Mutations in membrane cofactor protein (CD46) gene in Indian children with hemolytic uremic syndrome

Anti-factor B antibodies in atypical hemolytic uremic syndrome

BACKGROUND

The etiology of atypical hemolytic uremic syndrome (aHUS) is unknown in 30-40% of patients. Anti-factor B (FB) antibodies are reported in C3 glomerulopathy (C3G) and immune-complex membranoproliferative glomerulonephritis (IC-MPGN), though not in aHUS.

METHODS

We screened patients < 18-year-old from cohorts of aHUS and C3G/idiopathic IC-MPGN. Anti-FB IgG antibodies were measured by ELISA and confirmed by Western blot. Normative levels were based on antibody levels in 103 healthy blood donors.

RESULTS

Prevalence of anti-FB antibodies was 9.7% (95% CI 6.1-14.5%; n = 21) in 216 patients with aHUS, including 11.5% (95% CI 6.4-18.5%; n = 14) in anti-FH associated aHUS and 11.8% (95% CI 4.4-23.9%; n = 6) in patients without a definitive genetic or autoimmune etiology. Patients with significant genetic variants did not show anti-FB antibodies. In patients with concomitant anti-FB and anti-FH antibodies, median anti-FH titers were higher (11,312 AU/mL vs. 4920 AU/mL; P = 0.04). Anti-FB antibody titer correlated with disease severity (hemoglobin and platelets; P < 0.05), declined following plasma exchange and increased during relapse. While 4/64 patients with C3G (6.3%) and 1/17 with IC-MPGN showed anti-FB antibodies, titers were higher in aHUS (544.8 AU/mL vs. 1028.8 AU/mL; P = 0.003).

CONCLUSION

Anti-FB antibodies are present in 6-10% of patients with aHUS and C3G/IC-MPGN, with higher titers in the former. The diagnostic and therapeutic implication of anti-FB antibodies in aHUS needs confirmation and further studies. The study shows propensity for autoantibody generation and co-existence of multiple risk factors for aHUS in Indian children.

Atypical HUS with multiple complement system mutations triggered by synthetic psychoactive drug abuse: a case report

Atypical hemolytic uremic syndrome is a rare disorder with an estimated annual incidence of about two cases per million in the adult population. It is caused by the overactivation of the alternative pathway of the complement system. The disease can be triggered by many factors, including pregnancy, viral diseases, and sepsis; approximately 30% of atypical hemolytic uremic syndrome cases are caused by unknown processes. We present a case of a patient with C3-complement system mutations and aHUS triggered by the use of a new synthetic psychoactive drug.

Novel homozygous CD46 variant with C-isoform expression affects C3b inactivation in atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy that may lead to organ failure. Dysregulation of the complement system can cause aHUS, and various disease-related variants in the complement regulatory protein CD46 are described. We here report a pediatric patient with aHUS carrying a hitherto unreported homozygous variant in CD46 (NM_172359.3:c.602C>T p.(Ser201Leu)). In our functional analyses, this variant caused complement dysregulation through three separate mechanisms. First, CD46 surface expression on the patient's blood cells was significantly reduced. Second, stably expressing CD46(Ser201Leu) cells bound markedly less to patterns of C3b than CD46 WT cells. Third, the patient predominantly expressed the rare isoforms of CD46 (C dominated) instead of the more common isoforms (BC dominated). Using BC1 and C1 expressing cell lines, we found that the C1 isoform bound markedly less C3b than the BC1 isoform. These results highlight the coexistence of multiple mechanisms that may act synergistically to disrupt CD46 function during aHUS development.

Membrane cofactor protein (MCP; CD46): deficiency states and pathogen connections

Membrane cofactor protein (MCP; CD46), a ubiquitously expressed complement regulatory protein, serves as a cofactor for serine protease factor I to cleave and inactivate C3b and C4b deposited on host cells. However, CD46 also plays roles in human reproduction, autophagy, modulating T cell activation and effector functions and is a member of the newly identified intracellular complement system (complosome). CD46 also is a receptor for 11 pathogens ('pathogen magnet'). While CD46 deficiencies contribute to inflammatory disorders, its overexpression in cancers and role as a receptor for some adenoviruses has led to its targeting by oncolytic agents and adenoviral-based therapeutic vectors, including coronavirus disease of 2019 (COVID-19) vaccines. This review focuses on recent advances in identifying disease-causing CD46 variants and its pathogen connections.

