Apolipoprotein L1 Risk Variants Research Articles

Relevance of repeated analyses of albuminuria and glomerular filtration rate in African children with sickle cell anaemia.

Glomerular hyperfiltration and albuminuria are frequent kidney abnormalities in children with sickle cell anaemia (SCA). However, little is known about their persistence in African SCA children. This prospective study included 600 steady-state SCA children aged 2-18 years from the Democratic Republic of Congo. Participants were genotyped for apolipoprotein L1 (APOL1) risk variants (RVs) and haem oxygenase-1 (HMOX1) GT-dinucleotide repeats. Kidney abnormalities were defined as albuminuria, hyperfiltration or decreased estimated creatinine-based glomerular filtration rate (eGFRcr). At baseline, 247/600 (41.2%) participants presented with kidney abnormalities: 82/592 (13.8%) with albuminuria, 184/587 (31.3%) with hyperfiltration and 15/587 (2.6%) with decreased eGFRcr. After a median follow-up of 5 months, repeated testing was performed in 180/247 (72.9%) available participants. Persistent hyperfiltration and persistent albuminuria (PA) were present in 29.2% (38/130) and 39.7% (23/58) respectively. eGFR normalized in all participants with a baseline decreased eGFRcr. Haemoglobinuria (p = 0.017) and male gender (p = 0.047) were significantly associated with PA and persistent hyperfiltration respectively. APOL1 RVs (G1G1/G2G2/G1G2) were borderline associated with PA (p = 0.075), while HMOX1 long repeat was not associated with any persistent kidney abnormality. This study reveals that a single screening can overestimate the rate of kidney abnormalities in children with SCA and could lead to overtreatment.

The Two Levels of Podocyte Dysfunctions Induced by Apolipoprotein L1 Risk Variants

The Two Levels of Podocyte Dysfunctions Induced by Apolipoprotein L1 Risk Variants

African ancestry-derived APOL1 risk genotypes show proximal epigenetic associations

Apolipoprotein L1 (APOL1) coding variants, termed G1 and G2, are established genetic risk factors for a growing spectrum of diseases, including kidney disease, in individuals of African ancestry. Evidence suggests that the risk variants, which show a recessive mode of inheritance, lead to toxic gain-of-function changes of the APOL1 protein. Disease occurrence and presentation vary, likely due to modifiers or second hits. To understand the role of the epigenetic landscape in relation to APOL1 risk variants, we performed methylation quantitative trait locus (meQTL) analysis to identify differentially methylated CpGs influenced by APOL1 risk variants in 611 African American individuals. We identified five CpGs that were significantly associated with APOL1 risk alleles in discovery and replication studies, and one CpG-APOL1 association was independent of other genomic variants. Our study highlights proximal DNA methylation alterations that may help explain the variable disease risk and clinical manifestation of APOL1 variants.

Osteonecrosis is associated with APOL1 variants in African Americans with systemic lupus erythematosus

Background/purposeAfrican Americans (AA) with systemic lupus erythematosus (SLE) are at higher risk for both kidney disease and Osteonecrosis (ON). Two Apolipoprotein L1 (APOL1) risk variants (RV), G1 and G2, have been associated with chronic kidney disease (CKD), hypertension, and microvascular disease in AAs, which are independent risk factors for ON. Accordingly, we investigated the association between carriers of the APOL1 risk variants and the prevalence of ON in AA SLE patients.MethodsA cohort of 121 adult participants of self-reported AA ancestry and meeting at least four of the American College of Rheumatology (ACR) revised criteria for SLE were recruited from a high volume urban SLE clinical site. PCR/sequencing was used to stratify participants by APOL1 genotype. Medical records, including clinical notes and imaging reports, were retrospectively reviewed for documentation of ON. Association between the number of APOL1 risk variants with time to first ON was tested.ResultsIn our cohort, 18 individuals developed ON; across the APOL1 genotype groups, 2/37 0RV, 11/59 1RV, and 5/15 2RV participants were affected. The mean time to ON was 27 years, 22 years, and 18 years in 0RV, 1RV, and 2RV carriers, respectively. An adjusted Cox regression model showed that carrying the APOL1 risk variants associated with shorter ON free survival with hazard ratios (HR) of 3.1 (95% CI: 1.6–6.2) and 9.6 (95% CI 2.4–37.8) for 1RV and 2RV carriers, respectively. 2RV carriers more often exhibited multiple and bilateral joint sites affected by ON. Disease duration was longer in ON-affected participants at 20.5 years compared to 9.0 years in those unaffected (p < 0.001). In individuals who had received glucocorticoids, median cumulative prednisone equivalent dose was higher in ON-affected participants, though this did not reach statistical significance (18.7 g vs. 9.0 g; p-value = 0.3).ConclusionOur analysis suggests a higher risk of osteonecrosis among African American SLE patients who carry the APOL1 risk variants. In addition, disease duration increased the rate of ON. Given the high frequency of the APOL1 risk variants in African Americans, APOL1 high-risk genotype carriers may represent an ON-vulnerable subgroup within the AA population. Further work is necessary to uncover the mechanism of this association.

