Organ Regeneration within the Human body

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Whole body regeneration (A. Hydra) vs Organ regeneration (B. Human liver)

(Source: Maranda Cardiel blog on Need a hand just grow it back)

Regeneration is the process where a tissue or an organ grows back to its normal size and function after an injury. Regeneration could be whole body regeneration such as seen in hydra or just a part of the body such as seen in star fish. A more common example of part regeneration is seen in our household. Have you ever observed the broken tail of a lizard growing back in few days? Wondering how does it happen? In simple terms it happens by the activity of several genes which promote active division of the cells to regrow the lost tissue or organ.

Can we think of the same regeneration happening with us? The answer is Yes, but definitely not our limbs but regeneration is seen in an internal organ- the liver. Liver is the only organ in the body with a regenerative potential.  The concept of liver regeneration made its mark since pre-historic times, where according to Greek mythology, the Titan Prometheus was punished by the Greek Gods by chaining him and an eagle would eat a part of his liver everyday, while the liver would regrow back overnight. Though what we see in real is not overnight but regrowth of the liver happens over a period of few days.  Even a 1/4th portion of the adult liver has the capacity to regrow to the full liver, hence liver transplantation is the only solid organ transplantation where a healthy donor can share a part of this liver with a patient who is in dire need of a liver transplantation. Post surgery, both the remaining part of liver in the donor and the part transferred to the patient, both regrow and thus one organ comes to the aid to two people. This form of regeneration where the physical loss in the tissue is replaced involves the adult mature liver specific parenchymal cells (hepatocytes) by increase in cell numbers through cell division. Hepatocytes are amongst the very few functionally mature cells which can rapidly divide when the need arises and give rise to more number of cells in a highly orchestrated and well regulated process.

Liver is the largest visceral organ of the vertebrates and essentially the metabolic factory of the body.  Of the numerous functions performed by the liver, the major ones are regulation of glycogen storage, digestion and most importantly, drug detoxification. Alcohol, drugs, toxins, chemicals etc. which are taken in finally reach the liver and are detoxified by the liver metabolic functional cells- the hepatocytes. Being the mini metabolic machines these cells (hepatocytes) are directly exposed to the toxins and are the first cells to be affected. With the constant pressure to perform and survive, these cells have the built-in capacity to divide and give rise to more number of cells. However, constant long term abuse of the liver (drug/alcohol or viral infections) leads to a chronic injury within specific zones of the liver, where the hepatocytes have a limited potential. During such times, the liver regeneration happens through special population of cells other than the hepatocytes known as the stem cells which aid in the recovery of the liver. Several research groups across the world are now working actively to use the potential of these cells as models for cell therapy and aid in liver regeneration

With the alarming rise in liver diseases across the globe, which are often fatal, there is a huge demand to probe for better regenerative mechanisms to aid in the recovery from liver diseases. Hence the challenge for the younger generations is already in place, to search for newer and efficient mechanisms for regenerative therapy of liver diseases.

 

Article by:

Dr. Chaturvedula B. Tripura

Scientist

CSIR-Centre for Cellular and Molecular Biology

Hyderabad – 500007

Email: tripura@ccmb.res.in