The prevalence of chronic kidney disease is quickly increasing over the last few decades, due to the global increase in diabetes, and cardiovascular diseases [1]. Dialysis greatly compromises the life quality of patients, at the same time the demand for transplantable kidneys cannot be met, emphasizing the need to establish novel therapeutic approaches to stop or reverse chronic kidney disease progression [1].

Animal models and cell culture are the traditional ways of investigating kidney diseases[1]. On the other hand, 3D kidney organoids have been successfully generated from different types of source cells, including human pluripotent stem cells (hPSCs), adult/fetal renal tissues, and kidney cancer biopsies [1].

In the recent review article published by the Frontiers, Liu al et described the recent development in kidney disease modelling using organoid models, the major hurdles that have hindered the application of kidney organoids in disease modelling and drug evaluation, as well as the proposed prospective solutions. Dolly the reporter from Lab-A-Porter extracted some of the highlights from the review article while we selected some commonly used compositions and recipes of kidney organoids for your next kidney research.

• Overview of chronic kidney diseases
• Conventional models for studying kidney diseases
• Organoid models for kidney disease research
• Limitations of kidney organoids 
• Perspective solutions
• Selected compositions for kidney organoid culture recipe by Lab-A-Porter

Why chronic kidney disease and end-stage renal disease are studied?

• The global prevalence of chronic kidney disease and end-stage renal disease is increasing at an alarming rate [1].
• The clinical presentation of chronic kidney disease and end-stage renal disease is often associated with cardiovascular diseases, diabetes, and hypertension [1].
• Currently, hemodialysis and transplantation remain to be primary treatment options for end-stage renal disease [1]:
  • • Dialysis substantially reduces patients’ life quality.
    • The availability of transplantable kidneys is consistently insufficient.
    • These limitations strongly suggest that there is an urgency to develop new therapeutic approaches to fight the global burden of kidney diseases.

What are the examples of chronic kidney diseases?

• The underlying causes of chronic kidney disease can be broadly classified into genetic and non-genetic [1].
  • Genetic kidney disease includes polycystic kidney disease, glomerular nephropathy, and renal cancer [1].
  • Non-generic kidney diseases can lead to acute kidney injury, which may be caused by infections, toxic chemicals or systemic vascular complications such as diabetes and hypertension [1].

What are the conventional models for studying kidney diseases?

• Traditionally, animal models and monolayer cell cultures have been used to understand kidney development and disease [1].
  • These models have a profound impact on the way we approach disease modelling and drug discovery.
  • However, knowledge derived from traditional model systems cannot always be inferred from a human due to interspecies differences.
• Among animal models, mouse models have been heavily used to recapitulate kidney diseases due to the evolutionarily conserved developmental program and the similarity in organ architecture and physiological functions [1].

What is the limitation of using mouse models for studying kidney diseases?

1. When studying polycystic kidney disease (PKD)

• • Genetic PKD mouse models recapitulate key pathological features of PKD, however, they cannot mimic many complex mechanisms and the highly variable disease severity caused by different mutations [1].

2. When studying glomerular nephropathy

• • Glomerular nephropathy is characterized by disruption of glomerular filtration, such as focal segmental glomerulosclerosis (FSGS) and IgA nephropathy [1].
    • Genetic mouse models that recapitulate the secondary forms of focal segmental glomerulosclerosis are available, however, primary FSGS models with the unknown cause are lacking [1].
    • Besides, spontaneous ddY mouse and CD89 transgenic mouse have been widely used for modelling IgA nephropathy, however, they could not mirror complex real-life scenarios in different patients [1].
    • Moreover, spontaneous lupus mouse strain NZB/NZWF1 develops glomerulonephritis and vasculitis has been widely used for lupus study, however, the differences between mice and humans in immune system activation and response to challenge, suggest we exercise extra caution when we translate paradigms in mouse to human [1].

3. When studying diabetic nephropathy (DN)

• • Both genetic and non-genetic mouse models are available for studying diabetic nephropathy.
  • Unfortunately, the correlation between genetic background and phenotype severity in different mouse strains remains a challenge for diabetic nephropathy studies [1].

4. When studying acute kidney injury (AKI)

• • Acute kidney injury can be induced by ischemia-reperfusion injury (IRI), drug toxicity or sepsis [1].
  • The most used IRI mouse models are unstable, due to variable surgery proficiency [1].

5. When studying renal cancer

• • Renal cancer studies have used either mouse models with genetic modification of oncogenes and/or tumour suppressors, or xenograft models with tumour biopsies derived from patients [1].
  • However, these models are far from being able to recapitulate the human renal tumour microenvironment [1].

What is the limitation of using monolayer cell lines for studying kidney diseases?

1. When studying donor-specific phenotypes using patient-derived primary kidney cells

• • Limited expansion capability and complicated tissue processes have caused the generation of immortalized cell lines [1].

2. When studying podocytes

• • Monolayer cell culture, regardless of its simplicity, accessibility, and low cost, prohibited the recapitulation of disease phenotypes that involve cell-cell or cell-extracellular matrix interactions [1].

How did kidney organoids evolve?

