T Otonkoski

University of Helsinki, Helsinki, Southern Finland Province, Finland

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Publications (136)796.82 Total impact

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    ABSTRACT: Purpose: Retinopathy is an important manifestation of trifunctional protein (TFP) deficiencies but not of other defects of fatty acid oxidation. The common homozygous mutation in the TFP alpha subunit gene HADHA (hydroxyacyl-CoA dehydrogenase), c.1528G>C, affects the long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) activity of TFP, and blindness in infancy. The pathogenesis of the retinopathy is unknown. This study aims to utilize human induced pluripotent stem cell (hiPSC) technology to create a disease model for the disorder, and to derive clues for retinopathy pathogenesis. Methods: We implemented hiPSC technology to generate LCHAD deficiency (LCHADD) patient specific retinal pigment epithelial (RPE) monolayers. These patient and control RPEs were extensively characterised for function and structure, as well as for lipid composition by mass spectrometry. Results: The hiPSC derived RPE monolayers of patients and controls were functional, as they both were able to phagocytose the photoreceptor outer segments in vitro. Interestingly, the patient RPEs had intense cytoplasmic neutral lipid accumulation and lipidomic analysis revealed an increased triglyceride accumulation. Further, patient RPEs were small and irregular in shape, and their tight junctions were disorganized. Their ultrastructure showed decreased pigmentation, few melanosomes, and more melanolysosomes. Conclusion: We demonstrate that RPE cell model reveals novel early pathogenic changes in LCHADD retinopathy, with robust lipid accumulation, inefficient pigmentation that is evident soon after differentiation, and a defect in forming tight junctions inducing apoptosis. We propose that LCHADD-RPEs are an important model for mitochondrial TFP retinopathy, and that their early pathogenic changes contribute to infantile blindness of LCHADD.
    Investigative ophthalmology & visual science. 06/2014;
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    ABSTRACT: All forms of diabetes mellitus (DM) are characterized by the loss of functional pancreatic β cell mass, leading to insufficient insulin secretion. Thus, identification of novel approaches to protect and restore β cells is essential for the development of DM therapies. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-stress-inducible protein, but its physiological role in mammals has remained obscure. We generated MANF-deficient mice that strikingly develop severe diabetes due to progressive postnatal reduction of β cell mass, caused by decreased proliferation and increased apoptosis. Additionally, we show that lack of MANF in vivo in mouse leads to chronic unfolded protein response (UPR) activation in pancreatic islets. Importantly, MANF protein enhanced β cell proliferation in vitro and overexpression of MANF in the pancreas of diabetic mice enhanced β cell regeneration. We demonstrate that MANF specifically promotes β cell proliferation and survival, thereby constituting a therapeutic candidate for β cell protection and regeneration.
    Cell reports. 04/2014;
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    ABSTRACT: Neural crest (NC) cells are specified at the border of neural plate and epiderm. They are capable of differentiating into various somatic cell types, including craniofacial and peripheral nerve tissues. Notch signaling plays significant roles during neurogenesis; however, its function during human NC development is poorly understood. Here, we generated self-renewing premigratory NC-like cells (pNCCs) from human pluripotent stem cells and investigated the roles of Notch signaling during the NC differentiation. pNCCs expressed various NC specifier genes, including SLUG, SOX10 and TWIST1, and were able to differentiate into most NC derivatives. Blocking Notch signaling during the pNCC differentiation suppressed the expression of NC specifier genes. In contrast, ectopic expression of activated Notch1 intracellular domain (NICD1) augmented the expression of NC specifier genes, and NICD1 was found to bind at their promoter regions. Notch activity was also required for the maintenance of premigratory NC state, and suppression of Notch led to generation of NC-derived neurons. Taken together, we provide a protocol for the generation of pNCCs, and show that Notch signaling regulates the formation, migration and differentiation of NC from hPSCs.
