Phenotypic Expansion of DGKE-Associated Diseases

Westland, Rik; Bodria, Monica; Carrea, Alba; Lata, Sneh; Scolari, Francesco; Frémeaux‐Bacchi, Véronique; D’Agati, Vivette D.; Lifton, Richard P.; Gharavi, Ali G.; Ghiggeri, Gian Marco; Sanna‐Cherchi, Simone

doi:10.1681/asn.2013080886

Cited by 59 publications

(63 citation statements)

References 25 publications

(26 reference statements)

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“…However, 20% to 30% of aHUS patients do not exhibit any complement gene mutation, suggesting that the etiology of aHUS is diverse and that our understanding of its pathophysiologic mechanisms still remains incomplete. This was recently highlighted by the identification of recessive forms of aHUS linked to DGKE deficiency, 16,17 which is not directly related to the complement cascade. Here, we studied the role of DGKe in EC responses and demonstrated that its expression is critical to maintain EC integrity and normal angiogenesis, because DGKe deficiency impairs EC angiogenic responses and promotes an activated and prothrombotic state of these cells.…”

Section: Discussionmentioning

confidence: 99%

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Loss of DGKε induces endothelial cell activation and death independently of complement activation

Bruneau

Néel

Roumenina

et al. 2015

Blood

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Key Points• Loss of DGKe in endothelial cells induces cell death, impairs angiogenic responses, and leads to an activated and prothrombotic phenotype.• DGKE silencing in resting endothelial cells does not affect complement activation at their surface.Atypical hemolytic uremic syndrome (aHUS) is classically described to result from a dysregulation of the complement alternative pathway, leading to glomerular endothelial cell (EC) damage and thrombosis. However, recent findings in families with aHUS of mutations in the DGKE gene, which is not an integral component of the complement cascade, led us to consider other pathophysiologic mechanisms for this disease. Here, we demonstrate that loss of DGK« expression/activity in EC induces an increase in ICAM-1 and tissue factor expression through the upregulation of p38-MAPK-mediated signals, thus highlighting a proinflammatory and prothrombotic phenotype of DGK«-deficient ECs. More interestingly, DGKE silencing also increases EC apoptosis and impairs EC migration and angiogenesis in vitro, suggesting that DGKE loss-of-function mutations impair EC repair and angiogenesis in vivo. Conversely, DGKE knockdown moderately decreases the expression of the complement inhibitory protein MCP on quiescent EC, but does not induce complement deposition on their surface in vitro. Collectively, our data strongly suggest that in DGKE-associated aHUS patients, thrombotic microangiopathy results from impaired EC proliferation and angiogenesis rather than complement-mediated EC lesions. Our study expands the current knowledge of aHUS mechanisms and has implications for the treatment of patients with isolated DGKE mutations. (Blood. 2015;125(6):1038-1046 IntroductionAtypical hemolytic uremic syndrome (aHUS) is a severe form of thrombotic microangiopathy (TMA) that affects primarily the kidney. It is characterized by the occurrence of endothelial damage and fibrin/ platelet thrombi in the kidney microvasculature, leading to its typical triad of hemolytic microangiopathic anemia, thrombocytopenia, and acute renal injury.1 aHUS has a poor prognosis, with a 2% to 10% mortality rate, and about two-thirds of patients progress toward end-stage renal disease, and there is a high risk of recurrence of the disease after kidney transplantation.2 Over the past decade, many studies have highlighted the central role of complement alternative pathway dysregulations in the development of aHUS. [3][4][5] Several mutations in genes encoding complement regulatory proteins (factor H, 6 MCP, 7 factor I, 8 thrombomodulin 9 ) or components of the alternative C3 convertase (C3, 10 factor B 11 ), as well as the presence of circulating inhibitory anti-factor H antibodies, 12 have been shown to predispose to the development of aHUS. It is currently assumed that complement alternative pathway activation triggered mainly by infection or pregnancy 13 leads to endothelial cell (EC) damage and TMA. These observations led to the development of complement-targeted therapies for the treatment of aHUS, 14 and eculizumab, a mo...

