PUMA inactivation protects against oxidative stress through p21/Bcl-XL inhibition of bax death

Burn-Induced Apoptosis in the Livers of Aged Mice Is Associated With Caspase Cleavage of Bcl-xL

INTRODUCTION

Older adult burn victims have poorer outcomes than younger burn victims. The liver is critical for the recovery of patients with burns. Postburn hepatic apoptosis in young individuals compromises liver integrity; however, this pathway has not yet been studied in older individuals. Because aged animals with burns suffer significant liver damage, we hypothesized that apoptosis is altered in these animals and may affect liver function. Understanding postburn hepatic apoptosis and its effects on liver function in aged animals may help improve outcomes in older patients.

METHODS

We compared the protein and gene expression levels in young and aged mice after a 15% total-body-surface-area burn. Liver and serum samples were collected at different time points after injury.

RESULTS

Caspase-9 expression in liver tissue was downregulated by 47% in young animals and upregulated by 62% in aged animals 9 h postburn (P < 0.05). The livers of aged mice showed a Bcl-extra-large (Bcl-xL) transcription increase only after 6 h; however, the livers of young mice exhibited 4.3-fold, 14.4-fold, and 7.8-fold Bcl-xL transcription increases at 3, 6, and 9 h postburn, respectively (P < 0.05). The livers of young mice showed no changes in Caspase-9, Caspase-3, or Bcl-xL protein levels during the early postburn period. In contrast, the livers of aged mice contained cleaved caspase-9, reduced full-length caspase-3, and an accumulation of ΔN-Bcl-x at 6 and 9 h postburn (P < 0.05). p21 expression decreased in aged mice; however, it was significantly increased in the liver tissue of young mice postburn (P < 0.05). Serum amyloid A1 and serum amyloid A2 serum protein levels were 5.2- and 3.1-fold higher in young mice than in aged mice, respectively, at 6 and 9 h postburn (P < 0.05).

CONCLUSIONS

Livers of aged mice exhibited different apoptotic processes compared to those of young mice early after burn injury. Collectively, burn-induced liver apoptosis in aged mice compromises hepatic serum protein production.

The role of the exogenous supply of adenosine triphosphate in the expression of Bax and Bcl2L1 genes in intestinal ischemia and reperfusion in rats 1

PURPOSE

To investigate the role of the exogenous supply of adenosine triphosphate (ATP) in the expression of Bax and Bcl2L1 genes in intestinal ischemia and reperfusion (IR) in rats.

METHODS

The study was designed as a randomized controlled trial with a blinded assessment of the outcome. Eighteen adult male Wistar-EPM1 rats were housed under controlled temperature and light conditions (22-23°C, 12 h light/dark cycle). The animals were randomly divided into 3 groups: 1. Sham group (SG): no clamping of the superior mesenteric artery; 2. Ischemia and reperfusion group (IRG): 3. Ischemia and reperfusion plus ATP (IRG + ATP). ATP was injected in the femoral vein before and after ischemia. Afterwards, intestinal segments were appropriately removed and processed for Endothelial Cell Biology Rat RT2 Profiler PCR Array.

RESULTS

ATP promoted the upregulation of Bcl2L1 gene expression, whereas it did not have significant effects on Bax gene expression. In addition, the relation of Bax/Bcl2L1 gene expression in the IRG group was 1.39, whereas it was 0.43 in the IRG + ATP group. Bcl2L1 plays a crucial role in protecting against intestinal apoptosis after ischemia and reperfusion. Increased Bcl2L1 expression can inhibit apoptosis while decreased Bcl2L1 expression can trigger apoptosis.

CONCLUSION

Adenosine triphosphate was associated with antiapoptotic effects on the rat intestine ischemia and reperfusion by upregulating of Bcl2L1 gene expression.

Lung omics signatures in a bronchopulmonary dysplasia and pulmonary hypertension-like murine model

Bronchopulmonary dysplasia (BPD), the most common chronic lung disease in infants, is associated with long-term morbidities, including pulmonary hypertension (PH). Importantly, hyperoxia causes BPD and PH; however, the underlying mechanisms remain unclear. Herein, we performed high-throughput transcriptomic and proteomic studies using a clinically relevant murine model of BPD with PH. Neonatal wild-type C57BL6J mice were exposed to 21% oxygen (normoxia) or 70% oxygen (hyperoxia) during postnatal days (PNDs) 1-7. Lung tissues were collected for proteomic and genomic analyses on PND 7, and selected genes and proteins were validated by real-time quantitative PCR and immunoblotting analysis, respectively. Hyperoxia exposure dysregulated the expression of 344 genes and 21 proteins. Interestingly, hyperoxia downregulated genes involved in neuronal development and maturation in lung tissues. Gene set enrichment and gene ontology analyses identified apoptosis, oxidoreductase activity, plasma membrane integrity, organ development, angiogenesis, cell proliferation, and mitophagy as the predominant processes affected by hyperoxia. Furthermore, selected deregulated proteins strongly correlated with the expression of specific genes. Collectively, our results identified several potential therapeutic targets for hyperoxia-mediated BPD and PH in infants.

