigated the effects of tetramethylpyrazine (TMP) on HSC activation induced by Ang II in order to elucidate the underlying mechanisms. Our results demonstrated that Ang II significantly promoted cell growth, upregulated the expression of the fibrotic markers α-smooth muscle actin (α-SMA) and α1(I) procollagen, and enhanced the invasion capacity in HSCs. TMP inhibited proliferation and arrested the cell cycle at the G2/M checkpoint associated with altering several cell cycle regulatory proteins in Ang II-treated HSCs. TMP also modulated Bcl-2 family proteins and activated the caspase cascade leading to apoptosis in Ang II-treated HSCs. Moreover, TMP reduced the expression of α-SMA and α1(I) procollagen at mRNA and protein levels, and these effects were associated with interference of the platelet-derived growth factor β receptor (PDGF-βR) mediated PI3K/AKT/mTOR pathway in HSCs exposed to Ang II. Furthermore, Ang II-enhanced HSC invasion capacity was diminished by TMP, which was associated with interference of PDGF-βR/FAK signaling. These data collectively indicated that interference of PDGF-βR-mediated fibrotic pathways was involved in TMP inhibition of HSC activation caused by Ang II, providing novel mechanistic insights into TMP as a potential therapeutic remedy for hepatic fibrosis.

Layered silicate clay functionalized with amino acids: wound healing application

Laponite holds amino acid between its interlayer spaces and releases it in contact with wound fluid through ionic exchange process.

Mammalian target of rapamycin regulates Nox4-mediated podocyte depletion in diabetic renal injury

Podocyte apoptosis is a critical mechanism for excessive loss of urinary albumin that eventuates in kidney fibrosis. Pharmacological doses of the mammalian target of rapamycin (mTOR) inhibitor rapamycin reduce albuminuria in diabetes. We explored the hypothesis that mTOR mediates podocyte injury in diabetes. High glucose (HG) induces apoptosis of podocytes, inhibits AMP-activated protein kinase (AMPK) activation, inactivates tuberin, and activates mTOR. HG also increases the levels of Nox4 and Nox1 and NADPH oxidase activity. Inhibition of mTOR by low-dose rapamycin decreases HG-induced Nox4 and Nox1, NADPH oxidase activity, and podocyte apoptosis. Inhibition of mTOR had no effect on AMPK or tuberin phosphorylation, indicating that mTOR is downstream of these signaling molecules. In isolated glomeruli of OVE26 mice, there is a similar decrease in the activation of AMPK and tuberin and activation of mTOR with increase in Nox4 and NADPH oxidase activity. Inhibition of mTOR by a small dose of rapamycin reduces podocyte apoptosis and attenuates glomerular injury and albuminuria. Our data provide evidence for a novel function of mTOR in Nox4-derived reactive oxygen species generation and podocyte apoptosis that contributes to urinary albumin excretion in type 1 diabetes. Thus, mTOR and/or NADPH oxidase inhibition may represent a therapeutic modality of diabetic kidney disease.

GCN2 kinase is a key regulator of fibrogenesis and acute and chronic liver injury induced by carbon tetrachloride in mice

General control nonderepresible 2 (GCN2) is a highly conserved cytosolic kinase that modulates a complex response for coping with the stress owing to lack of amino acids. GCN2 has been recently shown to be involved in the regulation of metabolic balance and lipid degradation rate in the liver. We hypothesized that GCN2 could have a role in in hepatic fibrogenesis and in the response to acute or chronic liver injury. Activation of GCN2 in primary or immortalized human hepatic stellate cells by incubation with medium lacking the essential amino acid histidine correlated with decreased levels of collagen type I protein and mRNA, suggesting an antifibrogenic effect of GCN2. In vivo studies with Gcn2 knock-out mice (Gcn2(-/-)) showed increased susceptibility to both acute or chronic liver damage induced by CCl(4), as shown by higher alanine aminotransferase and aspartate aminotransferase activities, increased necrosis and higher inflammatory infiltrates compared with wild-type mice (WT). Chronic CCl(4) treatment increased deposition of interstitial collagen type I more in Gcn2(-/-) mice than in WT mice. Col1a1 and col1a2 mRNA levels also increased in CCl(4)-treated Gcn2(-/-) mice compared with WT mice. These results suggest that GCN2 is a key regulator of the fibrogenic response to liver injury.

Butein inhibits ethanol-induced activation of liver stellate cells through TGF-β, NFκB, p38, and JNK signaling pathways and inhibition of oxidative stress

BACKGROUND

Butein has been reported to prevent and partly reverse liver fibrosis in vivo; however, the mechanisms of its action are poorly understood. We, therefore, aimed to determine the antifibrotic potential of butein.

