Sébastien Conus

Bcl-2 prolongs cell survival after Bax-induced release of cytochrome c.

Following exposure of cells to stimuli that trigger programmed cell death (apoptosis), cytochrome c is rapidly released from mitochondria into the cytoplasm where it activates proteolytic molecules known as caspases that specifically cleave the amino-acid sequence DEVD and are crucial for the execution of apoptosis. The protein Bcl-2 interferes with this activation of caspases by preventing the release of cytochrome c. Here we study these molecular interactions during apoptosis induced by the protein Bax, a pro-apoptotic homologue of Bcl-2 (refs 5, 6). We show that in cells transiently transfected with bax, Bax localizes to mitochondria and induces the release of cytochrome c, activation of caspase-3, membrane blebbing, nuclear fragmentation, and cell death. Caspase inibitors do not affect Bax-induced cytochrome c release but block caspase-3 activation and nuclear fragmentation. Unexpectedly, Bcl-2 also fails to prevent Bax-induced cytochrome c release, although it co-localizes with Bax to mitochondria. Cells overexpressing both Bcl-2 and Bax show no signs of caspase activation and survive with significant amounts of cytochrome c in the cytoplasm. These findings indicate that Bcl-2 can interfere with Bax killing downstream of and independently of cytochrome c release.

Budesonide Is Effective in Adolescent and Adult Patients With Active Eosinophilic Esophagitis

BACKGROUND & AIMS Eosinophilic esophagitis (EoE) is a chronic inflammatory disease of the esophagus characterized by dense tissue eosinophilia; it is refractory to proton pump inhibitor therapy. EoE affects all age groups but most frequently individuals between 20 and 50 years of age. Topical corticosteroids are effective in pediatric patients with EoE, but no controlled studies of corticosteroids have been reported in adult patients. METHODS We performed a randomized, double-blind, placebo-controlled trial to evaluate the effect of oral budesonide (1 mg twice daily for 15 days) in adolescent and adult patients with active EoE. Pretreatment and posttreatment disease activity was assessed clinically, endoscopically, and histologically. The primary end point was reduced mean numbers of eosinophils in the esophageal epithelium (number per high-power field [hpf] = esophageal eosinophil load). Esophageal biopsy and blood samples were analyzed using immunofluorescence and immunoassays, respectively, for biomarkers of inflammation and treatment response. RESULTS A 15-day course of therapy significantly decreased the number of eosinophils in the esophageal epithelium in patients given budesonide (from 68.2 to 5.5 eosinophils/hpf; P < .0001) but not in the placebo group (from 62.3 to 56.5 eosinophils/hpf; P = .48). Dysphagia scores significantly improved among patients given budesonide compared with those given placebo (5.61 vs 2.22; P < .0001). White exudates and red furrows were reversed in patients given budesonide, based on endoscopy examination. Budesonide, but not placebo, also reduced apoptosis of epithelial cells and molecular remodeling events in the esophagus; no serious adverse events were observed. CONCLUSIONS A 15-day course of treatment with budesonide is well tolerated and highly effective in inducing a histologic and clinical remission in adolescent and adult patients with active EoE.

Anti-interleukin-5 antibody treatment (mepolizumab) in active eosinophilic oesophagitis: a randomised, placebo-controlled, double-blind trial

Objective: Eosinophilic oesophagitis (EoO) is a clinicopathological condition defined by proton pump inhibitor-refractory oesophageal symptoms combined with oesophageal eosinophilia. The pharmacodynamic effect of mepolizumab (a humanised anti-interleukin-5 monoclonal antibody) in EoO was evaluated. Methods: Eleven adults with active EoO (>20 peak eosinophil number/high power field (hpf) and dysphagia) were randomised to 750 mg of mepolizumab (n = 5) or placebo (n = 6) and received two intravenous infusions, 1 week apart. Those not in complete remission (<5 peak eosinophil number/hpf) after 8 weeks received two further doses 4 weeks apart, 1500 mg of mepolizumab or placebo. The effect of mepolizumab was assessed clinically, endoscopically, histologically, and via blood and tissue biomarkers. Results: As assessed by immunofluorescence, a marked reduction of mean oesophageal eosinophilia (p = 0.03) was seen in the mepolizumab group (−54%) compared with the placebo group (−5%) 4 weeks after initiation of treatment. No further reduction of eosinophil numbers was observed in response to the two additional infusions in either group. Mepolizumab reduced tenascin C (p = 0.033) and transforming growth factor β1 (p = 0.05) expression in the oesophageal epithelial layer 13 weeks after initiation of treatment. Clinically, limited improvement of symptoms was seen, although a trend was seen between 4 and 13 weeks after initiation of mepolizumab treatment. Mepolizumab was well tolerated. Conclusions: Mepolizumab significantly reduced eosinophil numbers in oesophageal tissues in adult patients with active EoO, and changes in the expression of molecules associated with oesophageal remodelling were reversed. Minimal clinical improvement was achieved in a subgroup of patients with EoO. Mepolizumab had an acceptable safety profile, even at the high 1500 mg dose level. Trial registration number: NCT00274703

