Pekka Ihalmo

University of Helsinki, Helsinki, Southern Finland Province, Finland

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Publications (10)42.62 Total impact

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    ABSTRACT: CD2-associated protein (CD2AP) is essential for podocyte function. CD2AP mutations have been found in patients with focal segmental glomerulosclerosis, a disease histologically resembling diabetic nephropathy and often progressing to end-stage renal disease (ESRD). We hypothesised that variations in the CD2AP gene may contribute to susceptibility to glomerular injury in diabetes and investigated if single-nucleotide polymorphisms (SNPs) in CD2AP are associated with diabetic nephropathy in patients with type 1 diabetes. The discovery cohort consisted of 2,251 Finnish patients with type 1 diabetes. SNPs were selected from the HapMap database to cover the CD2AP gene. The associations between genotyped SNPs and diabetic nephropathy or ESRD were analysed with the chi-squared test and logistic regression. Three SNPs were selected for replication in cohorts from Denmark, Italy, the United Kingdom and Ireland. None of the 15 successfully genotyped SNPs were associated with diabetic nephropathy when compared to patients with normal albumin excretion rate. However, when genotype frequencies in patients with ESRD were compared with all other patients, two CD2AP SNPs, rs9369717 and rs9349417, were found to be associated with ESRD. The meta-analysis of the original and two additional European cohorts resulted in significant p values <0.01 for these SNPs. A third SNP, rs6936632, was suggestively associated with ESRD in the Finnish patients and in the meta-analysis of four cohorts. CD2AP gene variants may contribute to susceptibility to ESRD in patients with type 1 diabetes.
    Acta Diabetologica 05/2013; · 4.63 Impact Factor
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    ABSTRACT: Aims  To investigate if the INPPL1 (inositol polyphosphate phosphatase-like 1) gene is associated with metabolic syndrome and insulin resistance in Finnish people with Type 1 diabetes. Methods  Participants were selected from the FinnDiane study for this cross-sectional study. The individuals were divided into controls without the metabolic syndrome (n = 1074) and cases with the metabolic syndrome (n = 1328), or into groups based upon their albumin excretion rate. Nine single-nucleotide polymorphisms covering the INPPL1 gene +/- 20 kb were genotyped. The associations between the single-nucleotide polymorphisms and outcome variables were analysed with the χ(2) test and logistic regression. Results  Two INPPL1 single-nucleotide polymorphisms, rs2276048 (silent mutation) and rs2276047 (intronic), were associated with the metabolic syndrome in men with odds ratios of 0.23 (95% CI 0.11-0.45, P = 2.1 × 10(-5) ), and 0.37 (0.21-0.65, P = 0.001), adjusted for age, duration of diabetes and history of smoking. When both sexes were included, these associations were less significant. No association between the genotyped single-nucleotide polymorphisms and diabetic nephropathy was observed. Conclusions  INPPL1 gene variants may contribute to susceptibility to the metabolic syndrome in men with Type 1 diabetes, but not to diabetic nephropathy. © 2012 The Authors. Diabetic Medicine © 2012 Diabetes UK.
    Diabetic Medicine 04/2012; · 3.24 Impact Factor
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    ABSTRACT: Although metabolic derangement plays a central role in diabetic nephropathy, a better understanding of secondary mediators of injury may lead to new therapeutic strategies. Expression of macrophage migration inhibitory factor (MIF) is increased in experimental diabetic nephropathy, and increased tubulointerstitial mRNA expression of its receptor, CD74, has been observed in human diabetic nephropathy. Whether CD74 transduces MIF signals in podocytes, however, is unknown. Here, we found glomerular and tubulointerstitial CD74 mRNA expression to be increased in Pima Indians with type 2 diabetes and diabetic nephropathy. Immunohistochemistry confirmed the increased glomerular and tubular expression of CD74 in clinical and experimental diabetic nephropathy and localized glomerular CD74 to podocytes. In cultured human podocytes, CD74 was expressed at the cell surface, was upregulated by high concentrations of glucose and TNF-alpha, and was activated by MIF, leading to phosphorylation of extracellular signal-regulated kinase 1/2 and p38. High glucose also induced CD74 expression in a human proximal tubule cell line (HK2). In addition, MIF induced the expression of the inflammatory mediators TRAIL and monocyte chemoattractant protein 1 in podocytes and HK2 cells in a p38-dependent manner. These data suggest that CD74 acts as a receptor for MIF in podocytes and may play a role in the pathogenesis of diabetic nephropathy.