#4385 RELEVANCE OF REPEATED ALBUMINURIA AND GLOMERULAR FILTRATION RATE IN A LARGE COHORT OF SICKLE CELL ANEMIA CHILDREN LIVING IN A RESOURCE-LIMITED AREA

Abstract Background and Aims Chronic kidney disease (CKD) is associated with significant morbidity and mortality among patients with sickle cell anemia (SCA). Glomerular hyperfiltration (GHF) and albuminuria are known as early manifestations of kidney disease occurring in early childhood and can predict the progression to CKD in these patients. Studies reported the prevalence of these kidney abnormalities in SCA children using a single measure and their association with genetic risk factors, especially the co-inheritance of APOL1 risk variants (RVs). However, data on the prevalence of persistent kidney abnormalities (based on the KDIGO CKD definition) and their association with APOL1 RVs are limited in SCA children, particularly those living in sub-Saharan Africa. This study aimed: (i) to determine the prevalence of persistent kidney abnormalities (albuminuria and/or GHF) in SCA children living in the Democratic Republic of Congo (DRC); and (ii) to assess the association between persistent kidney abnormalities with clinical and genetic risk factors. Method From March 2021 to December 2022, we prospectively enrolled 585 steady state SCA children aged 2 to 18 years (male gender 278/585; 47.5%). The SCA status was confirmed through the molecular sequencing of beta-globin gene. Clinical and biological parameters were obtained. All participants were genotyped for apolipoprotein-L1 (APOL1) G1 (rs73885319, rs60910145) and G2 (rs71785313) variants. APOL1 high-risk genotype (HRG) was defined by the presence of 2 risk variants (G1/G1, G2/G2, and G1/G2), and low-risk genotype (LRG) by the presence of 0 or 1 risk variant. Albuminuria was defined as urinary albumin-to-creatinine ratio (ACR) ≥ 30mg/g. The estimated glomerular filtration rate (eGFRcr) was calculated using the original Schwartz formula and GHF was defined as eGFRcr ≥ 180 ml/min/1.73 m2 for children between 2-10 years of age and > 140 ml/min/1.73 m2 for children more than 10 years of age. All measurements were repeated at least three months later in participants who presented with kidney abnormalities at the first screening. The main outcome parameter was persistent albuminuria or persistent GHF for more than three months. Results At enrollment, 234/585 (40.0%) participants presented with kidney abnormalities, among which 80/585 (13.7%) with albuminuria and 171/585 (29.2%) with hyperfiltration. From participants found with kidney abnormalities at the first screening, 176/234 (75.2%) were available for repeated screening: 56/176 (31.8%) presented with persistent kidney abnormalities and 120/176 (68.2%) had a regression of kidney abnormalities without any treatment. Out of 176 participants who benefited from repeated screening, 57 had baseline albuminuria and 130 had baseline GHF. Persistent albuminuria and persistent GHF were found in 38.6% (22/57) and 28.5% (37/130), respectively. Multivariate logistic regression revealed that APOL1 HRG was significantly associated with persistent albuminuria (OR 3.4, 95CI 1.1-10.7, p = 0.037), while male gender was significantly associated with persistent GHF (OR 2.1, 95CI 1.0-4.2, p = 0.042). Conclusion A significant proportion (almost 70.0%) of SCA children who had kidney abnormalities at the first measure, presented regression of these abnormalities without any reno-protective drugs. This result emphasizes the importance of repeating screening at least three months later to confirm CKD, as recommended by the KDIGO Guidelines. This strategy will reduce the need for unnecessary treatment, which represents a high financial burden in a resource-limited area.

The metabolic effects of APOL1 in humans.

