Disease relevance of NPHS2

• NPHS2 was recently identified as a gene whose mutations cause autosomal recessive steroid-resistant nephrotic syndrome [1].
• We sequenced NPHS2 promoter region from -628 to ATG in a large cohort of 260 nephrotic patients (161 with FSGS) who were presenting proteinuria from moderate to severe and were receiving or had received modular therapies according to their sensitivity to steroids and other immune modulators [2].
• Using a positional cloning approach, our group identified a gene, NPHS2, involved in a specific entity of familial SRNS characterized by early onset, complete steroid-resistance, rapid progression to ESRD and no recurrence after renal transplantation [3].
• Podocin (NPHS2) expression in podocytes is associated with variable degrees of proteinuria and progression to renal failure in different glomerular diseases that suggests different expression profiles in NPHS2 promoter [4].
• In conclusion, NPHS2 gene mutations are not a major cause of chronic renal insufficiency caused by sporadic SRNS or heavy proteinuria in Japanese children [5].

High impact information on NPHS2

• We found ten different NPHS2 mutations, comprising nonsense, frameshift and missense mutations, to segregate with the disease, demonstrating a crucial role for podocin in the function of the glomerular filtration barrier [6].
• NPHS2, encoding the glomerular protein podocin, is mutated in autosomal recessive steroid-resistant nephrotic syndrome [6].
• Using gel shift assays, we demonstrated that LMX1B bound to two AT-rich sequences in the promoter region of NPHS2, the gene encoding podocin [7].
• However, mRNA and protein levels for CD2AP and podocin were greatly reduced, suggesting a cooperative role for these molecules in foot process and slit diaphragm formation [8].
• We used in vitro-translated podocin and purified nephrin to investigate the effect of R229Q on their interaction and found decreased nephrin binding to the R229Q podocin [9].

Chemical compound and disease context of NPHS2

• Mutations of NPHS1 and NPHS2, which encode the slit diaphragm components nephrin and podocin, cause CNS and autosomal-recessive familial steroid-resistant nephrotic syndrome, respectively [10].
• The high NPHS2 promoter profile -116C/-51G haplotype was more frequent in patients with IgA nephropathy (P-value=0.005) and was associated with a better clinical outcome in terms of proteinuria and creatinine levels [4].
• Here, we show that brefeldin A induces accumulation of newly synthesized podocin in the endoplasmic reticulum, suggesting that podocin biosynthesis follows the classical secretory pathway, and we study the effect of 12 NPHS2 mutations associated with steroid-resistant nephrotic syndrome on the trafficking of the protein [11].

Biological context of NPHS2

• Genotype/phenotype correlations of NPHS1 and NPHS2 mutations in nephrotic syndrome advocate a functional inter-relationship in glomerular filtration [12].
• In conclusion, the 2.5-kb NPHS2 promoter fragment may be useful for podocyte-specific transgenic expression when extrarenal expression of a transgene is problematic [13].
• Twelve of twlve NPHS2 mouse founder lines expressed beta-gal exclusively in podocytes (100% penetrance) [13].
• Our findings reveal a novel role for the slit diaphragm proteins nephrin, CD2AP, and podocin and demonstrate that these three proteins, in addition to their structural functions, initiate PI3K/AKT-dependent signal transduction in glomerular podocytes [14].
• A causative gene, NPHS2, has been mapped to chromosome 1q25-q31 and was recently identified by positional cloning [15].

Anatomical context of NPHS2

• With the use of a conditionally immortalized human podocyte cell line, it first was shown that exposure to normal and non-nephrotic human plasma leads to a concentration of nephrin, podocin, CD2AP, and actin at the cell surface [16].
• Disease-causing missense mutations in NPHS2 gene alter normal nephrin trafficking to the plasma membrane [17].
• Our data suggest that most of NPHS2 mutations lead to retention of podocin in the endoplasmic reticulum and therefore provide a rationale for devising therapeutic approaches aimed at correcting the protein processing defect [11].
• Podocin is a stomatin protein family member with a predicted hairpin-like structure localizing to the insertion site of the slit diaphragm of podocytes, the visceral glomerular epithelial cells of the kidney [18].
• Co-localization of nephrin, podocin, and the actin cytoskeleton: evidence for a role in podocyte foot process formation [19].

Associations of NPHS2 with chemical compounds

• Molecular basis of the functional podocin-nephrin complex: mutations in the NPHS2 gene disrupt nephrin targeting to lipid raft microdomains [18].
• Mutations in both podocin gene (NPHS2) alleles lead to a wide range of human disease, from childhood-onset steroid-resistant FSGS and minimal change disease to adult-onset FSGS [20].
• None of 29 patients with homozygous or compound heterozygous mutations in NPHS2 who were treated with cyclosporine A or cyclophosphamide demonstrated complete remission of NS [21].
• Inaugural Article: Podocin and MEC-2 bind cholesterol to regulate the activity of associated ion channels [22].
• Photostimulated reactions of vinyl phosphate esters with triorganostannides. evidence for an SRN1 vinylic mechanism [23].

Regulatory relationships of NPHS2

• USF1 was identified as the transcriptional factor regulating NPHS2 at this site [2].

Other interactions of NPHS2

• In mutant kidneys, NPHS1 and NPHS2 were only moderately downregulated (25 to 30%) at birth but not at 2 or 4 months [24].
• We have excluded linkage with candidate regions for nephrin, CD2AP, WT1, and podocin in this sample [25].
• CONCLUSIONS: In this study, we exhaustively analyzed the NPHS2 and the exon 8 of the ACTN4 genes in a series of sporadic 'adult-onset' FSGS patients [26].
• Secondary changes in the distribution of nephrin, CD2AP, and alpha-actinin are additional evidences for the scaffolding role of podocin in the organization of the slit diaphragm [27].
• METHODS: Using renal biopsies of six patients, we analyzed the in vivo consequences of different types of NPHS2 mutations on (1) the podocyte expression and distribution of podocin using in situ hybridization and immunohistology and (2) the distribution of related podocyte proteins and glomerular extracellular matrix components [27].

Analytical, diagnostic and therapeutic context of NPHS2

• Our findings provide the first evidence for a functional inter-relationship between NPHS1 and NPHS2 in human nephrotic disease, thus underscoring their critical role in the regulation of glomerular filtration [12].
• The whole coding region, all intron/exon boundaries and flanking intronic regions of NPHS2 gene and the exon 8, i.e. hot-spot mutations of the ACTN4 gene, were analyzed in all patients by denaturing high-performance liquid chromatography (DHPLC) to search disease-causing defects [26].
• Heterozygous NPHS2 variants may play a role in atypical cases with mild, late-onset course, and recurrence after transplantation [28].
• Direct sequencing was performed after PCR amplification of all 29 and 8 exons of the NPHS1 and NPHS2 genes, respectively [29].
• Our insight into the association between NPHS2 variants and nephrotic disease is hampered by the limitations of the existing studies, including small numbers of affected individuals and suboptimal control groups [30].

References