Apolipoprotein L1 and mechanisms of kidney disease susceptibility

HIV-associated kidney disease: the changing spectrum and treatment priorities

PURPOSE OF REVIEW

This review examines the impact of HIV on kidney disease, which remains significant despite advances in antiretroviral therapy (ART). The review is timely due to the shifting epidemiology of kidney disease in people with HIV (PWH), driven by increased ART access, noncommunicable diseases, and region-specific opportunistic infections like tuberculosis.

RECENT FINDINGS

The literature highlights a decline in HIV-associated nephropathy (HIVAN) and a rise in tubulointerstitial diseases and noncommunicable diseases among PWH. Studies from the United States and South Africa report decreased HIVAN prevalence and increased rates of tubulointerstitial diseases linked to tenofovir disoproxil fumarate (TDF) toxicity and tuberculosis (TB). Immune complex glomerulonephritis (ICGN) and diabetic kidney disease (DKD) are also prevalent.

SUMMARY

The findings underscore the need for improved diagnostic tools for opportunistic infections, management of ART-related complications, and strategies to address noncommunicable diseases in PWH. There is a need to centralize care to address all health needs simultaneously. Future research should focus on APOL1-targeted therapies and the role of SGLT2 inhibitors in CKD. Enhanced transplantation outcomes and the development of guidelines for managing DKD in PWH are critical for advancing clinical practice and improving patient outcomes.

Genomics in Diabetic Kidney Disease: A 2024 Update

Diabetic Kidney Disease (DKD) remains the leading cause of Chronic and End Stage Kidney Disease (ESKD) worldwide, with an increasing epidemiological burden. However, still, the disease awareness remains low, early diagnosis is difficult, and therapeutic management is ineffective. These might be attributed to the fact that DKD is a highly heterogeneous disease, with disparities and variability in clinical presentation and progression patterns. Besides environmental risk factors, genetic studies have emerged as a novel and promising tool in the field of DKD. Three decades ago, family studies first reported that inherited genetic factors might confer significant risk to DKD development and progression. During the past decade, genome-wide association studies (GWASs) screening the whole genome in large and multi-ethnic population-based cohorts identified genetic risk variants associated with traits defining DKD in both type 1 and 2 diabetes. Herein, we aim to summarize the existing data regarding the progress in the field of genomics in DKD, present how the revolution of GWAS expanded our understanding of pathophysiologic disease mechanisms and finally, suggest potential future directions.

The changing landscape of HIV-associated kidney disease

The HIV epidemic has devastated millions of people globally, with approximately 40 million deaths since its start. The availability of antiretroviral therapy (ART) has transformed the prognosis of millions of individuals infected with HIV such that a diagnosis of HIV infection no longer automatically confers death. However, morbidity and mortality remain substantial among people living with HIV. HIV can directly infect the kidney to cause HIV-associated nephropathy (HIVAN) - a disease characterized by podocyte and tubular damage and associated with an increased risk of kidney failure. The reports of HIVAN occurring primarily in those of African ancestry led to the discovery of its association with APOL1 risk alleles. The advent of ART has led to a substantial decrease in the prevalence of HIVAN; however, reports have emerged of an increase in the prevalence of other kidney pathology, such as focal segmental glomerulosclerosis and pathological conditions associated with co-morbidities of ageing, such as hypertension and diabetes mellitus. Early initiation of ART also results in a longer cumulative exposure to medications, increasing the likelihood of nephrotoxicity. A substantial body of literature supports the use of kidney transplantation in people living with HIV, demonstrating significant survival benefits compared with that of people undergoing chronic dialysis, and similar long-term allograft and patient survival compared with that of HIV-negative kidney transplant recipients.