Harboring apolipoprotein L1 (APOL1) variants coded by the G1 or G2 alleles of the APOL1 gene increases the risk for collapsing glomerulopathy, focal segmental glomerulosclerosis, albuminuria, chronic kidney disease, and accelerated kidney function decline towards end-stage kidney disease. However, most subjects carrying APOL1 variants do not develop the kidney phenotype unless a second clinical condition adds to the genotype, indicating that modifying factors modulate the genotype-phenotype correlation. Subjects with an APOL1 high-risk genotype are more likely to develop essential hypertension or obesity, suggesting that carriers of APOL1 risk variants experience more pronounced insulin resistance compared to noncarriers. Likewise, arterionephrosclerosis (the pathological correlate of hypertension-associated nephropathy) and glomerulomegaly take place among carriers of APOL1 risk variants, and these pathological changes are also present in conditions associated with insulin resistance, such as essential hypertension, aging, and diabetes. Insulin resistance may contribute to the clinical features associated with the APOL1 high-risk genotype. Unlike carriers of wild-type APOL1, bearers of APOL1 variants show impaired formation of lipid droplets, which may contribute to inducing insulin resistance. Nascent lipid droplets normally detach from the endoplasmic reticulum into the cytoplasm, although the proteins that enable this process remain to be fully defined. Wild-type APOL1 is located in the lipid droplet, whereas mutated APOL1 remains sited at the endoplasmic reticulum, suggesting that normal APOL1 may participate in lipid droplet biogenesis. The defective formation of lipid droplets is associated with insulin resistance, which in turn may modulate the clinical phenotype present in carriers of APOL1 risk variants.

DGAT2 Inhibition Potentiates Lipid Droplet Formation To Reduce Cytotoxicity in APOL1 Kidney Risk Variants.

Two variants in the gene encoding apolipoprotein L1 (APOL1) that are highly associated with African ancestry are major contributors to the large racial disparity in rates of human kidney disease. We previously demonstrated that recruitment of APOL1 risk variants G1 and G2 from the endoplasmic reticulum to lipid droplets leads to reduced APOL1-mediated cytotoxicity in human podocytes. We used CRISPR-Cas9 gene editing of induced pluripotent stem cells to develop human-derived APOL1G0/G0 and APOL1G2/G2 kidney organoids on an isogenic background, and performed bulk RNA sequencing of organoids before and after treatment with IFN-γ. We examined the number and distribution of lipid droplets in response to treatment with inhibitors of diacylglycerol O-acyltransferases 1 and 2 (DGAT1 and DGAT2) in kidney cells and organoids. APOL1 was highly upregulated in response to IFN-γ in human kidney organoids, with greater increases in organoids of high-risk G1 and G2 genotypes compared with wild-type (G0) organoids. RNA sequencing of organoids revealed that high-risk APOL1G2/G2 organoids exhibited downregulation of a number of genes involved in lipogenesis and lipid droplet biogenesis, as well as upregulation of genes involved in fatty acid oxidation. There were fewer lipid droplets in unstimulated high-risk APOL1G2/G2 kidney organoids than in wild-type APOL1G0/G0 organoids. Whereas DGAT1 inhibition reduced kidney organoid lipid droplet number, DGAT2 inhibition unexpectedly increased organoid lipid droplet number. DGAT2 inhibition promoted the recruitment of APOL1 to lipid droplets, with associated reduction in cytotoxicity. Lipogenesis and lipid droplet formation are important modulators of APOL1-associated cytotoxicity. Inhibition of DGAT2 may offer a potential therapeutic strategy to attenuate cytotoxic effects of APOL1 risk variants.

Vignette-Based Reflections to Inform Genetic Testing Policies in Living Kidney Donors.

Family history of kidney disease increases risk of end-stage kidney disease (ESKD) in donors. Pre-donation genetic testing is recommended in evaluation guidelines and regulatory policy. Collaborating across several institutions, we describe cases to illustrate the utility as well as practical issues in incorporating genetic testing in transplant protocols. Case 1 is from 2009, before pervasive genetic testing. A healthy 27-year-old Caucasian male had an uneventful donor evaluation for his mother, who had early onset ESKD of unclear cause. He participated in paired-exchange kidney donation, but developed progressive kidney disease and gout over the next 10 years. A uromodulin gene mutation (NM_003361.3(UMOD):c.377 G>A p.C126Y) was detected and kidney biopsy showed tubulointerstitial kidney disease. The patient subsequently required kidney transplantation himself. Case 2 was a 36-year-old African American female who had an uneventful kidney donor evaluation. She underwent gene panel-based testing to rule out ApolipoproteinL1 risk variants, for which was negative. Incidentally, a sickle-cell trait (NM_000518.5(HBB):c.20A>T p.Glu7Val) was noted, and she was declined for kidney donation. This led to significant patient anguish. Case 3 was a 26-year-old Caucasian female who underwent panel-based testing because the potential recipient, her cousin, carried a variant of uncertain significance in the hepatocyte nuclear factor-1-β (HNF1B) gene. While the potential donor did not harbor this variant, she was found to have a likely pathogenic variant in complement factor I (NM_000204.4(CFI):c.1311dup:p.Asp438Argfs*8), precluding kidney donation. Our cases emphasize that while genetic testing can be invaluable in donor evaluation, transplant centers should utilize detailed informed consent, develop care pathways for secondary genetic findings, and share experience to develop best practices around genetic testing in donors.

