Evolution of Excited-State Behaviors of Gold Complexes, Nanoclusters and Nanoparticles.

Metal nanomaterials have been extensively investigated owing to their unique properties in contrast to bulk counterparts. Gold nanoparticles (e. g., 3-100 nm) show quasi-continuous energy bands, while gold nanoclusters (<3 nm) and complexes exhibit discrete energy levels and display entirely different photophysical properties than regular nanoparticles. This review summarizes the electronic dynamics of these three types of gold materials studied by ultrafast spectroscopy. Briefly, for gold nanoparticles, their electronic relaxation is dominated by heat dissipation between the electrons and the lattice. In contrast, gold nanoclusters exhibit single-electron transitions and relatively long excited-state lifetimes being analogous to molecules. In gold complexes, the excited-state dynamics is dominated by intersystem crossing and phosphorescence. A detailed understanding of the photophysical properties of gold nanocluster materials is still missing and thus calls for future efforts. The fundamental insights into the discrete electronic structure and the size-induced evolution in quantum-sized nanoclusters will promote the exploration of their applications in various fields.

Near-unity NIR phosphorescent quantum yield from a room-temperature solvated metal nanocluster.

Metal nanoclusters have emerged as promising near-infrared (NIR)-emissive materials, but their room-temperature photoluminescence quantum yield (PLQY), especially in solution, is often low (<10%). We studied the photophysics of Au22(tBuPhC≡C)18 (Au22) and its alloy counterpart Au16Cu6(tBuPhC≡C)18 (Au16Cu6) (where tBu is tert-butyl and Ph is phenyl) and found that copper (Cu) doping suppressed the nonradiative decay (~60-fold less) and promoted intersystem crossing rate (~300-fold higher). The Au16Cu6 nanocluster exhibited >99% PLQY in deaerated solution at room temperature with an emission maximum at 720 nanometers tailing to 950 nanometers and 61% PLQY in the oxygen-saturated solution. The approach to achieve near-unity PLQY could enable the development of highly emissive metal cluster materials.

Atomically Precise Silver Clusters Stabilized by Lacunary Polyoxometalates with Photocatalytic CO2 Reduction Activity.

The syntheses of atomically precise silver (Ag) clusters stabilized by multidentate lacunary polyoxometalate (POM) ligands have been emerging as a promising but challenging research direction, the combination of redox-active POM ligands and silver clusters will render them unexpected geometric structures and catalytic properties. Herein, we report the successful construction of two structurally-new lacunary POM-stabilized Ag clusters, TBA6 H14 Ag14 (DPPB)4 (CH3 CN)9 [Ag24 (Si2 W18 O66 )3 ] ⋅ 10CH3 CN ⋅ 9H2 O ({Ag24 (Si2 W18 O66 )3 }, TBA=tetra-n-butylammonium, DPPB=1,4-Bis(diphenylphosphino)butane) and TBA14 H6 Ag9 Na2 (H2 O)9 [Ag27 (Si2 W18 O66 )3 ] ⋅ 8CH3 CN ⋅ 10H2 O ({Ag27 (Si2 W18 O66 )3 }), using a facile one-pot solvothermal approach. Under otherwise identical synthetic conditions, the molecular structures of two POM-stabilized Ag clusters could be readily tuned by the addition of different organic ligands. In both compounds, the central trefoil-propeller-shaped {Ag24 }14+ and {Ag27 }17+ clusters bearing 10 delocalized valence electrons are stabilized by three C-shaped {Si2 W18 O66 } units. The femtosecond/nanosecond transient absorption spectroscopy revealed the rapid charge transfer between {Ag24 }14+ core and {Si2 W18 O66 } ligands. Both compounds have been pioneeringly investigated as catalysts for photocatalytic CO2 reduction to HCOOH with a high selectivity.

Atractylodes Processing Products Protect against Gastric Ulcers in Rats by Influencing the NF-κB-MMP-9/TIMP-1 Regulatory Mechanism and Intestinal Flora.