    Journal of Cell Science 02/2014; · 5.88 Impact Factor
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    ABSTRACT: EGF receptor (EGFR) signalling is required for normal beta cell development and postnatal beta cell proliferation. We tested whether beta cell proliferation can be triggered by EGFR activation at any age and whether this can protect beta cells against apoptosis induced by diabetogenic insults in a mouse model. We generated transgenic mice with doxycycline-inducible expression of constitutively active EGFR (L858R) (CA-EGFR) under the insulin promoter. Mice were given doxycycline at various ages for different time periods, and beta cell proliferation and mass were analysed. Mice were also challenged with streptozotocin and isolated islets exposed to cytokines. Expression of EGFR (L858R) led to increased phosphorylation of EGFR and Akt in pancreatic islets. CA-EGFR expression during pancreatic development (embryonic day [E]12.5 to postnatal day [P]1) increased beta cell proliferation and mass in newborn mice. However, CA-EGFR expression in adult mice did not affect beta cell mass. Expression of the transgene improved glycaemia and markedly inhibited beta cell apoptosis after a single high dose, as well as after multiple low doses of streptozotocin. In vitro mechanistic studies showed that CA-EGFR protected isolated islets from cytokine-mediated beta cell death, possibly by repressing the proapoptotic protein BCL2-like 11 (BIM). Our findings show that the expression of CA-EGFR in the developing, but not in the adult pancreas stimulates beta cell replication and leads to increased beta cell mass. Importantly, CA-EGFR protects beta cells against streptozotocin- and cytokine-induced death.
    Diabetologia 02/2014; · 6.49 Impact Factor
  • Jere Weltner, Ras Trokovic, Timo Otonkoski
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    ABSTRACT: Pluripotent stem cells are capable of differentiating into cells of any tissue. The fact that iPS cell lines can be produced from skin cells or blood cells and directed to differentiate into a desired direction makes it possible to investigate e.g. myocardial or nerve cells having a disease-associated genotype. This will enable the development of experimental models of disease mechanisms and also apply them to drug screening, which may allow the development of novel types of treatment. In the future it may become possible to replace injured cells of a patient with autologous iPS cell derived transplants.
    Duodecim; lääketieteellinen aikakauskirja 01/2014; 130(8):785-92.
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    ABSTRACT: Placental lactogen (PL) induced serotonergic signaling is essential for gestational β-cell mass expansion. We have previously shown that intact Epidermal growth factor -receptor (EGFR) function is a crucial component of this pathway. We now explored more specifically the link between EGFR and pregnancy-induced β-cell mass compensation. Islets were isolated from wild-type and β-cell-specific EGFR-dominant negative mice (E1-DN), stimulated with PL and analyzed for β-cell proliferation and expression of genes involved in gestational β-cell growth. β-cell mass dynamics were analyzed both with traditional morphometrical methods and three-dimensional optical projection tomography (OPT) of whole-mount insulin-stained pancreata. Insulin-positive volume analyzed with OPT increased 1.4-fold at gestational day 18.5 (GD18.5) when compared to non-pregnant mice. Number of islets peaked by GD13.5 (680 vs 1134 islets per pancreas, non-pregnant vs. GD13.5). PL stimulated beta cell proliferation in the wild-type islets, whereas the proliferative response was absent in the E1-DN mouse islets. Serotonin synthesizing enzymes were upregulated similarly in both the wild-type and E1-DN mice. However, while survivin (Birc5) mRNA was upregulated 5.5-fold during pregnancy in the wild-type islets, no change was seen in the E1-DN pregnant islets. PL induced survivin expression also in isolated islets and this was blocked by EGFR inhibitor gefitinib, mTOR inhibitor rapamycin and MEK inhibitor PD0325901. Our 3D-volumetric analysis of β-cell mass expansion during murine pregnancy revealed that islet number increases during pregnancy. In addition, our results suggest that EGFR signaling is required for lactogen-induced survivin expression via MAPK and mTOR pathways.
    PLoS ONE 01/2014; 9(4):e93651. · 3.73 Impact Factor
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    ABSTRACT: Mitochondrial DNA (mtDNA) mutations manifest with vast clinical heterogeneity. The molecular basis of this variability is mostly unknown because the lack of model systems has hampered mechanistic studies. We generated induced pluripotent stem cells from patients carrying the most common human disease mutation in mtDNA, m.3243A>G, underlying mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome. During reprogramming, heteroplasmic mtDNA showed bimodal segregation toward homoplasmy, with concomitant changes in mtDNA organization, mimicking mtDNA bottleneck during epiblast specification. Induced pluripotent stem cell-derived neurons and various tissues derived from teratomas manifested cell-type specific respiratory chain (RC) deficiency patterns. Similar to MELAS patient tissues, complex I defect predominated. Upon neuronal differentiation, complex I specifically was sequestered in perinuclear PTEN-induced putative kinase 1 (PINK1) and Parkin-positive autophagosomes, suggesting active degradation through mitophagy. Other RC enzymes showed normal mitochondrial network distribution. Our data show that cellular context actively modifies RC deficiency manifestation in MELAS and that autophagy is a significant component of neuronal MELAS pathogenesis.
