Accumulation of senescent cells in tissues is the main catalyst of aging in humans. Old cells have altered gene expression, highlighted by a strong increase in secreted cytokines, chemokines and extracellular proteinases known as the senescence-associated secretory phenotype (SASP) which has a negative impact on skin and epidermal stem cells (ESC). Expression of the enzyme telomerase prevents cell aging and maintains their young phenotype. In this project we will explore the potential for skin regeneration and rejuvenation by using a cell micro-seeding technique. We will analyse changes in the skin following an increase in proportion of young or rejuvenated healthy cells in a rat skin model and in human organotypic epidermal equivalent model. This will be achieved by introducing a large proportion (>35%, up to 55%) of young cells or telomerase revitalized cells into skin. We expect to observe increase in regenerative capacity of dermis and epidermis as well as increase in ESC viability. Besides aging, various genetic disorders can disrupt protective function of the skin. Among most severe of such disorders is Epidermolysis bullosa (EB). EB is a heterogeneous group of hereditary skin fragility disorders caused by mutations in 18 different genes important for dermal-epidermal connections, among which is Collagen VII (C7) that anchor the basal membrane. Affected animals have fragile and blister-prone skin showing all major signs of EB in humans. Therefore we will also analyse changes in the EB rat skin following an increase in proportion of cells carrying wild type C7. So far we have established a protocol for micro-transplantation of cells into skin tissue which allows for manipulation of various cell populations. The main objective of this project is to directly show that it is possible to alter the cellular composition of tissues and with that alter the local tissue metabolic profile, improve viability of ESC in vivo and increase skin healing and regeneration.