Stem Cell Aging and Reprogramming: Implications for Regenerative Medicine

Cardiovascular disease is the leading cause of mortality worldwide.
Regarded as the therapeutic gold standard, treatment
with autologous grafts suffers from several technical and
patient-related risks. Tissue-engineered small-diameter blood
vessels may provide a promising alternative solution as replacement
grafts. In this study, we employed adult and induced
pluripotent stem cells to engineer fully functional vascular grafts
that were implanted into the arterial circulation of a physiologically
relevant ovine animal model, where they remained patent
and underwent successful remodeling. During the course of
these studies we observed that mesenchymal stem cells (MSC)
originating from older donors suffer from limited proliferative
capacity and signifi cantly reduced myogenic differentiation
potential. This is a major concern, as the patients most likely to
suffer from cardiovascular disease are elderly and are in need
of vascular grafts.

Notably, we discovered that delivery of a single pluripotency
associate transcription factor, Nanog, reversed the proliferation
and differentiation potential of MSC from adult donors. I will
present data supporting this claim and our efforts to understand
the mechanism of how Nanog promotes myogenic differentiation,
contractile function and extracellular matrix synthesis
of senescent MSC. In addition to MSC, we recently discovered
that Nanog restored the ability of senescent skeletal muscle
cells (SkMC) to form myotubes, suggesting that molecular engineering
strategies can reverse the effects of organismal aging
and restore the potential of adult stem cells for use in cellular
therapies and tissue regeneration.

In the second part of my presentation I will focus on reprogramming
of skin cells to neural crest stem cells (NC) and their
derivatives. NC cells are induced by signaling events at the neural
plate border during development of vertebrate embryos.
Initially arising within the central nervous system, NC cells subsequently
undergo an epithelial to mesenchymal transition to
migrate into the periphery, where they differentiate into diverse
cell types. We discovered that postnatal human epidermal
keratinocytes (KC) can be reprogrammed toward the NC fate
without genetic modifi cation or reprogramming to the pluripotent
state. Genome-wide transcriptome analyses show that
KC-derived NC cells are similar to NC cells derived from human
embryonic stem cells. Moreover, KC-NC give rise in vitro and in
vivo to NC derivatives such as peripheral neurons, melanocytes, Schwann cells and mesenchymal cells (osteocytes, chondrocytes, adipocytes, and smooth muscle cells). Lineage tracing studies by implantation of KC-NC into chick embryos confirmed
the NC phenotype of these cells. This work represents a paradigm
shift, as it demonstrates the plasticity of human epidermal
cells to be reprogrammed into cells of common developmental
origin — both originate from the ectoderm — without genetic
modifi cation and under defi ned culture conditions. Finally,
our work has the potential to provide a novel source of abundant,
readily accessible, autologous stem cells for treatment of
neurodegenerative diseases, for which cell sourcing remains a
severe impediment, hampering cell therapy approaches.