The evolving story of apolipoprotein L1 nephropathy: the end of the beginning.

Genetic coding variants in APOL1, which encodes apolipoprotein L1 (APOL1), were identified in 2010 and are relatively common among individuals of sub-Saharan African ancestry. Approximately 13% of African Americans carry two APOL1 risk alleles. These variants, termed G1 and G2, are a frequent cause of kidney disease — termed APOL1 nephropathy — that typically manifests as focal segmental glomerulosclerosis and the clinical syndrome of hypertension and arterionephrosclerosis. Cell culture studies suggest that APOL1 variants cause cell dysfunction through several processes, including alterations in cation channel activity, inflammasome activation, increased endoplasmic reticulum stress, activation of protein kinase R, mitochondrial dysfunction and disruption of APOL1 ubiquitinylation. Risk of APOL1 nephropathy is mostly confined to individuals with two APOL1 risk variants. However, only a minority of individuals with two APOL1 risk alleles develop kidney disease, suggesting the need for a ‘second hit’. The best recognized factor responsible for this ‘second hit’ is a chronic viral infection, particularly HIV-1, resulting in interferon-mediated activation of the APOL1 promoter, although most individuals with APOL1 nephropathy do not have an obvious cofactor. Current therapies for APOL1 nephropathies are not adequate to halt progression of chronic kidney disease, and new targeted molecular therapies are in clinical trials.

Inhibition of endoplasmic reticulum stress signaling rescues cytotoxicity of human apolipoprotein-L1 risk variants in Drosophila

Risk variants of the apolipoprotein-L1 (APOL1) gene are associated with severe kidney disease, putting homozygous carriers at risk. Since APOL1 lacks orthologs in all major model organisms, a wide range of mechanisms frequently in conflict have been described for APOL1-associated nephropathies. The genetic toolkit in Drosophila allows unique invivo insights into disrupted cellular homeostasis. To perform a mechanistic analysis, we expressed human APOL1 control and gain-of-function kidney risk variants in the podocyte-like garland cells of Drosophila nephrocytes and a wing precursor tissue. Expression of APOL1 risk variants was found to elevate endocytic function of garland cell nephrocytes that simultaneously showed early signs of cell death. Wild-type APOL1 had a significantly milder effect, while a control transgene with deletion of the short BH3 domain showed no overt phenotype. Nephrocyte endo-lysosomal function and slit diaphragm architecture remained unaffected by APOL1 risk variants, but endoplasmic reticulum (ER) swelling, chaperone induction, and expression of the reporter Xbp1-EGFP suggested an ER stress response. Pharmacological inhibition of ER stress diminished APOL1-mediated cell death and direct ER stress induction enhanced nephrocyte endocytic function similar to expression of APOL1 risk variants. We confirmed APOL1-dependent ER stress in the Drosophila wing precursor where silencing the IRE1-dependent branch of ER stress signaling by inhibition with Xbp1-RNAi abrogated cell death, representing the first rescue of APOL1-associated cytotoxicity invivo. Thus, we uncovered ER stress as an essential consequence of APOL1 risk variant expression invivo in Drosophila, suggesting a central role of this pathway in the pathogenesis of APOL1-associated nephropathies.

APOL1 Risk Variants Associated with Serum Albumin in a Population-Based Cohort Study

