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

Impaired Autophagic Activity Contributes to the Pathogenesis of Bronchopulmonary Dysplasia. Evidence from Murine and Baboon Models

Bronchopulmonary dysplasia (BPD) is a common and serious complication associated with preterm birth. The pathogenesis of BPD is incompletely understood, and there is an unmet clinical need for effective treatments. The role of autophagy as a potential cytoprotective mechanism in BPD remains to be fully elucidated. In the present study, we investigated the role and regulation of autophagy in experimental models of BPD. Regulation and cellular distribution of autophagic activity during postnatal lung development and in neonatal hyperoxia-induced lung injury (nHILI) were assessed in the autophagy reporter transgenic GFP-LC3 (GFP-microtubule-associated protein 1A/1B-light chain 3) mouse model. Autophagic activity and its regulation were also examined in a baboon model of BPD. The role of autophagy in nHILI was determined by assessing lung morphometry, injury, and inflammation in autophagy-deficient Beclin 1 heterozygous knockout mice (Becn1^+/-). Autophagic activity was induced during alveolarization in control murine lungs and localized primarily to alveolar type II cells and macrophages. Hyperoxia exposure of neonatal murine lungs and BPD in baboon lungs resulted in impaired autophagic activity in association with insufficient AMPK (5'-AMP-activated protein kinase) and increased mTORC1 (mTOR complex 1) activation. Becn1^+/- lungs displayed impaired alveolarization, increased alveolar septal thickness, greater neutrophil accumulation, and increased IL-1β concentrations when exposed to nHILI. Becn1^+/- alveolar macrophages isolated from nHILI-exposed mice displayed increased expression of proinflammatory genes. In conclusion, basal autophagy is induced during alveolarization and disrupted during progression of nHILI in mice and BPD in baboons. Becn1^+/- mice are more susceptible to nHILI, suggesting that preservation of autophagic activity may be an effective protective strategy in BPD.

Dysregulated autophagy in muscle precursor cells from humans with type 2 diabetes

Autophagy is active during cellular remodeling including muscle differentiation. Muscle differentiation is dysregulated in type 2 diabetes and we therefore hypothesize that muscle precursor cells from people with type 2 diabetes (T2DM) have a dysregulation of their autophagy leading to impaired myogenesis. Muscle precursor cells were isolated from people with T2DM or healthy controls and differentiated in vitro. Autophagy marker levels were assessed by immunoblotting. Differentially expressed autophagy-related genes between healthy and T2DM groups were identified based on a previously published RNA-sequencing data-set, which we verified by RT-qPCR. siRNA was used to assess the function of differentially expressed autophagy genes. Basal autophagy increases during human muscle differentiation, while T2DM muscle cells have reduced levels of autophagy marker ATG7 and show a blunted response to starvation. Moreover, we demonstrate that the 3 non-canonical autophagy genes DRAM1, VAMP8 and TP53INP1 as differentially expressed between healthy and T2DM groups during myoblast differentiation, and that T53INP1 knock-down alters expression of both pro-and anti-apoptotic genes. In vitro differentiated T2DM muscle cells show differential expression of autophagy-related genes. These genes do not regulate myogenic transcription factors but may rather be involved in p53-associated myoblast apoptosis during early myogenesis.

The cardiomyocyte "redox rheostat": Redox signalling via the AMPK-mTOR axis and regulation of gene and protein expression balancing survival and death

Reactive oxygen species (ROS) play a key role in development of heart failure but, at a cellular level, their effects range from cytoprotection to induction of cell death. Understanding how this is regulated is crucial to develop novel strategies to ameliorate only the detrimental effects. Here, we revisited the fundamental hypothesis that the level of ROS per se is a key factor in the cellular response by applying different concentrations of H2O2 to cardiomyocytes. High concentrations rapidly reduced intracellular ATP and inhibited protein synthesis. This was associated with activation of AMPK which phosphorylated and inhibited Raptor, a crucial component of mTOR complex-1 that regulates protein synthesis. Inhibition of protein synthesis by high concentrations of H2O2 prevents synthesis of immediate early gene products required for downstream gene expression, and such mRNAs (many encoding proteins required to deal with oxidant stress) were only induced by lower concentrations. Lower concentrations of H2O2 promoted mTOR phosphorylation, associated with differential recruitment of some mRNAs to the polysomes for translation. Some of the upregulated genes induced by low H2O2 levels are cytoprotective. We identified p21Cip1/WAF1 as one such protein, and preventing its upregulation enhanced the rate of cardiomyocyte apoptosis. The data support the concept of a "redox rheostat" in which different degrees of ROS influence cell energetics and intracellular signalling pathways to regulate mRNA and protein expression. This sliding scale determines cell fate, modulating survival vs death.

