Regenerative medicine

iPSC derived kidney organoids

Human induced pluripotent stem cells (hiPSCs) are derived in the laboratory by reprogramming somatic cells. These can self-replicate indefinitely in culture and differentiate to all cells of the human body, including kidney cells. We make use of a unique culture protocol to differentiate these cells to intermediate mesoderm that subsequently further specializes to form kidney organoids that contain complete nephrons. These nephrons include all cap mesenchyme derived elements such as podocytes, proximal and distal tubular segments, stromal cells and endothelium. Furthermore, scanning and transmission electron microscopy analysis shows the presence of foot processes in the glomerular structures and characteristic microvilli and mitochondria in the tubular structures that have an open lumen.

Our studies show that transplantation of these nephron structures results in vascularization and maturation of these tissues and glomerular structures even start to filtrate the blood and show size size-selective glomerular sieving.

To move forward in clinical application of these kidney organoids in patients, our research focuses on the their vascularization, the expansion of these tissues in size and immune-evasive strategies for iPSCs to prevent rejection of the tissues.

With the introduction of human induced pluripotent stem cells (hiPSCs) and various differentiation protocols to rebuild human tissue for therapy, medicinal efficacy testing or disease modeling, substantial challenges remain. For organs as complex as the human kidney, its functional unit, the nephron, is composed of >10 different epithelial cell types with supporting vascular and stromal areas that are composed of an even larger array of different cells, comprehension of this complex organ during development and in health and disease has proven to be intricate. Metabolism has been proposed as driver of cell differentiation during development, where intermediates of glycolysis, oxidative phosphorylation and other biosynthetic pathways have been implicated in epigenetic control. In the healthy adult kidney metabolic pathways vary widely from one cell type to another, with tubular epithelial cells depending on mitochondrial respiration and podocytes relying on glycolysis.

To better understand the role of metabolic differences between various cells but also throughout differentiation from hiPSC to kidney organoids we have recently started to setup to unravel spatial metabolic programs. We developed, in collaboration with the LUMC Center of Proteomics and Metabolomics, a novel approach to characterize cellular metabolism at single cell resolution in association with phenotypic and transcriptomic characteristics using high spatial resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry imaging (MALDI-MSI) to detect metabolites and lipids directly on tissue.

The increasing prevalence of noncommunicable diseases such as diabetes and hypertension have caused an alarming increase in chronic kidney disease (CKD). Augmenting the capacity of the kidney to regenerate intrinsically is a major challenge that could prevent irreversible kidney failure. While the cells of the Renin-Lineage (CoRL) play a critical role in regulating blood pressure and fluid and electrolyte homeostasis, recently they were also found to be a niche of pluripotent progenitor cells that can replace injured kidney tissue. This newly discovered intrinsic mechanism of regeneration may provide a promising therapeutic target to prevent the development of CKD. By modulating the physiological hemodynamic microenvironment we aim to stimulate CoRL to switch from a physiological phenotype to a progenitor phenotype that facilitates intrinsic kidney regeneration.

Amongst others, we found evidence that microRNAs coordinate a post-transcriptional regulatory network that drives the regenerative phenotype of the CoRL. By implementing in vitro and in vivo approaches involving mouse models that allow fate-tracing of CoRL (and conditional knockout models as well as knockdown/overexpression strategies), we aim to demonstrate that modulation of (post)transcriptional regulation can stimulate the regenerative capacity of the CoRL. Taken together, the regenerative switch of the CoRL provides the kidney with an elegant mechanism to translate impaired kidney function into a reparative response. Our studies aim to provide novel options to modulate the intrinsic regenerative capacity of the kidney for the development of innovative approaches to counteract CKD.

The insulin-producing beta cells in the Islets of Langerhans of the pancreas play a key role in all types of diabetes mellitus. The islets of Langerhans are the main focus of both clinical and basic research projects. The Islet group started in 2006 when a human islet isolation laboratory was established in the Leiden University Medical Center followed by a clinical islet transplantation program in 2007. This enabled the establishment of basic and clinical research programs involving human islet cells. Basic research focuses on human islet cell identity, islet survival and function, and strategies in order to generate new insulin-producing cells. Clinical research is focused on improvement of current human islet isolation and beta cell replacement therapy, and on assessment of islet function and damage in patients with severe beta cell failure (in particular type 1 diabetes). The following topics are key areas of research:

Human islet isolation and clinical beta-cell replacement therapy
Diabetes due to loss and/or failure of the insulin-producing beta cells (in particular type 1 diabetes, but also severe forms of chronic pancreatitis (cystic fibrosis), or pancreatectomy) requires administration of exogenous insulin and is usually associated with instable glycemic control compared to patients with substantial residual beta cell function. Patients with severe beta cell failure due to type 1 diabetes often develop this disease at a young age. Beta cell replacement is the only therapeutic modality to restore normal sugar levels without the risk of hypoglycemia side effects. In the LUMC beta cell replacement is an integrated program consisting of pancreas transplantation (since 1984) and islet transplantation (since 2007).

Our research focuses on improvement of human islet isolation and transplantation outcome. Areas of research include pancreas preservation strategies and new techniques to isolate human islets. Preclinical studies on human islets are performed to improve islet survival. And novel immunosuppressive regimes and peri-transplant strategies are tested. In collaboration with the group of Aart van Apeldoorn (University of Maastricht) preclinical studies are performed using scaffolds in order to create alternative transplantation sites and improve islet function and survival. This work was also part of the Diabetes Cell Therapy Initiative, a Dutch consortium focused on improvement of islet transplantation, coordinated by our group.