Introduction: The association of apolipoprotein L1 (APOL1) nephropathy risk variants (APOL1), unique to African-ancestry (African-American [AA]) populations, with systemic inflammation, a contributor to chronic kidney disease (CKD) and end-stage kidney disease (ESKD) is ill-defined. This study aimed to describe the role of inflammatory markers in the relationship between APOL1 and incident kidney outcomes using a prospective cohort study. Methods: APOL1 high-risk status under a recessive genetic model was studied in 10,605 AA adults aged ≥45 years from the Reasons for Geographic and Racial Differences in Stroke study. The primary variables of interest were inflammatory markers: C-reactive protein (mg/dL), white blood cell count (cells/mm³), and serum albumin (sALB) (mg/dL). High inflammation status was defined if at least one of these inflammatory markers exceeded clinical threshold. The association between APOL1 and biomarkers were assessed using regression models adjusting for age, sex, ancestry, hypertension, lipid medications, albumin-to-creatinine ratio, and estimated glomerular filtration rate (eGFR). Models were stratified by diabetes status. We identified incident ESKD using USRDS linkage, and we defined incident CKD as an eGFR <60 mL/min/1.73 m² and ≥25% decline in the eGFR and normal baseline eGFR and tested for mediation of APOL1 and outcomes by biomarkers using the causal inference approach. Results: Among 7,151 participants with data available on all inflammation markers, 4,479 participants had ≥1 marker meeting the clinical threshold. APOL1 high-risk status was associated with lower adjusted odds of reduced sALB {odds ratio (OR) (95% confidence interval [CI]): 0.59 [0.36, 0.96])}, and this association was significant in people with diabetes (OR [95% CI]: 0.40 [0.18, 0.89]) but not in those without diabetes. There was no association of APOL1 high-risk status with other markers or high inflammation status. APOL1 was independently associated with ESKD (OR [95% CI] = 1.78 [1.28, 2.48]) and CKD (OR [95% CI] = 1.38 [1.00, 1.91]). On mediation analysis, the direct effect between APOL1 and ESKD strengthened after accounting for sALB, but the estimated mediated effect was not statistically significant (OR [95% CI]: 0.98 [0.92, 1.05], p = 0.58). Conclusion: APOL1 high-risk variants were associated with sALB. However, sALB did not statistically mediate the association between APOL1 and incident ESKD.

APOL1 risk variants in individuals of African genetic ancestry drive endothelial cell defects that exacerbate sepsis

The incidence and severity of sepsis is higher among individuals of African versus European ancestry. We found that genetic risk variants (RVs) in the trypanolytic factor apolipoprotein L1 (APOL1), present only in individuals of African ancestry, were associated with increased sepsis incidence and severity. Serum APOL1 levels correlated with sepsis and COVID-19 severity, and single-cell sequencing in human kidneys revealed high expression of APOL1 in endothelial cells. Analysis of mice with endothelial-specific expression of RV APOL1 and invitro studies demonstrated that RV APOL1 interfered with mitophagy, leading to cytosolic release of mitochondrial DNA and activation of the inflammasome (NLRP3) and the cytosolic nucleotide sensing pathways (STING). Genetic deletion or pharmacological inhibition of NLRP3 and STING protected mice from RV APOL1-induced permeability defects and proinflammatory endothelial changes in sepsis. Our studies identify the inflammasome and STING pathways as potential targets to reduce APOL1-associated health disparities in sepsis and COVID-19.

Novel Human Podocyte Cell Model Carrying G2/G2 APOL1 High-Risk Genotype.

Apolipoprotein L1 (APOL1) high-risk genotypes (HRG), G1 and G2, increase the risk of various non-diabetic kidney diseases in the African population. To date, the precise mechanisms by which APOL1 risk variants induce injury on podocytes and other kidney cells remain unclear. Trying to unravel these mechanisms, most studies have used animal or cell models created by gene editing. We developed and characterised conditionally immortalised human podocyte cell lines derived from urine of a donor carrying APOL1 HRG G2/G2. Following induction of APOL1 expression by polyinosinic-polycytidylic acid (poly(I:C)), we assessed functional features of APOL1-induced podocyte dysfunction. As control, APOL1 wild type (G0/G0) podocyte cell line previously generated from a Caucasian donor was used. Upon exposure to poly(I:C), G2/G2 and G0/G0 podocytes upregulated APOL1 expression resulting in podocytes detachment, decreased cells viability and increased apoptosis rate in a genotype-independent manner. Nevertheless, G2/G2 podocyte cell lines exhibited altered features, including upregulation of CD2AP, alteration of cytoskeleton, reduction of autophagic flux and increased permeability in an in vitro model under continuous perfusion. The human APOL1 G2/G2 podocyte cell model is a useful tool for unravelling the mechanisms of APOL1-induced podocyte injury and the cellular functions of APOL1.

