Efficacy of renal functions depends on kidney epithelial cells. Their diverse form and gene expression highlight their value by catering to the various regions of the nephron and their functions. Mouse kidney epithelial cell experiments provide an easy-to-use, cost-effective platform for research. They have facilitated the renal research, outlining the role of epithelium in health and disease. Their single-cell sequencing has particularly received attention to demarcate the different sub-populations and their contribution to tissue functions and pathology. This article takes a deep dive into renal epithelium and its role in regeneration and diseases.
Kidney Epithelial Cells
Kidneys perform a range of functions, including blood filtration, excretion, hormone production, and water homeostasis. Nephron is the structural unit that conducts these biological processes. It is composed of multiple cell populations, such as epithelial, endothelial, stromal, and immune cell types. The kidney epithelial cells drive the reabsorption by their channels and transporters in their plasma membrane. They contribute to renal immune response by displaying toll-like receptors and other immune molecules.
Due to the distinct functions of different regions of the nephron, epithelial cell modifications are present to adapt to the local functionality. For instance, channels and transporters require ATP for the transport of solutes and ions, which explains the presence of large mitochondria in the tubular region.
Types of Kidney Epithelial Cells
Podocytes
These are glomerular epithelial cells that secrete collagen to maintain the glomerular basement membrane and drive filtration selectivity. They selectively express Nphs1, Nphs2, Synpo, Wt1, and Cdkn1c. Any mutation in them can result in a renal disorder. With their distinct morphology of foot-like extension, they cover the glomerular vasculature.
Proximal Tubule
Epithelial cells of this region are the predominant renal cell type, accounting for a significant amount of the renal protein mass. They absorb the maximum amount of electrolytes and water. This high level of activity is supported by increased mitochondrial content and leaky junctions in comparison to the epithelium of other regions of the nephron. However, they also show increased sensitivity to injury.
Distal Tubule
Their epithelial cells regulate salt balance and pH. The thiazide-sensitive NaCl co-transporter is their primary identification marker and also serves as the target for thiazide diuretics. They lack aquaporins for water transport. Due to their presence in the hypoxic regions of the medulla, they have a higher capacity for anaerobic glycolysis. Loss-of-function mutation in them can cause polyuria and metabolic alkalosis.
Collecting Duct
The epithelial cells of this segment regulate electrolytes, acid-base balance, and water. They have two distinct cell types: principal and intercalated. Intercalated cells express vacuolar proton ATPase and chloride/bicarbonate exchanger. Principal cells highly express aquaporin AQP2 and vasopressin receptor (AVPR2), which assist in water transport. Antidiuretic hormone inhibits diuresis by binding to its receptor and activating adenylate cyclase, protein kinase A, and CREB, leading to the translocation of aquaporins to the plasma membrane and water reabsorption. ATP and prostaglandin E2 negatively regulate the process. Aldosterone controls the electrolyte transport of these cells.
Isolation of Mouse Kidney Epithelial Cells
The process involves the extraction of mouse kidneys, mincing them into small fragments, incubating them in an enzymatic solution (collagenase or hyaluronidase), and filtering the pieces through a nylon mesh. After centrifugation, the culture of cells, present in the pellet, on a collagen-coated culture dish yields mouse kidney primary cells. Antibody-based separation can provide specific cell populations. Additionally, selective growth media enhance the proliferation of specific epithelial cell types.
For instance, proximal tubular epithelial cells grow optimally in DMEM with Ham’s F-12 media containing transferrin, insulin, selenium, and hydrocortisone. Similarly, altering the pore size of the filter membrane can yield a particular cell type. Bigger pore sizes retain podocytes, whereas smaller diameters can wash tubular cells. Cultivating them on Transwell inserts can mimic the in vivo transport, forming apical and basal surfaces. Despite being a cost-effective method, two-dimensional cultures lose specific gene expression. Therefore, three-dimensional models are under construction.
Acute Kidney Injury
Acute tubular injury results from ischemic injury that depletes ATP levels in tubular cells, leading to cell death and direct cell death due to nephrotoxins. The injury triggers the repair mechanisms, where tubular regeneration compensates for cellular loss. However, the origin of the regenerating cells is still a debatable issue. With the dismissal of the extratubular origins, two hypotheses have emerged. One hypothesis believes in the existence of progenitors in the tubular region, and the other proposes the transient epithelial cell dedifferentiation, their proliferation, and differentiation into mature cell types.
A research group confirmed the latter hypothesis by developing a mouse model to analyze the molecular events behind regeneration. The group observed the upregulation of Sox9 in tubular epithelium, the re-entry of cells into mitosis, and the reestablishment of the epithelial barrier. Several other reports also documented similar results, suggesting that the surviving cells after injury undergo expansion.
Renal Fibrosis
It is a well-known fact that aging causes cellular senescence; however, kidney injury accelerates the senescent process. The senescent epithelial cells do not proliferate or repair. Additionally, they secrete several pro-inflammatory and pro-fibrotic factors such as TGFβ, IL-6, MMPs, etc. These factors induce senescence in the surrounding area by paracrine signaling. Furthermore, they also stimulate the differentiation of fibroblasts to myofibroblasts. The increase in matrix deposition progresses injury towards fibrosis, causing irreversible structural damage.
One of the key signaling pathways is Wnt/β-catenin/Ras. Wnt/β-catenin contributes to tissue development and repair, but it is absent in the kidney. The injury activates this pathway, leading to the expression of downstream genes. This pathway results in cell proliferation, ECM accumulation, RAAS activation, and epithelial-to-mesenchymal transition, driving the renal pathology. Downregulation of nuclear factor erythroid 2-related factor (Nrf2)/antioxidant response element (ARE) while upregulation of STAT3/NF-κB elevates the oxidative stress, advancing senescence.
Product-Related Queries, Or Partnership Inquiries
Conclusion
The high incidence and mortality rates of kidney diseases have promoted renal research. Due to the scarcity of human renal epithelial cells, mouse kidney primary cells are now frequently used as substitutes in in vitro studies. Their cells are a suitable model as a number of mouse models have been created to investigate the molecular mechanisms and genetic expression underlying renal form and function. Research with regard to kidney injury, epithelial regeneration, epithelium-cell interaction, and identification of different cell populations is underway.
It can generate new therapeutic targets, potentially leading to a definitive cure for kidney injuries. These cells are now incorporated into three-dimensional constructs to retain in vivo characteristics. Kosheeka has been accelerating renal research by providing premium-quality mouse kidney epithelial cells. The team of scientists knows the value of your research and therefore characterizes it thoroughly, along with screening it for contaminants.
FAQs
Q: Which media is suitable for culturing mouse kidney epithelial cells?
DMEM and Ham’s F-12 are used for mouse kidney epithelial cell culture. The addition of growth factors can boost the growth of a particular epithelial cell type.
Q: Why does the proximal tubular epithelium show higher sensitivity to injury?
Proximal tubular regions contain higher mitochondrial content to assist in active transport. High mitochondria also increase the susceptibility of these cells to injury.
Q: How does renal fibrosis occur?
Renal fibrosis occurs due to the excessive accumulation of extracellular matrix by renal fibroblasts during injury. It disrupts the structure and thereby the function of the kidney.
Q: What role does kidney epithelium play in renal fibrosis?
The renal epithelium secretes pro-fibrotic and pro-inflammatory factors that contribute to renal fibrosis. It also stimulates the differentiation of fibroblasts into myofibroblasts, which are responsible for the secretion of extracellular matrix.