METHODS

We assessed the influence of the incubation of hepatic stellate cells (HSCs) and hepatoma cells (HepG2) with butein on sensitivity to ethanol- or acetaldehyde-induced toxicity; the production of reactive oxygen species (ROS); the expression of markers of HSC activation, including smooth muscle α-actin (α-SMA) and procollagen I; and the production of transforming growth factor-β1 (TGF-β1), metalloproteinases-2 and -13 (MMP-2and MMP-13), and tissue inhibitors of metalloproteinases (TIMPs). The influence of butein on intracellular signals in HSCs; i.e., nuclear factor-κB (NFκB), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38 MAPK) induced by ethanol was estimated.

RESULTS

Butein protected HSCs and HepG2 cells against ethanol toxicity by the inhibition of ethanol- or acetaldehyde-induced production of ROS when cells were incubated separately or in co-cultures; butein also inhibited HSC activation measured as the production of α-SMA and procollagen I. As well, butein downregulated ethanol- or acetaldehyde-induced HSC migration and the production of TGF-β, TIMP-1, and TIMP-2; decreased the activity of MMP-2; and increased the activity of MMP-13. In ethanol-induced HSCs, butein inhibited the activation of the p38 MAPK and JNK transduction pathways as well as significantly inhibiting the phosphorylation of NF κB inhibitor (IκB) and Smad3.

CONCLUSIONS

The results indicated that butein inhibited ethanol- and acetaldehyde-induced activation of HSCs at different levels, acting as an antioxidant and inhibitor of ethanol-induced MAPK, TGF-β, and NFκB/IκB transduction signaling; this result makes butein a promising agent for antifibrotic therapies.

The endocannabinoid N-arachidonoyl dopamine (NADA) selectively induces oxidative stress-mediated cell death in hepatic stellate cells but not in hepatocytes

The endocannabinoid system is a crucial regulator of hepatic fibrogenesis. We have previously shown that the endocannabinoid anandamide (AEA) is a lipid mediator that blocks proliferation and induces death in hepatic stellate cells (HSCs), the main fibrogenic cell type in the liver, but not in hepatocytes. However, the effects of other endocannabinoids such as N-arachidonoyl dopamine (NADA) have not yet been investigated. The NADA-synthesizing enzyme tyrosine hydroxylase was mainly expressed in sympathetic neurons in portal tracts. Its expression pattern stayed unchanged in normal or fibrotic liver. NADA dose dependently induced cell death in culture-activated primary murine or human HSCs after 2-4 h, starting from 5 μM. Despite caspase 3 cleavage, NADA-mediated cell death showed typical features of necrosis, including ATP depletion. Although the cannabinoid receptors CB1, CB2, or transient receptor potential cation channel subfamily V, member 1 were expressed in HSCs, their pharmacological or genetic blockade failed to inhibit NADA-mediated death, indicating a cannabinoid-receptor-independent mechanism. Interestingly, membrane cholesterol depletion with methyl-β-cyclodextrin inhibited AEA- but not NADA-induced death. NADA significantly induced reactive oxygen species formation in HSCs. The antioxidant glutathione (GSH) significantly decreased NADA-induced cell death. Similar to AEA, primary hepatocytes were highly resistant against NADA-induced death. Resistance to NADA in hepatocytes was due to high levels of GSH, since GSH depletion significantly increased NADA-induced death. Moreover, high expression of the AEA-degrading enzyme fatty acid amide hydrolase (FAAH) in hepatocytes also conferred resistance towards NADA-induced death, since pharmacological or genetic FAAH inhibition significantly augmented hepatocyte death. Thus the selective induction of cell death in HSCs proposes NADA as a novel antifibrogenic mediator.

Osteopontin, an oxidant stress sensitive cytokine, up-regulates collagen-I via integrin α(V)β(3) engagement and PI3K/pAkt/NFκB signaling

