Günter Päth

Multiple, temporal-specific roles for HNF6 in pancreatic endocrine and ductal differentiation.

Within the developing pancreas Hepatic Nuclear Factor 6 (HNF6) directly activates the pro-endocrine transcription factor, Ngn3. HNF6 and Ngn3 are each essential for endocrine differentiation and HNF6 is also required for embryonic duct development. Most HNF6(-/-) animals die as neonates, making it difficult to study later aspects of HNF6 function. Here, we describe, using conditional gene inactivation, that HNF6 has specific functions at different developmental stages in different pancreatic lineages. Loss of HNF6 from Ngn3-expressing cells (HNF6(Delta endo)) resulted in fewer multipotent progenitor cells entering the endocrine lineage, but had no effect on beta cell terminal differentiation. Early, pancreas-wide HNF6 inactivation (HNF6(Delta panc)) resulted in endocrine and ductal defects similar to those described for HNF6 global inactivation. However, all HNF6(Delta panc) animals survived to adulthood. HNF6(Delta panc) pancreata displayed increased ductal cell proliferation and metaplasia, as well as characteristics of pancreatitis, including up-regulation of CTGF, MMP7, and p8/Nupr1. Pancreatitis was most likely caused by defects in ductal primary cilia. In addition, expression of Prox1, a known regulator of pancreas development, was decreased in HNF6(Delta panc) pancreata. These data confirm that HNF6 has both early and late functions in the developing pancreas and is essential for maintenance of Ngn3 expression and proper pancreatic duct morphology.

PDX1- and NGN3-mediated in vitro reprogramming of human bone marrow-derived mesenchymal stromal cells into pancreatic endocrine lineages

BACKGROUND AIMS Reprogramming of multipotent adult bone marrow (BM)-derived mesenchymal stromal/stem cells (MSC) (BM-MSC) represents one of several strategies for cell-based therapy of diabetes. However, reprogramming primary BM-MSC into pancreatic endocrine lineages has not yet been consistently demonstrated. METHODS To unravel the role and interaction of key factors governing this process, we used well-characterized telomerase-immortalized human MSC (hMSC-TERT). Pancreatic endocrine differentiation in hMSC-TERT was induced by two major in vitro strategies: (i) endocrine-promoting culture conditions and (ii) ectopic expression of two master regulatory genes of the endocrine lineage, human neurogenin 3 (NGN3) and human pancreatic duodenal homeobox 1 (PDX1). RESULTS Both approaches triggered pancreatic endocrine gene expression, notably insulin, glucose-transporter 2 and somatostatin. Transgenic overexpression of NGN3 and/or PDX1 proteins not only induced direct target genes, such as NEUROD1 and insulin, and but also triggered parts of the gene expression cascade that is involved in pancreatic endocrine differentiation. Notably, ectopic NGN3 alone was sufficient to initiate the expression of specific beta-cell lineage-associated genes, most importantly PDX1 and insulin. This was demonstrated both transcriptionally by mRNA expression and reporter gene analyzes and at a protein level by Western blotting. Such reprogramming of hMSC-TERT cells induced glucose-insensitive insulin biosynthesis and secretion. CONCLUSIONS Our results indicate that establishment of glucose-dependent insulin secretion in partially reprogrammed human MSC may depend on additional maturation factors. Moreover, hMSC-TERT provides a suitable cell model for investigating further the molecular mechanisms of reprogramming and maturation of adult MSC towards pancreatic endocrine lineages.

