Analysis of the promoters and 5'-UTR of mouse Cd59 genes, and of their functional activity in erythrocytes

Emerging role of complement in COVID-19 and other respiratory virus diseases

The complement system, a key component of innate immunity, provides the first line of defense against bacterial infection; however, the COVID-19 pandemic has revealed that it may also engender severe complications in the context of viral respiratory disease. Here, we review the mechanisms of complement activation and regulation and explore their roles in both protecting against infection and exacerbating disease. We discuss emerging evidence related to complement-targeted therapeutics in COVID-19 and compare the role of the complement in other respiratory viral diseases like influenza and respiratory syncytial virus. We review recent mechanistic studies and animal models that can be used for further investigation. Novel knockout studies are proposed to better understand the nuances of the activation of the complement system in respiratory viral diseases.

Mouse Cd59b but not Cd59a is upregulated to protect cells from complement attack in response to inflammatory stimulation

Universally expressed CD59 is the sole membrane complement regulatory protein that protects host cells from complement damage by restricting membrane attack complex assembly. The human gene encodes a single CD59, whereas the mouse gene encodes a duplicated CD59, comprising mCd59a and mCd59b, with distinct tissue distribution. Recently, we revealed that Sp1 regulates constitutive CD59 transcription and that canonical nuclear factor kappa light chain enhancer of activated B cells (NF-κB) and cyclic AMP-responsive element-binding protein (CREB) regulate inducible CD59 transcription. However, the mechanisms that underlie mCd59 regulation remain unclear. Here we demonstrate that Sp1 controls broadly distributed mCd59a expression, whereas serum response factor (SRF) and canonical NF-κB regulate selectively expressed mCd59b. Tumor necrosis factor-α in vitro and lipopolysaccharide in vivo remarkably enhance the expression of mCd59b but not mCd59a by activating SRF and NF-κB, thus protecting cells from complement attack. In addition, cAMP analog treatment also dramatically increases mCd59b but not mCd59a expression in a manner independent of CREB, SRF and NF-κB. Therefore, mCd59b but not mCd59a may be the responder to external inflammatory stimuli and may have an important role in complement-mediated mouse models of disease.

CD59 underlines the antiatherosclerotic effects of C-phycocyanin on mice

The effects of C-phycocyanin (C-PC) on atherosclerosis and the regulatory effects of CD59 gene on anti-atherosclerotic roles of C-PC were investigated. Apolipoprotein E knockout (ApoE(−/−)) mice were randomly divided into four groups: control group, C-PC treatment group, CD59 transfection group and C-PC+CD59 synergy group. The mice were fed with high-fat-diet and treated with drug intervention at the same time. Results showed the atherosclerotic mouse model was successfully established. CD59 was over-expressed in blood and tissue cells. Single CD59 or C-PC could reduce blood lipid levels and promote the expression of anti-apoptotic Bcl-2 but inhibit pro-apoptotic Fas proteins in endothelial cells. The expression levels of cell cycle protein D1 (Cyclin D1) and mRNA levels of cyclin dependent protein kinase 4 (CDK4) in smooth muscle cells were restrained by CD59 and C-PC. CD59 or C-PC alone could inhibit the formation of atherosclerotic plaque by suppressing MMP-2 protein expression. In addition, C-PC could promote CD59 expression. So both CD59 and C-PC could inhibit the progress of atherosclerosis, and the anti-atherosclerotic effects of C-PC might be fulfilled by promoting CD59 expression, preventing smooth muscle cell proliferation and the apoptosis of endothelial cells, reducing blood fat levels, and at last inhibiting the development of atherosclerosis.

Cell surface complement regulators moderate experimental myasthenia gravis pathology

INTRODUCTION

Intrinsic mouse complement regulators influence the severity of passively induced experimental acquired myasthenia gravis (EAMG). To assess the potential influence of CD59b in the absence of CD59a background, we used the mCD59ab(-/-) mouse model to re-evaluate mCD59 in protecting the neuromuscular junction (NMJ).

METHODS

EAMG was induced with monoclonal antibody to the acetylcholine receptor (AChR) in Daf1(-/-) , CD59ab(-/-) , Daf1(-/-) CD59ab(-/-) , and wild-type C57Bl/6 mice. Animals were monitored throughout the experiment. Diaphragms were analyzed for NMJ injury.

RESULTS

Daf1(-/-) CD59ab(-/-) mice required euthanasia 24 hours after disease induction because of severe weakness. Histological assessment demonstrated reduced AChR density, simplification of synaptic folds, and disrupted mitochondria. CD59ab-deficient mice demonstrated mild weakness and reduction in weight after 24 hours. In contrast, Daf1(-/-) had more severe weakness at 60 hours. The NMJ of EAMG-induced Daf1(-/-) and CD59ab(-/-) mice demonstrated similar AChR density.

CONCLUSION

NMJs of CD59 and DAF mice are protected from complement-mediated injury of passive EAMG.

DAF/CD55 and Protectin/CD59 modulate adaptive immunity and disease outcome in experimental autoimmune myasthenia gravis

The role of regulators of complement activity (RCA) involving CD55 and CD59 in the pathogenesis of experimental autoimmune myasthenia gravis (EAMG) remains unclear. CD55 and CD59 restrict complement activation by inhibiting C3/C5 convertases' activities and membrane attack complex formation, respectively. Actively immunized EAMG mice deficient in either CD55 or CD59 showed significant differences in adaptive immune responses and worsened disease outcome associated with increased levels of serum cytokines, modified production of acetylcholine receptor antibodies, and more complement deposition at the neuromuscular junction. We conclude that modulation of complement activity by RCA represents an alternative in controlling of autoimmune processes in EAMG.

