Direct conversion of human fibroblasts into mature and functional neurons, termed induced neurons (iNs), was achieved for the first time 6 years ago. This technology offers a promising shortcut for obtaining patient‐ and disease‐specific neurons for disease modeling, drug screening, and other biomedical applications. However, fibroblasts from adult donors do not reprogram as easily as fetal donors, and no current reprogramming approach is sufficiently efficient to allow the use of this technology using patient‐derived material for large‐scale applications. Here, we investigate the difference in reprogramming requirements between fetal and adult human fibroblasts and identify REST as a major reprogramming barrier in adult fibroblasts. Via functional experiments where we overexpress and knockdown the REST‐controlled neuron‐specific microRNAs miR‐9 and miR‐124, we show that the effect of REST inhibition is only partially mediated via microRNA up‐regulation. Transcriptional analysis confirmed that REST knockdown activates an overlapping subset of neuronal genes as microRNA overexpression and also a distinct set of neuronal genes that are not activated via microRNA overexpression. Based on this, we developed an optimized one‐step method to efficiently reprogram dermal fibroblasts from elderly individuals using a single‐vector system and demonstrate that it is possible to obtain iNs of high yield and purity from aged individuals with a range of familial and sporadic neurodegenerative disorders including Parkinson's, Huntington's, as well as Alzheimer's disease.

BackgroundMesenchymal stem cells (MSC) have not only been implicated in the development of lung diseases, but they have also been proposed as a future cell-based therapy for lung diseases. However, the cellular identity of the primary MSC in human lung tissues has not yet been reported. This study therefore aimed to identify and characterise the ‘bona fide’ MSC in human lungs and to investigate if the MSC numbers correlate with the development of bronchiolitis obliterans syndrome in lung-transplanted patients.MethodsPrimary lung MSC were directly isolated or culture-derived from central and peripheral transbronchial biopsies of lung-transplanted patients and evaluated using a comprehensive panel of in vitro and in vivo assays.ResultsPrimary MSC were enriched in the CD90/CD105 mononuclear cell fraction with mesenchymal progenitor frequencies of up to four colony-forming units, fibroblast/100 cells. In situ staining of lung tissues revealed that CD90/CD105 MSCs were located perivascularly. MSC were tissue-resident and exclusively donor lung-derived even in biopsies obtained from patients as long as 16 years after transplantation. Culture-derived mesenchymal stromal cells showed typical in vitro MSC properties; however, xenotransplantation into non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice showed that lung MSC readily differentiated into adipocytes and stromal tissues, but lacked significant in vivo bone formation.ConclusionsThese data clearly demonstrate that primary MSC in human lung tissues are not only tissue resident but also tissue-specific. The identification and phenotypic characterisation of primary lung MSC is an important first step in identifying the role of MSC in normal lung physiology and pulmonary diseases.

Mesenchymal stromal cells (MSC) are multipotent cells with regenerative and immune-modulatory properties. Therefore, MSC have been proposed as a potential cell-therapy for bronchiolitis obliterans syndrome (BOS). On the other hand, there are publications demonstrating that MSC might be involved in the development of BOS. Despite limited knowledge regarding the functional role of tissue-resident lung-MSC, several clinical trials have been performed using MSC, particularly bone marrow (BM)-derived MSC, for various lung diseases. We aimed to compare lung-MSC with the well-characterized BM-MSC. Furthermore, MSC isolated from lung-transplanted patients with BOS were compared to patients without BOS. Our study show that lung-MSCs are smaller, possess a higher colony-forming capacity and have a different cytokine profile compared to BM-MSC. Utilizing gene expression profiling, 89 genes including lung-specific FOXF1 and HOXB5 were found to be significantly different between BM-MSC and lung-MSC. No significant differences in cytokine secretion or gene expression were found between MSC isolated from BOS patients compared recipients without BOS. These data demonstrate that lung-resident MSC possess lung-specific properties. Furthermore, these results show that MSC isolated from lung-transplanted patients with BOS do not have an altered phenotype compared to MSC isolated from good outcome recipients.

Mesenchymal stem or stromal cells (MSCs), a heterogeneous subset of adult stem/progenitor cells, have surfaced as potential therapeutic units with significant clinical benefit for a wide spectrum of disease conditions, including those affecting the lung. Although MSCs carry both self-renewal and multilineage differentiation abilities, current dogma holds that MSCs mainly contribute to tissue regeneration and repair by modulating the host tissue via secreted cues. Thus, the therapeutic benefit of MSCs is thought to derive from so called bystander effects. The regenerative mechanisms employed by MSCs in the lung include modulation of the immune system as well as promotion of epithelial and endothelial repair. Apart from secreted factors, a number of recent findings suggest that MSCs engage in mitochondrial transfer and shedding of membrane vesicles as a means to enhance tissue repair following injury. Furthermore, it is becoming increasingly clear that MSCs are an integral component of epithelial lung stem cell niches. As such, MSCs play an important role in coupling information from the environment to stem and progenitor populations, such that homeostasis can be ensured even in the face of injury. It is the aim of this review to outline the major mechanisms by which MSCs contribute to lung regeneration, synthesizing recent preclinical findings with data from clinical trials and potential for future therapy.

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