Urinary Plasminogen as a Marker of Disease Progression in Human Glomerular Disease.

RATIONALE & OBJECTIVE: Glomerular disorders have a highly variable clinical course, and biomarkers that reflect the molecular mechanisms underlying their progression are needed. Based on our previous work identifying plasminogen as a direct cause of podocyte injury, we designed this study to test the association between urine plasmin(ogen) (ie, plasmin and its precursor plasminogen) and end-stage kidney disease (ESKD). STUDY DESIGN: Multicenter cohort study. SETTING & PARTICIPANTS: 1,010 patients enrolled in the CureGN Cohort with biopsy-proven glomerular disease (focal segmental glomerulosclerosis, membranous nephropathy, and immunoglobulin A nephropathy). PREDICTORS: The main predictor was urine plasmin(ogen) at baseline. Levels were measured by an electrochemiluminescent immunoassay developed de novo. Traditional clinical and analytical characteristics were used for adjustment. The ratio of urine plasmin(ogen)/expected plasmin(ogen) was evaluated as a predictor in a separate model. OUTCOME: Progression to ESKD. ANALYTICAL APPROACH: Cox regression was used to examine the association between urinary plasmin(ogen) and time to ESKD. Urinary markers were log2 transformed to approximate normal distribution and normalized to urinary creatinine (Log2uPlasminogen/cr, Log2 urinary protein/cr [UPCR]). Expected plasmin(ogen) was calculated by multiple linear regression. RESULTS: Adjusted Log2uPlasminogen/cr was significantly associated with ESKD (HR per doubling Log2 uPlasminogen/cr 1.31 [95% CI, 1.22-1.40], P<0.001). Comparison of the predictive performance of the models including Log2 uPlasminogen/cr, Log2 UPCR, or both markers showed the plasmin(ogen) model superiority. The ratio of measured/expected urine plasmin(ogen) was independently associated with ESKD: HR, 0.41 (95% CI, 0.22-0.77) if ratio<0.8 and HR 2.42 (95% CI, 1.54-3.78) if ratio>1.1 (compared with ratio between 0.8 and 1.1). LIMITATIONS: Single plasmin(ogen) determination does not allow for the study of changes over time. The use of a cohort of mostly white patients and the restriction to patients with 3 glomerular disorders limits the external validity of our analysis. CONCLUSIONS: Urinary plasmin(ogen) and the ratio of measured/expected plasmin(ogen) are independently associated with ESKD in a cohort of patients with glomerular disease. Taken together with our previous experimental findings, urinary plasmin(ogen) could be a useful biomarker in prognostic decision making and a target for the development of novel therapies in patients with proteinuria and glomerular disease. PLAIN-LANGUAGE SUMMARY: Glomerular diseases are an important cause of morbidity and mortality in patients of all ages. Knowing the individual risk of progression to dialysis or transplantation would help to plan the follow-up and treatment of these patients. Our work studies the usefulness of urinary plasminogen as a marker of progression in this context, since previous studies indicate that plasminogen may be involved in the mechanisms responsible for the progression of these disorders. Our work in a sample of 1,010 patients with glomerular disease demonstrates that urinary plasminogen (as well as the ratio of measured to expected plasminogen) is associated with the risk of progression to end-stage kidney disease. Urine plasminogen exhibited good performance and, if further validated, could enable risk stratification for timely interventions in patients with proteinuria and glomerular disease.

Examining the Trajectory of Health-Related Quality of Life among Coronavirus Disease Patients.

