Sensing Dying Cells in Health and Disease: The Importance of Kidney Injury Molecule-1.

Kidney injury molecule-1 (KIM-1), also known as T-cell Ig and mucin domain-1 (TIM-1), is a widely recognized biomarker for AKI, but its biological function is less appreciated. KIM-1/TIM-1 belongs to the T-cell Ig and mucin domain family of conserved transmembrane proteins, which bear the characteristic six-cysteine Ig-like variable domain. The latter enables binding of KIM-1/TIM-1 to its natural ligand, phosphatidylserine, expressed on the surface of apoptotic cells and necrotic cells. KIM-1/TIM-1 is expressed in a variety of tissues and plays fundamental roles in regulating sterile inflammation and adaptive immune responses. In the kidney, KIM-1 is upregulated on injured renal proximal tubule cells, which transforms them into phagocytes for clearance of dying cells and helps to dampen sterile inflammation. TIM-1, expressed in T cells, B cells, and natural killer T cells, is essential for cell activation and immune regulatory functions in the host. Functional polymorphisms in the gene for KIM-1/TIM-1, HAVCR1 , have been associated with susceptibility to immunoinflammatory conditions and hepatitis A virus-induced liver failure, which is thought to be due to a differential ability of KIM-1/TIM-1 variants to bind phosphatidylserine. This review will summarize the role of KIM-1/TIM-1 in health and disease and its potential clinical applications as a biomarker and therapeutic target in humans.

The CaMK Family Differentially Promotes Necroptosis and Mouse Cardiac Graft Injury and Rejection.

Organ transplantation is associated with various forms of programmed cell death which can accelerate transplant injury and rejection. Targeting cell death in donor organs may represent a novel strategy for preventing allograft injury. We have previously demonstrated that necroptosis plays a key role in promoting transplant injury. Recently, we have found that mitochondria function is linked to necroptosis. However, it remains unknown how necroptosis signaling pathways regulate mitochondrial function during necroptosis. In this study, we investigated the receptor-interacting protein kinase 3 (RIPK3) mediated mitochondrial dysfunction and necroptosis. We demonstrate that the calmodulin-dependent protein kinase (CaMK) family members CaMK1, 2, and 4 form a complex with RIPK3 in mouse cardiac endothelial cells, to promote trans-phosphorylation during necroptosis. CaMK1 and 4 directly activated the dynamin-related protein-1 (Drp1), while CaMK2 indirectly activated Drp1 via the phosphoglycerate mutase 5 (PGAM5). The inhibition of CaMKs restored mitochondrial function and effectively prevented endothelial cell death. CaMKs inhibition inhibited activation of CaMKs and Drp1, and cell death and heart tissue injury (n = 6/group, p < 0.01) in a murine model of cardiac transplantation. Importantly, the inhibition of CaMKs greatly prolonged heart graft survival (n = 8/group, p < 0.01). In conclusion, CaMK family members orchestrate cell death in two different pathways and may be potential therapeutic targets in preventing cell death and transplant injury.

The effect of late-onset CMV infection on the outcome of renal allograft considering initial graft function.

BACKGROUND: Delayed graft function (DGF) increases the renal allograft failure risk. Late-onset Cytomegalovirus (CMV) infection's effect on the association between DGF and allograft failure has not been determined. METHODS: In this retrospective cohort, we included all renal allograft recipients at London Health Sciences Centre from January 1, 2014 to December 30, 2017, and continued clinical follow-up until February 28, 2020. We determined whether late-onset CMV infection affects the association between DGF and allograft failure in stratified and Cox proportional hazard analyses. RESULTS: Of 384 patients (median age [interquartile range]: 55 [43.3-63]; 38.7% female), 57 recipients (14.8%) were diagnosed with DGF. Patients with DGF were at a greater risk of CMV infection than patients without DGF (22.8% vs. 11.3%, p = .017). Late-onset CMV infection (odds ratio [OR]: 4.7, 95% CI: 2.07-10.68) and rejection (OR: 9.59, 95% CI: 4.15-22.16) significantly increased the risk of allograft failure in recipients with DGF. Patients with DGF had a significantly greater risk of graft failure than those without DGF (17.5% vs. 6.1%, p = .007). In the adjusted Cox hazard model, CMV infection significantly increased the risk of allograft failure (aHR: 3.19, 95% CI: 1.49-6.84). CONCLUSION: Late-onset CMV infection considerably increased the risk of graft failure in patients with DGF. A hybrid preventive model including prophylaxis followed by CMV-specific cell-mediated immunity monitoring may decrease the risk of allograft failure in recipients with DGF.

