The sclerosing glomerulus in mice and man: novel insights

Therapeutic trials in adult FSGS: lessons learned and the road forward

Focal segmental glomerulosclerosis (FSGS) is not a specific disease entity but a lesion that primarily targets the podocyte. In a broad sense, the causes of the lesion can be divided into those triggered by a presumed circulating permeability factor, those that occur secondary to a process that might originate outside the kidneys, those caused by a genetic mutation in a podocyte or glomerular basement membrane protein, and those that arise through an as yet unidentifiable process, seemingly unrelated to a circulating permeability factor. A careful attempt to correctly stratify patients with FSGS based on their clinical presentation and pathological findings on kidney biopsy is essential for sound treatment decisions in individual patients. However, it is also essential for the rational design of therapeutic trials in FSGS. Greater recognition of the pathophysiology underlying podocyte stress and damage in FSGS will increase the likelihood that the cause of an FSGS lesion is properly identified and enable stratification of patients in future interventional trials. Such efforts will facilitate the identification of effective therapeutic agents.

Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a leading cause of kidney disease worldwide. The presumed etiology of primary FSGS is a plasma factor with responsiveness to immunosuppressive therapy and a risk of recurrence after kidney transplant-important disease characteristics. In contrast, adaptive FSGS is associated with excessive nephron workload due to increased body size, reduced nephron capacity, or single glomerular hyperfiltration associated with certain diseases. Additional etiologies are now recognized as drivers of FSGS: high-penetrance genetic FSGS due to mutations in one of nearly 40 genes, virus-associated FSGS, and medication-associated FSGS. Emerging data support the identification of a sixth category: APOL1 risk allele-associated FSGS in individuals with sub-Saharan ancestry. The classification of a particular patient with FSGS relies on integration of findings from clinical history, laboratory testing, kidney biopsy, and in some patients, genetic testing. The kidney biopsy can be helpful, with clues provided by features on light microscopy (e.g, glomerular size, histologic variant of FSGS, microcystic tubular changes, and tubular hypertrophy), immunofluorescence (e.g, to rule out other primary glomerulopathies), and electron microscopy (e.g., extent of podocyte foot process effacement, podocyte microvillous transformation, and tubuloreticular inclusions). A complete assessment of renal histology is important for establishing the parenchymal setting of segmental glomerulosclerosis, distinguishing FSGS associated with one of many other glomerular diseases from the clinical-pathologic syndrome of FSGS. Genetic testing is beneficial in particular clinical settings. Identifying the etiology of FSGS guides selection of therapy and provides prognostic insight. Much progress has been made in our understanding of FSGS, but important outstanding issues remain, including the identity of the plasma factor believed to be responsible for primary FSGS, the value of routine implementation of genetic testing, and the identification of more effective and less toxic therapeutic interventions for FSGS.

Bortezomib treatment prevents glomerulosclerosis associated with lupus nephritis in a murine model through suppressive effects on the immune and renin-angiotensin systems

OBJECTIVE

To clarify the mechanisms underlying lupus nephritis (LN) amelioration following bortezomib treatment.

METHODS

Bortezomib was administered subcutaneously every 3 days to NZB/W F1 mice, and the serum anti-double stranded (ds) deoxyribonucleic acid (DNA) antibody titers and proteinuria levels were measured. The renal samples and the splenocytes were examined histologically or used for real-time quantitative reverse transcription-polymerase chain reaction analysis after 18 weeks of treatment. Serum cytokine and anti-dsDNA antibody levels were measured using flow cytometry and enzyme-linked immunoassays every 3 weeks. Transforming growth factor (TGF)-β, angiotensin II type-1 receptor (AT1R), and type I collagen expression levels in the glomeruli were evaluated using immunohistochemistry.

RESULTS

Bortezomib reduced the serum anti-dsDNA antibody titers and the proteinuria levels. It prevented inflammatory cell infiltrations into and the deposition of immunoglobulin G within the glomeruli. Bortezomib reduced the interferon-γ, interleukin (IL)-4, and IL-10 levels in the serum and the ribonucleic acid expression levels for these cytokines within the splenocytes. Bortezomib prevented type I collagen synthesis by downregulating TGF-β and AT1R expression in the glomeruli.

CONCLUSIONS

Bortezomib exerts multiple immunosuppressive effects and thus ameliorates LN. Furthermore, bortezomib can prevent glomerulosclerosis formation in NZB/W F1 mice through suppressive effects on the renin-angiotensin system.

Integration of Cistromic and Transcriptomic Analyses Identifies Nphs2, Mafb, and Magi2 as Wilms' Tumor 1 Target Genes in Podocyte Differentiation and Maintenance

The Wilms' tumor suppressor gene 1 (WT1) encodes a zinc finger transcription factor. Mutation of WT1 in humans leads to Wilms' tumor, a pediatric kidney tumor, or other kidney diseases, such as Denys-Drash and Frasier syndromes. We showed previously that inactivation of WT1 in podocytes of adult mice results in proteinuria, foot process effacement, and glomerulosclerosis. However, the WT1-dependent transcriptional network regulating podocyte development and maintenance in vivo remains unknown. Here, we performed chromatin immunoprecipitation followed by high-throughput sequencing with glomeruli from wild-type mice. Additionally, we performed a cDNA microarray screen on an inducible podocyte-specific WT1 knockout mouse model. By integration of cistromic and transcriptomic analyses, we identified the WT1 targetome in mature podocytes. To further analyze the function and targets of WT1 in podocyte maturation, we used an Nphs2-Cre model, in which WT1 is deleted during podocyte differentiation. These mice display anuria and kidney hemorrhage and die within 24 hours after birth. To address the evolutionary conservation of WT1 targets, we performed functional assays using zebrafish as a model and identified Nphs2, Mafb, and Magi2 as novel WT1 target genes required for podocyte development. Our data also show that both Mafb and Magi2 are required for normal development of the embryonic zebrafish kidney. Collectively, our work provides insights into the transcriptional networks controlled by WT1 and identifies novel WT1 target genes that mediate the function of WT1 in podocyte differentiation and maintenance.

Causes and pathogenesis of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) describes both a common lesion in progressive kidney disease, and a disease characterized by marked proteinuria and podocyte injury. The initial injuries vary widely. Monogenetic forms of FSGS are largely due to alterations in structural genes of the podocyte, many of which result in early onset of disease. Genetic risk alleles in apolipoprotein L1 are especially prevalent in African Americans, and are linked not only to adult-onset FSGS but also to progression of some other kidney diseases. The recurrence of FSGS in some transplant recipients whose end-stage renal disease was caused by FSGS points to circulating factors in disease pathogenesis, which remain incompletely understood. In addition, infection, drug use, and secondary maladaptive responses after loss of nephrons from any cause may also cause FSGS. Varying phenotypes of the sclerosis are also manifest, with varying prognosis. The so-called tip lesion has the best prognosis, whereas the collapsing type of FSGS has the worst prognosis. New insights into glomerular cell injury response and repair may pave the way for possible therapeutic strategies.