BACKGROUND: Recent studies have reported a reduction in health-related quality of life (HR-QoL) among post-coronavirus disease 2019 (COVID-19) patients. However, there remains a gap in research examining the heterogeneity and determinants of HR-QoL trajectory in these patients. OBJECTIVE: To describe and identify factors explaining the variability in HR-QoL trajectories among a cohort of patients with history of COVID-19. DESIGN: A prospective study using data from a cohort of COVID-19 patients enrolled into a registry established at a health system in New York City. PARTICIPANTS: Participants were enrolled from July 2020 to June 2022, and completed a baseline evaluation and two follow-up visits at 6 and 12 months. METHODS: We assessed HR-QoL with the 29-item Patient Reported Outcomes Measurement Information System instrument, which was summarized into mental and physical health domains. We performed latent class growth and multinomial logistic regression to examine trajectories of HR-QoL and identify factors associated with specific trajectories. RESULTS: The study included 588 individuals with a median age of 52 years, 65% female, 54% White, 18% Black, and 18% Hispanic. We identified five physical health trajectories and four mental health trajectories. Female gender, having pre-existing hypertension, cardiovascular disease, asthma, and hospitalization for acute COVID-19 were independently associated with lower physical health. In addition, patients with increasing body mass index were more likely to experience lower physical health over time. Female gender, younger age, pre-existing asthma, arthritis and cardiovascular disease were associated with poor mental health. CONCLUSIONS: We found significant heterogeneity of HR-QoL after COVID-19, with women and patients with specific comorbidities at increased risk of lower HR-QoL. Implementation of targeted psychological and physical interventions is crucial for enhancing the quality of life of this patient population.

Barriers to Telehealth Utilization Among Patients of Limited Income with Chronic Conditions and a Gap in Care.

Objective: This study assessed barriers and facilitators to telehealth utilization among patients living in New York City public housing with chronic conditions and a gap in clinical care. Methods: Community health workers performed outreach to eligible patients by telephone between January and March 2021. Consenting respondents answered questions about telehealth barriers, including internet and cell phone access, ownership of digital devices, comfort with using digital devices, comfort with telehealth, cost, awareness, and availability of written materials in patients' preferred language. We obtained demographic and medical information from patients' electronic health records. We used multivariable logistic regression to estimate the association of barriers with the odds of self-reported prior telehealth utilization. Results: A total of 304 consenting patients participated in the program. The average patient had 3.1 telehealth barriers; 76% reported at least one barrier. Regression analysis showed sizable reductions in prior telehealth utilization associated with the barriers of unlimited cell phone minutes (odds ratio [OR]: 0.21 [0.05-0.88], p = 0.033), technological comfort (OR: 0.33 [0.13-0.82], p = 0.016), conceptual comfort with telehealth (OR: 0.15 [0.04-0.54], p = 0.004), and materials in the patient's preferred language (OR: 0.23 [0.07-0.79], p = 0.02). Discussion: With a high prevalence of telehealth barriers, patients with limited income, a chronic condition, and a care gap may benefit from greater technological access and supportive programs for awareness, telehealth comfort, and navigation support. Addressing telehealth barriers could increase the quality of medical care and improve health outcomes for this population.

Association of Vaccination with the Persistence of Post-COVID Symptoms.

BACKGROUND: Patients who have had COVID-19 often report persistent symptoms after resolution of their acute illness. Recent reports suggest that vaccination may be associated with improvement in post-acute symptoms. We used data from a prospective cohort to assess differences in post-acute sequelae of COVID (PASC) among vaccinated vs. unvaccinated patients. METHODS: We used data from a cohort of COVID-19 patients enrolled into a prospective registry established at a tertiary care health system in New York City. Participants underwent a baseline evaluation before COVID-19 vaccines were available and were followed 6 months later. We compared unadjusted and propensity score-adjusted baseline to 6-month change for several PASC-related symptoms and measures: anosmia, respiratory (cough, dyspnea, phlegm, wheezing), depression, anxiety, post-traumatic stress disorder (PTSD; COVID-19-related and other trauma), and quality-of-life domains among participants who received vs. those who did not receive COVID-19 vaccination. RESULTS: The study included 453 COVID-19 patients with PASC, of which 324 (72%) were vaccinated between the baseline and 6-month visit. Unadjusted analyses did not show significant differences in the baseline to 6-month change in anosmia, respiratory symptoms, depression, anxiety, PTSD, or quality of life (p > 0.05 for all comparisons) among vaccinated vs. unvaccinated patients. Similar results were found in propensity-adjusted comparisons and in secondary analyses based on the number of vaccine doses received. CONCLUSIONS: Our findings suggest that COVID vaccination is not associated with improvement in PASC. Additional studies are needed to better understand the mechanisms underlying PASC and to develop effective treatments.

