Functional validation of tensin2 SH2-PTB domain by CRISPR/Cas9-mediated genome editing

Automated scoring of glomerular injury in TNS2-deficient nephropathy

Several artificial intelligence (AI) systems have been developed for glomerular pathology analysis in clinical settings. However, the application of AI systems in nonclinical fields remains limited. In this study, we trained a convolutional neural network model, which is an AI algorithm, to classify the severity of Tensin 2 (TNS2)-deficient nephropathy into seven categories. A dataset consisting of 803 glomerular images was generated from kidney sections of TNS2-deficient and wild-type mice. Manual evaluations of the images were conducted to assess their glomerular injury scores. The trained AI achieved approximately 70% accuracy in predicting the glomerular injury score for TNS2-deficient nephropathy. However, the AI achieved approximately 100% accuracy when considering predictions within one score of the true label as correct. The AI's predicted mean score closely matched the true mean score. In conclusion, while the AI model may not replace human judgment entirely, it can serve as a reliable second assessor in scoring glomerular injury, offering potential benefits in enhancing the accuracy and objectivity of such assessments.

Tensins in Kidney Function and Diseases

Tensins are focal adhesion proteins that regulate various biological processes, such as mechanical sensing, cell adhesion, migration, invasion, and proliferation, through their multiple binding activities that transduce critical signals across the plasma membrane. When these molecular interactions and/or mediated signaling are disrupted, cellular activities and tissue functions are compromised, leading to disease development. Here, we focus on the significance of the tensin family in renal function and diseases. The expression pattern of each tensin in the kidney, their roles in chronic kidney diseases, renal cell carcinoma, and their potentials as prognostic markers and/or therapeutic targets are discussed in this review.

Tensin 2-deficient nephropathy - mechanosensitive nephropathy, genetic susceptibility

Tensin 2 (TNS2), a focal adhesion protein, is considered to anchor focal adhesion proteins to β integrin as an integrin adaptor protein and/or serve as a scaffold to facilitate the interactions of these proteins. In the kidney, TNS2 localizes to the basolateral surface of glomerular epithelial cells, i.e., podocytes. Loss of TNS2 leads to the development of glomerular basement membrane lesions and abnormal accumulation of extracellular matrix in maturing glomeruli during the early postnatal stages. It subsequently results in podocyte foot process effacement, eventually leading to glomerulosclerosis. Histopathological features of the affected glomeruli in the middle stage of the disease include expansion of the mesangial matrix without mesangial cell proliferation. In this review, we provide an overview of TNS2-deficient nephropathy and discuss the potential mechanism underlying this mechanosensitive nephropathy, which may be applicable to other glomerulonephropathies, such as CD151-deficient nephropathy and Alport syndrome. The onset of TNS2-deficient nephropathy strictly depends on the genetic background, indicating the presence of critical modifier genes. A better understanding of molecular mechanisms of mechanosensitive nephropathy may open new avenues for the management of patients with glomerulonephropathies.

Tensins - emerging insights into their domain functions, biological roles and disease relevance

Tensins are a family of focal adhesion proteins consisting of four members in mammals (TNS1, TNS2, TNS3 and TNS4). Their multiple domains and activities contribute to the molecular linkage between the extracellular matrix and cytoskeletal networks, as well as mediating signal transduction pathways, leading to a variety of physiological processes, including cell proliferation, attachment, migration and mechanical sensing in a cell. Tensins are required for maintaining normal tissue structures and functions, especially in the kidney and heart, as well as in muscle regeneration, in animals. This Review discusses our current understanding of the domain functions and biological roles of tensins in cells and mice, as well as highlighting their relevance to human diseases.