Apolipoproteins L1 and L3 control mitochondrial membrane dynamics

Apolipoproteins L1 and L3 (APOLs) are associated at the Golgi with the membrane fission factors phosphatidylinositol 4-kinase-IIIB (PI4KB) and non-muscular myosin 2A. Either APOL1 C-terminal truncation (APOL1Δ) or APOL3 deletion (APOL3-KO [knockout]) reduces PI4KB activity and triggers actomyosin reorganization. We report that APOL3, but not APOL1, controls PI4KB activity through interaction with PI4KB and neuronal calcium sensor-1 or calneuron-1. Both APOLs are present in Golgi-derived autophagy-related protein 9A vesicles, which are involved in PI4KB trafficking. Like APOL3-KO, APOL1Δ induces PI4KB dissociation from APOL3, linked to reduction of mitophagy flux and production of mitochondrial reactive oxygen species. APOL1 and APOL3, respectively, can interact with the mitophagy receptor prohibitin-2 and the mitophagosome membrane fusion factor vesicle-associated membrane protein-8 (VAMP8). While APOL1 conditions PI4KB and APOL3 involvement in mitochondrion fission and mitophagy, APOL3-VAMP8 interaction promotes fusion between mitophagosomal and endolysosomal membranes. We propose that APOL3 controls mitochondrial membrane dynamics through interactions with the fission factor PI4KB and the fusion factor VAMP8.

Apolipoprotein L1 (APOL1) cation current in HEK-293 cells and in human podocytes

Two heterozygous missense variants (G1 and G2) of Apolipoprotein L1 (APOL1) found in individuals of recent African ancestry can attenuate the severity of infection by some forms of Trypanosoma brucei. However, these two variants within a broader African haplotype also increase the risk of kidney disease in Americans of African descent. Although overexpression of either variant G1 or G2 causes multiple pathogenic changes in cultured cells and transgenic mouse models, the mechanism(s) promoting kidney disease remain unclear. Human serum APOL1 kills trypanosomes through its cation channel activity, and cation channel activity of recombinant APOL1 has been reconstituted in lipid bilayers and proteoliposomes. Although APOL1 overexpression increases whole cell cation currents in HEK-293 cells, the ion channel activity of APOL1 has not been assessed in glomerular podocytes, the major site of APOL1-associated kidney diseases. We characterize APOL1-associated whole cell and on-cell cation currents in HEK-293 T-Rex cells and demonstrate partial inhibition of currents by anti-APOL antibodies. We detect in primary human podocytes a similar cation current inducible by interferon-γ (IFNγ) and sensitive to inhibition by anti-APOL antibody as well as by a fragment of T. brucei Serum Resistance-Associated protein (SRA). CRISPR knockout of APOL1 in human primary podocytes abrogates the IFNγ-induced, antibody-sensitive current. Our novel characterization in HEK-293 cells of heterologous APOL1-associated cation conductance inhibited by anti-APOL antibody and our documentation in primary human glomerular podocytes of endogenous IFNγ-stimulated, APOL1-mediated, SRA and anti-APOL-sensitive ion channel activity together support APOL1-mediated channel activity as a therapeutic target for treatment of APOL1-associated kidney diseases.

APOL1 G3 Variant Is Associated with Cardiovascular Mortality and Sudden Cardiac Death in Patients Receiving Maintenance Hemodialysis of European Ancestry

INTRODUCTION

The G1 and G2 variants in the APOL1 gene convey high risk for the progression of chronic kidney disease in African Americans. The G3 variant in APOL1 is more common in patients of European ancestry (EA); outcomes associated with this variant have not been explored previously in EA patients receiving dialysis.

METHODS

DNA was collected from approximately half of the patients enrolled in the Evaluation of Cinacalcet HCl Therapy to Lower Cardiovascular Events (EVOLVE) trial and genotyped for the G3 variants. We utilized an additive genetic model to test associations of G3 with the EVOLVE adjudicated endpoints of all-cause mortality, cardiovascular mortality, sudden cardiac death (SCD), and heart failure. EA and African ancestry samples were analyzed separately. Validation was done in the Vanderbilt BioVU using ICD codes for cardiovascular events that parallel the adjudicated endpoints in EVOLVE.

RESULTS

In EVOLVE, G3 in EA patients was associated with the adjudicated endpoints of cardiovascular mortality and SCD. In a validation cohort from the Vanderbilt BioVU, cardiovascular events and cardiovascular mortality defined by ICD codes showed similar associations in EA participants who had been on dialysis for 2 to <5 years.