RNA-Sequencing of Isolated Cell Populations Expressing Human APOL1 Risk Variants Reveals Molecular Correlates of Sickle Cell Nephropathy in Zebrafish Podocytes

Background: Kidney failure occurs in 5-13% of individuals with sickle cell disease (SCD), and is associated with early mortality. We have shown previously that genetic variation in apolipoprotein L1 (APOL1) is associated with increased risk for developing SCD nephropathy (Ashley-Koch et al, 2011). Two APOL1 alleles (G1 and G2) have been identified as risk factors for SCD nephropathy, as well as chronic kidney disease (CKD) in African Americans without SCD (Limou et al, 2014). Both risk alleles are highly prevalent in individuals of African descent. Despite the strong association of G1 and G2 with kidney dysfunction, the mechanisms by which these variants contribute to increased CKD risk remain poorly understood. However, the observation of podocyte effacement in CKD patients suggests that podocytes and/or endothelial cells are likely implicated in pathogenesis. We established zebrafish models of these human risk alleles previously for the purpose of better understanding the underlying pathology contributing to SCD nephropathy (Anderson et al, 2015). Here, we have utilized these models to explore further the cell-type specific transcriptomic perturbations contributing to nephropathy.Methods: To investigate the effects of the APOL1 G2 risk variant on cell-type specific transcriptomes, we injected human APOL1 mRNA into embryos from 3 different zebrafish lines expressing cell-type specific reporters to permit the isolation of podocytes (pod:NTR-mCherry), endothelial cells (fli1:egfp), or peripheral neurons (hb9:gfp; control). Three populations from each line were utilized: (1) uninjected controls; (2) embryos injected with canonical human APOL1 (G0); and (3) embryos injected with human APOL1 (G2) mRNA. Larvae were dissociated at 4 days post-fertilization (4 dpf), and fluorescent cell types were isolated via fluorescence activated cell-sorting (FACS). Messenger RNA was extracted from sorted cell populations (n=3 FACS sorted cell populations per condition) and subsequently amplified to obtain a sufficient amount of RNA for sequencing. The amplified RNA was prepared into cDNA libraries, and sequenced on an Illumina HiSeq 2500. We performed pairwise comparisons between uninjected and G0 injected larvae in each cell type to ascertain the effects of canonical human APOL1 on the zebrafish kidney transcriptome. Additionally, to measure the effects of APOL1 G2 expression on the transcriptome, we compared APOL1 G0 and APOL1 G2 samples. Transcripts were considered to be differentially expressed if they achieved an FDR-adjusted q-value of less than 0.05. To understand better the biological processes altered by injection condition, we conducted gene ontology enrichment analyses (GOEA) on sets of differentially expressed genes.Results: Our analysis of uninjected and APOL1 G0 libraries identified 38, 154, and 204 differentially expressed (DE) genes in endothelial cells, podocytes, and motor neurons, respectively. No significant enrichment of gene ontology terms was detected, suggesting that canonical G0 APOL1 did not have a substantial impact on the zebrafish transcriptome. In contrast, the comparison of APOL1 G0 and APOL1 G2 samples found 95, 7400 (Figure below), and 652 DE genes in endothelial cells, podocytes, and motor neurons, respectively. GOEA of the podocyte DE gene list showed enrichment for several autophagy-associated terms, including “Lysosome” and “Phagosome”. Close inspection of these autophagy-associated genes revealed that the majority are up-regulated in G2 relative to G0 (68/75 genes for “Lysosome” and 52/78 genes for “Phagosome”). Thus, the G2 allele appears to induce transcription of genes involved in autophagy in podocytes.Summary: Taken together, these data suggest that podocytes are the predominant cell type affected by the expression of APOL1 G2. The comparison of podocytes injected with APOL1 G0 or APOL1 G2 yielded an order of magnitude more DE transcripts than any other comparison. The GOEA results of the podocyte comparison are consistent with a recent study of transgenic mice expressing the G1 or G2 APOL1 high risk variants, which showed alterations in endocytic vesicle content and autophagic flux (Beckerman et al 2017). Ongoing work includes molecular analysis to characterize the effects of the APOL1 G1 allele. This work will continue to shed light on the molecular pathology of SCD nephropathy and provide insight into new therapeutic strategies. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

APOL1 genotyping in kidney transplantation: to do or not to do, that is the question? (contra)

