BACKGROUND
Kidney-on-a-chip devices offer the promise to revolutionize the study of disease and the pre-clinical testing of drug compounds, as they possess several advantages over animal models. Since the kidney is a complex organ containing multiple cell types with different roles and functionalities, devices usually recapitulate certain renal structural elements (e.g. tubular structure, collecting duct, proximal tubule, glomerulus) that may be involved in disease. At the glomerulus, podocytes comprise an important part of the filtration barrier and breakdown of their sophisticated branching pattern has been linked to a significant proportion of kidney diseases. Challenges to podocyte organ-on-a-chip (OOC) systems include immature phenotypes and a lack of comprehensive readouts of podocyte function.
TECHNOLOGY
Researchers at the University of Toronto have developed an organ-on-a-chip system to reflect the fractal, branching nature of the glomerulus. They started with the glomerular structure and, through a sequence of steps, generated a slice of the branching glomerular pattern (Figure 1). This pattern can be moulded into the base of cell culture wells in an out-of-plane fashion to give a 2.5-Dimensional system. Podocytes can then be grown in the wells, after layering the surface with Collagen I, whereupon the podocytes are then subjected to the more native microscale curved shape cues experienced in the glomerulus. Furthermore, they have coupled this OOC system to a “Mosaic assay” to provide an easy readout of podocyte health and function. In this assay, a fraction of podocytes is selectively labelled with GFP enabling identification of multiple-level branching and interdigitation of podocyte foot processes.
Figure 1. Steps involved in the fabrication of a biometic 2.5-D scaffold for podocyte culture.
COMPETITIVE ADVANTAGE
- Fractality better mimics the glomerular structural environment
- Increased maturity and development of podocytes with increasing fractality (reached ~ 1/4 stage of developmental maturation as compared to native podocytes)
- Expression and cytoplasmic localization of key proteins increased
- YAP1, p-ILK, Nephrin, Podocin, CD2aP, Synpo, and F-actin expression increased ~ 35%-100% and the cytoplasmic/nuclear localization ratio generally increased ~ 60-100% compared to 2D culture
- Cytoskeletal branching increased; evidence of interdigitated foot processes
- Gene expression profiles significantly changed with increasing fractality
- 2169 genes significantly different compared to 2D culture
- Increased maturation (measured by Pluritest)
- Gene expression increases corresponded to relaxation/contractility and protein localization/organization processes, as well as developmental and membrane morphology processes
- Expression and cytoplasmic localization of key proteins increased
- Easy readout of podocyte health and function through the “Mosaic assay”
- Easy to manufacture
- Compatible with standard 2D approaches in cell culture
APPLICATIONS
- Research and study of diseases related to podocyte dysfunction
- Minimal change disease, focal segmental glomerulosclerosis, diabetic nephropathy, membranous nephropathy and lupus nephritis
- Serological diagnosis – diseases caused by injurious serum circulating factors
- E.g. Recurring from non-recurring FSGS kidney disease
- Fractality may extend to other tissue engineering and regenerative medicine applications
INTELLECTUAL PROPERTY
- Provisional filed (June, 2022)
PROJECT STATUS
Proof-of-concept studies have been conducted. High and low fractal models reflective of glomerular structure were constructed, along with appropriate controls. Podocytes were cultured on the OOC devices and the impact of fractality on podocyte health and functionality characterized by assessing structural and proteomic differences. The podocyte OOC system was then tested as a research model by assessing the impact of several inducers (i.e. coronaviruses and a drug) of kidney dysfunction.
