- Email: [email protected]
The elusive podocyte crossmatch for recurrent focal segmental glomerulosclerosis
commentary
2. Garofalo C, Borrelli S, Minutolo R, et al. A systematic review and meta-analysis suggests obesity predicts onset of chronic kidney disease in the general population. Kidney Int. 2017;91:1224–1235. 3. Panwar B, Hanks LJ, Tanner RM, et al. Obesity, metabolic health, and the risk of end-stage renal disease. Kidney Int. 2015;87:1216–1222. 4. D’Agati VD, Chagnac A, de Vries AP, et al. Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis. Nat Rev Nephrol. 2016;12:453–471. 5. Kambham N, Markowitz GS, Valeri AM, et al. Obesity-related glomerulopathy: an emerging epidemic. Kidney Int. 2001;59:1498–1509.
6. Salvatore SP, Chevalier JM, Kuo SF, et al. Kidney disease in patients with obesity: it is not always obesity-related glomerulopathy alone. Obes Res Clin Pract. 2017;11:597–606. 7. Sharma SG, Bomback AS, Radhakrishnan J, et al. The modern spectrum of renal biopsy indings in patients with diabetes. Clin J Am Soc Nephrol. 2013;8:1718–1724. 8. Serra A, Romero R, Lopez D, et al. Renal injury in the extremely obese patients with normal renal function. Kidney Int. 2008;73:947–955. 9. Choung H-YG, Bomback AS, Stokes MB, et al. The spectrum of kidney biopsy findings in patients with morbid obesity. Kidney Int. 2019;95:647–654.
The elusive podocyte crossmatch for recurrent focal segmental glomerulosclerosis George W. Burke III1,2 and Alessia Fornoni2,3 Focal segmental glomerulosclerosis is a glomerular disorder with a high rate of recurrence. Although kidney biopsies remain the gold standard to diagnose recurrent focal segmental glomerulosclerosis, non-invasive prognostic assays could facilitate preventive treatments and offer insight into disease pathogenicity and heterogeneity. Srivastava et al. describe a simple, cell-based assay to predict recurrence of focal segmental glomerulosclerosis. Although the study needs to be optimized and validated, its novelty is that it does not depend on the specificity of a given permeability factor. Kidney International (2019) 95, 498–500; https://doi.org/10.1016/j.kint.2018.11.032 Copyright ª 2019, Published by Elsevier, Inc., on behalf of the International Society of Nephrology.
see technical notes on page 708
P
rimary focal segmental glomerulosclerosis (FSGS) is a common glomerular disorder that manifests clinically with nephrotic syndrome and > 80% foot process effacement.
1 Department of Surgery and Miami Transplant Institute, University of Miami, Miller School of Medicine, Miami, Florida, USA; 2Peggy and Harold Katz Family Drug Discovery Center, University of Miami, Miller School of Medicine, Miami, Florida, USA; and 3Katz Family Division of Nephrology and Hypertension, Department of Medicine, University of Miami, Miller School of Medicine, Miami, Florida, USA
Correspondence: Alessia Fornoni, Katz Family Division of Nephrology and Hypertension and Peggy and Harold Katz Family Drug Discovery Center, University of Miami, 1580 NW 10th Ave, Miami, Florida 33136, USA. E-mail: [email protected] 498
Progression to end-stage renal disease occurs in 40% to 60% of patients within 10 to 20 years from diagnosis,1 making this the most common primary glomerular disease leading to renal replacement therapies in the United States. After transplantation, recurrence of FSGS occurs in 30% to 40% of adults and up to 80% in high-risk patients,2 leading to early graft loss.3 Risk factors for recurrent FSGS (rFSGS) include younger age (children less than 6 years of age at onset), rapid progression to end-stage renal disease in less than 3 years from diagnosis, severe proteinuria immediately before transplantation, and the loss of a previous allograft(s) to recurrence.1–3 The observations that recurrence of FSGS can happen within
minutes to hours of kidney transplantation/reperfusion4 and that kidneys affected by rFSGS undergo complete resolution of the disease when explanted and transplanted into a non-FSGS recipient5 strongly support the existence of permeability factors causing podocyte injury and proteinuria. Although biopsy of the kidney transplant is the mainstay of diagnosis of rFSGS, less invasive assays that can be implemented in diagnostic laboratories would be highly desirable. Furthermore, no prognostic indicators of rFSGS have been developed yet. The first elegant demonstration of a permeability factor occurred through the development on an ex vivo albumin permeability assay that also allowed differentiation of patients at risk for rFSGS.6 Because this ex vivo test was based on the permeability to albumin in isolated glomeruli exposed to the sera of patients with FSGS, it would be difficult to implement it in clinical practice. Since then, a large variety of potential permeability factors has been identified. Although clinical grade assays for these factors