Probucol attenuates hyperoxia-induced lung injury in mice

Hyperoxic lung injury is pathologically characterized by alveolar edema, interlobular septal edema, hyaline membrane disease, lung inflammation, and alveolar hemorrhage. Although the precise mechanism by which hyperoxia causes lung injury is not well defined, oxidative stress, epithelial cell death, and proinflammatory cytokines are thought to be involved. Probucol—a commercially available drug for treating hypercholesterolemia—has been suggested to have antioxidant and antiapoptotic effects. This study aimed to assess whether probucol could attenuate hyperoxic lung injury in mice. Mice were exposed to 95% O₂ for 72 h, with or without pre-treatment with 130 μg/kg probucol intratracheally. Probucol treatment significantly decreased both the number of inflammatory cells in the bronchoalveolar lavage fluid and the degree of lung injury in hyperoxia-exposed mice. Probucol treatment reduced the number of cells positive for 8-hydroxyl-2′-deoxyguanosine or terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and suppressed NF-κB activation, Bax expression, and caspase-9 activation in lung tissues from hyperoxia-exposed mice. These results suggest that probucol can reduce oxidative DNA damage, apoptotic cell death, and inflammation in lung tissues. Intratracheal administration of probucol may be a novel treatment for lung diseases induced by oxidative stress, such as hyperoxic lung injury and acute respiratory distress syndrome.

L-Arginine Modulates Intestinal Inflammation in Rats Submitted to Mesenteric Ischemia-Reperfusion Injury

BACKGROUND

The goal of this study was to investigate whether exogenous offer of L-arginine (LARG) modulates the gene expression of intestinal dysfunction caused by ischemia and reperfusion.

METHODS

Eighteen Wistar-EPM1 male rats (250-300 g) were anesthetized and subjected to laparotomy. The superior mesenteric vessels were exposed, and the rats were randomized into 3 groups (n = 6): the control group (CG), with no superior mesenteric artery interruption; the ischemia/reperfusion group (IRG), with 60 minutes of ischemia and 120 minutes of reperfusion and saline injections; and the L-arginine group (IRG + LARG), with L-arginine injected in the femoral vein 5 minutes before ischemia, 5 minutes after reperfusion, and after 55 minutes of reperfusion. The total RNA was extracted and purified from samples of the small intestine. The concentration of each total RNA sample was determined by using spectrophotometry. The first-strand complementary DNA (cDNA) was synthesized in equal amounts of cDNA and the Master Mix SYBR Green qPCR Mastermix (SABiosciences, a Qiagen Company, Frederick, Md). Amounts of cDNA and Master Mix SYBR Green qPCR Mastermix were distributed to each well of the polymerase chain reaction microarray plate containing the predispensed gene-specific primer sets for Bax and Bcl2. Each sample was evaluated in triplicate, and the Student t test was applied to validate the homogeneity of each gene expression reaction (P < .05).

RESULTS

The gene expression of Bax in IRG (+1.48) was significantly higher than in IRG-LARG (+9.69); the expression of Bcl2L1 in IRG (+1.01) was significantly higher than IRG-LARG (+22.89).

CONCLUSIONS

The apoptotic cell pathway of 2 protagonists showed that LARG improves the gene expression of anti-apoptotic Bcl2l1 (Bcl2-like 1) more than the pro-apoptotic Bax (Bcl2-associated X protein).

