Glomerulus-on-a-chip to recapitulate the human glomerular filtration barrier
The unmet needs in nephrology
One of the major roadblocks for the development of successful therapeutics for chronic kidney disease depends on the ability to effectively establish 3D models that can mimic the complex structure and function of the glomerular filtration barrier.
In the majority of the current glomerular models, podocytes and glomerular endothelial cells are separated by a synthetic membrane, equipped with openings (pores) that allow free exchange of media and growth factors, but they do not allow the proper crosstalk between glomerular cells that is key for glomerular filtration barrier function.
To meet this need, researchers from Children’s Hospital Los Angeles (CHLA) developed a glomerulus-on-a-chip model composed of human podocytes and human glomerular endothelial cells in the MIMETAS OrganoPlate®, characterized by the absence of an artificial membrane and direct contact between the two cell types.
This system mimics the glomerular filtration barrier, the structure responsible for filtering the blood and preventing the loss of proteins from the body. The MIMETAS OrganoPlate® 3-lane comprises 40 microfluidic chips sandwiched between two glass plates. Each chip constitutes three lanes (Fig 1). Lane E is filled with collagen I, lane C contains the vascular and perivascular cells (endothelial cells and podocytes) of the glomerular filtration barrier, and lane F represents the urinary space of Bowman’s capsule. There is no membrane separating the different compartments, allowing for direct contact between the two different cell types and free exchange of nutrients, gasses, and growth factors between the different lanes.
Fig 1. The MIMETAS OrganoPlate® 3-lane comprises 40 microfluidic chips that allow modelling of 40 glomerulus-on-a-chip models
Therefore, the interaction of the two cell types can recapitulate the in vivo glomerular filtration barrier, composed of endothelial cells, the glomerular basement membrane, podocytes, and the urinary space of Bowman’s capsule.
The authors used three different types of podocytes of human origin in their experiments: primary podocytes, obtained from discarded kidneys harvested from patients with non-nephrological cause of death, thus the cells were healthy; immortalized podocytes, considered for many years the golden standard for in vitro cultures; and amniotic fluid-derived podocytes. They isolated primary glomerular endothelial cells from the same kidneys that were used for the primary podocytes.
The data showed that it is possible to combine human podocytes and glomerular endothelial cells with the MIMETAS technology to create a functional glomerular filtration barrier in vitro. Glomerular cells can properly interact and generate extracellular matrix, which is the major component of the glomerular basement membrane in vivo.
Fig 2. Representation of the glomerulus-on-a-chip model in the MIMETAS OrganoPlate® (GBM: glomerulus basement membrane)
These cells maintain their phenotype and function for at least a month which makes the system applicable for long-term experiments.
Glomerulus-on-a-chip mimics the function and injury manifestations of the glomerular filtration barrier
One of the main features of the glomerular filtration barrier is the permselectivity of albumin. Leakage of albumin into the urine is considered a sign of kidney dysfunction. The permselectivity of the glomerulus on-a-chip model was tested by adding a physiological concentration of FITC-conjugated albumin to the media and the results showed that this system prevents albumin leakage.
To further prove the glomerulus-on-a-chip permselectivity, they tested its capacity of filtering molecules that are freely filtered by glomerulus in vivo, such as inulin. The results showed that the developed model can filter inulin, thus confirming that the model is constituted by a functional glomerular filtration barrier that can accurately perform differential clearance, like the in vivo glomerular filtration barrier.
The glomerulus-on-a-chip can also model a kidney injury state, which was tested by exposing the system to a nephrotoxic agent that alters podocyte morphology and function. The results showed albumin leakage at similar levels for the three different types of podocytes used in our system.
Glomerulus-on-a-chip for disease modeling
In further research, the authors exposed the glomerulus-on-a-chip to sera from membranous nephropathy patients with anti-podocyte autoantibodies and the chips showed albuminuria proportional to patients’ proteinuria and signs of injury in the endothelial cells, which also occurs in endothelial cells in the glomeruli of affected patients. Altogether, these results validate this system as a feasible model to study membranous nephropathy pathophysiology in vitro.
To test disease-modeling applications, they generated a glomerulus-on-a-chip using amniotic fluid-derived podocytes from a patient affected by Alport syndrome with defective glomerular basement membrane. As predicted, chips exhibited marked and statistically significant albumin leakage, showing that the glomerulus-on-a-chip may be used to model abnormalities in vitro in the glomerular filtration barrier due to genetic abnormalities in podocytes.
Glomerulus-on-a-chip for drug screening
Glomerulus-on-a-chip represents a unique platform for screening drugs targeting the glomerular filtration barrier, as it responds to human nephrotoxic serum and nephroprotective treatment similarly to the in vivo human glomerulus.
The researchers exposed the glomerulus-on-a-chip to serum of a membranous nephropathy patient, in the presence or absence of an agent that is clinically used in membranous nephropathy patients to reduce proteinuria and the results showed that this treatment prevents proteinuria in this system as well.
They further showed that this system could replicate glucose-induced damage, by exposing it to medium containing 10, 15, and 50 mM glucose and the chips presented with a significant loss of albumin permselectivity.
Glomerulus-on-a-chip is a unique platform
Glomerulus-on-a-chip represents a transformative unique system that mimics the human renal filtration barrier. It is an ideal tool to study the pathophysiology of glomerular diseases and for drug screening studies, fulfilling major unmet needs in nephrology research.
The strong association between functional data in the glomerulus-on-a-chip and in vivo renal parameters also indicates that this system may be used as a platform to identify new biomarkers of glomerular injury in response to various stimuli and to test glomerular toxicity of new compounds.
Chips generated with diseased podocyte lines will increase our understanding of the cellular and molecular mechanisms responsible for glomerular injury and podocyte loss. Furthermore, they will advance the design and evaluation of therapeutics strategically targeted to the glomerulus. Ultimately, this will result in new treatments for patients affected by chronic kidney disease and renal failure.
- Astgik Petrosyan, Paolo Cravedi, Valentina Villani, Andrea Angeletti, Joaquin Manrique, Alessandra Renieri, Roger E. De Filippo, Laura Perin & Stefano Da Sacco. A glomerulus-on-a-chip to recapitulate the human glomerular filtration barrier. Nature Communications, (2019) 10:3656, DOI: 10.1038/s41467-019-11577-z