Mapping and functional characterization of murine kidney injury molecule-1 proteolytic cleavage site.

Kidney injury molecule-1 (KIM-1), also known as T cell immunoglobulin and mucin domain 1 (TIM-1), is a transmembrane glycoprotein expressed on proximal tubule epithelia during acute kidney injury (AKI). Extracellular domain of KIM-1 undergoes spontaneous and activated ectodomain shedding into urine and blood via metalloproteases. Soluble KIM-1 (blood and urinary) is a reliable clinical biomarker of proximal tubular injury, but the biological significance of shedding remains unknown. The aim of this study was to identify the specific shedding enzyme and the proteolytic cleavage site of murine KIM-1, followed by the characterization of its functional relevance. In this regard, isoleucine (I) I202 was identified as the potential cleavage site. Mutation of isoleucine I202 to glutamine (I202Q) or alanine (I202A) significantly reduced both constitutive and induced KIM-1 shedding and ultimately efferocytosis. It was also uncovered that ADAM10 is the major sheddase that mediates the proteolytic cleavage of murine KIM-1. In addition, ADAM10-induced KIM-1 shedding was required for efficient phagocytic clearance of apoptotic cells. Importantly, the findings that the addition of exogenous shed KIM-1 rescued the phagocytic impairment suggest that shed KIM-1 is capable of modulating efferocytosis of apoptotic bodies and could represent a potential functional role of the soluble ectodomain KIM-1 during AKI.

Short-term antibody response after 1 dose of BNT162b2 vaccine in patients receiving hemodialysis.

BACKGROUND: Patients receiving in-centre hemodialysis are at high risk of exposure to SARS-CoV-2 and death if infected. One dose of the BNT162b2 SARS-CoV-2 vaccine is efficacious in the general population, but responses in patients receiving hemodialysis are uncertain. METHODS: We obtained serial plasma from patients receiving hemodialysis and health care worker controls before and after vaccination with 1 dose of the BNT162b2 mRNA vaccine, as well as convalescent plasma from patients receiving hemodialysis who survived COVID-19. We measured anti-receptor binding domain (RBD) immunoglobulin G (IgG) levels and stratified groups by evidence of previous SARS-CoV-2 infection. RESULTS: Our study included 154 patients receiving hemodialysis (135 without and 19 with previous SARS-CoV-2 infection), 40 controls (20 without and 20 with previous SARS-CoV-2 infection) and convalescent plasma from 16 patients. Among those without previous SARS-CoV-2 infection, anti-RBD IgG was undetectable at 4 weeks in 75 of 131 (57%, 95% confidence interval [CI] 47% to 65%) patients receiving hemodialysis, compared with 1 of 20 (5%, 95% CI 1% to 23%) controls (p < 0.001). No patient with nondetectable levels at 4 weeks developed anti-RBD IgG by 8 weeks. Results were similar in non-immunosuppressed and younger individuals. Three patients receiving hemodialysis developed severe COVID-19 after vaccination. Among those with previous SARS-CoV-2 infection, median anti-RBD IgG levels at 8 weeks in patients receiving hemodialysis were similar to controls at 3 weeks (p = 0.3) and to convalescent plasma (p = 0.8). INTERPRETATION: A single dose of BNT162b2 vaccine failed to elicit a humoral immune response in most patients receiving hemodialysis without previous SARS-CoV-2 infection, even after prolonged observation. In those with previous SARS-CoV-2 infection, the antibody response was delayed. We advise that patients receiving hemodialysis be prioritized for a second BNT162b2 dose at the recommended 3-week interval.

Heterotrimeric Gα12/13 proteins in kidney injury and disease.

Gα12 and Gα13 are ubiquitous members of the heterotrimeric guanine nucleotide-binding protein (G protein) family that play central and integrative roles in the regulation of signal transduction cascades within various cell types in the kidney. Gα12/Gα13 proteins enable the kidney to adapt to an ever-changing environment by transducing stimuli from cell surface receptors and accessory proteins to effector systems. Therefore, perturbations in Gα12/Gα13 levels or their activity can contribute to the pathogenesis of various renal diseases, including renal cancer. This review will highlight and discuss the complex and expanding roles of Gα12/Gα13 proteins on distinct renal pathologies, with emphasis on more recently reported findings. Deciphering how the different Gα12/Gα13 interaction networks participate in the onset and development of renal diseases may lead to the discovery of new therapeutic strategies.

