**2. Stem cells**

Stem cell research is considered one of the most promising areas in cell biology and regenerative medicine due to stem cells' unique properties of self-renewing and differentiation into all types of cells. These cells represent nowadays the main tool in the regenerative medicine field because they permit to generate cells needed for transplantation in several degenerative diseases [1], such as rheumatoid arthritis [5], diabetes mellitus [6], heart failure [7], liver diseases [8], and neurological disorders [9–11]. Moreover, stem cells represent an important tool for modeling human diseases, in particular for diseases that affect cells that cannot be easily collected and cultivated. One of the biggest issues in the study of neurodegenerative diseases is the lack of good cellular models that recapitulate the mechanisms underlying their pathophysiology, and in the last decade, stem cells played a major role in the study of these diseases.
