Stem cell therapy is a potential treatment for spinal cord injury and different stem cell types have been grafted into animal models and humans suffering from spinal trauma. Due to inconsistent results, it is still an important and clinically relevant question which stem cell type will prove to be therapeutically effective. Thus far, stem cells of human sources grafted into spinal cord mostly included barely defined heterogeneous mesenchymal stem cell populations derived from bone marrow or umbilical cord blood. Here, we have transplanted a well-defined unrestricted somatic stem cell isolated from human umbilical cord blood into an acute traumatic spinal cord injury of adult immune suppressed rat. Grafting of unrestricted somatic stem cells into the vicinity of a dorsal hemisection injury at thoracic level eight resulted in hepatocyte growth factor-directed migration and accumulation within the lesion area, reduction in lesion size and augmented tissue sparing, enhanced axon regrowth and significant functional locomotor improvement as revealed by three behavioural tasks (open field Basso-Beattie-Bresnahan locomotor score, horizontal ladder walking test and CatWalk gait analysis). To accomplish the beneficial effects, neither neural differentiation nor long-lasting persistence of the grafted human stem cells appears to be required. The secretion of neurite outgrowth-promoting factors in vitro further suggests a paracrine function of unrestricted somatic stem cells in spinal cord injury. Given the highly supportive functional characteristics in spinal cord injury, production in virtually unlimited quantities at GMP grade and lack of ethical concerns, unrestricted somatic stem cells appear to be a highly suitable human stem cell source for clinical application in central nervous system injuries.

Stem cell transplantation is a promising therapeutic strategy to enhance axonal regeneration after spinal cord injury. Unrestricted somatic stem cells (USSC) isolated from human umbilical cord blood is an attractive stem cell population available at GMP grade without any ethical concerns. It has been shown that USSC transplantation into acute injured rat spinal cords leads to axonal regrowth and significant locomotor recovery, yet lacking cell replacement. Instead, USSC secrete trophic factors enhancing neurite growth of primary cortical neurons in vitro. Here, we applied a functional secretome approach characterizing proteins secreted by USSC for the first time and validated candidate neurite growth promoting factors using primary cortical neurons in vitro. By mass spectrometric analysis and exhaustive bioinformatic interrogation we identified 1156 proteins representing the secretome of USSC. Using Gene Ontology we revealed that USSC secretome contains proteins involved in a number of relevant biological processes of nerve regeneration such as cell adhesion, cell motion, blood vessel formation, cytoskeleton organization and extracellular matrix organization. We found for instance that 31 well-known neurite growth promoting factors like, e.g. Injury to the spinal cord leads to a multiple damaging process including axonal contusion and transection with subsequent degeneration, massive apoptosis of oligodendrocytes and break-down of the blood-spinal cord barrier accompanied by invasion of immune cells resulting in sustained motoric and sensory impairments. Glial-fibrotic scarring and the lack of growth promoting factors impair axonal regrowth, which is currently the main target for therapeutic interventions to treat spinal cord injury. In addition, modulation of neuronal survival, remyelination of axons, and the immune reaction could promote functional regeneration (1-3). The inhibition of axonal regeneration might be overcome by exogenous application of growth factors or by transplantation of stem cells directly into the lesion site, which locally release trophic factors and thus support axonal regrowth. For clinical applications, stem cells should be ideally available on a clinical scale without ethical concerns or invasive interventions. Human umbilical cord blood (hUCB) 1 is

The contribution of microRNA-mediated posttranscriptional regulation on the final proteome in differentiating cells remains elusive. Here, we evaluated the impact of microRNAs (miRNAs) on the proteome of human umbilical cord blood-derived unrestricted somatic stem cells (USSC) during retinoic acid (RA) differentiation by a systemic approach using next generation sequencing analysing mRNA and miRNA expression and quantitative mass spectrometry-based proteome analyses. Interestingly, regulation of mRNAs and their dedicated proteins highly correlated during RA-incubation. Additionally, RA-induced USSC demonstrated a clear separation from native USSC thereby shifting from a proliferating to a metabolic phenotype. Bioinformatic integration of up-and downregulated miRNAs and proteins initially implied a strong impact of the miRNome on the XXL-USSC proteome. However, quantitative proteome analysis of the miRNA contribution on the final proteome after ectopic overexpression of downregulated miR-27a-5p and miR-221-5p or inhibition of upregulated miR-34a-5p, respectively, followed by RA-induction revealed only minor proportions of differentially abundant proteins. In addition, only small overlaps of these regulated proteins with inversely abundant proteins in non-transfected RA-treated USSC were observed. Hence, mRNA transcription rather than miRNAmediated regulation is the driving force for protein regulation upon RA-incubation, strongly suggesting that miRNAs are fine-tuning regulators rather than active primary switches during RA-induction of USSC. MicroRNAs (miRNAs) are small non-coding RNAs which primarily bind to the 3′UTR of target mRNAs in a sequence-specific manner resulting in translational repression or destabilization and degradation of the targeted mRNA 1. In animals, primary miRNA transcripts are trimmed in a two-step process involving double strand-specific nucleases Drosha and Dicer. The mature single-stranded miRNA is then incorporated into the RNA-induced silencing complex (RISC) where functional binding to the mRNA target sequence takes place 1. As a most important feature, miRNA-mediated regulation is characterised by a bidirectional target gene redundancy. This allows a single miRNA to target the 3′ UTRs of hundreds of mRNAs in parallel 2. Vice versa, binding sites for several miRNAs can be found on a single 3′ UTR. In consequence of these properties, miRNAs primarily can act as network regulators being able to affect large numbers of regulatory targets in parallel 2,3 .

No abstract