    Journal of the American Society of Nephrology 11/2008; 20(2):353-62. · 8.99 Impact Factor
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    ABSTRACT: Oxysterol-binding protein (OSBP)-related protein 3 (ORP3) is highly expressed in epithelial, neuronal and hematopoietic cells, as well as in certain forms of cancer. We assessed the function of ORP3 in HEK293 cells and in human macrophages. We show that ORP3 interacts with R-Ras, a small GTPase regulating cell adhesion, spreading and migration. Gene silencing of ORP3 in HEK293 cells results in altered organization of the actin cytoskeleton, impaired cell-cell adhesion, enhanced cell spreading and an increase of beta1 integrin activity--effects similar to those of constitutively active R-Ras(38V). Overexpression of ORP3 leads to formation of polarized cell-surface protrusions, impaired cell spreading and decreased beta1 integrin activity. In primary macrophages, overexpression of ORP3 leads to the disappearance of podosomal structures and decreased phagocytotic uptake of latex beads, consistent with a role in actin regulation. ORP3 is phosphorylated when cells lose adhesive contacts, suggesting that it is subject to regulation by outside-in signals mediated by adhesion receptors. The present findings demonstrate a new function of ORP3 as part of the machinery that controls the actin cytoskeleton, cell polarity and cell adhesion.
    Journal of Cell Science 04/2008; 121(Pt 5):695-705. · 5.88 Impact Factor
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    ABSTRACT: The slit diaphragm is an adhesion and signalling protein complex linking the interdigitating podocyte foot processes in the kidney glomerulus, and mutations in slit diaphragm-associated genes result in severe proteinuria. Here we report a genetic association analysis of four slit diaphragm genes, LRRC7, KIRREL, NPHS2 and ACTN4, in a Finnish diabetic nephropathy cohort. A total of 40 single nucleotide polymorphisms (SNPs) were genotyped in 1103 patients with type 1 diabetes. The patients were classified according to their renal status, and the genotype data were analysed in a cross-sectional case-control setting. To confirm positive associations, four SNPs were genotyped in 1,025 additional patients with type 1 diabetes. No associations with diabetic nephropathy were observed for any of the analysed SNPs. The SNPs were not associated with the time from the onset of diabetes to the diagnosis of nephropathy or with glomerular filtration rate or AER as quantitative variables. In a sex-specific sub-analysis, the variants rs979972 and rs749701 in the first intron of ACTN4 were nominally associated with diabetic nephropathy in females, with odds ratios of 1.81 (95% CI 1.18-2.79, p = 0.007) and 1.93 (95% CI 1.26-2.96, p = 0.003) respectively. Our study has not found any evidence that common variants in LRRC7, KIRREL, NPHS2 and ACTN4 contribute to susceptibility to diabetic nephropathy in Finnish patients with type 1 diabetes.
    Diabetologia 02/2008; 51(1):86-90. · 6.49 Impact Factor
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    ABSTRACT: Filtrin (NEPH3/KIRREL2) is a recently characterized member of the nephrin-like proteins of the immunoglobulin superfamily, and it has been suggested to participate in the maintenance of the glomerular filtration barrier in the kidney. In this study, the gene and protein expression of filtrin were examined in patients with acquired proteinuric diseases. Filtrin mRNA levels in renal biopsies were measured with quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in two sets of patients with proteinuria. The mRNA levels were normalized to the housekeeping gene GAPDH and also related to the podocyte-specific genes nephrin and podocin. Immunofluorescence microscopy was employed to explore changes in the glomerular distribution of filtrin. Reduced glomerular expression of filtrin mRNA was observed in all studied diagnostic groups. In focal segmental glomerulosclerosis, the filtrin mRNA level was only one-tenth of the control samples (P approximately 5.0x10(-6)), and this finding was confirmed in a second set of samples. The ratios of filtrin to nephrin and podocin demonstrated a marked decrease in the expression of filtrin relative to the podocyte marker genes. However, no correlation between the expression of filtrin and the levels of serum creatinine and proteinuria was observed. Immunostaining showed changes in the expression pattern of filtrin in renal biopsies. Immunoelectron microscopic studies localized filtrin at the slit diaphragm of the podocyte foot processes. Down-regulation of the filtrin gene and protein expression in the renal biopsies together with the localization to the inter-podocyte filtration slit imply a potential role for this molecule in the pathogenesis of proteinuric diseases.