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Section: Discussionmentioning

confidence: 99%

“…Complement activation in patients with DGKE mutations is variable, 16,17 suggesting that DGKE loss of function may be in itself the main trigger of TMA. Little data are available regarding the role of DGKe in EC, which adds to the complexity of the physiopathology of DGKE-related aHUS.…”

mentioning

confidence: 99%

Loss of DGKε induces endothelial cell activation and death independently of complement activation

Bruneau

Néel

Roumenina

et al. 2015

Blood

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“…First, this mutation cosegregates with disease following a recessive pattern in both families: it is homozygous for family 1 and compound heterozygous for family 2 in concert with a known nonsense DGKE mutation (14). Second, the probability of having by chance two unrelated kindreds with phenotype concordant with that of DGKE-associated aHUS (14,17) and the same novel intronic mutation is very low. Third, we demonstrate that this intronic mutation acts as a neo-splice site that not only results in the transcription of mutant mRNA isoforms predicted to be deleterious to DGKE catalytic activity, but also completely abrogates wild-type DGKE mRNA transcription.…”

Section: Discussionmentioning

confidence: 99%

“…However, this assumption has been challenged by the report of a DGKE-truncating mutation in two patients with moderate C3 consumption (17). The recent finding of combined DGKE and complement gene mutations in three patients suggests that complement dysregulation may have a role in modulating disease severity in DGKE mutation carriers (18).…”

Section: Introductionmentioning

confidence: 99%

Characterization of a New DGKE Intronic Mutation in Genetically Unsolved Cases of Familial Atypical Hemolytic Uremic Syndrome

Mele¹,

Lemaire²,

Iatropoulos³

et al. 2015

Clinical Journal of the American Society of Nephrology

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Background and objectives Genetic and acquired abnormalities causing dysregulation of the complement alternative pathway contribute to atypical hemolytic uremic syndrome (aHUS), a rare disorder characterized by thrombocytopenia, nonimmune microangiopathic hemolytic anemia, and acute kidney failure. However, in a substantial proportion of patients the disease-associated alterations are still unknown.Design, setting, participants, & measurements Whole-exome and whole-genome sequencing were performed in two unrelated families with infantile recessive aHUS. Sequencing of cDNA from affected individuals was used to test for the presence of aberrant mRNA species. Expression of mutant diacylglycerol kinase epsilon (DGKE) protein was evaluated with western blotting.Results Whole-exome sequencing analysis with conventional variant filtering parameters did not reveal any obvious candidate mutation in the first family. The report of aHUS-associated mutations in DGKE, encoding DGKE, led to re-examination of the noncoding DGKE variants obtained from next-generation sequencing, allowing identification of a novel intronic DGKE mutation (c.888+40A.G) that segregated with disease. Sequencing of cDNA from affected individuals revealed aberrant forms of DGKE mRNA predicted to cause profound abnormalities in the protein catalytic site. By whole-genome sequencing, the same mutation was found in compound heterozygosity with a second nonsense DGKE mutation in all affected siblings of another unrelated family. Homozygous and compound heterozygous patients presented similar clinical features, including aHUS presentation in the first year of life, multiple relapsing episodes, and proteinuria, which are prototypical of DGKE-associated aHUS.Conclusions This is the first report of a mutation located beyond the exon-intron boundaries in aHUS. Intronic mutations such as these are underreported because conventional filtering parameters used to process nextgeneration sequencing data routinely exclude these regions from downstream analyses in both research and clinical settings. The results suggest that analysis of noncoding regions of aHUS-associated genes coupled with mRNA sequencing might provide a tool to explain genetically unsolved aHUS cases.

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“…The authors aimed to determine the contribution of diacylglycerol kinase « (DGK«) mutations to aHUS in this Spanish population. DGK« is the most recent gene causally related to aHUS (8)(9)(10). The novelty of this discovery resides in the presumed mechanism by which DGK« causes aHUS.…”

Section: On the Verge Of A Revolutionmentioning

confidence: 99%