GWAS in Mice Maps Susceptibility to HIV-Associated Nephropathy to the Ssbp2 Locus

BACKGROUND

To gain insight into the pathogenesis of collapsing glomerulopathy, a rare form of FSGS that often arises in the setting of viral infections, we performed a genome-wide association study (GWAS) among inbred mouse strains using a murine model of HIV-1 associated nephropathy (HIVAN).

METHODS

We first generated F1 hybrids between HIV-1 transgenic mice on the FVB/NJ background and 20 inbred laboratory strains. Analysis of histology, BUN, and urinary NGAL demonstrated marked phenotypic variation among the transgenic F1 hybrids, providing strong evidence for host genetic factors in the predisposition to nephropathy. A GWAS in 365 transgenic F1 hybrids generated from these 20 inbred strains was performed.

RESULTS

We identified a genome-wide significant locus on chromosome 13-C3 and multiple additional suggestive loci. Crossannotation of the Chr. 13 locus, including single-cell transcriptomic analysis of wildtype and HIV-1 transgenic mouse kidneys, nominated Ssbp2 as the most likely candidate gene. Ssbp2 is highly expressed in podocytes, encodes a transcriptional cofactor that interacts with LDB1 and LMX1B, which are both previously implicated in FSGS. Consistent with these data, older Ssbp2 null mice spontaneously develop glomerulosclerosis, tubular casts, interstitial fibrosis, and inflammation, similar to the HIVAN mouse model.

CONCLUSIONS

These findings demonstrate the utility of GWAS in mice to uncover host genetic factors for rare kidney traits and suggest Ssbp2 as susceptibility gene for HIVAN, potentially acting via the LDB1-LMX1B transcriptional network.

Childhood HIV-associated nephropathy: 36 years later

HIV-associated nephropathy (HIVAN) predominantly affects people of African ancestry living with HIV who do not receive appropriate antiretroviral therapy (ART). Childhood HIVAN is characterized by heavy proteinuria and decreased kidney function. Kidney histology shows mesangial expansion, classic or collapsing glomerulosclerosis, and microcystic renal tubular dilatation leading to kidney enlargement. The pathogenesis of HIVAN involves the kidney recruitment of inflammatory cells and the infection of kidney epithelial cells. In addition, both viral and genetic factors play key roles in this disease. Modern ART has improved the outcome and decreased the prevalence of childhood HIVAN. However, physicians have had modest success providing chronic ART to children and adolescents, and we continue to see children with HIVAN all over the world. This article discusses the progress made during the last decade in our understanding of the pathogenesis and treatment of childhood HIVAN, placing particular emphasis on the mechanisms that mediate the infection of kidney epithelial cells, and the roles of cytokines, the HIV-Tat gene, and the Apolipoprotein-1 (APOL1) gene risk variants in this disease. In view of the large number of children living with HIV at risk of developing HIVAN, better prevention and treatment programs are needed to eradicate this disease.

Circulating fibroblast growth factor-2 precipitates HIV nephropathy in mice

People of African ancestry living with the human immunodeficiency virus-1 (HIV-1) are at risk of developing HIV-associated nephropathy (HIVAN). Children with HIVAN frequently show high plasma fibroblast growth factor-2 (FGF-2) levels; however, the role of circulating FGF-2 in the pathogenesis of childhood HIVAN is unclear. Here, we explored how circulating FGF-2 affected the outcome of HIVAN in young HIV-Tg26 mice. Briefly, we demonstrated that FGF-2 was preferentially recruited in the kidneys of mice without pre-existing kidney disease, precipitating HIVAN by activating phosphorylated extracellular signal-regulated kinase (pERK) in renal epithelial cells, without inducing the expression of HIV-1 genes. Wild-type mice injected with recombinant adenoviral FGF-2 (rAd-FGF-2) vectors carrying a secreted form of human FGF-2 developed transient and reversible HIVAN-like lesions, including proteinuria and glomerular enlargement. HIV-Tg26 mice injected with rAd-FGF-2 vectors developed more-significant proliferative and pro-fibrotic inflammatory lesions, similar to those seen in childhood HIVAN. These lesions were partially reversed by treating mice with the FGF/VEGF receptor tyrosine kinase inhibitor PD173074. These findings suggest that high plasma FGF-2 levels may be an independent risk factor for precipitating HIVAN in young children.