Atractylodes macrocephala Koidz. (AM) is a Chinese herbal medicine that is widely used for treating gastrointestinal diseases. However, little research has focused on it as a single medicine for treating gastric ulcers. Honey-bran stir-frying is a characteristic method of concocting AM, so we speculated that AM is more effective after this preparation process. Analysis by ultra-high-performance liquid chromatography-hybrid quadrupole-Orbitrap high-resolution mass spectrometry revealed changes in the chemical composition of raw Atractylodes (SG), bran-fried Atractylodes (FG), and honey-bran-fried Atractylodes (MFG). MFG was superior to SG and FG in improving the pathological structure of gastric tissue in rats with acute gastric ulcers, reducing inflammatory cell infiltration in gastric tissue, and significantly reducing malondialdehyde while increasing superoxide dismutase and glutathione peroxidase, and reducing the damage caused by free radical accumulation in the gastric mucosa. In addition, MFG reduced the expression of matrix metalloproteinase-9 (MMP-9), an inhibitor of metalloproteinase-1 (TIMP-1) and nuclear factor kappa-B (NF-κB)proteins, inhibited inflammatory response, and regulated the degradation and rebalancing of the extracellular matrix. Fecal microbiota analysis also revealed that MFG normalized the intestinal flora to some extent. Our study shows that AM had a protective effect on rats with alcohol-induced acute gastric ulcers before and after processing, and AM-processed products were more effective than raw ones. Compared with MF, MFG had a higher rate of ulcer inhibition and a stronger anti-inflammatory effect, and its mechanism of action was related to the NF-κB-MMP-9/TIMP-1 signaling pathway.

Research on the Eco-Efficiency of Rice Production and Its Improvement Path: A Case Study from China.

The eco-efficiency of rice production is an important indicator in the measurement of sustainable rice development. Scientific evaluation of the eco-efficiency of rice production facilitates accurate evaluation of the real level of rice ecosystems to realize efficient utilization of agricultural resources. This paper measured the eco-efficiency of farms growing rice using both the life cycle assessment (LCA) and the data envelopment analysis (DEA) methods based on survey data from 370 farms mainly growing rice conducted in 2020 in the Hubei Province, the middle reaches of the Yangtze River in China. Then, sensitivity analysis and scenario analysis were carried out on the comprehensive index of the rice environmental impact and eco-efficiency of rice production, respectively. The results indicate that the comprehensive index of the rice environmental impact was 2.0971. Water toxicity, soil toxicity and eutrophication were the main influencing factors. The mean value of the eco-efficiency reached 0.51. More specifically, the proportion of farms in the low-, middle- and high-efficiency groups was 87.03%, 1.89% and 11.08%, respectively, with mean values up to 0.42, 0.86 and 1.14, respectively. A sensitivity analysis revealed that the pesticide sensitivity was higher than the fertilizer sensitivity in terms of the environmental impact sensitivity of rice systems. When comprehensively considering environmental and economic benefits, the fertilizer sensitivity was higher than that of pesticides. Moreover, reducing the application of both fertilizers and pesticides by 50% could promote the eco-efficiency of rice production systems by 6%, and the value could reach 0.54. Thus, reducing the application of fertilizers and pesticides and improving the utilization efficiency are effective ways to improve green rice production.

Bak interacts with AKT and is involved in TNFα/CHX-induced apoptosis.

Bak is important for TNFα/CHX-induced neuronal death, but the precise molecular mechanism remains unclear. At the same time, TNFα/CHX concomitantly activates the phosphorylation of the MAPK and PI3K/AKT kinases. This study for the first time clarified the association between the MAPK and AKT under the TNFα/CHX stimulation upon addition of different kinase inhibitors to show whether Bak is associated with the kinase activation. The bioinformatics software HDOCK predicted the interaction between Bak and AKT. The addition of TNFα/CHX was proposed to destroy the complex, such that the dissociated Bak would exert a proapoptosis effect AKT can influence the inhibition of cell apoptosis. There was no cell death upon inducing TNFα/CHX for 3 h. AKT was less obvious with apoptosis but in the Bak knockout cells, the anti-apoptotic effect of AKT was very obvious. This study, therefore, provides the theoretical basis for the molecular mechanism of apoptosis induced by TNFα/CHX, providing a new target and direction for studying drug resistance.