Functional Signature of Human Islet-Derived Precursor Cells Compared to Bone Marrow-Derived Mesenchymal Stem Cells

Pancreatic islet beta-cell replenishment can be driven by epithelial cells from exocrine pancreas via epithelial-mesenchymal transition (EMT) and the reverse process MET, while specified pancreatic mesenchymal cells control islet cell development and maintenance. The role of human islet-derived precursor cells (hIPCs) in regeneration and support of endocrine islets is under investigation. Here, we analyzed hIPCs as to their immunophenotype, multilineage differentiation capacity, and gene profiling, in comparison to human bone marrow-derived mesenchymal stem cells (hBM-MSCs). hIPCs and hBM-MSCs display a common mesenchymal character and express lineage-specific marker genes upon induction toward pancreatic endocrine and mesenchymal pathways of differentiation. hIPCs can go further along endocrine pathways while lacking some core mesenchymal differentiation attributes. Significance analysis of microarray (SAM) from 5 hBM-MSC and 3 hIPC donors mirrored such differences. Candidate gene cluster analysis disclosed differential expression of key lineage regulators, indicated a HoxA gene-associated positional memory in hIPCs and hBM-MSCs, and showed as well a clear transition state from mesenchyme to epithelium or vice versa in hIPCs. Our findings raise new research platforms to further clarify the potential of hIPCs to undergo complete MET thus contributing to islet cell replenishment, maintenance, and function.

DJ-1 Protects Pancreatic Beta Cells from Cytokine- and Streptozotocin-Mediated Cell Death.

A hallmark feature of type 1 and type 2 diabetes mellitus is the progressive dysfunction and loss of insulin-producing pancreatic beta cells, and inflammatory cytokines are known to trigger beta cell death. Here we asked whether the anti-oxidant protein DJ-1 encoded by the Parkinson’s disease gene PARK7 protects islet cells from cytokine- and streptozotocin-mediated cell death. Wild type and DJ-1 knockout mice (KO) were treated with multiple low doses of streptozotocin (MLDS) to induce inflammatory beta cell stress and cell death. Subsequently, glucose tolerance tests were performed, and plasma insulin as well as fasting and random blood glucose concentrations were monitored. Mitochondrial morphology and number of insulin granules were quantified in beta cells. Moreover, islet cell damage was determined in vitro after streptozotocin and cytokine treatment of isolated wild type and DJ-1 KO islets using calcein AM/ethidium homodimer-1 staining and TUNEL staining. Compared to wild type mice, DJ-1 KO mice became diabetic following MLDS treatment. Insulin concentrations were substantially reduced, and fasting blood glucose concentrations were significantly higher in MLDS-treated DJ-1 KO mice compared to equally treated wild type mice. Rates of beta cell apoptosis upon MLDS treatment were twofold higher in DJ-1 KO mice compared to wild type mice, and in vitro inflammatory cytokines led to twice as much beta cell death in pancreatic islets from DJ-1 KO mice versus those of wild type mice. In conclusion, this study identified the anti-oxidant protein DJ-1 as being capable of protecting pancreatic islet cells from cell death induced by an inflammatory and cytotoxic setting.

Protein Phosphatase 1 (PP-1)-Dependent Inhibition of Insulin Secretion by Leptin in INS-1 Pancreatic β-Cells and Human Pancreatic Islets

Leptin inhibits insulin secretion from pancreatic β-cells, and in turn, insulin stimulates leptin biosynthesis and secretion from adipose tissue. Dysfunction of this adipoinsular feedback loop has been proposed to be involved in the development of hyperinsulinemia and type 2 diabetes mellitus. At the molecular level, leptin acts through various pathways, which in combination confer inhibitory effects on insulin biosynthesis and secretion. The aim of this study was to identify molecular mechanisms of leptin action on insulin secretion in pancreatic β-cells. To identify novel leptin-regulated genes, we performed subtraction PCR in INS-1 β-cells. Regulated expression of identified genes was confirmed by RT-PCR and Northern and Western blotting. Furthermore, functional impact on β-cell function was characterized by insulin-secretion assays, intracellular Ca²(+) concentration measurements, and enzyme activity assays. PP-1α, the catalytic subunit of protein phosphatase 1 (PP-1), was identified as a novel gene down-regulated by leptin in INS-1 pancreatic β-cells. Expression of PP-1α was verified in human pancreatic sections. PP-1α mRNA and protein expression is down-regulated by leptin, which culminates in reduction of PP-1 enzyme activity in β-cells. In addition, glucose-induced insulin secretion was inhibited by nuclear inhibitor of PP-1 and calyculin A, which was in part mediated by a reduction of PP-1-dependent calcium influx into INS-1 β-cells. These results identify a novel molecular pathway by which leptin confers inhibitory action on insulin secretion, and impaired PP-1 inhibition by leptin may be involved in dysfunction of the adipoinsular axis during the development of hyperinsulinemia and type 2 diabetes mellitus.