are being developed, none have been shown to predict outcome with sufficient specificity and sensitivity, probably because primary FSGS is caused by many different factors. One alternative approach to the identification of a specific factor would be the development of a simple, reproducible assay to test the permeability potential of sera collected from patients with FSGS, irrespective of a specific permeability factor. In prior studies, we used a combination of (i) an actin cytoskeleton phenotypic readout, (ii) the expression of sphingomyelin phosphodiesterase acid–like 3B in podocytes exposed to the sera of 22 patients with FSGS/endstage renal disease, and (iii) sphingomyelin phosphodiesterase acid–like 3B expression in post-reperfusion kidney biopsies, which was found to correlate with the development of posttransplant proteinuria.7 We reported a correlation with the development of posttransplant proteinuria in the highrisk pediatric population.7 Not surprisingly, when we performed a larger (more than 40 patients) prospective Kidney International (2019) 95, 487–500
commentary
study in (i) mostly adults with kidney transplants for FSGS and (ii) a low rate of rFSGS, we found different results (NCT01164098). This gives us reason to suggest caution in the adoption of predictive assays for rFSGS. The study by Srivastava et al.8 (2019) represents an improvement in the ability to predict rFSGS by using a minimally invasive, cell-based assay with sensitivity and specificity above 80%. After an initial screening of the mRNA profile of human podocytes exposed to the plasma of 2 patients with rFSGS and 1 control, 3 strongly upregulated candidate genes that are also involved in cellular apoptosis were selected: BCl12 modifying factor, interleukin (IL)-1b, and insulin growth factor binding protein 3. Lysosomal-associated membrane protein 3 was chosen as a negative control. Human podocyte cell lines expressing luciferase under control of the promoter of these genes were then made and exposed to plasma from 10 to 14 patients with rFSGS and control patients affected by FSGS without recurrence or by other nephropathies. The discriminative performance between rFSGS and nonrecurrent FSGS (nrFSGS) was found to range between 0.81 and 0.86 for IL-1b and for BCl12 modifying factor, and the overall assay specificity was found to be greater than 80% for these 2 genes, while it was 64% for insulin growth factor binding protein 3. Validation of these findings in other cell types such as HEK293 (human embryonic kidney cells) and COS (primate kidney cell line) cells suggested that the response is independent of host cell line. Future work will be aimed at validating these results, expanding the pool of candidate genes to increase specificity and sensitivity, as well as profiling additional patients from wellestablished longitudinal cohorts. The authors suggest that this assay to predict rFSGS may lead to the reduction in the overall incidence of rFSGS and improved graft survival.8 Because there is currently no generally accepted successful therapy for rFSGS (plasmapheresis, steroids, and rituximab are potential therapeutic tools), this assay may instead set the Kidney International (2019) 95, 487–500
stage for prophylactic use of these therapies. In the context of a positive prediction for rFSGS, there also may be more reason to perform pre- and post-reperfusion kidney transplant biopsies, looking for biomarkers that could potentially lead to targeted therapy.7 The suggestion that this assay may lead to the development of similar assays for other causes of nephrotic syndromes is currently limited by the identification of circulating factors (proteins, lipids, or autoantibodies) involved in the pathogenesis of other primary glomerular disorders. In this respect, assays for both nephrotic and nephritic syndrome could be developed, and use of plasma and/or sera may reveal the specific role of complement in causing podocyte injury in these different disorders. The use of this assay to monitor response to specific treatment strategies, such as plasmapheresis, would also need to be addressed. A major concern in further developing this assay is the choice of the control group (non-recurrent FSGS cohort), because it involves a group of patients with FSGS who did not receive a kidney transplant with very heterogeneous characteristics including: age range from 9 to 84 years, urine protein/creatinine ratios from .6 to 28.5, unknown duration of disease, and no available data on serum creatinine/estimated glomerular filtration rate to help determine disease progression. Future time course analysis will be particularly important in determining the prognostic use of this assay. Availability of serum and plasma collected at different time points will also more likely be helpful to understand its true prognostic value and/or the ability to use it to monitor response to treatment and disease progression. Finally, although the specificity and sensitivity were encouraging, particularly for the 2 genes BCl12 modifying factor and IL1b, the magnitude of the response in this luciferase-based assay was “nominal” (1.5–2.0 fold). It is also notable that this entire work is based on 3 genes found to be modulated in 1 podocyte cell line when exposed to the sera of 2