Effects of bone marrow mesenchymal stem cells transfected with Ang-1 gene on hyperoxia-induced optic nerve injury in neonatal mice

Optic nerve injury triggered retinal ganglion cell (RGC) death and optic nerve atrophy lead to visual loss. Bone marrow mesenchymal stem cells (BMSCs) are stromal cells, capable of proliferating and differentiating into different types of tissues. This aims of this study is to investigate the role of BMSCs transfected with angiopoietin-1 (Ang-1) in optic nerve injury induced by hyperoxia in a neonatal mice model. Ang-1 overexpression vector was constructed and used to transfect BMSCs. Reverse transcription-quantitative polymerase chain reaction was performed to detect Ang-1 expression in BMSCs. The hyperoxia-induced optic nerve injury model was established. The optic nerves at 6-7 mm posterior to the eyeball were extracted, and were treated with luxol fast blue staining, immunohistochemistry, immunofluorescence, and transmission electron microscopy to examine the effects of Ang-1-modified BMSCs on optic nerve injury induced by hyperoxia. The mice in the Ang-1 + BMSCs and BMSCs groups showed remarkably improved myelin sheaths of nerve fibers compared to the hyperoxia saline group. The positive expression and integrated optic density of Ang-1 in the Ang-1 + BMSCs group were significantly higher compared to the air control, hyperoxia saline and BMSCs groups. The number and diameter of myelinated nerve fibers, the diameter of axons and the thickness of myelin sheath in the air control and Ang-1 + BMSCs groups were higher compared to the hyperoxia saline group. Our study provides evidence supporting that Ang-1-modified BMSCs may have preventive and therapeutic effects on hyperoxia-induced optic nerve injury in neonatal mice.

The dipeptidyl peptidase-4 (DPP-4) inhibitor teneligliptin functions as antioxidant on human endothelial cells exposed to chronic hyperglycemia and metabolic high-glucose memory

Dipeptidyl peptidase-4 inhibitors are widely used in type 2 diabetes. Endothelium plays a crucial role maintaining vascular integrity and function. Chronic exposure to high glucose drives to endothelial dysfunction generating oxidative stress. Teneligliptin is a novel dipeptidyl peptidase-4 inhibitor with antioxidant properties. This study is aimed to verify a potential protective action of teneligliptin in endothelial cells exposed to high glucose. Human umbilical vein endothelial cells were cultured under normal (5 mmol/L) or high glucose (25 mmol/L) during 21 days, or at high glucose during 14 days followed by 7 days at normal glucose, to reproduce the high-metabolic memory state. During this period, different concentrations of teneligliptin (0.1, 1.0 and 3.0 µmol/L) or sitagliptin (0.5 µmol/L) were added to cells. Ribonucleic acid and protein expression were assessed for antioxidant response, proliferation, apoptosis and endoplasmic reticulum stress markers. Teneligliptin promotes the antioxidant response in human umbilical vein endothelial cells, reducing ROS levels and inducing Nrf2-target genes messenger ribonucleic acid expression. Teneligliptin, but not sitagliptin, reduces the expression of the nicotine amide adenine dinucleotide phosphate oxidase regulatory subunit P22 -phox , however, both blunt the high glucose-induced increase of TXNIP. Teneligliptin improves proliferation rates in human umbilical vein endothelial cells exposed to high glucose, regulating the expression of cell-cycle inhibitors markers (P53, P21 and P27), and reducing proapoptotic genes (BAX and CASP3), while promotes BCL2 expression. Teneligliptin ameliorates high glucose-induced endoplasmic reticulum stress reducing the expression of several markers (BIP, PERK, ATF4, CHOP, IRE1a and ATF6). Teneligliptin has antioxidant properties, ameliorates oxidative stress and apoptotic phenotype and it can overcome the metabolic memory effect, induced by chronic exposure to high glucose in human endothelial cells.