Diagnosis, Education, and Care of Patients with APOL1-Associated Nephropathy: A Delphi Consensus and Systematic Review

BACKGROUND

APOL1 variants contribute to the markedly higher incidence of ESKD in Blacks compared with Whites. Genetic testing for these variants in patients with African ancestry who have nephropathy is uncommon, and no specific treatment or management protocol for APOL1-associated nephropathy currently exists.

METHODS

A multidisciplinary, racially diverse group of 14 experts and patient advocates participated in a Delphi consensus process to establish practical guidance for clinicians caring for patients who may have APOL1-associated nephropathy. Consensus group members took part in three anonymous voting rounds to develop consensus statements relating to the following: (1) counseling, genotyping, and diagnosis; (2) disease awareness and education; and (3) a vision for management of APOL1-associated nephropathy in a future when treatment is available. A systematic literature search of the MEDLINE and Embase databases was conducted to identify relevant evidence published from January 1, 2009 to July 14, 2020.

RESULTS

The consensus group agreed on 55 consensus statements covering such topics as demographic and clinical factors that suggest a patient has APOL1-associated nephropathy, as well as key considerations for counseling, testing, and diagnosis in current clinical practice. They achieved consensus on the need to increase awareness among key stakeholders of racial health disparities in kidney disease and of APOL1-associated nephropathy and on features of a successful education program to raise awareness among the patient community. The group also highlighted the unmet need for a specific treatment and agreed on best practice for management of these patients should a treatment become available.

CONCLUSIONS

A multidisciplinary group of experts and patient advocates defined consensus-based guidance on the care of patients who may have APOL1-associated nephropathy.

HIV-Positive Kidney Donor Selection for HIV-Positive Transplant Recipients

The risks associated with transplanting HIV-positive kidneys into HIV-positive recipients have not been well studied. Since 2008, 43 kidneys from 25 HIV-positive deceased donors have been transplanted into patients who are HIV positive in Cape Town, South Africa. Among the donors, 19 (76%) died secondary to trauma. The average age for donors was 34 (interquartile range, 19-52) years old. In some donors, only one kidney was used because of a limited number of suitable recipients on the waiting list. Only two donors had been previously exposed to antiretroviral triple therapy. In 23 of the deceased organ donors, the HIV status was not known before the time of death. Initial concerns about transplanting HIV-positive allografts into HIV-positive recipients in this clinic revolved around the possibility of HIV superinfection. However, all recipients remained virally suppressed several years after the transplant. Only one recipient experienced an increased viral load after the transplant, which was related to a period of noncompliance on her medication. After counseling and improved compliance, the viral load decreased and became suppressed again. Herein, we discuss the findings of this study and review the literature available on this crucial topic.

Kidney Disease in HIV: Moving beyond HIV-Associated Nephropathy

In developed countries, remarkable advances in antiretroviral therapy have transformed HIV infection into a chronic condition. As a result, HIV-associated nephropathy, the classic HIV-driven kidney lesion among individuals of African descent, has largely disappeared in these regions. However, HIV-positive blacks continue to have much higher rates of ESRD than HIV-positive whites, which could be attributed to the APOL1 renal risk variants. Additionally, HIV-positive individuals face adverse consequences beyond HIV itself, including traditional risk factors for CKD and nephrotoxic effects of antiretroviral therapy. Concerns for nephrotoxicity also extend to HIV-negative individuals using tenofovir disoproxil fumarate-based pre-exposure prophylaxis for the prevention of HIV infection. Therefore, CKD remains an important comorbid condition in the HIV-positive population and an emerging concern among HIV-negative persons receiving pre-exposure prophylaxis. With the improved longevity of HIV-positive individuals, a kidney transplant has become a viable option for many who have progressed to ESRD. Herein, we review the growing knowledge regarding the APOL1 renal risk variants in the context of HIV infection, antiretroviral therapy-related nephrotoxicity, and developments in kidney transplantation among HIV-positive individuals.

