The original properties of tissue-specific stem cells, regardless of their tissue origins, are inevitably altered during in vitro culturing, lessening the clinical and research utility of stem cell cultures. Specifically, neural stem cells derived from the ventral midbrain lose their dopamine neurogenic potential, ventral midbrain-specific phenotypes, and repair capacity during in vitro cell expansion, all of which are critical concerns in using the cultured neural stem cells in therapeutic approaches for Parkinson's disease. In this study, we observed that the culture-dependent changes of neural stem cells derived from the ventral midbrain coincided with loss of RNA-binding protein LIN28A expression. When LIN28A expression was forced and sustained during neural stem cell expansion using an inducible expression-vector system, loss of dopamine neurogenic potential and midbrain phenotypes after long-term culturing was blocked. Furthermore, dopamine neurons that differentiated from neural stem cells exhibited remarkable survival and resistance against toxic insults. The observed effects were not due to a direct action of LIN28A on the differentiated dopamine neurons, but rather its action on precursor neural stem cells as exogene expression was switched off in the differentiating/differentiated cultures. Remarkable and reproducible behavioural recovery was shown in all Parkinson's disease rats grafted with neural stem cells expanded with LIN28A expression, along with extensive engraftment of dopamine neurons expressing mature neuronal and midbrain-specific markers. These findings suggest that LIN28A expression during stem cell expansion could be used to prepare therapeutically competent donor cells.

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Inflammation-mediated oncogenesis has been implicated in a variety of cancer types. Rheumatoid synovial tissues can be viewed as a tumor-like mass, consisting of hyperplastic fibroblast-like synoviocytes (FLSs). FLSs of rheumatoid arthritis (RA) patients have promigratory and invasive characteristics, which may be caused by chronic exposure to genotoxic stimuli, including hypoxia and growth factors. We tested whether a transformed phenotype of RA-FLSs is associated with placental growth factor (PlGF), a representative angiogenic growth factor induced by hypoxia. In this study, we identified PlGF-1 and PlGF-2 as the major PlGF isoforms in RA-FLSs. Global gene expression profiling revealed that cell proliferation, apoptosis, angiogenesis, and cell migration were mainly represented by differentially expressed genes in RA-FLSs transfected with small interfering RNA for PlGF. Indeed, PlGF-deficient RA-FLSs showed a decrease in cell proliferation, migration, and invasion, but an increase in apoptotic death in vitro. PlGF gene overexpression resulted in the opposite effects. Moreover, exogeneous PlGF-1 and PlGF-2 increased survival, migration, and invasiveness of RA-FLSs by binding their receptors, Flt-1 and neuropilin-1, and upregulating the expression of antiapoptotic molecules, pErk and Bcl2. Knockdown of PlGF transcripts reduced RA-FLS proliferation in a xenotransplantation model. Collectively, in addition to their role for neovascularization, PlGF-1 and -2 promote proliferation, survival, migration, and invasion of RA-FLSs in an autocrine and paracrine manner. These results demonstrated how primary cells of mesenchymal origin acquired an aggressive and transformed phenotype. PlGF and its receptors thus offer new targets for anti-FLS therapy.