Inhibition of endoplasmic reticulum stress signaling rescues cytotoxicity of human apolipoprotein-L1 risk variants in Drosophila.

Risk variants of the apolipoprotein-L1 (APOL1) gene are associated with severe kidney disease, putting homozygous carriers at risk. Since APOL1 lacks orthologs in all major model organisms, a wide range of mechanisms frequently in conflict have been described for APOL1-associated nephropathies. The genetic toolkit in Drosophila allows unique in vivo insights into disrupted cellular homeostasis. To perform a mechanistic analysis, we expressed human APOL1 control and gain-of-function kidney risk variants in the podocyte-like garland cells of Drosophila nephrocytes and a wing precursor tissue. Expression of APOL1 risk variants was found to elevate endocytic function of garland cell nephrocytes that simultaneously showed early signs of cell death. Wild-type APOL1 had a significantly milder effect, while a control transgene with deletion of the short BH3 domain showed no overt phenotype. Nephrocyte endo-lysosomal function and slit diaphragm architecture remained unaffected by APOL1 risk variants, but endoplasmic reticulum (ER) swelling, chaperone induction, and expression of the reporter Xbp1-EGFP suggested an ER stress response. Pharmacological inhibition of ER stress diminished APOL1-mediated cell death and direct ER stress induction enhanced nephrocyte endocytic function similar to expression of APOL1 risk variants. We confirmed APOL1-dependent ER stress in the Drosophila wing precursor where silencing the IRE1-dependent branch of ER stress signaling by inhibition with Xbp1-RNAi abrogated cell death, representing the first rescue of APOL1-associated cytotoxicity in vivo. Thus, we uncovered ER stress as an essential consequence of APOL1 risk variant expression in vivo in Drosophila, suggesting a central role of this pathway in the pathogenesis of APOL1-associated nephropathies.

COVID-19 associated collapsing glomerulopathy presenting as acute kidney injury on chronic kidney disease: a case report and review of the literature.

Traditionally collapsing glomerulopathy (CG) is associated with medications, autoimmune disease, viral infection and the APOL1 gene variant seen in blacks/African Americans. Most reported cases of acute kidney injury (AKI) in COVID-19 infected individuals have been in individuals without prior CKD. In this report, we present a 49-year-old African American female with a past medical history of chronic kidney disease (CKD) stage 4, hypertension, type 2 diabetes mellitus, recent COVID-19 infection, and a repeat positive blood test for COVID-19 more than 21 days after the initial result, who presented with an AKI on CKD. Renal biopsy revealed a collapsing glomerulopathy. She was started on hemodialysis and did not receive immunosuppressive therapy due to the advanced scaring seen on the renal biopsy. Concerning the pathophysiology of COVID-19-associated CG, researchers have postulated different mechanisms such as a direct cytopathic effect of the virus on podocytes, immune dysregulation, and fluid imbalance. This is one of a few cases of AKI on CKD due to CG related to COVID-19. The mechanism of CG was, however, unclear. Currently, there is no specific interventions to prevent the development of CG in patients with COVID-19 infection. Further studies should investigate measures to prevent the development of CG.

Longitudinal Outcomes of COVID-19-Associated Collapsing Glomerulopathy and Other Podocytopathies.

BACKGROUND: The long-term outcome of COVID-19-associated collapsing glomerulopathy is unknown. METHODS: We retrospectively identified 76 native kidney biopsies from patients with history of COVID-19 between March 2020 and April 2021. Presenting and outcome data were obtained for all 23 patients with collapsing glomerulopathy and for seven patients with noncollapsing podocytopathies. We performed APOL1 genotyping by Sanger sequencing, immunostaining for spike and nucleocapsid proteins, and in situ hybridization for SARS-CoV-2. RESULTS: The 23 patients with COVID-19-associated collapsing glomerulopathy were median age 57 years (range, 35-72), included 16 men, and were predominantly (91%) Black. Severity of COVID-19 was mild or moderate in most (77%) patients. All but one patient presented with AKI, 17 had nephrotic-range proteinuria, and six had nephrotic syndrome. Fourteen (61%) patients required dialysis at presentation. Among 17 patients genotyped, 16 (94%) were high-risk APOL1. Among 22 (96%) patients with median follow-up at 155 days (range, 30-412), 11 (50%) received treatment for COVID-19, and eight (36%) received glucocorticoid therapy for podocytopathy. At follow-up, 19 (86%) patients were alive, and 15 (68%) were dialysis free, including seven of 14 who initially required dialysis. The dialysis-free patients included 64% (seven of 11) of those treated for COVID-19 and 75% (six of eight) of those treated with glucocorticoids for podocytopathy. Overall, 36% achieved partial remission of proteinuria, 32% had no remission, and 32% reached combined end points of ESKD or death. Viral infection of the kidney was not detected. CONCLUSIONS: Half of 14 patients with COVID-19-associated collapsing glomerulopathy requiring dialysis achieved dialysis independence, but the long-term prognosis of residual proteinuric CKD remains guarded, indicating a need for more effective therapy.

Glomerular filtration barrier dysfunction in a self-limiting, RNA virus-induced glomerulopathy resembles findings in idiopathic nephrotic syndromes.

