Mitochondrial ceramide-rich macrodomains functionalize Bax upon irradiation.

Background: Evidence indicates that Bax functions as a "lipidic" pore to regulate mitochondrial outer membrane permeabilization (MOMP), the apoptosis commitment step, through unknown membrane elements. Here we show mitochondrial ceramide elevation facilitates MOMP-mediated cytochrome c release in HeLa cells by generating a previously-unrecognized mitochondrial ceramide-rich macrodomain (MCRM), which we visualize and isolate, into which Bax integrates.

Methodology/principal Findings: MCRMs, virtually non-existent in resting cells, form upon irradiation coupled to ceramide synthase-mediated ceramide elevation, optimizing Bax insertion/oligomerization and MOMP.

Ceramide formation as a target in beta-cell survival and function.

Introduction: Ceramide may be synthesized de novo or generated by sphingomyelinase-dependent hydrolysis of sphingomyelin.

Areas Covered: The role of ceramide, ceramide-sensitive signaling and ion channels in β-cell apoptosis, lipotoxicity and amyloid-induced β-cell death.

Expert Opinion: Ceramide participates in β-cell dysfunction and apoptosis after exposure to TNFα, IL-1β and IFN-γ, excessive amyloid and islet amyloid polypeptide or non-esterified fatty acids (lipotoxicity).

Activity of secretory sphingomyelinase is increased in plasma of alcohol-dependent patients.

Background: Acid sphingomyelinase (ASM, EC 3.1.4.

Activation of the permeability transition pore by Bax via inhibition of the mitochondrial BK channel.

Mitochondria are crucially involved in the intrinsic pathway of apoptosis. Upon induction of apoptosis, proapoptotic proteins of the Bcl-2 family, in particular Bax and Bak, transfer the death signal to the organelle. The outcome is release of proapoptotic factors, such as cytochrome c, and mitochondrial changes, such as depolarization.

DC-SIGN mediated sphingomyelinase-activation and ceramide generation is essential for enhancement of viral uptake in dendritic cells.

As pattern recognition receptor on dendritic cells (DCs), DC-SIGN binds carbohydrate structures on its pathogen ligands and essentially determines host pathogen interactions because it both skews T cell responses and enhances pathogen uptake for cis infection and/or T cell trans-infection. How these processes are initiated at the plasma membrane level is poorly understood. We now show that DC-SIGN ligation on DCs by antibodies, mannan or measles virus (MV) causes rapid activation of neutral and acid sphingomyelinases followed by accumulation of ceramides in the outer membrane leaflet.

Kinase suppressor of Ras-1 protects against pulmonary Pseudomonas aeruginosa infections.

Pseudomonas aeruginosa is a Gram-negative pathogen that causes severe infections in immunocompromised individuals and individuals with cystic fibrosis or chronic obstructive pulmonary disease (COPD). Here we show that kinase suppressor of Ras-1 (Ksr1)-deficient mice are highly susceptible to pulmonary P. aeruginosa infection accompanied by uncontrolled pulmonary cytokine release, sepsis and death, whereas wild-type mice clear the infection.

Accumulation of ceramide in the trachea and intestine of cystic fibrosis mice causes inflammation and cell death.

Cystic fibrosis is a hereditary metabolic disorder caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene and characterized by severe intestinal and pulmonary symptoms, in particular intestinal obstruction, pancreatic insufficiency, chronic pulmonary inflammation, and microbial lung infections. Recent studies have demonstrated an accumulation of ceramide in the lungs of cystic fibrosis patients and in several mouse models. These findings showed that pulmonary ceramide concentrations play an important role in pulmonary inflammation and infection.

Syntaxin 4 is required for acid sphingomyelinase activity and apoptotic function.

Acid sphingomyelinase (A-SMase) is an important enzyme in sphingolipid metabolism and plays key roles in apoptosis, immunity, development, and cancer. In addition, it mediates cytotoxicity of cisplatin and some other chemotherapeutic drugs. The mechanism of A-SMase activation is still undefined.

CFTR-dependent susceptibility of the cystic fibrosis-host to Pseudomonas aeruginosa.

Cystic fibrosis is the most common autosomal recessive disorder in western countries. The disease is characterized by recurrent and chronic infections of the lung in particular with Pseudomonas aeruginosa, Staphylococcus aureus, Burkholderia cepacia, and Haemophilus influenzae. Albeit intensive research in the last years, the molecular mechanisms causing the high susceptibility of cystic fibrosis patients to bacterial infections are still unknown.

Single-point mutations of a lysine residue change function of Bax and Bcl-xL expressed in Bax- and Bak-less mouse embryonic fibroblasts: novel insights into the molecular mechanisms of Bax-induced apoptosis.

Members of the Bcl-2 family play key roles as proapoptotic (e.g., Bax) and antiapoptotic (e.

Cationic cell-penetrating peptides induce ceramide formation via acid sphingomyelinase: implications for uptake.