Lycopene attenuates high glucose-mediated apoptosis in MPC5 podocytes by promoting autophagy via the PI3K/AKT signaling pathway

Podocyte injury serves an important role during the progression of diabetic nephropathy (DN), and lycopene (Lyc) may display a potential protective effect against DN progression. The effects of Lyc on high glucose (HG)-induced podocyte apoptosis and the underlying mechanisms are not completely understood; therefore, the present study aimed to investigate the effects of Lyc on HG-induced MPC5 podocyte apoptosis and the underlying mechanism. In the present study, MPC5 podocytes were exposed to HG and different doses of Lyc. MPC5 podocyte viability and apoptosis were assessed by performing the MTT assay and flow cytometry, respectively. To explore the effects of Lyc on the PI3K/AKT signaling pathway and autophagy, LY294002 (LY) and 3-methyladenine (3-MA) were used as PI3K and autophagy inhibitors, respectively. The expression levels of nephrin, podocin, apoptosis-related proteins (Bax, Bcl-2 and cleaved caspase-3), autophagy-related proteins [Beclin-1 and microtubule associated protein 1 light chain 3 (LC3)II/LC3I] and certain key proteins involved in the PI3K/AKT signaling pathway were measured via western blotting. The results suggested that Lyc reversed the inhibitory effect of HG on cell viability, and the protein expression levels of nephrin and podocin, as well as the promoting effect of HG on MPC5 podocyte apoptosis. In addition, under HG conditions, Lyc upregulated the phosphorylation levels of PI3K and AKT, and reduced HG- and LY-mediated MPC5 podocyte apoptosis. Moreover, Lyc further increased HG-induced protein expression levels of Beclin-1 and LC3II/LC3I, and attenuated LY-mediated inhibition of HG-induced MPC5 podocyte autophagy. In addition, the effects of Lyc on HG-mediated MPC5 podocyte apoptosis were alleviated by 3-MA. Therefore, the present study suggested that Lyc may protect against HG-induced MPC5 podocyte apoptosis by promoting autophagy activity via activation of the PI3K/AKT signaling pathway.

New Role for Growth/Differentiation Factor 15 in the Survival of Transplanted Brown Adipose Tissues in Cooperation with Interleukin-6

To identify factors involved in the earliest phase of the differentiation of human embryonic stem cells (hESCs) into brown adipocytes (BAs), we performed multi-time point microarray analyses. We found that growth/differentiation factor 15 (GDF15) expressions were specifically upregulated within three days of differentiation, when expressions of immature hESC markers were sustained. Although GDF15 expressions continued to increase in the subsequent differentiation phases, GDF15-deficient hESCs differentiated into mature BAs (Day 10) without apparent abnormalities. In addition, GDF15-deficient mice had normal brown adipose tissue (BAT) and were metabolically healthy. Unexpectedly, we found that interleukin-6 (IL6) expression was significantly lowered in the BAT of GDF15^-/- mice. In addition, GDF15^-/- hESCs showed abortive IL6 expressions in the later phase (>Day 6) of the differentiation. Interestingly, GDF15 expression was markedly repressed throughout the whole course of the differentiation of IL6^-/- hESCs into BAs, indicating IL6 is essential for the induction of GDF15 in the differentiation of hESCs. Finally, intraperitoneally transplanted BAT grafts of GDF15^-/- donor mice, but not those of wild-type (WT) mice, failed in the long-term survival (12 weeks) in GDF15^-/- recipient mice. Collectively, GDF15 is required for long-term survival of BAT grafts by creating a mutual gene induction loop with IL6.

Deletion of the Tensin2 SH2-PTB domain, but not the loss of its PTPase activity, induces podocyte injury in FVB/N mouse strain

Tensin2 (TNS2) is a focal adhesion-localized protein possessing N-terminal tandem protein tyrosine phosphatase (PTPase) and C2 domains, and C-terminal tandem Src homology 2 (SH2) and phosphotyrosine binding (PTB) domains. Genetic deletion of Tns2 in a susceptible murine strain leads to podocyte alterations after birth. To clarify the domain contributions to podocyte maintenance, we generated two Tns2-mutant mice with the genetic background of the susceptible FVB/NJ strain, Tns2^∆C and Tns2^CS mice, carrying a SH2-PTB domain deletion and a PTPase domain inactivation, respectively. The Tns2^∆C mice developed massive albuminuria, severe glomerular injury and podocyte alterations similarly to those in Tns2-deficient mice. In contrast, the Tns2^CS mice showed no obvious phenotypic abnormalities. These results indicate that the TNS2 SH2-PTB domain, but not its PTPase activity, plays a role in podocyte maintenance. Furthermore, in a podocyte cell line, the truncated TNS2 mutant lacking the SH2-PTB domain lost the ability to localize to focal adhesion. Taken together, these data suggest that TNS2 recruitment to focal adhesion is required to maintain postnatal podocytes on a susceptible genetic background.

