Making Bone From Fat Cells

Adipose tissue.
Our fat contains a variety of cells with the potential to become bone, cartilage, or more fat if properly prompted. This makes adipose tissue a key potential resource for regenerative therapies such as bone healing if doctors can get enough of those cells and compel them to produce bone. In a new study, published in Stem Cell Research & Therapy, scientists demonstrate a new method for extracting a wide variety of potential bone-producing cells from human fat. They developed a fluorescent tag that could find and identify cells expressing a gene called ALPL. Expression of the gene is an indicator of bone-making potential. If the tag finds the RNA produced when the gene is expressed, it latches on and glows. A machine that detects the fluorescing light then separates out the ALPL-expressing cells.
 
In the paper, the scientists report that their method produced more than twice the yield of potential bone-makers (9 percent) compared to their best application of another method: sorting cells based on surface proteins presumed to indicate that a cell is a stem cell (4 percent). Meanwhile, the ALPL-expressing cells produced on average more than twice as much bone matrix (and as much as nine times more in some trials) during three weeks of subsequent cultivation than a similar-sized population of unsorted adipose tissue cells and almost four times more bone matrix than cells that don't express ALPL. ALPL-expressing cells were also better at making cartilage or fat.

A couple of other research groups have also sorted stem cells based on gene expression, but they have not done so specifically with the goal of enriching cell populations for a specific tissue, the researchers said. Targeting gene expression rather than surface proteins for the purpose of gathering cells to make a new tissue is a "paradigm shift" in the following regard: Gene expression provides a way to target any cell based on whether it can produce another tissue, while targeting surface proteins limits researchers to harvesting cells that fit a presumed definition of being a stem cell. The new approach is more pragmatic for the purpose.
 
In future research, the team would like to target a gene expressed much earlier in the differentiation process to see if they can avoid a priming period. If they can apply the method based on a gene that's expressible within a matter of hours, that could allow future surgeons working on bone healing to take out some of a patient's fat cells, sort out the best bone-producers (primed or not) and then implant those cells in the bone break within the same surgical session.
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