Discussions regarding genetic testing for variants in apolipoprotein L1 (APOL1), a gene located on chromosome 22 whose risk variants are strongly associated with end-stage kidney disease (ESKD), in the context of kidney transplantation must address donors (deceased and living) and recipients. In addition, these discussions must occur in the context of known genetic epidemiology regarding APOL1. Specifically, APOL1 risk variants are only found among individuals of African descent, as these variants are derived from exposure to African sleeping sickness that is largely confined to countries along the west coast of Africa. 1 Genovese G. Friedman D.J. Ross M.D. et al. Association of trypanolytic ApoL1 variants with kidney disease in African Americans. Science. 2010; 329: 841-845 Crossref PubMed Scopus (1388) Google Scholar In other words, not every individual who self identifies as Black or African American will even be at risk for carrying these genetic variants, and in fact, 87% of African Americans do not actually carry 2 APOL1 renal risk variants. 2 Foster M.C. Coresh J. Fornage M. et al. APOL1 variants associate with increased risk of CKD among African Americans. J Am Soc Nephrol. 2013; 24: 1484-1491 Crossref PubMed Scopus (180) Google Scholar More important, among the 13% of African Americans who do carry 2 APOL1 renal risk variants, the presence of these variants alone is insufficient to cause ESKD. 2 Foster M.C. Coresh J. Fornage M. et al. APOL1 variants associate with increased risk of CKD among African Americans. J Am Soc Nephrol. 2013; 24: 1484-1491 Crossref PubMed Scopus (180) Google Scholar We question the rationale for routine testing of all African American donors and recipients. Those in favor would likely remind us of the Hippocratic Oath—first do no harm—and that it is our duty to assign and avoid such risk. Paternalistic strategies such as this, although good intentioned, often overlook the broader context of how such dogmas may eliminate patient autonomy in decision making and even exacerbate existing disparities. In the following paragraphs, we will lay the foundation for the case against routine APOL1 testing in kidney transplantation with the hope of encouraging a more balanced approach to the care of donors and recipients alike. APOL1 genotyping in kidney transplantation: a look into the futureKidney InternationalVol. 100Issue 1PreviewChronic kidney disease (CKD) and end-stage kidney disease disproportionately affect individuals with African ancestry.1 African Americans have a lower rate of referral for kidney transplantation and lower graft survival than other ethnic groups.2 The risk of end-stage kidney disease is higher in Black living donors compared with White counterparts.3 Variants in the apolipoprotein L1 (APOL1) gene (G1: S342G and I384M; and G2: del N388 and Y389) explain most of this disparate risk for nondiabetic kidney disease, with the magnitude of risk varying depending on the clinical phenotype. Full-Text PDF

APOL1 genotype-associated morphologic changes among patients with focal segmental glomerulosclerosis.

The G1 and G2 alleles of apolipoprotein L1 (APOL1) are common in the Black population and associated with increased risk of focal segmental glomerulosclerosis (FSGS). The molecular mechanisms linking APOL1 risk variants with FSGS are not clearly understood, and APOL1's natural absence in laboratory animals makes studying its pathobiology challenging. In a cohort of 90 Black patients with either FSGS or minimal change disease (MCD) enrolled in the Nephrotic Syndrome Study Network (58% pediatric onset), we used kidney biopsy traits as an intermediate outcome to help illuminate tissue-based consequences of APOL1 risk variants and expression. We tested associations between APOL1 risk alleles or glomerular APOL1 mRNA expression and 83 light- or electron-microscopy traits measuring structural and cellular kidney changes. Under both recessive and dominant models in the FSGS patient subgroup (61%), APOL1 risk variants were significantly correlated (defined as FDR <0.1) with decreased global mesangial hypercellularity, decreased condensation of cytoskeleton, and increased tubular microcysts. No significant correlations were detected in MCD cohort. Independent of risk alleles, glomerular APOL1 expression in FSGS patients was not correlated with morphologic features. While APOL1-associated FSGS is associated with two risk alleles, both one and two risk alleles are associated with cellular/tissue changes in this study of FSGS patients. Our lack of discovery of a large group of tissue differences in FSGS and no significant difference in MCD may be due to the lack of power but also supports investigating whether machine learning methods may more sensitively detect APOL1-associated changes.

Design and methods of the prevalence and pharmacogenomics of tenofovir nephrotoxicity in HIV-positive adults in south-western Nigeria study