Novel murine model of congenital diabetes: The insulin hyposecretion mouse

AIMS/INTRODUCTION

Diabetic animal models have made an enormous contribution to our understanding of the etiology of diabetes and the development of new medications. The aim of the present study was to develop and characterize a novel, non-obese murine strain with spontaneous diabetes - the insulin hyposecretion (ihs) mouse.

MATERIALS AND METHODS

During the development of the ICGN.B6-Tns2WT strain as the control for the ICGN-Tns2nph congenital nephrotic strain, diabetic mice were discovered and named ihs mice. Intraperitoneal insulin tolerance test, oral glucose tolerance test and an insulin secretion experiment by the pancreas perfusion system were carried out on ihs mice. The pancreatic islets were examined histologically, and the mRNA expression of pancreatic β-cell-specific genes or genes associated with monogenic diabetes was examined by RT-qPCR.

RESULTS

The ihs mice showed several distinctive diabetes-related characteristics: (i) the onset of diabetes was observed only in the male mice; (ii) there were no differences in insulin content between the ihs and control mice; (iii) impaired insulin secretion was elicited by glucose, potassium chloride and sulfonylureas; (iv) there was a significant reduction of relative β-cell volume with no signs of inflammation or fibrosis; (v) they showed a normal glycemic response to exogenous insulin; and (vi) the mice were not obese.

CONCLUSIONS

The ihs mouse provides a novel murine model of congenital diabetes that shows insulin secretion failure. This model allows not only an analysis of the progression of diabetes, but also the identification of unknown genes involved in insulin secretion.

Genetics of Childhood Steroid Sensitive Nephrotic Syndrome: An Update

Advances in genome science in the last 20 years have led to the discovery of over 50 single gene causes and genetic risk loci for steroid resistant nephrotic syndrome (SRNS). Despite these advances, the genetic architecture of childhood steroid sensitive nephrotic syndrome (SSNS) remains poorly understood due in large part to the varying clinical course of SSNS over time. Recent exome and genome wide association studies from well-defined cohorts of children with SSNS identified variants in multiple MHC class II molecules such as HLA-DQA1 and HLA-DQB1 as risk factors for SSNS, thus stressing the central role of adaptive immunity in the pathogenesis of SSNS. However, evidence suggests that unknown second hit risk loci outside of the MHC locus and environmental factors also make significant contributions to disease. In this review, we examine what is currently known about the genetics of SSNS, the implications of recent findings on our understanding of pathogenesis of SSNS, and how we can utilize these results and findings from future studies to improve the management of children with nephrotic syndrome.

Precision gene editing technology and applications in nephrology

The expanding field of precision gene editing is empowering researchers to directly modify DNA. Gene editing is made possible using synonymous technologies: a DNA-binding platform to molecularly locate user-selected genomic sequences and an associated biochemical activity that serves as a functional editor. The advent of accessible DNA-targeting molecular systems, such as zinc-finger nucleases, transcription activator-like effectors (TALEs) and CRISPR-Cas9 gene editing systems, has unlocked the ability to target nearly any DNA sequence with nucleotide-level precision. Progress has also been made in harnessing endogenous DNA repair machineries, such as non-homologous end joining, homology-directed repair and microhomology-mediated end joining, to functionally manipulate genetic sequences. As understanding of how DNA damage results in deletions, insertions and modifications increases, the genome becomes more predictably mutable. DNA-binding platforms such as TALEs and CRISPR can also be used to make locus-specific epigenetic changes and to transcriptionally enhance or suppress genes. Although many challenges remain, the application of precision gene editing technology in the field of nephrology has enabled the generation of new animal models of disease as well as advances in the development of novel therapeutic approaches such as gene therapy and xenotransplantation.

Genetic loci for resistance to podocyte injury caused by the tensin2 gene deficiency in mice

Background

Tensin2 is a focal adhesion-localized multidomain protein expressed in various tissues, and its dysfunction leads to alterations in podocytes. However, these podocyte-related manifestations are dependent on murine strain. Tensin2 dysfunction results in susceptible strains developing podocyte foot process effacement and massive albuminuria, whereas podocytes in resistant strains remain almost intact. In our previous studies, quantitative trait loci analysis and congenic analysis using resistant C57BL/6J and susceptible ICGN mice identified a modifier locus associated with podocyte injury caused by tensin2 dysfunction on chromosome 2. However, the effect of this modifier locus on chromosome 2 is insufficient to explain the resistance of C57BL/6J mice to tensin2 dysfunction, indicating the existence of other modifier genes.

