Induced pluripotent stem cells: cell therapy and disease modeling

In 2012 ontving Shinya Yamanaka de Nobelprijs voor Geneeskunde voor zijn ontdekking dat gewone lichaamscellen omgezet kunnen worden tot een soort embryonale stamcellen, de zogenaamde induced pluripotente stamcellen of iPS-cellen. Deze iPS-technologie maakt het mogelijk om onbeperkte aantallen van alle mogelijke celtypen van een patiënt te verkrijgen voor toepassing, door middel van transplantatie, in regeneratieve geneeskunde en voor gedetailleerde studies over ziekte mechanismes in tal van erfelijke aandoeningen. In het proefschrift van Arun Thiruvalluvan wordt onderzoek beschreven dat gericht is op deze beide toepassingen van humane iPS cellen. Uit iPS cellen, verkregen uit huidcellen, van multiple sclerose (MS) patiënten konden grote aantallen oligodendrocyten (gespecialiseerde, myeline-producerende hersencellen) worden gegenereerd. Het idee dat deze oligodendrocyten na implantatie bij MS patiënten hersenlaesies kunnen herstellen werd succesvol getest in een primaat-model voor MS. Daarnaast wordt in het proefschrift de productie van grote aantallen zenuwcellen uit iPS cellen van patiënten met de erfelijke motorische aandoening spinocerebellaire ataxie (SCA-3) beschreven. Hierdoor was het mogelijk om het mechanisme achter de degeneratie van zenuwcellen, ten gevolge van mutaties in het SCA-3 gen in detail te bestuderen. Het via de IPS-technologie verkregen begrip van deze ziekte kan in de nabije toekomst nieuwe therapeutische benaderingen mogelijk maken

Insulin-like growth factor 2 (IGF2) protects against Huntington's disease through the extracellular disposal of protein aggregates

Impaired neuronal proteostasis is a salient feature of many neurodegenerative diseases, highlighting alterations in the function of the endoplasmic reticulum (ER). We previously reported that targeting the transcription factor XBP1, a key mediator of the ER stress response, delays disease progression and reduces protein aggregation in various models of neurodegeneration. To identify disease modifier genes that may explain the neuroprotective effects of XBP1 deficiency, we performed gene expression profiling of brain cortex and striatum of these animals and uncovered insulin-like growth factor 2 (Igf2) as the major upregulated gene. Here, we studied the impact of IGF2 signaling on protein aggregation in models of Huntington's disease (HD) as proof of concept. Cell culture studies revealed that IGF2 treatment decreases the load of intracellular aggregates of mutant huntingtin and a polyglutamine peptide. These results were validated using induced pluripotent stem cells (iPSC)-derived medium spiny neurons from HD patients and spinocerebellar ataxia cases. The reduction in the levels of mutant huntingtin was associated with a decrease in the half-life of the intracellular protein. The decrease in the levels of abnormal protein aggregation triggered by IGF2 was independent of the activity of autophagy and the proteasome pathways, the two main routes for mutant huntingtin clearance. Conversely, IGF2 signaling enhanced the secretion of soluble mutant huntingtin species through exosomes and microvesicles involving changes in actin dynamics. Administration of IGF2 into the brain of HD mice using gene therapy led to a significant decrease in the levels of mutant huntingtin in three different animal models. Moreover, analysis of human postmortem brain tissue and blood samples from HD patients showed a reduction in IGF2 level. This study identifies IGF2 as a relevant factor deregulated in HD, operating as a disease modifier that buffers the accumulation of abnormal protein species

Induced pluripotent stem cells: cell therapy and disease modeling

In 2012 ontving Shinya Yamanaka de Nobelprijs voor Geneeskunde voor zijn ontdekking dat gewone lichaamscellen omgezet kunnen worden tot een soort embryonale stamcellen, de zogenaamde induced pluripotente stamcellen of iPS-cellen. Deze iPS-technologie maakt het mogelijk om onbeperkte aantallen van alle mogelijke celtypen van een patiënt te verkrijgen voor toepassing, door middel van transplantatie, in regeneratieve geneeskunde en voor gedetailleerde studies over ziekte mechanismes in tal van erfelijke aandoeningen. In het proefschrift van Arun Thiruvalluvan wordt onderzoek beschreven dat gericht is op deze beide toepassingen van humane iPS cellen. Uit iPS cellen, verkregen uit huidcellen, van multiple sclerose (MS) patiënten konden grote aantallen oligodendrocyten (gespecialiseerde, myeline-producerende hersencellen) worden gegenereerd. Het idee dat deze oligodendrocyten na implantatie bij MS patiënten hersenlaesies kunnen herstellen werd succesvol getest in een primaat-model voor MS. Daarnaast wordt in het proefschrift de productie van grote aantallen zenuwcellen uit iPS cellen van patiënten met de erfelijke motorische aandoening spinocerebellaire ataxie (SCA-3) beschreven. Hierdoor was het mogelijk om het mechanisme achter de degeneratie van zenuwcellen, ten gevolge van mutaties in het SCA-3 gen in detail te bestuderen. Het via de IPS-technologie verkregen begrip van deze ziekte kan in de nabije toekomst nieuwe therapeutische benaderingen mogelijk maken

