New function of the myostatin/activin type I receptor (ALK4) as a mediator of muscle atrophy and muscle regeneration.

Skeletal muscle fibrosis and impaired muscle regeneration are major contributors to muscle wasting in Duchenne muscular dystrophy (DMD). Muscle growth is negatively regulated by myostatin (MSTN) and activins. Blockage of these pathways may improve muscle quality and function in DMD. Antisense oligonucleotides (AONs) were designed specifically to block the function of ALK4, a key receptor for the MSTN/activin pathway in skeletal muscle. AON-induced exon skipping resulted in specific Alk4 down-regulation, inhibition of MSTN activity, and increased myoblast differentiation in vitro Unexpectedly, a marked decrease in muscle mass (10%) was found after Alk4 AON treatment in mdx mice. In line with in vitro results, muscle regeneration was stimulated, and muscle fiber size decreased markedly. Notably, when Alk4 was down-regulated in adult wild-type mice, muscle mass decreased even more. RNAseq analysis revealed dysregulated metabolic functions and signs of muscle atrophy. We conclude that ALK4 inhibition increases myogenesis but also regulates the tight balance of protein synthesis and degradation. Therefore, caution must be used when developing therapies that interfere with MSTN/activin pathways.-Pasteuning-Vuhman, S., Boertje-van der Meulen, J. W., van Putten, M., Overzier, M., ten Dijke, P., Kielbasa, S. M., Arindrarto, W., Wolterbeek, R., Lezhnina, K. V., Ozerov, I. V., Aliper, A. M., Hoogaars, W. M., Aartsma-Rus, A., Loomans, C. J. M. New function of the myostatin/activin type I receptor (ALK4) as a mediator of muscle atrophy and muscle regeneration.

Unlimited in vitro expansion of adult bi-potent pancreas progenitors through the Lgr5/R-spondin axis.

Lgr5 marks adult stem cells in multiple adult organs and is a receptor for the Wnt-agonistic R-spondins (RSPOs). Intestinal, stomach and liver Lgr5(+) stem cells grow in 3D cultures to form ever-expanding organoids, which resemble the tissues of origin. Wnt signalling is inactive and Lgr5 is not expressed under physiological conditions in the adult pancreas. However, we now report that the Wnt pathway is robustly activated upon injury by partial duct ligation (PDL), concomitant with the appearance of Lgr5 expression in regenerating pancreatic ducts. In vitro, duct fragments from mouse pancreas initiate Lgr5 expression in RSPO1-based cultures, and develop into budding cyst-like structures (organoids) that expand five-fold weekly for >40 weeks. Single isolated duct cells can also be cultured into pancreatic organoids, containing Lgr5 stem/progenitor cells that can be clonally expanded. Clonal pancreas organoids can be induced to differentiate into duct as well as endocrine cells upon transplantation, thus proving their bi-potentiality.

Sequential intravital imaging reveals in vivo dynamics of pancreatic tissue transplanted under the kidney capsule in mice.

AIMS/HYPOTHESIS: Dynamic processes in pancreatic tissue are difficult to study. We aimed to develop an intravital imaging method to longitudinally examine engraftment, vascularisation, expansion and differentiation in mature islets or embryonic pancreases transplanted under the kidney capsule. METHODS: Isolated pancreatic islets from adult mice and murine embryonic day (E)12.5 pancreases containing fluorescent biomarkers were transplanted under the kidney capsule of immunodeficient recipient mice. Human islet cells were dispersed, transduced with a lentivirus expressing a fluorescent label and reaggregated before transplantation. Graft-containing kidneys were positioned subcutaneously and an imaging window was fitted into the skin on top of the kidney. Intravital imaging using multiphoton microscopy was performed for up to 2 weeks. Volumes of fluorescently labelled cells were determined as a measure of development and survival. RESULTS: Transplanted islets and embryonic pancreases showed good engraftment and remained viable. Engraftment and vascularisation could be longitudinally examined in murine and human islet cells. Murine islet beta cell volume was unchanged over time. Transplanted embryonic pancreases increased to up to 6.1 times of their original volume and beta cell volume increased 90 times during 2 weeks. CONCLUSIONS/INTERPRETATION: This method allows for repeated intravital imaging of grafts containing various sources of pancreatic tissue transplanted under the kidney capsule. Using fluorescent markers, dynamic information concerning engraftment or differentiation can be visualised and measured.

Developmental pathways during in vitro progression of human islet neogenesis.