Caspase-3 Is a Pivotal Regulator of Microvascular Rarefaction and Renal Fibrosis after Ischemia-Reperfusion Injury.

Background Ischemia-reperfusion injury (IRI) is a major risk factor for chronic renal failure. Here, we characterize the different modes of programmed cell death in the tubular and microvascular compartments during the various stages of IRI-induced AKI, and their relative importance to renal fibrogenesis.Methods We performed unilateral renal artery clamping for 30 minutes and contralateral nephrectomy in wild-type mice (C57BL/6) or caspase-3-/- mice.Results Compared with their wild-type counterparts, caspase-3-/- mice in the early stage of AKI had high urine cystatin C levels, tubular injury scores, and serum creatinine levels. Electron microscopy revealed evidence of tubular epithelial cell necrosis in caspase-3-/- mice, and immunohistochemistry showed upregulation of the necroptosis marker receptor-interacting serine/threonine-protein kinase 3 (RIPK3) in renal cortical sections. Western blot analysis further demonstrated enhanced levels of phosphorylated RIPK3 in the kidneys of caspase-3-/- mice. In contrast, caspase-3-/- mice had less microvascular congestion and activation in the early and extension phases of AKI. In the long term (3 weeks after IRI), caspase-3-/- mice had reduced microvascular rarefaction and renal fibrosis, as well as decreased expression of α-smooth muscle actin and reduced collagen deposition within peritubular capillaries. Moreover, caspase-3-/- mice exhibited signs of reduced tubular ischemia, including lower tubular expression of hypoxia-inducible factor-1α and improved tubular injury scores.Conclusions These results establish the pivotal importance of caspase-3 in regulating microvascular endothelial cell apoptosis and renal fibrosis after IRI. These findings also demonstrate the predominant role of microvascular over tubular injury as a driver of progressive renal damage and fibrosis after IRI.

Tctex-1, a novel interaction partner of Kidney Injury Molecule-1, is required for efferocytosis.

Kidney injury molecule-1 (KIM-1) is a phosphatidylserine receptor that is specifically upregulated on proximal tubular epithelial cells (PTECs) during acute kidney injury and mitigates tissue damage by mediating efferocytosis (the phagocytic clearance of apoptotic cells). The signaling molecules that regulate efferocytosis in TECs are not well understood. Using a yeast two-hybrid screen, we identified the dynein light chain protein, Tctex-1, as a novel KIM-1-interacting protein. Immunoprecipitation and confocal imaging studies suggested that Tctex-1 associates with KIM-1 in cells at baseline, but, dissociates from KIM-1 within 90 min of initiation of efferocytosis. Interfering with actin or microtubule polymerization interestingly prevented the dissociation of KIM-1 from Tctex-1. Moreover, the subcellular localization of Tctex-1 changed from being microtubule-associated to mainly cytosolic upon expression of KIM-1. Short hairpin RNA-mediated silencing of endogenous Tctex-1 in cells significantly inhibited efferocytosis to levels comparable to that of knock down of KIM-1 in the same cells. Importantly, Tctex-1 was not involved in the delivery of KIM-1 to the cell-surface. On the other hand, KIM-1 expression significantly inhibited the phosphorylation of Tctex-1 at threonine 94 (T94), a post-translational modification which is known to disrupt the binding of Tctex-1 to dynein on microtubules. In keeping with this, we found that KIM-1 bound less efficiently to the phosphomimic (T94E) mutant of Tctex-1 compared to wild type Tctex-1. Surprisingly, expression of Tctex-1 T94E did not influence KIM-1-mediated efferocytosis. Our studies uncover a previously unknown role for Tctex-1 in KIM-1-dependent efferocytosis in epithelial cells.

Donor kidney injury molecule-1 promotes graft recovery by regulating systemic necroinflammation.

