Mammalian kidney identified as a ‘blood-generating’ organ for the first time.


Kidney failure is a growing problem in the United States, every year, approximately 10,000 kidneys become available for transplant into patients with end-stage kidney disease.  However, the waiting lists for kidney transplants can run as high as 100,000 individuals, so the majority are treated with dialysis. The therapy, though life-saving, can be inconvenient for patients and itself causes accelerated heart disease. The risk of death for an average dialysis patient is 20% per year, with techniques to grow new kidneys to-order, a priority.

However, the challenge of growing a kidney is that it is a very complicated organ; with hundreds of different types of cells needed in the exact configuration for the kidney to work.  Now, researchers at the University of Virginia have identified the cells that give rise to the blood vessels and blood within the kidney, a significant step toward growing replacement kidneys. The team state that their findings are of critical importance, as efforts to grow kidneys have long been frustrated by the inability to create the vasculature necessary for a functional organ.

Previous studies show that researchers have long been able to grow kidney tissue in a lab dish, successfully forming various components of the organ. Within the embryonic kidney, several putative progenitors marked by the expression of either the winged-forkhead transcription factor 1, the aspartyl-protease renin, and/or hemangioblasts are likely to differentiate and endow most of the cells of the renal arterial tree. However, the lineage relationships and the role of these distinct progenitors in renal vascular morphogenesis have not been delineated.  Without the understanding of how the normal vasculature develops, researchers cannot reproduce or force cells to make it.  The current study identifies the stem cells that develop into the vessels, and provides a target to manipulate to produce complete organs.

The current study identifies the cells which form the inner layer of the kidney and an important molecule that regulates the development of the kidney vasculature.  The lab state that they have finally found the precursor to these cells, so the next step is to determine the controllers.  As they were doing their work, the group noted something very unusual about the formation of the vessels in the kidney; as they formed, so did the blood they contained.  Results show that when the vessels are created, so is the blood that fills them. The team state that, to their knowledge, it had not been known that the kidney was a blood-generating organ; blood generation occurs within the kidney in fish, however, this is a notable discovery in mammals.

The team surmise that a characteristic of this new precursor is that it can also make blood cells, not only the endothelial layer, the inner layer of the vessel.  They go on to add that rarely is this found in organs, and for the first time this phenomenon has been identified in the developing mammalian kidney.  For the future, the researchers state that this knowledge will be crucial in the replacement therapy or making a functioning kidney from cells from a patient.

Source: UVA Health System

 

Arterial vasculature of the rat kidney filled with Microfil. Longitudinal section. The vascular patterns of the cortex and the three zones of the medulla are distinctly different.  Vascular-tubular relationships in the mammalian kidney.  Credit: Lise Bankir.

Arterial vasculature of the rat kidney filled with Microfil. Longitudinal section. The vascular patterns of the cortex and the three zones of the medulla are distinctly different. Vascular-tubular relationships in the mammalian kidney. Credit: Lise Bankir.

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