Plasminogenuria is associated with podocyte injury, edema, and kidney dysfunction in incident glomerular disease.

Urinary plasminogen/plasmin, or plasmin (ogen) uria, has been demonstrated in proteinuric patients and exposure of cultured podocytes to plasminogen results in injury via oxidative stress pathways. A causative role for plasmin (ogen) as a "second hit" in kidney disease progression has yet to have been demonstrated in vivo. Additionally, association between plasmin (ogen) uria and kidney function in glomerular diseases remains unclear. We performed comparative studies in a puromycin aminonucleoside (PAN) nephropathy rat model treated with amiloride, an inhibitor of plasminogen activation, and measured changes in plasmin (ogen) uria. In a glomerular disease biorepository cohort (n = 128), we measured time-of-biopsy albuminuria, proteinuria, and plasmin (ogen) uria for correlations with kidney outcomes. In cultured human podocytes, plasminogen treatment was associated with decreased focal adhesion marker expression with rescue by amiloride. Increased glomerular plasmin (ogen) was found in PAN rats and focal segmental glomerulosclerosis (FSGS) patients. PAN nephropathy was associated with increases in plasmin (ogen) uria and proteinuria. Amiloride was protective against PAN-induced glomerular injury, reducing CD36 scavenger receptor expression and oxidative stress. In patients, we found associations between plasmin (ogen) uria and edema status as well as eGFR. Our study demonstrates a role for plasmin (ogen)-induced podocyte injury in the PAN nephropathy model, with amiloride having podocyte-protective properties. In one of the largest glomerular disease cohorts to study plasminogen, we validated previous findings while suggesting a potentially novel relationship between plasmin (ogen) uria and estimated glomerular filtration rate (eGFR). Together, these findings suggest a role for plasmin (ogen) in mediating glomerular injury and as a viable targetable biomarker for podocyte-sparing treatments.

LIM-Nebulette Reinforces Podocyte Structural Integrity by Linking Actin and Vimentin Filaments.

BACKGROUND: Maintenance of the intricate interdigitating morphology of podocytes is crucial for glomerular filtration. One of the key aspects of specialized podocyte morphology is the segregation and organization of distinct cytoskeletal filaments into different subcellular components, for which the exact mechanisms remain poorly understood. METHODS: Cells from rats, mice, and humans were used to describe the cytoskeletal configuration underlying podocyte structure. Screening the time-dependent proteomic changes in the rat puromycin aminonucleoside-induced nephropathy model correlated the actin-binding protein LIM-nebulette strongly with glomerular function. Single-cell RNA sequencing and immunogold labeling were used to determine Nebl expression specificity in podocytes. Automated high-content imaging, super-resolution microscopy, atomic force microscopy (AFM), live-cell imaging of calcium, and measurement of motility and adhesion dynamics characterized the physiologic role of LIM-nebulette in podocytes. RESULTS: Nebl knockout mice have increased susceptibility to adriamycin-induced nephropathy and display morphologic, cytoskeletal, and focal adhesion abnormalities with altered calcium dynamics, motility, and Rho GTPase activity. LIM-nebulette expression is decreased in diabetic nephropathy and FSGS patients at both the transcript and protein level. In mice, rats, and humans, LIM-nebulette expression is localized to primary, secondary, and tertiary processes of podocytes, where it colocalizes with focal adhesions as well as with vimentin fibers. LIM-nebulette shRNA knockdown in immortalized human podocytes leads to dysregulation of vimentin filament organization and reduced cellular elasticity as measured by AFM indentation. CONCLUSIONS: LIM-nebulette is a multifunctional cytoskeletal protein that is critical in the maintenance of podocyte structural integrity through active reorganization of focal adhesions, the actin cytoskeleton, and intermediate filaments.

Implementation of a quality improvement strategy to increase outpatient kidney transplant referrals.

