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Pathologies of the central nervous system are characterized by loss of brain tissue and neuronal function which cannot be adequately restored by endogenous repair processes. This stresses the need for novel treatment options such as cell-based therapies that are able to restore damaged tissue or stimulate repair. This study investigated the neuroregenerative potential of the conditioned medium of human dental pulp stem cells (CM-hDPSCs) on neural stem cell (NSC) proliferation and migration as well as on neurite outgrowth of primary cortical neurons (pCNs). Additionally, the effect of leukocyte- and platelet-rich fibrin (L-PRF) priming on the neuroregenerative potential of the hDPSC secretome on NSCs and pCNs was evaluated. L-PRF contains factors that enhance stem cell-induced regeneration, but its effect on hDPSC-mediated neuroregeneration is unknown. This study demonstrated that CM-hDPSCs enhanced neuritogenesis. Moreover, CM-hDPSCs had a chemoattractant effect on NSCs. Although priming hDPSCs with L-PRF increased brain-derived neurotrophic factor secretion, no additional effects on the paracrine-mediated repair mechanisms were observed. These data support the neuroregenerative potential of hDPSCs, and although priming had no additional effect, the potential of L-PRF-primed hDPSCs on distinct regenerative mechanisms remains to be clarified. The authors would like to send out a word of gratitude to Mr. Marc Jans for his expertise in preparing TEM samples and to Dr. Dearbhaile Dooley for her help with the isolation of NSCs. Pascal Gervois, Esther Wolfs, Jessica Ratajczak, Tim Vangansewinkel, Yörg Dillen, Annelies Bronckaers, and Ivo Lambrichts are funded by FWO grants 12U7718N, G0A7514N, G089213N, G029112N, 1134717N, 1508015N, and G026112N. Greet Merckx is supported by Bijzonder Onderzoeksfonds grant BOF16DOC06.

Bacterial genomes accommodate a variety of mobile genetic elements, including bacteriophage-related clusters that encode phage tail-likeprotein complexesplaying a role ininteractions with eukaryoticorprokaryotic cells. Such tailocins areunable toreplicate inside target cells due to the lack of a phage head with associatedDNA. Asubset of tailocins mediate antagonistic activitieswith bacteriocin-like specificity. Functional characterization of bactericidal tailocins of two Pseudomonas putida rhizosphere isolates revealed not only extensive similarity with the tail assembly module of the Pseudomonas aeruginosa R-type pyocins but also differences in genomic integration site, regulatory genes, and lytic releasemodules. Conversely, these three features are quite similar between strains of the P. putidaandPseudomonasfluorescens clades, althoughphylogenetic analysisof tailgenes suggeststhemtohave evolved separately. Unlike P. aeruginosa R pyocin elements, the tailocin gene clusters of other pseudomonads frequently carry cargo genes, including bacteriocins. Compared with P. aeruginosa, the tailocin tail fiber sequences that act as specificity determinants have divergedmuch more extensively among the other pseudomonad species, mostly isolates from soil and plant environments. Activity of the P. putida antibacterial particles requires a functional lipopolysaccharide layer on target cells, but contrary to R pyocins from P. aeruginosa, strain susceptibilities surpass species boundaries. This work was partially supported by the FNRS under grant "Grand equipement" no. 2877824 to R.W. M.G.K.G. is the recipient of an FWO postdoctoral fellowship (12M4615N). The authors thank Dr Sandra Van Puyvelde for technical assistance. They acknowledge the valuable comments provided by the reviewers.

Within the field of tissue engineering, natural tissues are reconstructed by combining growth factors, stem cells, and different biomaterials to serve as a scaffold for novel tissue growth. As adequate vascularization and innervation are essential components for the viability of regenerated tissues, there is a high need for easily accessible stem cells that are capable of supporting these functions. Within the human tooth and its surrounding tissues, different stem cell populations can be distinguished, such as dental pulp stem cells, stem cells from human deciduous teeth, stem cells from the apical papilla, dental follicle stem cells, and periodontal ligament stem cells. Given their straightforward and relatively easy isolation from extracted third molars, dental stem cells (DSCs) have become an attractive source of mesenchymal-like stem cells. Over the past decade, there have been numerous studies supporting the angiogenic, neuroprotective, and neurotrophic effects of the DSC secretome. Together with their ability to differentiate into endothelial cells and neural cell types, this makes DSCs suitable candidates for dental tissue engineering and nerve injury repair.

Throughout time humans have been born with the curiosity to explore. Crossing the oceans on Earth to those in interplanetary space, the motivations behind exploration by humanity have not changed profoundly during these last five centuries. Some of the obstacles that were met by the explorers in the past and those that we will encounter in the future are similar, funding issues being one such topic. However, obstacles regarding the environmental conditions that will be encountered in interplanetary space are very different from those found on Earth. Indeed, the space weather that presides in interplanetary space is unlike anything we are familiar with in our daily lives. However, be it an ocean storm or a solar storm, the objective remains the same-to understand and protect the transportation device and the crew against the environment that it will encounter.