patients with rFSGS and 1 control. This obviously represents the major limiting factor of this assay, placing greater emphasis on the need for validation with larger numbers. Yet, it is important to note that most of the regulated genes in this initial experiment were inflammatory mediators, primarily chemokine ligands and interacting proteins, cytokines (tumor necrosis factor alpha, IL1b, IL-6, colony stimulating factor 3 [CSF3] and Nuclear Factor kappa B [NFkB]), proteins regulating toll-like receptor–mediated signaling, and other proteins important in the immune response, supporting an important role of these pathways in the pathogenesis of rFSGS. Given the success of system biology approaches to understand the pathogenesis of FSGS,9 a strategy to look at the entire molecular signature of podocytes exposed to patients’ sera may better allow for patient stratification, personalized treatment strategies, and identification of novel therapeutic targets specific for rFSGS. Because identifying causative permeability factors is still an interesting possibility, should this assay achieve its intended success, the use of different plasma fractions could be the first step in that direction. It could also help identify patients that are likely to respond to a specific treatment, as we have suggested using rituximab to prevent rFSGS.7 In this study, a combination of cell-based assay and histopathological and ultrastructural characteristics in pre-implantation and post-reperfusion kidney biopsies were used to predict rFSGS.4,7 Most importantly, this study included kidney transplant recipients with FSGS who did not experience recurrent proteinuria after kidney transplantation as a control group, in contradistinction to the control group in the paper by Srivastava et al.8 In the era of precision medicine, it is likely that a combination of different assays will be needed to determine the susceptibility of a patient to develop rFSGS. These include proteomic/metabolomic/lipidomic approaches in the plasma/sera and urine of patients enrolled in natural history studies, a system biology approach to study pre499
commentary
DISCLOSURE
Electronic medical record/machine learning FSGS diagnosis
ESKD transplant
rFSGS Graft loss
GWB and AF are inventors on pending or issued patents aimed to diagnose or treat proteinuric kidney diseases. They stand to gain royalties from their future commercialization. ACKNOWLEDGMENTS
Sera/plasma/urine +/– drug
Circulating factors
Podocytes
Pre- and post-reperfusion kidney biopsies Diagnostic biopsies RNA-seq and omics data RT–PCR
This work was supported by National Institutes of Health grant 1R01 DK 09031601A1 (AF/GB). AF is currently supported by the National Institutes of Health grants R01DK117599, R01DK104753, R01CA227493, U54DK083912, UM1DK100846, U01DK116101, and UL1TR000460 (Miami Clinical Translational Science Institute). REFERENCES
RNA-seq and omics data RT–PCR Luciferase–reporter assays
Histology Morphometry Digital Pathology
Phenotype screening Prognostic/diagnostic assay Personalized medicine Patient stratification Target identification Drug screening Figure 1 | Translational tools to advance knowledge relevant to the understanding of recurrent focal segmental glomerulosclerosis (rFSGS) are summarized here. In red is the tool used by Srivastava et al.8 to develop the assay presented in this study. ESKD, end-stage kidney disease; FSGS, focal segmental glomerulosclerosis; RT–PCR, reverse transcriptase polymerase chain reaction. To optimize viewing of this image, please see the online version of this article at www.kidney-international.org.
and post-reperfusion kidney biopsies, a digital pathology approach, cell-based assays combining phenotypic readouts to gene expression and functional readouts, and a machine learning tool that incorporates these data sets into key clinical parameters available through the electronic medical record (Figure 1). These tools also will be essential to develop connectivity maps that allow translating clinically derived data into meaningful
500
tools for drug discovery and patient stratification. In conclusion, although a simple crossmatch assay testing how the promoter activation of 3 genes in a normal podocyte exposed to the sera of a patient with FSGS may help us predict rFSGS, the path ahead to translate this assay into clinical applications requires significant validation and integration into other relevant strategies.