Balancing role of nitric oxide in complement-mediated activation of platelets from mCd59a and mCd59b double-knockout mice

CD59 is a membrane protein inhibitor of the membrane attack complex (MAC) of complement. mCd59 knockout mice reportedly exhibit hemolytic anemia and platelet activation. This phenotype is comparable to the human hemolytic anemia known as paroxysmal nocturnal hemoglobinuria (PNH), in which platelet activation and thrombosis play a critical pathogenic role. It has long been suspected but not formally demonstrated that both complement and nitric oxide (NO) contribute to PNH thrombosis. Using mCd59a and mCd59b double knockout mice (mCd59ab(-/-) mice) in complement sufficient (C3(+/+)) and deficient (C3(-/-)) backgrounds, we document that mCd59ab(-/-) platelets are sensitive to complement-mediated activation and provide evidence for possible in vivo platelet activation in mCd59ab(-/-) mice. Using a combination of L-NAME (a NO-synthase inhibitor) and NOC-18 or SNAP (NO-donors), we further demonstrate that NO regulates complement-mediated activation of platelets. These results indicate that the thrombotic diathesis of PNH patients could be due to a combination of increased complement-mediated platelet activation and reduced NO-bioavailability as a consequence of hemolysis.

Generation and phenotyping of mCd59a and mCd59b double-knockout mice

CD59 is a membrane protein inhibitor of the membrane attack complex (MAC) of complement. Humans express only one, whereas mice express two CD59 genes. We previously reported the targeted deletion of the mCd59b gene in which absence of mCd59b together with an unintended down regulation of mCd59a caused hemolytic anemia with spontaneous platelet activation. To confirm the complement role in the hemolytic anemia caused by abrogation of mCd59 function, we have developed a mCd59a and mCd59b double knock out mice and analyzed its phenotype in complement sufficient and deficient (C3(-/-)). We report here that total abrogation of mCd59 function in mCd59ab(-/-) mice results in complement-mediated hemolytic anemia that is rescued by the deficiency of C3 in compound mCd59ab(-/-)/C3(-/-) mice.

Complement regulator CD59 protects against atherosclerosis by restricting the formation of complement membrane attack complex

Complement is a central effector system within the immune system and is implicated in a range of inflammatory disorders. CD59 is a key regulator of complement membrane attack complex (MAC) assembly. The atherogenic role of terminal complement has long been suspected but is still unclear. Here, we demonstrate that among mice deficient in apolipoprotein (Apo)E, the additional loss of murine CD59 (mCd59ab(-/-)/ApoE(-/-)) accelerated advanced atherosclerosis featuring occlusive coronary atherosclerosis, vulnerable plaque, and premature death and that these effect could be attenuated by overexpression of human CD59 in the endothelium. Complement inhibition using a neutralizing anti-mouse C5 antibody attenuated atherosclerosis in mCd59ab(-/-)/ApoE(-/-) mice. Furthermore, MAC mediated endothelial damage and promoted foam cell formation. These combined results highlight the atherogenic role of MAC and the atheroprotective role of CD59 and suggest that inhibition of MAC formation may provide a therapeutic approach for the treatment of atherosclerosis.

Nonclassic functions of human topoisomerase I: genome-wide and pharmacologic analyses

The biological functions of nuclear topoisomerase I (Top1) have been difficult to study because knocking out TOP1 is lethal in metazoans. To reveal the functions of human Top1, we have generated stable Top1 small interfering RNA (siRNA) cell lines from colon and breast carcinomas (HCT116-siTop1 and MCF-7-siTop1, respectively). In those clones, Top1 is reduced approximately 5-fold and Top2alpha compensates for Top1 deficiency. A prominent feature of the siTop1 cells is genomic instability, with chromosomal aberrations and histone gamma-H2AX foci associated with replication defects. siTop1 cells also show rDNA and nucleolar alterations and increased nuclear volume. Genome-wide transcription profiling revealed 55 genes with consistent changes in siTop1 cells. Among them, asparagine synthetase (ASNS) expression was reduced in siTop1 cells and in cells with transient Top1 down-regulation. Conversely, Top1 complementation increased ASNS, indicating a causal link between Top1 and ASNS expression. Correspondingly, pharmacologic profiling showed L-asparaginase hypersensitivity in the siTop1 cells. Resistance to camptothecin, indenoisoquinoline, aphidicolin, hydroxyurea, and staurosporine and hypersensitivity to etoposide and actinomycin D show that Top1, in addition to being the target of camptothecins, also regulates DNA replication, rDNA stability, and apoptosis. Overall, our studies show the pleiotropic nature of human Top1 activities. In addition to its classic DNA nicking-closing functions, Top1 plays critical nonclassic roles in genomic stability, gene-specific transcription, and response to various anticancer agents. The reported cell lines and approaches described in this article provide new tools to perform detailed functional analyses related to Top1 function.

The mouse complement regulator CD59b is significantly expressed only in testis and plays roles in sperm acrosome activation and motility

In mouse, genes encoding complement regulators CD55 and CD59 have been duplicated. The first described form of CD59, CD59a, is broadly distributed in mouse tissues, while the later identified CD59b was originally described as testis specific. Subsequent studies have been contradictory, some reporting widespread and abundant expression of CD59b. Resolution of the distribution patterns of the CD59 isoforms is important for interpretation of disease studies utilising CD59 knockout mice. Here we have performed a comprehensive distribution study of the CD59 isoforms at the mRNA and protein levels. These data confirm that expression of CD59b is essentially restricted to adult testis; trace expression in other tissues is a consequence of contamination with blood cells, shown previously to express CD59b at low level. In testis, onset of expression of CD59b coincided with puberty and was predominant on the spermatozoal acrosome. Ligation of CD59b, but not CD59a, markedly reduced spermatozoal motility, suggesting a specific role in reproductive function.