Transmembrane TNF-α Facilitates HIV-1 Infection of Podocytes Cultured from Children with HIV-Associated Nephropathy

Studies have shown that podocytes and renal tubular epithelial cells from patients with HIV-associated nephropathy (HIVAN) express HIV-1 transcripts, suggesting that productive infection of renal epithelial cells precipitates development of HIVAN. However, podocytes and renal tubular epithelial cells do not express CD4 receptors, and it is unclear how these cells become productively infected in vivo We investigated the mechanisms underlying the infection by HIV-1 of podocytes cultured from the urine of children with HIVAN. We observed low-level productive infection on exposure of these cells to primary cell-free HIV-1 supernatants. However, envelope-defective recombinant HIV-1 did not infect the renal epithelial cell lines. Moreover, treatment of podocytes to inhibit endocytic transport or dynamin activity or remove cell surface heparan sulfate proteoglycans reduced infection efficiency. Transfection of CD4- 293T cells with a cDNA expression library developed from a podocyte cell line derived from a child with HIVAN led to the identification of TNF-α as a possible mediator of HIV-1 infection. Overexpression of transmembrane TNF-α in cultured CD4- renal tubular epithelial cells, 293T cells, and HeLa cells enabled the infection of these cells; exposure to soluble TNF-α did not. Immunohistochemistry showed TNF-α expression in podocytes of renal sections from children with HIVAN. Furthermore, we found that TNF-α enhanced NF-κB activation and integration of HIV-1 into the podocyte DNA. Finally, inhibition of dynamin activity blocked TNF-α-mediated infection. These data establish a role for transmembrane TNF-α in facilitating the viral entry and integration of HIV-1 into the DNA of renal epithelial cells.

APOL1 Risk Variants Are Strongly Associated with HIV-Associated Nephropathy in Black South Africans

APOL1 variants are associated with HIV-associated nephropathy and FSGS in African Americans. The prevalence of these variants in African populations with CKD in HIV-1 infection has not been investigated. We determined the role of APOL1 variants in 120 patients with HIV-associated nephropathy and CKD and 108 controls from a South-African black population. Patients with CKD were selected on the basis of histology. Genotypes were successfully determined for APOL1 G1 and G2 variants and 42 single nucleotide polymorphisms, including 18 ancestry informative markers, for 116 patients with CKD (96.7%; 38 patients with HIV-associated nephropathy, 39 patients with HIV-positive CKD, and 39 patients with HIV-negative CKD), and 108 controls (100%). Overall, 79% of patients with HIV-associated nephropathy and 2% of population controls carried two risk alleles. In a recessive model, individuals carrying any combination of two APOL1 risk alleles had 89-fold higher odds (95% confidence interval, 18 to 912; P<0.001) of developing HIV-associated nephropathy compared with HIV-positive controls. Population allele frequencies were 7.3% for G1 and 11.1% for G2. APOL1 risk alleles were not significantly associated with other forms of CKD. These results indicate HIV-positive, antiretroviral therapy-naïve South-African blacks with two APOL1 risk alleles are at very high risk for developing HIV-associated nephropathy. Further studies are required to determine the effect of APOL1 risk variants on kidney diseases in other regions of sub-Saharan Africa.