1. D’Agati VD, Kaskel FJ, Falk RJ. Focal segmental glomerulosclerosis. N Engl J Med. 2011;365: 2398–2411. 2. Hubsch H, Montane B, Abitbol C, et al. Recurrent focal glomerulosclerosis in pediatric renal allografts: the Miami experience. Pediatr Nephrol. 2005;20:210–216. 3. Cravedi P, Kopp JB, Remuzzi G. Recent progress in the pathophysiology and treatment of FSGS recurrence. Am J Transplant. 2013;13:266–274. 4. Chang JW, Pardo V, Sageshima J, et al. Podocyte foot process effacement in postreperfusion allograft biopsies correlates with early recurrence of proteinuria in focal segmental glomerulosclerosis. Transplantation. 2012;93:1238–1244. 5. Gallon L, Leventhal J, Skaro A, et al. Resolution of recurrent focal segmental glomerulosclerosis after retransplantation. N Engl J Med. 2012;366:1648–1649. 6. Savin VJ, Sharma R, Sharma M, et al. Circulating factor associated with increased glomerular permeability to albumin in recurrent focal segmental glomerulosclerosis. N Engl J Med. 1996;334:878–883. 7. Fornoni A, Sageshima J, Wei C, et al. Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis. Sci Transl Med. 2011;3:85ra46. 8. Srivastava P, Solanki AK, Arif E, et al. Development of a novel cell-based assay to diagnose recurrent focal and segmental glomerulosclerosis patients. Kidney Int. 2019;95:708–716. 9. Gipson DS, Troost JP, Lafayette RA, et al. Complete remission in the nephrotic syndrome study network. Clin J Am Soc Nephrol. 2016;11:81–89.
Kidney International (2019) 95, 487–500
2. Garofalo C, Borrelli S, Minutolo R, et al. A systematic review and meta-analysis suggests obesity predicts onset of chronic kidney disease in the general population. Kidney Int. 2017;91:1224–1235. 3. Panwar B, Hanks LJ, Tanner RM, et al. Obesity, metabolic health, and the risk of end-stage renal disease. Kidney Int. 2015;87:1216–1222. 4. D’Agati VD, Chagnac A, de Vries AP, et al. Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis. Nat Rev Nephrol. 2016;12:453–471. 5. Kambham N, Markowitz GS, Valeri AM, et al. Obesity-related glomerulopathy: an emerging epidemic. Kidney Int. 2001;59:1498–1509.
6. Salvatore SP, Chevalier JM, Kuo SF, et al. Kidney disease in patients with obesity: it is not always obesity-related glomerulopathy alone. Obes Res Clin Pract. 2017;11:597–606. 7. Sharma SG, Bomback AS, Radhakrishnan J, et al. The modern spectrum of renal biopsy indings in patients with diabetes. Clin J Am Soc Nephrol. 2013;8:1718–1724. 8. Serra A, Romero R, Lopez D, et al. Renal injury in the extremely obese patients with normal renal function. Kidney Int. 2008;73:947–955. 9. Choung H-YG, Bomback AS, Stokes MB, et al. The spectrum of kidney biopsy findings in patients with morbid obesity. Kidney Int. 2019;95:647–654.
The elusive podocyte crossmatch for recurrent focal segmental glomerulosclerosis George W. Burke III1,2 and Alessia Fornoni2,3 Focal segmental glomerulosclerosis is a glomerular disorder with a high rate of recurrence. Although kidney biopsies remain the gold standard to diagnose recurrent focal segmental glomerulosclerosis, non-invasive prognostic assays could facilitate preventive treatments and offer insight into disease pathogenicity and heterogeneity. Srivastava et al. describe a simple, cell-based assay to predict recurrence of focal segmental glomerulosclerosis. Although the study needs to be optimized and validated, its novelty is that it does not depend on the specificity of a given permeability factor. Kidney International (2019) 95, 498–500; https://doi.org/10.1016/j.kint.2018.11.032 Copyright ª 2019, Published by Elsevier, Inc., on behalf of the International Society of Nephrology.
see technical notes on page 708
P
rimary focal segmental glomerulosclerosis (FSGS) is a common glomerular disorder that manifests clinically with nephrotic syndrome and > 80% foot process effacement.
