Fluorescence light micrograph of human stem cells derived from adipose (fat) tissue. Photo by Riccardo Cassiani-Ingoni/SPL
Human fat cells can be used to regenerate damaged hearts and ageing joints. So should we start piling on the pounds?
by Jalees Rehman
(Jalees Rehman is an associate professor of medicine and pharmacology at the University of Illinois at Chicago. He blogs on stem cell biology and regenerative medicine at SciLogs: The Next Regeneration, and on science, culture and religion at Fragments of Truth.)
Why don’t you use fat?’
I stared at Keith, not quite sure whether he was serious or just kidding. Did he really think we could use fat to regenerate the heart?
I had joined Keith March’s research laboratory at Indiana University as a postdoctoral fellow in the summer of 2001. At the time, his group was trying to improve upon stents, small mesh tubes that can be placed inside blocked coronary arteries to keep them open, restoring an adequate supply of blood and oxygen to the heart. But even the best stents were no cure for heart tissue that had already been irreversibly damaged by a heart attack. The wave of the future, I felt, was the newly emerging field of cardiovascular regeneration, the idea of using stem cells to repair the heart and grow new blood vessels.
Yet when Keith suggested I use fat to generate those cells, I thought he was making an inside joke. We were both overweight and often made fun of ourselves. And the history of fat cures was rife with superstition and myth. For centuries, people had believed that rubbing one’s arms and legs with balms made out of human fat could cure broken bones, crippled limbs and joint pains. Societal mores prevented the dissection of human bodies for the purpose of removing human fluids or tissues, but these rules didn’t apply to executed criminals, especially when there were no family members to claim the body. Until the mid-18th century, this presented a lucrative opportunity for a group of social outcasts: executioners, who became expert extractors, with a skill-set and knowledge of anatomy that often surpassed that of academic physicians. In her book, Defiled Trades and Social Outcasts (2000), the historian Kathy Stuart from the University of California, Davis, gives a gripping account of the work and lives of executioners. Some executioners even started their own medical practices, selling products such as human fat themselves.
Today we understand that rubbing human fat on one’s limbs lacks any medical benefit – yet there was Keith suggesting that fat could be rediscovered as a therapeutic source of material to regenerate the heart. I took him seriously only after he showed me a paper written in 2001 by the cell biologist Patricia Zuk and her colleagues at the Regenerative Bioengineering and Repair Lab then run by Marc Hedrick at the University of California, Los Angeles (UCLA). Analysing fat obtained through liposuction, the team of researchers and plastic surgeons had discovered an abundance of adult stem cells! It was an extraordinary find: it was in part the scarcity of adult stem cells, after all, that had stymied organ regeneration efforts in the past.
Stem cells can be tapped as engines of regeneration because they have not yet committed to a specific cell fate. They are so pliable that they can be converted into a variety of prized cell types, such as neurons or beating heart cells, if exposed to the proper chemical and environmental cues in the lab. That makes them ideally suited to repair or regenerate diseased organs and tissues. For example, if the heart is damaged and scarred by a severe heart attack, stem cells could be used to replace the scar tissue with beating heart muscle cells (cardiomyocytes).
In 2001, researchers had access to two types of human stem cells: embryonic stem cells and adult stem cells. The advantage of using embryonic stem cells is that they can be converted into every major cell type required for organ or tissue regeneration: liver cells, neurons, or cardiomyocytes, to name just a few.
Yet use of human embryonic stem cells, generally derived from leftover fertilised eggs culled en masse from fertilisation clinics, has long been controversial in the US, even compared by some religious groups to murder. In response, in August 2001 the government restricted use to the few human lines of embryonic stem cells already cultured in labs…