Therapeutic Potential of Stem Cells in Neurodegenerative Diseases

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number of cases is dramatically rising from day to day. Alzheimer’s Disease

(AD), Parkinson’s Disease (PD), Huntington’s Disease (HD), Multiple Sclero-

sis (MS), Amyotrophic Lateral Sclerosis (ALS), and Spinal Muscular Atrophy

(SMA) are the leading and most prevalent neuropathologies worldwide that

adversely affect the global economy and life quality. Despite the fact that re-

searchers are consistently studying in this field, there are still many biological

issues that need to be clarified.

Consequently, understanding the molecular mechanisms underlying the

background of neurodegeneration and developing more effective strategies are

indispensable. Herein, stem cells appear as alternative cellular sources to elu-

cidate the developmental basis through disease modeling and/or to utilize

them in cellular therapies. Various types of stem cells, such as embryonic

stem cells, mesenchymal stem cells, and induced pluripotent stem cells, are

currently the focus of many scientists and clinicians to evaluate their great

potential in both modeling and therapeutic applications. That is to say that

stem cells have become promising tools in translational medicine to bridge

the gap between molecular pathways and a definite treatment. Within this

context, prominent stem cell-based approaches for the treatment of certain

neurodegenerative disorders, which advanced the investigations at pre-clinical

and clinical levels to date, have been discussed in this chapter.

2.2

Stem Cells

Stem cells (SCs) are an unspecialized, unique population in multicellular or-

ganisms, holding two common characteristics: self-renewal and potency. Stem

cells have enormous capability of cell division, or self-renewal capacity, to am-

plify and maintain the undifferentiated SC population in the body. Potency

designates the ability of SCs to differentiate into particular cell lineages. In

other terms, potency refers to a spectrum of potential cell fates that cells are

able to commit under supporting conditions. Hereby, SCs are standing by to

give rise to essential cell types when required at any time throughout the lifes-

pan of an organism to maintain homeostasis. However, all characteristics of

SCs, including self-renewal, potency, fate decision, commitment, and differen-

tiation, are spatiotemporally orchestrated via complex internal (genetic and

epigenetic mechanisms) and external (extracellular signaling, environmental

conditions, etc.) factors [1].

One of the SC classification approaches is based on potency. Differentia-

tion capacity is narrowing while going from totipotency to oligopotency. On

the top, totipotency defines the capability to generate any embryonic cell

type along with extraembryonic structures. Zygote is the most cult example

of totipotent cells. Pluripotent stem cells (PSCs) can turn into any embry-

onic germ layer but not extraembryonic tissues. Embryonic stem cells and

induced pluripotent stem cells represent pluripotency. Certain SCs exhibit