Caspases: therapeutic targets in neurologic disease

The active components of Erzhi wan and their anti-Alzheimer's disease mechanisms determined by an integrative approach of network pharmacology, bioinformatics, molecular docking, and molecular dynamics simulation

Erzhi Wan (EZW), a classic Traditional Chinese Medicine formula, has shown promise as a potential therapeutic option for Alzheimer's disease (AD), yet its mechanism remains elusive. Herein, we employed an integrative in-silico approach to investigate the active components and their mechanisms against AD. We screened four active components with blood-brain barrier permeabilities from TCMSP, along with 307 corresponding targets predicted by SwissTargetPrediction, PharmMapper, and TCMbank websites. Then, we retrieved 2260 AD-related targets from Genecards, OMIM, and NCBI databases. Furthermore, we constructed the protein-protein interaction (PPI) network of the intersected targets via the STRING database and performed the GO and KEGG enrichment analyses using the "clusterProfiler" R package. The results showed that the intersected targets were intimately related to the p53/PI3K/Akt signaling pathway, serotonergic synapse, and response to oxygen level. Subsequently, 25 core targets were found differentially expressed in brain regions by bioinformatics analyses of GEO datasets of clinical samples from the Alzdata database. The binding sites and stabilities between the active components and the core targets were investigated by the molecular docking approach using Autodock 4.2.6 software, followed by pocket detection and druggability assessment via the DoGSiteScorer server. The results showed that acacetin, β-sitosterol, and 3-O-acetyldammarenediol-II strongly interacted with the druggable pockets of AR, CASP8, POLB, and PREP. Eventually, the docking results were further cross-referenced with the literature research and validated by 100 ns of molecular dynamics simulations using GROMACS software. Binding free energies were calculated via MM/PBSA strategy combined with interaction entropy. The simulation results indicated stable bindings between four docking pairs including acacetin-AR, acacetin-CASP8, β-sitosterol-POLB, and 3-O-acetyldammarenediol-II-PREP. Overall, our study demonstrated a theoretical basis for how three active components of EZW confer efficacy against AD. It provides a promising reference for subsequent research regarding drug discoveries and clinical applications.

Commensal Bacillus siamensis LF4 ameliorates β-conglycinin induced inflammation in intestinal epithelial cells of Lateolabrax maculatus

β-conglycinin and glycinin, two major heat-stable anti-nutritional factors in soybean meal (SM), have been suggested as the key inducers of intestinal inflammation in aquatic animals. In the present study, a spotted seabass intestinal epithelial cells (IECs) were used to compare the inflammation-inducing effects of β-conglycinin and glycinin. The results showed that IECs co-cultured with 1.0 mg/mL β-conglycinin for 12 h or 1.5 mg/mL glycinin for 24 h significantly decreased the cell viability (P < 0.05), and overstimulated inflammation and apoptosis response by significantly down-regulating anti-inflammatory genes (IL-2, IL-4, IL-10 and TGF-β1) expressions and significantly up-regulated pro-inflammatory genes (IL-1β, IL-8 and TNF-α) and apoptosis genes (caspase 3, caspase 8 and caspase 9) expressions (P < 0.05). Subsequently, a β-conglycinin based inflammation IECs model was established and used for demonstrating whether commensal probiotic B. siamensis LF4 can ameliorate the adverse effects of β-conglycinin. The results showed β-conglycinin-induced cell viability damage was completely repaired by treated with 10⁹ cells/mL heat-killed B. siamensis LF4 for ≥12 h. At the same time, IECs co-cultured with 10⁹ cells/mL heat-killed B. siamensis LF4 for 24 h significantly ameliorated β-conglycinin-induced inflammation and apoptosis by up-regulating anti-inflammatory genes (IL-2, IL-4, IL-10 and TGF-β1) expressions and down-regulated pro-inflammatory genes (IL-1β, IL-8 and TNF-α) and apoptosis genes (caspase 3, caspase 8 and caspase 9) expressions (P < 0.05). In summary, both β-conglycinin and glycinin can lead to inflammation and apoptosis in spotted seabass IECs, and β-conglycinin is more effective; commensal B. siamensis LF4 can efficiently ameliorate β-conglycinin induced inflammation and apoptosis in IECs.

