9 research outputs found
Mitochondria and inflammation: cell death heats up
Mitochondrial outer membrane permeabilization (MOMP) is essential to initiate mitochondrial apoptosis. Due to the disruption of mitochondrial outer membrane integrity, intermembrane space proteins, notably cytochrome c, are released into the cytosol whereupon they activate caspase proteases and apoptosis. Beyond its well-established apoptotic role, MOMP has recently been shown to display potent pro-inflammatory effects. These include mitochondrial DNA dependent activation of cGAS-STING signaling leading to a type I interferon response. Secondly, via an IAP-regulated mechanism, MOMP can engage pro-inflammatory NF-ÎșB signaling. During cell death, apoptotic caspase activity inhibits mitochondrial dependent inflammation. Importantly, by engaging an immunogenic form of cell death, inhibiting caspase function can effectively inhibit tumorigenesis. Unexpectedly, these studies reveal mitochondria as inflammatory signaling hubs during cell death and demonstrate its potential for therapeutic exploitation
Mitochondria and cell death-associated inflammation
Mitochondria have recently emerged as key drivers of inflammation associated with cell death. Many of the pro-inflammatory pathways activated during cell death occur upon mitochondrial outer membrane permeabilization (MOMP), the pivotal commitment point to cell death during mitochondrial apoptosis. Permeabilised mitochondria trigger inflammation, in part, through the release of mitochondrial-derived damage-associated molecular patterns (DAMPs). Caspases, while dispensable for cell death during mitochondrial apoptosis, inhibit activation of pro-inflammatory pathways after MOMP. Some of these mitochondrial-activated inflammatory pathways can be traced back to the bacterial ancestry of mitochondria. For instance, mtDNA and bacterial DNA are highly similar thereby activating similar cell autonomous immune signalling pathways. The bacterial origin of mitochondria suggests that inflammatory pathways found in cytosol-invading bacteria may be relevant to mitochondrial-driven inflammation after MOMP. In this review, we discuss how mitochondria can initiate inflammation during cell death highlighting parallels with bacterial activation of inflammation. Moreover, we discuss the roles of mitochondrial inflammation during cell death and how these processes may potentially be harnessed therapeutically, for instance to improve cancer treatment
A stromal lysolipid-autotaxin signaling axis promotes pancreatic tumor progression
Pancreatic ductal adenocarcinoma (PDAC) develops a pronounced stromal response reflecting an aberrant wound-healing process. This stromal reaction features transdifferentiation of tissue-resident pancreatic stellate cells (PSC) into activated cancer-associated fibroblasts, a process induced by PDAC cells but of unclear significance for PDAC progression. Here, we show that PSCs undergo a dramatic lipid metabolic shift during differentiation in the context of pancreatic tumorigenesis, including remodeling of the intracellular lipidome and secretion of abundant lipids in the activated, fibroblastic state. Specifically, stroma-derived lysophosphatidylcholines support PDAC cell synthesis of phosphatidylcholines, key components of cell membranes, and also facilitate production of the potent wound-healing mediator lysophosphatidic acid (LPA) by the extracellular enzyme autotaxin, which is overexpressed in PDAC. The autotaxinâLPA axis promotes PDAC cell proliferation, migration, and AKT activation, and genetic or pharmacologic autotaxin inhibition suppresses PDAC growth in vivo. Our work demonstrates how PDAC cells exploit the local production of wound-healing mediators to stimulate their own growth and migration. Significance: Our work highlights an unanticipated role for PSCs in producing the oncogenic LPA signaling lipid and demonstrates how PDAC tumor cells co-opt the release of wound-healing mediators by neighboring PSCs to promote their own proliferation and migration
Understanding the immunogenicity of caspase-independent cell death
Abstract not currently available
Discovery of pyridoxal reductase activity as part of human vitamin B6 metabolism
BACKGROUND: Pyridoxal 5'-phosphate (PLP) is the active form of vitamin B6. Mammals cannot synthesize vitamin B6, so they rely on dietary uptake of the different B6 forms, and via the B6 salvage pathway they interconvert them into PLP. Humans possess three enzymes in this pathway: pyridoxal kinase, pyridox(am)ine phosphate oxidase and pyridoxal phosphatase. Besides these, a fourth enzyme has been described in plants and yeast but not in humans: pyridoxal reductase. METHODS: We analysed B6 vitamers in remnant CSF samples of PLP-treated patients and four mammalian cell lines (HepG2, Caco2, HEK293 and Neuro-2a) supplemented with PL as the sole source of vitamin B6. RESULTS: Strong accumulation of pyridoxine (PN) in CSF of PLP-treated patients was observed, suggesting the existence of a PN-forming enzyme. Our in vitro studies show that all cell lines reduce PL to PN in a time- and dose-dependent manner. We compared the amino acid sequences of known PL reductases to human sequences and found high homology for members of the voltage-gated potassium channel beta subunits and the human aldose reductases. Pharmacological inhibition and knockout of these proteins show that none of the candidates is solely responsible for PL reduction to PN. CONCLUSIONS: We show evidence for the presence of PL reductase activity in humans. Further studies are needed to identify the responsible protein. GENERAL SIGNIFICANCE: This study expands the number of enzymes with a role in B6 salvage pathway. We hypothesize a protective role of PL reductase(s) by limiting the intracellular amount of free PL and PLP
Mitochondrial dynamics regulate genome stability via control of caspase-dependent DNA damage