A National Study of Outcomes among HIV-Infected Kidney Transplant Recipients

Kidney transplantation is a viable treatment for select patients with HIV and ESRD, but data are lacking regarding long-term outcomes and comparisons with appropriately matched HIV-negative patients. We analyzed data from the Scientific Registry of Transplant Recipients (SRTR; 2002-2011): 510 adult kidney transplant recipients with HIV (median follow-up, 3.8 years) matched 1:10 to HIV-negative controls. Compared with HIV-negative controls, HIV-infected recipients had significantly lower 5-year (75.3% versus 69.2%) and 10-year (54.4% versus 49.8%) post-transplant graft survival (GS) (hazard ratio [HR], 1.37; 95% confidence interval [95% CI], 1.15 to 1.64; P<0.001) that persisted when censoring for death (HR, 1.43; 95% CI, 1.12 to 1.84; P=0.005). However, compared with HIV-negative/hepatitis C virus (HCV)-negative controls, HIV monoinfected recipients had similar 5-year and 10-year GS, whereas HIV/HCV coinfected recipients had worse GS (5-year: 64.0% versus 52.0%, P=0.02; 10-year: 36.2% versus 27.0%, P=0.004 [HR, 1.38; 95% CI, 1.08 to 1.77; P=0.01]). Patient survival (PS) among HIV-infected recipients was 83.5% at 5 years and 51.6% at 10 years and was significantly lower than PS among HIV-negative controls (HR, 1.34; 95% CI, 1.08 to 1.68; P<0.01). However, PS was similar for HIV monoinfected recipients and HIV-negative/HCV-negative controls at both times. HIV/HCV coinfected recipients had worse PS compared with HIV-negative/HCV-infected controls (5-year: 67.0% versus 78.6%, P=0.007; 10-year: 29.3% versus 56.23%, P=0.002 [HR, 1.57; 95% CI, 1.11 to 2.22; P=0.01]). In conclusion, HIV-negative and HIV monoinfected kidney transplant recipients had similar GS and PS, whereas HIV/HCV coinfected recipients had worse outcomes. Although encouraging, these results suggest caution in transplanting coinfected patients.

Association of urine α1-microglobulin with kidney function decline and mortality in HIV-infected women

BACKGROUND AND OBJECTIVES

Despite advances in therapy, HIV-infected individuals remain at higher risk for kidney dysfunction than uninfected individuals. It was hypothesized that urine levels of α1-microglobulin, a biomarker of proximal tubular dysfunction, would predict kidney function decline and mortality risk in HIV-infected and uninfected women.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In the Women's Interagency HIV Study, urine α1-microglobulin and creatinine concentrations were measured in 903 HIV-infected and 287 uninfected women using stored urine from 1999 to 2000, when prevalence of tenofovir use was <1%. Participants were categorized into three categories by level of α1-microglobulin-to-creatinine ratio, and associations with kidney decline and all-cause mortality over 8 years were evaluated.

RESULTS

Urine α1-microglobulin was detectable in 60% of HIV-infected and 40% of uninfected women (P<0.001). Among HIV-infected women, there were 177 (22%), 61 (7%), and 128 (14%) patients with incident CKD, with 10% annual eGFR decline, and who died, respectively. Compared with HIV-infected women in the lowest α1-microglobulin category, HIV-infected women in the highest α1-microglobulin category had a 2.1-fold risk of incident CKD (95% confidence interval, 1.3 to 3.4), 2.7-fold risk of 10% annual eGFR decline (95% confidence interval, 1.2 to 5.9), and 1.6-fold mortality risk (95% confidence interval, 1.0 to 2.6) in models adjusting for kidney risk factors, baseline eGFR, and albuminuria. Among uninfected women, the highest α1-microglobulin category was associated with 3% (relative risk, 2.2; 95% confidence interval, 1.4 to 3.5) and 5% (relative risk, 2.2; 95% confidence interval, 1.1 to 4.3) annual eGFR decline relative to the lowest α1-microglobulin category.

CONCLUSIONS

Proximal tubular dysfunction, indicated by urine α1-microglobulin, was independently associated with kidney function decline in HIV-infected and uninfected women and mortality risk among HIV-infected women.

