Markers for the Characterization of Liver Mesenchymal Stem Cell

Mesenchymal stem cells (MSCs) have the characteristics of self-renewal, immune regulation and multipotency. Due to their multi-lineage differentiation potential [1], MSCs can be induced to differentiate into adipocytes, osteoblasts, chondrocytes, muscle cells, nerve cells, liver cells and pancreatic beta cells in vivo and in vitro. These characteristics make MSCs promising candidates for use in cell therapy and regenerative medicine [24]. MSCs were first described as stromal stem cells from the bone marrow that have a spindle shape in culture. However, although the bone marrow is considered the standard source for MSCs, MSCs isolated from other sources have different features in terms of surface markers, proliferation rates, and differentiation capability [5-7]. MSCs have been isolated from a number of other sources, such as adipose tissue, dental pulp, umbilical cord blood, and amniotic fluid [8-10]. One alternative source for MSCs is liver tissue. Scientists have isolated liver mesenchymal stem cells (LMSCs) from different species and attempted to characterize them in hopes that these cells could be a better alternative to bone marrow mesenchymal stem cells (BMSCs), especially for liver diseases [8]. One of the challenging aspects concerning MSCs in general is their characterization. In this mini-review, we will focus on studies that characterized LMSCs from different species, such as humans, mice, rats, rabbits, sheep, chickens and cattle. Human LMSCs and human BMSCs


Introduction
Mesenchymal stem cells (MSCs) have the characteristics of self-renewal, immune regulation and multipotency. Due to their multi-lineage differentiation potential [1], MSCs can be induced to differentiate into adipocytes, osteoblasts, chondrocytes, muscle cells, nerve cells, liver cells and pancreatic beta cells in vivo and in vitro. These characteristics make MSCs promising candidates for use in cell therapy and regenerative medicine [2][3][4]. MSCs were first described as stromal stem cells from the bone marrow that have a spindle shape in culture. However, although the bone marrow is considered the standard source for MSCs, MSCs isolated from other sources have different features in terms of surface markers, proliferation rates, and differentiation capability [5][6][7]. MSCs have been isolated from a number of other sources, such as adipose tissue, dental pulp, umbilical cord blood, and amniotic fluid [8][9][10]. One alternative source for MSCs is liver tissue. Scientists have isolated liver mesenchymal stem cells (LMSCs) from different species and attempted to characterize them in hopes that these cells could be a better alternative to bone marrow mesenchymal stem cells (BMSCs), especially for liver diseases [8]. One of the challenging aspects concerning MSCs in general is their characterization. In this mini-review, we will focus on studies that characterized LMSCs from different species, such as humans, mice, rats, rabbits, sheep, chickens and cattle.

Human LMSCs and human BMSCs
The International Society of Cell Therapy (ISCT) states that cultured human BMSCs are positive for expression of CD105, CD73, and CD90 and negative for expression of CD11b or CD14, CD19 or CD79a, CD34, CD45, and HLA-DR (11). CD105 is TGFbeta receptor III, which plays a role in TGF-beta signalling during differentiation into chondrocytes [12]. CD73 is known to be involved in MSC migration and to modulate adaptive immunity [13,14].
CD90 plays roles in mediating cell-cell interactions and leukocyte adhesion to endothelial cells [15,16]. Human LMSCs are also positive for expression of CD105, CD73 and CD90 Table 1. However, Najimi et al. [17] reported that LMSCs have low expression of CD105, and most other studies reported that LMSCs are positive for CD105. Additionally, LMSCs are positive for expression of CD44, CD29, CD166, and CD146, which is consistent with BMSC expression patterns [18][19][20].

International Journal of Cell Science & Molecular Biology Conclusion
Many markers have been tested on LMSCs, especially on human and mouse samples, and BMSCs and LMSCs have been reported to share most markers. However, additional studies are required to establish a standard panel of positive/negative markers for LMSCs, and studies are also required for further characterization of LMSCs from other species, especially species that are used as in vivo models for many diseases.

Data Availability
The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
The authors have no conflicts of interest.