New Insights of Early Brain Injury after Subarachnoid Hemorrhage: A Focus on the Caspase Family

Spontaneous subarachnoid hemorrhage (SAH), primarily caused by ruptured intracranial aneurysms, remains a prominent clinical challenge with a high rate of mortality and morbidity worldwide. Accumulating clinical trials aiming at the prevention of cerebral vasospasm (CVS) have failed to improve the clinical outcome of patients with SAH. Therefore, a growing number of studies have shifted focus to the pathophysiological changes that occur during the periods of early brain injury (EBI). New pharmacological agents aiming to alleviate EBI have become a promising direction to improve outcomes after SAH. Caspases belong to a family of cysteine proteases with diverse functions involved in maintaining metabolism, autophagy, tissue differentiation, regeneration, and neural development. Increasing evidence shows that caspases play a critical role in brain pathology after SAH. Therefore, caspase regulation could be a potential target for SAH treatment. Herein, we provide an overview pertaining to the current knowledge on the role of caspases in EBI after SAH, and we discuss the promising therapeutic value of caspase-related agents after SAH.

Caspase-mediated regulation of the distinct signaling pathways and mechanisms in neuronal survival

Caspases are intimately associated with altering various signaling pathways, resulting in programmed cell death or apoptosis. Apoptosis is necessary for the normal homeostasis of cells and their development. The untoward activation of apoptotic pathways indirectly or directly results in pathologies of various diseases. Identifying different caspases in apoptotic pathways directed the research to develop caspase inhibitors as therapeutic agents. However, no drug is available in the market that targets caspase inhibition and produces a therapeutic effect. Here, we will shed light on the role of caspases in the number of neuronal disorders and neurodegenerative diseases. The article reviews the findings about the activation of various upstream mechanisms associated with caspases in neurodegenerative disorders along with the recent progress in the generation of caspase inhibitors and the challenge faced in their development as therapeutic agents for neurological indications.

Diosmetin Targeted at Peroxisome Proliferator-Activated Receptor Gamma Alleviates Advanced Glycation End Products Induced Neuronal Injury

The present study aimed to evaluate the role of diosmetin in alleviating advanced glycation end products (AGEs)-induced Alzheimer’s disease (AD)-like pathology and to clarify the action mechanisms. Before stimulation with AGEs (200 μg/mL), SH-SY5Y cells were treated with diosmetin (10 μmol/L), increasing cell viability. The induction of AGEs on the reactive oxygen species overproduction and downregulation of antioxidant enzyme activities, including superoxide dismutase, glutathione peroxidase, and catalase, were ameliorated by diosmetin. Amyloid precursor protein upregulation, accompanied by increased production of amyloid-β, caused by AGEs, was reversed by diosmetin. In the presence of diosmetin, not only β-site amyloid precursor protein cleaving enzyme1 expression was lowered, but the protein levels of insulin-degrading enzyme and neprilysin were elevated. Diosmetin protects SH-SY5Y cells from endoplasmic reticulum (ER) stress response to AGEs by suppressing ER stress-induced glucose regulated protein 78, thereby downregulating protein kinase R-like endoplasmic reticulum kinase, eukaryotic initiation factor 2 α, activating transcription factor 4, and C/EBP homologous protein. Diosmetin-pretreated cells had a lower degree of apoptotic DNA fragmentation; this effect may be associated with B-cell lymphoma (Bcl) 2 protein upregulation, Bcl-2-associated X protein downregulation, and decreased activities of caspase-12/-9/-3. The reversion of diosmetin on the AGEs-induced harmful effects was similar to that produced by pioglitazone. The peroxisome proliferator-activated receptor (PPAR)γ antagonist T0070907 (5 μmol/L) abolished the beneficial effects of diosmetin on AGEs-treated SH-SY5Y cells, indicating the involvement of PPARγ. We conclude that diosmetin protects neuroblastoma cells against AGEs-induced ER injury via multiple mechanisms and may be a potential option for AD.

