Edited by Mike Shipston Transient receptor potential cation channel subfamily C member 6 (TRPC6) is a widely expressed ion channel. Gainof-function mutations in the human TRPC6 channel cause autosomal-dominant focal segmental glomerulosclerosis, but the molecular components involved in disease development remain unclear. Here, we found that overexpression of gainof-function TRPC6 channel variants is cytotoxic in cultured cells. Exploiting this phenotype in a genome-wide CRISPR/Cas screen for genes whose inactivation rescues cells from TRPC6associated cytotoxicity, we identified several proteins essential for TRPC6 protein expression, including the endoplasmic reticulum (ER) membrane protein complex transmembrane insertase. We also identified transmembrane protein 208 (TMEM208), a putative component of a signal recognition particle-independent (SND) ER protein-targeting pathway, as being necessary for expression of TRPC6 and several other ion channels and transporters. TRPC6 expression was also diminished by loss of the previously uncharacterized WD repeat domain 83 opposite strand (WDR83OS), which interacted with both TRPC6 and TMEM208. Additionally enriched among the screen hits were genes involved in N-linked protein glycosylation. Deletion of the mannosyl (␣-1,3-)-glycoprotein ␤-1,2-Nacetylglucosaminyltransferase (MGAT1), necessary for the generation of complex N-linked glycans, abrogated TRPC6 gain-of-function variant-mediated Ca 2؉ influx and extracellular signal-regulated kinase activation in HEK cells, but failed to diminish cytotoxicity in cultured podocytes. However, mutating the two TRPC6 N-glycosylation sites abrogated the cytotoxicity of mutant TRPC6 and reduced its surface expression. These results expand the targets of TMEM208-mediated ER translocation to include multipass transmembrane proteins and suggest that TRPC6 N-glycosylation plays multiple roles in modulating channel trafficking and activity.

Mucin-type O-linked glycosylation, a posttranslational modification affecting the stability and biophysical characteristics of proteins, requires C1GalT1 (T synthase) and its obligate, X-linked chaperone Cosmc. Hypomorphic C1GalT1 mutations cause renal failure via not yet established mechanisms. We hypothesize that impaired Cosmc-dependent O-glycosylation in podocytes is sufficient to cause disease. Podocyte-specific Cosmc knockout mice were generated and phenotyped to test this hypothesis. Female heterozygous mice displaying mosaic inactivation of Cosmc in podocytes due to random X-linked inactivation were also examined. Mice with podocyte-specific Cosmc deletion develop profound albuminuria, foot process effacement, glomerular sclerosis, progressive renal failure, and impaired survival. Glomerular transcriptome analysis reveals early changes in cell adhesion, extracellular matrix organization, and chemokine-mediated signaling pathways, coupled with podocyte loss. Expression of the O-glycoprotein podoplanin was lost, while Tn antigen, representing immature O-glycans, was most abundantly found on podocalyxin. In contrast to hemizygous male and homozygous female animals, heterozygous female mosaic animals developed only mild albuminuria, focal foot process effacement, and nonprogressive kidney disease. Ultrastructurally, Cosmc-deficient podocytes formed Tn antigen-positive foot processes interdigitating with those of normal podocytes but not with other Cosmc-deficient cells. This suggests a cell nonautonomous mechanism for mucin-type O-glycoproteins in maintaining podocyte function. In summary, our findings demonstrated an essential and likely cell nonautonomous role for mucin-type O-glycosylation for podocyte function.

Background: Performing adequately powered clinical trials in pediatric diseases such as systemic lupus erythematosus (SLE) is challenging. Improved recruitment strategies are needed for identifying patients. Design, Setting, Participants, and Measurements: Electronic health record (EHR) algorithms were developed and tested to identify children with SLE both with and without lupus nephritis. We used single center EHR data to develop computable phenotypes comprised of diagnosis, medication, procedure, and utilization codes. These were evaluated iteratively against a manually assembled SLE patient database. The highest performing phenotypes were then evaluated across institutions in PEDSnet, a national healthcare systems network of >6.7 million children. Reviewers blinded to case status used standardized forms to review random samples of cases (n=350) and non-cases (n=350). Results: Final algorithms consisted of both utilization and diagnostic criteria. For both, utilization criteria included ≥2 in-person visits with nephrology or rheumatology and ≥60 days follow-up. SLE diagnostic criteria included absence of neonatal lupus, ≥1 hydroxychloroquine exposure, and either ≥3 qualifying diagnosis codes separated by ≥30 days, or ≥1 diagnosis code and ≥1 kidney biopsy procedure code. Sensitivity was 100% (95%CI, 99-100); specificity, 92% (95% CI, 88-94); positive predictive value, 91% (95%CI, 87-94); negative predictive value, 100% (95%CI, 99-100). Lupus nephritis diagnostic criteria included either ≥3 qualifying lupus nephritis diagnosis codes (or SLE codes on same day as glomerular/kidney codes) separated by ≥30 days, or ≥1 SLE diagnosis code and ≥1 kidney biopsy procedure code. Sensitivity was 90% (95%CI, 85-94); specificity, 93% (95% CI, 89-97); positive predictive value, 94% (95%CI, 89-97); negative predictive value, 90% (95%CI, 84-94). Algorithms identified 1,508 children with SLE at PEDSnet institutions (537 with LN), 809 of whom were seen in the past 12 months. Conclusions: EHR-based algorithms for SLE and Lupus nephritis demonstrated excellent classification accuracy across PEDSnet institutions.

