During lifetime, the human organism is exposed to a progressive decline in organ function and regeneration considered as the ageing process. Several age-associated diseases such as cardiovascular- and neurodegenerative diseases or cancer are described along with their cellular pathologies. Although tissue regeneration substantially relies on the functionality of endogenous adult stem cell populations found in various organs including the heart, a complex interaction with systemic factors carried by the blood is evident. Thus, young blood or blood products are increasingly recognized as potential therapeutic agents to target age-associated malignancies. In this regard, prominent studies in the murine model gained attention by rejuvenating old mice with blood or blood products from young mice. However, the transition of these promising results to the human system remains challenging. Here, adequate cellular models need to be established to study the effects of human blood plasma on the regeneration of human tissues and particularly the heart.

Facing this challenge, this thesis describes the age-specific effects of human blood plasma and blood serum on a human cardiac stem cell (hCSC)-based model for heart regeneration in terms of proliferation, migration, senescence, and global gene expression. Here, the identification of a novel multipotent hCSC population from the heart auricle of patients undergoing routine cardiac surgery enabled the establishment of a cellular model to study human cardiac regeneration. These cells can easily be isolated and expanded in culture and express common markers for cardiac stem cell populations. Moreover, hCSCs showed neural crest-specific stem cell markers and high transcriptional similarities with a known neural crest-derived stem cell population. Their differentiation capacities into mesodermal as well as neuro-ectodermal derivates further suggest a potential relation to the neural crest. Treatment of hCSCs with human plasma and serum greatly induced their proliferation with no significant differences regarding age and sex of the plasma donors. In contrast, age-dependent effects were detectable in the serum-mediated protection against senescence with serum from old (> 60 years) female donors showing the highest rate of protection compared to male or young female donors. Further, the migrative capacities of hCSCs in terms of migration distance and velocity were significantly increased after serum treatment. A global transcriptomic analysis of serum-treated hCSCs revealed an age-dependent increase of differential gene expression in hCSCs treated with young sera compared to untreated cells and the upregulation of genes associated to the p38 mitogen-activated protein kinase (p38-MAPK)-pathway. Pharmacological inhibition of p38-MAPK significantly reduced the beneficial effects of human blood serum in terms of decreased proliferation and migration as well as increased senescence. Next to its beneficial effects on the successfully established cellular model system for cardiac ageing and regeneration, human serum was applied to *ex vivo* cultured mouse hippocampal slices as an experimental model for neurodegenerative diseases. Here, human blood plasma as well as human serum albumin (HSA) as the most abundant plasma protein revealed significant neuroprotective effects against kainic acid (KA)-mediated neuronal cell death compared to untreated hippocampal slice cultures.

In summary, the here presented results show the identification of a novel hCSC population and its developmental relation to the neural crest as well as its successful application as a screening system for human blood plasma-mediated regenerative responses. On functional level, p38-MAPK was identified as crucial mediator of the blood-plasma-based induction of hCSC-proliferation and -migration as well as protection of hCSCs against senescence. Future studies will carefully investigate the regulatory mechanisms upstream and downstream of p38-MAPK signaling in serum-treated hCSCs and might enable the identification of the responsible plasma components. Finally, this work provides valuable insights into the beneficial effects of human blood plasma on the regenerative function of adult human cardiac stem cells and builds a basis for the potential clinical use of human blood plasma as well as cardiac stem cells in regenerative medicine.