Mitochondrial dysfunction is interconnected with cancer. Nevertheless, how defective mitochondria promote cancer is poorly understood. We find that mitochondrial dysfunction promotes DNA damage under conditions of increased apoptotic priming. Underlying this process, we reveal a key role for mitochondrial dynamics in the regulation of DNA damage and genome instability. The ability of mitochondrial dynamics to regulate oncogenic DNA damage centers upon the control of minority mitochondrial outer membrane permeabilization (MOMP), a process that enables non-lethal caspase activation leading to DNA damage. Mitochondrial fusion suppresses minority MOMP and its associated DNA damage by enabling homogeneous mitochondrial expression of anti-apoptotic BCL-2 proteins. Finally, we find that mitochondrial dysfunction inhibits pro-apoptotic BAX retrotranslocation, causing BAX mitochondrial localization and thereby promoting minority MOMP. Unexpectedly, these data reveal oncogenic effects of mitochondrial dysfunction that are mediated via mitochondrial dynamics and caspase-dependent DNA damage
Mitochondrial outer membrane integrity regulates a ubiquitin-dependent and NF-ÎșB-mediated inflammatory response
Mitochondrial outer membrane permeabilisation (MOMP) is often essential for apoptosis, by enabling cytochrome c release that leads to caspase activation and rapid cell death. Recently, MOMP has been shown to be inherently pro-inflammatory with emerging cellular roles, including its ability to elicit anti-tumour immunity. Nonetheless, how MOMP triggers inflammation and how the cell regulates this remains poorly defined. We find that upon MOMP, many proteins localised either to inner or outer mitochondrial membranes are ubiquitylated in a promiscuous manner. This extensive ubiquitylation serves to recruit the essential adaptor molecule NEMO, leading to the activation of pro-inflammatory NF-ÎșB signalling. We show that disruption of mitochondrial outer membrane integrity through different means leads to the engagement of a similar pro-inflammatory signalling platform. Therefore, mitochondrial integrity directly controls inflammation, such that permeabilised mitochondria initiate NF-ÎșB signalling
GLS hyperactivity causes glutamate excess, infantile cataract and profound developmental delay
Loss-of-function mutations in glutaminase (GLS), the enzyme converting glutamine into glutamate, and the counteracting enzyme glutamine synthetase (GS) cause disturbed glutamate homeostasis and severe neonatal encephalopathy. We report a de novo Ser482Cys gain-of-function variant in GLS encoding GLS associated with profound developmental delay and infantile cataract. Functional analysis demonstrated that this variant causes hyperactivity and compensatory downregulation of GLS expression combined with upregulation of the counteracting enzyme GS, supporting pathogenicity. Ser482Cys-GLS likely improves the electrostatic environment of the GLS catalytic site, thereby intrinsically inducing hyperactivity. Alignment of +/-12.000 GLS protein sequences from >1000 genera revealed extreme conservation of Ser482 to the same degree as catalytic residues. Together with the hyperactivity, this indicates that Ser482 is evolutionarily preserved to achieve optimal-but submaximal-GLS activity. In line with GLS hyperactivity, increased glutamate and decreased glutamine concentrations were measured in urine and fibroblasts. In the brain (both grey and white matter), glutamate was also extremely high and glutamine was almost undetectable, demonstrated with magnetic resonance spectroscopic imaging at clinical field strength and subsequently supported at ultra-high field strength. Considering the neurotoxicity of glutamate when present in excess, the strikingly high glutamate concentrations measured in the brain provide an explanation for the developmental delay. Cataract, a known consequence of oxidative stress, was evoked in zebrafish expressing the hypermorphic Ser482Cys-GLS and could be alleviated by inhibition of GLS. The capacity to detoxify reactive oxygen species was reduced upon Ser482Cys-GLS expression, providing an explanation for cataract formation. In conclusion, we describe an inborn error of glutamate metabolism caused by a GLS hyperactivity variant, illustrating the importance of balanced GLS activity
GLS hyperactivity causes glutamate excess, infantile cataract and profound developmental delay
Loss-of-function mutations in glutaminase (GLS), the enzyme converting glutamine into glutamate, and the counteracting enzyme glutamine synthetase (GS) cause disturbed glutamate homeostasis and severe neonatal encephalopathy. We report a de novo Ser482Cys gain-of-function variant in GLS encoding GLS associated with profound developmental delay and infantile cataract. Functional analysis demonstrated that this variant causes hyperactivity and compensatory downregulation of GLS expression combined with upregulation of the counteracting enzyme GS, supporting pathogenicity. Ser482Cys-GLS likely improves the electrostatic environment of the GLS catalytic site, thereby intrinsically inducing hyperactivity. Alignment of +/-12.000 GLS protein sequences from >1000 genera revealed extreme conservation of Ser482 to the same degree as catalytic residues. Together with the hyperactivity, this indicates that Ser482 is evolutionarily preserved to achieve optimal-but submaximal-GLS activity. In line with GLS hyperactivity, increased glutamate and decreased glutamine concentrations were measured in urine and fibroblasts. In the brain (both grey and white matter), glutamate was also extremely high and glutamine was almost undetectable, demonstrated with magnetic resonance spectroscopic imaging at clinical field strength and subsequently supported at ultra-high field strength. Considering the neurotoxicity of glutamate when present in excess, the strikingly high glutamate concentrations measured in the brain provide an explanation for the developmental delay. Cataract, a known consequence of oxidative stress, was evoked in zebrafish expressing the hypermorphic Ser482Cys-GLS and could be alleviated by inhibition of GLS. The capacity to detoxify reactive oxygen species was reduced upon Ser482Cys-GLS expression, providing an explanation for cataract formation. In conclusion, we describe an inborn error of glutamate metabolism caused by a GLS hyperactivity variant, illustrating the importance of balanced GLS activity