APOL1 at 10 years: progress and next steps

Genetic Inhibition of APOL1 Pore-Forming Function Prevents APOL1-Mediated Kidney Disease

SIGNIFICANCE STATEMENT

African Americans are at increased risk of CKD in part due to high-risk (HR) variants in the apolipoprotein L1 ( APOL1 ) gene, termed G1/G2. A different APOL1 variant, p.N264K , reduced the risk of CKD and ESKD among carriers of APOL1 HR variants to levels comparable with individuals with APOL1 low-risk variants in an analysis of 121,492 participants of African ancestry from the Million Veteran Program (MVP). Functional genetic studies in cell models showed that APOL1 p.N264K blocked APOL1 pore-forming function and ion channel conduction and reduced toxicity of APOL1 HR mutations. Pharmacologic inhibitors that mimic this mutation blocking APOL1 -mediated pore formation may be able to prevent and/or treat APOL1 -associated kidney disease.

BACKGROUND

African Americans are at increased risk for nondiabetic CKD in part due to HR variants in the APOL1 gene.

METHODS

We tested whether a different APOL1 variant, p.N264K , modified the association between APOL1 HR genotypes (two copies of G1/G2) and CKD in a cross-sectional analysis of 121,492 participants of African ancestry from the MVP. We replicated our findings in the Vanderbilt University Biobank ( n =14,386) and National Institutes of Health All of Us ( n =14,704). Primary outcome was CKD and secondary outcome was ESKD among nondiabetic patients. Primary analysis compared APOL1 HR genotypes with and without p.N264K . Secondary analyses included APOL1 low-risk genotypes and tested for interaction. In MVP, we performed sequential logistic regression models adjusting for demographics, comorbidities, medications, and ten principal components of ancestry. Functional genomic studies expressed APOL1 HR variants with and without APOL1 p.N264K in cell models.

RESULTS

In the MVP cohort, 15,604 (12.8%) had two APOL1 HR variants, of which 582 (0.5%) also had APOL1 p.N264K . In MVP, 18,831 (15%) had CKD, 4177 (3%) had ESKD, and 34% had diabetes. MVP APOL1 HR, without p.N264K , was associated with increased odds of CKD (odds ratio [OR], 1.72; 95% confidence interval [CI], 1.60 to 1.85) and ESKD (OR, 3.94; 95% CI, 3.52 to 4.41). In MVP, APOL1 p.N264K mitigated the renal risk of APOL1 HR, in CKD (OR, 0.43; 95% CI, 0.28 to 0.65) and ESKD (OR, 0.19; CI 0.07 to 0.51). In the replication cohorts meta-analysis, APOL1 p.N264K mitigated the renal risk of APOL1 HR in CKD (OR, 0.40; 95% CI, 0.18 to 0.92) and ESKD (OR, 0.19; 95% CI, 0.05 to 0.79). In the mechanistic studies, APOL1 p.N264K blocked APOL1 pore-forming function and ion channel conduction and reduced toxicity of APOL1 HR variants.

CONCLUSIONS

APOL1 p.N264K is associated with reduced risk of CKD and ESKD among carriers of APOL1 HR to levels comparable with individuals with APOL1 low-risk genotypes.

Repetitive administration of rituximab can achieve and maintain clinical remission in patients with MCD or FSGS

Minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are glomerulopathies associated with nephrotic syndrome. Primary forms of these diseases are treated with various regimes of immunosuppression. Frequently relapsing or glucocorticoid-dependent courses remain challenging. Here, a B-cell-depleting strategy with rituximab represents a salvage option although data are sparse in the adult population. In particular, there is limited evidence on the efficacy of restoring remission after initial successful treatment with rituximab and whether patients benefit from an individualized, relapse-based approach. We identified 13 patients who received multiple therapies with rituximab from the FOrMe-registry (NCT03949972), a nationwide registry for MCD and FSGS in Germany, or from the University Hospital of Cologne. Disease status, changes in serum creatinine, proteinuria, and time to relapse were evaluated. Relapse-free survival was compared to the patients' previous therapy regimens. Through all treatment cycles, an improvement of disease activity was shown leading to a complete remission in 72% and partial remission in 26% after 3 ([Formula: see text]0.001) and 6 months ([Formula: see text]0.001). Relapse-free survival increased from 4.5 months (95%-CI 3-10 months) to 21 months (95%-CI 16-32 months) ([Formula: see text]0.001) compared to previous immunosuppression regimens with no loss in estimated glomerular filtration over time (p = 0.53). Compared to continuous B-cell depletion, an individualized relapse-based approach led to a reduced rituximab exposure and significant cost savings. Relapse-based administration of rituximab in patients with MCD/FSGS with an initial good clinical response did not result in a decreased efficacy at a median follow-up duration of 110 months. Thus, reinduction therapies may provide an alternative to continuous B-cell-depletion and reduce the long-term side effects of continuous immunosuppression.

Epidemiology and Outcomes of Glomerular Diseases in Low- and Middle-Income Countries

Glomerular diseases account for a significant proportion of chronic kidney disease in low-income and middle-income countries (LMICs). The epidemiology of glomerulonephritis is characterized inadequately in LMICs, largely owing to unavailable nephropathology services or uncertainty of the safety of the kidney biopsy procedure. In contrast to high-income countries where IgA nephropathy is the dominant primary glomerular disease, focal segmental glomerulosclerosis is common in large populations across Latin America, Africa, Middle East, and South East Asia, while IgA nephropathy is common in Chinese populations. Despite having a high prevalence of known genetic and viral risk factors that trigger focal segmental glomerulosclerosis, membranoproliferative glomerulonephritis also is common in adults and children in some African countries. Treatment of glomerular diseases in adults and children in LMICs largely is dependent on corticosteroids in combination with other immunosuppressive therapy, which often is cyclophosphamide because of its ready availability and low cost of treatment, despite significant adverse effects. Partial and/or complete remission status reported from studies of glomerular disease subtypes vary across LMIC regions, with high rates of kidney failure, mortality, and disease, and treatment complications often reported. Improving the availability of nephropathology services and ensuring availability of specific therapies are key measures to improving glomerular disease outcomes in LMICs.

Transcriptomic Analysis of Human Podocytes In Vitro: Effects of Differentiation and APOL1 Genotype

Introduction

The mechanisms in podocytes that mediate the pathologic effects of the APOL1 high-risk (HR) variants remain incompletely understood, although various molecular and cellular mechanisms have been proposed. We previously established conditionally immortalized human urine-derived podocyte-like epithelial cell (HUPEC) lines to investigate APOL1 HR variant-induced podocytopathy.

Methods

We conducted comprehensive transcriptomic analysis, including mRNA, microRNA (miRNA), and transfer RNA fragments (tRFs), to characterize the transcriptional profiles in undifferentiated and differentiated HUPEC with APOL1 HR (G1/G2, 2 cell lines) and APOL1 low-risk (LR) (G0/G0, 2 cell lines) genotypes. We reanalyzed single-cell RNA-seq data from urinary podocytes from focal segmental glomerulosclerosis (FSGS) subjects to characterize the effect of APOL1 genotypes on podocyte transcriptomes.

Results

Differential expression analysis showed that the ribosomal pathway was one of the most enriched pathways, suggesting that altered function of the translation initiation machinery may contribute to APOL1 variant-induced podocyte injury. Expression of genes related to the elongation initiation factor 2 pathway was also enriched in the APOL1 HR urinary podocytes from single-cell RNA-seq, supporting a prior report on the role of this pathway in APOL1-associated cell injury. Expression of microRNA and tRFs were analyzed, and the profile of small RNAs differed by both differentiation status and APOL1 genotype.

