Introduction

Mesenchymal Stem Cells (MSCs) are amongst non-hematopoietic cell types present in various tissues, varied from bone marrow and umbilical cord to adipose tissues [1]. The bone marrow mesenchymal stem cells were initially isolated by Friedenstein during mid-1970 decade [2]. MSCs are a heterogeneous subgroup of stromal stem cells presenting behaviours of non-hematopoietic multi-potential cells including the capacity of self-renewality which are able to differentiate into different types of mesodermal, ectodermal, and endodermal tissues, especially bone, fat, and cartilage. They phenotypically are fibroblastic or spindle-shape in culture media and adhere to the culture flask. Approximately, over 90% of MSCs express CD73, CD90, and CD105 whilst CD34, CD45, CD11b, CD14, CD19, CD79a, HLA-DR, CD80, and CD81 are expressed on less than 2% of MSCs membrane [3,4].

Several various applications have been demonstrated for MSCs, based on in vitro and in vivo studies, animal models, and clinical practices [5,6]. A large body of evidence exists regarding the efficiency of MSCs in regenerative medicine, tissue engineering, and immunotherapy [7,8]. The increased expression of antitumor genes is achieved by MSCs genetic modification and this in turn paves the path for successful application of MSCs as anticancer therapies in clinical practice [9]. Simple in vitro culture is an advantage of MSCs, so that their seeding, maintenance, and proliferation becomes cost-effective, they are easily extracted from various sources, and their handling is a convenient task [10].

Despite all of the mentioned benefits and features, MSCs are not immortal and have limited life span in vitro [11,12], exhibiting aging processes accompanied by lower proliferation potential and morphological changes following a certain number of passage (about 6-12) [13,14]. To date, multiple various methods have been proposed for resolve in above-mentioned problems; however, they have their own advantages and disadvantages. Most studies have been undertaken to increase proliferation rate, life span, in addition to immortality of MSCs. These investigations have supported the transfection of genes involved in increasing proliferation and lifetime of MSCs [15]. As an instance, different studies have used viral methods to induce hTERT gene expression and inactivate P16 (cell proliferation inhibitor) gene, which are involved in the immortalization process and higher lifespan of MSCs. These methods contribute to the survival of virus inside the cell but are costly and time consuming [16]; therefore, studies have focused on non-viral methods.

LG-DMEM (Low Glucose-Dulbecco's Modified Eagle Medium) containing 10% FBS (fetal Bovine serum) and 1% PenicillinStreptomycin is known as a conventional culture medium for mesenchymal stem cells for long time [17]. The Serum Rich in Growth Factors (SRGF) and platelet lysate (prepared by centrifugation of platelet products) are both able to provide good conditions for cell growth and affect the expression of genes involved in MSCs proliferation and longevity due to the fact that SRGF contains many growth factors and proteins [18,19]. Growth factors such as TGF-b, b-FGF, PDGF-A, B, and EGF that are all present in platelet granules play pivotal parts in stimulating of MSCs and epithelial cells proliferation [20].

Considering the paramount importance and prominent parts played by MSCs in cell therapy, hematopoietic stem cell transplantation, improvement of clinical symptom of various diseases, and their limited lifespan properties and benefits of SRGF, this study was aimed to investigate the SRGF impacts on the expression of c-Myc, P16, P53 and hTERT genes in MSCs, as major genes involved in proliferation and longevity of the MSCs isolated from the umbilical cord.