October 28, 2011

Rejuvenating Old Eggs

By Alicia Rose DelGallo, Ivanhoe Health Correspondent

(Ivanhoe Newswire) — The accepted view of female reproduction includes a pre-determined amount of eggs in the ovaries. This population of eggs becomes depleted over time, resulting in infertility among older women. Jonathon L. Tilly, PhD, Director of the Vincent Center for Reproductive Biology at MassGeneral Hospital and professor at Harvard Medical School, presented new ideas about ovarian cells at the 67th annual meeting of the American Society for Reproductive Medicine.

Tilly spoke about germ line stem cells, or oogonial stem cells (OSCs), found in the ovaries of mice. Germ Line stem cells are typically associated with the male reproductive system, continually renewing the sperm pool.

In the study, Tilly removed the ovarian stem cells from aged mice and exposed them to a young adult mouse ovary. The aged germ line stem cells reactivated. They began making new oocytes, immature versions of eggs.

”The cells persist after dormancy and their dormancy is reversible,” explains Tilly. “It raises the prospect that ovaries failing as a consequence of age aren´t necessarily an irreversible event.”

Based on his findings, Tilly thinks young women may be able to bank rare ovarian stem cells that can be transplanted back into their bodies later when their supply has diminished because of age.  He adds that these stem cells contain very little cytoplasm, so they are able to freeze and thaw with significantly lower damage than mature ovarian eggs.

Other factors Tilly said are involved in the aging of ovarian cells include caloric intake and mitochondria activity.

“A critical threshold number of mitochondria are required for mammalian reproduction, this number lowers with age,” Tilly said. “We may be able to use OSCs to screen for factors that enhance mitochondrial numbers or activity in female germ cells.”

Tilly and his colleagues hope to continue their research with OSCs based procedures to improve and restore female fertility and IVF success.

A phase II study is completed and will be published soon.

SOURCE: ASRM 2011, Orlando FL