BACKGROUND: Kidney transplantation remains the optimal therapy for patients with end stage kidney disease (ESKD), though a small fraction of patients on dialysis are on organ waitlists. An important barrier to both preemptive kidney transplantation and successful waitlisting is timely referral to a kidney transplant center. We implemented a quality improvement strategy to improve outpatient kidney transplant referrals in a single center academic outpatient nephrology clinic. METHODS: Over a 3 month period (July 1-September 30, 2016), we assessed the baseline kidney transplantation referral rate at our outpatient nephrology clinic for patients 18-75 years old with an estimated glomerular filtration rate (eGFR) of less than 20 mL/min/1.73m2 (2 values over 90 days apart). Charts were manually reviewed by two reviewers to look for kidney transplant referrals and documentation of discussions about kidney transplantation. We then performed a root cause analysis to explore potential barriers to kidney transplantation. Our intervention began on July 1, 2017 and included the implementation of a column in the electronic medical record (EMR) which displayed the patient's last eGFR as part of the clinic schedule. In addition, physicians were given a document listing their patients to be seen that day with an eGFR of < 20 mL/min/1.73m2. Annual education sessions were also held to discuss the importance of timely kidney transplant referral. RESULTS: At baseline, 54 unique patients with eGFR ≤20 ml/min/1.73 m2 were identified who were seen in the Clinic between July 1, 2016 and September 30, 2016. 29.6% (16) eligible patients were referred for kidney transplantation evaluation. 69.5% (37) of these patients were not referred for kidney transplant evaluation. 46.3% (25) did not have documentation regarding kidney transplant in the EMR. nephrologist's most recent note. Following the intervention, 66 unique patients met criteria for eligibility for kidney transplant evaluation. Kidney transplant referrals increased to 60.6% (p <  0.001). CONCLUSIONS: Our pilot implementation study of a strategy to improve outpatient kidney transplant referrals showed that a free, simple, scalable intervention can significantly improve kidney transplant referrals in the outpatient setting. This intervention targeted the nephrologist's role in the transplant referral, and facilitated the process of patient recognition and performing the referral itself without significantly interrupting the workflow. Next steps include further investigation to study the impact of early referral to kidney transplant centers on preemptive and living donor kidney transplantation as well as successful waitlisting.

Disruption of MAGI2-RapGEF2-Rap1 signaling contributes to podocyte dysfunction in congenital nephrotic syndrome caused by mutations in MAGI2.

The essential role of membrane associated guanylate kinase 2 (MAGI2) in podocytes is indicated by the phenotypes of severe glomerulosclerosis of both MAGI2 knockout mice and in patients with congenital nephrotic syndrome (CNS) caused by mutations in MAGI2. Here, we show that MAGI2 forms a complex with the Rap1 guanine nucleotide exchange factor, RapGEF2, and that this complex is lost when expressing MAGI2 CNS variants. Co-expression of RapGEF2 with wild-type MAGI2, but not MAGI2 CNS variants, enhanced activation of the small GTPase Rap1, a central signaling node in podocytes. In mice, podocyte-specific RapGEF2 deletion resulted in spontaneous glomerulosclerosis, with qualitative glomerular features comparable to MAGI2 knockout mice. Knockdown of RapGEF2 or MAGI2 in human podocytes caused similar reductions in levels of Rap1 activation and Rap1-mediated downstream signaling. Furthermore, human podocytes expressing MAGI2 CNS variants show severe abnormalities of cellular morphology and dramatic loss of actin cytoskeletal organization, features completely rescued by pharmacological activation of Rap1 via a non-MAGI2 dependent upstream pathway. Finally, immunostaining of kidney sections from patients with congenital nephrotic syndrome and MAGI2 mutations showed reduced podocyte Rap1-mediated signaling. Thus, MAGI2-RapGEF2-Rap1 signaling is essential for normal podocyte function. Hence, disruption of this pathway is an important cause of the renal phenotype induced by MAGI2 CNS mutations.

DUET: A Phase 2 Study Evaluating the Efficacy and Safety of Sparsentan in Patients with FSGS.

