Tissue repair and regeneration following injury or disease are often thought to recapitulate embryonic development by using similar molecular and cellular pathways. In addition, many embryonic tissues, such as the spinal cord, heart, and limbs, have some regenerative potential and may utilize mechanisms that can be exogenously activated in adult tissues. For example, BMP signaling regulates nervous system development, and SMAD reactivation plays a critical role in adult nerve regeneration and repair in animal models of spinal cord injury. While similar molecular pathways are utilized during embryogenesis and adult tissue regeneration, recent reports suggest the mechanisms by which these developmental programs are reactivated and maintained may vary in adult tissues.
Adult fish and amphibians have a remarkable capacity for tissue regeneration, while mammals have a limited regenerative capacity. Given the shortage of organs available for transplant, tissue engineering may be an alternative. Recent studies have described the ability of tissue-resident adult (somatic) stem cells to repopulate organs such as the liver and pancreas. Additionally, induced pluripotent stem cells have demonstrated potential for repair and regeneration of diverse tissues including the heart following ischemia, retinal pigmented epithelium in studies of age-related macular degeneration, and pancreas following loss of insulin-secreting beta-cells.