Podocyte injury has recently been described as unifying feature in idiopathic nephrotic syndromes (INS). Puumala hantavirus (PUUV) infection represents a unique RNA virus-induced renal disease with significant proteinuria. The underlying pathomechanism is unclear. We hypothesized that PUUV infection results in podocyte injury, similar to findings in INS. We therefore analyzed standard markers of glomerular proteinuria (e.g. immunoglobulin G [IgG]), urinary nephrin excretion (podocyte injury) and serum levels of the soluble urokinase plasminogen activator receptor (suPAR), a proposed pathomechanically involved molecule in INS, in PUUV-infected patients. Hantavirus patients showed significantly increased urinary nephrin, IgG and serum suPAR concentrations compared to healthy controls. Nephrin and IgG levels were significantly higher in patients with severe proteinuria than with mild proteinuria, and nephrin correlated strongly with biomarkers of glomerular proteinuria over time. Congruently, electron microcopy analyses showed a focal podocyte foot process effacement. suPAR correlated significantly with urinary nephrin, IgG and albumin levels, suggesting suPAR as a pathophysiological mediator in podocyte dysfunction. In contrast to INS, proteinuria recovered autonomously in hantavirus patients. This study reveals podocyte injury as main cause of proteinuria in hantavirus patients. A better understanding of the regenerative nature of hantavirus-induced glomerulopathy may generate new therapeutic approaches for INS.

COVID-19-Associated Glomerular Disease.

BACKGROUND: Studies have documented AKI with high-grade proteinuria in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In some patients, biopsies have revealed collapsing glomerulopathy, a distinct form of glomerular injury that has been associated with other viruses, including HIV. Previous patient reports have described patients of African ancestry who developed nephrotic-range proteinuria and AKI early in the course of disease. METHODS: In this patient series, we identified six patients with coronavirus disease 2019 (COVID-19), AKI, and nephrotic-range proteinuria. COVID-19 was diagnosed by a positive nasopharyngeal swab RT-PCR for SARS-CoV-2 infection. We examined biopsy specimens from one transplanted kidney and five native kidneys. Three of the six patients underwent genetic analysis of APOL1, the gene encoding the APOL1 protein, from DNA extracted from peripheral blood. In addition, we purified genomic DNA from paraffin-embedded tissue and performed APOL1 genotype analysis of one of the native biopsies and the donor kidney graft. RESULTS: All six patients were of recent African ancestry. They developed COVID-19-associated AKI with podocytopathy, collapsing glomerulopathy, or both. Patients exhibited generally mild respiratory symptoms, and no patient required ventilator support. Genetic testing performed in three patients confirmed high-risk APOL1 genotypes. One APOL1 high-risk patient developed collapsing glomerulopathy in the engrafted kidney, which was transplanted from a donor who carried a low-risk APOL1 genotype; this contradicts current models of APOL1-mediated kidney injury, and suggests that intrinsic renal expression of APOL1 may not be the driver of nephrotoxicity and specifically, of podocyte injury. CONCLUSIONS: Glomerular disease presenting as proteinuria with or without AKI is an important presentation of COVID-19 infection and may be associated with a high-risk APOL1 genotype.

Covid-19 and kidney injury: Pathophysiology and molecular mechanisms.

The novel coronavirus (SARS-CoV-2) has turned into a life-threatening pandemic disease (Covid-19). About 5% of patients with Covid-19 have severe symptoms including septic shock, acute respiratory distress syndrome, and the failure of several organs, while most of them have mild symptoms. Frequently, the kidneys are involved through direct or indirect mechanisms. Kidney involvement mainly manifests itself as proteinuria and acute kidney injury (AKI). The SARS-CoV-2-induced kidney damage is expected to be multifactorial; directly it can infect the kidney podocytes and proximal tubular cells and based on an angiotensin-converting enzyme 2 (ACE2) pathway it can lead to acute tubular necrosis, protein leakage in Bowman's capsule, collapsing glomerulopathy and mitochondrial impairment. The SARS-CoV-2-driven dysregulation of the immune responses including cytokine storm, macrophage activation syndrome, and lymphopenia can be other causes of the AKI. Organ interactions, endothelial dysfunction, hypercoagulability, rhabdomyolysis, and sepsis are other potential mechanisms of AKI. Moreover, lower oxygen delivery to kidney may cause an ischaemic injury. Understanding the fundamental molecular pathways and pathophysiology of kidney injury and AKI in Covid-19 is necessary to develop management strategies and design effective therapies.

Spectrum of podocytopathies in new-onset nephrotic syndrome following COVID-19 disease: a report of 2 cases.

BACKGROUND: Coronavirus disease-2019 (COVID-19) is an ongoing pandemic which has affected over 12 million people across the globe. Manifestations in different organs systems are being reported regularly. Renal biopsy findings in hospitalized COVID-19 patients presenting solely with acute kidney injury (AKI) have recently been described in published literature in few case reports. The findings include diffuse acute tubular injury (ATI) along with the glomerular lesion of collapsing glomerulopathy (CG). However, nephrotic syndrome as the presenting complaint of COVID-19 has not been reported widely, neither has any other glomerular lesion other than CG. CASE PRESENTATION: We describe the kidney biopsy findings of two patients who had recent diagnoses of COVID-19 and presented with new-onset nephrotic syndrome. Renal biopsy in both patients showed ATI (as in previous reports) and distinct glomerular findings on light microscopy - that of minimal change disease (MCD) initially in one patient followed by CG in a subsequent biopsy and CG at the outset in the other patient. The electron microscopic findings in both patients were that of severe podocytopathy (diffuse and severe podocyte foot process effacement). CONCLUSION: Our cases highlight a novel clinical presentation of COVID-19 renal disease, not described before, that of new-onset nephrotic syndrome. While all published case reports describe CG as the glomerular pathology, we describe a non-CG pathology (MCD) in one of our cases, thereby adding to the repertoire of renal pathology described in association with COVID-19 patients. However, the exact mechanism by which podocyte injury or podocytopathy occurs in all such cases is still unknown. Optimal treatment options for these patients also remains unknown at this time.