A key feature in the pathogenesis of liver fibrosis is fibrillar Collagen-I deposition; yet, mediators that could be key therapeutic targets remain elusive. We hypothesized that osteopontin (OPN), an extracellular matrix (ECM) cytokine expressed in hepatic stellate cells (HSCs), could drive fibrogenesis by modulating the HSC pro-fibrogenic phenotype and Collagen-I expression. Recombinant OPN (rOPN) up-regulated Collagen-I protein in primary HSCs in a transforming growth factor beta (TGFβ)-independent fashion, whereas it down-regulated matrix metalloprotease-13 (MMP13), thus favoring scarring. rOPN activated primary HSCs, confirmed by increased α-smooth muscle actin (αSMA) expression and enhanced their invasive and wound-healing potential. HSCs isolated from wild-type (WT) mice were more profibrogenic than those from OPN knockout (Opn(-/-)) mice and infection of primary HSCs with an Ad-OPN increased Collagen-I, indicating correlation between both proteins. OPN induction of Collagen-I occurred via integrin α(v)β(3) engagement and activation of the phosphoinositide 3-kinase/phosphorylated Akt/nuclear factor kappa B (PI3K/pAkt/NFκB)-signaling pathway, whereas cluster of differentiation 44 (CD44) binding and mammalian target of rapamycin/70-kDa ribosomal protein S6 kinase (mTOR/p70S6K) were not involved. Neutralization of integrin α(v) β(3) prevented the OPN-mediated activation of the PI3K/pAkt/NFκB-signaling cascade and Collagen-I up-regulation. Likewise, inhibition of PI3K and NFκB blocked the OPN-mediated Collagen-I increase. Hepatitis C Virus (HCV) cirrhotic patients showed coinduction of Collagen-I and cleaved OPN compared to healthy individuals. Acute and chronic liver injury by CCl(4) injection or thioacetamide (TAA) treatment elevated OPN expression. Reactive oxygen species up-regulated OPN in vitro and in vivo and antioxidants prevented this effect. Transgenic mice overexpressing OPN in hepatocytes (Opn(HEP) Tg) mice developed spontaneous liver fibrosis compared to WT mice. Last, chronic CCl(4) injection and TAA treatment caused more liver fibrosis to WT than to Opn(-/-) mice and the reverse occurred in Opn(HEP) Tg mice.

CONCLUSION

OPN emerges as a key cytokine within the ECM protein network driving the increase in Collagen-I protein contributing to scarring and liver fibrosis.

A role for autophagy during hepatic stellate cell activation

BACKGROUND & AIMS

Autophagy is a metabolic process that degrades and recycles intracellular organelles and proteins with many connections to human disease and physiology. We studied the role of autophagy during hepatic stellate cell (HSC) activation, a key event in liver fibrogenesis.

METHODS

Analysis of the autophagic flux during in vitro activation of primary mouse HSCs was performed using a DsRed-GFP-LC3B encoding plasmid. The effect of autophagy inhibition by bafilomycin A1 on the in vitro activation process of human and mouse HSCs was examined by measuring proliferation, presence of activation markers by RT-qPCR, immunofluorescence, and Western blotting. Analysis of lipid droplet and microtubule-associated protein light chain 3 beta (LC3B) colocalization in the presence of PDGF-BB was investigated by immunocytochemistry.

RESULTS

A significant increased autophagic flux was observed during culture induced mouse HSC activation. Treatment of mouse HSCs and human HSCs with autophagy inhibitor bafilomycin A1 results in a significant decreased proliferation and expression of activation markers. In addition, lipid droplets and LC3B colocalization was increased after PDGF-BB treatment in quiescent HSCs.

CONCLUSIONS

During HSC activation, autophagic flux is increased. The demonstration of partly inhibition of in vitro HSC activation after treatment with an autophagy inhibitor unveils a potential new therapeutic strategy for liver fibrosis.

Proteomic and metabolomic analysis of H2O2-induced premature senescent human mesenchymal stem cells

Stress induced premature senescence (SIPS) occurs after exposure to many different sublethal stresses including H(2)O(2), hyperoxia, or tert-butylhydroperoxide. Human mesenchymal stem cells (hMSCs) exhibit limited proliferative potential in vitro, the so-called Hayflick limit. According to the free-radical theory, reactive oxygen species (ROS) might be the candidates responsible for senescence and age-related diseases. H(2)O(2) may be responsible for the production of high levels of ROS, in which the redox balance is disturbed and the cells shift into a state of oxidative stress, which subsequently leads to premature senescence with shortening telomeres. H(2)O(2) has been the most commonly used inducer of SIPS, which shares features of replicative senescence (RS) including a similar morphology, senescence-associated β-galactosidase activity, cell cycle regulation, etc. Therefore, in this study, the senescence of hMSC during SIPS was confirmed using a range of different analytical methods. In addition, we determined five differentially expressed spots in the 2-DE map, which were identified as Annexin A2 (ANXA2), myosin light chain 2 (MLC2), peroxisomal enoyl-CoA hydratase 1 (ECH1), prosomal protein P30-33K (PSMA1) and mutant β-actin by ESI-Q-TOF MS/MS. Also, proton ((1)H) nuclear magnetic resonance spectroscopy (NMR) was used to elucidate the difference between metabolites in the control and hMSCs treated with H(2)O(2). Among these metabolites, choline and leucine were identified by (1)H-NMR as up-regulated metabolites and glycine and proline were identified as down-regulated metabolites.