Detoxification of Mitochondrial Oxidants and Apoptotic Signaling Are Facilitated by Thioredoxin-2 and Peroxiredoxin-3 during Hyperoxic Injury

Mitochondria play a fundamental role in the regulation of cell death during accumulation of oxidants. High concentrations of atmospheric oxygen (hyperoxia), used clinically to treat tissue hypoxia in premature newborns, is known to elicit oxidative stress and mitochondrial injury to pulmonary epithelial cells. A consequence of oxidative stress in mitochondria is the accumulation of peroxides which are detoxified by the dedicated mitochondrial thioredoxin system. This system is comprised of the oxidoreductase activities of peroxiredoxin-3 (Prx3), thioredoxin-2 (Trx2), and thioredoxin reductase-2 (TrxR2). The goal of this study was to understand the role of the mitochondrial thioredoxin system and mitochondrial injuries during hyperoxic exposure. Flow analysis of the redox-sensitive, mitochondrial-specific fluorophore, MitoSOX, indicated increased levels of mitochondrial oxidant formation in human adenocarcinoma cells cultured in 95% oxygen. Increased expression of Trx2 and TrxR2 in response to hyperoxia were not attributable to changes in mitochondrial mass, suggesting that hyperoxic upregulation of mitochondrial thioredoxins prevents accumulation of oxidized Prx3. Mitochondrial oxidoreductase activities were modulated through pharmacological inhibition of TrxR2 with auranofin and genetically through shRNA knockdown of Trx2 and Prx3. Diminished Trx2 and Prx3 expression was associated with accumulation of mitochondrial superoxide; however, only shRNA knockdown of Trx2 increased susceptibility to hyperoxic cell death and increased phosphorylation of apoptosis signal-regulating kinase-1 (ASK1). In conclusion, the mitochondrial thioredoxin system regulates hyperoxic-mediated death of pulmonary epithelial cells through detoxification of oxidants and regulation of redox-dependent apoptotic signaling.

Upregulation of p21 activates the intrinsic apoptotic pathway in β-cells

Diabetes manifests from a loss in functional β-cell mass, which is regulated by a dynamic balance of various cellular processes, including β-cell growth, proliferation, and death as well as secretory function. The cell cycle machinery comprised of cyclins, kinases, and inhibitors regulates proliferation. However, their involvement during β-cell stress during the development of diabetes is not well understood. Interestingly, in a screen of multiple cell cycle inhibitors, p21 was dramatically upregulated in INS-1-derived 832/13 cells and rodent islets by two pharmacological inducers of β-cell stress, dexamethasone and thapsigargin. We hypothesized that β-cell stress upregulates p21 to activate the apoptotic pathway and suppress cell survival signaling. To this end, p21 was adenovirally overexpressed in pancreatic rat islets and 832/13 cells. As expected, p21 overexpression resulted in decreased [(3)H]thymidine incorporation. Flow cytometry analysis in p21-transduced 832/13 cells verified lower replication, as indicated by a decreased cell population in the S phase and a block in G2/M transition. The sub-G0 cell population was higher with p21 overexpression and was attributable to apoptosis, as demonstrated by increased annexin-positive stained cells and cleaved caspase-3 protein. p21-mediated caspase-3 cleavage was inhibited by either overexpression of the antiapoptotic mitochondrial protein Bcl-2 or siRNA-mediated suppression of the proapoptotic proteins Bax and Bak. Therefore, an intact intrinsic apoptotic pathway is central for p21-mediated cell death. In summary, our findings indicate that β-cell apoptosis can be triggered by p21 during stress and is thus a potential target to inhibit for protection of functional β-cell mass.

Bcl-X(L) is the primary mediator of p21 protection against hyperoxia-induced cell death

A tight balance between anti- and proapoptotic members of the Bcl-2 family controls cell survival and death. Exposure to hyperoxia shifts this balance towards a prodeath state that ultimately activates Bak- and Bax-dependent cell death. Mechanisms underlying this shift are undefined; however, the cell cycle inhibitor p21 delays the loss of antiapoptotic Mcl-1 and Bcl-X(L), and protects against hyperoxia. Here, H1299 human lung adenocarcinoma cells are used to investigate how these and other members of the Bcl-2 family cooperate with p21 to protect against hyperoxia. Expression of antiapoptotic Mcl-1 and Bcl-X(L), but not Bcl-2 or A1, declined during hyperoxia, whereas proapoptotic Bak, but not Bax, increased. Conditional overexpression of p21 selectively delayed the loss of Mcl-1 and Bcl-X(L), without affecting expression of the other members. siRNA knockdown of Mcl-1 and Bcl-X(L) sensitized cells to hyperoxia, but only the loss of Bcl-X(L) ablated the protective effects of p21. Conversely, overexpression of Mcl-1 and Bcl-X(L) protected against hyperoxia, but only Bcl-X(L) bound Bak and Bax. Altogether, these data suggest that Bcl-X(L) is the primary mediator by which p21 protects against hyperoxia-induced Bak/Bax-dependent cell death.