Ischemia-reperfusion injury during kidney transplantation predisposes to delayed graft function, rejection, and premature graft failure. Exacerbation of tissue damage and alloimmune responses may be explained by necroinflammation: an autoamplification loop of cell death and inflammation, which is mediated by the release of damage-associated molecular patterns (eg, high-mobility group box-1; HMGB1) from necrotic cells that activate both innate and adaptive immune pathways. Kidney injury molecule-1 (KIM-1) is a phosphatidylserine receptor that is upregulated on injured proximal tubular epithelial cells and enables them to clear apoptotic and necrotic cells. Here we show a pivotal role for clearance of dying cells in regulating necroinflammation in a syngeneic murine kidney transplant model. We found persistent KIM-1 expression in KIM-1+/+ kidney grafts posttransplantation. Compared to recipients of KIM-1+/+ kidneys, recipients of KIM-1-/- kidneys exhibited significantly more renal dysfunction, apoptosis and necrosis, tubular obstruction, and graft failure. KIM-1-/- grafts also had more inflammatory cytokines, infiltrating neutrophils, and macrophages compared to KIM-1+/+ grafts. Most significantly, passive release of HMGB1 from apoptotic and necrotic cells led to dramatically higher serum HMGB1 levels and increased proinflammatory macrophages in recipients of KIM-1-/- grafts. Our data identify an endogenous protective mechanism against necroinflammation in kidney grafts that may be of therapeutic relevance in transplantation.

Cardiovascular magnetic resonance left ventricular strain in end-stage renal disease patients after kidney transplantation.

BACKGROUND: Cardiovascular disease is a significant cause of morbidity and mortality in patients with end-stage renal disease (ESRD) and kidney transplant (KT) patients. Compared with left ventricular (LV) ejection fraction (LVEF), LV strain has emerged as an important marker of LV function as it is less load dependent. We sought to evaluate changes in LV strain using cardiovascular magnetic resonance imaging (CMR) in ESRD patients who received KT, to determine whether KT may improve LV function. METHODS: We conducted a prospective multi-centre longitudinal study of 79 ESRD patients (40 on dialysis, 39 underwent KT). CMR was performed at baseline and at 12 months after KT. RESULTS: Among 79 participants (mean age 55 years; 30% women), KT patients had significant improvement in global circumferential strain (GCS) (p = 0.007) and global radial strain (GRS) (p = 0.003), but a decline in global longitudinal strain (GLS) over 12 months (p = 0.026), while no significant change in any LV strain was observed in the ongoing dialysis group. For KT patients, the improvement in LV strain paralleled improvement in LVEF (57.4 ± 6.4% at baseline, 60.6% ± 6.9% at 12 months; p = 0.001). For entire cohort, over 12 months, change in LVEF was significantly correlated with change in GCS (Spearman's r = - 0.42, p < 0.001), GRS (Spearman's r = 0.64, p < 0.001), and GLS (Spearman's r = - 0.34, p = 0.002). Improvements in GCS and GRS over 12 months were significantly correlated with reductions in LV end-diastolic volume index and LV end-systolic volume index (all p < 0.05), but not with change in blood pressure (all p > 0.10). CONCLUSIONS: Compared with continuation of dialysis, KT was associated with significant improvements in LV strain metrics of GCS and GRS after 12 months, which did not correlate with blood pressure change. This supports the notion that KT has favorable effects on LV function beyond volume and blood pessure control. Larger studies with longer follow-up are needed to confirm these findings.

G protein α12 (Gα12) is a negative regulator of kidney injury molecule-1-mediated efferocytosis.

Kidney injury molecule-1 (KIM-1) is a receptor for the "eat me" signal, phosphatidylserine, on apoptotic cells. The specific upregulation of KIM-1 by injured tubular epithelial cells (TECs) enables them to clear apoptotic cells (also known as efferocytosis), thereby protecting from acute kidney injury. Recently, we uncovered that KIM-1 binds directly to the α-subunit of heterotrimeric G12 protein (Gα12) and inhibits its activation by reactive oxygen species during renal ischemia-reperfusion injury (Ismail OZ, Zhang X, Wei J, Haig A, Denker BM, Suri RS, Sener A, Gunaratnam L. Am J Pathol 185: 1207-1215, 2015). Here, we investigated the role that Gα12 plays in KIM-1-mediated efferocytosis by TECs. We showed that KIM-1 remains bound to Gα12 and suppresses its activity during phagocytosis. When we silenced Gα12 expression using small interefering RNA, KIM-1-mediated engulfment of apoptotic cells was increased significantly; in contrast overexpression of constitutively active Gα12 (QLGα12) resulted in inhibition of efferocytosis. Inhibition of RhoA, a key effector of Gα12, using a chemical inhibitor or expression of dominant-negative RhoA, had the same effect as inhibition of Gα12 on efferocytosis. Consistent with this, silencing Gα12 suppressed active RhoA in KIM-1-expressing cells. Finally, using primary TECs from Kim-1+/+ and Kim-1-/- mice, we confirmed that engulfment of apoptotic cells requires KIM-1 expression and that silencing Gα12 enhanced efferocytosis by primary TECs. Our data reveal a previously unknown role for Gα12 in regulating efferocytosis and that renal TECs require KIM-1 to mediate this process. These results may have therapeutic implications given the known harmful role of Gα12 in acute kidney injury.

