Chronic kidney disease (CKD), affecting over 26 million Americans, frequently leads to kidney failure. More than 100,000 individuals develop end stage kidney disease (ESKD) annually and nearly 500,000 receive kidney transplants or are ongoing dialysis patients at an annual cost of $30 billion dollars. We and others showed that APOL1 coding variants within this region comprising 2 missense variants in absolute linkage disequilibrium (G1 allele) and an in frame 6 base pair deletion (G2 allele) were responsible for the increased risk of chronic kidney disease in black Americans. ApoL1 provides protection against infection with Trypanosoma brucei brucei. The APOL1 risk alleles emerged recently in sub-Saharan Africa, but are found in other regions of the world as a result of the African Diaspora. The combined frequencies of G1 and G2 alleles are approximately 35% in African Americans. These alleles explain nearly all the excess risk of kidney disease in African Americans, thus providing a genetic basis for a major global health disparity. We have now extended our research to investigate the independent and interactive effects of sickle cell trait on cardiovascular and kidney diseases. The role of APOL1 risk variants in cardiovascular disease is conflicted with some studies showing a protective association and others reporting a susceptible or no association. We are investigating the role of APOL1 in cardiovascular disease in large well-powered community-based studies to separate the mediating effects of underlying co-morbidities (CKD and diabetes) from APOL1 associations. Accomplishments: 1) APOL1 coding variants and risk of heart failure in aging women. Compared to whites, stroke and heart failure is more common among African American women as they age. We found that among post-menopausal women enrolled in the Women's' Health Initiative, APOL1 was not associated with increased risk of cardiovascular diseases; however, APOL1 is associated with heart failure with preserved injection fraction, possibly mediated by underlying chronic kidney disease. 2) Cardiovascular disease, including ischemic stroke and myocardial infarction, is more common among African Americans. We evaluated nearly 10,000 African Americans enrolled in the REasons for Geographic and Racial Differences in Stroke (REGARDS) for APOL1 risk variants and determined that carriers of two APOL1 risk alleles were at a 2.3 -fold higher than for non-carriers for composite cardiovascular events; however, these associations were driven ischemic stroke. Carriers of high risk APOL1 genotypes were over 5-fold more likely to experience small vessel ischemic stroke compared to those with low-risk genotypes who did not have chronic kidney disease or diabetes, indicating that APOL1 is a direct contributor to these outcomes and not a moderator acting through underlying co-morbidities. These results have important public health policy implications for genetic counseling of high risk carriers. 3) Sickle cell trait has long been considered a benign condition however, its role in health and disease as not been analyzed in large-scale studies or by meta-analysis. We contributed our REGARDS APOL1 genotyping results for a meta-analysis of the association of sickle cell trait with ischemic stroke. Fortunately, SCT, which is carried by 7% of African Americans does not appear to be a risk factor for stroke. 4) Because of power issues, it is difficult to assess the role of APOL1 in premature death or sudden death. Age, cause of death, and nephrosclerosis were studied in 162 African Americans and 136 whites experiencing sudden death who were genotyped for APOL1 variants. Among those with dying from cardiovascular death, carriers of one APOL1 risk allele died 7 years earlier, and those with two risk alleles died 12.2 years earlier than African Americans with no risk alleles and 8.7 and 13.9 years younger than whites, who do carry APOL1 risk alleles. Carriage of APOL1 risk variants is associated with earlier deaths due to sudden death due to coronary artery or cardiomyopathy. 5) On the other hand, we did not find APOL1 associations with subclinical atherosclerosis or left ventricular hypertrophy in middle aged blacks or with hypertension in young black adults, nor did we find evidence of cardiovascular disease associations with APOL1 in persons with underlying the co-morbidity of chronic kidney disease attributable to hypertension. 6) Black living kidney donors are at higher risk of developing kidney disease than white donors. Because APOL1 high risk status (carriage of two risk alleles) is such a strong risk factor for chronic kidney disease, we asked if APOL1 genotype of living kidney donors might affect the donors' health following nephrectomy for kidney donation. We studied 136 living donors with APOL1 genotyping and found that pre-donation characteristics were similar between those having 2 APOL1 risk alleles (high-risk status) and those with one or no risk alleles (low-risk status). At a median time of 12 years post-donation, APOL1 high-risk donors had lower estimated glomerular filtration (eGFR) rates and more rapid loss of kidney function (steeper trajectories) compared to their APOL1 low-risk counterparts. Two donors developed end stage kidney disease and both had carried two risk alleles. In a subgroup of 115 donors matched to 115 non-donors, we found that the trajectories were similar between donors and non-donors. This study suggests that donors carrying two risk alleles might be at greater risk for greater decline in kidney function and kidney failure, but larger studies are required to validate this finding. 7) Using genetic data provided by our laboratory, academic investigators found that a tripartite complex of suPAR (soluble urokinase plasminogen activator receptor), APOL1 risk variants, and integrin is responsible for decline in kidney function. Mechanistically, the APOL1 variant alleles have a higher affinity for suPAR, which augments integrin activation leading to proteinuria in mice. In humans decline in kidney function in patients with APOL1 high risk genotypes is positively correlated with suPAR levels. 8) We found that APOL1 high risk genotypes were not associated with hypertension in young adults with preserve kidney function enrolled in the CARDIA study and were not associated with cardiovascular disease (CVD) in persons with chronic kidney disease (CKD). On the other hand, we find a 2-fold increased risk of stroke and trend towards increased risk of myocardial infarction in patients without the well-established CVD risk factors of diabetes or chronic kidney disease. In participants with albuminuria, chronic kidney disease or diabetes, we found no association between APOL1 and CVD events. 9) Constitutive expression of both wildtype and variant APOL1 in transgenic mice causes loss of pups and preeclampsia and death of the mothers. Incidence rates for preeclampsia are higher for African Americans and Africans compared to Europeans. In two cohorts, we found that carriage of APOL1 high risk genotypes by the fetus, but not the mother, increases the risk of preeclampsia by two-fold. We are now investigating genetic modifiers of APOL1-associated preeclampsia and RNA transcriptional profiles in APOL1 high and low risk placentas from mothers with and without preeclampsia to better understand the pathogenic mechanisms and perturbed pathways. 10) We have also contributed DNA samples, genotyping data, and expertise to several important genetic studies. Mesoamerican samples collected in remote villages in Oaxaca Mexico over 20 years ago have been used for a series of studies to understand the genetic architecture of asthma in Hispanics.
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