Epithelial ablation of Bcl-XL increases sensitivity to oxygen without disrupting lung development

Recent studies indicate that the antiapoptotic Bcl-X(L), one of five isoforms expressed by the Bcl-X gene, protects a variety of cell lines exposed to hyperoxia. However, its role in lung development and protection against oxidative stress in vivo is not known. Here, we show Bcl-X(L) is the predominant isoform expressed in the lung, and the only isoform detected in respiratory epithelium. Because loss of Bcl-X(L) is embryonically lethal, Bcl-X(L) was ablated throughout the respiratory epithelium by mating mice with a floxed exon II of the Bcl-X gene with mice expressing Cre under control of the surfactant protein-C promoter. Interestingly, the loss of Bcl-X(L) in respiratory epithelium was perinatally lethal in approximately 50% of the expected offspring. However, some adult mice lacking the gene were obtained. The epithelial-specific ablation of Bcl-X(L) did not disrupt pulmonary function, the expression of epithelial cell-specific markers, or lung development. However, it shifted the lung toward a proapoptotic state, defined by a reduction in antiapoptotic Mcl-1, an increase in proapoptotic Bak, and increased sensitivity of the respiratory epithelium to hyperoxia. Intriguingly, increased 8-oxoguanine lesions seen during hyperoxia were also evident as lungs transitioned to room air at birth, a time when perinatal lethality in some mice lacking Bcl-X(L) was observed. These findings reveal that the epithelial-specific expression of Bcl-X(L) is not required for proper lung development, but functions to protect respiratory epithelial cells against oxygen-induced toxicity, such as during hyperoxia and the lung's first exposure to ambient air.

IL-6 cytoprotection in hyperoxic acute lung injury occurs via PI3K/Akt-mediated Bax phosphorylation

IL-6 overexpression protects mice from hyperoxic acute lung injury in vivo, and treatment with IL-6 protects cells from oxidant-mediated death in vitro. The mechanisms of protection, however, are not clear. We characterized the expression, localization, and regulation of Bax, a proapoptotic member of the Bcl-2 family, in wild-type (WT) and IL-6 lung-specific transgenic (Tg(+)) mice exposed to 100% O(2) and in human umbilical vein endothelial cells (HUVEC) treated with H(2)O(2) and IL-6. In control HUVEC treated with H(2)O(2) or in WT mice exposed to 100% O(2), a marked induction of Bax translocation and dimerization was associated with increased JNK and p38 kinase activity. In contrast, specific JNK or p38 kinase inhibitors or treatment with IL-6 inhibited Bax mitochondrial translocation and apoptosis of HUVEC. IL-6 Tg(+) mice exposed to 100% O(2) exhibited enhanced phosphatidylinositol 3-kinase (PI3K)/Akt kinase and increased serine phosphorylation of Bax at Ser(184) compared with WT mice. The PI3K-specific inhibitor LY-2940002 blocked this IL-6-induced Bax phosphorylation and promoted cell death. Furthermore, IL-6 potently blocked hyperoxia- or oxidant-induced Bax insertion into mitochondrial membranes. Thus IL-6 functions in a cytoprotective manner, in part, by suppressing Bax translocation and dimerization through PI3K/Akt-mediated Bax phosphorylation.

p21(Cip1) protects against oxidative stress by suppressing ER-dependent activation of mitochondrial death pathways

Although it is well established that the cell cycle inhibitor p21 protects against genotoxic stress by preventing the replication of damaged DNA, recent studies have shown that the cytoplasmic form can also protect. It protects by delaying the loss of the antiapoptotic proteins Mcl-1 and Bcl-X(L); however, the mechanism of regulation is unknown. Utilizing hyperoxia as a model of chronic oxidative stress and DNA damage, p21 was detected in the nucleus and cytoplasm and cytoplasmic expression of p21 was sufficient for cytoprotection. p21 was enriched in a subcellular fraction containing mitochondria and endoplasmic reticulum (ER), suggesting that it may be coordinating ER and mitochondrial stress pathways. Consistent with this, p21 suppressed hyperoxic downregulation of BiP and subsequent activation of ER stress signaling, which affected Mcl-1, but not Bcl-X(L); though both inhibited hyperoxic cell death. Taken together, these data show that p21 integrates the DNA damage response with ER stress signaling, which then regulates mitochondrial death pathways during chronic genotoxic stress.