Loss of manganese superoxide dismutase leads to abnormal growth and signal transduction in mouse embryonic fibroblasts

Manganese superoxide dismutase (MnSOD) in the mitochondria plays an important role in cellular defense against oxidative damage. Homozygous MnSOD knockout (Sod2(-/-)) mice are neonatal lethal, indicating the essential role of MnSOD in early development. To investigate the potential cellular abnormalities underlying the aborted development of Sod2(-/-) mice, we examined the growth of isolated mouse embryonic fibroblasts (MEFs) from Sod2(-/-) mice. We found that the proliferation of Sod2(-/-) MEFs was significantly decreased compared with wild-type MEFs despite the absence of morphological differences. The Sod2(-/-) MEFs produced less cellular ATP, had lower O(2) consumption, generated more superoxide, and expressed less Prdx3 protein. Furthermore, the loss of MnSOD dramatically altered several markers involved in cell proliferation and growth, including decreased growth stimulatory function of mTOR signaling and enhanced growth inhibitory function of GSK-3β signaling. Interestingly, the G-protein-coupled receptor-mediated intracellular Ca(2+) signal transduction was also severely suppressed in Sod2(-/-) MEFs. Finally, the ratio of microtubule-associated protein light chain 3 (LC3)-II/LC3-I, an index of autophagic activity, was increased in Sod2(-/-) MEFs, consistent with a reduction in mTOR signal transduction. These data demonstrate that MnSOD deficiency results in alterations in several key signaling pathways, which may contribute to the lethal phenotype of Sod2(-/-) mice.

A role for p38 stress-activated protein kinase in regulation of cell growth via TORC1

The target of rapamycin (TOR) complex 1 (TORC1) signaling pathway is a critical regulator of translation and cell growth. To identify novel components of this pathway, we performed a kinome-wide RNA interference (RNAi) screen in Drosophila melanogaster S2 cells. RNAi targeting components of the p38 stress-activated kinase cascade prevented the cell size increase elicited by depletion of the TOR negative regulator TSC2. In mammalian and Drosophila tissue culture, as well as in Drosophila ovaries ex vivo, p38-activating stresses, such as H(2)O(2) and anisomycin, were able to activate TORC1. This stress-induced TORC1 activation could be blocked by RNAi against mitogen-activated protein kinase kinase 3 and 6 (MKK3/6) or by the overexpression of dominant negative Rags. Interestingly, p38 was also required for the activation of TORC1 in response to amino acids and growth factors. Genetic ablation either of p38b or licorne, its upstream kinase, resulted in small flies consisting of small cells. Mutants with mutations in licorne or p38b are nutrition sensitive; low-nutrient food accentuates the small-organism phenotypes, as well as the partial lethality of the p38b null allele. These data suggest that p38 is an important positive regulator of TORC1 in both mammalian and Drosophila systems in response to certain stresses and growth factors.

Translational responses to growth factors and stress

Cellular stresses can induce a wide range of biological responses, depending on the type of stress, the type of cell and the cellular environment. Stress-mediated changes in translational output cover a broad spectrum of potential responses, including an overall decrease in translation or an increase in the translation of specific mRNAs. Many of these changes involve post-translational modifications of components of the translational machinery. The mTOR (mammalian target of rapamycin) pathway is a critical regulator of growth and translation in response to a wide variety of signals, including growth factors, amino acids and energy availability. Through its kinase activity, mTOR activation results in the phosphorylation of translational components and an increase in translation. As stress-mediated changes in translational output are context-dependent, the interplay between stress and mTOR in the control of translation is also likely to depend on factors such as the strength and type of incident stress. In the present paper, we review mTOR-dependent and -independent translational responses, and discuss their regulation by stress.

Novel role of the CXC chemokine receptor 3 in inflammatory response to arterial injury: involvement of mTORC1

Atherosclerosis, restenosis, and posttransplant graft atherosclerosis are characterized by endothelial damage, infiltration of inflammatory cells, and proliferation of smooth muscle cells. The CXCR3-activating chemokines interferon-gamma inducible protein 10 (IP10) and MIG (monokine induced by interferon-gamma) have been implicated in vascular repair and remodeling. The underlying molecular mechanisms, however, remain elusive. Here, we show that wire-mediated arterial injury induced local and systemic expression of IP10 and MIG, resulting in enhanced recruitment of CXCR3(+) leukocytes and hematopoietic progenitor cells. This was accompanied by profound activation of mammalian target of rapamycin complex (mTORC)1, increased reactive oxygen species production, apoptosis, and intimal hyperplasia. Genetic and pharmacological inactivation of CXCR3 signaling not only suppressed recruitment of inflammatory cells but also abolished mTORC1 activation, reduced reactive oxygen species generation, and blocked apoptosis of vascular cells, resulting in significant reduction of intimal hyperplasia in vivo. In vitro, stimulation of T cells with IP10 directly activated mTORC1 and induced generation of reactive oxygen species and apoptosis in an mTORC1-dependent manner. These results strongly indicate that CXCR3-dependent activation of mTORC1 directly links stimulation of the Th1 immune system with the proliferative response of intimal cells in vascular remodeling.