    Proceedings of the National Academy of Sciences 09/2013; · 9.74 Impact Factor
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    ABSTRACT: Activin/Nodal and Wnt signaling are known to play important roles in the regional specification of endoderm. Here we have investigated the effect of the length of stimulation with Activin A plus Wnt3a on the development of hepatic and pancreatic progenitors from the definitive endoderm (DE) cells derived from human pluripotent stem cells (hPSC). We show that DE-cells derived from hPSC with three days high Activin A and Wnt3a treatment were able to differentiate further into both tested endodermal lineages. When prolonging the DE-induction protocol from three to five or seven days, almost pure DE-marker positive cell populations were obtained. However, these cells had an impaired pancreatic differentiation capacity, while they still developed into hepatocyte-like cells. Further propagation of the DE-cells in the presence of Wnt3a and Activin A led to the complete loss of differentiation capacity into hepatic or pancreatic lineages. When Wnt3a was removed after 24h from the initiation of the differentiation, the cells were able to differentiate into PDX1+/NKX6.1+ pancreatic progenitors even with longer DE induction time while efficiency of hepatic differentiation was lower. Our results suggest that both the length and the timing of Wnt3a treatment during DE induction is crucial for the final differentiation outcome. Although it is possible to derive apparently pure DE cells with prolonged Activin A/Wnt-stimulation, their progenitor capacity is restricted to a limited time window.
    Experimental Cell Research 08/2013; · 3.56 Impact Factor
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    ABSTRACT: Loss-of-function mutations in the KATP channel genes KCNJ11 and ABCC8 cause neonatal hyperinsulinism in humans. Dominantly inherited mutations cause less severe disease, which may progress to glucose intolerance and diabetes in later life (e.g. SUR1-E1506K). We generated a mouse expressing SUR1-E1506K in place of SUR1. KATP channel inhibition by MgATP was enhanced in both homozygous (homE1506K) and heterozygous (hetE1506K) mutant mice, due to impaired channel activation by MgADP. As a consequence, mutant beta-cells showed less on-cell KATP channel activity and fired action potentials in glucose-free solution. HomE1506K mice exhibited enhanced insulin secretion and lower fasting blood glucose within 8 weeks of birth, but reduced insulin secretion and impaired glucose tolerance at 6 months of age. These changes correlated with a lower insulin content; unlike wild-type or hetE1506K mice, insulin content did not increase with age in homE1506K mice. There was no difference in the number and size of islets or beta-cells in the three types of mice, or evidence of beta-cell proliferation. We conclude that the gradual development of glucose intolerance in patients with the SUR1-E1506K mutation might, as in the mouse model, result from impaired insulin secretion due a failure of insulin content to increase with age.
    Diabetes 07/2013; · 7.90 Impact Factor
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    ABSTRACT: Functional hepatocytes, cardiomyocytes, neurons, and retinal pigment epithelial (RPE) cells derived from human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) could provide a defined and renewable source of human cells relevant for cell replacement therapies, drug discovery, toxicology testing, and disease modeling. In this study, we investigated the differences between the differentiation potentials of three hESC lines, four retrovirally derived hiPSC lines, and one hiPSC line derived with the nonintegrating Sendai virus technology. Four independent protocols were used for hepatocyte, cardiomyocyte, neuronal, and RPE cell differentiation. Overall, cells differentiated from hESCs and hiPSCs showed functional similarities and similar expression of genes characteristic of specific cell types, and differences between individual cell lines were also detected. Reactivation of transgenic OCT4 was detected specifically during RPE differentiation in the retrovirally derived lines, which may have affected the outcome of differentiation with these hiPSCs. One of the hiPSC lines was inferior in all directions, and it failed to produce hepatocytes. Exogenous KLF4 was incompletely silenced in this cell line. No transgene expression was detected in the Sendai virus-derived hiPSC line. These findings highlight the problems related to transgene expression in retrovirally derived hiPSC lines.
