Stem cells are a special type of cells that can continuously proliferate in the laboratory, and can be converted into different types of mature cells. Scientists are exploring these properties as a new form of therapy, in which tissues and organs can be repaired or replaced by cells generated from stem cells. But we need to know more about the biological process in which stem cells are turned into mature cell types, in order to have better control over its effectiveness and safety. In this project, we used a technique known as proteomics to listen to the changes of proteins inside the cells. Since proteins are the functional molecules of cells, this technique allows us to glimpse at the molecular makeup of stem cells during their induced differentiation into other cell types. We have developed a new proteomic approach that targets the newly synthesized proteins. This enables us to accurately read which genes are turned on at different phase of stem cell differentiation. We have applied this technique on the identification of nascent proteins in a type of stem cells called mesenchymal stem cells. Furthermore, we have successfully identified the nascent proteomes of Neuro2A cells during neuronal differentiation and neurite outgrowth. In parallel, we have discovered that behaviour of mesenchymal stem cells can be dramatically manipulated by the physical properties of the cell culture surface. Remarkably, stem cells can be reprogrammed in vitro into differentiated cells when exposed to a surface that mimics the corresponding tissue microenvironment. We discovered that mesenchymal stem cells seeded on the histological section of bovine Achilles tendon quickly adopted a highly elongated and aligned morphology, and expressed a significantly higher level of tendon specific proteins. This suggests that the section contains biological cues that instruct the stem cells to commit to the tenogenic lineage. Next, we prepared polymer replicas by using tendon sections as the mould. The resulting replica faithfully copied the physical shape of the tendon sections. When coated with the major extracellular matrix component of tendon, this bio-mimic culture surface promoted a similar morphological and biochemical changes in mesenchymal stem cells that indicated a tenocytic differentiation. This novel method opens a new horizon in stem cell biology and tissue engineering. We invented a new material, by directly copying the endogenous tissue environment, that can turn mesenchymal stem cells into tendon cells. These discoveries will allow a cheaper and simpler procedure for the production of tendon cells, and potentially other mature cell types, for cell-based therapy.

　

　

　

The research team led by Dr Yun-Wah Lam (back row, first from the left) applies proteomic techniques in the understanding of fundamental cellular processes.