BACKGROUND: We evaluated and compared the effects of sparsentan, a dual endothelin type A (ETA) and angiotensin II type 1 receptor antagonist, with those of the angiotensin II type 1 receptor antagonist irbesartan in patients with primary FSGS. METHODS: In this phase 2, randomized, double-blind, active-control Efficacy and Safety of Sparsentan (RE-021), a Dual Endothelin Receptor and Angiotensin Receptor Blocker, in Patients with Focal Segmental Glomerulosclerosis (FSGS): A Randomized, Double-blind, Active-Control, Dose-Escalation Study (DUET), patients aged 8-75 years with biopsy-proven FSGS, eGFR>30 ml/min per 1.73 m2, and urinary protein-to-creatinine ratio (UP/C) ≥1.0 g/g received sparsentan (200, 400, or 800 mg/d) or irbesartan (300 mg/d) for 8 weeks, followed by open-label sparsentan only. End points at week 8 were reduction from baseline in UP/C (primary) and proportion of patients achieving FSGS partial remission end point (FPRE) (UP/C: ≤1.5 g/g and >40% reduction [secondary]). RESULTS: Of 109 patients randomized, 96 received study drugs and had baseline and week 8 UP/C measurements. Sparsentan-treated patients had greater reductions in UP/C than irbesartan-treated patients did when all doses (45% versus 19%; P=0.006) or the 400 and 800 mg doses (47% versus 19%; P=0.01) were pooled for analysis. The FSGS partial remission end point was achieved in 28% of sparsentan-treated and 9% of irbesartan-treated patients (P=0.04). After 8 weeks of treatment, BP was reduced with sparsentan but not irbesartan, and eGFR was stable with both treatments. Overall, the incidence of adverse events was similar between groups. Hypotension and edema were more common among sparsentan-treated patients but did not result in study withdrawals. CONCLUSIONS: Patients with FSGS achieved significantly greater reductions in proteinuria after 8 weeks of sparsentan versus irbesartan. Sparsentan was safe and well tolerated.

SHROOM3-FYN Interaction Regulates Nephrin Phosphorylation and Affects Albuminuria in Allografts.

BACKGROUND: We previously showed that the presence of a CKD-associated locus in SHROOM3 in a donor kidney results in increased expression of SHROOM3 (an F-actin-binding protein important for epithelial morphogenesis, via rho-kinase [ROCK] binding); this facilitates TGF-b signaling and allograft fibrosis. However, other evidence suggests Shroom3 may have a protective role in glomerular development. METHODS: We used human data, Shroom3 knockdown podocytes, and inducible shRNA-mediated knockdown mice to study the role of Shroom3 in adult glomeruli. RESULTS: Expression data from the Nephroseq database showed glomerular and nonglomerular SHROOM3 had opposing associations with renal function in CKD biopsy samples. In human allografts, homozygosity at rs17319721, the SHROOM3 locus linked with lower GFR, was associated with reduced albuminuria by 2 years after transplant. Although our previous data showed reduced renal fibrosis with tubular Shroom3 knockdown, this study found that glomerular but not tubular Shroom3 knockdown induced albuminuria. Electron microscopy revealed diffuse foot process effacement, and glomerular RNA-sequencing showed enrichment of tyrosine kinase signaling and podocyte actin cytoskeleton pathways in knockdown mice. Screening SHROOM3-interacting proteins identified FYN (a src-kinase) as a candidate.We confirmed the interaction of endogenous SHROOM3 with FYN in human podocytes via a critical Src homology 3-binding domain, distinct from its ROCK-binding domain. Shroom3-Fyn interaction was required in vitro and in vivo for activation of Fyn kinase and downstream nephrin phosphorylation in podocytes. SHROOM3 knockdown altered podocyte morphology, cytoskeleton, adhesion, and migration. CONCLUSIONS: We demonstrate a novel mechanism that may explain SHROOM3's dichotomous associations in glomerular versus nonglomerular compartments in CKD.

The Hippo pathway regulator KIBRA promotes podocyte injury by inhibiting YAP signaling and disrupting actin cytoskeletal dynamics.