    Stem cells translational medicine. 01/2013;
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    ABSTRACT: Correct interactions with extracellular matrix are essential to human pluripotent stem cells (hPSC) to maintain their pluripotent self-renewal capacity during in vitro culture. hPSCs secrete laminin 511/521, one of the most important functional basement membrane components, and they can be maintained on human laminin 511 and 521 in defined culture conditions. However, large-scale production of purified or recombinant laminin 511 and 521 is difficult and expensive. Here we have tested whether a commonly available human choriocarcinoma cell line, JAR, which produces high quantities of laminins, supports the growth of undifferentiated hPSCs. We were able to maintain several human pluripotent stem cell lines on decellularized matrix produced by JAR cells using a defined culture medium. The JAR matrix also supported targeted differentiation of the cells into neuronal and hepatic directions. Importantly, we were able to derive new human induced pluripotent stem cell (hiPSC) lines on JAR matrix and show that adhesion of the early hiPSC colonies to JAR matrix is more efficient than to matrigel. In summary, JAR matrix provides a cost-effective and easy-to-prepare alternative for human pluripotent stem cell culture and differentiation. In addition, this matrix is ideal for the efficient generation of new hiPSC lines.
    PLoS ONE 01/2013; 8(10):e76205. · 3.73 Impact Factor
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    ABSTRACT: Lectins are carbohydrate-binding proteins, which occur ubiquitously in nature and are abundant in all living organisms from bacteria to mammals. They have several biological functions among which cell adhesion is well known and characterized. Based on the characterisation of the glycome of human embryonic stem cells (hESC), we have investigated the properties of glycan-binding lectins as a novel class of culture support matrices supporting hESC culture. We report that an Erythrina cristagalli lectin (ECA) matrix supported the undifferentiated growth and significantly increased the plating efficiency of both hESC and hiPSC when used in conjunction with pinacidil, an antihypertensive drug with ROCK-inhibition activity. As matrix, ECA maintained pluripotency, robust proliferation with a normal karyotype, and the ability to differentiate both in vitro and in vivo. Therefore, our findings indicate that lectins are potential candidates for design of culture and differentiation methods and that ECA is a potent simple defined matrix for human pluripotent stem cells.
    Stem cells and development 10/2012; · 4.15 Impact Factor
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    ABSTRACT: AIMS/HYPOTHESIS: Exercise-induced hyperinsulinism (EIHI) is a hypoglycaemic disorder characterised by inappropriate insulin secretion following anaerobic exercise or pyruvate load. Activating promoter mutations in the MCT1 gene (also known as SCLA16A1), coding for monocarboxylate transporter 1 (MCT1), were shown to associate with EIHI. Recently, transgenic Mct1 expression in pancreatic beta cells was shown to introduce EIHI symptoms in mice. To date, MCT1 has not been demonstrated in insulin-producing cells from an EIHI patient. METHODS: In vivo insulin secretion was studied during an exercise test before and after the resection of an insulinoma. The presence of MCT1 was analysed using immunohistochemistry followed by laser scanning microscopy, western blot analysis and real-time RT-PCR of MCT1. The presence of MCT1 protein was analysed in four additional insulinoma patients. RESULTS: Clinical testing revealed massive insulin secretion induced by anaerobic exercise preoperatively, but not postoperatively. MCT1 protein was not detected in the patient's normal islets. In contrast, immunoreactivity was clearly observed in the insulinoma tissue. Western blot analysis and real-time RT-PCR showed a four- to fivefold increase in MCT1 in the insulinoma tissue of the EIHI patient compared with human pancreatic islets. MCT1 protein was detected in three of four additional insulinomas. CONCLUSIONS/INTERPRETATION: We show for the first time that an MCT1-expressing insulinoma was associated with EIHI and that MCT1 might be present in most insulinomas. Our data suggest that MCT1 expression in human insulin-producing cells can lead to EIHI and warrant further studies on the role of MCT1 in human insulinoma patients.
    Diabetologia 10/2012; · 6.49 Impact Factor
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    ABSTRACT: Genomic integrity of human pluripotent stem cell (hPSC) lines requires routine monitoring. We report here that novel karyotyping assay, utilizing bead-bound bacterial artificial chromosome probes, provides a fast and easy tool for detection of chromosomal abnormalities in hPSC lines. The analysis can be performed from low amounts of DNA isolated from whole cell pools with simple data analysis interface. The method enables routine screening of stem cell lines in a cost-efficient high-throughput manner.
