Phenotypic quantification of Nphs1-deficient mice.

BACKGROUND: Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of chronic kidney disease in children and young adults. The most severe form of steroid-resistant nephrotic syndrome is congenital nephrotic syndrome Finnish type (CNSF), caused by biallelic loss-of-function variants in NPHS1, encoding nephrin. Since each of the 68 monogenic causes of steroid-resistant nephrotic syndrome represents a rare cause of the disease, tailoring therapeutic interventions to multiple molecular targets remains challenging, suggesting gene replacement therapy (GRT) as a viable alternative. To set the ground for a gene replacement study in vivo, we established rigorous, quantifiable, and reproducible phenotypic assessment of a conditional Nphs1 knockout mouse model. METHODS: By breeding a floxed Nphs1fl/- mouse (Nphs1tm1Afrn/J) previously studied for pancreatic ß-cell survival with a podocin promoter-driven Cre recombinase mouse model (Tg(NPHS2-Cre)295Lbh/J), we generated mice with podocyte-specific nephrin deficiency (Nphs1fl/fl NPHS2-Cre +). RESULTS: We observed a median survival to postnatal day P5 in nephrin-deficient mice, whereas heterozygous control mice and wild type (WT) control group showed 90% and 100% survival, respectively (at P50 days). Light microscopy analysis showed a significantly higher number of renal-tubular microcysts per kidney section in nephrin-deficient mice compared to the control groups (P < 0.0022). Transmission electron microscopy demonstrated reduced foot process (FP) density in nephrin-deficient mice compared to controls (P < 0.0001). Additionally, proteinuria quantitation using urine albumin-to-creatinine ratio (UACR) was significantly higher in nephrin-deficient mice compared to controls. CONCLUSIONS: This study represents the first comprehensive description of the kidney phenotype in a nephrin-deficient mouse model, laying the foundation for future gene replacement therapy endeavors.

Quantifiable and reproducible phenotypic assessment of a constitutive knockout mouse model for congenital nephrotic syndrome of the Finnish type.

Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of childhood chronic kidney disease. Congenital nephrotic syndrome of the Finnish type (CNF) (MIM# 256300) is caused by biallelic variants in the gene NPHS1, encoding nephrin, an integral component of the kidney filtration barrier. No causal treatments exist, and children inevitably require kidney replacement therapy. In preparation for gene replacement therapy (GRT) in CNF, we established a quantifiable and reproducible phenotypic assessment of the nephrin-deficient CNF mouse model: 129/Sv-Nphs1tm1Rkl/J. We assessed the phenotypic spectrum of homozygous mice (Nphs1tm1Rkl/Nphs1tm1Rkl) compared to heterozygous controls (Nphs1tm1Rkl/Nphs1WT) by the following parameters: 1. cohort survival, 2. podocyte foot process (FP) density per glomerular basement membrane (GBM) using transmission electron microscopy, 3. tubular microcysts in brightfield microscopy, and 4. urinary albumin/creatinine ratios. Nphs1tm1Rkl/Nphs1tm1Rkl mice exhibited: 1. perinatal lethality with median survival of 1 day, 2. FP effacement with median FP density of 1.00 FP/µm GBM (2.12 FP/µm in controls), 3. tubular dilation with 65 microcysts per section (6.5 in controls), and 4. increased albumin/creatinine ratio of 238 g/g (4.1 g/g in controls). We here established four quantifiable phenotyping features of a CNF mouse model to facilitate future GRT studies by enabling sensitive detection of phenotypic improvements.

Recessive variants in the intergenic NOS1AP-C1orf226 locus cause monogenic kidney disease responsive to anti-proteinuric treatment.

In genetic disease, an accurate expression landscape of disease genes and faithful animal models will enable precise genetic diagnoses and therapeutic discoveries, respectively. We previously discovered that variants in NOS1AP , encoding nitric oxide synthase 1 (NOS1) adaptor protein, cause monogenic nephrotic syndrome (NS). Here, we determined that an intergenic splice product of N OS1AP / Nos1ap and neighboring C1orf226/Gm7694 , which precludes NOS1 binding, is the predominant isoform in mammalian kidney transcriptional and proteomic data. Gm7694 -/- mice, whose allele exclusively disrupts the intergenic product, developed NS phenotypes. In two human NS subjects, we identified causative NOS1AP splice variants, including one predicted to abrogate intergenic splicing but initially misclassified as benign based on the canonical transcript. Finally, by modifying genetic background, we generated a faithful mouse model of NOS1AP -associated NS, which responded to anti-proteinuric treatment. This study highlights the importance of intergenic splicing and a potential treatment avenue in a mendelian disorder.

Quantitative phenotyping of Nphs1 knockout mice as a prerequisite for gene replacement studies.

Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of chronic kidney disease before the age of 25 yr. Nephrin, encoded by NPHS1, localizes to the slit diaphragm of glomerular podocytes and is the predominant structural component of the glomerular filtration barrier. Biallelic variants in NPHS1 can cause congenital nephrotic syndrome of the Finnish type, for which, to date, no causative therapy is available. Recently, adeno-associated virus (AAV) vectors targeting the glomerular podocyte have been assessed as a means for gene replacement therapy. Here, we established quantitative and reproducible phenotyping of a published, conditional Nphs1 knockout mouse model (Nphs1tm1.1Pgarg/J and Nphs2-Cre+) in preparation for a gene replacement study using AAV vectors. Nphs1 knockout mice (Nphs1fl/fl Nphs2-Cre+) exhibited 1) a median survival rate of 18 days (range: from 9 to 43 days; males: 16.5 days and females: 20 days); 2) an average foot process (FP) density of 1.0 FP/µm compared with 2.0 FP/µm in controls and a mean filtration slit density of 2.64 µm/µm2 compared with 4.36 µm/µm2 in controls; 3) a high number of proximal tubular microcysts; 4) the development of proteinuria within the first week of life as evidenced by urine albumin-to-creatinine ratios; and 5) significantly reduced levels of serum albumin and elevated blood urea nitrogen and creatinine levels. For none of these phenotypes, significant differences between sexes in Nphs1 knockout mice were observed. We quantitatively characterized five different phenotypic features of congenital nephrotic syndrome in Nphs1fl/fl Nphs2-Cre+ mice. Our results will facilitate future gene replacement therapy projects by allowing for sensitive detection of even subtle molecular effects.NEW & NOTEWORTHY To evaluate potential, even subtle molecular, therapeutic effects of gene replacement therapy (GRT) in a mouse model, prior rigorous quantifiable and reproducible disease phenotyping is necessary. Here, we, therefore, describe such a phenotyping effort in nephrin (Nphs1) knockout mice to establish the basis for GRT for congenital nephrotic syndrome. We believe that our findings set an important basis for upcoming/ongoing gene therapy approaches in the field of nephrology, especially for monogenic nephrotic syndrome.

The differential roles of contralesional frontoparietal areas in cortical reorganization after stroke.

BACKGROUND: Studies examining the contribution of contralesional brain regions to motor recovery after stroke have revealed conflicting results comprising both supporting and disturbing influences. Especially the relevance of contralesional brain regions beyond primary motor cortex (M1) has rarely been studied, particularly concerning the temporal dynamics post-stroke. METHODS: We, therefore, used online transcranial magnetic stimulation (TMS) interference to longitudinally assess the role of contralesional (right) frontoparietal areas for recovery of hand motor function after left hemispheric stroke: contralesional M1, contralesional dorsal premotor cortex (dPMC), and contralesional anterior intraparietal sulcus (IPS). Fourteen stroke patients and sixteen age-matched healthy subjects performed motor tasks of varying complexity with their (paretic) right hand. Motor performance was quantified using three-dimensional kinematic data. All patients were assessed twice, (i) in the first week, and (ii) after more than three months post-stroke. RESULTS: While we did not observe a significant effect of TMS interference on movement kinematics following the stimulation of contralesional M1 and dPMC in the first week post-stroke, we found improvements of motor performance upon interference with contralesional IPS across motor tasks early after stroke, an effect that persisted into the later phase. By contrast, for dPMC, TMS-induced deterioration of motor performance was only evident three months post-stroke, suggesting that a supportive role of contralesional premotor cortex might evolve with reorganization. CONCLUSION: We here highlight time-sensitive and region-specific effects of contralesional frontoparietal areas after left hemisphere stroke, which may influence on neuromodulation regimes aiming at supporting recovery of motor function post-stroke.

Age affects the contribution of ipsilateral brain regions to movement kinematics.

Healthy aging is accompanied by changes in brain activation patterns in the motor system. In older subjects, unilateral hand movements typically rely on increased recruitment of ipsilateral frontoparietal areas. While the two central concepts of aging-related brain activity changes, "Hemispheric Asymmetry Reduction in Older Adults" (HAROLD), and "Posterior to Anterior Shift in Aging" (PASA), have initially been suggested in the context of cognitive tasks and were attributed to compensation, current knowledge regarding the functional significance of increased motor system activity remains scarce. We, therefore, used online interference transcranial magnetic stimulation in young and older subjects to investigate the role of key regions of the ipsilateral frontoparietal cortex, that is, (a) primary motor cortex (M1), (b) dorsal premotor cortex (dPMC), and (c) anterior intraparietal sulcus (IPS) in the control of hand movements of different motor demands. Our data suggest a change of the functional roles of ipsilateral brain areas in healthy age with a reduced relevance of ipsilateral M1 and a shift of importance toward dPMC for repetitive high-frequency movements. These results support the notion that mechanisms conceptualized in the models of "PASA" and "HAROLD" also apply to the motor system.