Biological complexity: kidney cells self-renew (Introduction)

by David Turell , Saturday, July 15, 2023, 13:29 (287 days ago) @ David Turell

Pinch it off to throw it out:

https://www.sciencedaily.com/releases/2023/07/230713192852.htm

"Scientists have discovered a previously unknown 'housekeeping' process in kidney cells that ejects unwanted content, resulting in cells that rejuvenate themselves and remain functioning and healthy. The self-renewal process, which is fundamentally different from how other bodily tissues are thought to regenerate, helps explain how, barring injury or disease, the kidneys can remain healthy for a lifetime.

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"Unlike the liver and skin, where cells divide to create new daughter cells and regenerate the organ, cells in the proximal tubules of the kidney are mitotically quiescent -- they do not divide to create new cells. In cases of mild injury or disease, kidney cells do have limited repair capabilities, and stem cells in the kidney can form new kidney cells, but only up to a point, said Dr. Jie Zheng, professor of chemistry and biochemistry in the School of Natural Sciences and Mathematics

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"Research has shown that gold nanoparticles generally pass unscathed through a structure in the kidney called the glomerulus and then travel into proximal tubules, which make up over 50% of the kidney. Proximal tubular epithelial cells have been shown to internalize the nanoparticles, which eventually escape those cells to be excreted in urine. But just how they escape the cells has been unclear.

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"'Using the EM, we saw gold nanoparticles encapsulated in lysosomes inside of large vesicles in the lumen, which is the space outside the epithelial cells," Yu said.

"Vesicles are small fluid-filled sacks found both inside and outside of cells that transport various substances.

"'But we also observed the formation of these vesicles containing both nanoparticles and organelles outside of cells, and it was not something we had seen before," Yu said.

"The researchers found proximal tubular cells that had formed outwardly facing bulges in their luminal membranes that contained not only gold nanoparticles but also lysosomes, mitochondria, endoplasmic reticulum and other organelles typically confined to a cell's interior. The extruded contents were then pinched off into a vesicle that floated off into the extracellular space.

"'At that moment, we knew this was an unusual phenomenon," Yu said. "This is a new method for cells to remove cellular contents."

"The extrusion-mediated self-renewal mechanism is fundamentally different from other known regenerative processes -- such as cell division -- and housecleaning tasks like exocytosis. In exocytosis, foreign substances such as nanoparticles are encapsulated in a vesicle inside the cell. Then, the vesicle membrane fuses with the inside of the cell's membrane, which opens to release the contents to the outside.

"'What we discovered is totally different from the previous understanding of how cells eliminate particles. There is no membrane fusion in the extrusion process, which eliminates old content from normal cells and allows the cells to update themselves with fresh contents," Huang said. "It happens whether foreign nanoparticles are present or not. It's an intrinsic, proactive process these cells use to survive longer and function properly.'"

Comment: a new method for automatic cellular garbage disposal to preserve kidney function for life.