    Stem Cell Research 07/2012; 9(3):192-195. · 4.47 Impact Factor
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    ABSTRACT: Human somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) by ectopic expression of key transcription factors. iPSCs have been generated from a variety of cell types. However, iPSC induction from human myoblasts has not yet been reported. Human primary skeletal myoblasts can be cultured from diagnostic muscle biopsy specimens, and thousands of lines are frozen and stored in biobanks, and are a valuable source for iPSC-based etiological and pathogenic studies. Our aim was to generate iPSCs from human skeletal myoblasts enriched from muscle biopsy samples. We used retro- or Sendai virus vector-mediated reprogramming of enriched human myoblasts from 7 donors. We show that stable iPSC lines can be generated from human myoblasts at efficiency similar to that of fibroblasts when appropriate media is used, and the efficiency of the feeder-free iPSC generation can be significantly improved by inhibitors of histone deacetylase (sodium butyrate) and TGF-β signaling (SB431542).
    Stem cells and development 06/2012; · 4.15 Impact Factor
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    ABSTRACT: Fibroblasts can be reprogrammed into induced pluripotent stem cells (iPSC) by ectopic expression of key transcription factors. Current methods for the generation of integration-free iPSC are limited by the low efficiency of iPSC generation and by challenges in reprogramming methodology. Recombinant adeno-associated virus (rAAV) is a potent gene delivery vehicle capable of efficient transduction of transgenic DNA into cells. rAAV stays mainly as an episome in nondividing cells, and the extent of integration is still poorly defined for various replicating cells. In this study, we aimed to induce iPSC from mouse and human fibroblasts by using rAAV vector-mediated transient delivery of reprogramming factors. We succeeded in deriving induced pluripotent stem cells from mouse but not human fibroblasts. Unexpectedly, the rAAV vector-mediated reprogramming led to frequent genomic integration of vector sequences during the reprogramming process, independent of the amount of virus used, and to persistent expression of reprogramming factors in generated iPSC clones. It thus appears that rAAV vectors are not compatible with the derivation of integration-free iPSC.
    Journal of Virology 02/2012; 86(8):4463-7. · 5.08 Impact Factor
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    ABSTRACT: We have previously characterized the molecular composition of human islet basement membranes and shown that human beta cells bind to laminin 511 (LM511) through integrin α3β1 and Lutheran glycoprotein. We have now investigated the impact of physical contact between cultured human beta cells and the laminin isoforms occurring in their natural niche. Human islet preparations derived from 15 donors were used, beta cells and duct cells were purified by magnetic sorting. Overall beta-cell proliferation was low or undetectable. However, in many experiments the only proliferating beta cells were detected in contact with the laminin isoforms that are found in the human islets in vivo (511 and 411). Purified ductal and beta cells underwent epithelial-mesenchymal transition (EMT). LM511 partially blocked this dedifferentiation of purified beta cells, and did not affect purified duct cells. Interactions with the surrounding basement membrane are important for the growth and function of human beta cells. However, only a very limited level of beta-cell proliferation can be induced by exogenous factors. LM511 may be a useful substrate for human beta-cell maintenance in vitro.
    Molecular and Cellular Endocrinology 01/2012; 355(1):78-86. · 4.04 Impact Factor
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    ABSTRACT: Fibroblast feeder cells play an important role in supporting the derivation and long term culture of undifferentiated, pluripotent human embryonic stem cells (hESCs). The feeder cells secrete various growth factors and extracellular matrix (ECM) proteins into extracellular milieu. However, the roles of the feeder cell-secreted factors are largely unclear. Animal feeder cells and use of animal serum also make current feeder cell culture conditions unsuitable for derivation of clinical grade hESCs. We established xeno-free feeder cell lines using human serum (HS) and studied their function in hESC culture. While human foreskin fibroblast (hFF) feeder cells were clearly hESC supportive, none of the established xeno-free human dermal fibroblast (hDF) feeder cells were able to maintain undifferentiated hESC growth. The two fibroblast types were compared for their ECM protein synthesis, integrin receptor expression profiles and key growth factor secretion. We show that hESC supportive feeder cells produce laminin-511 and express laminin-binding integrins α3ß1, α6ß1 and α7ß1. These results indicate specific laminin isoforms and integrins in maintenance of hESC pluripotency in feeder-dependent cultures. In addition, several genes with a known or possible role for hESC pluripotency were differentially expressed in distinct feeder cells.