Fe3O4@polydopamine nanoparticle-loaded human umbilical cord mesenchymal stem cells improve the cognitive function in Alzheimer's disease mice by promoting hippocampal neurogenesis.

One of the most promising treatments for neurodegenerative diseases is the stem cell therapy; however, there are still some limitations in the treatment of Alzheimer's disease. In this study, superparamagnetic nanoparticles composed of magnetic Fe3O4 and polydopamine shells were used to label human umbilical cord mesenchymal stem cells (hUC-MSCs) in order to increase the targeting of hUC-MSCs. Our data suggested that Fe3O4@PDA labeling increase the efficiency of hUC-MSCs entering the brain. Moreover, the water maze test showed that compared with hUC-MSCs only, Fe3O4@PDA-labeled hUC-MSCs improved the cognitive ability of APP/PS1 transgenic mice more significantly. Other experimental data showed that the expression of essential proteins in the hippocampus, such as Aß, synaptophysin, brain-derived neurotrophic factor, are affected by Fe3O4@PDA coated-hUC-MSCs. The regulation of Fe3O4@PDA coated-hUC-MSCs could improve the memory and cognitive ability of AD mice by excessive generation of neuroprotective factors, which might be considered a viable therapy to treat AD.

Multi-omics analysis revealed the role of CCT2 in the induction of autophagy in Alzheimer's disease.

Chaperonin containing TCP1 subunit 2 (CCT2) is essential in various neurodegenerative diseases, albeit its role in the pathogenesis of Alzheimer's disease (AD) remains elusive. This study aimed to evaluate the role of CCT2 in Alzheimer's disease. First, bioinformatics database analysis revealed that CCT2 was significantly downregulated in patients with Alzheimer's disease and associated with autophagic clearance of ß-amyloid. The 789 differentially expressed genes overlapped in AD-group and CCT2-low/high group, and the CCT2-high-associated genes screened by Pearson coefficients were enriched in protein folding, autophagy, and messenger RNA stability regulation pathways. These results suggest that CCT2 is significantly and positively associated with multiple pathways linked to autophagy and negatively associated with neuronal death. The logistic prediction model with 13 key genes, such as CCT2, screened in this study better predicts Alzheimer's disease occurrence (AUC = 0.9671) and is a favorable candidate for predicting potential biological targets of Alzheimer's disease. Additionally, this study predicts reciprocal micro RNAs and small molecule drugs for hub genes. Our findings suggest that low CCT2 expression may be responsible for the autophagy suppression in Alzheimer's disease, providing an accurate explanation for its pathogenesis and new targets and small molecule inhibitors for its treatment.

Digestion-Promoting Effects and Mechanisms of Dashanzha Pill Based on Raw and Charred Crataegi Fructus.

Emerging evidence suggests that a high-fat diet (HFD) can influence endoplasmic reticulum (ER) stress and gut microbiota. Crataegi Fructus is a traditional Chinese herb widely used in formulas for dyspepsia, with Dashanzha Pill composed of raw Crataegi Fructus (DR) being a representative drug. Processing products of Crataegi Fructus, however, have a stronger pro-digestive effect, and we hypothesized that Dashanzha Pill composed of charred Crataegi Fructus (DC) is more effective. We found that the contents of glucose 1-phosphate and luteolin in DR and DC were substantially different via ultra-high performance liquid chromatography-hybrid quadrupole-Orbitrap high-resolution mass spectrometry. DC outperformed DR in improving histopathological changes, increasing gastrin and motilin, and decreasing vasoactive intestinal peptides in rats with HFD induced dyspepsia. Fecal microbiota analysis revealed that DC could restore the disturbed intestinal microbiota composition, including that of Bacteroides, Akkermansia, and Intestinimonas to normal levels. Furthermore, DC significantly reduced the mRNA and protein levels of glucose-regulated protein 78, protein kinase R-like ER kinase, and eukaryotic initiation factor 2α. Taken together, DC outperformed DR in relieving dyspepsia by regulating gut microbiota and alleviating ER stress.