Kidney podocytes represent a key constituent of the glomerular filtration barrier. Identifying the molecular mechanisms of podocyte injury and survival is important for better understanding and management of kidney diseases. KIBRA (kidney brain protein), an upstream regulator of the Hippo signaling pathway encoded by the Wwc1 gene, shares the pro-injury properties of its putative binding partner dendrin and antagonizes the pro-survival signaling of the downstream Hippo pathway effector YAP (Yes-associated protein) in Drosophila and MCF10A cells. We recently identified YAP as an essential component of the glomerular filtration barrier that promotes podocyte survival by inhibiting dendrin pro-apoptotic function. Despite these recent advances, the signaling pathways that mediate podocyte injury remain poorly understood. Here we tested the hypothesis that, similar to its role in other model systems, KIBRA promotes podocyte injury. We found increased expression of KIBRA and phosphorylated YAP protein in glomeruli of patients with biopsy-proven focal segmental glomerulosclerosis (FSGS). KIBRA/WWc1 overexpression in murine podocytes promoted LATS kinase phosphorylation, leading to subsequent YAP Ser-127 phosphorylation, YAP cytoplasmic sequestration, and reduction in YAP target gene expression. Functionally, KIBRA overexpression induced significant morphological changes in podocytes, including disruption of the actin cytoskeletal architecture and reduction of focal adhesion size and number, all of which were rescued by subsequent YAP overexpression. Conversely, constitutive KIBRA knockout mice displayed reduced phosphorylated YAP and increased YAP expression at baseline. These mice were protected from acute podocyte foot process effacement following protamine sulfate perfusion. KIBRA knockdown podocytes were also protected against protamine-induced injury. These findings suggest an important role for KIBRA in the pathogenesis of podocyte injury and the progression of proteinuric kidney disease.

Protecting Podocytes: A Key Target for Therapy of Focal Segmental Glomerulosclerosis.

BACKGROUND: Focal segmental glomerulosclerosis (FSGS) is a histologic pattern of injury demonstrated by renal biopsy that can arise from a diverse range of causes and mechanisms. It has an estimated incidence of 7 per 1 million and is the most common primary glomerular disorder leading to end-stage renal disease in the United States. This review focuses on damage to the podocyte and the consequences of this injury in patients with FSGS, the genetics of FSGS, and approaches to treatment with a focus on the effects on podocytes. SUMMARY: The podocyte is central to the glomerular filtration barrier and is particularly vulnerable because of its highly differentiated post-mitotic phenotype. The progressive structural changes involved in the pathology of FSGS include podocyte foot process effacement, death of podocytes and exposure of the glomerular basement membrane, filtration of nonspecific plasma proteins, expansion of capillaries, misdirected filtration at points of synechiae, and mesangial matrix proliferation. Although damage to and death of podocytes can result from single-gene disorders, evidence also suggests a role for soluble factors, such as soluble urokinase-type plasminogen activator receptor, cardiotrophin-like cytokine-1, and anti-CD40 antibodies, that promote FSGS recurrence post transplant. Several classes of medications, including corticosteroids, calcineurin inhibitors, endothelin receptor antagonists, adrenocorticotropic hormone, and rituximab, have been shown to be effective for the treatment of FSGS and have been demonstrated to have significant protective effects on podocytes. Key Messages: Greater understanding of podocyte biology is essential to the identification of new treatment targets and medications for the management of patients with FSGS.

MAGI-1 Interacts with Nephrin to Maintain Slit Diaphragm Structure through Enhanced Rap1 Activation in Podocytes.