Islet neogenesis, or the differentiation of islet cells from precursor cells, is seen in vitro and in vivo both embryonically and after birth. However, little is known about the differentiation pathways during embryonic development for human pancreas. Our previously reported in vitro generation of islets from human pancreatic tissue provides a unique system to identify potential markers of neogenesis and to determine the molecular mechanisms underlying this process. To this end, we analyzed the gene expression profiles of three different stages during in vitro islet generation: the Initially Adherent, Expanded, and Differentiated stages. Samples from four human pancreases were hybridized to Affymetrix U95A GeneChips, and data analyzed using GeneSpring 7.0/9.0 software. Using scatter plots we selected genes with a 2-fold or greater differential expression. Of the 12,000 genes/ESTs present on these arrays, 295 genes including 38 acinar-enriched genes were selectively lost during the progression from the Initially Adherent stage to the Expanded stage; 468 genes were increased in this progression to Expanded tissue; and 529 genes had a two-fold greater expression in the Differentiated stage than in the Expanded tissue. Besides the expected increases in insulin, glucagon, and duct markers (mucin 6, aquaporin 1 and 5), the beta cell auto-antigen IA-2/phogrin was increased 5-fold in Differentiated. In addition, developmentally important pathways, including notch/jagged, Wnt/frizzled, TGFbeta superfamily (follistatin, BMPs, and SMADs), and retinoic acid (COUP-TFI, CRABP1, 2, and RAIG1) were differentially regulated during the expansion/differentiation. Two putative markers for islet precursor cells, UCHL1/PGP9.5 and DMBT1, were enhanced during the progression to differentiated cells, but only the latter could be a marker of islet precursor cells. We suggest that appropriate manipulation of these differentiation-associated pathways will enhance the efficiency of differentiation of insulin-producing beta-cells in this in vitro model.

Development of a human primary gut-on-a-chip to model inflammatory processes.

Inflammatory bowel disease (IBD) is a complex multi-factorial disease for which physiologically relevant in vitro models are lacking. Existing models are often a compromise between biological relevance and scalability. Here, we integrated intestinal epithelial cells (IEC) derived from human intestinal organoids with monocyte-derived macrophages, in a gut-on-a-chip platform to model the human intestine and key aspects of IBD. The microfluidic culture of IEC lead to an increased polarization and differentiation state that closely resembled the expression profile of human colon in vivo. Activation of the model resulted in the polarized secretion of CXCL10, IL-8 and CCL-20 by IEC and could efficiently be prevented by TPCA-1 exposure. Importantly, upregulated gene expression by the inflammatory trigger correlated with dysregulated pathways in IBD patients. Finally, integration of activated macrophages offers a first-step towards a multi-factorial amenable IBD platform that could be scaled up to assess compound efficacy at early stages of drug development or in personalized medicine.

Differentiation of bone marrow-derived endothelial progenitor cells is shifted into a proinflammatory phenotype by hyperglycemia.

Bone marrow (BM)-derived endothelial progenitor cells (EPC) contribute to vascular maintenance by participating in angiogenesis, re-endothelialization, and remodeling. Myeloid progenitor cells in the BM are functionally and quantitatively an important precursor pool for cells that contribute to these processes. However, these precursor pools in the BM also give rise to important effector cells of the innate immune system, such as macrophages and dendritic cells. We hypothesized that the disturbed repair responses that are being observed in diabetes mellitus are also related to an effect on functional and differentiation characteristics at the level of this bone marrow precursor pool. Indeed, we observed that bone marrow differentiation cultures for EPC, macrophages (Mph), or dendritic cells (DC) from hyperglycemic BM yielded 40% fewer EPC and 50% more Mph compared with control BM. These changes were directly related to the hemoglobin A(1C) levels of the donor mice. BM-derived DC numbers were not affected by hyperglycemia. The composition of the BM was not altered; in particular, the numbers of CD31+/Ly6C+ cells, which serve as common progenitors for EPC, Mph, and DC, were unaffected. In addition, BM-derived EPC from hyperglycemic mice were less angiogenic and more proinflammatory in regards to endocytosis, T-cell activation, and interleukin 12 production. HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase inhibition by statin supplementation of the culture medium counteracted these hyperglycemia-induced changes. Our study results show that hyperglycemia alters the differentiation fate of BM precursor cells, reducing the potential to generate vascular regenerative cells and favoring the development of proinflammatory cells.

Expansion of Adult Human Pancreatic Tissue Yields Organoids Harboring Progenitor Cells with Endocrine Differentiation Potential.