Kidney injury molecule-1 protects against Gα12 activation and tissue damage in renal ischemia-reperfusion injury.

Ischemic acute kidney injury is a serious untreatable condition. Activation of the G protein α12 (Gα12) subunit by reactive oxygen species is a major cause of tissue damage during renal ischemia-reperfusion injury. Kidney injury molecule-1 (KIM-1) is a transmembrane glycoprotein that is highly up-regulated during acute kidney injury, but the physiologic significance of this up-regulation is unclear. Here, we report for the first time that Kim-1 inhibits Gα12 activation and protects mice against renal ischemia-reperfusion injury. We reveal that Kim-1 physically interacts with and inhibits cellular Gα12 activation after inflammatory stimuli, including reactive oxygen species, by blocking GTP binding to Gα12. Compared with Kim-1(+/+) mice, Kim-1(-/-) mice exhibited greater Gα12 and downstream Src activation both in primary tubular epithelial cells after in vitro stimulation with H2O2 and in whole kidneys after unilateral renal artery clamping. Finally, we show that Kim-1-deficient mice had more severe kidney dysfunction and tissue damage after bilateral renal artery clamping, compared with wild-type mice. Our results suggest that KIM-1 is an endogenous protective mechanism against renal ischemia-reperfusion injury through inhibition of Gα12.

Hydrogen Sulfide Treatment Mitigates Renal Allograft Ischemia-Reperfusion Injury during Cold Storage and Improves Early Transplant Kidney Function and Survival Following Allogeneic Renal Transplantation.

PURPOSE: Ischemia-reperfusion injury is unavoidable during organ transplantation. Prolonged ischemia-reperfusion injury is detrimental to short-term and long-term graft function and survival. H2S is a recently characterized, endogenously produced gaseous molecule with important physiological roles that has been shown to be cytoprotective during tissue ischemia-reperfusion injury. The current study aimed to determine whether H2S could mitigate cold renal ischemia-reperfusion injury in the clinically relevant context of allogeneic renal transplantation. MATERIALS AND METHODS: Following bilateral native nephrectomy Lewis rats underwent renal transplantation with kidneys from Brown Norway donor rats that were flushed with cold (4C) standard University of Wisconsin preservation solution (University of Wisconsin preservation solution group) or cold University of Wisconsin preservation solution plus 150 µM NaHS (H2S group) solution. Kidneys were stored for 6 hours at 4C in the same solution. Recipient animals were monitored for 14 days or until sacrifice using metabolic cages to assess various parameters of renal graft function. RESULTS: H2S treatment improved early allograft survival and function, and decreased early levels of necrosis, apoptosis and Kim-1 compared to University of Wisconsin preservation solution alone. H2S treatment did not affect allograft rejection. Rather, it modulated the early allograft transcriptome to decrease the expression of renal injury, coagulation and cellular stress response genes, and increase the expression of cellular proliferation and Ifn-γ induced genes compared to University of Wisconsin preservation solution alone. CONCLUSIONS: To our knowledge our findings are the first to show that H2S protects donor kidneys against cold ischemia-reperfusion injury in the context of allogeneic renal transplantation. This potentially represents a novel cost-effective therapeutic solution to mitigate ischemia-reperfusion injury and improve the clinical outcomes of renal transplantation.

Kidney injury molecule-1 expression in IgA nephropathy and its correlation with hypoxia and tubulointerstitial inflammation.