Purpose of review Acute kidney injury (AKI) in the setting of hematopoietic stem cell transplantation (HSCT) is common in pediatric and adult patients. The incidence ranges from 12 to 66%, and development of AKI in the posttransplant course is independently associated with higher mortality. Recent findings Patients who undergo HSCT have many risk factors for developing AKI, including sepsis, use of nephrotoxic medications, graft versus host disease (GVHD), and veno-occlusive disease (VOD). In addition, engraftment syndrome/cytokine storm, transplant-associated thrombotic microangiopathy (TA-TMA), and less common infections with specific renal manifestations, such as BK and adenovirus nephritis, may lead to kidney injury. There has been significant advancement in the understanding of TA-TMA in particular, especially the role of the complement system in its pathophysiology. The role of early dialysis has been explored in the pediatric population, but not well studied in adult HSCT recipients Summary This review provides an update on the risk factors, causes, and treatment approaches to HSCT-associated AKI. Video abstract http://links.lww.com/COCC/A29

Lupus nephritis (LN) is a life-threatening manifestation of systemic lupus erythematosus (SLE) and is more common in children than adults. The epidemiology and management of childhood-onset SLE (cSLE) have changed over time, prompting the need to reassess expected outcomes. The purpose of this study is to use the Childhood Arthritis and Rheumatology Research Alliance (CARRA) prospective registry to validate historical principles of LN in a contemporary, real-world cohort. After an extensive literature review, six principles of LN in cSLE were identified. The CARRA registry was queried to evaluate these principles in determining the rate of LN in cSLE, median time from cSLE diagnosis to LN, short-term renal outcomes, and frequency of rituximab as an induction therapy. Of the 677 cSLE patients in the CARRA registry, 32% had documented LN. Decline in kidney function was more common in Black cSLE patients than non-Black patients ( p = 0.04). Black race was associated with worse short-term renal outcomes. In short-term follow up, most children with LN had unchanged or improved kidney function, and end stage kidney disease (ESKD) was rare. Ongoing follow-up of cSLE patients in the CARRA registry will be necessary to evaluate long-term outcomes to inform risk, management, and prognosis of LN in cSLE.

The renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in a host of renal and cardiovascular functions. Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), drugs that disrupt RAAS function, are effective in treating hypertension and offer other renoprotective effects independent of blood pressure (BP) reduction. As our understanding of RAAS physiology and the feedback mechanisms of ACE inhibition and angiotensin receptor blockade have improved, questions have been raised as to whether combination ACEI/ARB therapy is warranted in certain patients with incomplete angiotensin blockade on one agent. In this review, we discuss the rationale for combination ACEI/ARB therapy and summarize the results of key adult studies and the limited pediatric literature that have investigated this therapeutic approach. We additionally review novel therapies that have been developed over the past decade as alternative approaches to combination ACEI/ARB therapy, or that may be potentially used in combination with ACEIs or ARBs, in which further adult and pediatric studies are needed.

Mutations in TRPC6 are a cause of autosomal dominant focal segmental glomerulosclerosis in humans. Many of these mutations are known to have a gain-of-function effect on the non-specific cation channel function of TRPC6. In vitro studies have suggested these mutations affect several signaling pathways, but in vivo studies have largely compared wild-type and Trpc6-deficient rodents. We developed mice carrying a gain-of-function Trpc6 mutation encoding an E896K amino acid change, corresponding to a known FSGS mutation in TRPC6. Homozygous mutant Trpc6 animals have no appreciable renal pathology, and do not develop albuminuria until very advanced age. The animals show a slight delay in recovery from the albumin overload model. In response to chronic angiotensin II infusion, the mice have slightly greater albuminuria initially compared to wild-type animals, an effect that is lost at later time points, and a statistically non-significant trend toward more glomerular injury. This phenotype is nearly opposite to that of Trpc6-deficient animals previously described. The Trpc6 mutation does not appreciably impact renal interstitial fibrosis in response to either angiotensin II infusion, or folate-induced kidney injury. TRPC6 protein and TRPC6-agonist induced calcium influx could not be detected in glomeruli. In sum, these findings suggest that gain-of-function Trpc6 mutations confer only a mild susceptibility to glomerular injury in the mouse.

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