Generating an unlimited source of human insulin-producing cells is a prerequisite to advance ß cell replacement therapy for diabetes. Here, we describe a 3D culture system that supports the expansion of adult human pancreatic tissue and the generation of a cell subpopulation with progenitor characteristics. These cells display high aldehyde dehydrogenase activity (ALDHhi), express pancreatic progenitors markers (PDX1, PTF1A, CPA1, and MYC), and can form new organoids in contrast to ALDHlo cells. Interestingly, gene expression profiling revealed that ALDHhi cells are closer to human fetal pancreatic tissue compared with adult pancreatic tissue. Endocrine lineage markers were detected upon in vitro differentiation. Engrafted organoids differentiated toward insulin-positive (INS+) cells, and circulating human C-peptide was detected upon glucose challenge 1 month after transplantation. Engrafted ALDHhi cells formed INS+ cells. We conclude that adult human pancreatic tissue has potential for expansion into 3D structures harboring progenitor cells with endocrine differentiation potential.

CD34+ cells home, proliferate, and participate in capillary formation, and in combination with CD34- cells enhance tube formation in a 3-dimensional matrix.

OBJECTIVE: Emerging evidence suggests that human blood contains bone marrow (BM)-derived endothelial progenitor cells that contribute to postnatal neovascularization. Clinical trials demonstrated that administration of BM-cells can enhance neovascularization. Most studies, however, used crude cell populations. Identifying the role of different cell populations is important for developing improved cellular therapies. METHODS AND RESULTS: Effects of the hematopoietic stem cell-containing CD34+ cell population on migration, proliferation, differentiation, stimulation of, and participation in capillary-like tubule formation were assessed in an in vitro 3-dimensional matrix model using human microvascular endothelial cells. During movement over the endothelial monolayer, CD34+ cells remained stuck at sites of capillary tube formation and time- and dose-dependently formed cell clusters. Immunohistochemistry confirmed homing and proliferation of CD34+ cells in and around capillary sprouts. CD34+ cells were transduced with the LNGFR marker gene to allow tracing. LNGFR gene-transduced CD34+ cells integrated in the tubular structures and stained positive for CD31 and UEA-1. CD34+ cells alone stimulated neovascularization by 17%. Coculture with CD34- cells led to 68% enhancement of neovascularization, whereas CD34- cells displayed a variable response by themselves. Cell-cell contact between CD34+ and CD34- cells facilitated endothelial differentiation of CD34+ cells. CONCLUSIONS: Our data suggest that administration of CD34+-enriched cell populations may significantly improve neovascularization and point at an important supportive role for (endogenous or exogenous) CD34- cells.

Endothelial progenitor cell dysfunction: a novel concept in the pathogenesis of vascular complications of type 1 diabetes.

Type 1 diabetes is associated with reduced vascular repair, as indicated by impaired wound healing and reduced collateral formation in ischemia. Recently, endothelial progenitor cells (EPCs) have been identified as important regulators of these processes. We therefore explored the concept that EPCs are dysfunctional in diabetes. The number of EPCs obtained from type 1 diabetic patients in culture was 44% lower compared with age- and sex-matched control subjects (P < 0.001). This reduction was inversely related to levels of HbA(1c) (R = -0.68, P = 0.01). In addition, we demonstrated that patient EPCs were also impaired in function using an in vitro angiogenesis assay. Conditioned media from patient EPCs were significantly reduced in their capacity to support endothelial tube formation in comparison to control EPCs. Therefore, despite culturing the EPCs under normoglycemic conditions, functional differences between patient and control EPCs were maintained. Our findings demonstrate that adverse metabolic stress factors in type 1 diabetes are associated with reduced EPC numbers and angiogenicity. We hypothesize that EPC dysfunction contributes to the pathogenesis of vascular complications in type 1 diabetes.

Endothelial progenitor cell dysfunction in type 1 diabetes: another consequence of oxidative stress?

Endothelial progenitor cells (EPC) have been shown to contribute to neovascularization and vascular maintenance and repair in adults. Recently, the concept has evolved that EPC dysfunction, in patients at risk for cardiovascular disease, may contribute to the development of atherosclerosis and ischemic vascular disease. Particularly, patients with diabetes mellitus are likely to be affected by EPC dysfunction as several studies have shown a reduced number and function of EPC in patients, as well as in preclinical models for type 1 diabetes. Here, we review our current understanding of EPC (dys)function in diabetes and discuss some potential mechanisms underlying their altered properties. Moreover, we provide circumstantial evidence indicating that increased oxidative stress could play a role in the development of EPC dysfunction in type 1 diabetes. Finally, we discuss the potential implication of our findings for EPC-based therapies and the potential impact of pharmacological interventions on the vascular regenerative capacity of EPC.

Topologically heterogeneous beta cell adaptation in response to high-fat diet in mice.

