Stem cells obey to growth and differentiating factors

http://news.sciencemag.org/biology/2014/05/young-blood-renews-old-mice?rss=1
First key GDF 11:

Rejuvenated. Reconstructions of blood vessels in an old mouse's brain (left) and in an old mouse that received young mouse blood.

And also hippocampus

http://www.nature.com/nm/journal/vaop/ncurrent/full/nm.3569.html

Or heart

http://www.medpagetoday.com/Cardiology/CHF/39018

http://phys.org/news/2014-05-closer-cell-reprogramming.html