Structure-Based Design and Biological Evaluation of Novel Caspase-2 Inhibitors Based on the Peptide AcVDVAD-CHO and the Caspase-2-Mediated Tau Cleavage Sequence YKPVD314

Alzheimer's disease (AD) was first described by Alois Alzheimer over 100 years ago, but there is still no overarching theory that can explain its cause in detail. There are also no effective therapies to treat either the cause or the associated symptoms of this devastating disease. A potential approach to better understand the pathogenesis of AD could be the development of selective caspase-2 (Casp2) probes, as we have shown that a Casp2-mediated cleavage product of tau (Δtau314) reversibly impairs cognitive and synaptic function in animal models of tauopathies. In this article, we map out the Casp2 binding site through the preparation and assay of a series of 35 pentapeptide inhibitors with the goal of gaining selectivity against caspase-3 (Casp3). We also employed computational docking methods to understand the key interactions in the binding pocket of Casp2 and the differences predicted for binding at Casp3. Moreover, we crystallographically characterized the binding of selected pentapeptides with Casp3. Furthermore, we engineered and expressed a series of recombinant tau mutants and investigated them in an in vitro cleavage assay. These studies resulted in simple peptidic inhibitors with nanomolar affinity, for example, AcVDV(Dab)D-CHO (24) with up to 27.7-fold selectivity against Casp3. Our findings provide a good basis for the future development of selective Casp2 probes and inhibitors that can serve as pharmacological tools in planned in vivo studies and as lead compounds for the design of bioavailable and more drug-like small molecules.

Procyanidin B2 inhibits lipopolysaccharide‑induced apoptosis by suppressing the Bcl‑2/Bax and NF‑κB signalling pathways in human umbilical vein endothelial cells

Human umbilical vein endothelial cells (HUVECs) serve a critical role in maintaining normal vascular function. Lipopolysaccharide (LPS), which is released from pathogenic bacteria in the blood, induces HUVEC apoptosis and injury to cause vascular dysfunction and infectious vascular diseases. Procyanidin B2 (PB2) possesses numerous functions, including antioxidant, antitumor, anti‑inflammatory and antiapoptosis effects, but the molecular mechanism is not completely understood. The present study investigated the effects of PB2 on LPS‑induced cytotoxicity and apoptosis in HUVECs, as well as the underlying mechanisms. The effects of PB2 on LPS‑mediated alterations to cytotoxicity, mitochondrial membrane potential, apoptosis were assessed by performing Cell Counting Kit‑8, JC‑1 fluorescence, Hoechst 33258 staining assays, respectively. IL‑1β, IL‑6 and TNF‑α mRNA expression and protein levels were measured by performing reverse transcription‑quantitative PCR and ELISAs, respectively. Bcl‑2, Bax, cleaved caspase‑3, cleaved caspase‑7, cleaved caspase‑9, phosphorylated (p)‑IκB‑α, p‑IκB‑β, p‑NF‑κB‑p65 and total NF‑κB p65 protein expression levels were determined via western blotting. NF‑κB p65 nuclear translocation was assessed via immunofluorescence. PB2 pretreatment markedly attenuated LPS‑induced cytotoxicity and apoptosis in HUVECs. PB2 also significantly downregulated the expression levels of IL‑1β, IL‑6, TNF‑α, Bax, cleaved caspase‑3, cleaved caspase‑7, cleaved caspase‑9 and p‑NF‑κB‑p65, but upregulated the expression levels of Bcl‑2, p‑IκB‑α and p‑IκB‑β in LPS‑induced HUVECs. Moreover, PB2 markedly inhibited LPS‑induced NF‑κB p65 nuclear translocation in HUVECs. The results suggested that the potential molecular mechanism underlying PB2 was associated with the Bax/Bcl‑2 and NF‑κB signalling pathways. Therefore, PB2 may serve as a useful therapeutic for infectious vascular diseases.

GardeninA confers neuroprotection against environmental toxin in a Drosophila model of Parkinson's disease

Parkinson’s disease is an age-associated neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons from the midbrain. Epidemiological studies have implicated exposures to environmental toxins like the herbicide paraquat as major contributors to Parkinson’s disease etiology in both mammalian and invertebrate models. We have employed a paraquat-induced Parkinson’s disease model in Drosophila as an inexpensive in vivo platform to screen therapeutics from natural products. We have identified the polymethoxyflavonoid, GardeninA, with neuroprotective potential against paraquat-induced parkinsonian symptoms involving reduced survival, mobility defects, and loss of dopaminergic neurons. GardeninA-mediated neuroprotection is not solely dependent on its antioxidant activities but also involves modulation of the neuroinflammatory and cellular death responses. Furthermore, we have successfully shown GardeninA bioavailability in the fly heads after oral administration using ultra-performance liquid chromatography and mass spectrometry. Our findings reveal a molecular mechanistic insight into GardeninA-mediated neuroprotection against environmental toxin-induced Parkinson’s disease pathogenesis for novel therapeutic intervention.

