Therapeutic Potential of Stem Cells in Neurodegenerative Diseases

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differentiate into related cell lineages to expand the tissue and replenish dam-

aged or dead cells. As understood, ASCs are requisite for tissue maintenance,

tissue repair, growth, and development in multicellular organisms. The main

types of ASCs have been summarized below.

2.2.2.1

Mesenchymal Stem Cells (MSCs)

Mesenchymal stem cells (MSCs) are mesoderm-originated multipotent pro-

genitors that transform into a wide range of cell types, involving osteocytes,

chondrocytes, adipocytes, myoblasts, and fibroblasts. In addition to these

mesodermal cells, MSCs also have transdifferentiation capacity, which means

establishing somatic cells from different embryonic germ layers. Here, MSCs

have been reported to give rise to neurons, glial cells, epithelial cells, hepato-

cytes, and so on [4]. MSCs are easily accessible from niches in various adult

and neonatal tissues, such as bone marrow, adipose, dental tissues, menstrual

blood, umbilical cord, placental tissues, amniotic fluid, etc. [5, 6]. Even though

MSCs share common properties, but there are minor characteristic distinctions

in surface markers, differentiation capacity and plasticity, self-renewal rate,

survival time in the culture, and isolation procedures between cells taken from

different niches [5–7].

MSCs have been proven to be safe for allogenic and autologous administra-

tion by alternative delivery routes, such as systemic injection, subcutaneous

injection, intraarticular, intramuscular, surgical engraftment, intramedullary,

intraperitoneal, and intracardiac [8]. In addition to the utilization of MSCs in

tissue regeneration, they have versatile effects in vitro and in vivo. These bio-

logical functions may be carried out either directly by the cells themselves or

by the MSC-derived secretome and exosome (extracellular vesicles; EVs) [8, 9]:

1.

MSCs are able to regulate immune cell activity, proliferation, sur-

vival, infiltration, homing, and migration (immunomodulation) by

secreting several cytokines and chemokines. They also exert anti-

inflammatory effects.

2.

MSCs regulate apoptosis in neighboring cells, usually downregulat-

ing cell death (anti-apoptosis) via paracrine or contact-dependent

signaling. RNA derivatives in EVs may alter protein expression in

apoptotic pathways.

3.

MSCs promote the formation of blood vessels or vascularization,

through the release of angiogenic factors and cytokines.

4.

MSCs nurse the other stem cells and progenitor cells by modulating

their proliferation, survival, activity, homing, and mobility through

complex interactions.

5.

MSCs can secrete antimicrobial peptides to struggle pathogens.

6.

MSCs have also been reported to be resistant to several cytotoxic

agents and intriguingly migrate toward the tumor microenviron-

ment, supposing them as cellular vehicles for targeted drug delivery

[10].