Abstract
The use of stem cells in regenerative medicine, including tissue engineering and transplantation, has generated a great deal of enthusiasm. Mesenchymal stromal/stem cells (MSCs) can be isolated from various tissues, most commonly, bone marrow but more recently adipose tissue, dental pulp, and Wharton's jelly, to name a few. MSCs display varying phenotypic profiles and osteogenic differentiating capacity depending and their site of origin. MSCs have been successfully differentiated into osteoblasts both in vitro an in vivo but discrepancies exist when the two are compared: what happens in vitro does not necessarily happen in vivo, and it is therefore important to understand why these differences occur. The osteogenic process is a complex network of transcription factors, stimulators, inhibitors, proteins, etc., and in vivo experiments are helpful in evaluating the various aspects of this osteogenic process without distractions and confounding variables. With that in mind, the results of in vitro experiments need to be carefully considered and interpreted with caution as they do not perfectly replicate the conditions found within living organisms. This is where in vivo experiments help us better understand interactions that might occur in the osteogenic process that cannot be replicated in vitro. Potentially, these differences could also be exploited to develop an optimal MSC cell therapeutic product that can be used for bone disorders. There are many bone disorders, most of which cause a great deal of discomfort. Clinically acceptable protocols could be developed in which MSCs are used to aid in bone regeneration providing relief for patients with chronic pain. The aim of this review is to examine the differences between studies conducted in vitro and in vivo with regard to the osteogenic process to better define the gaps in current osteogenic research. By better understanding osteogenic differentiation, we can better define treatment strategies for various bone disorders.
Highlights
In vitro experiments have increased in complexity over the past several years from the use of omic technologies to study the cellular activity of primary cells to immortalized cells that overexpress telomerase allowing one to create human cell lines with normal or abnormal phenotypes
Mohamed-Ahmed et al [182] compared the osteogenic potential of Mesenchymal stromal/stem cells (MSCs) isolated from bone marrow and adipose tissue and reported that bone marrowderived MSCs (BM-MSC) possess enhanced osteogenic potential when compared to adipose tissue-derived stromal/stem cells (ASCs)
MSCs can successfully differentiate into osteoblasts in vitro, and multiple studies in this setting have provided methods to improve the differentiation process
Summary
In vitro experiments have increased in complexity over the past several years from the use of omic technologies to study the cellular activity of primary cells to immortalized cells that overexpress telomerase allowing one to create human cell lines with normal or abnormal phenotypes They have been allowed for the use of stromal/stem cells that have the ability to differentiate into various tissues under the influence of diverse stimuli outside the living organism. All of these in vitro developments have allowed us to better understand the mechanisms of how cells operate under set experimental conditions at relatively low cost These in vitro models have helped us to study a wide range of diseases and have provided the basis for many treatment strategies. In vivo osteogenic experiments are if not more important to understand the osteogenic process as a whole
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