MAGI-1 is a multidomain cytosolic scaffolding protein that in the kidney is specifically located at the podocyte slit diaphragm, a specialized junction that is universally injured in proteinuric diseases. There it interacts with several essential molecules, including nephrin and neph1, which are required for slit diaphragm formation and as an intracellular signaling hub. Here, we show that diminished MAGI-1 expression in cultured podocytes reduced nephrin and neph1 membrane localization and weakened tight junction integrity. Global magi1 knock-out mice, however, demonstrated normal glomerular histology and function into adulthood. We hypothesized that a second mild but complementary genetic insult might induce glomerular disease susceptibility in these mice. To identify such a gene, we utilized the developing fly eye to test for functional complementation between MAGI and its binding partners. In this way, we identified diminished expression of fly Hibris (nephrin) or Roughest (neph1) as dramatically exacerbating the effects of MAGI depletion. Indeed, when these combinations were studied in mice, the addition of nephrin, but not neph1, heterozygosity to homozygous deletion of MAGI-1 resulted in spontaneous glomerulosclerosis. In cultured podocytes, MAGI-1 depletion reduced intercellular contact-induced Rap1 activation, a pathway critical for proper podocyte function. Similarly, magi1 knock-out mice showed diminished glomerular Rap1 activation, an effect dramatically enhanced by concomitant nephrin haploinsufficiency. Finally, combined overexpression of MAGI-1 and nephrin increased Rap1 activation, but not when substituting a mutant MAGI-1 that cannot bind nephrin. We conclude that the interaction between nephrin and MAGI-1 regulates Rap1 activation in podocytes to maintain long term slit diaphragm structure.

Revisiting the determinants of the glomerular filtration barrier: what goes round must come round.

The glomerular filtration barrier (GFB) is characterized by a very high hydraulic permeability, combined with a marked permselectivity that excludes macromolecules such as albumin. Thus, the GFB retains most of the plasma proteins, with only 0.06% of albumin getting across the basement membrane. The GFB consists of 3 layers: fenestrated endothelial cells, the glomerular basement membrane, and podocytes. Injury to any of these components can result in the development of proteinuria. The contribution of the major components of the GFB has recently been reexamined and is discussed in the context of our past and present understanding.

Chronic kidney disease and risk factor prevalence in Saint Kitts and Nevis: a cross-sectional study.

BACKGROUND: The prevalence of chronic kidney disease (CKD) in St. Kitts and Nevis, islands of the West Indies, is unknown. We sought to determine estimates of CKD and its risk factors (e.g. diabetes, hypertension and obesity) in St. Kitts and Nevis. METHODS: This was a chronic disease screening program. Three community-based locations in St. Kitts and Nevis were included in the program. Participants were adult community residents aged ≥18 years. The main outcome measures were estimated CKD prevalence (by serum creatinine-based estimated glomerular filtration rate (eGFR) and dipstick urine albumin); and estimated prevalence of CKD risk factors (diabetes, hypertension and obesity). Logistic regression was used to determine independent predictors of CKD. RESULTS: One thousand nine hundred seventy eight persons, from Nevis (n = 950) and St. Kitts (n = 1028) were screened by the Caribbean Health and Education Foundation. Participants' mean age was 49 ± 15 years, 65% were female, and 99% were black. Fully, 21.5% had diabetes and 53.1% had hypertension; and 40.3% were obese. Mean estimated eGFR was 98 ml/min/1.73 m2 (standard deviation = 30) and 4.7% had an eGFR <60 ml/min/1.73 m2, indicating CKD. Age [Odds Ratio (OR) = 1.08, 95% Confidence Interval (CI) 1.05-1.11], hypertension (OR = 2.89, 95% CI 1.18-7.07) and diabetes (OR = 3.12, 95% CI 1.80-5.43) were independent predictors of reduced eGFR in models adjusted for age, gender and obesity status. Of those with urine testing in Nevis (n = 929), 13.5% had urine albumin ≥30 mg/dL, and diabetes was an independent predictor of this finding (OR = 2.43, 95% CI 1.53-3.87). CONCLUSIONS: CKD and its risk factors were prevalent among adults in St. Kitts and Nevis. Public policy strategies for prevention and treatment of these conditions may be needed to reduce their associated morbidity, mortality and costs.

Podocyte-Specific Deletion of Yes-Associated Protein Causes FSGS and Progressive Renal Failure.