Single-cell transcriptomics of human traumatic brain injury reveals activation of endogenous retroviruses in oligodendroglia

Traumatic brain injury (TBI) is a leading cause of chronic brain impairment and results in a robust, but poorly understood, neuroinflammatory response that contributes to the long-term pathology. We used single-nuclei RNA sequencing (snRNA-seq) to study transcriptomic changes in different cell populations in human brain tissue obtained acutely after severe, life-threatening TBI. This revealed a unique transcriptional response in oligodendrocyte precursors and mature oligodendrocytes, including the activation of a robust innate immune response, indicating an important role for oligodendroglia in the initiation of neuroinflammation. The activation of an innate immune response correlated with transcriptional upregulation of endogenous retroviruses in oligodendroglia. This observation was causally linked in vitro using human glial progenitors, implicating these ancient viral sequences in human neuroinflammation. In summary, this work provides insight into the initiating events of the neuroinflammatory response in TBI, which has therapeutic implications

CD146 increases stemness and aggressiveness in glioblastoma and activates YAP signaling

Glioblastoma (GBM), a highly malignant and lethal brain tumor, is characterized by diffuse invasion into the brain and chemo-radiotherapy resistance resulting in poor prognosis. In this study, we examined the involvement of the cell adhesion molecule CD146/MCAM in regulating GBM aggressiveness. Analyses of GBM transcript expression databases revealed correlations of elevated CD146 levels with higher glioma grades, IDH-wildtype and unmethylated MGMT phenotypes, poor response to chemo-radiotherapy and worse overall survival. In a panel of GBM stem cells (GSCs) variable expression levels of CD146 were detected, which strongly increased upon adherent growth. CD146 was linked with mesenchymal transition since expression increased in TGF-ss-treated U-87MG cells. Ectopic overexpression of CD146/GFP in GG16 cells enhanced the mesenchymal phenotype and resulted in increased cell invasion. Conversely, GSC23-CD146 knockouts had decreased mesenchymal marker expression and reduced cell invasion in transwell and GBM-cortical assembloid assays. Moreover, using GSC23 xenografted zebrafish, we found that CD146 depletion resulted in more compact delineated tumor formation and reduced tumor cell dissemination. Stem cell marker expression and neurosphere formation assays showed that CD146 increased the stem cell potential of GSCs. Furthermore, CD146 mediated radioresistance by stimulating cell survival signaling through suppression of p53 expression and activation of NF-kappa B. Interestingly, CD146 was also identified as an inducer of the oncogenic Yes-associated protein (YAP). In conclusion, CD146 carries out various pro-tumorigenic roles in GBM involving its cell surface receptor function, which include the stimulation of mesenchymal and invasive properties, stemness, and radiotherapy resistance, thus providing an interesting target for therapy

DNAJB6, a Key Factor in Neuronal Sensitivity to Amyloidogenesis

CAG-repeat expansions in at least eight different genes cause neurodegeneration. The length of the extended polyglutamine stretches in the corresponding proteins is proportionally related to their aggregation propensity. Although these proteins are ubiquitously expressed, they predominantly cause toxicity to neurons. To understand this neuronal hypersensitivity, we generated induced pluripotent stem cell (iPSC) lines of spinocerebellar ataxia type 3 and Huntington's disease patients. iPSC generation and neuronal differentiation are unaffected by polyglutamine proteins and show no spontaneous aggregate formation. However, upon glutamate treatment, aggregates form in neurons but not in patient-derived neural progenitors. During differentiation, the chaperone network is drastically rewired, including loss of expression of the antiamyloidogenic chaperone DNAJB6. Upregulation of DNAJB6 in neurons antagonizes glutamate-induced aggregation, while knockdown of DNAJB6 in progenitors results in spontaneous polyglutamine aggregation. Loss of DNAJB6 expression upon differentiation is confirmed in vivo, explaining why stem cells are intrinsically protected against amyloidogenesis and protein aggregates are dominantly present in neurons