Theory of the exterior-interior relationship between the lungs and the large intestine to explore the mechanism of Eriobotrya japonica leaf water extract in the treatment of cough variant asthma.

ETHNOPHARMACOLOGICAL RELEVANCE: Eriobotrya japonica (Thunb.) Lindl leaf (EJL) is used as a traditional Chinese medicine. E. japonica is a member of the Rosaceae family. EJL suppresses cough and relieves asthma and is widely used to treat lung diseases. In the present study, guided by the traditional Chinese medicine theory of the exterior-interior relationship between the lungs and the large intestine, the pathogenesis of cough variant asthma (CVA) and the treatment mechanism of EJL on CVA were explored. AIM OF THE STUDY: This study aimed to explore the airway remodeling effects of EJL in CVA from the perspective of the intestinal flora and the matrix metallopeptidase 9/tissue inhibitor of metalloproteinases-1 (MMP-9/TIMP-1) pathway. MATERIALS AND METHODS: The oleanolic acid and ursolic acid contents in EJL were measured by high-performance liquid chromatography (HPLC) to ensure the quality of EJL. BALB/c mice were used to establish a CVA model through ovalbumin (OVA) sensitization and atomization. EJL (at 5, 10, or 20 g/kg/day) was intragastrically administered. The body weight, ratio of total bronchial wall area (WAt) to bronchial basement membrane perimeter (Pbm) (WAt/Pbm), the number of coughs, and cough latency were measured. The pathological changes of the lung tissue were analyzed by hematoxylin and eosin (HE) staining. The expression of α-smooth muscle actin (α-SMA) was measured by immunohistochemistry (IHC). The expressions of MMP-9 and TIMP-1 were detected in the lung tissue by reverse transcription quantitative polymerase chain reaction (RT-PCR) and Western blot analysis. Additionally, an Illumina Hiseq platform was used for 16S ribosomal DNA (16S rDNA) high-throughput sequencing to detect the intestinal flora in feces samples. RESULTS: The results confirmed the positive effects of EJL on CVA. After administration of EJL, the number of coughs and the WAt/Pbm ratio decreased, the cough latency was prolonged, body weight was increased, and the general status was better than that of the CVA model mice. HE staining revealed that EJL decreased inflammatory cell infiltration and improved the histopathological structure of the lung tissue. EJL also showed significant inhibitory effects on the expression of α-SMA, MMP-9, and TIMP-1 and normalized the intestinal flora to a certain extent. CONCLUSIONS: The results demonstrated that EJL alleviated airway remodeling of CVA mice, which might be related to the inhibition of the MMP-P/TIMP-1 pathway and the regulation of intestinal flora.

Proapoptotic Mitochondrial Carrier Homolog Protein PSAP Mediates Death Receptor 6 Induced Apoptosis.