Maitra and colleagues identify the neuroprotective properties of GardeninA against environmental toxin-induced neurodegeneration in Drosophila. This study has the potential to influence future research into toxin-induced Parkinson’s disease pathogenesis.

Neuronal changes and cognitive deficits in a multi-hit rat model following cumulative impact of early life stressors

Perinatal protein malnourishment (LP) is a leading cause for mental and physical retardation in children from poor socioeconomic conditions. Such malnourished children are vulnerable to additional stressors that may synergistically act to cause neurological disorders in adulthood. In this study, the above mentioned condition was mimicked via a multi-hit rat model in which pups born to LP mothers were co-injected with polyinosinic:polycytidylic acid (Poly I:C; viral mimetic) at postnatal day (PND) 3 and lipopolysaccharide (LPS; bacterial mimetic) at PND 9. Individual exposure of Poly I:C and LPS was also given to LP pups to correlate chronicity of stress. Similar treatments were also given to control pups. Hippocampal cellular apoptosis, β III tubulin catastrophe, altered neuronal profiling and spatial memory impairments were assessed at PND 180, using specific immunohistochemical markers (active caspase 3, β III tubulin, doublecortin), golgi studies and cognitive mazes (Morris water maze and T maze). Increase in cellular apoptosis, loss of dendritic arborization and spatial memory impairments were higher in the multi-hit group, than the single-hit groups. Such impairments observed due to multi-hit stress mimicked conditions similar to many neurological disorders and hence, it is hypothesized that later life neurological disorders might be an outcome of multiple early life hits.This article has an associated First Person interview with the first author of the paper.

Caspase-Activated Oligonucleotide Probe

Light-activated ("caged") oligonucleotides provide a strategy for modulating the activity of antisense oligos, siRNA, miRNA, aptamers, DNAzymes, and mRNA-capturing probes with high spatiotemporal resolution. However, the near-UV and visible wavelengths that promote these bond-breaking reactions poorly penetrate living tissue, which limits some biological applications. To address this issue, we describe the first example of a protease-activated oligonucleotide probe, capable of reporting on caspase-3 during cellular apoptosis. The 2'-F RNA-peptide substrate-peptide nucleic acid (PNA) hairpin structure was generated in 30% yield in a single bioconjugation step.

Apoptosis as the main type of cell death induced by calcium electroporation in rhabdomyosarcoma cells

Calcium electroporation (CaEP) has been previously reported as an effective method of rhabdomyosarcoma cells reduction. CaEP causes temporary cell membrane permeabilization with simultaneous calcium ions influx. A rapid influx of calcium ions leads to mitochondrial overload by Ca²⁺, loss of mitochondrial membrane potential causing cytochrome c release, caspase cascade activation and, as a consequence, cell death. This study was conducted on two cell lines: normal muscle cells (C2C12) and rhabdomyosarcoma cells (RD), which showed different cellular responses to CaEP. Our study defined apoptosis as the main cell death type occurring after CaEP in RD cells. Increased activity of caspase 3/7, Parp-1 and cleaved Parp-1 were proven in the case of RD cells. RD cells compartment rearrangement was observed in the time-lapse by holotomographic microscopy (HTM). C2C12 cells were less sensitive to electroporation and increased Ca²⁺ concentration, and viability was maintained at the level of control cells, only slight changes in pro-apoptotic factors were observed. The results reveal CaEP as a promising therapeutic approach in cancers which develop from muscle tissue.

Integrative X-ray Structure and Molecular Modeling for the Rationalization of Procaspase-8 Inhibitor Potency and Selectivity

Caspases are a critical class of proteases involved in regulating programmed cell death and other biological processes. Selective inhibitors of individual caspases, however, are lacking, due in large part to the high structural similarity found in the active sites of these enzymes. We recently discovered a small-molecule inhibitor, 63-R, that covalently binds the zymogen, or inactive precursor (pro-form), of caspase-8, but not other caspases, pointing to an untapped potential of procaspases as targets for chemical probes. Realizing this goal would benefit from a structural understanding of how small molecules bind to and inhibit caspase zymogens. There have, however, been very few reported procaspase structures. Here, we employ X-ray crystallography to elucidate a procaspase-8 crystal structure in complex with 63-R, which reveals large conformational changes in active-site loops that accommodate the intramolecular cleavage events required for protease activation. Combining these structural insights with molecular modeling and mutagenesis-based biochemical assays, we elucidate key interactions required for 63-R inhibition of procaspase-8. Our findings inform the mechanism of caspase activation and its disruption by small molecules and, more generally, have implications for the development of small molecule inhibitors and/or activators that target alternative (e.g., inactive precursor) protein states to ultimately expand the druggable proteome.