Status quo und Perspektive des Einsatzes von Stammzellen in der b-Zell-Ersatztherapie des Diabetes mellitus

Zusammenfassung.q Typ-1-Diabetiker sind nach der autoimmunen Zerstörung der Insulin produzierenden b-Zellen im endokrinen Pankreas und Typ-2-Diabetiker im Sekundärversagen lebenslang auf die Substitution mit Insulin angewiesen. Eine klinisch eingeführte Alternative zur Insulintherapie ist die Transplantation von humanen Langerhansschen Inseln, die aber durch die geringe Verfügbarkeit von Spenderorganen limitiert ist. Bei der intensiven Suche nach neuen Quellen für b-Zellen sind humane Stammzellen in den Fokus des wissenschaftlichen Interesses gerückt. Sowohl aus embryonalen als auch aus adulten Stammzellen des endokrinen Pankreas lassen sich in vitro Insulin produzierende Zellen für die Transplantation generieren. Beide Stammzelltypen besitzen jedoch hinsichtlich Verfügbarkeit, In-vitro-Expansion, Differenzierungspotential und Tumorigenität ganz unterschiedliche Eigenschaften, welche von den Autoren näher erläutert werden. Vor dem klinischen Einsatz einer zelltherapeutischen Strategie für den Diabetes mellitus beim Menschen müssen darüber hinaus Aspekte der therapeutischen Effektivität, Sicherheit und Kosten-Nutzen-Relation für den individuellen Patienten umfassend bewertet werden. Dennoch lässt eine Abschätzung der Kosten-Nutzen-Relation erwarten, dass in Zukunft eine Stammzelltherapie für die Behandlung des Diabetes mellitus sowohl sicher als auch kosteneffektiv klinisch umgesetzt werden kann.Abstract.q Due to autoimmune destruction of insulin-producing pancreatic b-cells, type 1 diabetic patients, and also patients with type 2 diabetes suffering from defective insulin secretion rely on lifelong substitution with insulin. A clinically established alternative therapy for diabetics with exogenous insulin substitution, the transplantation of human islets of Langerhans, is limited by the lack of donor organs. The intensive search for new sources of pancreatic b-cells now focuses on human stem cells. Insulin-producing cells for transplantation can be generated from both embryonic and adult pancreatic stem cells. Both types of stem cells, however, differ with respect to availability, in vitro expansion, potential for differentiation, and tumorigenicity, which is elucidated by the authors. Before stem cell therapeutic strategies for diabetes mellitus can be transferred to clinical application in humans, aspects of functional effectivity, safety, and cost-effectiveness have to be solved. Considering these prerequisites in the Diskuslight of currently available therapeutic options, however, it can be estimated, that stem cell therapy for diabetes mellitus may be cost-effectively introduced into clinical routine in the future.

Human Krüppel-like factor 11 differentially regulates human insulin promoter activity in β-cells and non-β-cells via p300 and PDX1 through the regulatory sites A3 and CACCC box.

Human Krüppel-like factor 11 (hKLF11) has been characterised to both activate and inhibit human insulin promoter (hInsP) activity. Since KLF11 is capable to differentially regulate genes dependent on recruited cofactors, we investigated the effects of hKLF11 on cotransfected hInsP in both β-cells and non-β-cells. hKLF11 protein interacts with hp300 but not with hPDX1. Overexpressed hKLF11 stimulates PDX1-transactivation of hInsP in HEK293 non-β-cells, but confers inhibition in INS-1E β-cells. Both hKLF11 functions can be neutralised by the p300 inhibitor E1A, increased hp300 levels (INS-1E), dominant negative (DN)-PDX1 and by mutation of the PDX1 binding site A3 or the CACCC box. In summary, hKLF11 differentially regulates hInsP activity depending on the molecular context via modulation of p300:PDX1 interactions with the A3 element and CACCC box. We postulate that KLF11 has a role in fine-tuning insulin transcription in certain cellular situations rather than representing a major transcriptional activator or repressor of the insulin gene.