    Nephrology Dialysis Transplantation 08/2007; 22(7):1903-9. · 3.37 Impact Factor
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    ABSTRACT: For more than three decades, the molecular composition of the interpodocyte slit diaphragm of the glomerular filtration barrier has remained elusive. The first electron microscopic studies described the slit diaphragm as a porous, 'zipper-like' structure, but it was not until 1998 that the first transmembrane molecule of the slit diaphragm was identified: nephrin is a cell surface receptor of the immunoglobulin superfamily participating in cell-cell adhesion and signaling functions. Mutations in nephrin lead to the congenital nephrotic syndrome of the Finnish type, suggesting that nephrin is of pivotal importance for maintaining the filtration barrier. In recent years, the mapping of the genetic background of other inherited and acquired nephropathies and generation of transgenic animal models have led to a beginning of a new era in nephrology, possibly promising new targeted therapies and advanced diagnostics. This review article will briefly summarize the main findings that explain the molecular architecture of the glomerular filter itself and causes of some glomerular diseases that lead to proteinuria and, eventually, to renal failure.
    Annals of Medicine 02/2006; 38(7):483-92. · 4.73 Impact Factor
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    ABSTRACT: Mutations of NPHS1, the gene encoding the kidney glomerular filtration barrier protein nephrin, cause congenital nephrotic syndrome of the Finnish type. Nephrin is a component of the interpodocyte-spanning slit diaphragm: it mediates outside-in signaling and forms a nexus for homo- and heterotypic molecular interactions. When studying the nephrin-deficient mouse line generated by random insertional mutagenesis we unexpectedly discovered an endogenous antisense transcript originating from the nephrin-encoding locus. Further evidence of the antisense transcript (Nphs1as) was obtained by searching for Nphs1-like expressed sequence tags. Surprisingly, one clone showed exact complementarity in the antisense orientation. Nphs1as is expressed in the brain, thymus, and peripheral lymph nodes as well as in the embryonic stem cells. However, the mesenteric lymph nodes and the main sites of nephrin expression, the kidney and pancreas, were negative. Nphs1as is a continuous, polyadenylated mRNA that spans Nphs1 exons from 7 to 12 in the reverse orientation. The relative amounts of sense and antisense mRNAs as well as nephrin protein were determined by semiquantitative RT-PCR and immunoblotting, respectively, in various mouse tissues. These results suggest that Nphs1as may be important for the regulation of the appropriate tissue- and cell-type-specific expression of nephrin.
    Genomics 07/2004; 83(6):1134-40. · 3.01 Impact Factor
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    ABSTRACT: NPHS1 encodes nephrin, the core protein of the interpodocyte slit diaphragm of the kidney glomerulus. NPHS1 is the causative gene for congenital nephrotic syndrome of the Finnish type (CNF) with massive, treatment resistant proteinuria. We report here the establishment of a novel nephrin-like gene, NLG1 encoding filtrin, a protein with substantial homology to human nephrin. Filtrin is a type I transmembrane protein consisting of 708 amino acids. Together with the recently cloned NEPH1, NLG1 establishes a new nephrin-like subgroup of genes belonging to the immunoglobulin superfamily of cell adhesion molecules. The RNA dot blot experiment revealed that the NLG1 mRNA expression is widely distributed but most prominently observed in the pancreas and lymph nodes. The expression of NLG1 mRNA in kidney glomeruli was verified with RT-PCR. Further immunoblotting studies with antifiltrin antibody showed a specific band at 107kDa in the human and rat glomeruli. In immunofluorescence microscopy specific staining of glomeruli but also proximal and distal parts of the nephron was seen in human kidney cortex. Due to its structural similarity and sequence homology as well as partially consistent expression pattern with nephrin we propose that filtrin belongs to a functionally important complex of proteins of the glomerular filtration barrier.