p21 induction plays a dual role in anti-cancer activity of ursolic acid

Previous studies have shown that induction of G1 arrest and apoptosis by ursolic acid is associated with up-regulation of cyclin-dependent kinase inhibitor (CDKI) protein p21 in multiple types of cancer cells. However, the functional role of p21 induction in G1 cell cycle arrest and apoptosis, and the mechanisms of p21 induction by ursolic acid have not been critically addressed. In the current study, we demonstrated that p21 played a mediator role in G1 cell cycle arrest by ursolic acid, whereas p21-mediated up-regulation of Mcl-1 compromised apoptotic effect of ursolic acid. These results suggest that p21 induction plays a dual role in the anti-cancer activity of ursolic acid in terms of cell cycle and apoptosis regulation. p21 induction by ursolic acid was attributed to p53 transcriptional activation. Moreover, we found that ursolic acid was able to inhibit murine double minute-2 protein (MDM2) and T-LAK cell-originated protein kinase (TOPK), the two negative regulator of p53, which in turn contributed to ursolic acid-induced p53 activation. Our findings provided novel insights into understanding of the mechanisms involved in cell cycle arrest and apoptosis induction in response to ursolic acid exposure.

Enhanced Resolution of Hyperoxic Acute Lung Injury as a result of Aspirin Triggered Resolvin D1 Treatment

Acute lung injury (ALI), which presents as acute respiratory failure, is a major clinical problem that requires aggressive care, and patients who require prolonged oxygen exposure are at risk of developing this disease. Although molecular determinants of ALI have been reported, the molecules involved in disease catabasis associated with oxygen toxicity have not been well studied. It has been reported that lung mucosa is rich in omega-3 fatty acid dicosahexanoic acid (DHA), which has antiinflammatory properties. Aspirin-triggered resolvin D1 (AT-RvD1) is a potent proresolution metabolite of DHA that can curb the inflammatory effects in various acute injuries, yet the effect of AT-RvD1 on hyperoxic acute lung injury (HALI) or in the oxygen toxicity setting in general has not been investigated. The effects of AT-RvD1 on HALI were determined for the first time in 8- to 10-week-old C57BL/6 mice that were exposed to hyperoxia (≥95% O2) for 48 hours. Mice were given AT-RvD1 (100 ng) in saline or a saline vehicle for 24 hours in normoxic (≈21% O2) conditions after hyperoxia. Lung tissue and bronchoalveolar lavage (BAL) fluid were collected for analysis associated with proinflammatory signaling and lung inflammation. AT-RvD1 treatment resulted in reduced oxidative stress, increased glutathione production, and significantly decreased tissue inflammation. AT-RvD1 treatment also significantly reduced the lung wet/dry ratio, protein in BAL fluid, and decreased apoptotic and NF-κB signaling. These results show that AT-RvD1 curbs oxygen-induced lung edema, permeability, inflammation, and apoptosis and is thus an effective therapy for prolonged hyperoxia exposure in this murine model.

Oxygen regulates molecular mechanisms of cancer progression and metastasis

Oxygen is the basic molecule which supports life and it truly is "god's gift to life." Despite its immense importance, research on "oxygen biology" has never received the light of the day and has been limited to physiological and biochemical studies. It seems that in modern day biology, oxygen research is summarized in one word "hypoxia." Scientists have focused on hypoxia-induced transcriptomics and molecular-cellular alterations exclusively in disease models. Interestingly, the potential of oxygen to control the basic principles of biology like homeostatic maintenance, transcription, replication, and protein folding among many others, at the molecular level, has been completely ignored. Here, we present a perspective on the crucial role played by oxygen in regulation of basic biological phenomena. Our conclusion highlights the importance of establishing novel research areas like oxygen biology, as there is great potential in this field for basic science discoveries and clinical benefits to the society.