Presenilin-associated protein (PSAP) was originally identified as a mitochondrial proapoptotic protein. To further explore the apoptotic pathway that involves PSAP, our yeast two-hybrid screen revealed that PSAP interacts with a death receptor, DR6. DR6 is a relatively less common member of the death receptor family and has been shown to mediate the neurotoxicity of amyloid-ß, mutant SOD1, and prion proteins and has also been implicated in the regulation of immune cell proliferation and differentiation. Our previous study showed that DR6 induces apoptosis via a unique mitochondria-dependent pathway different from the conventional death receptor-mediated extrinsic apoptotic pathways. Thus, the interaction of DR6 with PSAP established a direct molecular link between DR6 and mitochondrial apoptotic pathway. We investigated the possible role of PSAP in DR6-induced apoptosis. Interestingly, it was discovered that knockdown of PSAP strongly inhibited DR6-induced apoptosis. To further elucidate the mechanism by which PSAP mediates DR6-induced mitochondria-dependent apoptosis, our data demonstrated that knockdown of PSAP blocked DR6-induced Bax translocation and cytochrome c release from the mitochondria. Moreover, it was found that both PSAP and DR6 form complexes with Bax, but at different subcellular locations. The DR6-Bax complex was detected in the cytosolic fraction while the PSAP-Bax complex was detected in the mitochondrial fraction. The observation that knockdown of DR6 significantly reduced the amount of PSAP-Bax complex detected in mitochondria suggests a possibility that DR6-bound Bax is transferred to PSAP upon interaction with PSAP at the mitochondria, leading to cytochrome c release and eventually apoptosis.

Current status and future prospects of stem cell therapy in Alzheimer's disease.

Alzheimer's disease is a common progressive neurodegenerative disorder, pathologically characterized by the presence of ß-amyloid plaques and neurofibrillary tangles. Current treatment approaches using drugs only alleviate the symptoms without curing the disease, which is a serious issue and influences the quality of life of the patients and their caregivers. In recent years, stem cell technology has provided new insights into the treatment of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Currently, the main sources of stem cells include neural stem cells, embryonic stem cells, mesenchymal stem cells, and induced pluripotent stem cells. In this review, we discuss the pathophysiology and general treatment of Alzheimer's disease, and the current state of stem cell transplantation in the treatment of Alzheimer's disease. We also assess future challenges in the clinical application and drug development of stem cell transplantation as a treatment for Alzheimer's disease.

CRISPR/Cas9 Knockout of Bak Mediates Bax Translocation to Mitochondria in response to TNFα/CHX-induced Apoptosis.

TNFα/CHX-induced apoptosis is dependent on caspase-8 activation and regulated by Bcl-2. However, the specific participants and precise mechanisms underlying this apoptotic pathway are poorly understood. The proapoptotic proteins Bak and Bax-members of the Bcl-2 family-are essential for the functioning of the mitochondrial apoptotic pathway. In this study, we used the CRISPR/Cas9 system to knockout Bak in the human SH-SY5Y cell line and determined the effects of this knockout on TNFα/CHX-induced apoptosis. Our data showed that overexpression of Bcl-2 dramatically prevented TNFα/CHX-induced apoptosis, and then pro-apoptotic protein Bak was downregulated and became more resistant to TNFα/CHX-induced apoptosis, because both TNFα/CHX-induced PARP cleavage and caspase activation were blocked in BAK-/- cells or using specific siRNA, whereas Bax was dispensable in TNFα/CHX-induced apoptosis, as evidenced using specific siRNA. Bax translocated from the cytosol into the mitochondria in response to TNFα/CHX, and CRISPR/Cas9 knockout of Bak significantly decreased this translocation. These results indicate that TNFα/CHX-induced apoptosis does not occur in Bak-/- cells, suggesting that TNFα/CHX-induced apoptosis is Bak-dependent but Bax-independent.

Pen-2 and Presenilin are Sufficient to Catalyze Notch Processing.

Presenilin-1 (PS1) or presenilin-2 (PS2), nicastrin (NCT), anterior pharynx-defective 1 (Aph-1), and presenilin enhancer-2 (Pen-2) have been considered the minimal essential subunits required to form an active γ-secretase complex. Besides PS, which has been widely believed to function as the catalytic subunit of the complex, the functional roles of the other subunits in the γ-secretase complex remain debatable. In the current study, we set out to determine the role of Pen-2 in γ-secretase activity. To this end, using knockout cells in combination with siRNA and immunoprecipitation approaches, our results revealed that Pen-2 together with presenilin are sufficient to form a functionally active enzyme to process Notch. Specifically, our data demonstrated that Pen-2 plays a crucial role in substrate binding, a mechanism by which Pen-2 contributes directly to the catalytic mechanism of γ-secretase activity. Our data also suggested that there may be different requirements for components to process AßPP and Notch. This information would be important for therapeutic strategy aimed at inhibition or modulation of γ-secretase activity.