Apoptotic crosstalk between the endoplasmic reticulum and mitochondria controlled by Bcl-2

Apoptosis involves mitochondrial steps such as the release of the apoptogenic factor cytochrome c which are effectively blocked by Bcl-2. Although Bcl-2 may have a direct action on the mitochondrial membrane, it also resides and functions on the endoplasmic reticulum (ER), and there is increasing evidence for a role of the ER in apoptosis regulation as well. Here we uncover a hitherto unrecognized, apoptotic crosstalk between the ER and mitochondria that is controlled by Bcl-2. After triggering massive ER dilation due to an inhibition of secretion, the drug brefeldin A (BFA) induces the release of cytochrome c from mitochondria in a caspase-8- and Bid-independent manner. This is followed by caspase-3 activation and DNA/nuclear fragmentation. Surprisingly, cytochrome c release by BFA is not only blocked by wild-type Bcl-2 but also by a Bcl-2 variant that is exclusively targeted to the ER (Bcl-2/cb5). Similar findings were obtained with tunicamycin, an agent interfering with N-linked glycosylations in the secretory system. Thus, apoptotic agents perturbing ER functions induce a novel crosstalk between the ER and mitochondria that can be interrupted by ER-based Bcl-2.

Long-Term Budesonide Maintenance Treatment Is Partially Effective for Patients With Eosinophilic Esophagitis

BACKGROUND & AIMS Topical corticosteroids are effective in inducing clinical and histologic remission in patients with eosinophilic esophagitis (EoE). However, the best long-term management strategy for this chronic inflammatory disease has not been determined. METHODS In a randomized, double-blind, placebo-controlled, 50-week trial, we evaluated in 28 patients the efficacy of twice-daily swallowed budesonide (0.25 mg each) to maintain quiescent EoE in remission. Pretreatment and posttreatment activity was assessed clinically, endoscopically, histologically, immunohistologically, and by endosonography. The primary end point was the therapys ability to maintain EoE in histologic remission. Secondary end points were efficacy in symptom control, prevention of tissue remodeling, and safety. RESULTS In patients given low-dose budesonide, the load of esophageal eosinophils increased from 0.4 to 31.8 eosinophils/high-power field (P = .017). In patients given placebo, the load increased from 0.7 to 65.0 eosinophils/high-power field (P = .0001); this increase was significantly greater than in patients given budesonide (P = .024). The symptom scores developed in a similar manner in the 2 groups. Budesonide, but not placebo, reduced noneosinophilic markers of inflammation, epithelial cell apoptosis, and remodeling events. Compared with control individuals, patients had significantly thickened esophageal walls, based on endosonography (3.05 vs 2.18 mm; P < .0001). Budesonide therapy was associated with a significant reduction in mucosal thickness (0.75-0.45 mm; P = .025), but epithelial thickness remained stable (261.22 vs 277.23 μm; P = .576). No serious adverse events occurred. CONCLUSIONS Low-dose budesonide is more effective than placebo in maintaining EoE in histologic and clinical remission. Signs of esophageal remodeling showed a trend toward normalization. Long-term administration of topical corticosteroids was well tolerated without induction of epithelial atrophy.

Esophageal Dilation in Eosinophilic Esophagitis: Effectiveness, Safety, and Impact on the Underlying Inflammation

OBJECTIVES:Esophageal dilation often leads to long-lasting relief of dysphagia in eosinophilic esophagitis (EoE). The aim of this study was to define the effectiveness, safety, and patient acceptance of esophageal dilation in EoE. In addition, we examined the influence of dilation on the underlying esophageal inflammation.METHODS:Two databases including 681 EoE patients were reviewed. Cohort 1 consisted of patients treated with dilation alone, whereas cohort 2 included patients treated with a combination of dilation and antieosinophilic medication. Patients from cohort 1 underwent a prospective histological reexamination and an evaluation using a questionnaire.RESULTS:In total, 207 EoE patients were treated with esophageal dilation, 63 in cohort 1 and 144 in cohort 2. Dilation led to a significant increase in esophageal diameter and to an improvement in dysphagia in both the cohorts (P<0.001). After dilation, dysphagia recurred after 23±22 months in cohort 1 and 20±14 months in cohort 2. No esophageal perforation or major bleeding occurred. Among the patients surveyed, 74% reported retrosternal pain after dilation; however, all were agreeable to repeated dilation if required. Eosinophil peak infiltration, eosinophil load, and EoE-associated histological signs were not significantly affected by esophageal dilation.CONCLUSIONS:Esophageal dilation is highly effective in providing long-lasting symptom relief and can be performed safely with a high degree of patient acceptance. However, dilation is associated with postprocedural pain in most patients and does not influence the underlying inflammatory process. Symptom improvement despite persistence of inflammation suggests that tissue remodeling contributes substantially to symptom generation in EoE.