FSGS is the most common primary glomerular disease underlying ESRD in the United States and is increasing in incidence globally. FSGS results from podocyte injury, yet the mechanistic details of disease pathogenesis remain unclear. This has resulted in an unmet clinical need for cell-specific therapy in the treatment of FSGS and other proteinuric kidney diseases. We previously identified Yes-associated protein (YAP) as a prosurvival signaling molecule, the in vitro silencing of which increases podocyte susceptibility to apoptotic stimulus. YAP is a potent oncogene that is a prominent target for chemotherapeutic drug development. In this study, we tested the hypothesis that podocyte-specific deletion of Yap leads to proteinuric kidney disease through increased podocyte apoptosis. Yap was selectively silenced in podocytes using Cre-mediated recombination controlled by the podocin promoter. Yap silencing in podocytes resulted in podocyte apoptosis, podocyte depletion, proteinuria, and an increase in serum creatinine. Histologically, features characteristic of FSGS, including mesangial sclerosis, podocyte foot process effacement, tubular atrophy, interstitial fibrosis, and casts, were observed. In human primary FSGS, we noted reduced glomerular expression of YAP. Taken together, these results suggest a role for YAP as a physiologic antagonist of podocyte apoptosis, the signaling of which is essential for maintaining the integrity of the glomerular filtration barrier. These data suggest potential nephrotoxicity with strategies directed toward inhibition of YAP function. Further studies should evaluate the role of YAP in proteinuric glomerular disease pathogenesis and its potential utility as a therapeutic target.

Hippo signaling in the kidney: the good and the bad.

The Hippo signaling pathway is an evolutionarily conserved kinase cascade, playing multiple roles in embryonic development that controls organ size, cell proliferation, and apoptosis. At the center of this network lie the Hippo kinase target and downstream pathway effector Yes-associated protein (YAP) and its paralog TAZ. In its phosphorylated form, cytoplasmic YAP is sequestered in an inactive state. When it is dephosphorylated, YAP, a potent oncogene, is activated and relocates to the nucleus to interact with a number of transcription factors and signaling regulators that promote cell growth, differentiation, and survival. The identification of YAP activation in human cancers has made it an attractive target for chemotherapeutic drug development. Little is known to date about the function of the Hippo pathway in the kidney, but that is rapidly changing. Recent studies have shed light on the role of Hippo-YAP signaling in glomerular and lower urinary tract embryonic development, maintenance of podocyte homeostasis, the integrity of the glomerular filtration barrier, regulation of renal tubular cyst growth, renal epithelial injury in diabetes, and renal fibrogenesis. This review summarizes the current knowledge of the Hippo-YAP signaling axis in the kidney under normal and disease conditions.

Podocyte injury: the role of proteinuria, urinary plasminogen, and oxidative stress.

Podocytes are the key target for injury in proteinuric glomerular diseases that result in podocyte loss, progressive focal segmental glomerular sclerosis (FSGS), and renal failure. Current evidence suggests that the initiation of podocyte injury and associated proteinuria can be separated from factors that drive and maintain these pathogenic processes leading to FSGS. In nephrotic urine aberrant glomerular filtration of plasminogen (Plg) is activated to the biologically active serine protease plasmin by urokinase-type plasminogen activator (uPA). In vivo inhibition of uPA mitigates Plg activation and development of FSGS in several proteinuric models of renal disease including 5/6 nephrectomy. Here, we show that Plg is markedly increased in the urine in two murine models of proteinuric kidney disease associated with podocyte injury: Tg26 HIV-associated nephropathy and the Cd2ap-/- model of FSGS. We show that human podocytes express uPA and three Plg receptors: uPAR, tPA, and Plg-RKT. We demonstrate that Plg treatment of podocytes specifically upregulates NADPH oxidase isoforms NOX2/NOX4 and increases production of mitochondrial-dependent superoxide anion (O2-) that promotes endothelin-1 synthesis. Plg via O2- also promotes expression of the B scavenger receptor CD36 and subsequent increased intracellular cholesterol uptake resulting in podocyte apoptosis. Taken together, our findings suggest that following disruption of the glomerular filtration barrier at the onset of proteinuric disease, podocytes are exposed to Plg resulting in further injury mediated by oxidative stress. We suggest that chronic exposure to Plg could serve as a "second hit" in glomerular disease and that Plg is potentially an attractive target for therapeutic intervention.