Nicastrin is required for amyloid precursor protein (APP) but not Notch processing, while anterior pharynx-defective 1 is dispensable for processing of both APP and Notch.

The γ-secretase complex is composed of at least four components: presenilin 1 or presenilin-2, nicastrin (NCT), anterior pharynx-defective 1 (Aph-1), and presenilin enhancer 2. In this study, using knockout cell lines, our data demonstrated that knockout of NCT, as well as knockout of presenilin enhancer 2, completely blocked γ-secretase-catalyzed processing of C-terminal fragment (CTF)α and CTFß, the C-terminal fragments of ß-amyloid precursor protein (APP) produced by α-secretase and ß-secretase cleavages, respectively. Interestingly, in Aph-1-knockout cells, CTFα and CTFß were still processed by γ-secretase, indicating Aph-1 is dispensable for APP processing. Furthermore, our results indicate that Aph-1 as well as NCT is not absolutely required for Notch processing, suggesting that NCT is differentially required for APP and Notch processing. In addition, our data revealed that components of the γ-secretase complex are also important for proteasome- and lysosome-dependent degradation of APP and that endogenous APP is mostly degraded by lysosome while exogenous APP is mainly degraded by proteasome. There are unanswered questions regarding the roles of each component of the γ-secretase complex in amyloid precursor protein (APP) and Notch processing. The most relevant, novel finding of this study is that nicastrin (NCT) is required for APP but not Notch processing, while Aph-1 is not essential for processing of both APP and Notch, suggesting NCT as a therapeutic target to restrict Aß formation without impairing Notch signaling.

Cellular FLICE-like Inhibitory Protein (c-FLIP) and PS1-associated Protein (PSAP) Mediate Presenilin 1-induced γ-Secretase-dependent and -independent Apoptosis, Respectively.

Presenilin 1 (PS1) has been implicated in apoptosis; however, its mechanism remains elusive. We report that PS1-induced apoptosis was associated with cellular FLICE-like inhibitory protein (c-FLIP) turnover and that γ-secretase inhibitor blocked c-FLIP turnover and also partially blocked PS1-induced apoptosis. A complete inhibition of PS1-induced apoptosis was achieved by knockdown of PS1-associated protein (PSAP), a mitochondrial proapoptotic protein that forms a complex with Bax upon induction of apoptosis, in the presence of γ-secretase inhibitor. PS1-induced apoptosis was partially inhibited by knockdown of caspase-8, Fas-associated protein with death domain (FADD), or Bid. However, knockdown of Bax or overexpression of Bcl-2 resulted in complete inhibition of PS1-induced apoptosis. These data suggest that PS1 induces apoptosis through two pathways: the γ-secretase-dependent pathway mediated by turnover of c-FLIP and the γ-secretase-independent pathway mediated by PSAP-Bax complex formation. These two pathways converge on Bax to activate mitochondria-dependent apoptosis. These findings provide new insight into the mechanisms by which PS1 is involved in apoptosis and the mechanism by which PS1 exerts its pathogenic effects. In addition, our results suggest that PS2 induces apoptosis through a pathway that is different from that of PS1.

The matricellular protein Cyr61 is a key mediator of platelet-derived growth factor-induced cell migration.