Caspase-8 is activated by cathepsin D initiating neutrophil apoptosis during the resolution of inflammation

In the resolution of inflammatory responses, neutrophils rapidly undergo apoptosis. We describe a new proapoptotic pathway in which cathepsin D directly activates caspase-8. Cathepsin D is released from azurophilic granules in neutrophils in a caspase-independent but reactive oxygen species–dependent manner. Under inflammatory conditions, the translocation of cathepsin D in the cytosol is blocked. Pharmacological or genetic inhibition of cathepsin D resulted in delayed caspase activation and reduced neutrophil apoptosis. Cathepsin D deficiency or lack of its translocation in the cytosol prolongs innate immune responses in experimental bacterial infection and in septic shock. Thus, we identified a new function of azurophilic granules that is in addition to their role in bacterial defense mechanisms: to regulate the life span of neutrophils and, therefore, the duration of innate immune responses through the release of cathepsin D.

Apoptotic Pathways Are Inhibited by Leptin Receptor Activation in Neutrophils

Leptin regulates food intake as well as metabolic, endocrine, and immune functions. It exerts proliferative and antiapoptotic activities in a variety of cell types, including T cells. Leptin also stimulates macrophages and neutrophils, and its production is increased during inflammation. In this study, we demonstrate that human neutrophils express leptin surface receptors under in vitro and in vivo conditions, and that leptin delays apoptosis of mature neutrophils in vitro. The antiapoptotic effects of leptin were concentration dependent and blocked by an anti-leptin receptor mAb. The efficacy of leptin to block neutrophil apoptosis was similar to G-CSF. Using pharmacological inhibitors, we obtained evidence that leptin initiates a signaling cascade involving PI3K- and MAPK-dependent pathways in neutrophils. Moreover, leptin delayed the cleavage of Bid and Bax, the mitochondrial release of cytochrome c and second mitochondria-derived activator of caspase, as well as the activation of both caspase-8 and caspase-3 in these cells. Taken together, leptin is a survival cytokine for human neutrophils, a finding with potential pathologic relevance in inflammatory diseases.

Calpain-1 Regulates Bax and Subsequent Smac-dependent Caspase-3 Activation in Neutrophil Apoptosis

In the absence and in the resolution of inflammatory responses, neutrophils rapidly undergo spontaneous apoptosis. Here we report about a new apoptosis pathway in these cells that requires calpain-1 activation and is essential for the enzymatic activation of the critical effector caspase-3. Decreased levels of calpastatin, a highly specific intrinsic inhibitor of calpain, resulted in activation of calpain-1, but not calpain-2, in neutrophils undergoing apoptosis, a process that was blocked by a specific calpain-1 inhibitor or by intracellular delivery of a calpastatin peptide. Further support for the importance of the calpastatin-calpain system was obtained by analyzing neutrophils from patients with cystic fibrosis that exhibited delayed apoptosis, associated with markedly increased calpastatin and decreased calpain-1 protein levels compared with neutrophils from control individuals. Additional studies were designed to place calpain-1 into the hierarchy of biochemical events leading to neutrophil apoptosis. Pharmacological calpain inhibition during spontaneous and Fas receptor-induced neutrophil apoptosis prevented cleavage of Bax into an 18-kDa fragment unable to interact with Bcl-xL. Moreover, calpain blocking prevented the mitochondrial release of cytochrome c and Smac, which was indispensable for caspase-3 processing and enzymatic activation, both in the presence and absence of agonistic anti-Fas receptor antibodies. Taken together, calpastatin and calpain-1 represent critical proximal elements in a cascade of pro-apoptotic events leading to Bax, mitochondria, and caspase-3 activation, and their altered expression appears to influence the life span of neutrophils under pathologic conditions.

Cathepsins and their involvement in immune responses

The immune system is composed of an enormous variety of cells and molecules that generate a collective and coordinated response on exposure to foreign antigens, called the immune response. Within the immune response, endo-lysosomal proteases play a key role. In this review we cover specific roles of cathepsins in innate and adaptive immunity, as well as their implication in the pathogenesis of several diseases.