CD46 splice variant enhances translation of specific mRNAs linked to an aggressive tumor cell phenotype in bladder cancer

CD46 is well known to be involved in diverse biological processes. Although several splice variants of CD46 have been identified, little is known about the contribution of alternative splicing to its tumorigenic functions. In this study, we found that exclusion of CD46 exon 13 is significantly increased in bladder cancer (BCa) samples. In BCa cell lines, enforced expression of CD46-CYT2 (exon 13-skipping isoform) promoted, and CD46-CYT1 (exon 13-containing isoform) attenuated, cell growth, migration, and tumorigenicity in a xenograft model. We also applied interaction proteomics to identify exhaustively the complexes containing the CYT1 or CYT2 domain in EJ-1 cells. 320 proteins were identified that interact with the CYT1 and/or CYT2 domain, and most of them are new interactors. Using an internal ribosome entry site (IRES)-dependent reporter system, we established that CD46 could regulate mRNA translation through an interaction with the translation machinery. We also identified heterogeneous nuclear ribonucleoprotein (hnRNP)A1 as a novel CYT2 binding partner, and this interaction facilitates the interaction of hnRNPA1 with IRES RNA to promote IRES-dependent translation of HIF1a and c-Myc. Strikingly, the splicing factor SRSF1 is highly correlated with CD46 exon 13 exclusion in clinical BCa samples. Taken together, our findings contribute to understanding the role of CD46 in BCa development.

Anti-complement factor I antibody associated atypical hemolytic uremic syndrome - A new insight for future perspective!

Atypical hemolytic uremic syndrome (aHUS) is caused mainly by complement dysregulation. Although various defects in the complement system explaining pathophysiology have been described in recent years, the etiology still remains unclear in about thirty percent of cases. In exploring other causes, similar to anti- complement factor H (anti-CFH) antibody associated HUS, we hypothesized that anti-complement factor I (anti-CFI) antibody could play a role in aHUS. Further, we tried to describe the clinical profile and outcome of those with high anti CFI antibody titers. Eleven of thirty five children (31 %) diagnosed with aHUS from July 2017 to December 2018 had high IgG anti-CFI antibody titers. Median age was 10 months (6, 33) with no sex difference. Thirty-six percent (4/11) had nephrotic-range proteinuria. C3 was low in 8 children (72.7 %) with mean C3 (68.1 ± 14.7 mg/dL). Plasmapheresis was done in 2 children who promptly responded, suggesting the possible role of anti-CFI antibody in pathogenesis of aHUS in these patients. Further studies examining role of anti-CFI antibodies in aHUS is warranted with longitudinal and genetic studies.

Hemolytic uremic syndrome in a developing country: Consensus guidelines

BACKGROUND

Hemolytic uremic syndrome (HUS) is a leading cause of acute kidney injury in children. Although international guidelines emphasize comprehensive evaluation and treatment with eculizumab, access to diagnostic and therapeutic facilities is limited in most developing countries. The burden of Shiga toxin-associated HUS in India is unclear; school-going children show high prevalence of anti-factor H (FH) antibodies. The aim of the consensus meeting was to formulate guidelines for the diagnosis and management of HUS in children, specific to the needs of the country.

METHODS

Four workgroups performed literature review and graded research studies addressing (i) investigations, biopsy, genetics, and differential diagnosis; (ii) Shiga toxin, pneumococcal, and infection-associated HUS; (iii) atypical HUS; and (iv) complement blockade. Consensus statements developed by the workgroups were discussed during a consensus meeting in March 2017.

RESULTS

An algorithm for classification and evaluation was developed. The management of Shiga toxin-associated HUS is supportive; prompt plasma exchanges (PEX) is the chief therapy in patients with atypical HUS. Experts recommend that patients with anti-FH-associated HUS be managed with a combination of PEX and immunosuppressive medications. Indications for eculizumab include incomplete remission with plasma therapy, life-threatening features, complications of PEX or vascular access, inherited defects in complement regulation, and recurrence of HUS in allografts. Priorities for capacity building in regional and national laboratories are highlighted.

CONCLUSIONS

Limited diagnostic capabilities and lack of access to eculizumab prevent the implementation of international guidelines for HUS in most developing countries. We propose practice guidelines for India, which will perhaps be applicable to other developing countries.