1 Department of Surgery and Miami Transplant Institute, University of Miami, Miller School of Medicine, Miami, Florida, USA; 2Peggy and Harold Katz Family Drug Discovery Center, University of Miami, Miller School of Medicine, Miami, Florida, USA; and 3Katz Family Division of Nephrology and Hypertension, Department of Medicine, University of Miami, Miller School of Medicine, Miami, Florida, USA
Correspondence: Alessia Fornoni, Katz Family Division of Nephrology and Hypertension and Peggy and Harold Katz Family Drug Discovery Center, University of Miami, 1580 NW 10th Ave, Miami, Florida 33136, USA. E-mail: [email protected] 498
Progression to end-stage renal disease occurs in 40% to 60% of patients within 10 to 20 years from diagnosis,1 making this the most common primary glomerular disease leading to renal replacement therapies in the United States. After transplantation, recurrence of FSGS occurs in 30% to 40% of adults and up to 80% in high-risk patients,2 leading to early graft loss.3 Risk factors for recurrent FSGS (rFSGS) include younger age (children less than 6 years of age at onset), rapid progression to end-stage renal disease in less than 3 years from diagnosis, severe proteinuria immediately before transplantation, and the loss of a previous allograft(s) to recurrence.1–3 The observations that recurrence of FSGS can happen within
minutes to hours of kidney transplantation/reperfusion4 and that kidneys affected by rFSGS undergo complete resolution of the disease when explanted and transplanted into a non-FSGS recipient5 strongly support the existence of permeability factors causing podocyte injury and proteinuria. Although biopsy of the kidney transplant is the mainstay of diagnosis of rFSGS, less invasive assays that can be implemented in diagnostic laboratories would be highly desirable. Furthermore, no prognostic indicators of rFSGS have been developed yet. The first elegant demonstration of a permeability factor occurred through the development on an ex vivo albumin permeability assay that also allowed differentiation of patients at risk for rFSGS.6 Because this ex vivo test was based on the permeability to albumin in isolated glomeruli exposed to the sera of patients with FSGS, it would be difficult to implement it in clinical practice. Since then, a large variety of potential permeability factors has been identified. Although clinical grade assays for these factors are being developed, none have been shown to predict outcome with sufficient specificity and sensitivity, probably because primary FSGS is caused by many different factors. One alternative approach to the identification of a specific factor would be the development of a simple, reproducible assay to test the permeability potential of sera collected from patients with FSGS, irrespective of a specific permeability factor. In prior studies, we used a combination of (i) an actin cytoskeleton phenotypic readout, (ii) the expression of sphingomyelin phosphodiesterase acid–like 3B in podocytes exposed to the sera of 22 patients with FSGS/endstage renal disease, and (iii) sphingomyelin phosphodiesterase acid–like 3B expression in post-reperfusion kidney biopsies, which was found to correlate with the development of posttransplant proteinuria.7 We reported a correlation with the development of posttransplant proteinuria in the highrisk pediatric population.7 Not surprisingly, when we performed a larger (more than 40 patients) prospective Kidney International (2019) 95, 487–500
commentary
study in (i) mostly adults with kidney transplants for FSGS and (ii) a low rate of rFSGS, we found different results (NCT01164098). This gives us reason to suggest caution in the adoption of predictive assays for rFSGS. The study by Srivastava et al.8 (2019) represents an improvement in the ability to predict rFSGS by using a minimally invasive, cell-based assay with sensitivity and specificity above 80%. After an initial screening of the mRNA profile of human podocytes exposed to the plasma of 2 patients with rFSGS and 1 control, 3 strongly upregulated candidate genes that are also involved in cellular apoptosis were selected: BCl12 modifying factor, interleukin (IL)-1b, and insulin growth factor binding protein 3. Lysosomal-associated membrane protein 3 was chosen as a negative control. Human podocyte cell lines expressing luciferase under control of the promoter of these genes were then made and exposed to plasma from 10 to 14 patients with rFSGS and control patients affected by FSGS without recurrence or by other nephropathies. The