Conclusion

We have profiled the transcriptomic landscape of human podocytes, including mRNA, miRNA, and tRF, to characterize the effects of differentiation and of different APOL1 genotypes. The candidate pathways, miRNAs, and tRFs described here expand understanding of APOL1-associated podocytopathies.

Apolipoprotein L1 High-Risk Genotypes and Albuminuria in Sub-Saharan African Populations

BACKGROUND AND OBJECTIVES

Recessive inheritance of African-specific APOL1 kidney risk variants is associated with higher risk of nondiabetic kidney disease, progression to kidney failure, and early-onset albuminuria that precedes eGFR decline. The effect of APOL1 risk variants on kidney disease in continental Africans is understudied. Objectives of this study were to determine APOL1 risk allele prevalence and associations between APOL1 genotypes and kidney disease in West, East, and South Africa.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This cross-sectional population-based study in four African countries included 10,769 participants largely aged 40-60 years with sociodemographic and health information, anthropometry data, and blood and urine tests for biomarkers of kidney disease. APOL1 risk alleles were imputed from the H3Africa genotyping array, APOL1 risk allele and genotype frequencies were determined, and genetic associations were assessed for kidney disease. Kidney disease was defined as the presence of eGFR <60 ml/min per 1.73 m², albuminuria, or a composite end point including eGFR <60 ml/min per 1.73 m² and/or albuminuria.

RESULTS

High G1 allele frequencies occurred in South and West Africa (approximately 7%-13%). G2 allele frequencies were highest in South Africa (15%-24%), followed by West Africa (9%-12%). Associations between APOL1 risk variants and albuminuria were significant for recessive (odds ratio, 1.63; 95% confidence interval, 1.25 to 2.12) and additive (odds ratio, 1.39; 95% confidence interval, 1.09 to 1.76) models. Associations were stronger for APOL1 G1/G1 genotypes versus G0/G0 (odds ratio, 3.87; 95% confidence interval, 2.16 to 6.93) compared with either G2/G2 (odds ratio, 1.65; 95% confidence interval, 1.09 to 2.51) or G1/G2 (odds ratio, 1.24; 95% confidence interval, 0.83 to 1.87). No association between APOL1 risk variants and eGFR <60 ml/min per 1.73 m² was observed.

CONCLUSIONS

APOL1 G1 and G2 alleles and high-risk genotype frequencies differed between and within West and South Africa and were almost absent from East Africa. APOL1 risk variants were associated with albuminuria but not eGFR <60 ml/min per 1.73 m². There may be differential effects of homozygous G1 and G2 genotypes on albuminuria that require further investigation.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_05_16_CJN14321121.mp3.

Antisense oligonucleotides ameliorate kidney dysfunction in podocyte specific APOL1 risk variant mice

Coding variants (named G1 and G2) in Apolipoprotein L1 (APOL1) can explain the most excess risk of kidney disease observed in African Americans. It has been proposed that risk variant APOL1 dose, such as increased risk variant APOL1 level serves as a trigger (second hit) for disease development. The goal of this study was to determine whether lowering risk variant APOL1 levels protects from disease development in podocyte specific transgenic mouse disease model. We administered antisense oligonucleotides (ASO) targeting APOL1 to podocyte specific G2APOL1 mice and observed efficient reduction of APOL1 levels. APOL1 ASO1, which more efficiently lowered APOL1 transcript levels, protected mice from albuminuria, glomerulosclerosis, tubulointerstitial fibrosis, and renal failure. The administration of APOL1 ASO1 was effective even for established disease in the NEFTA-rtTA/TRE-G2APOL1 (NEFTA/G2APOL1) mice. We observed a strong correlation between APOL1 transcript level and disease severity. We concluded that an APOL1 ASO1 may be an effective therapeutic approach for APOL1-associated glomerular disease.

APOL1 Risk Variants, Acute Kidney Injury, and Death in Participants With African Ancestry Hospitalized With COVID-19 From the Million Veteran Program

IMPORTANCE

Coronavirus disease 2019 (COVID-19) confers significant risk of acute kidney injury (AKI). Patients with COVID-19 with AKI have high mortality rates.

