In vivo Modeling Implicates APOL1 in Nephropathy: Evidence for Dominant Negative Effects and Epistasis under Anemic Stress.

Abstract

African Americans have a disproportionate risk for developing nephropathy. This disparity has been attributed to coding variants (G1 and G2) in apolipoprotein L1 (APOL1); however, there is little functional evidence supporting the role of this protein in renal function. Here, we combined genetics and in vivo modeling to examine the role of apol1 in glomerular development and pronephric filtration and to test the pathogenic potential of APOL1 G1 and G2. Translational suppression or CRISPR/Cas9 genome editing of apol1 in zebrafish embryos results in podocyte loss and glomerular filtration defects. Complementation of apol1 morphants with wild-type human APOL1 mRNA rescues these defects. However, the APOL1 G1 risk allele does not ameliorate defects caused by apol1 suppression and the pathogenicity is conferred by the cis effect of both individual variants of the G1 risk haplotype (I384M/S342G). In vivo complementation studies of the G2 risk allele also indicate that the variant is deleterious to protein function. Moreover, APOL1 G2, but not G1, expression alone promotes developmental kidney defects, suggesting a possible dominant-negative effect of the altered protein. In sickle cell disease (SCD) patients, we reported previously a genetic interaction between APOL1 and MYH9. Testing this interaction in vivo by co-suppressing both transcripts yielded no additive effects. However, upon genetic or chemical induction of anemia, we observed a significantly exacerbated nephropathy phenotype. Furthermore, concordant with the genetic interaction observed in SCD patients, APOL1 G2 reduces myh9 expression in vivo, suggesting a possible interaction between the altered APOL1 and myh9. Our data indicate a critical role for APOL1 in renal function that is compromised by nephropathy-risk encoding variants. Moreover, our interaction studies indicate that the MYH9 locus is also relevant to the phenotype in a stressed microenvironment and suggest that consideration of the context-dependent functions of both proteins will be required to develop therapeutic paradigms.

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Citation

Published Version (Please cite this version)

10.1371/journal.pgen.1005349

Publication Info

Anderson, Blair R, David N Howell, Karen Soldano, Melanie E Garrett, Nicholas Katsanis, Marilyn J Telen, Erica E Davis, Allison E Ashley-Koch, et al. (2015). In vivo Modeling Implicates APOL1 in Nephropathy: Evidence for Dominant Negative Effects and Epistasis under Anemic Stress. PLoS Genet, 11(7). p. e1005349. 10.1371/journal.pgen.1005349 Retrieved from https://hdl.handle.net/10161/10832.

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Scholars@Duke

Howell

David Noble Howell

Professor of Pathology

A major focus of both my clinical practice and investigative work is the diagnosis and treatment of disorders affecting solid-organ transplant recipients, particularly infectious complications. For the past 15 years, I have served as the primary pathologist for one of the largest lung transplant programs in the world; in the process contributing to over 20 peer-reviewed publications on complications of lung transplantation, including infections, gastroesophageal reflux, tumors, and antibody-mediated rejection; and writing a major book chapter on the subject (Howell DN and Palmer SM, Pathology of the Lung Transplant. 2006. In: Lynch JP, Ross D, eds. Lung and Heart-Lung Transplantation. Marcel Dekker, Inc., New York, pp. 683-722). I have also been the primary pathologist for Duke's renal and liver transplant programs, authoring or co-authoring a wide variety of journal articles and a book chapter in these areas (e.g., Plumb et al., Transplantation 2006;82:1224-1224; Snyder et al., Am. J. Respir. Crit. Care Med. 2010;181:1391-1396).

A second major area of interest is the pathogenesis of renal glomerular diseases. In collaboration with members of the Division of Nephrology at Duke, I have helped assemble and characterize a large registry of patients with familial focal segmental glomerulosclerosis (FFSGS)(Conlon et al., Kidney Int. 1999;56:1863-1871). Analysis of one of the families in this registry led to the discovery at Duke, in the laboratory of Dr. Michelle Winn, of mutations in the TRPC6 cation channel as a cause of FFSGS (Winn et al., Genomics 1999;58:113-120; Winn et al., Science 2005;308:1801-1804). We are continuing to collect data on additional families with focal segmental glomerulosclerosis. In addition, I have served as principle consultative pathologist for several investigators working in animal models of renal disease and transplantation (e.g., Crowley et al., Hypertension 2010;55:99-108).

Finally, I have devoted considerable time and energy to applications of correlative microscopy to diagnostic pathology, with particular emphasis electron microscopy. I am currently President of the Society for Ultrastructural Pathology, an international organization that promotes the use of ultrastructural examination in both diagnostic pathology and clinical and basic research. Much of my published work in this area involves the role of electron microscopy in the diagnosis of renal diseases (e.g., Howell et al., Ultrastruct. Pathol. 2003;17:295-312; Pavlisko and Howell, Ultrastruct. Pathol., in press), but I have also written extensively, with my colleague Dr. Sara Miller, on the ultrastructural diagnosis of infectious disorders, contributing, among other things, to the first description of a new polyomavirus-induced skin disorder, trichodysplasia spinulosa (Haycox et al., J. Investig. Dermatol. Symp. Proc. 1999;4:268-271).

Telen

Marilyn Jo Telen

Wellcome Clinical Distinguished Professor of Medicine in Honor of R. Wayne Rundles, M.D.

Dr. Telen is recognized as an expert in the biochemistry and molecular genetics of blood group antigens and the pathophysiological mechanisms of vaso-occlusion in sickle cell disease. She is the Director of the Duke Comprehensive Sickle Cell Center.

Dr. Telen's laboratory focuses on structure/function analysis of membrane proteins expressed by erythroid cells, as well as the role of these proteins in non-erythroid cells. Proteins are also studied in transfectant systems, and research focuses especially on adhesion receptors. The goals of this work are (1) to understand the mechanism and role of red cell adhesion to leukocytes and endothelium in sickle cell disease; (2) to understand the signaling mechanisms leading to activation (and inactivation) of red cell adhesion molecules; (3) to understand the molecular basis of blood group antigen expression, and (4) to understand the interactions of erythroid membrane proteins with other cells and with extracellular matrix..

Recent investigations have focused on the role of signaling pathways in the upregulation of sickle red cell adhesion. Present studies include (1) investigation of beta-adrenergic signaling pathway responsible for activation of B-CAM/LU and LW adhesion receptors; (2) understanding how nitric oxide and ATP downregulate sickle red cell adhesion; (3) studying the effect of these processes in animal models.

Dr. Telen is also involved in a large multicenter study looking for genetic polymorphisms that affect clinical outcomes in sickle cell disease, as well as a multi-center study investigating the mechanisms and treatment of pulmonary hypertension in sickle cell disease.


Key Words:

Adhesion molecules
Erythrocyte membrane
Sickle cell disease
Transfusion medicine
Immunohematology
CD44
B-CAM/LU
Genetic polymorphisms


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