    Stem Cell Research 01/2012; 8(1):97-108. · 4.47 Impact Factor
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    ABSTRACT: The International Stem Cell Initiative analyzed 125 human embryonic stem (ES) cell lines and 11 induced pluripotent stem (iPS) cell lines, from 38 laboratories worldwide, for genetic changes occurring during culture. Most lines were analyzed at an early and late passage. Single-nucleotide polymorphism (SNP) analysis revealed that they included representatives of most major ethnic groups. Most lines remained karyotypically normal, but there was a progressive tendency to acquire changes on prolonged culture, commonly affecting chromosomes 1, 12, 17 and 20. DNA methylation patterns changed haphazardly with no link to time in culture. Structural variants, determined from the SNP arrays, also appeared sporadically. No common variants related to culture were observed on chromosomes 1, 12 and 17, but a minimal amplicon in chromosome 20q11.21, including three genes expressed in human ES cells, ID1, BCL2L1 and HM13, occurred in >20% of the lines. Of these genes, BCL2L1 is a strong candidate for driving culture adaptation of ES cells.
    Nature Biotechnology 11/2011; 29(12):1132-44. · 32.44 Impact Factor
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    ABSTRACT: Congenital hyperinsulinism (CHI) is the major cause of persistent neonatal hypoglycemia. CHI most often occurs due to mutations in the ABCC8 (which encodes sulfonylurea receptor 1) or KCNJ11 (which encodes the potassium channel Kir6.2) gene, which result in a lack of functional KATP channels in pancreatic β cells. Diffuse forms of CHI (DiCHI), in which all β cells are abnormal, often require subtotal pancreatectomy, whereas focal forms (FoCHI), which are characterized by localized hyperplasia of abnormal β cells, can be cured by resection of the lesion. Here, we characterized the in vitro kinetics of insulin secretion by pancreatic fragments from 6 DiCHI patients and by focal lesion and normal adjacent pancreas from 18 FoCHI patients. Responses of normal pancreas were similar to those reported for islets from adult organ donors. Compared with normal pancreas, basal insulin secretion was elevated in both FoCHI and DiCHI tissue. Affected tissues were heterogeneous in their secretory responses, with increased glucose levels often producing a rapid increase in insulin secretion that could be followed by a paradoxical decrease below prestimulatory levels. The KATP channel blocker tolbutamide was consistently ineffective in stimulating insulin secretion; conversely, the KATP channel activator diazoxide often caused an unanticipated increase in insulin secretion. These observed alterations in secretory behavior were similar in focal lesion and DiCHI tissue, and independent of the specific mutation in ABCC8 or KCNJ11. They cannot be explained by classic models of β cell function. Our results provide insight into the excessive and sometimes paradoxical changes in insulin secretion observed in CHI patients with inactivating mutations of KATP channels.
    The Journal of clinical investigation 09/2011; 121(10):3932-42. · 15.39 Impact Factor

Publication Stats

4k Citations
796.82 Total Impact Points

Institutions

  • 1988–2014
    • University of Helsinki
      • • Institute of Biotechnology
      • • Biomedicum Stem Cell Center (BSCC)
      • • Hospital for Children and Adolescents and Biomedicum Helsinki
      • • The Hospital for Children and Adolescents
      • • Transplantation Laboratory
      Helsinki, Southern Finland Province, Finland
    • Helsinki University Central Hospital
      • Children's Hospital
      Helsinki, Southern Finland Province, Finland
  • 2005–2012
    • Åbo Akademi University
      • Turku Centre for Biotechnology
      Turku, Province of Western Finland, Finland
  • 2011
    • Samuel Lunenfeld Research Institute
      Toronto, Ontario, Canada
  • 2010
    • University of Eastern Finland
      Kuopio, Eastern Finland Province, Finland
  • 2008
    • Otto-von-Guericke-Universität Magdeburg
      Magdeburg, Saxony-Anhalt, Germany
    • University of Southampton
      Southampton, England, United Kingdom
  • 2000–2005
    • Kuopio University Hospital
      • Department of Paediatrics
      Kuopio, Province of Eastern Finland, Finland
  • 2004
    • Hospital Regional Universitario Carlos Haya Málaga
      Málaga, Andalusia, Spain
  • 2002–2003
    • University of Kuopio
      • Department of Paediatrics
      Kuopio, Eastern Finland Province, Finland
  • 2000–2002
    • National Public Health Institute
      Helsinki, Southern Finland Province, Finland
  • 1996–1999
    • University of California, San Diego
      • Department of Pediatrics
      San Diego, CA, United States
    • National University (California)
      San Diego, California, United States