Results

Whereas previous studies focused on the severity of chronic kidney disease, the present study focused on podocyte injury. We performed a genome-wide linkage analysis of backcrosses between two tensin2-deficient mouse strains, B6.ICGN-Tns2^nph and FVB.ICGN-Tns2^nph, and detected a novel major modifier locus on chromosome 10. The combined effect of the C57BL/6J alleles of the two loci on chromosomes 2 and 10 reduced the urinary albumin excretion caused by tensin2 dysfunction to a level comparable to that of C57BL/6J mice.

Conclusions

These data indicate that the resistance to podocyte injury caused by tensin2 dysfunction is mainly produced by the effects of the modifier genes on the two loci. The identification of these modifier genes is expected to help elucidate the mechanism underlying podocyte injury.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0611-1) contains supplementary material, which is available to authorized users.

C1-Ten is a PTPase of nephrin, regulating podocyte hypertrophy through mTORC1 activation

Hypertrophy is a prominent feature of damaged podocytes in diabetic kidney disease (DKD). mTORC1 hyperactivation leads to podocyte hypertrophy, but the detailed mechanism of how mTORC1 activation occurs under pathological conditions is not completely known. Moreover, reduced nephrin tyrosine phosphorylation has been observed in podocytes under pathological conditions, but the molecular mechanism linking nephrin phosphorylation and pathology is unclear so far. In this study, we observed a significant increase in C1-Ten level in diabetic kidney and in high glucose-induced damaged podocytes. C1-Ten acts as a protein tyrosine phosphatase (PTPase) at the nephrin-PI3K binding site and renders PI3K for IRS-1, thereby activating mTORC1. Furthermore, C1-Ten causes podocyte hypertrophy and proteinuria by increasing mTORC1 activity in vitro and in vivo. These findings demonstrate the relationship between nephrin dephosphorylation and the mTORC1 pathway, mediated by C1-Ten PTPase activity. We suggest that C1-Ten contributes to the pathogenesis of DKD by inducing podocyte hypertrophy under high glucose conditions.

Novel Blood Pressure Locus and Gene Discovery Using Genome-Wide Association Study and Expression Data Sets From Blood and the Kidney

Elevated blood pressure is a major risk factor for cardiovascular disease and has a substantial genetic contribution. Genetic variation influencing blood pressure has the potential to identify new pharmacological targets for the treatment of hypertension. To discover additional novel blood pressure loci, we used 1000 Genomes Project-based imputation in 150 134 European ancestry individuals and sought significant evidence for independent replication in a further 228 245 individuals. We report 6 new signals of association in or near HSPB7, TNXB, LRP12, LOC283335, SEPT9, and AKT2, and provide new replication evidence for a further 2 signals in EBF2 and NFKBIA. Combining large whole-blood gene expression resources totaling 12 607 individuals, we investigated all novel and previously reported signals and identified 48 genes with evidence for involvement in blood pressure regulation that are significant in multiple resources. Three novel kidney-specific signals were also detected. These robustly implicated genes may provide new leads for therapeutic innovation.

CRISPR/Cas9 targeting events cause complex deletions and insertions at 17 sites in the mouse genome

Although CRISPR/Cas9 genome editing has provided numerous opportunities to interrogate the functional significance of any given genomic site, there is a paucity of data on the extent of molecular scars inflicted on the mouse genome. Here we interrogate the molecular consequences of CRISPR/Cas9-mediated deletions at 17 sites in four loci of the mouse genome. We sequence targeted sites in 632 founder mice and analyse 54 established lines. While the median deletion size using single sgRNAs is 9 bp, we also obtain large deletions of up to 600 bp. Furthermore, we show unreported asymmetric deletions and large insertions of middle repetitive sequences. Simultaneous targeting of distant loci results in the removal of the intervening sequences. Reliable deletion of juxtaposed sites is only achieved through two-step targeting. Our findings also demonstrate that an extended analysis of F1 genotypes is required to obtain conclusive information on the exact molecular consequences of targeting events.