OBJECTIVE

Individuals with African ancestry with 2 copies of apolipoprotein L1 (APOL1) variants G1 or G2 (high-risk group) have significantly increased rates of kidney disease. We tested the hypothesis that the APOL1 high-risk group is associated with a higher-risk of COVID-19-associated AKI and death.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study included 990 participants with African ancestry enrolled in the Million Veteran Program who were hospitalized with COVID-19 between March 2020 and January 2021 with available genetic information.

EXPOSURES

The primary exposure was having 2 APOL1 risk variants (RV) (APOL1 high-risk group), compared with having 1 or 0 risk variants (APOL1 low-risk group).

MAIN OUTCOMES AND MEASURES

The primary outcome was AKI. The secondary outcomes were stages of AKI severity and death. Multivariable logistic regression analyses adjusted for preexisting comorbidities, medications, and inpatient AKI risk factors; 10 principal components of ancestry were performed to study these associations. We performed a subgroup analysis in individuals with normal kidney function prior to hospitalization (estimated glomerular filtration rate ≥60 mL/min/1.73 m2).

RESULTS

Of the 990 participants with African ancestry, 905 (91.4%) were male with a median (IQR) age of 68 (60-73) years. Overall, 392 (39.6%) patients developed AKI, 141 (14%) developed stages 2 or 3 AKI, 28 (3%) required dialysis, and 122 (12.3%) died. One hundred twenty-five (12.6%) of the participants were in the APOL1 high-risk group. Patients categorized as APOL1 high-risk group had significantly higher odds of AKI (adjusted odds ratio [OR], 1.95; 95% CI, 1.27-3.02; P = .002), higher AKI severity stages (OR, 2.03; 95% CI, 1.37-2.99; P < .001), and death (OR, 2.15; 95% CI, 1.22-3.72; P = .007). The association with AKI persisted in the subgroup with normal kidney function (OR, 1.93; 95% CI, 1.15-3.26; P = .01). Data analysis was conducted between February 2021 and April 2021.

CONCLUSIONS AND RELEVANCE

In this cohort study of veterans with African ancestry hospitalized with COVID-19 infection, APOL1 kidney risk variants were associated with higher odds of AKI, AKI severity, and death, even among individuals with prior normal kidney function.

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 in vitro 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.

The key role of NLRP3 and STING in APOL1-associated podocytopathy

Coding variants in apolipoprotein L1 (APOL1), termed G1 and G2, can explain most excess kidney disease risk in African Americans; however, the molecular pathways of APOL1-induced kidney dysfunction remain poorly understood. Here, we report that expression of G2 APOL1 in the podocytes of Nphs1rtTA/TRE-G2APOL1 (G2APOL1) mice leads to early activation of the cytosolic nucleotide sensor, stimulator of interferon genes (STING), and the NLR family pyrin domain-containing 3 (NLRP3) inflammasome. STING and NLRP3 expression was increased in podocytes from patients with high-risk APOL1 genotypes, and expression of APOL1 correlated with caspase-1 and gasdermin D (GSDMD) levels. To demonstrate the role of NLRP3 and STING in APOL1-associated kidney disease, we generated transgenic mice with the G2 APOL1 risk variant and genetic deletion of Nlrp3 (G2APOL1/Nlrp3 KO), Gsdmd (G2APOL1/Gsdmd KO), and STING (G2APOL1/STING KO). Knockout mice displayed marked reduction in albuminuria, azotemia, and kidney fibrosis compared with G2APOL1 mice. To evaluate the therapeutic potential of targeting NLRP3, GSDMD, and STING, we treated mice with MCC950, disulfiram, and C176, potent and selective inhibitors of NLRP3, GSDMD, and STING, respectively. G2APOL1 mice treated with MCC950, disulfiram, and C176 showed lower albuminuria and improved kidney function even when inhibitor treatment was initiated after the development of albuminuria.