DISCUSSION/CONCLUSIONS

G3 in APOL1 variant was associated with cardiovascular events and cardiovascular mortality in the EA patients receiving dialysis. This suggests that variations in the APOL1 gene that differ in populations of different ancestry may contribute to cardiovascular disease.

HIV-Associated Nephropathy in 2022

Background

HIV-associated nephropathy (HIVAN) is a renal parenchymal disease that occurs exclusively in people living with HIV. It is a serious kidney condition that may possibly lead to end-stage kidney disease, particularly in the HIV-1 seropositive patients.

Summary

The African-American population has increased susceptibility to this comorbidity due to a strong association found in the APOL1 gene, specifically two missense mutations in the G1 allele and a frameshift deletion in the G2 allele, although a "second-hit" event is postulated to have a role in the development of HIVAN. HIVAN presents with proteinuria, particularly in the nephrotic range, as with other kidney diseases. The diagnosis requires biopsy and typically presents with collapsing subtype focal segmental glomerulosclerosis and microcyst formation in the tubulointerstitial region. Gaps still exist in the definitive treatment of HIVAN - concurrent use of antiretroviral therapy and adjunctive management with like renal-angiotensin-aldosterone system inhibitors, steroids, or renal replacement therapy showed benefits.

Key Message

This study reviews the current understanding of HIVAN including its epidemiology, mechanism of disease, related genetic factors, clinical profile, and pathophysiologic effects of management options for patients.

Treatment potential in APOL1-associated nephropathy

PURPOSE OF REVIEW

More than 5 million African-Americans, and millions more in Africa and worldwide, possess apolipoprotein L1 gene (APOL1) high-risk genotypes with an increased risk for chronic kidney disease. This manuscript reviews treatment approaches for slowing the progression of APOL1-associated nephropathy.

RECENT FINDINGS

Since the 2010 discovery of APOL1 as a cause of nondiabetic nephropathy in individuals with sub-Saharan African ancestry, it has become apparent that aggressive hypertension control, renin-angiotensin system blockade, steroids and conventional immunosuppressive agents are suboptimal treatments. In contrast, APOL1-mediated collapsing glomerulopathy due to interferon treatment and HIV infection, respectively, often resolve with cessation of interferon or antiretroviral therapy. Targeted therapies, including APOL1 small molecule inhibitors, APOL1 antisense oligonucleotides (ASO) and inhibitors of APOL1-associated inflammatory pathways, hold promise for these diseases. Evolving therapies and the need for clinical trials support the importance of increased use of APOL1 genotyping and kidney biopsy.

SUMMARY

APOL1-associated nephropathy includes a group of related phenotypes that are driven by the same two genetic variants in APOL1. Clinical trials of small molecule inhibitors, ASO, and inflammatory pathway inhibitors may improve outcomes in patients with primary forms of APOL1-associated nephropathy.

The known unknowns of apolipoprotein glycosylation in health and disease

Apolipoproteins, the protein component of lipoproteins, play an important role in lipid transport, lipoprotein assembly, and receptor recognition. Apolipoproteins are glycosylated and the glycan moieties play an integral role in apolipoprotein function. Changes in apolipoprotein glycosylation correlate with several diseases manifesting in dyslipidemias. Despite their relevance in apolipoprotein function and diseases, the total glycan repertoire of most apolipoproteins remains undefined. This review summarizes the current knowledge and knowledge gaps regarding human apolipoprotein glycan composition, structure, glycosylation site, and functions. Given the relevance of glycosylation to apolipoprotein function, we expect that future studies of apolipoprotein glycosylation will contribute new understanding of disease processes and uncover relevant biomarkers and therapeutic targets. Considering these future efforts, we also provide a brief overview of current mass spectrometry based technologies that can be applied to define detailed glycan structures, site-specific compositions, and the role of emerging approaches for clinical applications in biomarker discovery and personalized medicine.