    Biochemical and Biophysical Research Communications 02/2003; 300(2):364-70. · 2.28 Impact Factor
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    Pekka Ihalmo
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    ABSTRACT: The glomerular epithelial cells and their intercellular junctions, termed slit diaphragms, are essential components of the filtration barrier in the kidney glomerulus. Nephrin is a transmembrane adhesion protein of the slit diaphragm and a signalling molecule regulating podocyte physiology. In congenital nephrotic syndrome of the Finnish type, mutation of nephrin leads to disruption of the permeability barrier and leakage of plasma proteins into the urine. This doctoral thesis hypothesises that novel nephrin-associated molecules are involved in the function of the filtration barrier in health and disease. Bioinformatics tools were utilized to identify novel nephrin-like molecules in genomic databases, and their distribution in the kidney and other tissues was investigated. Filtrin, a novel nephrin homologue, is expressed in the glomerular podocytes and, according to immunoelectron microscopy, localizes at the slit diaphragm. Interestingly, the nephrin and filtrin genes, NPHS1 and KIRREL2, locate in a head-to-head orientation on chromosome 19q13.12. Another nephrin-like molecule, Nphs1as was cloned in mouse, however, no expression was detected in the kidney but instead in the brain and lymphoid tissue. Notably, Nphs1as is transcribed from the nephrin locus in an antisense orientation. The glomerular mRNA and protein levels of filtrin were measured in kidney biopsies of patients with proteinuric diseases, and marked reduction of filtrin mRNA levels was detected in the proteinuric samples as compared to controls. In addition, altered distribution of filtrin in injured glomeruli was observed, with the most prominent decrease of the expression in focal segmental glomerulosclerosis. The role of the slit diaphragm-associated genes for the development of diabetic nephropathy was investigated by analysing single nucleotide polymorphisms. The genes encoding filtrin, densin-180, NEPH1, podocin, and alpha-actinin-4 were analysed, and polymorphisms at the alpha-actinin-4 gene were associated with diabetic nephropathy in a gender-dependent manner. Filtrin is a novel podocyte-expressed protein with localization at the slit diaphragm, and the downregulation of filtrin seems to be characteristic for human proteinuric diseases. In the context of the crucial role of nephrin for the glomerular filter, filtrin appears to be a potential candidate molecule for proteinuria. Although not expressed in the kidney, the nephrin antisense Nphs1as may regulate the expression of nephrin in extrarenal tissues. The genetic association analysis suggested that the alpha-actinin-4 gene, encoding an actin-filament cross-linking protein of the podocytes, may contribute to susceptibility for diabetic nephropathy. Munuaisten tehtävänä on poistaa verestä haitallisia kuona-aineita ja erittää ne virtsaan. Noin neljäsosa ihmisen verimäärästä kulkee jatkuvasti munuaisten läpi. Virtsan muodostuminen alkaa munuaiskeräsissä alkuvirtsan suodattumisella verestä. Munuaiskeräset koostuvat keräsen kotelosta ja sen sisäpuolella olevasta hiussuonikeräsestä. Podosyytti on monihaarainen epiteelisolu, joka verhoaa munuaisen hiussuonikeräsiä, ja ainutlaatuinen soluliitos eli välihila liittää solujen haarautuneet jalkalisäkkeet toisiinsa. Välihilan rakenne ja koostumus molekyylitasolla on ollut pitkään tuntematon. Synnynnäinen nefroosi on vastasyntyneillä ilmenevä vakava perinnöllinen munuaissairaus. Vuonna 1998 suomalainen tutkimusryhmä paikansi synnynnäistä nefroosia aiheuttavan NPHS1-geenin, jonka tuottama proteiini nefriini paikannettiin myöhemmin podosyyttien välihilaan. Nämä havainnot muodostavat väitöskirjatyön lähtökohdan. Diabeteksen aiheuttama munuaistauti on Suomessa yleisin pysyvää munuaisten vajaatoimintaa aiheuttava tauti. Lisäksi erityyppiset munuaiskerästulehdukset voivat johtavaa munuaisen vajaatoimintaan. Munuaistautien syynmukainen lääkehoito on toistaiseksi harvoin mahdollista. Munuaisen suodatusmekanismin toiminnan tarkempi tuntemus onkin tärkeää, kun kehitetään uusia munuaissairauksien hoitomenetelmiä. Väitöskirjatutkimuksessa havaitsimme, että aikaisemmin tuntematon, nefriinin kaltainen proteiini filtriini ilmentyy munuaiskeräsissä ja paikantuu podosyyttien väliseen soluliitokseen. Lisäksi totesimme kliinistä aineistoa hyödyntämällä, että filtriinin määrä on vähentynyt munuaiskerästulehdusta ja diabeettista munuaistautia sairastavilla potilailla. On mahdollista, että filtriini on osana munuaistaudin patologisissa prosesseissa. Tässä työssä myös eristimme ja kuvailimme hiiren Nphs1-geenin vastakkaiselta eli antisense-juosteelta tuotettavan lähetti-RNA:n, jota ei kuitenkaan tuoteta munuaisissa, mutta molekyyli saattaa osallistua nefriinin säätelyyn muissa kudoksissa. Antisense-RNA:n löytyminen voikin auttaa nefriinin biologisen toiminnan ymmärtämisessä. Väitöskirjan viimeinen osatyö kuuluu suomalaiseen FinnDiane-tutkimukseen, ja työssä kartoitimme diabeteksen aiheuttaman munuaistaudin perinnöllisiä taustatekijöitä. Valitsimme ehdokasgeeneiksi podosyyttien välihilan toimintaan osallistuvia geenejä ja tutkimme geenivaihteluja tyypin 1 diabeetikoilla. Tutkimustulokset viittaavat siihen, että tietyt muutokset alfa-aktiini-4 geenissä saattavat altistaa diabeettisen munuaistaudin kehittymiselle. Jatkotutkimuksissa on syytä hienokartoittaa alfa-aktiini-4:n geenialuetta ja varmentaa havaittujen muutosten merkitys muissa potilasaineistoissa.