miRNAs Identify Shared Pathways in Alzheimer's and Parkinson's Diseases

Despite the identification of several dozens of common genetic variants associated with Alzheimer's disease (AD) and Parkinson's disease (PD), most of the genetic risk remains uncharacterised. Therefore, it is important to understand the role of regulatory elements, such as miRNAs. Dysregulated miRNAs are implicated in AD and PD, with potential value in dissecting the shared pathophysiology between the two disorders. miRNAs relevant to both neurodegenerative diseases are related to axonal guidance, apoptosis, and inflammation, therefore, AD and PD likely arise from similar underlying biological pathway defects. Furthermore, pathways regulated by APP, L1CAM, and genes of the caspase family may represent promising therapeutic miRNA targets in AD and PD since they are targeted by dysregulated miRNAs in both disorders.

SkQ1 Controls CASP3 Gene Expression and Caspase-3-Like Activity in the Brain of Rats under Oxidative Stress

Here, we studied the effect of the mitochondria-targeted antioxidant SkQ1 (plastoquinone cationic derivative) on the CASP3 gene expression and caspase-3 activity in rat cerebral cortex and brain mitochondria under normal conditions and in oxidative stress induced by hyperbaric oxygenation (HBO). Under physiological conditions, SkQ1 administration (50 nmol/kg, 5 days) did not affect the CASP3 gene expression and caspase-3-like activity in the cortical cells, as well as caspase-3-like activity in brain mitochondria, but caused a moderate decrease in the content of primary products of lipid peroxidation (LPO) and an increase in the reduced glutathione (GSH) level. HBO-induced oxidative stress (0.5 MPa, 90 min) was accompanied by significant upregulation of CASP3 mRNA and caspase-3-like activity in the cerebral cortex, activation of the mitochondrial enzyme with simultaneous decrease in the GSH content, increase in the glutathione reductase activity, and stimulation of LPO. Administration of SkQ1 before the HBO session maintained the basal levels of the CASP3 gene expression and enzyme activity in the cerebral cortex cells and led to the normalization of caspase-3-like activity and redox parameters in brain mitochondria. We hypothesize that SkQ1 protects brain cells from the HBO-induced oxidative stress due to its antioxidant activity and stimulation of antiapoptotic mechanisms.

Non-apoptotic Caspase regulation of stem cell properties

The evolutionarily conserved family of proteins called caspases are the main factors mediating the orchestrated programme of cell suicide known as apoptosis. Since this protein family was associated with this essential biological function, the majority of scientific efforts were focused towards understanding their molecular activation and function during cell death. However, an emerging body of evidence has highlighted a repertoire of non-lethal roles within a large variety of cell types, including stem cells. Here we intend to provide a comprehensive overview of the key role of caspases as regulators of stem cell properties. Finally, we briefly discuss the possible pathological consequences of caspase malfunction in stem cells, and the therapeutic potential of caspase regulation applied to this context.

Apoptosis-inducing effects and growth inhibitory of a novel chalcone, in human hepatic cancer cells and lung cancer cells

Apoptosis is an important biological phenomenon, which affects many diseases, such as cancer and Alzheimer's disease. In the present study, we observed that chalcone 9X, an aromatic ketone, induced apoptosis of human hepatic and lung cancer cells and inhibited cancer cell migration and invasion. This compound strongly suppressed the growth of tumor in a mouse model of xenograft tumors. The anticancer activity of chalcone 9X was equivalent to 5-fluorouracil (5-FU) as a positive control agent, whereas the toxic effect of chalcone 9X in non-cancer cells was weaker than 5-FU. Molecular docking results showed that chalcone 9X could act on the active sites of pro-apoptotic proteins capspases-3 and -8 to induce apoptotic death of cancer cells. Our findings suggest that chalcone 9X might be considered a candidate compound of novel anticancer drug in the future.