Tubulointerstitial injury plays an important role in the development and progression of chronic kidney disease (CKD). Kidney injury molecule (KIM)-1 is induced in damaged proximal tubules in both acute renal injury and CKD. However, the dynamics of KIM-1 in CKD and effects of KIM-1 expression on disease progression are unknown. Here, we aimed to determine the associations between tubular KIM-1 expression levels, renal function, and inflammation in CKD. The relationships between levels of KIM-1 and clinicopathological parameters were analyzed in patients with progressive and nonprogressive IgA nephropathy. KIM-1 expression was increased in patients with IgA nephropathy, and its expression was significantly correlated with the decrease of renal function. KIM-1 was particularly evident at the site with reduced capillary density, and KIM-1-positive tubules were surrounded by infiltrates of inflammatory cells. Using in vitro cell models, we showed that cellular stressors, including hypoxia, induced KIM-1 expression. KIM-1-expressing cells produced more chemokines/cytokines when cultured under hypoxic conditions. Furthermore, we showed that tubular cells with KIM-1 expression can regulate the immune response of inflammatory cells through the secretion of chemotactic factors. These data suggest that KIM-1-expressing epithelial cells may play a role in the pathogenesis of tubulointerstitial inflammation during chronic renal injury through the secretion of chemokines/cytokines.

Accelerated receptor shedding inhibits kidney injury molecule-1 (KIM-1)-mediated efferocytosis.

Efficient clearance of apoptotic cells (efferocytosis) prevents inflammation and permits repair following tissue injury. Kidney injury molecule-1 (KIM-1) is a receptor for phosphatidylserine, an "eat-me" signal exposed on the surface of apoptotic cells that marks them for phagocytic clearance. KIM-1 is upregulated on proximal tubule epithelial cells (PTECs) during ischemic acute kidney injury (AKI), enabling efferocytosis by surviving PTECs. KIM-1 is spontaneously cleaved at its ectodomain region to generate a soluble fragment that serves a sensitive and specific biomarker for AKI, but the biological relevance of KIM-1 shedding is unknown. Here, we sought to determine how KIM-1 shedding might regulate efferocytosis. Using cells that endogenously and exogenously express KIM-1, we found that hydrogen peroxide-mediated oxidative injury or PMA treatment accelerated KIM-1 shedding in a dose-dependent manner. KIM-1 shedding was also accelerated when apoptotic cells were added. Accelerated shedding or the presence of excess soluble KIM-1 in the extracellular milieu significantly inhibited efferocytosis. We also identified that TNF-α-converting enzyme (TACE or ADAM17) mediates both the spontaneous and PMA-accelerated shedding of KIM-1. While accelerated shedding inhibited efferocytosis, we found that spontaneous KIM-1 cleavage does not affect the phagocytic efficiency of PTECs. Our results suggest that KIM-1 shedding is accelerated by worsening cellular injury, and excess soluble KIM-1 competitively inhibits efferocytosis. These findings may be important in AKI when there is severe cellular injury.

Characterizing Cluster-Based Frailty Phenotypes in a Multicenter Prospective Cohort of Kidney Transplant Candidates.

Frailty is associated with a higher risk of death among kidney transplant candidates. Currently available frailty indices are often based on clinical impression, physical exam or an accumulation of deficits across domains of health. In this paper we investigate a clustering based approach that partitions the data based on similarities between individuals to generate phenotypes of kidney transplant candidates. We analyzed a multicenter cohort that included several features typically used to determine an individual's level of frailty. We present a clustering based phenotyping approach, where we investigated two clustering approaches-i.e. neural network based Self-Organizing Maps (SOM) with hierarchical clustering, and KAMILA (KAy-means for MIxed LArge data sets). Our clustering results partition the individuals across 3 distinct clusters. Clusters were used to generate and study feature-level phenotypes of each group.

Vascular calcification in chronic kidney disease associated with pathogenic variants in ABCC6.

