Characterizing the Function of Pluripotent Progenitor Cells across the Lifespan and Defining Their Abilities to Facilitate Tissue Repair and Regeneration

It has been >30 years since a series of reports indicated that pluripotent cells that exhibited the characteristics of adult stem cells could be isolated from a variety of tissue sources (brain, bone marrow, adipose tissue, and cord blood, to name a few sources). These cells were subsequently detected in nearly all tissues examined from a variety of species. While pluripotency has been demonstrated consistently in vitro, it remains challenging to obtain long-term successful outcomes when such cells were injected as free cells or tissue engineered constructs in vivo to repair or regenerate tissues damaged by injury and/or disease. The recent emergence of a body of data indicating that such pluripotent progenitor cells were localized in a variety of tissues as pericytes that were able to secrete bioactive molecules and release exosomes or extracellular vesicles containing molecules that can influence other cells in a paracrine manner led to suggestions that the role of these cells is to release such materials to maintain the integrity of tissues they are associated with in vivo. In addition, subpopulations of these cells have been shown to exhibit immunomodulatory effects when injected into both preclinical models and patients with conditions such as osteoarthritis where they appear to impact inflammation and pain in diseased joints. Additional studies have supported the concept that these cells are heterogeneous and that subsets exist that may serve different functions.
Thus, much of the complexity of these cells remains to be elucidated particularly as it relates to the various functions of subsets of these cells in different in vivo environments, their involvement at different times in the lifecycle, their roles in males versus females, as well as during pregnancy and menopause, in different species, and in different disease states. The purpose of this Special Issue is to encourage submission of manuscripts containing original data and reviews that address the functional roles and abilities of these pluripotent progenitor cells, as well as optimizing their tissue engineering potential. Submissions using model systems (in vivo and in vitro), as well as patient populations, are encouraged.