AIMS: Beta cells adapt to an increased insulin demand by enhancing insulin secretion via increased beta cell function and/or increased beta cell number. While morphological and functional heterogeneity between individual islets exists, it is unknown whether regional differences in beta cell adaptation occur. Therefore we investigated beta cell adaptation throughout the pancreas in a model of high-fat diet (HFD)-induced insulin resistance in mice. METHODS: C57BL/6J mice were fed a HFD to induce insulin resistance, or control diet for 6 weeks. The pancreas was divided in a duodenal (DR), gastric (GR) and splenic (SR) region and taken for either histology or islet isolation. The capacity of untreated islets from the three regions to adapt in an extrapancreatic location was assessed by transplantation under the kidney capsule of streptozotocin-treated mice. RESULTS: SR islets showed 70% increased beta cell proliferation after HFD, whereas no significant increase was found in DR and GR islets. Furthermore, isolated SR islets showed twofold enhanced glucose-induced insulin secretion after HFD, as compared with DR and GR islets. In contrast, transplantation of islets isolated from the three regions to an extrapancreatic location in diabetic mice led to a similar decrease in hyperglycemia and no difference in beta cell proliferation. CONCLUSIONS: HFD-induced insulin resistance leads to topologically heterogeneous beta cell adaptation and is most prominent in the splenic region of the pancreas. This topological heterogeneity in beta cell adaptation appears to result from extrinsic factors present in the islet microenvironment.

Intravital microscopy through an abdominal imaging window reveals a pre-micrometastasis stage during liver metastasis.

Cell dynamics in subcutaneous and breast tumors can be studied through conventional imaging windows with intravital microscopy. By contrast, visualization of the formation of metastasis has been hampered by the lack of long-term imaging windows for metastasis-prone organs, such as the liver. We developed an abdominal imaging window (AIW) to visualize distinct biological processes in the spleen, kidney, small intestine, pancreas, and liver. The AIW can be used to visualize processes for up to 1 month, as we demonstrate with islet cell transplantation. Furthermore, we have used the AIW to image the single steps of metastasis formation in the liver over the course of 14 days. We observed that single extravasated tumor cells proliferated to form "pre-micrometastases," in which cells lacked contact with neighboring tumor cells and were active and motile within the confined region of the growing clone. The clones then condensed into micrometastases where cell migration was strongly diminished but proliferation continued. Moreover, the metastatic load was reduced by suppressing tumor cell migration in the pre-micrometastases. We suggest that tumor cell migration within pre-micrometastases is a contributing step that can be targeted therapeutically during liver metastasis formation.

Isolated human islets contain a distinct population of mesenchymal stem cells.

Islet replacement is a promising approach for type-1 diabetes treatment, but the shortage of organ donors demands new sources of ß-cells. The use of stem/precursor cells may represent an attractive alternative. Islet-derived stem/precursor cells (hIPC) have been isolated from human islet preparations, but neither their origin, nor their contribution to ß-cell formation in the adult pancreas, are well understood. To study these cells in more detail hIPC were isolated from purified human islets, cultured and functionally characterized. Cultured hIPC did not express the genes for endocrine hormones. These cells exhibited the capacity to aggregate and form clusters when transferred to serum-free medium. In these clusters the expression of insulin, glucagon, and somatostatin genes is induced. Human IPC lack expression of Von Willebrand Factor, CD31, CD34, CD45, and CK19 and CA19.9, demonstrating that hIPC are neither of hematopoietic, endothelial, nor of ductal origin. The mesenchymal stem cells (MSC) markers CD105, CD90, CD73, CD44, CD29, and CD13 are expressed, as well as nestin and vimentin. With the appropriate stimuli the cells can differentiate into adipocytes and osteoblasts lineages. Also hIPC express the pericyte markers CD146, NG2, αSMA and PDGF-Rß. Immunoflowcytometry revealed that human islets contain 2.0 ± 0.8% of CD105/CD90 double-positive cells. Confocal microscopy showed that these cells reside within the human islets. Altogether our data revealed the presence of a distinct MSC-like stem cell population in isolated human islets.

Is endothelial progenitor cell dysfunction involved in altered angiogenic processes in patients with hypertension?

Hypertension represents one of the most frequent modifiable risk factors for cardiovascular disease (CVD). Despite the arrival of novel antihypertensive drugs and progress in primary prevention and screening, the improvement of blood pressure control does not similarly reduce the incidence of end-organ damage associated with hypertension. Recently, the concept of reduced angiogenesis as a new CVD risk factor has gained the interest of an increasing number of investigators in the field. Indeed, pharmacologic and stem cell-based strategies aimed to induce angiogenesis seem to improve the course of ischemic vascular disease. However, few to no reports have studied the possible therapeutic potential of angiogenesis in essential hypertension. In this review, we discuss the potential involvement of endothelial progenitor cells in modulating angiogenesis and their putative therapeutic role in improving capillary rarefaction and arterial stiffness in essential hypertensive patients.