Vascular calcification is prevalent in chronic kidney disease (CKD). Genetic causes of CKD account for 10-20% of adult-onset disease. Vascular calcification is thought to be one of the most important risk factors for increased cardiovascular morbidity and mortality in CKD patients and is detectable in 80% of patients with end stage kidney disease (ESKD). Despite the high prevalence of vascular calcification in CKD, no single gene cause has been described. We hypothesized that variants in vascular calcification genes may contribute to disease pathogenesis in CKD, particularly in families who exhibit a predominant vascular calcification phenotype. We developed a list of eight genes that are hypothesized to play a role in vascular calcification due to their involvement in the ectopic calcification pathway: ABCC6, ALPL, ANK1, ENPP1, NT5E, SLC29A1, SLC20A2, and S100A12. With this, we assessed exome data from 77 CKD patients, who remained unsolved following evaluation for all known monogenic causes of CKD. We also analyzed an independent cohort (Ontario Neurodegenerative Disease Research Initiative (ONDRI), n = 520) who were screened for variants in ABCC6 and compared this to a control cohort of healthy adults (n = 52). We identified two CKD families with heterozygous pathogenic variants (R1141X and A667fs) in ABCC6. We identified 10 participants from the ONDRI cohort with heterozygous pathogenic or likely pathogenic variant in ABCC6. Replication in a healthy control cohort did not reveal any variants. Our study provides preliminary data supporting the hypothesis that ABCC6 may play a role in vascular calcification in CKD. By screening CKD patients for genetic causes early in the diagnostic pathway, patients with genetic causes associated with vascular calcification can potentially be preventatively treated with new therapeutics with aims to decrease mortality.

Outcomes in ANCA-associated vasculitis patients with end-stage kidney disease on renal replacement therapy-A meta-analysis.

BACKGROUND: End-stage kidney disease (ESKD) is associated with poor prognosis in patients with anti-neutrophilic cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This study summarizes the existing evidence regarding outcomes in AAV patients with ESKD on renal replacement therapy. METHODS: Searches of the MEDLINE and Embase databases were performed from inception until December 2021. Any study reporting outcomes after ESKD in patients with AAV on haemodialysis or peritoneal dialysis was included. The mortality rate per 100 person-years (100 py) calculated with a random-effects meta-analysis model was the primary outcome. Rates of infections and relapses were secondary outcomes. RESULTS: 2470 citations were found; 22 studies of 952 adult patients with over 3600 person-years of follow-up were included. The pooled mortality rate was 10.90 per 100 py (95% CI: 7.11 - 14.68, I2 = 90.8%). The pooled 1-year survival was 80.9% (95% CI: 75.6 - 86.1%, I2 = 86.1%) while the pooled 5-year survival was 61.0% (95% CI: 46.0 - 76.0%, I2 = 0.0%). The pooled severe infection rate was 66.57 per 100 py (95% CI: 13.64 - 119.50, I2 = 99.6%). The pooled relapse rate was 6.22 per 100 py (95% CI: 4.64 - 7.80, I2 = 46.6%). Only 1 paediatric study met the inclusion criteria and reported a mortality rate of 11.7 ± 1.9 deaths per 100 py (95% CI: 0.23 - 23.20) amongst 9 patients. CONCLUSIONS: Patients with AAV and ESKD have a lower risk of relapse, but higher infection and mortality rates. More prospective research exploring the role of immunosuppression after ESKD is needed.

Impaired Efferocytosis by Synovial Macrophages in Patients With Knee Osteoarthritis.

OBJECTIVE: Osteoarthritis (OA) exposes all joint tissues to physiologic stresses, increasing the need to clear apoptotic cells from tissues, including the synovium. We undertook this study to assess the burden of apoptotic cells in synovial tissue in patients with late-stage knee OA and to investigate whether OA impairs the macrophage-mediated clearance of apoptotic cells via efferocytosis. METHODS: Synovial tissue was collected from individuals with healthy knees and patients with late-stage knee OA during arthroplasty. Synovial apoptotic cell burden was assessed by immunofluorescence for cleaved caspase 3. Efferocytosis of apoptotic Jurkat cells by CD14+ synovial tissue macrophages and peripheral blood-derived macrophages was quantified using immunofluorescence microscopy. Effects of OA on macrophage-mediated efferocytosis were modeled by stimulating blood-derived macrophages with synovial fluid collected from individuals with healthy knees and patients with early- or late-stage knee OA. RESULTS: Patients with late-stage knee OA had more apoptotic synovial cells compared to healthy individuals. There was a marked reduction in the fraction of synovial tissue macrophages engaging in efferocytosis and the quantity of material efferocytosed by individual macrophages in OA patients. Blood-derived macrophages exposed to synovial fluid from patients with knee OA recapitulated the defective efferocytosis, with the greatest effect from patients with early-stage knee OA and higher disease activity (pain and inflammation). CONCLUSION: Apoptotic cells accumulate in the synovium of patients with late-stage knee OA. Our results suggest that OA impairs critical homeostatic functions of synovial macrophages, leading to accumulation of apoptotic cells.