Gene-gene and gene-environment interactions in apolipoprotein L1 gene-associated nephropathy

Molecular genetics have revolutionized the understanding of susceptibility to the broad spectrum of kidney diseases with light microscopic appearance of FSGS, particularly in populations with recent African ancestry. These disorders include idiopathic FSGS, HIV-associated nephropathy, severe lupus nephritis, sickle cell nephropathy, and the primary kidney disorder focal global glomerulosclerosis, which had historically been ascribed to systemic hypertension. FSGS was once thought to include a multitude of unrelated disorders with similar histologic appearance. However, variation in the apolipoprotein L1 gene locus is now known to account for the vast majority of such cases in African Americans as well as nearly all the excess risk for FSGS and related forms of progressive nondiabetic nephropathy in populations with recent African ancestry, relative to European ancestry. Inheriting two coding apolipoprotein L1 gene nephropathy risk variants is necessary for susceptibility to CKD; however, these variants alone are insufficient to produce disease. This work reviews the evidence supporting second hits or modifying factors that affect risk for apolipoprotein L1 gene-associated nephropathy and produce the protean manifestations of this common and complex syndrome. Targeting modifiable second factors will lead to preventive therapies for slowing progression of nondiabetic nephropathy in many patients possessing two apolipoprotein L1 gene risk variants. This model of genetic risk coupled with modifiable second hits will serve as a paradigm applicable to patients with CKD of various etiologies as well as a host of other complex disorders.

The basic domain of HIV-tat transactivating protein is essential for its targeting to lipid rafts and regulating fibroblast growth factor-2 signaling in podocytes isolated from children with HIV-1-associated nephropathy

Podocyte injury has a critical role in the pathogenesis of HIV-associated nephropathy (HIVAN). The HIV-1 transactivator of transcription (Tat), combined with fibroblast growth factor-2 (FGF-2), can induce the dedifferentiation and proliferation of cultured human podocytes. Cellular internalization of Tat requires interactions with heparan sulfate proteoglycans and cholesterol-enriched lipid rafts (LRs). However, the specific distribution of Tat in human podocytes and its ability to associate with LRs have not been documented. Here, we found that Tat is preferentially recruited to LRs in podocytes isolated from children with HIVAN. Furthermore, we identified arginines in the basic domain (RKKRRQRRR) of Tat as essential for (1) targeting Tat to LRs, (2) Tat-mediated increases in the expression of Rho-A and matrix metalloproteinase-9 in LRs, and (3) Tat-mediated enhancement of FGF-2 signaling in human podocytes and HIV-transgenic mouse kidneys and the exacerbation of renal lesions in these mice. Tat carrying alanine substitutions in the basic domain (AKKAAQAAA) remained localized in the cytosol and did not associate with LRs or enhance FGF-2 signaling in cultured podocytes. These results show the specific association of Tat with LRs in podocytes isolated from children with HIVAN, confirm Tat as a regulator of FGF-2 signaling in LRs, and identify the key domain of Tat responsible for promoting these effects and aggravating renal injury in HIV-transgenic mice. Moreover, these results provide a molecular framework for developing novel therapies to improve the clinical outcome of children with HIVAN.

Nephrotic proteinuria and renal involvement in HIV-infected children

HIV-associated nephropathy (HIVAN) has been reported in HIV-infected adults. HIVAN in children has not been described previously from the Indian subcontinent though we had reported earlier about non-nephrotic range proteinuria in HIV-infected children and their response to antiretroviral therapy (ART). We now report two children with HIV and nephrotic range proteinuria who demonstrated proliferative glomerulonephritis and mesangial hyperplasia, respectively.

Nephrotic proteinuria and renal involvement in HIV-infected children

HIV-associated nephropathy (HIVAN) has been reported in HIV-infected adults. HIVAN in children has not been described previously from the Indian subcontinent though we had reported earlier about non-nephrotic range proteinuria in HIV-infected children and their response to antiretroviral therapy (ART). We now report two children with HIV and nephrotic range proteinuria who demonstrated proliferative glomerulonephritis and mesangial hyperplasia, respectively.