discriminative performance between rFSGS and nonrecurrent FSGS (nrFSGS) was found to range between 0.81 and 0.86 for IL-1b and for BCl12 modifying factor, and the overall assay specificity was found to be greater than 80% for these 2 genes, while it was 64% for insulin growth factor binding protein 3. Validation of these findings in other cell types such as HEK293 (human embryonic kidney cells) and COS (primate kidney cell line) cells suggested that the response is independent of host cell line. Future work will be aimed at validating these results, expanding the pool of candidate genes to increase specificity and sensitivity, as well as profiling additional patients from wellestablished longitudinal cohorts. The authors suggest that this assay to predict rFSGS may lead to the reduction in the overall incidence of rFSGS and improved graft survival.8 Because there is currently no generally accepted successful therapy for rFSGS (plasmapheresis, steroids, and rituximab are potential therapeutic tools), this assay may instead set the Kidney International (2019) 95, 487–500
stage for prophylactic use of these therapies. In the context of a positive prediction for rFSGS, there also may be more reason to perform pre- and post-reperfusion kidney transplant biopsies, looking for biomarkers that could potentially lead to targeted therapy.7 The suggestion that this assay may lead to the development of similar assays for other causes of nephrotic syndromes is currently limited by the identification of circulating factors (proteins, lipids, or autoantibodies) involved in the pathogenesis of other primary glomerular disorders. In this respect, assays for both nephrotic and nephritic syndrome could be developed, and use of plasma and/or sera may reveal the specific role of complement in causing podocyte injury in these different disorders. The use of this assay to monitor response to specific treatment strategies, such as plasmapheresis, would also need to be addressed. A major concern in further developing this assay is the choice of the control group (non-recurrent FSGS cohort), because it involves a group of patients with FSGS who did not receive a kidney transplant with very heterogeneous characteristics including: age range from 9 to 84 years, urine protein/creatinine ratios from .6 to 28.5, unknown duration of disease, and no available data on serum creatinine/estimated glomerular filtration rate to help determine disease progression. Future time course analysis will be particularly important in determining the prognostic use of this assay. Availability of serum and plasma collected at different time points will also more likely be helpful to understand its true prognostic value and/or the ability to use it to monitor response to treatment and disease progression. Finally, although the specificity and sensitivity were encouraging, particularly for the 2 genes BCl12 modifying factor and IL1b, the magnitude of the response in this luciferase-based assay was “nominal” (1.5–2.0 fold). It is also notable that this entire work is based on 3 genes found to be modulated in 1 podocyte cell line when exposed to the sera of 2
patients with rFSGS and 1 control. This obviously represents the major limiting factor of this assay, placing greater emphasis on the need for validation with larger numbers. Yet, it is important to note that most of the regulated genes in this initial experiment were inflammatory mediators, primarily chemokine ligands and interacting proteins, cytokines (tumor necrosis factor alpha, IL1b, IL-6, colony stimulating factor 3 [CSF3] and Nuclear Factor kappa B [NFkB]), proteins regulating toll-like receptor–mediated signaling, and other proteins important in the immune response, supporting an important role of these pathways in the pathogenesis of rFSGS. Given the success of system biology approaches to understand the pathogenesis of FSGS,9 a strategy to look at the entire molecular signature of podocytes exposed to patients’ sera may better allow for patient stratification, personalized treatment strategies, and identification of novel therapeutic targets specific for rFSGS. Because identifying causative permeability factors is still an interesting possibility, should this assay achieve its intended success, the use of different plasma fractions could be the first step in that direction. It could also help identify patients that are likely to respond to a specific treatment, as we have suggested using rituximab to prevent rFSGS.7 In this study, a combination of cell-based