Thomas Brunner

Bio: Thomas Brunner is an academic researcher from University of Konstanz. The author has contributed to research in topics: Apoptosis & Medicine. The author has an hindex of 75, co-authored 448 publications receiving 23438 citations. Previous affiliations of Thomas Brunner include University Medical Center Freiburg & University of Oxford.

Fas Ligand-Induced Apoptosis as a Mechanism of Immune Privilege

Abstract: The eye is a privileged site that cannot tolerate destructive inflammatory responses. Inflammatory cells entering the anterior chamber of the eye in response to viral infection underwent apoptosis that was dependent on Fas (CD95)-Fas ligand (FasL) and produced no tissue damage. In contrast, viral infection in gld mice, which lack functional FasL, resulted in an inflammation and invasion of ocular tissue without apoptosis. Fas-positive but not Fas-negative tumor cells were killed by apoptosis when placed within isolated anterior segments of the eyes of normal but not FasL-negative mice. FasL messenger RNA and protein were detectable in the eye. Thus, Fas-FasL interactions appear to be an important mechanism for the maintenance of immune privilege.

Cell-autonomous Fas (CD95)/Fas-ligand interaction mediates activation-induced apoptosis in T-cell hybridomas

Abstract: A number of murine T-cell hybridomas undergo apoptosis within a few hours of activation by specific antigens, mitogens, antibodies against the T-cell antigen receptor, or a combination of phorbol ester and calcium ionophore. This phenomenon has been extensively studied as a model for clonal deletion in the immune system, in which potentially autoreactive T cells eliminate themselves by apoptosis after activation, either in the thymus or in the periphery. Here we show that the Fas/CD95 receptor, which can transduce a potent apoptotic signal when ligand, is rapidly expressed following activation of T-cell hybridomas, as is its functional, membrane-bound ligand. Interference with the ensuing Fas/Fas-ligand interaction inhibits activation-induced apoptosis. Because T-cell receptor ligation can induce apoptosis in a single T hybridoma cell, we suggest that the Fas/Fas-ligand interaction can induce cell death in a cell-autonomous manner.

Calpain-mediated cleavage of Atg5 switches autophagy to apoptosis.

Abstract: Autophagy-related gene (Atg) 5 is a gene product required for the formation of autophagosomes. Here, we report that Atg5, in addition to the promotion of autophagy, enhances susceptibility towards apoptotic stimuli. Enforced expression of Atg5-sensitized tumour cells to anticancer drug treatment both in vitro and in vivo. In contrast, silencing the Atg5 gene with short interfering RNA (siRNA) resulted in partial resistance to chemotherapy. Apoptosis was associated with calpain-mediated Atg5 cleavage, resulting in an amino-terminal cleavage product with a relative molecular mass of 24,000 (Mr 24K). Atg5 cleavage was observed independent of the cell type and the apoptotic stimulus, suggesting that calpain activation and Atg5 cleavage are general phenomena in apoptotic cells. Truncated Atg5 translocated from the cytosol to mitochondria, associated with the anti-apoptotic molecule Bcl-xL and triggered cytochrome c release and caspase activation. Taken together, calpain-mediated Atg5 cleavage provokes apoptotic cell death, therefore, represents a molecular link between autophagy and apoptosis--a finding with potential importance for clinical anticancer therapies.

Induction of human IgE synthesis in B cells by mast cells and basophils

Abstract: Immunoglobulin E (IgE) is central to the induction of allergic diseases through its binding to the high-affinity receptor (Fc epsilon R1) on mast cells and basophils. Crosslinking by allergens of the bound IgE leads to the release of various inflammatory mediators. IgE production by B cells requires a physical interaction with T cells, involving a number of surface adhesion molecules, as well as the soluble factors interleukin-4 (IL-4) and IL-13 (ref. 5) produced by T cells, basophils and mast cells. Here we report that, in the presence of IL-4, mast and basophilic cell lines can provide the cell contact signals that are required for IgE synthesis. The human cell lines HMC-1 (mast) and KU812 (basophilic) both express the ligand for CD40 (CD40L) which is shown to be responsible for the IgE production. Moreover, freshly isolated purified human lung mast cells and blood basophils are also shown to express CD40L and to induce IgE production. This evidence suggests that mast cells and basophils may therefore play a key role in allergy not only by producing inflammatory mediators, but also by directly regulating IgE production independently of T cells.

Apoptosis: A Review of Programmed Cell Death

Abstract: The process of programmed cell death, or apoptosis, is generally characterized by distinct morphological characteristics and energy-dependent biochemical mechanisms. Apoptosis is considered a vital component of various processes including normal cell turnover, proper development and functioning of the immune system, hormone-dependent atrophy, embryonic development and chemical-induced cell death. Inappropriate apoptosis (either too little or too much) is a factor in many human conditions including neurodegenerative diseases, ischemic damage, autoimmune disorders and many types of cancer. The ability to modulate the life or death of a cell is recognized for its immense therapeutic potential. Therefore, research continues to focus on the elucidation and analysis of the cell cycle machinery and signaling pathways that control cell cycle arrest and apoptosis. To that end, the field of apoptosis research has been moving forward at an alarmingly rapid rate. Although many of the key apoptotic proteins have been identified, the molecular mechanisms of action or inaction of these proteins remain to be elucidated. The goal of this review is to provide a general overview of current knowledge on the process of apoptosis including morphology, biochemistry, the role of apoptosis in health and disease, detection methods, as well as a discussion of potential alternative forms of apoptosis.

Autophagy fights disease through cellular self-digestion

Abstract: Autophagy, or cellular self-digestion, is a cellular pathway involved in protein and organelle degradation, with an astonishing number of connections to human disease and physiology. For example, autophagic dysfunction is associated with cancer, neurodegeneration, microbial infection and ageing. Paradoxically, although autophagy is primarily a protective process for the cell, it can also play a role in cell death. Understanding autophagy may ultimately allow scientists and clinicians to harness this process for the purpose of improving human health.

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

Abstract: In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure flux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation, it is imperative to target by gene knockout or RNA interference more than one autophagy-related protein. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways implying that not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular assays, we hope to encourage technical innovation in the field.