BackgroundIndividuals of African descent are at higher risk of developing kidney disease than their European counterparts, and HIV infection is associated with increased risk of nephropathy. Despite a safe renal profile in the clinical trials, long-term use of tenofovir disoproxil fumarate (TDF) has been associated with proximal renal tubulopathy although the underlying mechanisms remain undetermined. We aim to establish the prevalence of and risk factors for TDF-induced kidney tubular dysfunction (KTD) among HIV-I and II individuals treated with TDF in south-west Nigeria. Association between TDF-induced KTD and genetic polymorphisms in renal drug transporter genes and the APOL1 (Apolipoprotein L1) gene will be examined.MethodsThis study has two phases. An initial cross-sectional study will screen 3000 individuals attending the HIV clinics in south-west Nigeria for KTD to determine the prevalence and risk factors. This will be followed by a case-control study of 400 KTD cases and 400 matched controls to evaluate single nucleotide polymorphism (SNP) associations. Data on socio-demographics, risk factors for kidney dysfunction and HIV history will be collected by questionnaire. Blood and urine samples for measurements of severity of HIV disease (CD4 count, viral load) and renal function (creatinine, eGFR, phosphate, uric acid, glucose) will also be collected. Utility of urinary retinol binding protein (RBP) and N-acetyl-beta-D-glucosaminidase (NAG) levels as surrogate markers of KTD will be evaluated. Genomic DNA will be extracted from whole blood and SNP analyses performed using the rhAMP SNP genotyping assays. Statistical analysis including univariate and multivariate logistic regression analyses will be performed to identify factors associated with KTD.DiscussionIn spite of TDF being the most commonly used antiretroviral agent and a key component of many HIV treatment regimens, it has potential detrimental effects on the kidneys. This study will establish the burden and risk factors for TDF-induced KTD in Nigerians, and explore associations between KTD and polymorphisms in renal transporter genes as well as APOL1 risk variants. This study may potentially engender an approach for prevention as well as stemming the burden of CKD in sub-Saharan Africa where GDP per capita is low and budgetary allocation for health is inadequate.

APOL1 Genetic Variants Are Associated with Serum-Oxidized Low-Density Lipoprotein Levels and Subclinical Atherosclerosis in South African CKD Patients

Introduction: Apolipoprotein L1 (APOL1) plays an important role in cholesterol metabolism and attenuation of low-density lipoprotein (LDL) oxidation. While protecting against Trypanosoma brucei rhodesiense infection, APOL1 risk alleles confer greater risk for CKD and cardiovascular disease among patients of African descent. Objectives: We investigated whether APOL1 risk variants are associated with atherosclerosis and oxidized LDL (OxLDL) levels among black South African CKD patients. Methods: A cross-sectional study of 120 adult CKD patients and 40 controls was undertaken. DNA samples of participants were genotyped for APOL1 G1 and G2 variants. High-sensitivity C-reactive protein, serum lipids, and OxLDL levels were measured, and carotid doppler ultrasonography was performed on all participants. Results: APOL1 alleles rs73885319, rs60910145, and rs71785313 had minor allele frequencies of 9.2, 8.8, and 17.5%, respectively, in the patients, and 8.8, 8.8, and 13.8%, respectively, in the controls. Of the 9 patients with 2 APOL1 risk alleles, 77.8% were compound G1/G2 heterozygotes and 22.2% were G2 homozygotes. Carriers of at least 1 APOL1 risk allele had a 3-fold increased risk of subclinical atherosclerosis (odds ratio 3.19; 95% confidence interval: 1.64–6.19; p = 0.01) compared to individuals with no risk alleles. Patients with 1 or 2 APOL1 risk alleles showed a significant increase in OxLDL levels when compared with those without the APOL1 risk allele. Conclusion: These findings suggest an increased risk for atherosclerosis in carriers of a single APOL1 risk variant, and the presence of APOL1 risk variants was associated with increased serum OxLDL levels in black South African CKD patients.

A focus on the association of Apol1 with kidney disease in children.

Individuals of African origin have an increased risk of developing various progressive chronic kidney diseases (CKD). This risk has been attributed to genetic variants (G1, G2) in apolipoprotein-L1 (APOL1) gene. In the pediatric population, especially in children affected by sickle cell disease (SCD), by human immunodeficiency virus (HIV), or with various glomerular diseases, APOL1 risk variants have been associated with the development of hypertension, albuminuria, and more rapid decline of kidney function. The present review focuses on existing APOL1-related epidemiological data in children with CKD. It also includes data from studies addressing racial disparities in CKD, the APOL1-related innate immunity, and the relationship between APOL1 and CKD and pathogenic pathways mediating APOL1-related kidney injury.

Apolipoprotein L1 associated nephropathy; an overview

Genetic variants of apolipoprotein L1 (APOL1) have been recognized as a risk factor for kidney disease in people of African ancestry. APOL1 mediate renal damage in podocytes through necrosis, apoptosis and pyroptosis processes. APOL1 gene contains G1 and G2 alleles that mediate in increasing risk of renal disorders in African Americans. People who carry APOL1 risk alleles have a three to four-fold increase risk for non-diabetic renal disease (NDRD), Idiopathic focal segmental glomerulosclerosis (FSGS) and HIV-associated nephropathy (HIVAN). Therefore, identifying genetic factors involved in the pathogenesis of renal disorders, including APOL1 risk variants, may help to improve our understanding of kidney problems.