Platelet-derived growth factor (PDGF), a potent chemoattractant, induces cell migration via the MAPK and PI3K/Akt pathways. However, the downstream mediators are still elusive. In particular, the role of extracellular mediators is largely unknown. In this study, we identified the matricellular protein Cyr61, which is de novo synthesized in response to PDGF stimulation, as the key downstream mediator of the ERK and JNK pathways, independent of the p38 MAPK and AKT pathways, and, thereby, it mediates PDGF-induced smooth muscle cell migration but not proliferation. Our results revealed that, when Cyr61 was newly synthesized by PDGF, it was promptly translocated to the extracellular matrix and physically interacted with the plasma membrane integrins α6ß1 and αvß3. We further demonstrate that Cyr61 and integrins are integral components of the PDGF signaling pathway via an "outside-in" signaling route to activate intracellular focal adhesion kinase (FAK), leading to cell migration. Therefore, this study provides the first evidence that the PDGF-induced endogenous extracellular matrix component Cyr61 is a key mediator in modulating cell migration by connecting intracellular PDGF-ERK and JNK signals with integrin/FAK signaling. Therefore, extracellular Cyr61 convergence with growth factor signaling and integrin/FAK signaling is a new concept of growth factor-induced cell migration. The discovered signaling pathway may represent an important therapeutic target in growth factor-mediated cell migration/invasion-related vascular diseases and tumorigenesis.

PSAP induces a unique Apaf-1 and Smac-dependent mitochondrial apoptotic pathway independent of Bcl-2 family proteins.

Presenilin-associated protein (PSAP) has been identified as a mitochondrial proapoptotic protein. However, the mechanism by which PSAP induces apoptosis remains unknown. To this end, we have established an inducible expression system. Using this system, we have examined the roles of B-cell lymphoma 2 (Bcl-2) family proteins, cytochrome c, Smac (Smac/Diablo, second mitochondria-derived activator of caspases/direct IAP binding protein with low PI), and Apaf-1 (apoptotic protease-activating factor) in PSAP-induced apoptosis. Our results demonstrate that knockdown of Apaf-1 abolished PSAP-induced caspase activation and poly(ADP ribose) polymerase (PARP) cleavage, indicating that the apoptosome formation triggered by cytochrome c is crucial for PSAP-induced apoptosis. Our data also demonstrate that knockdown of Smac abolished PSAP-induced caspase activation and PARP cleavage, indicating that, in addition to Apaf-1 or apoptosome formation, Smac is also essential for PSAP-induced apoptosis. However, interestingly, our data demonstrate that overexpression of Bcl-2 and Bcl-xL did not protect cells from PSAP-induced apoptosis, and that knockdown of Bid, Bax, and Bak had no effect on PSAP-induced cytochrome c and Smac release, indicating that PSAP-induced apoptosis is not regulated by Bcl-2 family proteins. These results strongly suggest that PSAP evokes mitochondrial apoptotic cascades via a novel mechanism that is not regulated by Bcl-2 family proteins, but that both the formation of cytochrome c-Apaf-1 apoptosome and the presence of Smac are absolutely required for PSAP-induced apoptosis.

Death receptor 6 induces apoptosis not through type I or type II pathways, but via a unique mitochondria-dependent pathway by interacting with Bax protein.

Cells undergo apoptosis through two major pathways, the extrinsic pathway (death receptor pathway) and the intrinsic pathway (the mitochondrial pathway). These two pathways can be linked by caspase-8-activated truncated Bid formation. Very recently, death receptor 6 (DR6) was shown to be involved in the neurodegeneration observed in Alzheimer disease. DR6, also known as TNFRSF21, is a relatively new member of the death receptor family, and it was found that DR6 induces apoptosis when it is overexpressed. However, how the death signal mediated by DR6 is transduced intracellularly is not known. To this end, we have examined the roles of caspases, apoptogenic mitochondrial factor cytochrome c, and the Bcl-2 family proteins in DR6-induced apoptosis. Our data demonstrated that Bax translocation is absolutely required for DR6-induced apoptosis. On the other hand, inhibition of caspase-8 and knockdown of Bid have no effect on DR6-induced apoptosis. Our results strongly suggest that DR6-induced apoptosis occurs through a new pathway that is different from the type I and type II pathways through interacting with Bax.