Betazellersatz und Stammzelltherapie des Diabetes – Wo stehen wir heute?

Patienten mit autoimmunem Typ-1-Diabetes sind nach Ausbruch der Erkrankung lebenslang auf exogene Insulingaben angewiesen. Trotz guter Insulineinstellung entstehen haufig schwerwiegende diabetische Langzeitkomplikationen. Dies zeigt, dass exogene Insulingaben den Blutzucker nicht so exakt regulieren konnen wie Insulin produzierende Betazellen. Die Wiederherstellung der endogenen Betazellen ist daher ein wichtiges therapeutisches Ziel. Klinisch etabliert sind Pankreas- und Inseltransplantation, deren Anwendung allerdings durch die notwendige Immunsuppression und den Mangel an Spenderorganen limitiert ist. Stammzellen vermehren sich in vitro ohne die Fahigkeit zu verlieren, sich in andere Zelltypen zu differenzieren. Die Forschung versucht diese Fahigkeit fur die Generierung von Surrogatbetazellen fur die Inseltransplantation zu nutzen. Adulte mesenchymale Knochenmarksstammzellen (MSC) besitzen zusatzlich immunmodulatorische, proangiogene und regenerative Eigenschaften, welche uber humorale Faktoren und Interaktionen mit regulatorischen T-Zellen vermittelt werden. MSC konnen daher im Tiermodell Inseltransplantatabstosung inhibieren, Typ-1-Diabetes mildern und eine diabetisch geschadigte Betazellmasse regenerieren. Dieser Ubersichtsartikel erlautert den aktuellen Stand der Forschung und die verbleibenden Probleme, die einem klinischen Einsatz von Stammzelltherapien derzeit noch im Wege stehen.

Glucose-dependent expansion of pancreatic beta-cells by the protein p8 in vitro and in vivo

p8 protein expression is known to be upregulated in the exocrine pancreas during acute pancreatitis. Own previous work revealed glucose-dependent p8 expression also in endocrine pancreatic beta-cells. Here we demonstrate that glucose-induced INS-1 beta-cell expansion is preceded by p8 protein expression. Moreover, isopropylthiogalactoside (IPTG)-induced p8 overexpression in INS-1 beta-cells (p8-INS-1) enhances cell proliferation and expansion in the presence of glucose only. Although beta-cell-related gene expression (PDX-1, proinsulin I, GLUT2, glucokinase, amylin) and function (insulin content and secretion) are slightly reduced during p8 overexpression, removal of IPTG reverses beta-cell function within 24 h to normal levels. In addition, insulin secretion of p8-INS-1 beta-cells in response to 0-25 mM glucose is not altered by preceding p8-induced beta-cell expansion. Adenovirally transduced p8 overexpression in primary human pancreatic islets increases proliferation, expansion, and cumulative insulin secretion in vitro. Transplantation of mock-transduced control islets under the kidney capsule of immunosuppressed streptozotocin-diabetic mice reduces blood glucose and increases human C-peptide serum concentrations to stable levels after 3 days. In contrast, transplantation of equal numbers of p8-transduced islets results in a continuous decrease of blood glucose and increase of human C-peptide beyond 3 days, indicating p8-induced expansion of transplanted human beta-cells in vivo. This is underlined by a doubling of insulin content in kidneys containing p8-transduced islet grafts explanted on day 9. These results establish p8 as a novel molecular mediator of glucose-induced pancreatic beta-cell expansion in vitro and in vivo and support the notion of existing beta-cell replication in the adult organism.