Caspase-8, association with Alzheimer's Disease and functional analysis of rare variants

The accumulation of amyloid beta (Aβ) peptide (Amyloid cascade hypothesis), an APP protein cleavage product, is a leading hypothesis in the etiology of Alzheimer's disease (AD). In order to identify additional AD risk genes, we performed targeted sequencing and rare variant burden association study for nine candidate genes involved in the amyloid metabolism in 1886 AD cases and 1700 controls. We identified a significant variant burden association for the gene encoding caspase-8, CASP8 (p = 8.6x10^-5). For two CASP8 variants, p.K148R and p.I298V, the association remained significant in a combined sample of 10,820 cases and 8,881 controls. For both variants we performed bioinformatics structural, expression and enzymatic activity studies and obtained evidence for loss of function effects. In addition to their role in amyloid processing, caspase-8 and its downstream effector caspase-3 are involved in synaptic plasticity, learning, memory and control of microglia pro-inflammatory activation and associated neurotoxicity, indicating additional mechanisms that might contribute to AD. As caspase inhibition has been proposed as a mechanism for AD treatment, our finding that AD-associated CASP8 variants reduce caspase function calls for caution and is an impetus for further studies on the role of caspases in AD and other neurodegenerative diseases.

Caspase-3-dependent cleavage of Akt modulates tau phosphorylation via GSK3β kinase: implications for Alzheimer's disease

The pathological hallmark of Alzheimer's disease (AD) is accumulation of misfolded amyloid-β peptides and hyperphosphorylated tau protein in the brain. Increasing evidence suggests that serine-aspartyl proteases-caspases are activated in the AD brain. Previous studies identified a caspase-3 cleavage site within the amyloid-β precursor protein, and a caspase-3 cleavage of tau as the mechanisms involved in the development of Aβ and tau neuropathology, respectively. However, the potential role that caspase-3 could have on tau metabolism remains unknown. In the current studies, we provide experimental evidence that caspase-3 directly and specifically regulates tau phosphorylation, and demonstrate that this effect is mediated by the GSK3β kinase pathway via a caspase-3-dependent cleavage of the protein kinase B (also known as Akt). In addition, we confirm these results in vivo by using a transgenic mouse model of AD. Collectively, our findings demonstrate a new role for caspase-3 in the neurobiology of tau, and suggest that therapeutic strategies aimed at inhibiting this protease-dependent cleavage of Akt may prove beneficial in preventing tau hyperphosphorylation and subsequent neuropathology in AD and related tauopathies.

Inhibition of cerebral ischemia/reperfusion injury-induced apoptosis: nicotiflorin and JAK2/STAT3 pathway

Nicotiflorin is a flavonoid extracted from Carthamus tinctorius. Previous studies have shown its cerebral protective effect, but the mechanism is undefined. In this study, we aimed to determine whether nicotiflorin protects against cerebral ischemia/reperfusion injury-induced apoptosis through the JAK2/STAT3 pathway. The cerebral ischemia/reperfusion injury model was established by middle cerebral artery occlusion/reperfusion. Nicotiflorin (10 mg/kg) was administered by tail vein injection. Cell apoptosis in the ischemic cerebral cortex was examined by hematoxylin-eosin staining and terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Bcl-2 and Bax expression levels in ischemic cerebral cortex were examined by immunohistochemial staining. Additionally, p-JAK2, p-STAT3, Bcl-2, Bax, and caspase-3 levels in ischemic cerebral cortex were examined by western blot assay. Nicotiflorin altered the shape and structure of injured neurons, decreased the number of apoptotic cells, down-regulates expression of p-JAK2, p-STAT3, caspase-3, and Bax, decreased Bax immunoredactivity, and increased Bcl-2 protein expression and immunoreactivity. These results suggest that nicotiflorin protects against cerebral ischemia/reperfusion injury-induced apoptosis via the JAK2/STAT3 pathway.

Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant

Lissencephaly is a malformation of cortical development typically caused by deficient neuronal migration resulting in cortical thickening and reduced gyration. Here we describe a “thin” lissencephaly (TLIS) variant characterized by megalencephaly, frontal predominant pachygyria, intellectual disability, and seizures. Trio-based whole-exome sequencing and targeted re-sequencing identified recessive mutations of CRADD in six individuals with TLIS from four unrelated families of diverse ethnic backgrounds. CRADD (also known as RAIDD) is a death-domain-containing adaptor protein that oligomerizes with PIDD and caspase-2 to initiate apoptosis. TLIS variants cluster in the CRADD death domain, a platform for interaction with other death-domain-containing proteins including PIDD. Although caspase-2 is expressed in the developing mammalian brain, little is known about its role in cortical development. CRADD/caspase-2 signaling is implicated in neurotrophic factor withdrawal- and amyloid-β-induced dendritic spine collapse and neuronal apoptosis, suggesting a role in cortical sculpting and plasticity. TLIS-associated CRADD variants do not disrupt interactions with caspase-2 or PIDD in co-immunoprecipitation assays, but still abolish CRADD’s ability to activate caspase-2, resulting in reduced neuronal apoptosis in vitro. Homozygous Cradd knockout mice display megalencephaly and seizures without obvious defects in cortical lamination, supporting a role for CRADD/caspase-2 signaling in mammalian brain development. Megalencephaly and lissencephaly associated with defective programmed cell death from loss of CRADD function in humans implicate reduced apoptosis as an important pathophysiological mechanism of cortical malformation. Our data suggest that CRADD/caspase-2 signaling is critical for normal gyration of the developing human neocortex and for normal cognitive ability.

MiR-34a and miR-203 Inhibit Survivin Expression to Control Cell Proliferation and Survival in Human Osteosarcoma Cells

Elevated expression of survivin is observed in a number of cancer types, including human osteosarcoma. Few studies have demonstrated that survivin expression levels can be considered an independent predictor of survival for human osteosarcoma patients. However, the underlying molecular mechanisms of survivin in the process of human osteosarcoma carcinogenesis remain unclear. In the current study, we evaluated the biological effects of survivin knockdown on osteosarcoma cell proliferation, colony formation rate, and sensitivity to the chemotherapeutic agent cisplatin. We found that two different osteosarcoma cell lines, U2OS and Saos-2, have relatively higher expression levels of survivin, and specific knockdown of survivin resulted in a number of effects, such as inhibition of cell proliferation, decreased colony formation rate, cell cycle arrest at G2/M phase, induction of apoptosis, and increased sensitivity to cisplatin. In addition, we identified two microRNAs, miR-34a and miR-203, that are aberrantly expressed in human osteosarcoma cells and specifically target survivin by inhibiting its expression, therefore repressing osteosarcoma cell maintenance and proliferation.

Survivin and Tumorigenesis: Molecular Mechanisms and Therapeutic Strategies

Survivin is the smallest member of the inhibitor of apoptosis protein family, which has key roles in regulating cell division and inhibiting apoptosis by blocking caspase activation. Survivin is highly expressed in most human cancers, such as lung, pancreatic and breast cancers, relative to normal tissues. Aberrant survivin expression is associated with tumor cell proliferation, progression, angiogenesis, therapeutic resistance, and poor prognosis. Studies on the underlying molecular mechanisms indicate that survivin is involved in the regulation of cytokinesis and cell cycle progression, as well as participates in a variety of signaling pathways such as the p53, Wnt, hypoxia, transforming growth factor, and Notch signaling pathways. In this review, recent progress in understanding the molecular basis of survivin is discussed. Therapeutic strategies targeting survivin in preclinical studies are also briefly summarized.

Clearing the corpses: regulatory mechanisms, novel tools, and therapeutic potential of harnessing microglial phagocytosis in the diseased brain

Apoptosis is a widespread phenomenon that occurs in the brain in both physiological and pathological conditions. Dead cells must be quickly removed to avoid the further toxic effects they exert in the parenchyma, a process executed by microglia, the brain professional phagocytes. Although phagocytosis is critical to maintain tissue homeostasis, it has long been either overlooked or indirectly assessed based on microglial morphology, expression of classical activation markers, or engulfment of artificial phagocytic targets in vitro. Nevertheless, these indirect methods present several limitations and, thus, direct observation and quantification of microglial phagocytosis is still necessary to fully grasp its relevance in the diseased brain. To overcome these caveats and obtain a comprehensive, quantitative picture of microglial phagocytosis we have developed a novel set of parameters. These parameters have allowed us to identify the different strategies utilized by microglia to cope with apoptotic challenges induced by excitotoxicity or inflammation. In contrast, we discovered that in mouse and human epilepsy microglia failed to find and engulf apoptotic cells, resulting in accumulation of debris and inflammation. Herein, we advocate that the efficiency of microglial phagocytosis should be routinely tested in neurodegenerative and neurological disorders, in order to determine the extent to which it contributes to apoptosis and inflammation found in these conditions. Finally, our findings point towards enhancing microglial phagocytosis as a novel therapeutic strategy to control tissue damage and inflammation, and accelerate recovery in brain diseases.