assay and histopathological and ultrastructural characteristics in pre-implantation and post-reperfusion kidney biopsies were used to predict rFSGS.4,7 Most importantly, this study included kidney transplant recipients with FSGS who did not experience recurrent proteinuria after kidney transplantation as a control group, in contradistinction to the control group in the paper by Srivastava et al.8 In the era of precision medicine, it is likely that a combination of different assays will be needed to determine the susceptibility of a patient to develop rFSGS. These include proteomic/metabolomic/lipidomic approaches in the plasma/sera and urine of patients enrolled in natural history studies, a system biology approach to study pre499
commentary
DISCLOSURE
Electronic medical record/machine learning FSGS diagnosis
ESKD transplant
rFSGS Graft loss
GWB and AF are inventors on pending or issued patents aimed to diagnose or treat proteinuric kidney diseases. They stand to gain royalties from their future commercialization. ACKNOWLEDGMENTS
Sera/plasma/urine +/– drug
Circulating factors
Podocytes
Pre- and post-reperfusion kidney biopsies Diagnostic biopsies RNA-seq and omics data RT–PCR
This work was supported by National Institutes of Health grant 1R01 DK 09031601A1 (AF/GB). AF is currently supported by the National Institutes of Health grants R01DK117599, R01DK104753, R01CA227493, U54DK083912, UM1DK100846, U01DK116101, and UL1TR000460 (Miami Clinical Translational Science Institute). REFERENCES
RNA-seq and omics data RT–PCR Luciferase–reporter assays
Histology Morphometry Digital Pathology
Phenotype screening Prognostic/diagnostic assay Personalized medicine Patient stratification Target identification Drug screening Figure 1 | Translational tools to advance knowledge relevant to the understanding of recurrent focal segmental glomerulosclerosis (rFSGS) are summarized here. In red is the tool used by Srivastava et al.8 to develop the assay presented in this study. ESKD, end-stage kidney disease; FSGS, focal segmental glomerulosclerosis; RT–PCR, reverse transcriptase polymerase chain reaction. To optimize viewing of this image, please see the online version of this article at www.kidney-international.org.
and post-reperfusion kidney biopsies, a digital pathology approach, cell-based assays combining phenotypic readouts to gene expression and functional readouts, and a machine learning tool that incorporates these data sets into key clinical parameters available through the electronic medical record (Figure 1). These tools also will be essential to develop connectivity maps that allow translating clinically derived data into meaningful
500
tools for drug discovery and patient stratification. In conclusion, although a simple crossmatch assay testing how the promoter activation of 3 genes in a normal podocyte exposed to the sera of a patient with FSGS may help us predict rFSGS, the path ahead to translate this assay into clinical applications requires significant validation and integration into other relevant strategies.
1. D’Agati VD, Kaskel FJ, Falk RJ. Focal segmental glomerulosclerosis. N Engl J Med. 2011;365: 2398–2411. 2. Hubsch H, Montane B, Abitbol C, et al. Recurrent focal glomerulosclerosis in pediatric renal allografts: the Miami experience. Pediatr Nephrol. 2005;20:210–216. 3. Cravedi P, Kopp JB, Remuzzi G. Recent progress in the pathophysiology and treatment of FSGS recurrence. Am J Transplant. 2013;13:266–274. 4. Chang JW, Pardo V, Sageshima J, et al. Podocyte foot process effacement in postreperfusion allograft biopsies correlates with early recurrence of proteinuria in focal segmental glomerulosclerosis. Transplantation. 2012;93:1238–1244. 5. Gallon L, Leventhal J, Skaro A, et al. Resolution of recurrent focal segmental glomerulosclerosis after retransplantation. N Engl J Med. 2012;366:1648–1649. 6. Savin VJ, Sharma R, Sharma M, et al. Circulating factor associated with increased glomerular permeability to albumin in recurrent focal segmental glomerulosclerosis. N Engl J Med. 1996;334:878–883. 7. Fornoni A, Sageshima J, Wei C, et al. Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis. Sci Transl Med. 2011;3:85ra46. 8. Srivastava P, Solanki AK, Arif E, et al. Development of a novel cell-based assay to diagnose recurrent focal and segmental glomerulosclerosis patients. Kidney Int. 2019;95:708–716. 9. Gipson DS, Troost JP, Lafayette RA, et al. Complete remission in the nephrotic syndrome study network. Clin J Am Soc Nephrol. 2016;11:81–89.
Kidney International (2019) 95, 487–500