MicroRNA-302 induces proliferation and inhibits oxidant-induced cell death in human adipose tissue-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a heterogeneous population of cells that proliferate in vitro as plastic-adherent cells, have a fibroblast-like morphology, form colonies in vitro and can differentiate into bone, cartilage and fat cells. The abundance, ease and repeatable access to subcutaneous adipose tissue and the simple isolation procedures provide clear advantages for the use of human adipose tissue-derived mesenchymal stem cells (hASDCs) in clinical applications. We screened microRNAs (miRNAs) that affected the proliferation and survival of hADSCs. Transfection of miR-302d mimic increased cell proliferation and protected cells from oxidant-induced cell death in hADSCs, which was supported by flow-cytometric analysis. miR-302d did not affect the expression of Bcl-2 family members or anti-oxidant molecules. The Nrf2-Keap1 system, which is one of the major mechanisms for the cellular defense against oxidative stress, was not altered by transfection of miR-302d mimic. To identify the target of the miR-302d actions on proliferation and survival of hADSCs, a microarray analysis was performed using miR-302d-overexpressing hADSCs. Real-time PCR analysis showed that transfection of miR-302d mimic inhibited the CDKN1A and CCL5 expression. Downregulation of CDKN1A with a specific siRNA mimicked the effect of miR-302d on hADSCs proliferation, but did not affect miR-302d-induced cell survival. Downregulation of CCL5 protected oxidant-induced cell death as miR-302d, inhibited oxidant-induced reactive oxygen species (ROS) generation and the addition of recombinant CCL5 inhibited the protective action of miR-302d on oxidant-induced cell death. This study indicates that miR-302 controls proliferation and cell survival of hADSCs through different targets and that this miRNA can be used to enhance the therapeutic efficacy of hADSCs transplantation in vivo.

IκBβ-mediated NF-κB activation confers protection against hyperoxic lung injury

Supplemental oxygen is frequently used in an attempt to improve oxygen delivery; however, prolonged exposure results in damage to the pulmonary endothelium and epithelium. Although NF-κB has been identified as a redox-responsive transcription factor, whether NF-κB activation exacerbates or attenuates hyperoxic lung injury is unclear. We determined that sustained NF-κB activity mediated by IκBβ attenuates lung injury and prevents mortality in adult mice exposed to greater than 95% O2. Adult wild-type mice demonstrated evidence of alveolar protein leak and 100% mortality by 6 days of hyperoxic exposure, and showed NF-κB nuclear translocation that terminated after 48 hours. Furthermore, these mice showed increased expression of NF-κB-regulated proinflammatory and proapoptotic cytokines. In contrast, mice overexpressing the NF-κB inhibitory protein, IκBβ (AKBI), demonstrated significant resistance to hyperoxic lung injury, with 50% surviving through 8 days of exposure. This was associated with NF-κB nuclear translocation that persisted through 96 hours of exposure. Although induction of NF-κB-regulated proinflammatory cytokines was not different between wild-type and AKBI mice, significant up-regulation of antiapoptotic proteins (BCL-2, BCL-XL) was found exclusively in AKBI mice. We conclude that sustained NF-κB activity mediated by IκBβ protects against hyperoxic lung injury through increased expression of antiapoptotic genes.

Carotid body growth during chronic postnatal hyperoxia

Rats reared in hyperoxia have smaller carotid bodies as adults. To study the time course and mechanisms underlying these changes, rats were reared in 60% O(2) from birth and their carotid bodies were harvested at various postnatal ages (P0-P7, P14). The carotid bodies of hyperoxia-reared rats were smaller than those of age-matched controls beginning at P4. In contrast, 7d of 60% O(2) had no effect on carotid body size in rats exposed to hyperoxia as adults. Bromodeoxyuridine (BrdU) and TdT-mediated dUTP nick end labeling (TUNEL) were used to assess cell proliferation and DNA fragmentation at P2, P4, and P6. Hyperoxia reduced the proportion of glomus cells undergoing cell division at P4; although a similar trend was evident at P2, hyperoxia no longer affected cell proliferation by P6. The proportion of TUNEL-positive glomus cells was modestly increased by hyperoxia. We did not detect changes in mRNA expression for proapoptotic (Bax) or antiapoptotic (Bcl-X(L)) genes or transcription factors that regulate cell cycle checkpoints (p53 or p21), although mRNA levels for cyclin B1 and cyclin B2 were reduced. Collectively, these data indicate that hyperoxia primarily attenuates postnatal growth of the carotid body by inhibiting glomus cell proliferation during the first few days of exposure.