Cationic cell-penetrating peptides (CPP) are receiving increasing attention as molecular transporters of membrane-impermeable molecules. Import of cationic CPP occurs both via endocytosis and - at higher peptide concentrations - in an endocytosis-independent manner via localized regions of the plasma membrane. At present, this endocytosis-independent import of cationic CPP is not well understood, but has been shown to be sensitive to various pharmacological inhibitors, suggesting a role of an unidentified enzymatic activity.

Role of acidic sphingomyelinase in thymol-mediated dendritic cell death.

Scope: Thymol is a component of several plants with antimicrobial activity. Little is known about the effects of thymol on immune cells of the host. This study addressed the effects of thymol on dendritic cells (DCs), regulators of innate and adaptive immunity.

The role of sphingolipids and ceramide in pulmonary inflammation in cystic fibrosis.

Sphingolipids and in particular ceramide have been shown to be critically involved in the response to many receptor-mediated, but also receptor-independent, mainly stress stimuli. Recent studies demonstrate that ceramide plays an important role in the pathogenesis of cystic fibrosis, a hereditary metabolic disorder caused by mutations of the Cystic Fibrosis Transmembrane Conductance Regulator. Patients with cystic fibrosis suffer from chronic pulmonary inflammation and microbial lung infections, in particular with Pseudomonas aeruginosa.

Ceramide in Pseudomonas aeruginosa infections and cystic fibrosis.

Cystic fibrosis is one of the most common autosomal recessive disorders, at least in Western countries. Patients with cystic fibrosis exhibit many symptoms, the most important of which are chronic inflammation and bacterial infections of the lung. Cystic fibrosis is caused by mutations of the cystic fibrosis conductance regulator (CFTR) gene; however, the molecular mechanisms leading to the clinical manifestations of cystic fibrosis are still unclear.

Functional Inhibitors of Acid Sphingomyelinase (FIASMAs): a novel pharmacological group of drugs with broad clinical applications.

Acid sphingomyelinase (ASM) is an important lipid-metabolizing enzyme cleaving sphingomyelin to ceramide, mainly within lysosomes. Acid ceramidase (AC) further degrades ceramide to sphingosine which can then be phosphorylated to sphingosine-1-phosphate. Ceramide and its metabolite sphingosine-1-phosphate have been shown to antagonistically regulate apoptosis, cellular differentiation, proliferation and cell migration.

Alterations in ceramide concentration and pH determine the release of reactive oxygen species by Cftr-deficient macrophages on infection.

We recently demonstrated that the accumulation of ceramide in Cftr-deficient epithelial cells is important for the pathophysiology of CF. However, the role of ceramide in other lung cells, particularly lung macrophages, requires definition. In this study, we report that ceramide is accumulated in Cftr-deficient lung macrophages.

Alveolar inflammation in cystic fibrosis.

Background: In infected lungs of the cystic fibrosis (CF) patients, opportunistic pathogens and mutated cystic fibrosis transmembrane conductance regulator protein (CFTR) contribute to chronic airway inflammation that is characterized by neutrophil/macrophage infiltration, cytokine release and ceramide accumulation. We sought to investigate CF lung inflammation in the alveoli.

Methods: Lung tissue from 14 CF patients and four healthy individuals was analyzed for numbers of effector cells, elastin and collagen concentrations, inflammatory markers and density of Pseudomonas aeruginosa.

Triggering of dendritic cell apoptosis by xanthohumol.

Xanthohumol, a flavonoid from beer with anticancer activity is known to trigger apoptosis in a variety of tumor cells. Xanthohumol further has anti-inflammatory activity. However, little is known about the effect of xanthohumol on survival and function of immune cells.

Role of Kv1.3 mitochondrial potassium channel in apoptotic signalling in lymphocytes.

Mitochondria have been shown to play a pivotal role in apoptotic signalling in various cell types. We have recently reported that in lymphocytes the voltage-gated potassium channel Kv1.3, known to reside in the plasma membrane, is active also in the inner mitochondrial membrane.

Contribution of voltage-gated potassium channels to the regulation of apoptosis.

Recent evidence points to the crucial involvement of voltage-gated potassium channels (Kv) in apoptotic volume decrease and in the regulation of apoptosis in several systems. We have recently described the presence of a Kv channel, Kv1.3, in the mitochondria of lymphocytes.

Sphingomyelinase dependent apoptosis of dendritic cells following treatment with amyloid peptides.

Amyloid peptides are formed during inflammation and modify the function of immune cells. The present study explored the effect of amyloid beta-peptide (Abeta(1-42)) and islet amyloid polypeptide (IAPP) on bone marrow derived dendritic cells (DCs). DCs were treated with Abeta(1-42) or IAPP with subsequent assessment of ceramide formation, caspase 8 and 3 activity, DNA fragmentation and phosphatidylserine exposure.

An investigation of the occurrence and properties of the mitochondrial intermediate-conductance Ca2+-activated K+ channel mtKCa3.1.

The mitochondrial intermediate-conductance Ca2+-activated K+ channel mtKCa3.1 has recently been discovered in the HCT116 colon tumor-derived cell line, which expresses relatively high levels of this protein also in the plasma membrane. Electrophysiological recordings revealed that the channel can exhibit different conductance states and kinetic modes, which we tentatively ascribe to post-translational modifications.