In 2013

• • 3 studies described successful differentiation of hPSCs into metanephric mesenchyme (MM) or ureteric bud (UB) lineages that are capable of self-organizing into 3D tubular structures upon either aggregation with mouse embryonic kidney cells or co-culture with mouse embryonic spinal cord. [1]
  • Simultaneous derivation of both MM and UB from hPSCs, followed by self-organization into 3D kidney tubular structures in the absence of embryonic mouse tissue. [1]

At the end of 2015

• • 2 seminal studies described for the first time that hPSCs can be efficiently differentiated into self-assembled 3D kidney organoids. [1]
  • Substantial structural and functional characterization of hPSC-derived kidney organoids have been performed. [1]
  • These organoids are comprised of segmentally patterned nephron-like structures, stromal cells and endothelial cells, showing high similarity with human fetal kidney.
  • More, these kidney organoids presented basic functions, such as tubular reabsorption represented by proximal tubule epithelium-mediated dextran uptake and secretion of functional renin. [1]

In 2017

• • A landmark study established the successful generation of UB organoids with a single collecting duct tree, forming properly patterned renal macro-anatomy upon aggregation with mouse PSC-derived MM and embryonic mouse kidney stromal progenitor cells. [1]

In 2019

• • Clevers team developed the first protocol to generate kidney organoids, termed tubuloids, from adult human kidney tubular epithelial cells and urine-derived tubular epithelial cells. [1]
  • Kidney tumoroids recapitulate the heterogeneity of the parental tumour tissue, displaying triphasic histology of epithelial-stromal, and blastema components. [1]

What are the examples of organoid models available for kidney disease research?

• • Polycystic kidney disease (PKD)
    • PKD has been most frequently studied using hPSC-derived kidney organoids. [1]
    • PKD organoid models offer a great prospect to evaluate the therapeutic effects of candidate drugs. [1]

• • Glomerular nephropathy
    • Understanding of glomerular nephropathy is hampered by the complex 3D structure of the glomerulus and the limited proliferation capacity of podocytes. [1]
    • hPSC-derived kidney organoids provide the possibility to overcome these limitations. [1]
• • Renal cancer
• • Pathogen-renal interaction, e.g., BK virus infection, a common cause of kidney transplant failure
• • Drug-induced nephrotoxicity represents a significant contributor to acute kidney injury (AKI) and chronic kidney disease.

What are the limitations of kidney organoids for disease modelling?

• • In vitro differentiation of kidney organoids does not necessarily follow the same course as in vivo development. [1]
• • In MM kidney organoid, there is a lack of specification within each of the nephron segments, such as proximal tubular segmentation or the establishment of descending, and ascending LoH. [1]
• • Organoid variability can be attributed to the presence of off-target cells and variations in temporal maturation. [1] The relative abundance of renal and non-renal cells may also be highly variable. [1]
    • • Generic cell populations are severely under-represented in hPSC-derived kidney organoids, including different types of vascular endothelial cells, renal stroma, immune components, etc. [1]
      • Many adult-onset kidney diseases are intimately associated with these ‘non-renal’ cells.
• • The absence of immune components within organoid. [1]
• • The presented phenotypes may be over-simplified compared with in vivo scenarios. [1]
• • The lack of close-to-native macro-anatomy [1]
    • • The 3D arrangement of current kidney organoids makes it impossible to access renal function that requires higher-order organ architecture, such as renal filtration, tubular reabsorption, and urine concentration. [1]

What is the future of kidney organoids in kidney disease research?

The establishment of kidney organoids has provided tremendous opportunities for modelling various types of human kidney diseases with complex pathological phenotypes. [1]

1. Human PSC-derived kidney organoids

• Human PSC-derived kidney organoids have shown great advantages in presenting phenotypes involving complex tissue architecture while retaining patient genetic composition, guiding a new era of personalized medicine. [1]
• To focus on the limitations of hPSC-derived kidney organoids, multiple bioengineering approaches are being developed and incorporated into organoid culture [1]:
  • • Microfluidic device
      • • Has successfully facilitated vascularization and maturation of in vitro kidney organoid culture
        • Has enabled the functional interaction between nephron epithelial and vascular cells which is required for the realization of proximal tubular reabsorption and glomerular
    • Several high-throughput culture methods e.g. 3D extrusion bioprinting, microwell culture and suspension bioreactor culture
      • • To avoid inter-organoid variability, as well as to scale up organoid production

2. Adult renal tissue-derived organoids

• • Adult renal tissue-derived organoids are expected to show greater potential in modelling kidney diseases that are revealed during adulthood, in comparison with hPSC-derived kidney organoids. [1]

3. Patient-derived tubuloids

• • Patient-derived tubuloids facilitate the investigation of genetic diseases and infectious diseases. [1]

4. Healthy adult-derived tubuloids

• • Healthy adult-derived tubuloids facilitate the investigation of genetic diseases and infectious diseases. [1]
  • It may provide a novel model system for studying renal tubule regeneration. [1]

5. Kidney cancer-derived tumoroids

• • Kidney cancer-derived tumoroids represent a great option for studying tumour heterogeneity and progression, as well as for patient-specific drug validation, in comparison with animal models or cancer cell lines. [1]
  • Although much remains to be done for the efficient and consistent derivation of tumoroids from kidney cancer biopsies, patient-specific tumoroids offer exciting opportunities to investigate the interaction between tumour cells and autologous immune cells, enabling immune-oncology investigation within the tumour microenvironment and investigation of personalized immunotherapy. [1]